Dissertations / Theses on the topic 'Biodegradable'
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Asplund, Basse. "Biodegradable Thermoplastic Elastomers." Doctoral thesis, Uppsala : Acta Universitatis Upsaliensis Acta Universitatis Upsaliensis, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-7434.
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Goodby, Amanda. "Biodegradable thermoplastic polyurethanes." Thesis, Aston University, 2015. http://publications.aston.ac.uk/32134/.
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The overall aim of this work was to investigate the biodegradability of a number of polyurethane elastomers synthesised by different methods and targeted for a specific agricultural purpose in which the polyurethane was required to be degradable in soil after its useful life. Polyurethanes were synthesised commercially using two different methods; a ‘one-shot’ method where all of the reactants were added simultaneously, and a ‘pre-polymer’ method, in which the isocyanate and polyol were reacted together before addition of the chain extender. The effect of the method of synthesis on the rate of degradation and biodegradation was investigated using accelerated alkaline hydrolysis, enzymatic hydrolysis and soil burial, where it was found that the polyurethane synthesised by the ‘pre-polymer’ method hydrolysed faster under alkaline conditions (21 days) than that synthesised by the ‘one-shot’ method (56 days). This was found to be due to differences in the polymer morphology, with an increase in microcrystalline domains occurring during the ‘one-shot’ process. The effect of the chemical constituents of the synthesised polyurethanes on the rate of degradation and biodegradation were also investigated. Comparison of polyurethanes synthesised with an aliphatic (H12MDI) and an aromatic isocyanate (MDI) resulted in an increase in the rate of alkaline hydrolysis with the use of H12MDI. This was found to be affected mainly by differences in the morphology, with an increase in microphase separation and a decrease in microcrystalline regions in the case of the use of H12MDI Polyurethanes were synthesised using different polyols; PEA, PCL, PEG and PCL/PEG (50:50) to investigate the effect of the polyol on the rate of biodegradation, where it was found that the polyurethane containing a combination of the two polyols, PCL/PEG (50:50), degraded under both accelerated hydrolysis conditions and soil burial. This was thought to be due to the combination of both hydrophilic (PEG) and hydrophobic (PCL) charactyers of the polyols, which had contributed to increasing the diffusion of water into the polymer matrix (hydrophilic PEG), and also to inducing the microbial degradation by hydrophobic interactions (PCL). The incorporation of the additives; iron stearate, cellulose and Cloisite 30B were examined as a means of increasing the degradation and biodegradation of the polyurethane polymers. Addition of iron stearate was found to decrease the thermal stability of the polyurethane, which resulted in an increase in polyurethane degradation under alkaline conditions at 45oC, and biodegradation under soil burial conditions at 50oC. The incorporation of cellulose into the polyurethane increased the rate of alkaline hydrolysis and biodegradation in soil. This polyurethane (PU CE) was also susceptible towards enzymatic degradation by Aspergillus niger. The incorporation of the organically-modified nanoclay Cloisite 30B has decreased the microcrystalline domain structure contained within the polyurethane, and this was found to decrease the rate of alkaline hydrolysis dramatically (degraded within 7 days).
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Casadio, Ylenia Silvia. "Biodegradable PHEMA-based biomaterials." University of Western Australia. School of Biomedical, Biomolecular and Chemical Sciences, 2009. http://theses.library.uwa.edu.au/adt-WU2009.0173.
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[Truncated abstract] The synthetic hydrogel poly(2-hydroxyethyl methacrylate) (PHEMA) has been used as a biocompatible biomaterial in ocular devices, such as soft contact lenses, intraocular lenses and an artificial cornea. Due to its favourable properties as an already established (but non-biodegradable) biomaterial, PHEMA is an interesting candidate for use as a material for scaffolds in tissue engineering. A tenant of tissue engineering scaffolds is obtaining the appropriate porous morphology to allow for successful cellular attachment and support. PHEMA hydrogels exhibit varied morphological features, which range from non-porous (homogeneous) to macroporous (heterogeneous) and can be readily obtained by fine-tuning the polymerisation conditions. A desirable feature for matrices that are to be used as tissue supports is the ability to biodegrade in a biological environment. This thesis describes the preparation and enzymatic biodegradation behaviour of novel porous PHEMA hydrogels that have been crosslinked with biodegradable peptide-based crosslinking agents. Peptide-based crosslinking agents were designed to contain two terminal polymerisable groups flanking an internal biodegradable backbone. This backbone was specifically designed to be targeted by the proteolytic enzyme papain. The general design template allowed for the development of a synthetic methodology that was readily implemented for the production of a range of olefin-peptide conjugates. A suite of olefin-peptide conjugates of general structure I were synthesised, characterised and further tested with papain to determine their biodegradation properties. ... The second strategy for producing bioresorbable degradation fragments involved the incorporation of the highly hydrophilic comonomer, poly(ethylene glycol) PEG into the PHEMA backbone. The addition of PEG to PHEMA resulted in the formation of homogeneous hydrogels that had an improved hydrophilicity compared to their heterogeneous PHEMA counterparts. The synthetic conditions for the preparation of PHEMA and PHEMA-co-PEG hydrogels by photoinitiated polymerisation were thoroughly investigated. It was found that the pore morphology and general properties (non-porous to macroporous) of these hydrogels could be controlled by the appropriate choice of polymerisation conditions. The hydrogels were characterised by scanning electron microscopy, thermal gravimetric analysis and differential scanning calorimetry. The peptide-based crosslinking agents were successfully co-polymerised with the HEMA and PEGMA via photoinitiated polymerisation to provide a range of PHEMA and PHEMA-co-PEG hydrogels that displayed both homogeneous and heterogeneous hydrogel properties. The final crosslinked hydrogels were characterised by scanning electron microscopy and were subjected to enzymatic hydrolysis. The PHEMA-peptide conjugate hydrogels proved to be biodegradable, with degradation behaviour dependent on the hydrogel formulation and the length of the peptide-based crosslinking agent.
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Suwattana, Siripan. "Biodegradable polymers via RAFT." Thesis, University of Leeds, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.549765.
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This research has shown that biodegradable monomer (5,6-benzo-2- methylene-1,3-dioxepane) (BMOO) can be achieved. Also its homo-and-eo- polymerisation can be successfully realised via RAFT and ROP polymerisation techniques. BMOO was synthesised with the modification via the dehydrobrornination of 5,6-benzo-2-(bromomethyl)-1,3-dioxepane in a good yield (95% yields). The homopolymerisation of BMOO were designed to produce a target OP of 200 via living "polymerisation" and complete ring-opening polymerisation. A narrow POI (1.09) and an M n= 4,697 g mol' were observed after 24 hours for the reaction in the presence of the CT A(MCPDB)' The copolymerisation of MMA and BMOO in the presence of the CT A(CPDB) gave better control over the polymerisation than that achieved using the CT A(MCPDB) and the CTA(ETSPE), at 120 "C. A narrow POI (1.36) and an Mn= 16,662 g mol' were observed after 24 hours. The copolymer was shown to be results of a combination of 1,2-addition polymerisation and of ring-opening copolymerisation. The reactivity ratio of the monomers was calculated using the Kelen- Tudos method (rMMA= 1.12 and rBMDO= 0.43). The copolymerisation of styrene with BMOO in the presence of the CTA(cPDB) gave the better control than that given by the CT A(MCPDB) and the CTA(ETSPE), at 120aC (Sty:BMOO, with an initial feed of 33%:67%). A narrow POI (1.18) and M n= 9,684 g rnol' were obtained after 24 hours. The % ratio of BMOO that was incorporated into the final polymeric chain was Sty:BMOO= 64.3%:35.7% and the copolymer was formed from ring-opening polymerisation only. The reactivity ratio of the monomers was calculated using the Kelen-TOdos method (rsty= 2',56 and rBMDO= 0.64). NMR, FTIR and UVlVis spectroscopy provided further evidence that the final polymers were the product of a ring-opening polymerisation. As required, thermal analysis techniques were used to ascertain the consequences of the copolymerisation, with respect to thermal consequences (decomposition) and compositional features.
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Tolentino, Chivite Ainhoa. "Ionic complexes of biodegradable polyelectrolytes." Doctoral thesis, Universitat Politècnica de Catalunya, 2014. http://hdl.handle.net/10803/144662.
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Biopolymers are polymers produced by living organisms. A more broad classification would embrace also those polymers synthesized from renewable sources which are able to display biodegradability. The demand of biopolymers has been continuously growing along these last decades. The main reason for such increasing interest is their sustainability; the renewable origin of biopolymers makes them inexhaustible in contrast with synthetic polymers produced from finite fossil sources. Biodegradability is a second advantage; due to the presence in the nature of enzymes able to degrade biopolymers under environmental conditions to give non-toxic products, their impact on the environment is basically trivial. Finally, the use of more or less modified biopolymers as biomaterials, owing to their unique properties of biocompatibility and biodegradability, has aroused their interest in several disciplines. As a result of all these considerations, great efforts in biopolymers research including chemical modification, characterization and property evaluation are today being carried out to develop new materials able to replace traditional plastics in a wide diversity of
applications.
In the present Thesis, a selection of carboxylic biopolymers has been studied for their capacity to form stable ionic complexes with cationic surfactants suitable to render new materials with advanced properties. Previous studies on polyelectrolytesurfactant complexes carried out in our group have demonstrated that these coupled systems tend to be self-assembled in well-ordered structures that can be exploited for building films and particles with singular properties as biomaterials.
The main goal of this Thesis is the study of polyelectrolyte-ionic complexes based on naturally occurring polyacids and cationic surfactants. One part of the work delves into the complexes of poly(g-glutamic acid), a system that has been object of continuous research in our group from 90s. The aim is to progress in the development by making them "greener" through coupling with bio-based surfactants, and by improving their basic properties through blending with nanoclays. The other part is dedicated to explore the ionic complexes made from poly(uronic acid)s and cationic surfactants. This is the first time that such complexes are examined and their structural features and properties compared to those displayed by complexes based on poly(glutamic acid).
Experimentally, the Thesis embodies a multidisciplinary task work including preparation, structural characterization and evaluation of thermal properties of a series of ionic complexes, as well as a preliminary valuation of the suitability of some of them to be used as drug delivery systems.
Hence, the specific objectives in this Thesis are enumerated as follows: 1. Synthesis and chemical characterization of ionic complexes of poly(uronic acid)s (pectinic, alginic and hyaluronic acids), with trimethylalkylammonium surfactants of n= 18, 20 and 22. Structural and thermal analysis of these complexes and critical comparison of results with those available for complexes made of poly(glutamic acid).
