Academic literature on the topic 'Microstructural modification'

Les alliages aluminium-silicium (Al-Si) ont attiré une attention considérable en raison de leur importance pour les applications industrielles. Dans le présent travail, des alliages à haute pureté (Al-12.7 wt. % Si) avec et sans ajout de strontium (400 ppm), solidifiés lentement en creuset ou de façon dirigée (DS), ont été préparés et traités thermiquement. L'influence de l'ajout de strontium et des post-traitements thermiques sur les caractéristiques microstructuraux et cristallographiques des phases eutectiques a été étudiée de façon systématique. Les caractéristiques de croissance du silicium eutectique (Si) dans l'alliage non modifié ainsi que dans l'Al-12.7Si Sr-modifié ont été étudiés. Pour le cas du non-modifié, la formation répétée de variantes de macles mono-orientées permet une croissance rapide du silicium eutectique selon le mécanisme twin plane re-entrant (TPRE). Microscopiquement, les cristaux de silicium ont une forme de plaque allongée dans la direction &lt;1 1 0&gt; non conforme à la croissance selon &lt;1 1 2&gt; présumée par le modèle TPRE. L'élongation selon &lt;1 1 0&gt; est réalisée par des paires en zigzag &lt;1 1 2&gt; sur des plans de maclage parallèles, conduisant à une disparition alternative et à la création de macles rentrantes à 141°. Ce mécanisme de croissance permet aux cristaux de silicium de n'exposer que les plans {1 1 1} à faible consommation d'énergie à la consolidation. Pour les alliages modifiés au strontium, des changements importants de morphologie apparaissent dans le silicium eutectique, attribuable à la croissance de TPRE restreinte et au maclage induit par les impuretés (IIT). Ce dernier améliore la croissance latérale en formant de nouvelles macles avec des plans de macles parallèles, tandis que le second conduit à une croissance isotrope en formant des macles orientées différemment. Le traitement thermique provoque l'affinement des grains des deux phases eutectiques. L'affinement de l'α-Al se produit en même temps que la fragmentation et la sphéroïdisation du silicium et est principalement lié à la fracture des grains de silicium en raison de leur capacité limitée à accommoder la très grande dilatation thermique l'α-Al, ainsi qu'à la diffusion des atomes d'aluminium au cours du traitement thermique. La rupture du silicium génère une force de "capillarité" qui active la diffusion d'atomes d'aluminium dans la fissure. En raison du caractère de substitution de la diffusion de l'aluminium, la migration des lacunes vers l'intérieur de l'α-Al est induite lorsque l'aluminium se déplace dans les fissures, ainsi les vides de la fracture du silicium sont transférés à l'α-Al. De cette façon, les cristaux d'α-Al sont altérés et déformés. Les défauts cristallins produits, à leur tour, initient la restauration et même la recristallisation du α-Al, ce qui entraîne une diminution de taille de grain. La phase α-Al dans l'alliage de Al-12.7Si-0.04Sr solidifiée directionnellement, affiche une forte texture de fibre &lt;1 0 0&gt; parallèle à la direction de solidification. De très gros grains &lt;1 0 0&gt; α-Al sont principalement formés à la périphérie de l'échantillon cylindrique en raison des directions d'évacuation de chaleur favorables disponibles pour les trois directions [1 0 0]. Après traitement thermique, l'intensité de la texture de la phase α-Al diminue en raison de la restauration et de la recristallisation, mais le type de texture ne change pas. Pour la phase de silicium eutectique dans l'alliage de coulée, il y a deux fibres principales de texture, &lt;1 0 0&gt; et &lt;1 1 0&gt; parallèles à la direction de solidification, accompagnées de deux composantes faibles, &lt;2 2 1&gt; et &lt;1 1 3&gt; dans la même direction. Les fibres &lt;1 0 0&gt; et &lt;1 1 0&gt; correspondent à des grains de silicium situés sur la périphérie et dans le centre de l'échantillon. Les composantes &lt;2 2 1&gt; et &lt;1 1 3&gt; proviennent de plusieurs macles de grains orientés &lt;1 1 0&gt; et &lt;1 0 0&gt;. Les faibles intensités de ces deux composantes sont liées à leur fraction volumique mineure [...]