Dissertations / Theses on the topic 'Biopolymer'

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Chemistry, 2017.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 125-129).
This thesis describes the development and application of fast flow solid phase synthesis for the preparation of peptides and phosphorodiamidate morpholino oligomers (PMOs), as well as the application of fast, reliable peptide synthesis to study non-natural protein folding and function. In the first chapter, solid supported peptide synthesis was accelerated using flow by continuously delivering preheated solvents and reagents to the solid support at high flow rate, thereby maintaining maximal concentrations, quickly exchanging reagents, and eliminating the need to heat reagents after they were added to the vessel. In the second chapter, these chemical principles were expanded upon and mechanical challenges particular to accelerated solid phase synthesis were overcome to build a fully automated fast flow peptide synthesizer than incorporates amino acids in as little as 40 seconds each. First, mechanical systems were developed to rapidly switch between the many reagents needed for peptide synthesis while maintaining the proper stoichiometry of all reaction components at all times. Second, conditions under which reagents did not appreciably degrade during storage or synthesis were found. Finally, synthetic outcomes were substantially improved by increasing temperature without degrading the protected, resin bound peptide. The third chapter describes the expansion of fast flow synthesis to PMOs. A 10-fold acceleration of PMO synthesis was realized using mechanical systems adapted from chapter 1, increasing the reaction temperature to 90°C, and introducing a Lewis acid catalyst. The acidity of the deprotection reagent was reduced to prevent cleavage of the backbone during 3' detritylation. In the final chapter, a "D-scan" of two small proteins, the disulfide-rich Ecballium elaterium trypsin inhibitor II (EETI-II) and a minimized Z domain of protein A (Z33), is reported. For each protein, the chirality of one amino acid at a time was inverted to generate a series of diastereomers, and study the critical stereocenters of EETI-I and Z33. Twelve out of 30 EETI-II analogs folded and were high-affinity trypsin inhibitors, but most active analogs were less stable to reduction than EETI-II. Similarly, twelve Z33 analogs retained high binding affinity to IgG, but most were substantially less stable than WT-Z33.
by Mark David Simon.
Ph. D.

The field of nanocomposites is gaining considerable attention due to its potential for providing new materials with extraordinary physical properties compared to traditional composite materials. In this thesis cellulose nanowhiskers (CNW) were separated from microcrystalline cellulose (MCC) and dispersed in different biopolymer matrices to obtain polymer nanocomposites based on renewable resources. Moving from microstructure to nanostructure creates new challenges for structure characterization of materials. The overall aim of this work was to characterize the structure of CNW and their nanocomposites with different matrices. The sample preparation and microscopic examination of the bionanocomposites showed to be challenging because they are non-conductive, soft and water sensitive materials and consist of low atomic number elements. In the studies field emission scanning electron microscope was found to be a convenient and important first step in the analysis of the nanocomposite structure. More detailed information about the distribution of CNW was however obtained using transmission electron microscope (TEM) and atomic force microscope. X-ray diffraction analysis showed that the MCC consisted of both amorphous and crystalline regions. The sulfuric acid isolation treatment removed the amorphous regions and separated the cellulose nanowhiskers. From TEM analysis the size of the whiskers was measured to be 210 ± 75 nm in length and 5 ± 2 nm in width. It was also possible to separate the CNW from MCC using dimethyl acetamide containing a small amount of LiCl. It was however difficult to remove the organic solvent after treatment. CNW were well distributed in a hydrophobic matrix by the aid of a surfactant. Untreated CNW or untreated layered silicates in a thermoplastic starch matrix resulted in well dispersed nanocomposites. It was further found that it was possible to obtain oriented CNW in a matrix after exposure to a magnetic field. The dynamic mechanical thermal analysis of the different nanocomposites in this thesis showed that well dispersed cellulose whiskers have a large potential for improving the thermal mechanical properties of biopolymers.

Paper VII: The original publication is available at www.springerlink.com

Hard gelatin capsules have been used for drug delivery for a long time. The current production process takes advantage of the very unusual properties of gelatin: gelation, very low viscosity, film mechanical properties and film solubility. Although the hard gelatin capsules present many advantages compared to other drug delivery systems, their uses are restricted because of the animal origin of the gelatin. A HPMC gelling agent system is currently used for producing animal product free hard capsules. This work examines the possibility of using a different system in a similar production process. The gelling conditions of the mixed system, the potential of various film formers and the mechanical properties of some films are considered. Gelling agent filler mixed systems were prepared, and the limit concentration of filler that allowed gelation was noted. It was shown that none of the gelling agents would always gel and gelation was never prevented by the maltodextrin (up to a concentration of 14%). The gelation inhibition obtained is likely to be due to phase separation. The charge densities of the various products were also measured. It showed that when there is little charge density difference, gelation is inhibited. Polymer compatibility is increased by increasing the charge density differences. However, an asymmetry is observed. This is explained by the necessary shift of the binodal that would predict prevention of incompatibility. Many films were cast from various biopolymers. The films were screened via sensory analysis. The process allowed to define terms that discriminate the films. The results showed that cellulose derivatives, alginate and alginate derivative films had sensory analysis scores similar to gelatin. Although none of the starch derivatives had such good scores, some presented some promising results. Alginate and caseinate films were selected for further analysis. The mechanical properties of gelatin and HPMC films were compared by puncture tests. The results at a relative humidity of 44% are similar. However, the effect of the moisture content on both films' mechanical properties showed differences. The fracture patterns and polarised microscopy observation were also very different. Alginate films' mechanical properties were similar to gelatin. However, alginate films are not soluble in acidic environments. The effects of molecular weight on the mechanical properties of cellulose derivatives and alginates films were different. Increasing the calcium content of the alginate sample gave similar results to those obtained by increasing the molecular weight. It is proposed that ultimate deformation occurs through different processes in various films. Alginate/gelatin films are thought to deform through crazing, and the fracture process generates many surfaces (lines). Molecular weight and crosslinking would stabilise the crazes. On the other hand, cellulose derivative would deform through slippage and the energy is dissipated during deformation. This is consistent with the orientation observed after fracture, the lack of new surfaces and the high hydrophobicity of these polymers. Caseinate films of sodium, potassium, calcium and magnesium were studied. Sodium caseinate presented the best mechanical properties. Glycerol proved to be the best plasticiser. Glyoxal crosslinking or increase in pH did not improve the mechanical properties of these films. Caseinate films are poorer than alginate, HPMC or gelatin films. Caseinate deformation processes might occur through both slippage and crazing owing to the low molecular weight and high hydrogen bonding ability. Overall, different deformation processes can lead to similar mechanical behaviour. None of the films studied is likely to replace gelatin or HPMC. More complex systems are proposed for further study.

Les constructions en terre crue, soit fabriquées à partir de sol, sont considérées comme des constructions durables en raison de leur faible empreinte environnementale : les matériaux de construction à base de terre crue non stabilisée ont une faible énergie intrinsèque, d'excellentes propriétés hygroscopiques et un fort potentiel de recyclage. Cependant, sous cette forme, les matériaux sont susceptibles de se détériorer au contact de l’eau. Ainsi, les éléments de constructions modernes en terre crue utilisent du ciment pour améliorer leur durabilité, mais entachent de ce fait leurs propriétés hygroscopiques et leur potentiel de recyclable. Il est donc impératif de développer des solutions alternatives à l’incorporation de ciment, pouvant améliorer la résistance à l’eau sans pour autant compromettre les propriétés qui constituent les atouts de ces matériaux durables. Ces travaux de doctorat étudient l'utilisation de deux biopolymères, la gomme de guar et le xanthane, comme stabilisants naturels pour les matériaux de construction en terre crue. Dans un premier temps, une campagne expérimentale a été menée pour comprendre le mécanisme de stabilisation de la terre par ces biopolymères et optimiser cette technique. Les résultats révèlent que la nature intrinsèque des biopolymères induit la formation d’hydrogels qui participent à renforcer le matériau et à modifier les phénomènes de succion. L’addition d’environ 2,0 % de biopolymère en masse de sol sec est suffisant pour obtenir un comportement mécanique comparable à la stabilisation au ciment à un taux de 8,0 %. Afin de mieux caractériser l’influence des biopolymères, les propriétés hydrauliques et mécaniques des sols ainsi stabilisés ont été étudiées. Les tests de caractérisation prouvent que, pour une même gamme de teneur en eau, la succion des sols stabilisés par les biopolymères est supérieure à celle des sols non stabilisés. Les courbes de rétention d'eau sol démontrent que la valeur d'entrée d'air est augmentée en présence des biopolymères, ce qui affecte la distribution de la taille des vides. Les paramètres de résistance au cisaillement ont été obtenus par des essais triaxiaux à teneur d’eau constante. Les deux biopolymères ont un effet significatif, et pourtant différent, sur la cohésion du sol et l'angle de friction interne. Dans le temps, la modification de résistance des sols stabilisés à la gomme de guar est liée à la variation de la composante de friction, tandis que pour les sols stabilisés à la gomme de xanthane cette variation est pilotée par la cohésion du sol. L'analyse microstructurale par micro tomographie X-RCT montre que les biopolymères favorisent l’agglomération des particules de sol, ce qui modifie la porosité globale. Les courbes de distribution de la taille des vides obtenues par balayage XRCT confirment les résultats des essais de succion. Pour finir, les performances en termes de durabilité de ces matériaux de construction stabilisés aux biopolymères en présence d'eau ont été validées par différents tests ainsi que leur potentiel de recyclage. Il apparait donc que l'utilisation de ces biopolymères comme stabilisant améliore la résistance mécanique des matériaux en terre crue et leur durabilité ; et que contrairement à la stabilisation au ciment le comportement hygroscopique est conservé - voire amélioré-, ainsi que le potentiel de recyclage
Earthen structures (i.e. structural units manufactured from soil) are often regarded as sustainable forms of construction due to their characteristically low carbon footprint. Unstabilised earthen construction materials have low embodied energy, excellent hygroscopic properties and recycling potential. However, in this form, the material is susceptible to deterioration against water ingress and most modern earthen construction materials rely on cement to improve their durability properties. Using cement leads to compromises in hygroscopicproperties and recyclability potential. In this situation, it is imperative to look for alternatives to cement, which can address these issues without compromising on the desired engineering properties of these materials. This thesis explores the use of biopolymers, namely guar and xanthan gum, as stabilisers for earthen construction materials. As an initial step, an experimental campaign was undertaken to understand biopolymer stabilisation and optimise their use to stabilise earthen construction materials. The results from this campaign reveal that biopolymer stabilised soils derive their strength through a combination of soil suction and hydrogel formation. The intrinsic chemical properties of the biopolymer affect the nature of hydrogel formation and in turn strength. In a subsequent campaign of experimental work, hydraulic and mechanical properties of these biopolymer stabilised soils were determined. The hydraulic properties of the biopolymer stabilised soils indicate that for the range of water contents, the suction values of biopolymer stabilised soils are higher than unamended soils. The soil water retention curves suggest that both biopolymers have increased the air entry value of the soil while affecting the void size distribution. Shear strength parameters of biopolymer stabilised soils were obtained through constant water triaxial tests, and it was noted that both biopolymers have a significant and yet different effect on soil cohesion and internal friction angle. With time, guar gum stabilised soils derive strength through the frictional component of the soil strength, while xanthan gum stabilised soil strength has a noticeable contribution from soil cohesion. Macrostructural analysis in the form of X-RCT scans indicate that both biopolymers form soil agglomerations and increase overall porosity. The void size distribution curves obtained from XRCT scanning complement the findings of the suction tests. As a final study, the performance of biopolymer stabilised earthen construction materials was assessed as a building material. Durability performance of these materials against water ingress was evaluated, and it was noted both biopolymers provide satisfactory stabilisation to improve the erosional resistance of the material. In conclusion, unlike cement, biopolymer stabilised earthen materials do not compromise on hygroscopic properties and have better mechanical performance than unamended earthen construction materials. Finally, recyclability tests suggest that apart from improving the strength, durability and hygroscopic properties of the material, biopolymer stabilised earthen construction materials have a better potential for recycling without any environmental concerns