2. Synthesis and characterization of choline-based surfactants for the preparation of fully bio-based polyglutamic complexes as an alternative to complexes based on trimethylalkylammonium surfactants in their potential use as biomaterials. Structural and thermal analysis of these complexes and their preliminary evaluation as nano-particulated drug delivery systems.
3. Preparation of composites of poly(glutamic acid)-cationic surfactant complexes with organo-modified nanoclays, their extensive structural characterization and the evaluation of their thermal and mechanical properties compared to those displayed by the neat complexes.
The Thesis is organized in five Chapters. After a very brief summary of the whole work with explicit definition of the objectives, Chapter I is an
introduction to the subject, in which an extensively referenced account of the main hints previously achieved in the field is provided and the state-of-art is described.
The following three Chapters correspond to the three specific objectives enumerated above. Chapter II gathers the synthesis, characterization and properties evaluation study carried out on ionic complexes of poly(uronic acid)s. Chapter III is focused on the study of ionic complexes of polyglutamic and alkanoylcholines, the synthesis and characterization of the surfactants, the preparation of their complexes with poly(glutamic acid) and their possibilities as potential biomaterials. Chapter IV covers the preparation of the composites made of Cloisite 30B and poly(glutamic
acid) complexes along with a detailed study of their structure by X-ray diffraction, electron microscopy and modeling, and a correlative analysis of their structure with their thermal and mechanical properties.
Chapter V contains the whole collection of conclusions that have been drawn from the Thesis. The author’s profile and published scientific production coming out from the Thesis constitute the body of the closing part.
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Lal, Sumit. "Biodegradable packaging from whey protein." Thesis, University of Auckland, 2012. http://hdl.handle.net/2292/13815.
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Biodegradable packaging films from whey protein concentrate were made in this study. A total of 46 formulations were made in the form of thin (50 - 120um) films by using solvent casting. Additives used in the formulations included plasticizers i.e glycerol and propylene glycol, chaotropic agent i.e guanidine thiocynate, gelation and crosslinker i.e glutaraldehyde. Tensile tests showed an increase in tensile strength with the addition of glutaraldehyde (1.2 v/v) and gelatin (upto 50% wt%). Addition of glycerol, propylene glycol and guanidine thiocynate increased elongation of films. Water vapor permeability and oxygen permeability of films containing glycerol, propylene glycol and guanidine thiocynate increased, while films made with gelatin, glutaraldehyde showed lower permeability for oxygen and water. Glass transition temperature was measured by DSC and results showed consistent decrease in Tg with increasing amount of plasticizer and chaotropic agent. Biodegradability was measured by degradation in 1% pancreatin. Results showed lower degradation time for formulations containing increasing proportions of glutaraldehyde and gelatin. Fourier transform infrared spectroscopy (FTIR) was used to evaluate changes in covalent bonding post glutaraldehyde crosslinking. Peaks corresponding to stretching of imine bonds were found at 1590 cm-1 suggesting crosslinking reaction between glutaraldehyde and terminal amine residues of whey/gelatin. Scanning electron micrographs showed an increase in relative porosity for compositions containing glycerol when compared to formulation containing only whey. Surface micrographs of formulations with gelatin showed phase separation. The phase separation may be attributed to partial immiscibility of whey with gelatin.
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Zorlutuna, Pinar. "Cornea Engineering On Biodegradable Polyesters." Master's thesis, METU, 2005. http://etd.lib.metu.edu.tr/upload/3/12605779/index.pdf.
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ABSTRACT
CORNEA ENGINEERING
ON
BIODEGRADABLE POLYESTERS
Zorlutuna, Pinar
M. Sc., Department of Biotechnology
Supervisor: Prof. Vasif Hasirci
Co-Supervisor: Asst. Prof. AySen Tezcaner
January 2005, 66 pages
Cornea is the outermost layer of the eye and has an important role in vision. Damage of cornea due to injuries or infections could lead to blindness lowering the quality of life of the patient severely. In such cases, transplantation or artificial corneas have been used for treatment but both had drawbacks. The novel approach for corneal replacements is the tissue engineering of the cornea, a promising method which would be free of these drawbacks, if successful.
In this study, carriers for tissue engineering of the cornea were designed and tested in vitro. Blends of biodegradable and biocompatible polyesters of natural (PHBV8) and synthetic (PLLA) origin were used to construct these carriers. For the epithelial layer of the cornea, PLLA-PHBV8 micropatterned films were prepared with solvent casting and seeded with D407 (retinal pigment epithelial) cells. In order to achieve proper cell growth, the films were coated with fibronectin. For the stromal layer of the cornea, highly porous foams of PLLA-PHBV8 were prepared by lyophilization and seeded with 3T3 cells (fibroblasts). A new approach was developed to create a combination of the film and the foam to obtain a surface patterned, 3 dimensional cell carrier. These carriers were seeded with Saos-2 cells (osteosarcoma cells) in the preliminary optimization studies and with D407 and 3T3 cells in further studies. The cell numbers on the carriers were quantified by using MTS assay (non-radioactive cell proliferation assay) and the cell proliferation on polymeric carriers was significantly higher than that of control (Tissue culture polystyrene) by the day 14. Characterization of these cells and the carrier was done using a variety of microscopic methods. The micrographs showed that the foam had a highly porous structure and the pores were interconnected. 3T3 cells were found to be distributed quite homogeneously at the seeding site, but due to the high thickness of the foam, the cells could not sufficiently populate the core (central parts of the foam) during the given incubation time. The micropatterned film allowed multilayer formation of D407 cells. The functionality of the cells seeded on the carriers was examined by immunohistochemistry. These analyses proved that the cells retained their phenotype during culturing. D407 cells formed tight junctions characteristic of epithelial cells, and 3T3 cells deposited collagen type I into the foams. Based on the results, it can be concluded that the 3-D PLLA-PHBV8 construct with surface patterns have a serious potential for use as a tissue engineering carrier for the reconstruction of the cornea.
Key words: Tissue engineering, cornea, polymeric carrier, biodegradable, polyester.
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Goksu, Emel Iraz. "Hemicellulose Based Biodegradable Film Production." Master's thesis, METU, 2005. http://etd.lib.metu.edu.tr/upload/12605940/index.pdf.
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Xylan was extracted from cotton waste, characterized by DSC and TGA analysis and used in biodegradable film production. Pure cotton waste xylan did not form film. The presence of an unknown compound, as an impurity, yielded composite films. The unknown compound was determined as a phenolic compound, and most probably lignin, by using DSC and TGA analysis and Folin-Ciocalteau method. The effects of xylan concentration of the film forming solutions, glycerol (plasticizer) and gluten additions on thickness, mechanical properties, solubility, water vapor transfer rate, color and microstructure of the films were investigated.
Films were formed within the concentration range of 8-14%. Below 8%, film forming solutions did not produce films, whereas xylan concentrations above 14% was not used because of high viscosity problems. The average tensile strength, strain at break, water vapor transfer rate and water solubility of the cotton waste xylan films were determined as about 1.3 MPa, 10%, 250 g/m2.24h and 99%, respectively. The addition of glycerol as the plasticizer resulted in a decrease in the tensile strength and an increase in strain at break. The change in water solubility due to the addition of glycerol was very small. In addition, water vapor transfer rate and the deviation of the color from the reference color for the plasticized films were found to be higher than the unplasticized films.
The effect of addition of wheat gluten in cotton waste xylan film forming solutions on film formation was investigated at different concentration ratios. However, the incorporation of wheat gluten worsen the film quality.
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Haider, Anita. "Synthesis of functionalised biodegradable polyesters." Thesis, Imperial College London, 2008. http://hdl.handle.net/10044/1/12037.
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Graf, Tyler A. "Poly(disulfidediamines) : new biodegradable polymers." Diss., University of Iowa, 2012. https://ir.uiowa.edu/etd/3457.
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The turnovers of a gold(III) chloride catalyst were increased by 3,300% with the addition of several equivalents of (2,2,6,6-tretramethyl-piperidin-1-yl)oxy and catalytic amounts of copper(II) chloride. A three component coupling reaction between piperidine, phenylacetylene, and benzaldehyde yielded a propargylamine in quantitative conversions and isolated yields when gold(III) chloride was added in catalytic amounts, but the gold catalyst decomposed and had little to no reactivity when a second set of piperidine, phenylacetylene, and benzaldehyde were added after the reaction was complete. The addition of (2,2,6,6-tretramethyl-piperidin-1-yl)oxy and copper(II) chloride to reactions with gold(III) chloride maintained the catalytic activity of the gold for up to 33 cycles. This result demonstrates a new way to greatly increase the turnovers of a gold(III) chloride catalyst with the addition of inexpensive, commercially available reagents.
The synthesis and some of the physical properties of the first poly(disulfidediamines) are reported. These polymers were synthesized in high yields and with conversions up to >98% by reactions between secondary diamines and a new disulfide monomer. The disulfide monomer was synthesized in two steps without the need for column chromatography. The polymerizations were robust and completed at room temperature, under ambient atmospheric conditions, and in solvents that were used as purchased. These polymers were stable, but they rapidly decomposed under acidic, aqueous conditions to release hydrogen sulfide. A method for quantifying the hydrogen sulfide released was also developed.
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Fromageot, Camille. "Modification of biodegradable polymer films." Thesis, Queensland University of Technology, 2019. https://eprints.qut.edu.au/131622/1/Camille_Fromageot_Thesis.pdf.
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This project aimed at tuning the photodegradability of a biodegradable polyester by employing a photosensitizing molecule, 2-oxepane-1,5-dione (OPD), as an additive mixed with commercial polymer and as a monomer to be copolymerized. Various processing techniques were employed, such as reactive extrusion, film blending or synthesis of polymers. The accelerated artificial ageing of modified polyesters revealed that OPD accelerated the rate of photodegradation of the polyester, with the differing mechanisms of degradation found for blends and copolymers providing scope for tuning the photodegradability of the polyester via alteration of the method of OPD incorporation.
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Liu, Yan. "New biodegradable polymers from renewable resources." Doctoral thesis, KTH, Polymer Technology, 2000. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-2952.