<br>Al-Si alloys have attracted considerable attention due to their importance to industrial applications. In the present work, both crucible slowly solidified and slowly directionally solidified (DS) high-purity Al-12.7 wt. % Si alloys with and without 400 ppm Sr addition have been prepared and heat treated. The influence of Sr addition and post heat treatments on the microstructural and crystallographic features of the eutectic phases has been systematically studied. The growth characteristics of eutectic Si in the unmodified and the Sr-modified Al-12.7Si alloys were investigated. For the non-modification case, the formation of repeated single-orientation twin variants enables rapid growth of eutectic Si according to the twin plane re-entrant (TPRE) mechanism. Microscopically, Si crystals are plate-like elongated in one &lt;1 1 0&gt; direction that is not in accordance with the &lt;1 1 2&gt; growth assumed by the TPRE model. The &lt;1 1 0&gt; extension is realized by paired &lt;1 1 2&gt; zigzag growth on parallel twinning planes, leading to alternative disappearance and creation of 141° re-entrants. This growth manner ensures Si crystals to expose only their low-energy {1 1 1} planes to the melt. For the Sr-modification case, substantial changes appear in eutectic Si morphology, attributable to the restricted TPRE growth and the impurity induced twinning (IIT) growth. The first enhances lateral growth by forming new twins with parallel twinning planes, while the second leads to isotropic growth by forming differently oriented twins. Heat treatment brings about refinement of both eutectic phases. The refinement of the α-Al occurs concomitantly with the fragmentation and spheroidization of Si and is mainly related to the fracture of the Si crystals due to their limited capacity to accommodate the giant thermal expansion of the α-Al and the diffusion of Al atoms to the cracks during the heat treatment. The Si fracture generates “capillarity” force that activates the diffusion of Al atoms to the gap of the crack. Due to the substitutional feature of Al diffusion, the migration of vacancies toward the interior of the α-Al is induced when Al moves to the gaps, thus the voids of the Si fracture are transferred to the α-Al. In this way, the crystals of α-Al are distorted and defected. The produced crystal defects, in turn, initiate recovery and even recrystallization of the α-Al, resulting in grain refinement. The α-Al phase in the directionally solidified Al-12.7Si-0.04Sr alloy, displays a strong &lt;1 0 0&gt; fiber texture in the solidification direction. Giant &lt;1 0 0&gt; α-Al grains are mainly formed in the outer circle region of the cylindrical specimen due to the favorable heat evacuation directions available for the three &lt;1 0 0&gt; directions. After heat treatment, the texture intensity of the α-Al phase decreases due to the recovery and recrystallization, but the texture type does not change. For the eutectic Si phase in the as-cast alloy, there are two main fiber texture components, &lt;1 0 0&gt; and &lt;1 1 0&gt; in the DS direction, accompanied by two weak components, &lt;2 2 1&gt; and &lt;1 1 3&gt; in the same direction. The &lt;1 0 0&gt; and &lt;1 1 0&gt; components are from Si crystals located in the outer circle and center regions of the cylindrical specimen. The &lt;2 2 1&gt; and the &lt;1 1 3&gt; components are from multiple twins of the &lt;1 1 0&gt; and &lt;1 0 0&gt; oriented crystals. The weak intensities of these two components are related to their minor volume fraction. Once heat treated, the twinned parts with minor volume fractions enlarge at the expense of their twin related matrix, thus the &lt;1 1 0&gt; component is weakened and accompanied by the intensification of the components from the twins. The disappearance of the &lt;1 1 3&gt; component and the appearance of the &lt;1 1 5&gt; component are due to crystallographic rotation of Si crystals during their fragmentation