This diploma thesis deals with experimental study of interaction based on polymer-lipid system. The main goal was to investigate interaction leading to phase separation. Three anionic polyelectrolytes were selected for this purpose: sodium hyaluronate, sodium chondroitin-6-sulfate and sodium poly(4-styrenesulfonate). The liposomes were formulated by sonication of lipid – cationic 1,2-dipalmitoyl-3-trimethylamonium-propane (chloride salt) and zwitterionic 1,2-dipalmitoyl-sn-glycero-phosphocholine. It was found that the phase separation occured at specific ratio of DPTAP and selected polymer. It was also explored that the strong electrostatic interaction which leads to the phase separation can be weaken by increasing the ionic strength in the sample. As we aspected the systems contain the hydrophobic domain and therefore these are able to incorporate hydrophobic substances in their structure.

Nanopores (1 – 10 nm diameter) constructed in solid-state membranes, have shown promise as next-generation biopolymer analysis devices offering both high resolution and high throughput. One promising application of nanopores is in the analysis of nucleic acids, such as DNA. This involves translocation experiments in which DNA is placed in an ionic solution and is forced through a nanopore with the aid of an applied electric field. The modulation of ionic current through the pore during DNA translocation can then be correlated to various properties of the biopolymer such as the length. To optimally design and operate nanopore devices, it would be advantageous to develop an accurate computer simulation methodology to predict the physics of the translocation process. Hence, I have developed a physically accurate, computationally efficient simulation methodology to predict and analyze the physics of biopolymer translocation through solid-state (silicon nitride) nanopores. The overall theme of this thesis is to use this simulation methodology to thoroughly investigate important issues in the physics underlying translocation experiments and thereby determine the effects of key structural and operation parameters, such as nanopore dimensions, applied voltage, hydrodynamic interactions, solvent viscosity, and the polymer chain length. The results from these simulation studies can assist in not only proper nanopore design, but also help determine the proper experimental environments and parameters for nanopore operation.

The aim of this study was to produce biopolymer-based nanocomposites using extrusion as an industrially adaptable manufacturing process, and to study how this production process influenced the structure and properties of the nanocomposites produced. Cellulose nanowhiskers (CNWs) were prepared and used as nanoreinforcement in two different biopolymers, polylactic acid (PLA) and cellulose acetate butyrate (CAB). The CNWs were added to PLA and CAB in order to improve the thermal and mechanical properties of these polymers. Two different preparation methods of CNWs were used; isolation by sulfuric acid hydrolysis and isolation by hydrochloric acid hydrolysis. Different feeding procedures were used and evaluated during compounding. The CNW suspension was either freeze-dried and dry-mixed with the polymer prior the extrusion, or fed as a suspension directly into the extruder during compounding. However, the CNW suspension required modification in order to prevent re-aggregation of the whiskers as the dispersing medium was removed and to uniformly disperse the whiskers in the polymer matrix. In order to improve the dispersion of the CNWs in the matrix, a surfactant and a water soluble polymer were used for PLA, and a plasticizer was used for CAB. No major improvements in mechanical or thermal properties were seen for the PLA/CNW nanocomposites, either because of degradation of the matrix or poor dispersion of the whiskers. The material system of CAB/CNW was more successful and showed great improvements in mechanical and thermal properties. This study demonstrated that it is possible to produce nanocomposites by pumping a suspension of CNWs into the extruder during compounding, but compatibility between the CNWs and the matrix is required.

The three major mechanical components of cells are the biopolymers actin, microtubules, and intermediate filaments. Cellular processes are all highly reliant on the mechanics of the specific biopolymers and the networks they form, rendering necessary the study of both the kinetics and mechanics of the cytoskeletal components. Here, we study the in vitro mechanics of actin and composite actin/vimentin networks, and the effect of various actin-binding proteins on these networks.
Engineering and Applied Sciences

As the world faces resource management problems such as providing sustainable energy and sourcing rare elements, demand is growing for new materials to help combat these. Biopolymer sol-gel synthesis has the potential to create a wide range of functional materials, in particular from the spontaneous foaming of gelatin and metal nitrates upon drying. If this process can be controlled and expanded to other biopolymers then catalytic systems could be designed for many applications. The gelatin foaming mechanism was investigated by a variety of techniques including small angle neutron scattering and rheology. The cause of the foaming was attributed to the evaporation of water and the gels ability to stabilise the bubbles formed. Links between the structural properties of the gel and porous carbon have been suggested as a way of predicting and selecting certain morphologies whilst in the liquid state. Research has also been carried out using microwaves as an alternative to conventional furnaces, this was done to make the synthesis more environmentally friendly. During this research several metal carbides/nitrides were synthesised, including metastable phases. Using this biopolymer sol-gel synthesis, materials were synthesised and tested as catalysts for both methanol steam reforming and hydrogen evolution reactions as examples of possible applications for this research. Both sets of materials showed activity for their respective reactions in line with current literature. Finally, further optimisation is possible on all aspects of this thesis and future research should be carried out to maximise the potential of this facile and versatile synthesis technique.

Many biological systems involve intricate, hierarchical networks formed from cross-linked filaments, including the cytoskeleton of eukaryotic cells and the collagen scaffold of the extracellular matrix. Experiments performed on these biopolymer networks have identified exotic and desirable mechanical behaviours that cannot be easily understood without discussing the underlying microstructures and their properties. As such, the theoretical and computational modelling of filament assemblies has increasingly utilized discrete fibre network (DFN) models to investigate their complex local and global mechanical properties. This thesis investigates some of the many structural aspects of these networks, and how details of the network architecture can influence the mechanics of the system. We discuss how the geometry of a fibrous substrate can influence the long-ranged displacement fields generated by contractile resident biological cells, and the extent to which long-ranged mechanical communication between distant cells is plausible. A variety of architecture choices are discussed and compared. Motivated by improvements in electrospinning technologies and recent experiments, we develop a new fibre network model, where cross-link density is allowed to vary while geometry is controlled. The affine-nonaffine transition in this model is discussed and characterized, and theoretical predictions for the scaling of the network shear modulus are presented. As much of the DFN literature focusses on monotypic fibre networks, the mechanics of polymer assemblies formed from two or more filament types, which often arise in Nature, is poorly understood. We seek to address this by extending monotypic fibre network models to incorporate two distinct fibre types. In the low density regime we present extensive theoretical predictions and supporting numerical results for the network response as numerous parameters are varied. The importance of network architecture is discussed in the context of nonaffine fluctuations and their influence on the mechanical response. Finally, dense, random heterotypic networks are studied, in light of experiments and theoretical models that observe `exceptional stiffening' in such systems. We propose a novel explanation for this phenomenon, and provide evidence for our interpretation over others given in the literature. The implications of the research presented here for higher dimensional systems and for finite strains are discussed. Together, this thesis constitutes an argument for the mechanical importance of the detailed structural properties possessed by biopolymer networks, in a variety of systems and at multiple scales.