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High molecular weight poly(ester-carbonate)s have beenprepared by a two-step chain-extension reaction performed onoligomeric αω-bishydroxyl-terminatedpoly(1,3-propylene succinate).αω-Bishydroxyl-terminated copolymeric oligomers of1,3-propylene succinate/1,4-cyclohexanedimethylene succinatewere obtained by thermal polycondensation of1,3-propanediol/1,4-cyclohexanedimethanol/succinic acidmixtures having different composition, and subsequently chainextended using phosgene as coupling agent, which leads toaliphatic/alicyclic copoly(ester-carbonate)s. New highmolecular weight amphiphilic block copolymers ofpoly(ester-ether-carbonate), containing poly(1,3-propylenesuccinate) and poly(ethylene glycol) (PEG) segments in theirmain chain, were synthesized by a two-step chain-extensionreaction performed on a thermally-polycondensed α,ω-bishydroxyl-terminated oligomeric poly(1,3-propylenesuccinate) with PEG1000 and PEG2000, respectively. The newpolymers, besides having a biodegradable backbone, derive fromtwo monomers, 1,3-propanediol and succinic acid respectively,which can be obtained from renewable resources. Therefore, theyhave a potential as environmental friendly materials.
The molecular characterization by1H-NMR and IR spectroscopy, the molecular weight andmolecular weight distribution by SEC and the main thermalproperties by DSC of all synthesized materials are reported.Spectroscopic characterizations were in full agreement with theproposed structures. Thermal characterization demonstrated thatan increase in the cyclic ester unit content leads to anincrease in Tm and Tg of the copolymers. Solubility testsindicated that the introduction of hydrophilic PEG segmentsinto the high molecular weight polysuccinate imparts apparentamphiphilic character to the new materials. This is expected toinfluence even their biocompatibility and biodegradability.
The properties of aliphatic homopolyesters from renewablemonomers, 1,3-propanediol and succinic acid, were improved byintroducing aromatic urethane into the main chain of polymers,which gives place to the formation of strong hydrogen bondsamong the macromolecular chains of the material. Segmentedpolyester-urethanes (PEU) were synthesizedfromdi-hydroxyl-terminated poly(trimethylene succinate), chainextended with 4,4'-diisophenylmethane diisocyanate (MDI). Thematerials were characterized using SEC, DSC,1H-NMR,13C-NMR and INSTRON. The maximum weight averagemolecular weight approached 7.5× 104. DSC detected the Tgof the soft segment from10 to19° C and the Tmof the hard segment from 175 to 210 ° C. Theaverage repeat number of hard segment ranges from 4.0 to 8.1,and the average repeat number of AnBmunit from 3.3 to 6.4. The average length of thehard segment decreases with increasing concentration ofpolyester in feeding.
The results clearly show that within the studied series theincrease in soft segment content reduced both crystallinity andmelting temperature of hard segment microcrystalline phase,which is accompanied by decrease in modulus due to weakerinteraction among polymer chains in microcrystalline phase. Thedegree of crystallinity, Tg, Tm, tensile strength, elongation, and Youngsmodulus were influenced by the ratio between hard and softsegment as well as the molecular weight of thepolyester-urethane. The introduction of the polyurethanesegments significantly reduces the degradability ofcorresponding aliphatic polyester, although there is stillenzymatic attack detectable during the enzymatic degradation.All samples exhibited significant weight losses after twomonths of compost simulation incubation. The highersoft-segment contents resulted in higher degradability. Weconcluded that the segmented polyester-urethane from1,3-propanediol and succinic acid is a promising, processable,soluble, and biodegradable thermoplastic elastomer.
Keywords:polycondensation, block copolymer, chainextension, isocyanate, phosgene, dichloroformatecharacterization, biodegradation, renewable resources,1,3-propanediol, succinic acid, polyurethane, polyester,thermoplastic elastomer.
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Holy, Chantal E. "Bone tissue engineering on biodegradable polymers." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape8/PQDD_0012/NQ59097.pdf.
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Verlinden, Rob A. J. "Biodegradable polyhdroxyalkanoates from waste frying oil." Thesis, University of Wolverhampton, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.542319.
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Mohammad, Muhanad Hassan. "Biodegradable polycaprolactone polymers for regenerative medicine." Thesis, University of Brighton, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.413097.
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Wong, Hoi-man, and 黃凱文. "Surface modification of biodegradable metallic material." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2008. http://hub.hku.hk/bib/B41290689.
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Lam, Ho-ching Dennis, and 林浩正. "Biodegradable plastics : feasible in Hong Kong?" Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2013. http://hdl.handle.net/10722/194554.
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Since their inception and invention, plastic materials have taken on an essential role in numerous applications within the lives of human beings for years now. Each year, the global figure for production of plastic is estimated to be more than 100 million tons. The major reason for the existence of such an enormous amount is due to plastics’ supremacy over other materials with their exceptionally useful properties. According to Hong Kong’s Environmental Protection Department, 13,458 tons of waste was disposed in Hong Kong’s landfills per day during 2011. Such an amount is very large in quantity, and it is predicted that the three strategic landfills of Hong Kong will be fully saturated in 2015-16 if the waste generation rate remains similar as present time and business as usual. Plastics made up approximately 19% of the overall composition of Hong Kong’s disposed municipal solid waste in 2011. Plastic material does not degrade efficiently, and since it has only been in production during the most current century, plastic specialists have not been able to conclude the final life span of the material before it completely degrades. Estimates for different plastic polymers range from 20 years to 400 years and above. To solve these increasingly serious environmental issues, the society has raised its demands and directed many researches into biodegradable polymers (i.e., plastics). They have now become more seriously considered as alternative solutions for conventional, non-biodegradable plastics. However, the creation of such biodegradable materials, the efficiency and cost of that creation and the true biodegradability of those materials is under much scrutiny and debate.
The purpose of this study was multi-faceted. It primarily focused on (1) the status and production of biodegradable products in Hong Kong and (2) assessment of the general public’s receptiveness towards using such products. This study aimed to evaluate the above two aspects via literature review and interviews of representatives from biodegradable plastics companies in Hong Kong as well as students and general working-class citizens. This element inquired whether the general public would be willing to pay extra money to use biodegradable plastic products, and whether they thought that these products had beneficial effects towards environmental conservation and protection. Also, the general public would be asked their opinion on a duty for biodegradable products and whether they would be adverse to a policy implementation involving such a duty. A large portion of this project’s critically significant data was generated from random, systematic sampling of different people, asking them about the aforementioned monetary scenarios. Results were insightful and informative giving evident trends that represented the public’s attitude towards biodegradable plastics. Overall, the public was positively supportive of biodegradable technology, which is relatively new. Concurrently, extensive literature review was conducted to assess foreign practices and policies regarding biodegradable plastics, as well as the life-cycle of a primary biopolymer called polylactic acid.
A concluding recommendation was constructed to envision the future waste management infrastructure in Hong Kong. That infrastructure could build off of the special region’s budding development of incinerators, composting facilities, waste-to-energy facilities, and sorting technologies. Then, to supplement biodegradable polymer production and post-use handling facilities, the Hong Kong SAR Government could implement strong waste management policies to motivate its society to aim for a more sustainable way of life.published_or_final_version
Environmental Management
Master
Master of Science in Environmental Management
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Jiang, Guozhan. "Monomer transfer moulding for biodegradable composites." Thesis, University of Nottingham, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.429083.
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Evans, Samantha Jane. "Modification of a biodegradable co-polyester." Thesis, University of Salford, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.426888.
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Blackwell, Catherine Jayne. "Synthesis and degradation of biodegradable polyurethanes." Thesis, Durham University, 2017. http://etheses.dur.ac.uk/11961/.
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A series of biodegradable star poly(ε-caprolactone) (PCL)-based polyols and PCL-based diisocyanate prepolymers were synthesised and fully characterised. Biodegradable polyurethanes (PUs) were synthesised using star PCL-based polyols and either biodegradable diisocyanate prepolymers 4,4’-methylenebis(phenyl isocyanate) (MDI) or 2,4-toluene diisocyanate (TDI). The resulting polyols, diisocyanate prepolymers and PUs were subjected to enzymatic degradation using lipase for up to 30 days. Chapter 1 is a general introduction to the reactions involved in the syntheses of PU foams and the ring-opening polymerisation of cyclic esters. The general components used in PU formulations including biodegradable polyols and diisocyanate prepolymers are discussed. Furthermore, polymer biodegradation testing methods and analytical methods to monitor degradation are investigated. Chapter 2 includes the syntheses and enzymatic degradation of a series of biodegradable four- and six-arm star PCL polyols. This was achieved through the tin(II)octoate (SnOct2) catalysed ring opening polymerisation (ROP) reaction of ε-caprolactone (ε-CL) using pentaerythritol, di(trimethylolpropane) and dipentaerythritol initiators. Furthermore, a series of six-arm star poly[(ε-caprolactone)-co-(β-butyrolactone)] were synthesised in a similar manner. Star PCL and star poly[(ε-CL)-co-(β-BL)] both exhibited almost 100% mass loss after 15 days of enzymatic degradation at a constant rate. Generally, an initial increase in % crystallinity (%χc) is seen for star PCL and star poly(ε-CL)-co-(β-BL) in the first few days (0-3 days) of enzymatic degradation. This was followed by a decrease in crystallinity (%χc), indicating amorphous regions of the polymer were preferentially degraded. This was supported by scanning electron microscopy (SEM) analyses showing surface pitting and occurrence of crystal spherulite structures within the first few days of enzymatic degradation. Chapter 3 concerns the synthesis and enzymatic degradation of a series novel four-arm dumbbell-shaped copolymers (PCL)2-(PEG)-(PCL)2 bridged with 2,2’-bis(hydroxymethyl)propionic acid (bisMPA) moieties. This was achieved by the synthesis of a tetra-hydroxyl PEG macro-initiator through a coupling reaction of poly(ethylene glycol) (PEG) and acetyl-protected bisMPA using dicyclocarbodiimide (DCC) and 4-dimethylaminopyridine (DMAP). Subsequently, the four-arm star structure was synthesised with the SnOct2 catalysed ROP of ε-CL using tetra-hydroxyl PEG macroinitiator. Contact angle and %water uptake (%WU) indicated the copolymers containing a higher %PEG showed increased hydrophilic nature and surface wetting. A dispersity (Ð) of 1.32-1.51 and a small molecular weight shoulder were seen due to using a polydisperse PEG macro-initiator and the high viscosity of the reaction mixture under bulk conditions. The novel star copolymers showed >90% mass loss within 7 days and an increase in %χc within the first few days of enzymatic degradation. Chapter 4 entails the synthesis and enzymatic degradation of biodegradable seven arm star PCL with a central acetylated β-cyclodextrin (β-CD) moiety. This was achieved through a four step synthetic route involving the protection of 1° OH groups on the β-CD moiety, acetylation of the 2° OH groups on the β-CD moiety, removal of protecting group on the 1° OH group and subsequent ROP of ε-CL catalysed by SnOct2. Contact angle and %WU analyses showed minimal surface wetting and high hydrophobicity. A very low rate of enzymatic degradation was seen with 7% mass loss and a general increase in %χc in 20 days. Chapter 5 involves the synthesis and enzymatic degradation of a series of biodegradable diisocyanate prepolymers containing a central PCL or PCL-b-PEG-b-PCL moiety and capped with either MDI or TDI moieties. This was achieved through the reaction of two molar equivalents of the diisocyanate moiety, MDI or TDI, and either PCL diol or PCL-PEG-PCL triblock copolymer. The diisocyanate prepolymers showed absorbances attributing to the C=N stretch in the NCO group as well as N-H and C-N in the urethane group in FT-IR spectra. Contact angle and %WU measurements of diisocyanate prepolymers with higher %PEG showed increased surface wetting and hydrophilicity. Generally the TDI-based diisocyanate prepolymer showing 100% mass loss in 4 days, degraded at a faster rate than MDI-based diisocyanate prepolymer of 23% in 40 days. Furthermore, the lower Mn MDI-based prepolymer showed a significantly faster rate of enzymatic degradation of 79% mass loss in 40 days than the higher Mn MDI-based prepolymer. Chapter 6 concerns the synthesis and enzymatic degradation of a series of biodegradable PUs using biodegradable PCL-based star polyols and diisocyanate prepolymer components synthesised in Chapter 2-5. PU gels were produced as a result of a minimal amount of dichloromethane (DCM) solvent to ensure complete mixing. Generally, PUs showed the disappearance of the C=N stretch in fourier transform infrared spectroscopy (FT-IR) analyses, indicating all NCO groups successfully reacted to give urethane groups. PUs showed up to 18.5% mass loss over the 30 days of enzymatic degradation. Comparisons of the PU degradation behaviour were made to demonstrate the effects of polyol type, diisocyanate type, and ratio of NCO:OH used, on the rate of PU enzymatic degradation. Chapter 7 surmises and concludes the work covered in Chapter 2-6 and suggests further work.
