Barbieri Thesis - BioMedical Materials program (BMM)

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Chapter 2 – The role of gels in instructive putties In the case of PVA–based putties, the gel was still present in all the explants. When comparing the in vitro and in vivo data, we could observe a possible relation between the in vitro dissolution and the in vivo clearance of the gels. It is noticeable that, as already reported in other studies, BCP granules are not expected to significantly degrade and/or resorbe in vivo over 12 weeks. [284] However it can be hypothesized that, when putties were implanted in vivo, the gels started to dissolve, probably due to the attack of water that started their hydrolysis, and were cleared away by body fluids. During their clearance, the available space between the BCP granules may have increased over time allowing soft tissues, including blood vessels, to gradually enter into the implants. This was possibly followed by colonisation of the micro–structured BCP surface by (stem) cells which finally may have been instructed to osteogenically differentiate and trigger heterotopic bone formation (Figures 3, 5). The lack of osteoinductive potential in PVA putty could be the result of preventing cells to reach the BCP surface. As already mentioned, after 12 weeks in vivo, the PVA gel was still completely present amongst BCP granules while no bone formed and cells were hardly seen in the implant. Meanwhile some residuals of CHI gel were observed and no traces of CMC and PLU gels were present. Bone and cells were abundant in CMC and PLU putties but they were less present in CHI putty. From these observations, a correlation between bone formation and gel dissolution (except ALG, as discussed here later) is likely. Although the dissolution rate and rapid clearance of the gels could be important factors controlling bone induction, other factors cannot be ruled out. For example, putties comprising the ALG gel, which had quicker dissolution rate than CMC and PLU gels, showed less bone formation. Thus, other factors must have influenced on osteoinduction, such as the chemistry of the gel or its degradation residuals. Alginate is a copolymer composed of guluronic (G) and mannuronic (M) acid blocks in different G/M content ratios that have been shown to influence the biological properties of the gels. [285–287] According to some studies, high content of G residuals provokes severe inflammation, [285, 286] while others suggested that it is caused by low G content. [287] We used native sodium alginate powder with low G content and did not observe clear signs of inflammatory reaction to ALG putties. The lower osteoinductive potential of ALG putties may be related to the biological inertia of alginate. It has been shown that native alginate does not promote significant cell adhesion [288, 289] while CMC and PLU gels were reported to support the cells adhesion and bone formation in vitro and in vivo. [290, 291] Thus, not only the dissolvability but also the chemistry of the gel and its degradation products may play a role in decreasing the osteoinductivity of some putties. 36
CChapter 2 – The role r of gels in innstructive puttie es Figure 5. High magnificatiion microscope observations of the explants af fter 12–week int tramuscular implantationn. (a) CMC puttyy. (b) PLU putty. (c) ALG putty. ( (d) CHI putty. (e) PVA putty. (f) BCP alone. Bone is forrmed in the matterials where the e gel has dissolvved, i.e. CMC, PLU, P CHI and ALG. A Active osteoblasticc cells on the ouuter bone surface e are visible (*), while adipocytes s (a) and blood vessels v (∆) can be seeen in the availablee space between n BCP particles iin the explants. Note N the traces of o gel in the CHI and PVVA putties (#). Thhe histology staining is methylene blue/basic fuch hsin where bone is red, soft tissues are violet and BCP ggranules are dark k brown/black. 37
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INSTRUCTIVE COMPOSITES FOR BONE REG
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INSTRUCTIVE COMPOSITES FOR BONE REG
Page 7: 献给潘臻 A mamma e papà A Stef
Page 11 and 12: Summary Summary Developing new biom
Page 13: Summary containing 96%mol. L-lactid
Page 16 and 17: Samenvatting De behoefte aan een de
Page 18 and 19: Samenvatting structuur, bespoedigt
Page 20 and 21: Riassunto velocità di dissoluzione
Page 22 and 23: Riassunto generale, ha migliorato i
Page 25 and 26: Chapter 1 - Introduction 1.1. Eukar
Page 27 and 28: Chap pter 1 - Introducction Interst
Page 29 and 30: Chapter 1 - Introduction bone marro
Page 31 and 32: Chap pter 1 - Introducction Figure
Page 33 and 34: Chapter 1 - Introduction regenerati
Page 35 and 36: Chapter 1 - Introduction Key concep
Page 37 and 38: Chapter 1 - Introduction grown in c
Page 39 and 40: Chapter 1 - Introduction Mainly, th
Page 41 and 42: Chapter 1 - Introduction All these
Page 43 and 44: Chap pter 1 - Introducction materia
Page 45 and 46: Chapter 1 - Introduction protein, m
Page 47: CHAPTER 2 The role of gels in bone
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Page 54 and 55: CChapter 2 - The role r of gels in
Page 69: CHAPTER 3 Instructive composites: e
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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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Chapter 5 - Al lkali surface treaat
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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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Figure 7. Mass left (a) annd fluid
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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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