Compared to conventional fibers, carbon nanotubes possess several significant properties, which make them as an excellent alternative reinforcement in multi-functional material industry. In this study, the possibility of dispersion of the multi-wall carbon nanotube (MWCNTs) in a thermoset bio-based resin (synthesized based on end-functionalized glycerol-lactic acid oligomers, GLA, at university of Borås) was investigated. Furthermore, the addition of the MWCNTs as reinforcement to improve the mechanical and thermal properties of was investigated. The nanocomposites were prepared in three different concentrations of MWCNTs, 0.3 wt.%, 1.0 wt.%, and 2.0 wt.%, and each sample was prepared using three different dispersion methods such as the high speed mixer(HSM), the ultra-sonication (US), and a combined method of HSM & US. The mechanical and thermal properties were analyzed by flexural test, thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). The results confirm that the nanotubes can be dispersed in GLA but the cured nanocomposite didn’t exhibit any considerable improvement in their thermal properties. Considering to the mechanical properties, the addition of 0.3 wt. % MWCNTs to the GLA increased the flexural strength a little but increasing the nanotubes to 1.0 wt. % decreases the flexural strength to almost 50%. This is mainly due to increase in the brittleness of the produced nanocomposites. Both the distribution methods dispersed the nanomaterials in the matrix initially but they are not efficient enough to stop the re-agglomeration which leads to undesired curing dynamics and low efficiency. Thus, these dispersion methods need to be optimized for improvement of nanocomposites’ properties.

The aim of this diploma thesis was to study the structure and to evaluate the properties of the hydrogel prepared by the interaction of the aminolclay with the biopolymer. Representatives of the biopolymers were selected from low to medium molecular weight sodium hyaluronate and sodium polystyrenesulfonate. On the basis of the experiments carried out, it was found that phase separation takes place only when the aminolclay interacts with medium molecular weight hyaluronan (MMW). In the experimental part, analyzes of this sample were carried out in order to determine the formation of phase-separated hydrogel by influencing the solution by ionic strength, investigation of hydrogel extinction in various organic solvents, stability of hydrogel under extreme temperature conditions, the effect of storage on its degradation, etc. Viscoelastic properties were experimentally proven by rheology and thermal analysis detected binding water. Inhibition of microorganisms was confirmed by antibacterial diffusion assays. All experiments were carried out for the use of the Aj-HyA hydrogel (MMW) in the field of medical applications, specifically for the modern method of wet wound healing of the skin.

2009/2010
Tissue engineering in the orthopedic field is mainly focused on the development and design of material to serve as a temporary extracellular matrix or scaffold to overcame the limitation of actual treatments. In fact, current treatments are based on autologous or autogenous bone grafts and as an alternative to these, metals and ceramics. The limitation of this kind of implants is related to shortage of autograft that can be obtained and to donor site morbidity; the possibility of immune rejection and of pathogen transmission from donor to host in the case of allograft; the poor overall integration with the tissue at the implantation site for the metal and ceramic. The aim of study is the development of bio-composite scaffolds for orthopedic applications, based on the combination of polysaccharides (mainly alginate, Alg) engineered with bioactive molecules and nano-hydroxyapatite (nHap). The first step was the synthesis and characterization of the different components of the scaffold. The nHap was synthesized with sol-gel method and the obtained crystals have been chemically and morphologically characterized by mean of Raman spectroscopy, X-Ray Diffraction and Transmission Electron Microscopy. All the collected results confirm the chemical composition of nHap and information about the average dimension of crystals (120nm). The synthesized nHap was used to produce composite hydrogels of Alg and nHap. The porous structure was achieved through freeze-casting. The obtained scaffold was characterized with µCT (µComputed tomography) and confocal microscopy; the histomorphometric data were compared with the parameters of native tissue with an high level of similarity between trabecular bone and scaffolds structure. Subsequently, the scaffolds have been investigated for their cytocompatibility and the results shows high rate of proliferation of cells seeded into the scaffold. The modification with specific proteins or peptides of the backbone of a polymer can be an effective strategy to tailor and control cell attachment, migration, proliferation and differentiation. Incorporation of peptide motifs containing sequences that are recognized by integrin receptors, such as arginine-glycine-aspartic acid (RGD)-based sequences, are now a common strategy to enhance the biological properties as well as differentiation and proliferation of a variety of cells, including osteoblasts. Along the same line, reducing bacterial adhesion is important since microorganism surface attachment is the first critical step in the development of implant-associated infections. To introduce bioactive molecules and antimicrobial agents, enhancing in this way the biological property of the scaffolds, Chitlac was exploited as vector. Chitlac is a lactitolated-derivative of chitosan that can be modified by chemical grafting of bioactive peptides like RGD and that can be use to produce and stabilize silver nanoparticles (nAg) with antimicrobial activity. By adsorbing the Chitlac on the scaffold’s surface we spread the bio-signal inside the structure to induce a specific cell reaction. Alg/nHap scaffolds were coated with Chitlac-RGD and Chitlac-nAg, respectively, and on those, biological and antimicrobial in vivo tests were performed. For both scaffolds we observed good cytocompatibility and, in the case of scaffold with RGD, an improved cell proliferation; moreover, the scaffold with nAg showed a high level of antimicrobial activity. According the results obtained from the previous cytocompatibility tests, preliminary cytocompatibility in vivo tests were performed. The animal model was New Zealand rabbit and the produced scaffolds were inserted into bone defects on femur. Post-operatively, three fluorochromes were administered sequentially every week. After 5 weeks the rabbits were sacrificed and all the implanted bones were analyzed using µ-CT and light and confocal microscopy. We observed a high level of osteointegration of the scaffolds and ingrowth of newly deposited structured lamellar bone inside them, indicating good osteoconductive properties. In conclusion, the developed scaffolds have suitable biological properties both bioactive and antimicrobial. The in vitro results shows a high level of cytocompatibility for all the scaffolds studied and that the presence of Chitlac-nAg does not compromise the compatibility of scaffolds. In the case of scaffolds modified with RGD the results confirm that the presence of bioactive molecule is able to enhance the healing process also with respect to the BAG (BioActive Glass) control. The findings of the present study revealed that the structures here developed could serve as promising filler for orthopedic application.
XXIII Ciclo
1983

I use an integrated approach of experiments, theory, and numerical evaluations to show that stiffening and softening/fluidization are natural consequences of the assumption that the cytoskeleton is mechanically essentially equivalent to a transiently crosslinked biopolymer network. I perform experiments on in vitro reconstituted actin/HMM networks and show that already these simple, inanimate systems display fludization and shake-down, but at the same time stress stiffening. Based on the well-established Wlc theory, I then develop a semi-phenomenological mean-field model of a transiently crosslinked biopolymer network, which I call the inelastic glassy wormlike chain (inelastic Gwlc). At the heart of the model is the nonlinear interplay between viscoelastic single-polymer stiffening and inelastic softening by bond breaking. The model predictions are in good agreement with the actin/HMM experiments. Despite of its simplicity, the inelastic Gwlc model displays a rich phenomenology. It reproduces the hallmarks of the mechanics of adherent cells such as power-law rheology, stress and strain stiffening, kinematic hardening, shake-down, fludization, and recovery. The model also may also be able to provide considerable theoretical insights into the underlying physics. For example, using the inelastic Gwlc model, I am able to resolve the apparent paradox between cell softening and stiffening in terms of a parameter-dependent competition of antagonistic nonlinear microscopic mechanisms. I further shed light on the mechanism responsible for fluidization. I identify pertinent parameters characterizing the microstructure and give criteria for the relevance of various effects, including the effect of catch-bonds on the network response. Finally, a way to incorporate irreversible plastic flow is proposed.

The main objective of the work presented in this thesis was to study the behaviour of biopolymer films with respect to their mechanical and physicochemical properties and to test hypotheses as to their molecular origins. The thesis describes four studies. In the first study the granule, paste and film properties of common starches from six different botanical sources; i.e. cassava, corn, pea, potato, rice and wheat; were characterised with the aim of identifying the main factors which affect the properties of the starch films.

This thesis examines a system consisting of two biopolymers, gelatine (a protein that forms a gel under certain conditions of temperature and concentration) and dextran (a non-gelling polysaccharide) in solution. At high temperatures the polymers are miscible but at low temperatures (less than ˜35°C) phase separation and gelation can occur. This thesis investigates this phenomenon using light scattering, microscopy and rheology. It is shown that very different structure are formed depending on the relative rates of phase separation and gelation. At high temperatures the gelation occurs slowly and confocal microscopy experiments have revealed that droplets of one phase in another result. At low temperatures the gelation occurs quickly and, for a sample in which the two polymers are present in similar quantities, an interconnected structure is produced. The evolution of these different structures is examined using several techniques, the main method being small angle light scattering, and analysed within the framework of several theories describing phase separation, the key one being the Cahn-Hilliard theory of spinodal decomposition. This theory was found to describe the early stages of phase separation well in spite of the effects of gelation, indicating the resilence of the underlying physical processes even in the presence of the molecular reorganisation that occurs in gelation. Effects of the gelation are seen at low temperatures (˜18°C), the principal effect it has is to alter the characteristic lengthscale produced in the sample - deeper quenches producing shorter lengthscales. In the later stages of phase separation the gelation has a more obvious effect, altering the mechanisms of the coarsening of the structure. In samples poor in gelatine coalescence of the droplets could occur, in others the gelation of the gelatine within the droplets prohibited coalescence over the period of observation. Rheology experiments also showed differences between samples quenched to different temperatures, the modulus of the sample depending to some extent on the concentration of gelatine in the continuous phase. The compositions of the phases produced were functions of temperature and the rates of phase separation and gelation.

The use of materials with osteointegrating and bactericidal properties is an important dental strategy. For this purpose, methods for the manufacture of composite material in the form of a film based on hydroxyapatite and natural polymer (alginate) with the addition of inorganic ions and the subsequent saturation of drugs and active substances were developed and investigated. The main theoretical prerequisite for the use of dental implants is the fact of tissue integration with the incorporation of biologically inert materials into the jawbone.