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Kim, Jina 1984. "Lamination of a biodegradable polymeric microchip." Thesis, Massachusetts Institute of Technology, 2006. http://hdl.handle.net/1721.1/35137.
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Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2006.Includes bibliographical references (leaf 22).
This work builds on the initial design of a polymer microchip for controlled-release drug delivery. Currently, the microchip employs a nonbiodegradable sealant layer, and the new design aims to fabricate it only of biodegradable parts. Experiments were conducted to evaluate two potential designs that are fabricated via lamination, and a final design was proposed based on the results. Design 1 sought to replace the sealant directly with a PLA backing layer, but the laminated backing layer was found to leak in 14C-dextran release experiments. Design 2 used a laminated film instead of the original injected membrane. The laminated film was optimized to a 200- [mu]m thick poly(D,L-lactic-co-glycolic acid) 2A membrane, and the film-laminated microchip was shown to release 14C-dextran within a 40-day period. The final proposed design was based on Design 2, which demonstrated more potential as a future means of drug delivery.
by Jina Kim.
S.B.
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Shieh, Lisa Y. "Erosion and release from biodegradable polyanhydrides." Thesis, Massachusetts Institute of Technology, 1995. http://hdl.handle.net/1721.1/38364.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Whitaker College of Health Sciences and Technology, 1995.Includes bibliographical references (leaves 105-109).
by Lisa Y. Shieh.
Ph.D.
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Fu, Karen 1967. "Stability of proteins within biodegradable microspheres." Thesis, Massachusetts Institute of Technology, 2000. http://hdl.handle.net/1721.1/8422.
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Thesis (Sc.D.)--Harvard--Massachusetts Institute of Technology Division of Health Sciences and Technology, 2000.Includes bibliographical references.
In the past decade, biodegradable polymers have become the materials of choice for a variety of biomaterials applications. In particular, poly(lactic-co-glycolic acid) (PLGA) microspheres have been extensively studied for controlled-release protein delivery. However, significant issues arise in formulating such delivery systems since few proteins have been successfully encapsulated and released from these microspheres. Here, methods are developed to determine the causes of protein instability and solutions are provided for overcoming these problems. A commonly used technique for protein encapsulation in PLGA microspheres is the double-emulsion method. The harsh processing associated with this method can cause denaturation of the encapsulated protein. Herein, we have used Fourier transform infrared (FTIR) spectroscopy to determine the secondary structures of two model proteins, bovine serum albumin (BSA) and chicken egg-white lysozyme, within PLGA microspheres. This is a novel technique for in situ evaluation of proteins within microspheres and potentially a powerful and quick method for assessment of formulations. Results for both proteins indicate changes in structure upon entrapment within the microspheres. However, addition of the stabilizing excipient trehalose prevents the denaturing effects incurred during processing. In addition, BSA released from microspheres is improved by incorporation of trehalose. With microspheres made by double emulsion, there is often a large, initial burst of drug release upon injection. This results in inefficient use of therapy. To prevent this loss, a modified spontaneous emulsification method was explored.
(cont.) With this procedure both protein and polymer are soluble in a single solvent system thus avoiding creation of a water/solvent interface. The process was optimized for microsphere size and protein loading. Addition of a charged surfactant served to improve protein solubility and thus increase protein loading. In vitro and in vivo release kinetics showed a minimal burst, lower than that found with double emulsion microspheres, followed by sustained release. Upon injection of the microspheres in vivo, the PLGA microspheres begin to degrade. Degradation of the polymer generates acidic monomers, and acidification of the inner polymer environment is a central issue in the development of these devices for drug delivery. To quantitatively determine the intraparticle acidity, pH-sensitive fluorescent dyes were entrapped within the microspheres and imaged with confocal fluorescence microscopy. The technique allows visualization of the spatial and temporal distribution of pH within the degrading microspheres. The data indicate the formation of a very acidic environment within the particles with the minimum pH as low as 1.5. The images show a pH gradient, with the most acidic environment at the center of the spheres and higher pH near the edges, which is characteristic of diffusion-controlled release of the acidic degradation products. Strategies to avoid the accumulation of acidic monomers involve decreasing the diffusion distance of the degradation products by either decreasing the overall diameter of the microspheres or creating porous particles.
by Karen Fu.
Sc.D.
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Isay, Alina, Vita Martynenko, Valeriya Kim, Nataliya Lepuha, and Victoria Vostrikova. "Biodegradable polymers for production of plastics." Thesis, Молодь у глобалізованому світі: академічні аспекти англомовних фахових досліджень (англ. мовою) / Укл., ред. А.І.Раду: збірник мат. конф. - Львів: ПП "Марусич", 2011. - 147 с, 2011. http://er.nau.edu.ua/handle/NAU/20867.
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Lee, Namheon. "Corrosion Analysis of Biodegradable Magnesium Implants." University of Cincinnati / OhioLINK, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1250274373.
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Tiasha, Tarannum R. "Biodegradable Magnesium Implants for Medical Applications." University of Cincinnati / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1491562059856412.
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Yu, Jiayi. "Tunable Biodegradable Polymers for Regenerative Medicine." University of Akron / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=akron1524821159786707.
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Fei, Dan. "Biodegradable polyanhydrides as drug delivery systems." Thesis, Aston University, 2003. http://publications.aston.ac.uk/10949/.
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Polyanhydrides are useful biodegradable vehicles for controlled drug delivery. In aqueous media the breaking of the anhydride bonds resulting in gradually polymer fragments collapse and release drugs in a controlled manner. In this study, two new biodegradable polyanhydrides copolymers were synthesised using a melt-polycondensation method. The first is poly (bis (p-carboxyphenoxy)-2-butene-co-sebacic acid) (CP2B: SA), which has double bonds along the polymer backbone. The second is crosslinked poly (glutamic acid-sebacic acid-co-sebacic acid) (GluSA: SA), where the conjugated unit of glutamic acid with sebacic acid (glutamic acid-SA) acted as a crosslinking fragment in producing the crosslinking polymer. The two polymers were applied to preparation of microspheres with bovine serum albumin (BSA) as a model protein, using both double emulsion solvent evaporation and spray drying methods. The characterisation of the microspheres, morphology, particle size, and drug loading, was studied. The in vitro hydrolytic degradation of polymers and blank microspheres was monitored using IR, GPC, and DSC. In vitro drug release behaviour was also studied. Though the studies showed cleavages of anhydride bonds occurred rapidly (<5 days), bulks of the polymer microspheres could be observed after a few weeks to a month; and only around 10-35% of the protein was detectable in a four-week period in vitro. We found the pH of the medium exerts a large impact on the release of the protein from the microspheres. The higher the pH, the faster the release. Therefore the release of the protein from the polyanhydride microspheres was pH-sensitive due mainly to the dissolution of monomers from the microspheres.
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Jia, Weiwei. "Polylactic acid fibre reinforced biodegradable composites." Thesis, University of Manchester, 2015. https://www.research.manchester.ac.uk/portal/en/theses/polylactic-acid-fibre-reinforced-biodegradable-composites(732904c8-584b-4fbb-b68a-3cf14dc84e9f).html.
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Polylactic acid (PLA) is a well-known biodegradable and sustainable polymer, derived from renewable agricultural sources. Its high price in the past limited its applications to mainly biomedical materials such as bone fixation devices. As the growth of awareness in global environment protection and sustainable development, PLA has attracted increased attention and development. Nowadays, the applications of PLA have been broadened into plastics, textiles and composites etc. Composites have been widely used in industrial applications for several decades, due to their high strength-to-weight ratio and good structural properties. However, most traditional composite materials are composed of two distinct fossil fuel based components. They are not eco-friendly and are difficult to recycle. This study aims at the development of PLA biodegradable composites and the optimisation of the processing parameters to achieve the best mechanical properties of PLA self-reinforced composites (PLA-SRC) for various end-uses. A variety of polymer analytical techniques were used to evaluate crystallinity, thermal properties, and chemical structures of the PLA reinforcement and matrix. Further study was carried out to assess the effects on mechanical properties of PLA-SRC caused by the processing temperature, pressure and holding time. The composites produced at high temperature and/or high pressure have significantly better matrix penetration (fibre wetting), which enhances mechanical properties. However, holding time was found to have no significant effect on the properties of PLA-SRC.
