Apatite-polymer composites

Poly(oxyethylene)-Si02 ormosils have been prepared as an approach to the preparation of biologically active polymer-apatite composites. For this purpose, Yamamoto et al. [72] obtained these Class II hybrids from triethoxysilyl-terminated poly(oxyethylene) (PEG) and TEOS by using the in situ sol-gel process. After being subjected to the biomimetic process to form the bone-like apatite layer, it was found that a dense apatite layer could be prepared on the hybrid materials, indicating that the silanol groups provide effective sites for CHA nucleation and growth. 

Figure 3. An Ashby diagram with the modulus of sintered hydroxylapatite, porous hydroxylapatite and polymer-apatite composites.

R. Zhang, PX. Ma, Biomimetic polymer/apatite composite scaffolds for mineraUzed tissue engineering, Macromol. Biosci. 4 (2)... 

Kim, S.S., Park, M.S., Gwak, S.J., Choi, C.Y., and Kim, B.S. (2006) Accelerated bonelike apatite growth on porous polymer/ceramic composite scaffolds in vitro. Tissue Eng.,... 

Wei, G. B. Ma, P. X. 2006. Macroporous and nanofibrous polymer scaffolds and polymer/bone-like apatite composite scaffolds generated by sugar spheres. Journal of Biomedical Materials Research Part A, 78A, 306-315. 

In an effort to enhance the osteoconductivity of PMMA bone cement, Rhee and Choi [ 16,46 ] incorporated silica nanoparticles into the polymer. This composite was synthesized by sol-gel processing with the goal of improving binding at the bone-implant interface. The authors observed high mechanical properties in addition to crystaUine apatite formation on implants in simulated body fluid. 

Kim, H.-M., Kishimoto, K., Miyaji, F., Kokubo, T., Yao, T., Suetsugu, Y., Tanaka, J. and Nakamura, T. (2000) Composition and structure of apatite formed on organic polymer in simulated body fluid with a high content of carbonate ion. Journal of Materials Science-Materials in Medicine, 11, 421—426. 

A more recent trend in polymer materials research is the hybridization of cellulosic polysaccharides with inorganic compounds natural and synthetic layered clays, silica, zeolites, metal oxides, and apatites are employable as nanoscale components. In addition, if mesoscopic assemblies such as liquid-crystalline ordering are used in the construction of new compositional systems, the variety of functionalized cellulosic materials will be further expanded. 

The solubility of apatites is becoming more important as emphasis is being placed on biomaterials for regeneration of tissues (Hench 1998b). Where apatites are incorporated with resorbable polymers for tissue engineering applications, it will become necessary to match the solubility rate of the inorganic and organic components within the composite. 

Bone is a natural composite comprised of type I collagen and calcium phosphate minerals, of which nanocrystalline apatite is the main component [39, 40]. Certain osteoconductive bioceramics exert an effect on bone cell attachment and growth factor binding or release, and can accelerate the treatment of bone defects [41-43]. Polymer composite scaffolds can be produced, via electrospinning, which contain a specific amount of electrical charge in order to form non-woven fibrous meshes with fibre dimensions in the nano- to microscale [44-46]. 

Bone is a natural composite of apatite-collagen. So a composite of polymer matrix containing bioactive particulate filler is a natural choice for substituting cortical bone. Bone substitutes can be easily made by using hydroxyapatite (HA) particles as the bioactive component because of its close similarity with bone apatite and its excellent bioactivity. So a composite made of HA with polymer matrix provides... 

Yin, YJ., Zhao, F., Song, XF., Yao, KD., Lu, WW., Leong, JC. 2000. Preparation and characterization of hydroxy-apatite/chitosan-gelatin network composite. Journal of Applied Polymer Science 77 2929-2938. 

FIGURE 14.1.20 Schematic representation of fabrication process of apatite-polymer composite with analogous three dimensional structure to that of natural bone. 

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