This Thesis utilises vibrational spectroscopy in combination with multivariate and two-dimensional analytical techniques to probe the interactions of a biopolymer in water-based systems. Chapter 1: This Chapter gives an introduction to the Thesis and briefly outlines the experimental tech- niques used to study biopolymeric systems before covering the theory and implementation of the multivariate and two-dimensional methods used. A brief introduction to carrageenan, the biopolymer of interest, is then given. Chapter 2: The general experimental procedures are discussed together with the development of a new low-temperature ATR system, which allows very precise control and variation of sample tem- perature. The latter is key to many of the measurements and analyses reported in this thesis. The ATR system is stable to 0.01 C over a temperature range of -30 to 80 C. Many of the tech- niques used within this thesis rely on the Matlab environment. Analysis methods that are not commercially available have been programmed as part of my work. The theoretical background is discussed and the scripts for these functions are included in the Appendix. Chapter 3: Three commercially available carrageenans, k-, i- and l-carrageenan are studied with infrared spectroscopy. The carrageenan solutions are cooled from ca. 80 to 10 C. k- and i-carrageenan undergo a gelation transition during the cooling and this is investigated with a variety of analysis methods. The gelation transition can be monitored with FTIR allowing insight into the struc- tural rearrangement of the biopolymer as a function of temperature. The spectral transitions are probed with multivariate (PCA & MCR) and two-dimensional (2DCOS, MW2D & PCMW2D) techniques. Structural rearrangement for k- and i-carrageenan is observed, with various sulfate based modes showing the most intense changes to temperature. As cooled from 80 to 10 C, k- and i-carrageenan showed sulfate vibrational modes changing predominantly before vibrations associated with the backbone of the polyelectrolyte (C-O-C), indicating a sequential order to the molecular rearrangement occurring during the gelation transition. Chapter 4: Investigation of a 2 % i-carrageenan in H2O is frozen and probed with infrared spectroscopy using a modified low-temperature ATR accessory. The sample is cooled past it’s freezing point and is then subjected to short term, constant temperature storage. Changes in structure of the water and carrageenan are observed as a function of time post-freezing. Analysis by multivariate, two-dimensional and band fitting routines is applied, allowing the post freezing spectral perturbations to be monitored. Several spectral changes within the fingerprint region occur at a different rate, these have been proposed as vibrations associated with the backbone and pro- truding groups of i-carrageenan showing di↵erent processes in response to being frozen. Initially post-freezing, large changes in the O-H stretch region for H2O are observed, before subsiding and and followed by changes in the structure of carrageenan. These effects suggests an interaction between i-carrageenan and ice. Chapter 5: The use of a confocal Raman microscope, installed at Unilever’s Colworth facility has been used to investigate i-carrageenan in frozen systems. A gradient temperature stage allows formation of ice-fronts and a variety of these type of systems are probed. Changes in the concentration of carrageenan are seen dependant on the movement of the ice-front. Progressing an ice front into a gelled (unfrozen) section of the sample results in a large increase in carrageenan concentration at the ice-front. This indicates that the slow growth of the ice crystal is excluding the carrageenan and causing a freeze-concentration effect at the ice-front.

Alors que l'adhésion entre matériaux synthétiques a été plutôt bien étudiée expérimentalement et théoriquement, les mécanismes de bioadhésion sont encore très peu compris. Une manière de les aborder serait d’utiliser des systèmes biopolymères qui pourraient imiter biosurfaces, biotissus et bioadhésifs. Cependant, cette idée est confrontée à la difficulté de concevoir une structure modèle et de contrôler les propriétés physico-chimiques des matériaux fabriqués à partir de biopolymères. Les mécanismes de bioadhésion peuvent être mieux compris en étudiant l'adhésion en milieu immergé entre adhésifs hydrogels et substrats solides modifiés par des films minces d'hydrogel. Cela permet de séparer la contribution interfaciale avec des interactions spécifiques moléculaires et de la contribution du volume avec les propriétés viscoélastiques à l'adhésion. Dans un premier temps, nous avons conçu un système modèle avec de la gélatine et noua avons étudié l'adhésion en milieu immergé favorisée par des interactions électrostatiques. D'une part, des films stables de gélatine attachés en surface d’épaisseur et de gonflement finement ajustables ont été réalisés en utilisant la stratégie Cross-Linking and Grafting (CLAG). D'autre part, des adhésifs hydrogels de gélatine à double réticulation ont été synthétisés en ajoutant des réticulations chimiques aux réseaux de gélatine physiques. La structure microscopique des réticulations physique et chimique a été bien contrôlée, avec la détermination de la longueur de chaîne entre les réticulations à partir du module de cisaillement et du modèle de réseau fantôme. L'adhésion en milieu immergé mesurée par des tests de probe-tack a montré que les hydrogels de gélatine à double réticulation ont les mêmes propriétés adhésives quelle que soit la température, même si leur résistance diminue avec le chauffage. Nous avons également été en mesure de séparer les effets des réseaux physiques et chimiques sur l'adhésion. Dans un deuxième temps, nous avons étudié l'adhésion en milieu immergé entre des réseaux doubles contenant du carraghénane et des substrats solides modifiés par des micro-motifs d’hydrogels. Il a été démontré que plus les micro-motifs sont petits, plus l'énergie d'adhésion est élevée. Ce travail a fourni un aperçu des paramètres physico-chimiques et physiques qui contrôlent l'adhésion en milieu immergé des systèmes biopolymères tels que les propriétés viscoélastiques en volume, la charge et la topographie de la surface. Il aidera à mieux comprendre la bioadhésion et à concevoir des adhésifs efficaces en milieux aqueux
While the adhesion between synthetic materials has been rather well-studied experimentally and theoretically, there is still a lack of knowledge on bioadhesion, which could be tackled with biopolymer systems which could mimic biosurfaces, biotissues and bioadhesives. However, this idea is limited by the difficulty in designing a model structure and controlling the physical chemistry properties of biopolymer-made materials. Bioadhesion mechanisms can be tackled by studying the underwater adhesion between hydrogel adhesives and solid substrates modified by hydrogel thin films. This allows to separate interfacial contribution with molecular specific interactions and bulk contribution with viscoelastic properties to adhesion. First, a model system based on gelatins has been designed and underwater adhesion promoted by electrostatic interactions was investigated. On one side, stable surface-attached gelatin films with finely adjustable thickness and swelling were achieved using Cross-Linking and Grafting (CLAG) strategy. On the other side, dual-crosslinked gelatin hydrogel adhesives were synthesized by adding chemical crosslinks to physical gelatin networks. The microscopic structure of both physical and chemical crosslinks was well-controlled, with the determination of the chain length between crosslinks from shear modulus and phantom network model. Underwater adhesion measured by probe tack tests showed that dual-crosslinked gelatin hydrogels have the same adhesive properties at all temperatures even if their strength decreases with heating. We were also able to separate the effects of physical and chemical networks on adhesion. Second, the underwater adhesion between double-networks containing carrageenan and solid substrates modified by micro-patterned hydrogels was investigated. It was shown that the smaller the micro-patterns the higher the adhesion energy. This work has provided an insight of the physico-chemical and physical parameters that control underwater adhesion of biopolymers systems such as the bulk viscoelastic properties, the charge and the topography of the surface. It would help for better understanding bioadhesion and designing underwater adhesives

Les alginates, des polysaccharides produits par les algues brunes, sont des copolymères à blocs linéaires, formés d’unités mannuronate (M) et guluronate (G). En raison de leur abondance naturelle, prix et propriétés physicochimiques avantageuses, les alginates représentent une classe de biopolymères très intéressante et relativement inexplorée pour des applications dans le domaine des matériaux avancés. Dans ce contexte, le présent travail vise à enrichir la gamme des applications des matériaux dérivés d’alginates, en exploitant les propriétés de cette classe de polysaccharides naturels. En particulier, la préparation de matériaux à base d'alginate pour la catalyse, l'adsorption et le domaine biomédical a été étudiée, avec des résultats encourageants dans toutes les applications testées. L'utilisation bénéfique de l'acide alginique en catalyse hétérogène a été démontrée, en tant que promoteur de réaction et support pour l’hétérogénéisation d'un organocatalyseur. L'activité du catalyseur a été trouvée très dépendante de l'accessibilité des groupes fonctionnels, mettant en évidence l’avantage de l’emploi de formulations plus accessibles. La texturation des alginates a été aussi avantageuse dans la préparation de matériaux pour applications en flux. Des mousses d'acide alginique, avec une structure hiérarchique macro-mésoporeuse, ont été développées à cet effet. Une caractérisation précise des matériaux a été réalisée, afin d'optimiser la procédure de préparation et de corréler les propriétés texturales obtenues avec les paramètres utilisés. L'intérêt dans l’utilisation de mousses à base d'acide alginique a été démontré dans une application modèle, l'adsorption de bleu de méthylène à partir de solutions aqueuses, à la fois en batch et en flux. La possibilité de modifier facilement les groupes fonctionnels de l’alginate, couplée avec la nature biocompatible et biodégradable de ces biopolymères, a finalement été exploitée pour le développement de gels auto-réparants, obtenus grâce à la formation de deux types d'interactions covalentes dynamiques : base de Schiff et ester de boronate. Les deux systèmes examinés ont présenté une remarquable habilité à se reconstruire après un dégât, même si l'ampleur de la reconstruction et la stabilité des gels étaient fortement dépendantes des paramètres de préparation des gels et des conditions environnementales utilisées. Les résultats obtenus dans le cadre de cette étude démontrent clairement comment la compréhension et un emploi conscient des propriétés physico-chimiques des alginates peuvent maximiser le potentiel que cette ressource durable dans le domaine de la chimie des matériaux
Alginates, polysaccharides produced by brown algae, are linear block-copolymers formed by mannuronate (M) and guluronate (G) units. Because of their huge natural abundance, cheapness and physicochemical properties, alginates represent a highly attractive and still relatively unexplored class of biopolymers for applications in the field of advanced materials. In this context, the present work aimed to enrich the range of possible applications of alginate-derived materials, making the most of the peculiar features of this class of natural polysaccharides. In particular, the preparation of alginate-based active materials to be employed in the catalysis, adsorption and biomedical field was studied, achieving encouraging results in all the tested applications. The beneficial use of alginic acid in heterogeneous catalysis, both as reaction promoter and as support for the heterogeneization of an organocatalyst, was demonstrated. The activity of the material was found highly dependent on the accessibility of the active functions, highlighting the advantage of employing more accessible alginate formulations. The texturation of alginates was further advantageous for the preparation of materials with improved flowability. Alginic acid foams, bearing a hierarchical macro-mesoporous structure were developed by means of a simple procedure. Accurate characterization was performed to optimize the preparation procedure and to correlate the textural properties of the obtained materials with the parameters used. The interest of the prepared alginic acid foams was demonstrated in a model application, the adsorption of methylene blue from aqueous solutions, both in batch and in flow conditions. The possibility to easily modify alginate functional groups, coupled with the biocompatible and biodegradable nature of alginates, was finally employed for the development of self-healing gels, thanks to the formation of two types of dynamic covalent interactions: Schiff base and boronate ester bonds. Both the examined systems presented a marked ability to recover after damage, even if the extent of the recovery and the stability of the gels was highly dependent on the preparation parameters and environmental conditions used. The results obtained in the course of this study clearly demonstrate how a full comprehension and conscious employment of alginate physicochemical properties can maximize the potential of this sustainable resource in the field of material chemistry