This dissertation investigates microstructure/property relations in ultrahigh carbon steel (UHCS) with the aim of improving toughness while retaining high hardness. Due to high C contents (ranging from 1 to 2 wt%), UHCS exhibit high strength, hardness, and wear resistance. Despite this, applications for UHCS are currently limited because they typically contain a continuous network of proeutectoid cementite that greatly reduces ductility and toughness. In previous research, thermomechanic processing had seen considerable success in breaking up the network. However, the processing is difficult and has thus far seen very limited industrial application. Chemical modification of the steel composition has also seen some success in network break-up, but is still not well understood. There have been relatively few fundamental studies of microstructure evolution in UHCS; studies in the literature typically focused on lower C steels (up to 1 wt% C) or on cast irons (>2.1 wt% C). Thus, this work was undertaken to gain a better understanding of microstructural changes that occur during heat treatment and/or chemical modification of UHCS with a focus on the distribution of proeutectoid cementite within the microstructure. This dissertation is composed of eight chapters. The first chapter presents an introduction to phases found in UHCS, descriptions of research materials used in each chapter, and the hypotheses and objectives guiding the work. The second chapter describes a study of the microstructure found in a 2C-4Cr UHCS before and after an industrial-scale austenitizating heat treatment that increased hardness and toughness and also produced discrete carbide particles in the matrix. The third chapter establishes and demonstrates a metric for measuring connectivity in carbide networks. The fourth chapter describes a series of heat treatments designed to investigate kinetics of spheroidization and coarsening of carbide particles and denuded zones near cementite network branches in 2C-4Cr UHCS. The fifth chapter describes an additional series of heat treatments comparing coarsening kinetics in 2C-1Cr and 2C-4Cr UHCS. Lowering the Cr content caused clustering of cementite particles near grain boundaries, in contrast to the denuded zones observed in the higher Cr UHCS. The fifth chapter details four in situ confocal laser scanning microscopy heat treatments of 2C-4Cr UHCS. The seventh chapter investigates the effects of a 2wt% Nb addition on 2C-4Cr UHCS. The eighth and final chapter summarizes the findings of all the experiments of the previous chapters and revisits the objectives and conclusions.

Aluminium alloys with Si as the major alloying element form a class of material providing the most significant part of all casting manufactured materials. These alloys have a wide range of applications in the automotive and aerospace industries due to an excellent combination of castability and mechanical properties, as well as good corrosion resistance and wear resistivity. Additions of minor alloying elements such as Cu and Mg improve the mechanical properties and make the alloy responsive to heat treatment. The aim of this work is studying the role of size and morphology of microstructural constituents (e.g SDAS, Si-particles and intermetalics) on mechanical properties of Al-Si based casting alloy at room temperatures up to 500 ºC. The cooling rate controls the secondary dendrite arm spacing (SDAS), size and distribution of secondary phases. As SDAS becomes smaller, porosity and second phase constituents are dispersed more finely and evenly. This refinement of the microstructure leads to substantial improvement in tensile properties (e.g. Rm and εF). Addition of about 280 ppm Sr to EN AC- 46000 alloy yields fully modified Si-particles (from coarse plates to fine fibres) regardless of the cooling conditions. Depression in eutectic growth temperature as a result of Sr addition was found to be strongly correlated to the level of modification irrespective of coarseness of microstructure. Modification treatment can improve elongation to failure to a great extent as long as the intermetallic compounds are refined in size. Above 300 ºC, tensile strength, Rp0.2 and Rm, of EN AC-46000 alloys are dramatically degraded while the ductility was increased. The fine microstructure (SDAS 10 μm) has superior Rm and ductility compared to the coarse microstructure (SDAS 25 μm) at all test temperature (from room to 500 ºC). Concentration of solutes (e.g. Cu and Mg) in the dendrites increases at 300 ºC and above where Rp0.2 monotonically decreased. The brittleness of the alloy below 300 ºC was related to accumulation of a high volume fraction damaged particles such as Cu- Fe-bearing phases and Si-particles. The initiation rate of damage in the coarse particles was significantly higher, which enhances the probability of failure and decreasing both Rm and εF compared to the fine microstructure. A physically-based model was adapted, improved and validated in order to predict the flow stress behaviour of EN AC- 46000 cast alloys at room temperature up to 400 ºC for various microstructures. The temperature dependant variables of the model were quite well correlated to the underlying physics of the material

