Barbieri Thesis - BioMedical Materials program (BMM)

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Chapter 4 – Conntrol of mechanical and degraddation properties s in composites Extrapolaating the data recorded at 1 Hz in dry c M50 had storage moduulus and loss tangent close bending aat 1 Hz, on dry human cortical bone e while otheer literature data show loss s tangent for h frequencyy range (i.e. 00.1–10 Hz) ran nging between than thosse measured bby Yamashita, on the annalytical methhods. In mois lower thaan cortical boone while the improvemments in the eelastic and vis applicatioons in vivo. TTo strengthen affect its mechanical pproperties, it phosphatte particles to the polymeric possibilityy to bind calcium phosphat coupling agents such aas isocyanate apatite wwould play a larger role propertiess from the loading frequenc Besides iinfluencing onn the mechan degradinng trends of tthe materials. led to larrger fluid uptaake when plac and polymmer hydrolysis could be tr different starting polymer intrinsic different. [338] conditions, it may m be conclu e to those mea asured, in thre extracted from m femora human bone i n 0.01 and 0.0 and this discrepancy i t conditions, the modulus tangent wass higher (Figu scoelastic propperties are ne the compositte and avoid would be useeful to chemi c chains. Seveeral groups ha te particles too polymer cha groups [341, 3422] or phosphon in controllingg the depen cy and the moiisture. ical propertiess, apatite part As mentioneed earlier, the ced for three months in sa iggered in all the samples viscosity, the polymer h [338] (F n physiologica 02, [339, 340] valu n tangent ma of the compo ure 7), [338] thu eeded for load that water ca cally bind the ave already s ains through th nic acid. [332] uded that ee–points Figure 7), al loading ues lower y depend osite was us further d–bearing an largely e calcium hown the he use of In this way, ndence of me echanical ticles also affe ected the higher apatite e content line solution (Table ( 4), . However, due to the ydrolysis tren nds were Figure 7. CComparison of (aa) storage modul lus and (b) loss tangent (measured at 1 Hz, 37º point bendinng, dry and wet cconditions) betwe een M50 and humman cortical bone e. [338] C in three– In particuular, there waas sharper de ecrease of thee viscosity in materials with higher starting inntrinsic viscossity and vice versa (Tablee 3). These results r are in line with literature, , where 96%mmol. L–lactide e/4%mol. D–lactide copoly ymer was deg graded in phosphatte buffered soolution for six months and llarger decreas se in molecular weight 84
Chapter 4 – Control of mechanical and degradation properties in composites was observed for copolymers having increasing initial molecular weight. [336] Further, the presence of aqueous fluid also dissolved apatite particles and, consistently, there was an increasing release of ions with the apatite content in the composites (Figure 5). The dissolution of apatite may have acted as buffering agent slowing down the polymer autocatalysis. In M0 hydrolysis could have been catalyzed by the acidic degradation residuals of the polymer. [349] On the contrary, in M25 and M50 the release of calcium and phosphate (Figure 5) may have buffered the acid polymer residuals hindering the polymer autocatalysis. Consequently, the intrinsic viscosity changes were smaller in M25 and M50 (Table 3). In terms of effective phase loss, M0 did not have polymer loss, while M50 had the largest polymer phase loss (Table 1). As observed earlier, M50 contained the polymer with the lowest starting intrinsic viscosity, which may have favored the loss of more polymer residuals from the composite. On the contrary, M25 showed the largest apatite phase loss (about –8%), which might be explained with its larger polymer content (i.e. ~75%wt.) that may have rendered the local pH more acidic favoring the dissolution and/or release of whole apatite particles. It should be mentioned that, however, M50 had the larger apatite content (i.e. ~50%wt.) than M25 and this is why the ion concentrations recorded in SPS were higher for M50. The phase loss results are consistent with the observed increasing mass loss of the materials with apatite content (Table 4). Considering all the results together, the whole degradation of the composite (i.e. mass loss) is accelerated by the increase of apatite content. Clashing with the results normally found in literature, in this case the degradation was accelerated by the apatite content. This might be explained with the fact that most of the composites presented in literature were prepared using solvent–based methods (by mixing, casting or sonication/freezing procedures), [239, 240, 242, 243] or co–precipitation. [235, 409] It is worth to remind that we have shown in Chapter 3 that solvent–based methods do not degrade the polymer phase, independently from the calcium phosphate phase content. We expect similar results also for other non–thermal methods used for the preparation of composite materials. In this study, the polymer was degraded during the extrusion, and the extent of this degradation was dependent on the apatite content. In particular, the intrinsic viscosity of the copolymer lowered with the increase of the added apatite amount. The differences in intrinsic viscosity amongst the three materials were, in this case, sufficiently large to justify the observed degradation trends. We cannot now affirm whether and how the composites degradation influenced on their mechanical properties. However, it is worthy to observe that the composite released ions, which may be important factors in bone regeneration. It has been speculated that ion release not only enhances the bioactivity of calcium phosphate–based materials, [241, 243] but also the proliferation and differentiation of cells into osteogenic 85
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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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Chapter 2 - The role of gels in ins
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CChapter 2 - The role r of gels in
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Figure 7. Mass left (a) annd fluid
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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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