The physics of phase separated water soluble biopolymer solutions is of great importance both academically and commercially. Of particular importance is the nature of the interface between the two aqueous biopolymer systems. The interface between phase separated water soluble biopolymers has considerable influence over the physical behaviour and properties of mixed biopolymer systems. Knowledge of the nature, and ultimately the ability to control, the aqueous biopolymerlbiopolymer interface is the aim ofthis research. This research examines a protein/polysaccharide biopolymer system: gelatin (a protein that under certain conditions forms a gel) and dextran (a non-gelling polysaccharide). It is known (from small angle light scattering) that the interface between 4.2% aqueous gelatin and dextran solutions is broad:::: 200nm. The phase diagram and the interfacial width of the aqueous gelatin/dextran system have been investigated in this thesis. The phase diagram of this system has been determined using Fourier Transform Infrared (FTIR) spectroscopy. A slight temperature dependence ofxwas found. Spectroscopic and angular ellipsometry have been used in order to try to measure the interfacial width in this system. The aqueous gelatin/dextran system is a liquid/liquid system. A special cell has been designed to enable the two liquids to be confined, but still enable the interface to be studied. A number of test systems (small molecule and macromolecular) have been used in order to test the liquid/liquid experimental cell and the data analysis program. No light was observed to reflect from the interface between aqueous solutions of gelatin and dextran. This is due to the width of the interface being too broad. For the interface between phase separated aqueous solutions (gelatin-rich phase/dextran-rich phase) no light was observed to reflect from the interface due to the width being to broad and the refractive index contrast being too small.

It was proposed that a phase separated system might be utilised to deliver a concentrated polysaccharide mucosal protective coating in gastro oesophageal reflux disease (GORD). In this context the phase behaviour of xanthan gum in combination with sodium alginate and other polymers was studied. Above a threshold concentration of alginate, aqueous mixtures of xanthan exhibited phase separation, resulting in loss of normal viscoelastic properties and the formation of a low viscosity system. The shape of the phase diagram showed behaviour typical of a segregative system, with the continuous phase composed exclusively of alginate and the disperse phase being rich in xanthan gum. Increasing alginate molecular weight reduced the threshold concentration for separation, as predicted by the Flory-Huggins theory, but changes in alginate mannuronate:guluronate ratio had no effect. Increasing ionic strength elevated the threshold concentration. Xanthan separation was elicited by other aqueous anionic polyelectrolytes, but not neutral water soluble polymers. Scleroglucan, another rigid-rod polysaccharide, was investigated as an alternative to xanthan but did not show similar separation behaviour, suggesting that the charge on the xanthan molecule is a necessary prerequisite. Reversal of phase separation by dilution across the phase boundary provided increases in viscosity. A 1% xanthan:2% alginate mixture doubled in viscosity whereas if diluted with simulated gastric fluid a seven-fold increase was seen, as a result of conversion to an alginic acid gel. This offers a mechanism for producing the desired viscosity barrier. Low viscosity polyelectrolytes, with concentrations close to the phase boundary yielded the greatest viscosity increases. In the phase separated system, the disperse phase exhibited an unusual strand-like morphology whose birefringence suggests a liquid crystalline structure. The variable size of the strands was explained in terms of kinetics of xanthan molecular aggregation in media of different viscosity.

In this thesis, bio-nanocomposites made from two alternative biopolymers and montmorillonite (Mnt) clay have been investigated by molecular modelling. These biopolymers are xyloglucan (XG) and chitosan (CHS), both of which are abundant, renewable, and cost-effective. After being reinforced by Mnt clay nanoparticles, the polymer nanocomposites gains in multifunctionality and in the possibility to register unique combinations of properties, like mechanical, biodegradable, electrical, thermal and gas barrier properties. I apply molecular dynamics (MD) simulations to study the interfacial mechanisms of the adhesion of these biopolymers to the Mnt nanoplatelets at an atomic level. For the XG-Mnt system, a strong binding affinity of XG to a fully hydrated Mnt interface was demonstrated. It was concluded that the dominant driving force for the interfacing is the enthalpy, i.e. the potential energy of the XG-Mnt interacting system. The adsorbed XG favors a flat conformation with a galactose residue in its side chain that facilitates the adsorption of the polymer to the nanoclay.  The XG adsorption was found do depend strongly on the hydration ability of counterions. The binding affinity of XG to Mnt was found to be strongest in the K-Mnt/XG system, followed by, in decreasing order, Na-Mnt/XG, Li-Mnt/XG, and Ca-Mnt/XG. The competing mechanism between ions, water and the XG in the interlayer region was shown to play an important role. The dimensional stability upon moisture exposure, i.e. the ability of a material to resist swelling, is an important parameter for biopolymer-clay nanocomposites. While pure clay swells significantly even at low hydration levels, it is here shown that for the XG-Mnt system, at a hydration level below 50%, the inter-lamellar spacing is well preserved, suggesting a stable material performance. However, at higher hydration levels, the XG-Mnt composite was found to exhibit swelling at the same rate as the pure hydrated Mnt clay. For the CHS-Mnt system, the significant electrostatic interactions from the direct charge-charge attraction between the polymer and the Mnt clay play a key role in the composite formation. Varying the degree of acetylation (DA) and the degree of protonation (DPr) resulted in different effects on the polymer-clay interaction. For the heavily acetylated CHS (DA > 50%, also known as chitin), the strong adhesion of the neutral chitin to the Mnt clay was attributed to strong correlation between the acetyl functional groups and the counterions which act as an electrostatic “glue”. Similarly, the poor adhesion of the fully deprotonated (DPr = 0%) neutral CHS to the clay is attributed to a weak correlation between the amino functional group and the counterions. The stress-strain behavior of the CHS-Mnt composite shows that the mechanical properties are highly affected by the volume fraction of the Mnt clay and the degree of exfoliation of the composite. The material structure has a close relationship to the material properties. Biopolymer-clay nanocomposites hold a bright future to replace petroleum-derived polymer plastics and will become widely used in common life. The theme of the thesis is that further critical improvements of these materials can be accomplished by development of the experimental methods in conjunction with increased understanding of the interactions between polymer, clay, water, ions, solutions in the polymer-clay mixtures provided by molecular modelling.
I denna avhandling har molekylär modellering och molekyldynamisk (MD) simulering använts för att studera modellsystem för bio-nanokompositer bestående av montmorillonit-lera samt två olika sorters biopolymerer – xyloglukan (XG) och kitosan (CHS). Båda dessa polymerer är naturligt förekommande och mycket vanliga. De är dessutom förnyelsebara och kostnadseffektiva. Då polymererna förstärkts med nanopartiklar av montmorillonit får det resulterande kompositmaterialet en unik kombination av egenskaper såsom mekaniska, elektriska, termiska och barriär egenskaper etc. Genom att använda molekyldynamiska (MD) simuleringar, studeras här växelverkan mellan dessa biopolymerer och lernanopartiklar (Mnt) på grundläggande atomistisk detaljnivå. Mellan XG och Mnt i ett fullt hydrerat system kunde stark bindningsaffinitet påvisas. Den dominerande drivkraften för affiniteten var entalpi, d.v.s. potentiell växelverkansenergi. Den adsorberade XG-kedjan antar en platt konformation på ytan. Ett förslag utifrån simuleringsresultaten var att galaktosresidyn i xyloglukanets sidokedja underlättar adsorptionen till lerytan. Simuleringarna kunde också visa att adsorption av XG till Mnt beror starkt på motjonernas hydreringsförmåga. Bindningsaffiniteten mellan XG och Mnt var som starkast i K-Mnt/XG- systemet. Därefter följde, i minskande ordning, Na-Mnt/XG, Li-Mnt/XG och Ca-Mnt/XG. Det kunde visas att strukturen vid gränsytan styrs av konkurrerande mekanismer mellan joner, vatten och XG. Dimensionsstabilitet vid fuktexponering, d.v.s. förmågan hos ett material att motverka svällning, är en viktig egenskap för biopolymer-lernanokompositer. Ren lera sväller signifikant även vid låga fukthalter. Dock kunde MD simuleringar visa att ett modellsystem av XG-Mnt behåller sitt ursprungliga interlamellära avstånd vid hydreringsnivåer under 50%, vilket indikerar ett stabilare material. Vid högre hydrering uppmättes dock svällningen vara densamma som för ren lera. I CHS-Mnt-systemet visade det sig att direkt elektrostatisk växelverkan med signifikant styrka mellan laddningar på polymer och Mnt-yta spelar störst roll för kompositformeringen. Olika effekt på polymer-lerväxelverkan uppnåddes genom att variera acetyleringsgraden (DA) respektive protoneringsgraden (DPr). För den tungt acetylerade CHS-polymeren (DA > 50%, även kallad kitin) visade sig den starka vidhäftningen bero på korrelation mellan acetylgrupperna och motjonerna som i sin tur verkade som ett elektrostatiskt “lim”. På liknande sätt kunde den svaga vidhäftningen mellan fullt deprotonerad (DPr = 0%) neutral CHS och lera förklaras med en betydligt svagare korrelation mellan aminogrupperna och motjonerna. Spänning-töjningsbeteendet hos CHS-Mnt modellen visar att dess mekaniska egenskaper beror kraftigt på volymsandelen Mnt och graden av exfoliering i kompositen. Materialets struktur är nära relaterat till materialegenskaperna. Framtiden för nanokompositer av biopolymerer och lera är ljus då de kan komma att ersätta oljebaserade plaster och användas frekvent i våra dagliga liv. Materialen kommer successivt förbättras genom utveckling av experimentella metoder i kombination med molekylmodellering för ökad förståelse för växelverkan mellan polymer, lera, vatten, joner och lösningsmedel.
本论文利用分子动力学模拟技术研究了两种备选生物大分子与蒙脱土(Montmorillonite, Mnt)（一种粘土）组成的生物纳米复合材料，分别是木葡聚糖（Xyloglucan, XG）/蒙脱土和壳聚糖(Chitosan, CHS)/蒙脱土。木葡聚糖与壳聚糖都是自然界广泛存在的生物大分子，资源丰富且取材面宽，提取及加工成本低廉，加之可以生物降解并可再生，是优秀的生物复合材料备选原料。经过蒙脱土纳米颗粒加固后，这些基于生物大分子的复合材料将获得多功能且有多种独特特性相结合的优点，比如，更好的力学性能，生物可降解，良好的导电性能，传热性能和屏蔽气体与液体侵扰的能力等等。论文中，我们采用分子动力学模拟的方法着重对生物大分子与蒙脱土在界面上的粘附相互作用机理进行了深入探讨。  首先，对于木葡聚糖/蒙脱土纳米复合材料，我们发现糖分子与土分子间有着很强的天然亲和力。研究证明它们之间的这种相互作用，热焓是主要的推动力，也就是糖和土分子间的相互作用势能。含有半乳糖残基的木葡聚糖分子（本文中亦称天然木葡聚糖分子）吸附到粘土表面后，分子构型呈现扁平状，半乳糖残基似有辅助木葡聚糖大分子吸附到粘土颗粒上的作用。  进一步研究发现，木葡聚糖分子在粘土表面上的吸附与溶液中抗衡离子的水和作用密切相关。在钾离子平衡的糖/粘土系统中，糖分子与土分子的相互作用最强，钠离子平衡的糖/粘土系统次之，紧接着是锂离子平衡的糖/粘土系统，最弱的是钙离子平衡的糖/粘土系统。研究发现，离子，水分子，以及糖分子在粘土层间的竞争机制在糖分子的粘附过程中起着重要的作用。  材料暴露于潮湿环境中的尺寸稳定性，也就是材料抗肿胀的能力是生物大分子/蒙脱土所构成的复合材料的重要参数。蒙脱土自身即使在很低的潮湿环境下就会有明显地膨胀现象，然而，对木葡聚糖/蒙脱土复合材料来说，尺寸稳定性可以在水和值低于50%以下有效保存。其夹层尺寸的稳定保持暗示了材料在这个程度的潮湿环境下的稳定性。然而，当水和值高于50%时，木葡聚糖/蒙脱土复合材料将出现明显的肿胀现象，表现在夹层尺寸的明显增大，且其膨胀速率与粘土自身的膨胀速率逐渐趋于相当水平。  其次，对于壳聚糖/蒙脱土复合材料，我们发现由电荷-电荷间直接产生地强烈的静电吸引作用是壳聚糖分子与蒙脱土分子相互粘附并构成复合材料的关键因素。通过改变壳聚糖分子的乙酰化程度（Degree of acetylation, DA）和质子化程度(Degree of protonation, DPr)，糖分子与土分子的相互作用有着显著地不同。对于乙酰化程度（DA）高于50%的壳聚糖分子（亦成为甲壳素分子chitin, CHT），电中性的甲壳素分子与土分子间的强吸附作用源于乙酰基功能团与抗衡离子的强相关性。抗衡离子此时扮演着类似于“电子胶”的作用，可以有效地将电中性的甲壳素分子与土分子粘结在一起。类似地，当质子化程度最低时，亦即壳聚糖分子完全非质子化，即呈现电中性时，较差的糖/土吸附作用源于氨基功能团与抗衡离子的较弱的相关性。  进一步对壳聚糖/蒙脱土复合材料的分子系统进行应力应变计算发现，复合材料的力学性能直接受蒙脱土体积分数和其剥离程度的影响，通常，粘土的体积分数越大体系的力学性能越高，且剥离程度对材料的整体性能也有直接影响。因此，材料的结构与其性能的表征有着密切联系。  我们相信生物大分子与蒙脱土构成的生物复合材料有着光明的前景，可以取代石油提取物制成的塑料材料，并将能够广泛应用在日常生活中。通过实验技术的改善和应用分子模拟技术对复合材料体系中生物大分子，蒙脱土分子，水分子，离子，溶液环境等混合物质相互作用的理解增加，这种可再生的新材料将会得到重要改进，这也是整本论文的主旋律。