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Tang, Min. "Novel biodegradable polyesters derived from carbohydrates." Thesis, Imperial College London, 2009. http://hdl.handle.net/10044/1/9017.
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This thesis concerns the synthesis of new biodegradable polyesters from carbohydrates.All the new products have been characterised using nuclear magnetic resonance (NMR)spectroscopy and mass spectrometry; some have been studied using X-raycrystallography. In Chapter 1, which is the introduction, some of the leadingbiodegradable polymers are introduced, in particular attention is paid to polyesterswhich are synthesised from carbohydrates. In addition, the standard polymerisationmethods for the polyester synthesis - ring opening polymerisation and steppolymerisation - are described. Chapter 2 details the synthesis and polymerisation ofacetic acid 5-acetoxy-6-oxo-tetrahydro-pyran-2-yl methyl ester. Three differentinitiating systems have been used for ring opening polymerisations; the kinetics and thepolymer product of the polymerisation are discussed. L-Lactide was used incopolymerisations with acetic acid 5-acetoxy-6-oxo-tetrahydro-pyran-2-yl methyl ester;the copolymers show distinct thermal properties and accelerated degradation ratescompared with poly(L-Lactide) (PLLA). Chapter 3 involves applying functionalisedcarbohydrates, with one free hydroxyl group, as the co-initiator for the ring openingpolymerisation (ROP) of L-lactide. The polymerisations were well controlled with linearrelationships between the percentage lactide conversion and the polymer?s molecularweight. The carbohydrates form the functionalised end group of the PLLA, which, inturn, improve the hydrophilicity of the resulting PLLA. These end-group functionalisedpolylactides have been used as the matrix for human-osteoblast-derived osteosarcomacells (SaOS-2 cells) culturing, and these studies proved that the carbohydrate endgroups were non toxic. Chapter 4 describes the synthesis of a series of othercarbohydrate lactones derived from D-glucono-1,5-lactone, D-xylose and 2-deoxy-Dribose;the lactones include 2,3,4-tri-O-benzyl-D-xylonolactone, 6-methyl-2-oxotetrahydro-2H-pyran-3-yl acetate, (S)-6-(benzyloxymethyl)-tetrahydropyran-2-one. TheROP of these lactones resulted in formation of low molecular weight oligomers, exceptfor 2,3,4-tri-O-benzyl-D-xylonolactone, which can not be polymerised. Chapter 5describes the overall conclusions resulting from the experiments described in the thesis.Chapter 6 is the experimental section and thus provides a detailed description of thesynthesis of all the compounds prepared in the thesis and their analytical data. TheAppendices include two papers that have already been published, describing some ofthe work in the thesis; important additional NMR spectra and MALDI-ToF spectra; andthe complete X-ray crystallography data.
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Mylonakis, Andreas Wei Yen. ""Biodegradable polymer adhesives, hybrids and anomaterials" /." Philadelphia, Pa. : Drexel University, 2008. http://hdl.handle.net/1860/2911.
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Wong, Hoi-man. "Surface modification of biodegradable metallic material." Click to view the E-thesis via HKUTO, 2008. http://sunzi.lib.hku.hk/hkuto/record/B41290689.
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Knight, Pamela Tiffany. "Polyester-based Biodegradable Systems Incorporating POSS." Cleveland, Ohio : Case Western Reserve University, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=case1250709236.
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Thesis(Ph.D.)--Case Western Reserve University, 2010Title from PDF (viewed on 2009-12-22) Department of Macromolecular Science and Engineering Includes abstract Includes bibliographical references and appendices Available online via the OhioLINK ETD Center
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Gide, Mussie. "Design, Synthesis, Application of Biodegradable Polymers." Scholar Commons, 2018. https://scholarcommons.usf.edu/etd/7625.
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Bacterial infections have posed a serious threat to the public health due to the significant rise of the infections caused by antibiotic-resistant bacteria. There has been considerable interest in the development of antimicrobial agents which mimic the natural HDPs, and among them biodegradable polymers are newly discovered drug candidates with ease of synthesis and low manufacture cost compared to synthetic host defense peptides. Herein, we present the synthesis of biocompatible and biodegradable polymers including polycarbonate polymers, unimolecular micelle hyperbranched polymers and dendrimers that mimic the antibacterial mechanism of HDPs by compromising bacterial cell membranes. The developed amphiphilic polycarbonates are highly selective to Gram-positive bacteria, including multidrug-resistant pathogens and the unimolecular micelle hyperbranched polymers showed promising broad-spectrum activity. However, lipidated amphiphilic dendrimers with low molecular weight display potent and selective antimicrobial activity against both Gram-positive and Gram-negative bacteria, including multidrug-resistant strains. In addition to antibacterial activity against planktonic bacteria, these dendrimers were also shown to inhibit bacterial biofilms effectively. These class of polymers may lead to a useful generation of antibiotic agents with practical applications.
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Joshi, Vijaya Bharti. "Biodegradable particles as vaccine delivery systems." Diss., University of Iowa, 2014. https://ir.uiowa.edu/etd/1343.
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Immunotherapy has been widely investigated in cancer, infectious diseases and allergies for prevention or amelioration of disease progression. In the case of vaccines, the key cellular target in stimulating an effective and appropriate immune response is the professional antigen presenting cell or dendritic cell (DC). Cancer vaccines are primarily aimed at the activation of a tumor-specific cytotoxic T lymphocyte (CTL) response whilst vaccines to allergies are aimed at reducing IgE responses. Such vaccines normally involve the administration tumor-associated antigens (TAAs) for cancer, or antigens (Ags) derived from infectious microbes and allergens in the case of allergies. Ags, whether derived from tumor or allergen, can be combined with adjuvants, that include immunostimulatory molecules recognized by the pathogen associated receptors expressed by DCs and can trigger the activation/maturation of DCs. Co-delivery of an appropriate adjuvant with an Ag can stimulate DCs to subsequently promote a robust Ag-specific CTL response which may favor anti-tumor immunity.
Cancer vaccines have been widely investigated in the clinics as a complementary therapy to surgery, radiation and chemotherapy. Activation of CTLs against tumor cells that express TAAs could lead to the complete eradication of a cancer and prevent its reoccurrence. In this study I developed microparticles using a polyanhydride polymer prepared from 1,8-bis(p-carboxyphenoxy)-3,6-dioxaoctane (CPTEG) and 1,6-bis(p-carboxyphenoxy) hexane (CPH) that has shown inherent adjuvant properties. I prepared 50:50 CPTEG:CPH microparticles encapsulating a model tumor Ag, ovalbumin (OVA), and synthetic oligonucleotide containing an unmethylated CpG motif, CpG, as an adjuvant. CpG has shown significant potential as an adjuvant for TAA-based vaccines leading to significant anti-tumor immune activity. I have shown that mice vaccinated with OVA-encapsulated 50:50 CPTEG:CPH microparticles developed OVA-specific CTL responses. These mice showed enhanced survival compared to the control treatment groups when challenged with OVA expressing tumor cells .
In a more novel in-situ cancer vaccine, TAAs from dying tumor cells (caused by certain chemotherapeutic drugs) can be used as the source of Ags delivered to DCs. The presence of an adjuvant with dying cancer cells can assist in appropriate maturation of DCs so as to promote the generation of an effective tumor/TAA-specific CTL response against released TAAs. In this work I developed a therapeutic in situ tumor vaccine encapsulating a chemotherapeutic drug and CpG. Doxorubicin (Dox) is a widely used chemotherapeutic drug that induces tumor cells to undergo an immunogenic form of apoptosis. Sustained release of Dox in solid tumors of mice can cause the release of a variety of TAAs which can be presented by DCs and, in the presence of CpG, stimulate a strong anti-tumor CTL response. I prepared formulations of poly(lactic-co-glycolic acid) (PLGA) particles loaded with Dox and CpG which demonstrated sustained release of their cargo. I show that among various formulations of Dox and CpG, co-delivery of Dox and CpG in the same PLGA particles in-vivo showed the highest reduction in tumor growth and longest survival when compared to treatment groups of PLGA particles delivering Dox and CpG either alone or in combination.
PLGA particles have also been investigated as a prophylactic vaccine delivery system that generates a robust Ag-specific CTL response. This system has been employed for the development of vaccines against various infectious diseases and allergies. However, there has been conflicting opinions regarding the optimum size of PLGA particles required to stimulate an active CTL response. Thus, I developed different sizes of PLGA particles encapsulating OVA and CpG to study the relationship of particle size with the magnitude of OVA-specific CTL responses. I showed that the degree of particle uptake and activation of DCs increased with decreasing size of PLGA particles. I also showed that immunization of mice with 300 nm sized particles demonstrated a higher proportion of OVA-specific CTLs and increased the secretion of IgG2a antibody responses. I also evaluated the efficacy of these particles with a clinically relevant Ag, Dermatophagoides pteronyssinus-2 (Der p2). Mice vaccinated with different sizes of PLGA particles loaded with CpG and coated with Der p2 displayed different magnitudes and types of immune activation against Der p2. The small sized particles decreased the airway hyperresponsiveness associated with allergy-induced asthma. The presence of CpG in the PLGA particle vaccines also reduced the airway hyperresponsiveness.
This thesis research has contributed to the identification and development of a delivery system for Dox in combination with CpG which gives sustained release of these molecules within tumors and show the longest survival in tumor bearing mice. This study also optimized the size of PLGA particles for the delivery of vaccine to produce a robust Ag specific immune response for development of vaccination against intracellular diseases, cancer and allergy.
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Fuoco, Tiziana. "Biodegradable and functional aliphatic co-polyesters." Doctoral thesis, Universita degli studi di Salerno, 2016. http://hdl.handle.net/10556/2171.