In modern turbine engines for propulsion and energy generation, thermal barrier coating (TBCs) protect hot-section blades and vanes, and play a critical role in enhancing reliability, durability and operation efficiency. In this study, thermal cyclic lifetime and microstructural degradation of electron beam physical vapor deposited (EB-PVD) Yttria Stabilized Zirconia (YSZ) with (Ni,Pt)Al bond coat and Hf- and/or Y- modified CMSX-4 superalloy substrates were examined. Thermal cyclic lifetime of TBCs was measured using a furnace thermal cycle test that consisted of 10-minute heat-up, 50-minute dwell at 1135C, and 10-minute forced-air-quench. TBC lifetime was observed to improve from 600 cycles to over 3200 cycles with appropriated Hf- and/or Y alloying of CMSX-4 superalloys. This significant improvement in TBC lifetime is the highest reported lifetime in literature with similar testing parameters. Beneficial role of reactive element (RE) on the durability of TBCS were systematically investigated in this study. Photostimulated luminescence spectroscopy (PL) was employed to non-destructively measure the residual stress within the TGO scale as a function of thermal cycling. Extensive microstructural analysis with emphasis on the YSZ/TGO interface, TGO scale, TGO/bond coat interface was carried out by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and scanning electron microscopy (STEM) as a funcion of thermal cycling including after the spallation failure. Focused ion beam in-situ lift-out (FIB-INLO) technique was employed to prepare site-specific TEM specimens. X-ray diffraction (XRD) and secondary ion mass spectroscopy (SIMS) were also employed for phase identification and interfacial chemical analysis. While undulation of TGO/bond coat interface (e.g., rumpling and ratcheting) was observed to be the main mechanism of degradation for the TBCs on baseline CMSX-4, the same interface remained relatively flat (e.g., suppressed rumpling and ratcheting) for durable TBCs on Hf- and/or Y-modified CMSX-4. The fracture paths changed from the YSZ/TGO interface to the TGO/bond coat interface when rumpling was suppressed. The geometrical incompatibility between the undulated TGO and EB-PVD YSZ lead to the failure at the YSZ/TGO interface for TBCs with baseline CMSX-4. The magnitude of copressive residual stress within the TGO scale measured by PL gradually decreased as a function of thermal cycling for TBCs with baseline CMSX-4 superalloy substrates. This gradual decrease corrsponds well to the undulation of the TGO scale that may lead to relaxation of the compressive residual stress within the TGO scale. For TBCs with Hf- and/or Y-modified CMSX-4 superalloy substrates, the magnitude of compressive residual stress within the TGO scale remained relatively constant throughout the thermal cycling, although PL corresponding to the stress-relief caused by localized cracks at the TGO/bond coat interface and within the TGO scale was observed frequently starting 50% of lifetime. A slightly smaller parabolic growth constant and grain size of the TGO scale was observed for TBCs with Hf- and/or Y- modified CMSX-4. Small monoclinic HfO2 precipitates were observed to decorate grain boundaries and the triple pointes within the alpha-Al2O3 scale for TBCs with Hf- and/or Y-modified CMSX-4 substrates. Segregation of Hf/Hf4+ at the TGO/bond coat interfaces was also observed for TBCs with Hf- and/or Y-modified CMSX-4 superalloys substrates. Adherent and pore-free YSZ/TGO interface was observed for TBCs with Hf- and/or Y-modified CMSX-4, while a significant amount of decohesion at the YSZ/TGO interface was observed for TBCs with baseline CMSX-4. The beta-NiAl(B2) phase in the (Ni,Pt)Al bond coat was observed to partially transform into gama prime-Ni3Al (L12) phase due to depletion of Al in the bond coat during oxidation. More importantly, the remaining beta-NiAl phase transformed into L10 martensitic phase upon cooling even though there was no significant difference in these phase transformations for all TBCs. Results from these microstructural observations are documented to elucidate mechanisms that suppress the rumpling of the TGO/bond coat interface, which is responsible for superior performance of EB-PVD TBCs with (Ni,Pt)Al bond coat and Hf- and/or Y-modified CMXS-4 superalloy.<br>Ph.D.<br>Department of Mechanical, Materials and Aerospace Engineering<br>Engineering and Computer Science<br>Materials Science & Engr PhD