QC 20150520

Bio-nanocomposites

The goal of the proposed study is to understand the morphology, physical, and responsive properties of synthetic polymer and biopolymer layer-by-layer (LbL) arrays using the inkjet printing and stamping technique, in order to develop patterned encapsulated thin films for controlled release and biosensor applications. In this study, we propose facile fabrication processes of hydrogen-bonded and electrostatic LbL microscopic dot arrays with encapsulated target organic and cell compounds. We study encapsulation with the controllable release and diffusion properties ofpoly(vinylpyrrolidone) (PVPON), poly(methacrylic acid) (PMAA), silk-polylysine, silk-polyglutamic acid, pure silk films, and E-coli cells from the multi-printing process. Specifically, we investigate the effect of thickness, the number of bilayers, and the hydrophobicity of substrates on the properties of inkjet/stamping multilayer films such as structural stability, responsiveness, encapsulation efficiency, and biosensing properties. We suggest that a more thorough understanding of the LbL assembly using inkjet printing and stamping techniques can lead to the development of encapsulation technology with no limitations on either the concentration of loading, or the chemical and physical properties of the encapsulated materials. In addition, this study offers new encapsulation concepts with simple, cost effective, highly scalable, living cell-friendly, and controllable patterning properties.

Silver nanoparticles (sub 10 nm), supported on, or in, cellulose, have been demonstrated to be well stabilised and immobilised during application in a model continuous reaction: the reduction of 4-nitrophenol (4-NP) to 4-aminophenol with sodium borohydride. The production of these silver nanoparticles (NP), within the cellulose supports, was carried out by either in situ reduction of silver precursors absorbed into the preformed cellulose supports, or, by inclusion of ex situ synthesised NPs (prepared in DMSO solutions) in the dissolution of cellulose and trapping upon subsequent coagulation of cellulose. The effects of NP synthesis method (affecting particle size and agglomeration) and the cellulose morphology and porous structure were examined with respect to the catalytic activity of the materials. The in situ reduction of a silver salt with aqueous NaBH4 solutions (0.03 to 1.0 wt. %) led to tuneable Ag NP sizes with mean diameters of 5 to 11 nm (TEM) and metal loadings of 0.5-1.0 wt. %. The catalytic activity of these samples in the 4-NP reduction reaction (0.05 mM, 0.167 M NaBH4, 30 °C) was demonstrated to increase upon decreasing NP size: TOF values of 22–356 h-1, consistent with a Langmuir-Hinshelwood mechanism. The porous structure of these Ag-cellulose materials (0.2 to 294 m2 g-1) was demonstrated to be variable and dependent on drying treatments of the regenerated cellulose hydrogel. Thermal drying, freeze-drying and critical point drying resulted in materials with different bulk structure and porosity. In turn the different porosities resulted in extremely different catalyst activities, e.g. Ag-cellulose catalyst (0.3 mm disks) thin film, hydrogel and cryogel phases exhibited TOF values of 2, 12 and 178 h-1, respectively. In addition, the NP synthesis could be carried out in either the cellulose hydrogel or cryogel, which led to different extents of Ag NP catalyst stabilisation against agglomeration during the 4-NP reaction and catalyst recovery and recycling. The Ag NPs synthesised in the cryogel cellulose disks were observed to undergo agglomeration (TEM) after use in 4 repeat batch reductions, whilst those NPs synthesised in the hydrogel cellulose, prior to freeze-drying to the final cryogel catalyst material, did not exhibit any agglomeration upon 4 repeat reduction reactions. The ex situ reduction of Ag and Au NPs was carried out by the reduction of AgOAc and Au(OAc)3 by DMSO and variation of the NP synthesis parameters, such as time (10 min – 1h) and temperature (50 – 80 °C), allowed for control of the NP sizes (3 to 6 nm Ag NPs and 4 to 11 nm Au NPs, TEM). It was demonstrated that the addition of the polysaccharide starch (0.42 wt. % in DMSO) allowed for consistent Ag NP size (ca. 4 nm) to be achieved throughout the 8 h synthesis, the starch acting as both the reducing and capping agent, maintaining the small sizes and narrow particle size distributions of the NPs upon aging (72 h). A kinetic model with a bimolecular nucleation step was developed to describe this reduction of the silver acetate by the starch/DMSO system. However, contact of the NPs with solutions of imidazolium ILs, 1-Ethyl-3-methylimidazolium acetate (EmimOAc) and 1-Butyl-3-methylimidazolium chloride (BmimCl) in DMSO, used in the dissolution of cellulose, led to the oxidation of the Ag(0) and Au(0) NPs. Thus, when these NP solutions were mixed in cellulose solutions regeneration by phase inversion with the aim of preparing cellulose/NP composites led to materials with negligible metal loadings (AAS). This oxidation, of the metal NPS, was partially overcome by stabilisation of the starch capped Ag NPs by pre-treatment with cellulose (1:1 mixture of α and MC cellulose). However, the activity of the resulting Ag-cellulose catalyst (0.5 wt. % AAS, 6.7 nm TEM) was much lower than the Ag-cellulose catalysts prepared by in situ reduction of silver in the cellulose hydrogel, despite the comparable NP sizes. This was presumed to be a result of encapsulation of the Ag NPs by the cellulose, leading to a decrease in the accessible surface of the NPs. Finally, the use of Ag NP / cellulose composites, prepared by in situ reduction of silver in cellulose hydrogel beads (0.19 wt. %, 6.4 nm), were demonstrated in the continuous reduction of 4-NP in a packed bed reactor (τ’ 100 g s dm-3). The activation energies of the reactions of 4-NP catalysed by the Ag-cellulose catalyst materials were determined (3.2 to 9.4 kJ mol-1) from Arrhenius plots, which demonstrated that above 20 °C the reaction was likely subject to diffusion limitations in the cellulose beads. The high degree of stabilisation of the Ag NPs against agglomeration imparted by the cellulose support was demonstrated: the rate of reaction was observed to be constant over 120 h, treating 45 L of 4-NP solution, with the catalyst material after use demonstrating no significant leaching of silver, or agglomeration, of NPs (AAS, TEM).