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2014 - 2015Over the past decades, aliphatic polyesters have found rapidly increasing interest. Linear aliphatic polyesters, such as poly(glycolide) (PGA), poly(lactide) (PLA), poly(ε−caprolactone) (PCL) and their copolymers have found a wide range of practical applications, from packaging to more sophisticated biomedical devices. This class of materials is biocompatible and biodegradable; the degradation products are excreted via the citric acid cycle. The uniqueness of this class of polymers lies in its immense diversity and synthetic versatility. They can be prepared by a variety of monomers via different approaches. The ring-opening polymerization of cyclic esters and lactone is the best strategy. There is still need for improvements to provide materials with enhanced features to address the new requirements of use. A precise control over properties, like hydrophilicity, glass transition, the presence of functional group is important to regulate the biodegradation rate, the thermomechanical properties and it relies on a controlled synthetic pathway. This doctoral thesis was focused on the development of synthetic pathways to obtain aliphatic polyesters with different and controlled microstructures and functional groups by extending the expertise in the ring-opening polymerization of cyclic esters by dimethyl(salicylaldiminato)aluminum compounds. Dimethyl(salicylaldiminato)aluminum compounds with a different steric hindrance at the ortho position of the phenolato ring were tested as catalysts in the ring-opening homo- and co-polymerization of GA, rac-LA and CL. These complexes resulted active for the production of PLGA copolymers with variable microstructure. This copolymer is one of the most used in biomedical field as temporary scaffolds and as drug delivery device. The degradation profile of PLGA is strongly influenced by the microstructure. The copolymerization of GA and LA were performed in bulk and in solution, by varying comonomers ratio, monomer/catalyst feed ratio, temperature, reaction time and solvent. By changing the reaction conditions, copolymers from random, to blocky, to di-block were obtained, demonstrating the versatility of such system in modulating the copolymers microstructure and the related thermal properties. The same catalytic approach was extended to the copolymerization of GA with CL and to the terpolymerization of GA, CL and rac-LA. The formation of random copolymers was favored by the steric hindrance of the catalyst and transesterification reactions contributed to randomize the structure. All the terpolymer samples resulted random and amorphous, the incorporation of the monomers is in this case determined by the bulkiness of the catalyst and by the higher coordination ability of the cyclic esters. While the physical properties can be tailored by copolymerization, the introduction of functional group extends the possible applications to new areas, especially in biomedical field where the binding of biological motifs could enable interactions with cells. Due to the ubiquity of thiol groups in the biological environment and to the pliability of thiol chemistry, an ad hoc lactide-type monomer possessing a pendant thiol-protected group, the 3-methyl-6-(tritylthiomethyl)-1,4-dioxane-2,5-dione was designed and synthetized. Then, this molecule was used as a “building block” for the preparation of functionalized aliphatic co-polyesters by copolymerization with LA and CL promoted by dimethyl(salicylaldiminato)aluminum compounds. After polymerization, the pendant groups incorporated along the chains were converted into pyridyl disulfide functionalities. This derivative was used to prepare porous scaffolds by salt-leaching method after blend with PCLA. The pyridildisulphide groups, which are very reactive in the disulphide exchange reaction, embedded in the 3D porous scaffolds were exploited to graft a cysteine terminated RGD peptide demonstrating the potential of such prepared materials. Finally, dimethyl(salicylaldiminato)aluminum compounds were employed as catalyst in the ring-opening polymerization of an unsaturated large lactone, the ω−6-hexadecenlactone (6HDL). Semicrystalline polyethylene-like unsaturated polyesters were obtained with a good control over the chain growth. The double bonds along the polymeric backbones were used to carry out further modification, which occurred without any change in the degree of polymerization, however, modifying the thermal and structural polymer features. Copolymerization of the 6HDL with the smaller ring size CL produced a true random semicrystalline copolymer. The pseudo-living behaviour of the catalytic system and the absence of transesterification reactions allowed also the preparation of linear block copolymers of 6HDL with CL and/or rac-LA by sequential addition of the monomers. These block copolymers were also semicrystalline. [edited by author]
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Capuano, G. "AMPHIPHILIC, BIODEGRADABLE ANDBIOCOMPATIBLE POLYMERS FOR INDUSTRIALAPPLICATIONS." Doctoral thesis, Università degli Studi di Milano, 2017. http://hdl.handle.net/2434/477898.
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The aim of this PhD work was to establish the synthetic procedures for new families of biocompatible and biodegradable and/or bioeliminable biomaterials that can be differently processed to obtain nanoparticles, core-shell nanofibres and hydrogel slabs or conduits, respectively. Depending on composition, size and morphology, these biomaterials may be intended for applications as drug delivery systems and/or tissue regeneration.
Specifically, the research project has been developed along two main lines:
• Synthesis of poly(lactic-glycolic acid)-g-poly(1-vinylpyrrolidin-2-one) (PLGA-g-PVP) copolymers whose architecture consisted of a long PLGA backbone with oligomeric PVP pendants. These were obtained by the radical polymerisation of 1-vinylpyrrolidin-2-one in molten PLGA 50:50, acting as chain transfer agent. The procedure was a single pot - single step one. Copolymers were characterized by FTIR, 1H- and 13C-NMR and thermal analyses. They were saponified giving, besides PLGA degradation products, also un-degraded PVP. This was isolated and analysed by size exclusion chromatography, to evaluate the molecular weights of grafted PVP chains. MALDI-TOF analysis allowed identifying the chemical structure of PVP terminals and unambiguously establishing that PVP chains had been grafted onto PLGA backbone
PLGA-g-PVP with different PVP content were formulated as drug nanocarriers by different procedures. Doxorubicin-loaded nanoparticles were prepared by the solvent diffusion method and fully characterised. In vitro drug release kinetics were studied and in vitro biological activity evaluated on several antitumoral cell lines.
PLGA-g-PVP were also used as coatings of lipid nanocapsules for the delivery of curcumin and artemisinin as antimalarials. Drug loaded-lipid micro-dispersions were first prepared by oil in water emulsion. The lipid drops were converted into nanometric ones by high pressure homogenization and finally surface coated by adding a DMSO/acetone PLGA-g-PVP solution. Growth inhibition assay were conducted on plasmodium falciparum (3D7) cultures. Haemoltic assays were conducted on healthy red blood cells.
PLGA-g-PVP- and PLGA-based scaffolds consisting of nanofibrous mats were produced by electrospinning. Starting materials were electrospun and their morphology was evaluated by scanning electron microscopy and wettability by contact angle measurements. Coaxial electrospinning of two materials, in which PLGA formed the core and PLGA-g-PVP the shell of fibres, were also conducted and compared with those obtained by mixed solutions of staritng materials. Chemical composition was evaluated by TGA, morphology by scanning electron microscopy and wettability by contact angle measurements. Nanofabric scaffold produced will be evaluated for drug release and tissue engineering applications.
• Synthesis of a new classes of poly(saccharide)-poly(aminoamine)s 3D-network intended as scaffolds for the regeneration of liver.
In particular, hyaluronic acid-polyamidoamine and hyaluronic acid-gelatin- polyamidoamine hydrogels were synthesised by amidation reaction between the carboxylic acid group of hyaluronic acid and amine groups of gelatin and or an NH2-functionalized PAA, promoted by 4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholinium chloride (DMTMM) as coupling agent. Chemical-physical characterization were carried out on hydrogels. In order to promote hepatic cell proliferation serotonin was bonded to both hydrogels, adding it to the initial recipe, exploiting the above reaction between carboxylic acid group of hyaluronic acid and amine group of serotonin. Serotonin-loaded hydrogels were tested in vitro to evaluate biological efficacy.
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Galgali, P. P. "Biodegradable polymers based on natural substances." Thesis(Ph.D.), CSIR-National Chemical Laboratory, Pune, 2004. http://dspace.ncl.res.in:8080/xmlui/handle/20.500.12252/2890.
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Pandey, Asutosh K. "Synthesis and characterization of biodegradable polymers." Thesis(Ph.D.), CSIR-National Chemical Laboratory, Pune, 2009. http://dspace.ncl.res.in:8080/xmlui/handle/20.500.12252/2728.
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Barragán, Dan Jarry. "Biodegradability in soil determination and fate of some emerging biodegradable materials for agricultural mulching." Doctoral thesis, Universitat de Lleida, 2012. http://hdl.handle.net/10803/107948.
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The purpose of this PhD thesis was to evaluate the biodegradability potential and ecotoxicological effects of several biodegradable plastics for agricultural use under controlled laboratory conditions in soil. In this study, commercial and still in experimental stage biodegradable plastic films were chosen: Mater-Bi® (corn starch), Bio-Flex® (polylactic acid), Biofilm® (cereal flour), Bioplast® (potato starch), MirelTM (polyhydroxyalcanoates) Ecovio® and Bionelle®. In addition, a sheet commercially known as MimGreen® paper was evaluated. Initially, a gravimetric and FTIR analyses were carried out to determine changes in both weight loss and molecular changes in the plastics respectively. A second experiment consisted in assessing the biodegradability of the materials by designing and building a respirometric system. This system allowed me to measure, with a higher sensitive, the biodegradation process of the materials under laboratory conditions in soil. In addition, I compared the biodegradability of these materials with the remains of a typical crop used for mulch application, tomato (Lycopersicum esculentum). Finally, the ecotoxicological effects of biodegradable films on Zea mays plants, earthworms Eisenia fetida and microbial soil activity were evaluated using the standardised regulations or existing methods. Thus, I was able to prove ecological advantages of these materials.El propòsit d'aquesta tesi doctoral ha estat valorar el potencial de biodegradabilitat i efectes ecotòxics de diferents plàstics biodegradables per a ús agrícola sota condicions controlades al laboratori. En l'estudi es van triar set films plàstics biodegradables de diferent composició química, tant comercial com encara en fase experimental: Mater-Bi® (midó de blat de moro), Bio-Flex® (àcid polilàctic), Biofilm® (farina de cereals), Bioplast® (midó de patates), MirelTM (polihidroxialcanoatos), Ecovio® i Bionelle®, a més d'una làmina de paper (Mimgreen®). Es van realitzar dos experiments. El primer concistía en realitzar un estudi gravimètric per mesurar el grau de degradació dels plàstics mitjançant la pèrdua de pes, a més es va dur a terme un anàlisi espectroscòpic FTIR, que va permetre discernir els canvis en els entorns moleculars que faciliten o dificulten el procés de biodegradació dels materials. El segon experiment va consistir a valorar la biodegradabilitat dels materials mitjançant el disseny i construcció d'un sistema respiromètric, que va permetre mesurar amb major sensibilitat el grau de biodegradació dels materials seleccionats sota condicions de laboratori en sòl. Addicionalment es va comparar la biodegradabilitat dels materials provats amb restes d'un cultiu típic d'ús de encoixinat com és el cas del tomàquet (Lycopersicum esculentum). Finalment, es van investigar els efectes ecotòxics dels films biodegradables sobre plantes de Zea mays, cucs Eisenia fetida i l'activitat microbial del sòl, els assaigs van ser realitzats a partir de les normatives o mètodes estandarditzats vigents el que va permetre comprovar els avantatges ecològics d'aquests materials.