Microparticles produced from kafirin, the sorghum grain prolamin protein, by molecular selfassembly using coacervation with acetic acid solvent are vacuolated. They have shown considerable potential for encapsulation of antioxidants and for preparation of high quality free-standing bioplastic films. However, the functional quality of these kafirin microstructures needs to be improved to exploit their potential application, particularly as biomaterials. Wet heat, transglutaminase and glutaraldehyde treatments were used to modify the physical structure and chemical properties of the kafirin microstructures. Heat treatment (50–96°C) increased microparticle average size by up to four-fold to ≈20 μm, probably due to disulphide cross-linking of kafirin proteins. The vacuoles within these microparticles enlarged up to >10-fold, probably due to greater expansion of air within the microparticles with higher temperature, as the vacuoles are probably footprints of air bubbles. As with heat treatment, glutaraldehyde (10–30%) treatment resulted in oval microparticles, up to about four-fold larger than the control, probably due to covalent glutaraldehyde-polypeptide linkage. Transglutaminase (0.1–0.6%) treatment had only slight effect on the size and shape of microparticles, probably because kafirin has very low lysine content, inhibiting transglutaminase-catalysed cross-linking through ε-(-glutamyl)-lysine bonding. Surface morphology using atomic force microscopy indicated that the microparticles apparently comprised coalesced nanostructures. With heat and transglutaminase treatments, the microparticles seemed to be composed of round nanostructures that coalesced into random irregular shapes, indicative of non-linear protein aggregation. In contrast, with glutaraldehyde treatment, the nanostructures were spindle-shaped and had a unidirectional orientation, probably due to linear alignment of the nanostructures controlled by glutaraldehyde-polypeptide linkage. Thin (<50 μm) films prepared from kafirin microparticles and conventional cast kafirin films were compared in terms of their water stability and other related properties. Films cast from microparticles were more water-stable compared to conventional kafirin films, probably because the large vacuoles within the kafirin microparticles may have enhanced protein solubility in the casting solution, thereby improving the film matrix cohesion. The films prepared from microparticles treated with glutaraldehyde were more water-stable compared to the control, despite the loss of plasticizer, probably due to formation of the covalent glutaraldehyde-polypeptide linkages. The potential of modified kafirin microparticles to bind bone morphogenetic protein-2 (BMP- 2) was investigated. Compared to a collagen standard, the BMP-2 binding capacity of control, heat-treated, transglutaminase-treated and glutaraldehyde-treated kafirin microparticles were 7%, 18%, 34% and 22% higher, respectively, probably mainly due to the vacuoles within the microparticles creating greater binding surface area. The safety, biodegradability and effectiveness of kafirin microparticle film and kafirin microparticle film-BMP-2 system in inducing bone growth were determined by a subcutaneous bioassay using a rat model. Kafirin microparticle film and kafirin microparticle film-BMP-2 system was non-irritant to the animals, probably because kafirin is non-allergenic. The kafirin microparticle film implants showed signs of some degradation but a large proportion of these implants was still intact by Day 28 post implantation, probably because of the low susceptibility of kafirin to mammalian proteolytic enzymes. Kafirin microparticle film-BMP-2 system did not induce bone growth, probably mainly due to low BMP-2 dosage and short study duration. Modification of kafirin microparticles by wet heat or glutaraldehyde treatment both