Barbieri Thesis - BioMedical Materials program (BMM)

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Chapter 6 – Fluid uptake as instructive factor adequate support framework for bone forming cells and hindering the continuation of bone induction process where activated. 6.4.2. Ceramics Ceramics had similar surface mineralizing potential as after two days in simulated body fluid the granules presented nano–textured apatite–like layers. Thanks to the smaller micro–structure (i.e. smaller grain size), TCPS had a higher surface area that increased its hydrophilicity as compared to TCPB. A larger amount of fluid was absorbed by TCPS, on which more serum proteins adsorbed as well. Similarly to what was said for the composites case, better contact with fluids transporting bio– molecules favors their adsorption onto materials surfaces. It has been proposed that the presence of micro–structure and pores with large surface area favor the accumulation of body fluid proteins, such as fibrogen, and growth factors like as rh– BMP2. [154, 228] Such molecules are acknowledged improving cell adhesion and trigger bone formation. Similarly to what was discussed for the composite, the larger fluid uptake may also have triggered inflammation cells to produce signals that later could initiate bone formation. [217–220, 255–257, 386] Besides enhancing protein adsorption, the surface micro– and nano–structural features such as grain and micro–pore size have been shown to play a crucial role in inducing the in vivo differentiation of stem cells into osteogenic lineages. When hydroxyapatite (HA) with and without a micro– structured surface was implanted in the muscle of dogs, it was reported that only those materials possessing a micro–structure could induce ectopic bone formation. [236, 237] Similar results were shown in studies comparing HA and biphasic calcium phosphate (BCP) ceramics with various micro–porosity. [228] One of the possible causes proposed as crucial for heterotopic bone induction is the resorption/degradation with release of calcium ions having positive effect on cellular differentiation and activity. [252, 321–323] Consistently with literature, we observed that the ceramic inducing more bone formation (i.e. TCPS) had quicker dissolution in vitro with higher calcium ions release compared to TCPB. Further, the in vitro trend was confirmed by the observation that after six months of implantation, TCPS cylinders lost their shape and little amount of material remained as compared to TCPB. We can correlate the fast degradation of TCPS with its higher capacity to absorb fluids in its bulk, which favored its dissolution. 6.4.3. Closing remarks By keeping separated the two families of materials, in this work we have reported that the capacity to uptake fluids influences the bone forming ability of calcium phosphate based biomaterials, where the materials absorbing more fluids induced 144
Chapter 6 – Fluid uptake as instructive factor larger heterotopic bone formation. As seen earlier, fluid uptake could favor various phenomena such as biomolecule adsorption and it accelerated the degradation facilitating the release of calcium and phosphate ions. These processes could later trigger osteogenic differentiation and bone formation by differentiated cells. Further to this, degradation leads to the formation of available space for bone ingrowth. However, when bone formation is slow (i.e. the case of composites) a too fast degradation might be detrimental as a framework for bone formation would no longer exist (i.e. the case of MDL). On the contrary, a fast degradation of the ceramic did not inhibit bone formation because the rate of bone growth was quite high (i.e. the case of TCPS). It is interesting to observe that both ceramics had a higher fluid uptake, with consequent larger protein adsorption and faster dissolution/degradation rate, as compared to the composites. Based on these considerations, we could explain a higher bone induction potential in both ceramics than the composites. However, MLDL and MDL composites triggered and supported larger heterotopic bone formation than TCPB ceramic which gave no bone formation. At the same time, TCPS induced most bone amongst all the materials analyzed. These discrepancies might be explained by the presence of multiple physicochemical factors between the two classes of materials. In fact, as mentioned earlier, composite materials differed only in their monomer chemistry, while the two ceramics differed in their surface grain size. On the contrary, when comparing the two classes of materials, they differ in chemistry (i.e. polymer and calcium phosphate) and surface topography (i.e. nano– and micro– texture), which have various implications on ion release, protein adsorption and, ultimately, bone induction potential. Therefore, applying the same principle, in this case the role of fluid uptake in driving bone formation, is feasible when considering materials belonging to the same class (i.e. composites and ceramics), but not in a more general view to compare materials of different classes due to the multi– factorial issue. 6.5. Conclusion We have reported that the capacity to uptake fluids influences the bone forming ability of calcium phosphate based biomaterials, where the materials absorbing more fluids induced larger heterotopic bone formation. This principle might be applied to all biomaterials as it held true for two different kinds of material (i.e. composites and ceramics). However, it cannot be applied to compare the osteoinductive potential between biomaterials from different families. 145
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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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CHAPTER 3 Instructive composites: e
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Chapter 3 - Instructive composites:
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Chapter 3 - Instructive compos site
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CChapter 3 - Instructive composit t
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CHAPTER 4 Controlling dynamic mecha
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Chapter 4 - Conntrol of mechanical
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Chapter 4 - Control of mechanical a
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CHAPTER 5 Effects of alkali surface
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Chapter 5 - Alkali surface treatmen
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Page 215 and 216: 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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