Barbieri Thesis - BioMedical Materials program (BMM)

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Chapter 4 – Control of mechanical and degradation properties in composites phenotypes. [241–243, 321, 322] It has therefore been hypothesized that the release of such ions might contribute in triggering and enhancing bone formation. However, the role of ions on the (stem) cell osteogenic differentiation onto biomaterials still needs to be fully demonstrated. It is interesting that, in literature, it was also shown that the formation of increasing amounts of L–lactide monomer was caused by the extrusion of 96%mol. L– lactide/4%mol. D–lactide copolymer with increasing initial molecular weight. It was postulated that the monomer formation was provoked during the thermal degradation. [336] Interestingly, those copolymers having higher post–extrusion amounts of L–lactide monomer also had higher hydrolytic degradation rate. [336] Therefore, it may be expected that, being the initial molecular weight of the copolymer used in this study high, significant amounts of L–lactide monomer could be generated after extrusion of the composites. Similarly to the monomer content, the processing method (i.e. history) may have influenced also on the polymer crystallinity affecting on the final degrading and mechanical properties. [387] It is expected that during high temperature extrusion all polymers lose their crystallinity and become amorphous. It is known that, after extrusion, the polymers need to be slowly cooled in order to let their chains re–arrange into a structure similar to the initial one. [387] Since we quickly cooled the extruded composite, we expect that the crystallinity level is lower than the initial one. However, the manufacturing methods and conditions (i.e. temperature and cooling step) used to make the three materials were the same, thus we do not expect much differences in monomer content or crystallinity between the three materials unless the ‘frictional’ degradation with apatite particles had any role. To verify any possible effect of apatite content on the post–extrusion monomer content and crystallinity changes, measurements on the post–extrusion monomer content and crystallinity are necessary in future studies. Mechanical performances may be also influenced my monomer content and crystallinity, particularly in moistened conditions. 4.5. Conclusion The data herein presented demonstrated that, despite its drawbacks, extrusion can be used to produce highly homogeneous composite materials with controllable phase content. However, apatite, during extrusion, generates friction enhancing the polymer degradation: the higher the filler content and the stronger the decrease in molecular weight with consequences on the mechanical and degradation behaviors of the final composites. The filler content also directs the hydrophilicity, with dramatic effects. For example, we observed that the dynamic elasticity of dry materials increases with the apatite content, but it abruptly decreases when the samples were moistened and this decrease was directly correlated with apatite content. On the other side, the 86
Chapter 4 – Control of mechanical and degradation properties in composites viscoelastic characteristics mainly depend on the polymer phase, where lower molecular weight gave better damping characteristics, which increase in presence of moisture. Further, the presence of apatite accelerates the degradation of the whole composite (i.e. mass loss) due to its effect on the polymer, but slowers down the polymer phase hydrolysis as its ions may act as buffers. Other factors, such as the post–extrusion monomer content and extrusion, are not expected in this study, but cannot be now completely excluded. 87
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INSTRUCTIVE COMPOSITES FOR BONE REG
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INSTRUCTIVE COMPOSITES FOR BONE REG
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献给潘臻 A mamma e papà A Stef
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Summary Summary Developing new biom
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Summary containing 96%mol. L-lactid
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Samenvatting De behoefte aan een de
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Samenvatting structuur, bespoedigt
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Riassunto velocità di dissoluzione
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Riassunto generale, ha migliorato i
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Chapter 1 - Introduction 1.1. Eukar
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Chap pter 1 - Introducction Interst
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Chapter 1 - Introduction bone marro
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Chap pter 1 - Introducction Figure
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Chapter 1 - Introduction regenerati
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Chapter 1 - Introduction Key concep
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Chapter 1 - Introduction grown in c
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Chapter 1 - Introduction Mainly, th
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Chapter 1 - Introduction All these
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Chap pter 1 - Introducction materia
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Chapter 1 - Introduction protein, m
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CHAPTER 2 The role of gels in bone
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Chapter 2 - The role of gels in ins
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CChapter 2 - The role r of gels in
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Page 58 and 59: Chapter 2 - The role of gels in ins
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Page 69: CHAPTER 3 Instructive composites: e
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Chapter 6 - Fluid uptake as instruc
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Chapter 6 - Flu uid uptake as insst
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Chapter 6 - Flu uid uptake as insst
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Chapter 7 - Polymer molecular weigh
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ūapatite = 100 · mdry · pap Chap
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Chapter 7 - Polymer mole ecular wei
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CHAPTER 8 General discussion
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Chapter 8 - General discussion can
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Chapter 8 - General discussion cons
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Chapter 8 - General discussion 8.1.
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Chapter 8 - General discussion rese
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References [1] Waggoner B. Eukaryot
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References induction of rank in ost
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References [72] Kokovay E, Wang Y,
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References [102] McBeath R, Pirone
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References molecule-mediated TGF- t
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References [159] Autumn K, Sitti M,
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References [189] Teixeira AI, McKie
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References [215] Tang L, Jennings T
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References [242] Wei G, Ma PX. Stru
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References [270] Atkinson BL, Hanks
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References [297] Sato I, Akizuki T,
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References hematopoietic stem cell
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References [352] Cullinane DM, Sali
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References [382] Norde W, Giacomell
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References differentiation of rat B
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Acknowledgments thank you for all t
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Acknowledgments desidero tutto il m
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Barbieri Thesis - BioMedical Materials program (BMM)

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