result in increased size of the microparticles with similar gross structure. However, it is apparent that with both treatments the proteins within the pre-formed kafirin microparticles undergo some form of further assisted-assembly through different mechanisms. It seems that heat-induced disulphide cross-linking reinforces a layer around the nanostructures, probably rich in γ- kafirin polypeptides, that stabilizes the structure of the nanostructures. In contrast, glutaraldehyde-treatment appears to destabilize this structure-stabilizing layer through formation of γ-kafirin polypeptide-glutaraldehyde covalent bonding. This probably offsets the balance of attractive and repulsive forces between the different kafirin subclasses within the nanostructures, thereby resulting in collapsed nanostructures and linear realignment. A deeper understanding of the mechanism of kafirin self-assembly will be important for further development of kafirin microstructures for different applications.<br>Thesis (PhD)--University of Pretoria, 2012.<br>Food Science<br>unrestricted

In this study we report the experimental results of researches of the effect on the microstructure of the Zn-Co coatings with laser radiation generated by a ruby laser operating of free oscillators regime (1.2 ms pulse duration, wavelength 0.69𝜇𝑚 and the power density of 104 to 106 W / cm2). It is shown how the microstructure of the investigating alloys after its modification by an impulse laser radiation depends on the power density.

Bone is the most transplanted tissue after blood. As pointed out by the World Health Organization, musculoskeletal diseases can potentially rise as the fourth largest cause of disability within the next years. Unfortunately, despite the natural ability of bone to self-heal it cannot bridge large bone defects without the help of a material. Still today the gold standard to restore bone function remains the use of natural bone grafts. However, they have several limitations that need to be overcome to accommodate the high demands of a global ageing population. Calcium phosphate (CaP) bone grafts have been known since the 1970s and stand as excellent synthetic candidates due to their composition, similar to the mineral phase of bone which consists of approximately 70 wt% of hydroxyapatite (HA). CaPs, and in particular HA, possess outstanding intrinsic properties such as biocompatibility, bioactivity and the ability to support bone growth. However, HA is too stable and once implanted it hardly degrades. Ideal synthetic bone grafts should integrate in the bone remodelling cycle, balancing implant resorption with its progressive replacement by new bone. This can be achieved either by modulating the material¿s physicochemical properties, or by combining the substrate with biological molecules capable of adequately orchestrating the various cells involved in the bone healing process. The present thesis seeks to explore, on the one hand, the feasibility of modulating the physicochemical properties of CaPs towards improving its degradation behavior, and, on the other hand, to investigate the potential CaP functionalization with heparin as a strategy to improve their biological performance at the various stages of bone healing: during the initial phase of inflammation, and during the stages of bone resorption and bone growth. The first part of the present thesis deals with the in vitro degradation of CaPs in a solution mimicking the osteoclastic environment, focusing specifically on the effect of some properties like porosity, specific surface area, microstructure and composition. The interrelation of all these parameters sometimes masks the relative importance of textural over compositional features, making difficult the prediction of their degradation behavior. Additionally, part of the work explores different strategies to incorporate carbonate ions in the crystal structure of HA as a route to obtain materials that more closely mimic natural bone. To further mimic the biological environment of bone, the second part of the thesis is focused on grafting heparin, a highly sulfated glycosaminoglycan present in the bone extracellular matrix, to CaPs. The affinity of heparin for growth factors (GF) makes this molecule an excellent candidate to capture endogenous GF bringing many benefits in the regulation of cell behavior. It is hypothesized that heparin, given its anti-inflammatory role, together with the known involvement in osteoblasts differentiation (bone forming cells) and osteoclastogenesis (bone resorbing cells formation) could enhance the biological performance of synthetic bone grafts. To this aim, CaPs were heparinized and their biological performance was assessed using human immune system cells, bone forming cells and bone resorbing cells, in an attempt to elucidate the synergies of both immune cells and cells of the skeletal system.