El propósito de la presente Tesis Doctoral ha sido valorar el potencial de biodegradabilidad y efectos ecotóxicos de diferentes plásticos biodegradables para uso agrícola bajo condiciones controladas de laboratorio en suelo. En el estudio se eligieron siete films plásticos biodegradables de diferente composición química tanto comercial como aún en fase experimental: Mater-Bi® (almidón de maíz), Bio-Flex®(ácido poliláctico), Biofilm® (harina de cereales), Bioplast® (almidón de patatas), MirelTM(polihidroxialcanoatos), Ecovio® y Bionelle®; además de una lámina para acolchado con el nombre de papel Mimgreen®. Como primer paso diferentes ensayos fueron realizados entre ellos uno gravimétrico para medir la pérdida de peso de los materiales y otro mediante análisis espectroscópico FTIR, lo que permitió discernir los cambios en los entornos moleculares que facilitan o dificultan el proceso de biodegradación de los materiales. El segundo experimento consistió en valorar la biodegradabilidad de los materiales mediante el diseño y construcción de un sistema respirométrico que permitió medir con mayor sensibilidad el grado de biodegradación de los materiales seleccionados bajo condiciones de laboratorio en suelo. Adicionalmente se comparó la biodegradabilidad de los materiales probados con restos de un cultivo típico de uso de acolchado como es el caso del tomate (Lycopersicum esculentum). Finalmente, se investigaron los efectos ecotóxicos de los films biodegradables sobre plantas de Zea mays, lombrices Eisenia fetida y la actividad microbial del suelo; los ensayos fueron realizados a partir de las normativas o métodos estandarizados vigentes lo que permitió comprobar las ventajas ecológicas de estos materiales.
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Wang, Liang. "Aerogels based on biodegradable polymers and clay." Doctoral thesis, Universitat Politècnica de Catalunya, 2015. http://hdl.handle.net/10803/336971.
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Foam-like aerogels based on biodegradable polymers and sodium montmorillonite (Na+-MMT) clay were prepared through an environmentally friendly freeze-drying process. Both synthesized and bio-based polymers were utilized in this thesis, including polyvinyl alcohol (PVOH), carboxylmethylcellulose (CMC), xanthan gum, agar, Arabic gum and starch. The morphologies of aerogels were characterized using scanning electron microscopy. The mechanical properties investigation included compression and impact tests. Porosities and solid densities were measured using a helium pycnometer while the pore size distribution was determined by automated mercury porosimeters.
Most of polymer-clay aerogels exhibited porous and layered structures that were formed via ice templating. However, high viscosity of the precursor solution may break the layered architecture by retarding the formation of ice crystals (e.g. 2.5 wt% agar aqueous solution). The structures as well as the properties of aerogels were mainly influenced by polymer/clay proportion. Polymer molecules play a role of glue linking the clay nanoparticles, improving the structural integrity and hence the mechanical performance of the aerogels. On the other hand, clay platelets serve as a physical barrier that increases the heat endurance.
Recycled cellulose fibers (RCF) that were isolated from waste paper pulp were also used to prepare bio-based aerogels. Adding another biopolymer CMC into RCF aerogels, the resultant RCF-CMC composite aerogels showed different microstructures and enhanced mechanical properties.
Physical blending and chemical crosslinking were used to tailor the mechanical properties of xanthan gum/clay aerogels and starch/clay aerogels, respectively. Blending agar with xanthan gum in aqueous solution, the resultant aerogels displayed a significant improvement in mechanical properties compared with those containing a single biopolymer. Moreover, they exhibited tunable microstructures and mechanical properties by changing agar/xanthan gum ratio in the aerogels. As to starch/clay aerogels, the incorporation of glutaraldehyde enhanced the structural integrity and mechanical properties of the aerogels through crosslinking reaction between glutaraldehyde and starch molecules, which was proved by Fourier-Transform infrared (FT-IR) spectroscopy analysis.
The evaluation of the flammability of aerogels was conducted with a cone colorimeter while the thermal stability was obtained from the results of thermogravimetric analysis. In regard to PVOH-clay aerogel, different types of flame retardant fillers, such as aluminum trihydroxide (ALH), ammonium polyphosphate (APP), silica gel and potassium carbonate, were adopted to modify their flame retardant properties. The results showed that ALH addition enhanced the flame retardancy as well as mechanical properties. For RCF-CMC aerogels, APP and clay played a synergetic effect on the flame retardancy and thermal stability.En esta Tesis se han preparado diversos aerogeles usando polímeros biodegradables como matriz y arcilla como refuerzo, a través de un proceso de fabricación amigable con el medio ambiente. Los polímeros empleados han sido tanto de origen natural (goma árabiga, agar-agar, goma xantana, almidón) o sintéticos como la carboximetilcelulosa (CMC) o el alcohol polivinílico. Los compuestos formados se han caracterizado a través de diferentes técnicas con el objeto de relacionar las morfologías generadas con las propiedades térmicas y mecánicas resultantes. La gran mayoría de los aerogeles polímero/arcilla exhiben una estructura porosa y laminar que se forma a raíz de la liofilización. Sin embargo, se ha apreciado que altas viscosidades en la solución precursora puede romper la arquitectura laminar al retardar el crecimiento de los cristales de hielo (ej. Solución acuosa de 2.5 % peso de agar). La estructura y las propiedades de los aerogeles están asimismo y en general influenciados por la relación polímero/arcilla. En estos sistemas, las moléculas de polímero actúan a manera de pegamento uniendo las partículas de arcilla, incrementando de esa manera notablemente la capacidad mecánica de los aerogeles. Por otro lado la arcilla actúa entre otras formas, como barrera térmica incrementando la resistencia térmica y al fuego de las espumas formadas. Dentro de este trabajo se han empleado fibras de celulosa recicladas de residuos de papel en un intento de preparar bio-aerogeles a partir de material de desecho. La unión de estas fibras con CMC permitió obtener aerogeles con propiedades mejoradas y la posibilidad de emplear estos residuos en un segundo uso. Además del mezclado físico, en algunos casos se ha realizado una reacción de entrecruzamiento para ajustar las propiedades finales, como en el caso de los aerogeles goma xantana/arcilla o almidón/arcilla. La mezcla de agar con goma xantana en solución acuosa resultó en un notable aumento de propiedades con respecto a las composiciones que contenían un único polímero, debido al cambio morfológico inducido, pasando de una estructura laminar a una de tipo panal de abeja (honeycomb). De esta forma y a través de la relación entre estos dos polímeros naturales ha sido posible balancear y definir las propiedades finales deseadas para el aerogel. En los sistemas almidón/arcilla el entrecruzamiento se ha conseguido a través de un agente externo como el glutaraldehido. Atendiendo a su posible uso final, unas de las propiedades más relevantes en los aerogeles que se ha estudiado ha sido la estabilidad térmica y la resistencia al fuego. En este sentido, se han preparado sistemas basados en Polivinilalcohol/arcilla modificados con diferentes retardantes de llama. De los diversos aditivos probados la combinación con hidróxido de aluminio ha mostrado un efecto sinérgico incrementando tanto de la resistencia a fuego como las propiedades mecánicas. En los sistemas basados en celulosa la presencia de polifosfato de amonio y arcilla ha demostrado así mismo un efecto potenciador de la estabilidad térmica y en el retardo de llama.
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Cleroux, Carolyne. "Biodegradable nanoparticles for sustained occular drug delivery." Thesis, University of Ottawa (Canada), 2010. http://hdl.handle.net/10393/28485.
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Apoptosis (programmed cell-death) is a common final pathway through which cells die in retinal degenerative diseases. The purpose of this project was to develop biodegradable nanoparticles that quickly deliver XIAP, an inhibitor of apoptosis, to retinal cells following acute insults. In vitro protein release profiles from different formulations were established, and two cell types were incubated with nanoparticles to assess cellular uptake. Subretinal injections were carried out in rats to assess in vivo localization and possible toxicity. In vitro studies showed an initial burst of protein followed by sustained release, with overall low levels of protein release. Cell culture experiments suggest that particles are mostly membrane-bound, and some may be internalized. In vivo experiments revealed no signs of toxicity, and protein localized within the photoreceptor layer. In conclusion, nanoparticles may provide a good delivery system for XIAP; however higher levels of protein release are needed for neuroprotection, warranting further investigation.
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Cao, Xudong. "Delivery of neuroactive molecules from biodegradable microspheres." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/tape16/PQDD_0012/MQ34112.pdf.
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Larsson, Mariann. "Electrochemical analysis of Zinc for biodegradable applications." Thesis, KTH, Skolan för informations- och kommunikationsteknik (ICT), 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-121526.