This thesis addresses both the theory and simulation of diffusion of moisture in water-based biopolymer films, whose preliminary use is as adhesives on glass bottles in the labelling industry. The first part explores the kinetics of dehydration of thin films of these biopolymer materials. The second part of the thesis deals with moisture intake into both dried thin films and into the wet biopolymer gel network. Mathematical simulations based on Fick's laws of diffusion have been developed as a tool to understand the underpinning mechanisms of diffusion and of evaporation to discover which, if either plays a more dominant role in controlling the dehydration process. By inputting a series of different initial and final moisture contents, a full spectra of scenarios has been examined to aid understanding of the dehydration process. Numerical calculations where diffusion is the controlling mechanism as well as simulations where evaporation controls the process have been considered and discussed. Models in which a combination of both diffusion and evaporation are equally important are also studied. Fixed and moving boundary conditions are applied to the models and compared with dehydration results obtained experimentally. A simple method has been developed to assess the rehydration process of a dried biopolymer film and similar simulations have also been constructed to describe the rehydration of a water droplet into the thin, dried films. A novel method to investigate the migration of water into casein biopolymer gels using acoustic techniques has been developed and validated. The preliminary results are promising, highlighting the potential capability of the method. As the composition of a material changes, the speed of a wave of sound being passed through the material changes, so by monitoring this change as a function of time, concentration profiles of the biopolymer material can be constructed. Simulated concentration profiles were successfully produced based on Fick's second law of diffusion, to obtain a diffusion coefficient dependent on both time and position. By fitting these curves to the experimental data, diffusion coefficients are obtained with values of the same order of magnitude as those calculated from the experiments on a dehydrating thin film of the same composition.

Thesis (MSc)--Stellenbosch University, 2012.
ENGLISH ABSTRACT: Biopolymers exhibit the required material properties to replace conventional, non-biodegradable, petroleum-based polymer products. They have a closed carbon cycle, making them carbon neutral and environmentally friendly. Biopolymers are produced from non-toxic substrates during in vivo enzymatic reactions. Biosynthesis of the most commercially important biopolymers is too complex to be reproduced in in vitro reactions. Identification of the genes responsible for their biosynthesis has been under investigation, with some pathways already elucidated. The genes involved in the biosynthesis of these polymers have been targeted for genetic manipulation to increase productivity, as well as create tailor-made polymers. Novel biopolymers and the genes responsible for their synthesis are of interest for their potential commercial applications. Bacteria produce a wide range of biopolymers and are being implemented as the bio-factories for biopolymer production. They are capable of utilising easily accessible and renewable carbon sources such as sucrose for polymer biosynthesis. Bacteria thus allow for economical production of these environmentally beneficial polymers. In this study, the gene responsible for the production of an unknown biopolymer from an unknown bacterium was identified. The biopolymer producing bacteria were grown on media enriched with sucrose as carbon source, during an expression library screening in a previous study. Expression library technology was used to search for the gene and it was identified as a 424 amino acid levansucrase which had a 100% homology to Leuconostoc mesenteroides M1FT levansucrase (AAT81165.1). Biopolymer analysis revealed that the biopolymer was a levan, a polysaccharide consisting of only fructose molecules with a molecular weight of ± 5 kDa. Analysis of a 516 bp fragment of the 16S rRNA determined that the unknown bacteria were a Pseudomonas species.
AFRIKAANSE OPSOMMING: Bio-polimere besit noodsaaklike materiële eienskappe wat toelaat dat dit konvensionele, nie bio-afbreekbare, petroleum-gebasseerde polimeer produkte kan vervang. Hulle het n geslote koolstof kringloop en is dus koolstof neutraal en omgewingsvriendelik. Bio-polimere word vervaardig van nie-toksiese substrate, gedurende ensiematiese reaksies in vivo. Die belangrikste kommersiële bio-polimere se ensiematiese produksie is te kompleks om in ʼn in vitro reaksie te herproduseer. Ondersoeke tot die identifikasie van die gene wat verantwoordelik is vir die produksie van die polimere is onderweg, en sommige produksie paaie is reeds bekend. Die bekende gene word geteiken vir genetiese manipulasie om hulle produktiwiteit te vermeerder en om unieke polimere te produseer. Unieke bio-polimere en die gene wat vir hul produksie verantwoordelik is, is van belang vir hulle potentiële implimentering in komersiële toepassings. Bakteria produseer ʼn verskeidenheid bio-polimere en word as die bio-fabrieke vir polimeerproduksie geimplimenteer. Hulle kan maklik bekombare koolstofbronne, soos sukrose, gebruik om bio-polimere te produseer. Bakteria laat dus die ekonomiese produksie van hierdie omgewingsvriendelike polimere toe. In hierdie studie word die geen wat verantwoordelik is vir die produksie van ʼn onbekende bio-polimeer van ʼn onbekende bakteria, geidentifiseer. Die bakteria was gevind op media, wat verryk was met sukrose as koolstofbron, tydens ʼn vorige studie, waartydens ʼn uitdrukkingsbiblioteek gesif was op hierdie media. Uitdrukkingsbiblioteek tegnologie was gebruik om die geen te vind. Die geen was geidentifiseer as ʼn 424 aminosuur, homo-fruktose-polimeer produseerende geen, ʼn “levansucrase”. Die geen het ʼn 100% homologie met die M1FT “levansucrase” geen (AAT81165.1) van Leuconostoc mesenteroides gehad. Analise van die bio-polimeer het bepaal dat die polimeer ʼn polisakkaried was, wat slegs uit fruktose molekules bestaan het. Die molekulêre gewig van die polimeer was ± 5 kDa. Analise van ʼn 516 bp fragment van die 16S rRNS het bepaal dat die bakteria van die Pseudomonas spesie afkomstig was.

