density and high porosity. Table10.1summarizes the porosity (f), strength (s), modulus (E), and the slopes (m, n) of fitted trend lines determined from Fig.10.7, corresponding to Eqs.10.4and10.5, modified from Gibson and Ashby [39]:
s s0HA
¼C1ð’HAÞm (10.4)
E
E0HA¼C2ð’HAÞn (10.5)
wheresandEare the measured compressive strength and modulus of the samples,s0HA¼800 MPa andE0HA¼112 GPa for fully dense HA [1],’HAis the volume fraction of HA in the samples,C1andC2are empirical constants, andmandnare the slopes of the power law fits. As seen in the Table10.1,mdecreases andnincreases when PHB is added to the HA scaffolds.
This result agrees with the conclusion that the rigid microstructure of the HA scaffolds plays a more significant role in adding stiffness to the composites, while the addition of PHB adds strength.
The HA-PHB composites develop in this work are fully biocompatible materials that may be useful in tissue engineering applications such as bone implant scaffolds. When fabricating bone implants it is desirable to make scaffolds with high porosity and large pore sizes that allow the migration, adhesion, and proliferation of cells such as osteoblasts to promote bone ingrowth. The biocompatibility, large pore sizes, high porosity, and natural trabecular architecture of the coated HA- PHB composites designed in this work may be ideal scaffold environments for the development of new tissues and bone ingrowth. Still, additional research on the exact mechanisms related to the fabrication and mechanical performance of these scaffolds is necessary before in vitro or in vivo implantation. It is important to understand why the PHB particles recovered by the two different methods either filled or coated the surfaces of the HA scaffolds. It is also necessary to optimize the fabrication process of the composites to further enhance HA-PHB interfacial adhesion and improve the compressive mechanical properties of the resulting composites.
Acknowledgements This work was supported by the National Science Foundation, Ceramics Program Grant 1006931. We would like to thank Tina Carvalho (BEMF, UHM) for help with transmission electron microscopy and Ryan Anderson (CalIT2, UCSD) for help with scanning electron microscopy.
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10 Porous Hydroxyapatite-Polyhydroxybutyrate Composites Fabricated by a Novel Method Via Centrifugation 71
Chapter 11
Isolation of Collagen from Cortical Bovine Bone for Preparation of Porous Collagen Sponges
Ana B. Castro-Cesen˜a, Ekaterina E. Novitskaya, Ameya Phadke, Shyni Varghese, and Joanna McKittrick
Abstract Fabrication of collagen sponges from type I collagen isolated from cortical bovine femur bone is reported.
Collagen was extracted with 0.1 M EDTA by refreshing the solution every 24 h for 9 days. Sodium dodecyl sulfate poly- acrylamide gel electrophoresis (SDS-PAGE) demonstrated the isolation of intact pure type I collagen. The sponges were fabricated by freeze-drying and heat-dehydration cross-linking of collagen solution. The resulting sponges showed fibrils arranged in a highly porous network. These sponges can be used for tissue engineering as well as for bone-like composite fabrication.
Keywords Collagen isolation • Sponges • Scaffolds • Cortical bone