<br>L'os és el teixit més trasplantats desprès de la sang. L'organització Mundial de la Salut ha posat de relleu l'increment de les malalties musculoesquelètiques, les quals esdevindran la quarta causa mundial de discapacitat en el següents anys. Malgrat la capacitat natural de l'ós per autoregenerar-se, els defectes ossis de grans dimensions necessiten l'ajuda de materials per restaurar-se completament. Actualment, l'ús d'empelts naturals és l'alternativa més emprada clínicament. Tot i això, els autoempelts comporten certes limitacions que requereixen ser adreçades per tal de fer front a les elevades demandes d'una població mundial amb un grau d'envelliment creixent. Els empelts basats en fosfats càlcics (CaPs) són coneguts des de la dècada del 1970 i són uns excel·lents candidats per a la regeneració òssia donada la seva composició, similar a la fase mineral de l'os, que consisteix en aproximadament un 70% d'hidroxiapatita (HA). Els CaPs, en particular l'HA, posseeixen unes propietats intrínseques excepcionals com ara la biocompatibilitat, bioactivitat o la capacitat de suportar el creixement de nou os. Malgrat la seva semblança amb l'os, l'HA és massa estable químicament, i un cop implantada es degrada molt lentament. L'empelt ossi sintètic idealment s'hauria d'integrar en el cicle de remodelació òssia, el que requereix d'un balanç entre la seva reabsorció i la progressiva substitució per os nou. Aquesta capacitat es pot modular mitjançant propietats inherents del material o per mitjà de la combinació de substrats amb molècules capaces d'orquestrar adequadament les respostes de les diverses cèl·lules implicades en la restauració o regeneració òssia. La present tesis cerca explorar, per una banda, la possibilitat de modular les propietats físico-químiques dels CaPs per tal de millorar la seva degradació, així com investigar el potencial de funcionalitzar els CaPs amb heparina, amb la finalitat de millorar les interaccions biològiques a les diferents etapes de la restauració òssia, tant durant la primera etapa inflamatòria, com durant la resorció i el creixement d'os nou. Concretament, la primera part de la present tesi explora la manera en què la modificació de propietats com la porositat, la superfície específica, la microestructura o la composició dels CaPs pot ser emprada per regular la degradació d'aquests materials en una solució acídica similar a l'emprada pels osteoclasts durant la resorció òssia. La interrelació de totes aquestes propietats emmascara de vegades la importància relativa de les propietats texturals, molt lligades a les composicionals, dificultant la predicció dels nivells de degradació dels materials depenent de cada propietat. Per tal de mimetitzar encara més la composició de l'os, s'estudiarà també diferents estratègies per incorporar ions carbonat en l'estructura cristal·lina de l'HA. El segon bloc de la tesi explora la funcionalització dels CaPs amb heparina, un tipus de glicosaminoglicà altament sulfonat present en la matriu extracel·lular de l'os. L'afinitat de l'heparina per captar factors de creixement fan d'aquesta molècula un candidat excel·lent per capturar factors de creixement endògens capaços de regular la resposta cel·lular. Així doncs, partint de les propietats anti-inflamatòries de l'heparina, i de la seva implicació en els processos d'osteogènesi i osteoclastogènesi s'ha formulat la hipòtesi de que aquesta biomolècula podria contribuir a millorar les prestacions dels empelts ossis sintètics. Amb aquest objectiu, s'ha posat a punt un procés d'heparinització de CaPs i s'ha avaluat el seu efecte sobre la resposta de cèl·lules humanes del sistema immune, cèl·lules osteogèniques i osteoclàstiques, per tal d'escatir les possibles sinèrgies de tots dos sistemes, l'immune i l'ossi en la regeneració.