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To avoid costly and risky secondary surgery after implantation, biodegradableimplants are of importance to the medical device industry. Theseshould be designed to degrade in a controlled manner, and to haverest products taken care of by the body’s internal mechanisms withoutcausing harm. Finding materials that corrodes predictably, are biocompatiblein itself and when decomposed is a great challenge. This study focused on the corrosion behaviour of zinc, which anearlier study pointed out as a promising subject for such an analysis.The properties of zinc samples were observed by electrochemical methodswhile immersed in phosphate buffered saline (PBS), Ringer solutionand human blood. Scanning electron microscopy (SEM) and energy dispersivex-ray spectroscopy (EDX) were used to characterise the structureand composition of the corrosion products. It was found that thecorrosion mechanisms are different in the three electrolytes studied. Samples immersed in Ringer solution showed a uniform corrosion,with an initial corrosion rate of 0.1 mm/yr - 0.5 mm/yr. Resultsfrom electrochemical impedance spectroscopy (EIS) suggest the corrosionproducts after time (12-24 h) correspond to a two-layer interface,interpreted as an outer diffusion controlled layer appearing first, witha homogenous layer being formed later between the metal and the initiallayer. EDX and SEM indicates that the corrosion products mainlyconsist of zinc carbonates. These findings were confirmed by FourierTransform Infrared (FTIR) spectroscopy. The zinc samples exposed to PBS solution exhibit a localized corrosion,with dendrite like structures growing out from the surface astime passes. The initial corrosion rate was determined to be somewherebetween 6 μm/yr- 22 μm/yr. The EIS model suggest that the corrosionproducts developed on the PBS exposed surface corresponds to a singleoxide layer covering the metal. The main corrosion products weredetermined to be zinc phosphates (FTIR and EDX). Human blood was used for a final set of experiments. Here the zincsamples corroded by an initial rate of 0.08 - 0.38 mm/yr. The corrosionwas uniform like the samples exposed to Ringer solution. Meanwhile,the electrochemical model (from EIS) appeared similar to the one encounteredin the PBS experiments, suggesting a single layer of corrosionproducts over the metal surface.För att undvika kostsamma och riskfyllda sekundära ingrepp är nedbrytbaraimplantat intressanta. Dessa designas för att för att kontrolleratbrytas ned och tas omhand av kroppens egna mekanismer. Den storautmaningen är att hitta material som bryts ner på ett ofarligt och förutsägbartsätt, i termer av hastighet, restprodukter och biokompatibilitet. Denna studie fokuserade på korrosionsförloppet hos zink, vilket en tidigarestudie visat vara en lämplig kandidat för denna sorts analys. Zinkprovernasegenskaper observerades med elektrokemiska metoder medan provernavar nedsänkta i/täckta av fosfatbuffrad saltlösning (PBS), Ringerlösningsamt mänskligt blod. Svepelektronmikroskopi (SEM), svenska ord för(EDX) var två metoder som användes för att undersöka strukturen ochsammansättningen av korrosionsprodukterna. Det visade sig att korrosionsmekanismenvar olika i de tre olika studerade elektrolyterna. Prover som var täckta av Ringerlösning visade homogen korrosionmed en initial korrosionshastighet på 0.1 mm/år - 0.5 mm/år. Resultatfrån den elektrokemiska impendansspektroskopin pekar mot att korrosionsprodukternaefter 12-24 h motsvarar ett två-lagers gränssnitt somkan tolkas som ett initialt (0-12 h) bildat yttre diffusionskontrolleratlager, följt av ett homogent lager som bildas mellan metallen och detinitiala lagret. EDX och SEM visar att korrosionsprodukterna till mestadelsbestår av zinkkarbonater. Dessa observationer är även styrkta avFTIR. Zinkproverna som utsattes för PBS uppvisade fläckvis korrosion,med dendrit-liknande strukturer som växte ut ur underlaget under provtiden.Initial korrosionshastighet uppmättes mellan 6 och 22 μm/år.Resultaten från EIS påvisar en elektrokemisk modell motsvarande ettenkelt oxidlager, som täcker hela den yta som exponeras för lösningen.Korrosionsprodukterna bestod huvudsakligen av zinkfosfater (FTIR, EDX).Slutligen användes människoblod i en omgång av experiment. Härkorroderade proverna initialt med en hastighet på 0.08-0.38 mm/år.Korrosionen var homogen, likt proverna som utsattes för Ringerlösning.Den elektrokemiska modellen (fastställd med EIS) överensstämde dockmed den som fanns i PBS-resultaten, med ett enkelt lager av korrosionsprodukteröver hela ytan.
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Bandyopadhyay, Sulalit. "Biodegradable Nano-Clusters as Drug Delivery Vehicles." Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for kjemisk prosessteknologi, 2012. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-22677.
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The master thesis has investigated primarily on the synthesis of different polymeric NPs viz PLA (synthesized in house as well as commercial grade), PLGA (commercial) and PCL(synthesized in house, having different functionalities ?COOH, -PEG and their blends) employing flash nano-precipitation technique in a multi inlet vortex mixer (MIVM), previously optimized in the Morbidelli group at ETH. These NPs were characterized using DLS (Dynamic Light Scattering) and Zeta-Sizer to report the variation of the sizes and zeta potentials respectively of the NPs as a function of polymer molecular weight and initial concentration of polymer. The lowest possible sizes of the NPs were then selected for further studies as the overall motivation of the work is to synthesize NCs composed of primary particles and thereafter compare and contrast drug loading, encapsulation efficiencies and release kinetics of a model drug between the two. Ibuprofen (model drug) was loaded into the primary NPs using the MIVM setup, following which drug loading and encapsulation efficiencies were measured using High Performance Liquid Chromatography (HPLC). The release kinetics experiments were performed at 37°C and also studied at room temperature (25°C) and 45°C to evaluate the effect of temperature on release mechanism. The drug-loaded NPs were separated from the free drug in solution at different times using centrifugal filtration. The amount of drug released over time was measured by analyzing these supernatants using HPLC. The MIVM setup is found to produce stable polymeric NPs as small as 50nm and as large as 155nm depending on polymer concentration and nature of polymer. The results indicate that this setup is capable of producing drug loaded NPs with high drug loading efficiencies varying between 75% and 88% differing with polymers. This particular aspect has been established to be both reproducible and valid for a wide range of polymers through subsequent experiments. On the contrary, the release kinetics from almost all the different types of polymeric systems is slow; lasting over several days and moreover, it is not possible to release the entire loaded drug. It is claimed that either the chemical interaction of the polymers with ibuprofen or the location of the drug inside the polymeric NPs is the potential reason for extremely slow release kinetics. It is therefore suggested that further investigation is needed for the same system with another drug, having similar solubility parameters as ibuprofen to confirm the observed behaviour or even a completely different synthesis method for drug loaded polymeric NPs using ibuprofen to substantiate the observed results.
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Lin, Angela Sheue-Ping. "Biodegradable implants produced using fiber coating technologies." Thesis, Georgia Institute of Technology, 2002. http://hdl.handle.net/1853/15927.
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Ankola, Dhawal Dhirajlal. "Biodegradable nanoparticles for oral delivery of Ciclosporin." Thesis, University of Strathclyde, 2010. http://oleg.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=12803.
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Buffet, Jean-Charles. "Homochiral metal complexes for biodegradable polymer synthesis." Thesis, University of Edinburgh, 2010. http://hdl.handle.net/1842/4618.
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Chapter One introduces the principle of alkoxide and phosphine oxide as ligands for lanthanides and electropositive metals, ligand self-recognition, stereoselective polymerisation of lactide, fixation of CO2 and finally copolymerisation of CO2 and epoxide. Chapter Two shows the synthesis of the proligands rac-HLR (a racemic phosphine oxide-alkoxide, A, where R = tBu, Ph or C6H3-Me-3,5) and explores the resolution into diastereomeric RRR- and SSS-M(LR)3 to afford C3–symmetric M(LR)3 complexes, B (where M = Sc, Lu, Y, In, Bi or La). It also demonstrates that the process is under thermodynamic control and driven by ligand self-recognition via the synthesis of bis(LR) adducts (LR)2MX, C, (where M = Y or In and X = N(SiMe3)2 or OC6H3-tBu2-2,6) and mono(LR) adducts (LR)MX2, D (where M = Al or In and X = N(SiMe3)2, CH2SiMe3 or Me). Finally, it outlines the fixation of CO2 into an indiumamide bond. Chapter Three contains a detailed investigation of the potential of the MIII complexes as initiators for the stereoselective polymerisation of lactide, - caprolactone, glycolide and copolymerisation of lactide and -caprolactone, lactide and glycolide and CO2 and epoxide. Chapter Four investigates the use of rac-HLtBu in the resolution into diastereomeric RR- and SS-M(LtBu)2 complexes, E (where M = Ca, Zn or Sn), and of rac-HLPh into [M(LR)2]2 complexes, F (where M = Mg, Co or Sn and R = Ph or C6H3-Me-3,5) and mono-(LtBu) adducts (LtBu)MgX, G (X = N(SiMe3)2 or OC6H3-tBu2-2,6). It also describes the synthesis of protonated MII complexes (HLR)MCl2, H (where M = Mg, Zn or Sn and R = tBu or Ph). Finally, it details the polymerisation of lactide and its copolymerisation with glycolide using MII complexes as initiators. Chapter Five gives full experimental details and analytical data for the herein described novel compounds.
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Ambardekar, Rohan. "Controlled drug release from oriented biodegradable polymers." Thesis, University of Bradford, 2015. http://hdl.handle.net/10454/14867.
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This research is the first systematic investigation of solid-state orientation as a novel method for controlling drug release from biodegradable polymers. The effect of various degrees of polymer orientation was studied in oriented Poly (L-lactic acid) (PLA) films containing curcumin and theophylline as model drugs. Additionally, direction specific drug release was studied from oriented PLA rods containing paracetamol. The films oriented to 2X uniaxial constant width (UCW) or 2X2Y biaxial draw ratio showed retardation of drug release, when their nematic structure was stabilised by the presence of crystalline theophylline. Contrarily, the same films when contained solid solution of curcumin, shrunk in the release medium and exhibited a release profile similar to the un-oriented films. All films oriented to the UCW draw ratio ≥ 3X contained α crystalline form of PLA and showed acceleration of drug release proportionate to the draw ratio. According to the proposed mechanism augmented formation of water filled channels in these films was responsible for faster drug release. Similarly, the paracetamol loaded PLA rods die-drawn to uniaxial draw ratios ≥ 3X exhibited enhancement of drug release. Importantly, the amount of drug released along the oriented chain axis was significantly larger than that in the perpendicular direction. Drug release from the die-drawn rods was accelerated by a greater degree than that observed from the oriented films. This can be correlated to the differences in their size, geometry and the crystalline form of PLA. In conclusion, the current study provided substantial evidence that solid-state orientation can offer a control over drug release from PLA.
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Sevim, Kevser. "Modelling of drug release from biodegradable polymers." Thesis, University of Leicester, 2017. http://hdl.handle.net/2381/40864.
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Biodegradable polymers have highly desirable applications in the field of biomedical engineering, such as coronary stents, tissue engineering scaffolds and controlled release formulations. All these applications are primarily rely on the fact that the polymers ultimately disappear after providing a desired function. In this respect, the mechanism of their degradation and erosion in aqueous media has attracted great attention. There are several factors affecting the rate of degradation such as composition, molecular weight, crystallinity and sample size. Experimental investigations showed that the type of drug also plays a major role in determining the degradation rate of polymers. However, so far there is no theoretical understanding for the changes in degradation rate during the degradation in the presence of acidic and basic drugs. Moreover, there exists no model to couple the hydrolysis reaction equations with the erosion phenomena for a total understanding of drug release from biodegradable polymers. A solid mathematical framework describing the degradation of bioresorbable polymers has been established through several Ph.D. projects at Leicester. This Ph.D. thesis consists of three parts: the first part reviews the existing literature of biodegradable polymers and drug delivery systems. In the second part, the previous models are refined by considering the presence of acidic and basic drugs. Full interactions between the drug and polyesters are taken into account as well as the further catalyst effect of the species on polymer degradation and the release rates. The third part of this thesis develops a mathematical model combining hydrolytic degradation and erosion in order to fully understand the mechanical behaviour of the biodegradable polymers. The combined model is then applied to several case studies for blank polymers and a drug eluting stent. The study facilitates understanding the various mass loss and drug release trends from the literature and the underlying mechanisms of each study.