In this work, the synthesis of biopolymer-based hydrogel networks with defined architecture is presented. In order to obtain materials with defined properties, the chemoselective copper-catalyzed azide-alkyne cycloaddition (or Click Chemistry) was used for the synthesis of gelatin-based hydrogels. Alkyne-functionalized gelatin was reacted with four different diazide crosslinkers above its sol-gel transition to suppress the formation of triple helices. By variation of the crosslinking density and the crosslinker flexibility, the swelling (Q: 150-470 vol.-%;) and the Young’s and shear moduli (E: 50 kPa - 635 kPa, G’: 0.1 kPa - 16 kPa) could be tuned in the kPa range. In order to understand the network structure, a method based on the labelling of free functional groups within the hydrogel was developed. Gelatin-based hydrogels were incubated with alkyne-functionalized fluorescein to detect the free azide groups, resulting from the formation of dangling chains. Gelatin hydrogels were also incubated with azido-functionalized fluorescein to check the presence of alkyne groups available for the attachment of bioactive molecules. By using confocal laser scanning microscopy and fluorescence spectroscopy, the amount of crosslinking, grafting and free alkyne groups could be determined. Dangling chains were observed in samples prepared by using an excess of crosslinker and also when using equimolar amounts of alkyne:azide. In the latter case the amount of dangling chains was affected by the crosslinker structure. Specifically, 0.1% of dangling chains were found using 4,4’-diazido-2,2’-stilbene-disulfonic acid as cosslinker, 0.06% with 1,8-diazidooctane, 0.05% with 1,12-diazidododecane and 0.022 % with PEG-diazide. This observation could be explained considering the structure of the crosslinkers. During network formation, the movements of the gelatin chains are restricted due to the formation of covalent netpoints. A further crosslinking will be possible only in the case of crosslinker that are flexible and long enough to reach another chain. The method used to obtain defined gelatin-based hydrogels enabled also the synthesis of hyaluronic acid-based hydrogels with tailorable properties. Alkyne-functionalized hyaluronic acid was crosslinked with three different linkers having two terminal azide functionalities. By variation of the crosslinking density and crosslinker type, hydrogels with elastic moduli in the range of 0.5-3 kPa have been prepared. The variation of the crosslinking density and crosslinker type had furthermore an influence also on the hydrolytic and enzymatic degradation of gelatin-based hydrogels. Hydrogels with a low crosslinker amount experienced a faster decrease in mass loss and elastic modulus compared to hydrogels with higher crosslinker content. Moreover, the structure of the crosslinker had a strong influence on the enzymatic degradation. Hydrogels containing a crosslinker with a rigid structure were much more resistant to enzymatic degradation than hydrogels containing a flexible crosslinker. During hydrolytic degradation, the hydrogel became softer while maintaining the same outer dimensions. These observations are in agreement with a bulk degradation mechanism, while the decrease in size of the hydrogels during enzymatic degradation suggested a surface erosion mechanism. Because of the use of small amount of crosslinker (0.002 mol.% 0.02 mol.%) the networks synthesized can still be defined as biopolymer-based hydrogels. However, they contain a small percentage of synthetic residues. Alternatively, a possible method to obtain biopolymer-based telechelics, which could be used as crosslinkers, was investigated. Gelatin-based fragments with defined molecular weight were obtained by controlled degradation of gelatin with hydroxylamine, due to its specific action on asparaginyl-glycine bonds. The reaction of gelatin with hydroxylamine resulted in fragments with molecular weights of 15, 25, 37, and 50 kDa (determined by SDS-PAGE) independently of the reaction time and conditions. Each of these fragments could be potentially used for the synthesis of hydrogels in which all components are biopolymer-based materials.
In dieser Arbeit wird die Synthese Biopolymer-basierter Hydrogelnetzwerke mit definierter Architektur beschrieben. Um Materialien mit definierten und einstellbaren Eigenschaften zu erhalten, wurde die chemoselektive Kupferkatalysierte Azid-Alkin-Cycloadditionsreaktion (auch als Click-Chemie bezeichnet) für die Synthese Gelatine-basierter Netzwerke eingesetzt. Alkin-funktionalisierte Gelatine wurde mit vier verschiedenen Diazid-Quervernetzern oberhalb der Gel-Sol-Übergangstemperatur umgesetzt, um die Formierung tripelhelikaler Bereiche durch Gelatineketten zu unterdrücken. Durch Variation der Menge an Quervernetzer (und damit der Netzdichte) sowie der Länge und Flexibilität der Quervernetzer konnten u.a. die Quellung (Q: 150-470 vol.-%) sowie der Young’s - und Schermodul im kPa Bereich eingestellt werden (E: 50 kPa - 635 kPa, G’: 0.1 kPa - 16 kPa). Um die Netzwerkarchitektur zu verstehen, wurde eine Methode basierend auf dem Labeln unreagierter Azid- und Alkingruppen im Hydrogel entwickelt. Die Gelatine-basierten Hydrogele wurden mit Alkin-funktionalisiertem Fluorescein umgesetzt, um freie Azidgruppen zu detektieren, die bei einem Grafting entstehen. Darüber hinaus wurden die Hydrogele mit Azid-funktionalisiertem Fluorescein reagiert, um die Menge an freien Alkingruppen zu bestimmen, die zudem potentiell für die Anbindung bioaktiver Moleküle geeignet sind. Quervernetzung, Grafting, und die Anzahl freier Alkingruppen konnten dann mit Hilfe der konfokalen Laser Scanning Mikroskopie und der Fluoreszenzmikroskopie qualitativ und quantitativ nachgewiesen werden. Gegraftete Ketten wurden in Systemen nachgewiesen, die mit einem Überschuss an Quervernetzer hergestellt wurden, entstanden aber auch beim Einsatz äquimolarer Mengen Alkin- und Azidgruppen. Im letzteren Fall wurde in Abhängigkeit von der Struktur des Diazids unterschiedliche Anteile gegrafteter Ketten festgestellt. 0.1 mol-% von gegrafteten Ketten wurden für 4,4’-Diazido-2,2’-stilbendisulfonsäure gefunden, 0.06 mol-% für 1,8-Diazidooktan, 0.05 mol% für 1,12-diazidododecan und 0.022 mol-% für PEG-Diazid. Diese Beobachtung kann durch die unterschiedliche Flexibilität der Vernetzer erklärt werden. Während der Netzwerkbildung werden die Bewegungen der Gelatineketten eingeschränkt, so dass kovalente Netzpunkte nur erhalten werden können, wenn der Vernetzer lang und flexibel genug ist, um eine andere Alkingruppe zu erreichen. Die Strategie zur Synthese von Biopolymer-basierten Hydrogelen mit einstellbaren Eigenschaften wurde von Gelatine- auf Hyaluronsäure-basierte Gele übertragen. Alkin-funktionalisierte Hyaluronäure wurde mit drei verschiedenen Diaziden quervernetzt, wobei Menge, Länge, und Flexibilität des Quervernetzers variiert wurden. In dieser Weise wurden sehr weiche Hydrogele mit E-Moduli im Bereich von 0.5-3 kPa hergestellt. Die Variation der Vernetzungsdichte und des Vernetzertyps beeinflusste weiterhin den hydrolytischen und enzymatischen Abbau der Hydrogele. Hydrogele mit einem geringerem Anteil an Quervernetzer wurden schneller abgebaut als solche mit einem höheren Quervernetzeranteil. Darüber hinaus konnte gezeigt werden, dass Hydrogele mit Quervernetzern mit einer rigiden Struktur deutlich langsamer degradierten als Hydrogele mit flexibleren Quervernetzern. Während des hydrolytischen Abbau wurden die Materialien weicher, behielten aber ihre Form bei, was mit einem Bulk-Abbau-Modell übereinstimmt. Während des enzymatischen Abbaus hingegen änderten sich die Materialeigenschaften kaum, jedoch wurden die Proben kleiner. Diese Beobachtung stimmt mit einem Oberflächenabbaumechanismus überein. Da in allen vorgestellten Systemen nur eine kleine Menge synthetischer Vernetzer eingesetzt wurde (0.002 – 0.02 mol%), können die Materialien noch als Biopolymer-basierte Materialien klassifiziert werden. Jedoch enthalten die Materialien synthetische Abschnitte. In Zukunft könnte es interessant sein, einen Zugang zu Materialien zu haben, die ausschließlich aus Biopolymeren aufgebaut sind. Daher wurde der Zugang zu Biopolymer basierten Telechelen untersucht, die potentiell als Vernetzer dienen können. Dazu wurden durch die kontrollierte Spaltung von Gelatine mit Hydroxylamin Gelatinefragmente mit definiertem Molekulargewicht hergestellt. Hydroxalamin reagiert unter Spaltung mit der Amidbindung zwischen Asparagin und Glycin, wobei Aspartylhydroxamate und Aminoendgruppen entstehen. Die Reaktion von Gelatine mit Hydroxylamin ergab Fragmente mit Molekulargewichten von 15, 25, 37, und 50 kDa (bestimmt mit SDS-PAGE), und die Formierung dieser Fragmente war unabhängig von den weiteren Reaktionsbedingungen und der Reaktionszeit. Jedes dieser Fragmente kann potentiell für die Synthese von Hydrogelen eingesetzt werden, die ausschließlich aus Biopolymeren bestehen.

Dissertation (Ph.D.) -- Worcester Polytechnic Institute.
Keywords: Ligament; ACL; Collagen; Fibrin; Microthread; Fiber; Thread; FGF-2; Fibroblast; Tissue regeneration; Tissue engineering. Includes bibliographical references.

CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO
O uso indiscriminado de polímeros derivados do petróleo como matériaprima tem resultado no acúmulo de resíduos de lenta biodegradabilidade nos aterros sanitários, pois os plásticos convencionais levam cerca de meio século para serem degradados. Diante desse cenário, o estudo de polímeros derivados de fontes renováveis, os biopolímeros, é totalmente relevante e, em muitos casos, os polímeros derivados do petróleo podem ser substituídos por biopolímeros. Pesquisas apontam a escova dental como um produto ideal para sofrer esta mudança, por ser um produto de uso pessoal rapidamente descartado e por ser, geralmente, produzido a partir do polipropileno (PP), polímero que apresenta lenta biodegradabilidade. Dessa forma, este trabalho multidisciplinar tem como objetivo o desenvolvimento de um protótipo de escova dental fabricado em poliuretano derivado do óleo de mamona, bem como a caracterização desse material a partir de ensaios de absorção de água e de saliva artificial, análise térmica dinâmico-mecânica (DMTA) e ensaios mecânicos de tração, estabelecendo uma comparação com o PP. A partir dos ensaios pode-se concluir que o PU derivado de mamona apresentou absorção de saliva superior à de água e esta, por sua vez, superior ao PP. Com relação a tração, o PP superou o PU em todos os aspectos, mostrando-se um material mais resistente e de maior rigidez. Contudo, concluiu-se que com algumas alterações no design, uma escova fabricada em PU derivado do óleo de mamona pode alcançar a mesma carga de ruptura e rigidez estrutural de uma escova convencional.
Indiscriminate use of raw materials by various industries such as polymers from petroleum has been causing an ever-increasing accumulation of slow biodegrading residue materials in sanitary pits. Many modern life utensils are made out of conventional plastic that are estimated to take up to half a century to decompose. In view of this situation, the study of polymers from renewable sources, the biopolymers, is key in the search for alternatives that may decrease the damaging effects on the environment. Petroleum based polymers can in many instances be replaced by biopolymers. Amongst such products, research has been indicating that toothbrush manufacturing can make use of alternative materials. A toothbrush is a personal hygiene device that should be used for relatively short periods. It is commonly made out of polypropylene (PP), a polymer with slow biodegrading characteristics. This study uses a multidisciplinary approach and its objective is the development of a toothbrush handle made out of polyurethane derived from castor oil. Water and artificial saliva absorption, DMTA and traction experiments were carried out to compare chemical and mechanical properties of traditional polypropylene and castor oil polyurethane toothbrushes. From the tests we can conclude that the derivative of castor oil PU showed absorption of saliva superior to water and also superior to PP. With respect to traction, the PP over the PU in all aspects and is a material more resistant and more rigid. However, it was concluded that with some changes in design, a brush made of PU derivative of castor oil might reach the same tensile strength and structural rigidity of a conventional toothbrush.