(646g) In Vivo Evaluation of Amorphous Nano Tricalcium Phosphate in Flexible Composites and Injectable Bone Cements
In reconstructive surgery, bioresorbable implant materials are in great demand for the repair of bone defects. Many current biomaterials consist of calcium phosphates which induces biocompatibility, bioactivity and osteoconductivity. However, most presently used commercial products are severely limited to specific clinical applications because of their brittleness, incompressibility and difficulty to shape. The present contribution shows two in vivo studies testing flexible composites and an injectable bone cements for their advantageous clinical use in non-load bearing, complex shaped bone defects. Bone wool An open structured highly porous nanocomposite based on flame spray derived amorphous tricalcium phosphate nanoparticles (TCP) and biodegradable poly(lactide-co-glycolide) (PLGA) was prepared by low-temperature electrospinning . The cotton-wool like scaffolds (Figure 1) were highly bioactive in vitro . An in vivo study was performed in New Zealand White rabbits by creating four circular non-critical size calvarial defects . After 4 weeks implantation, histological analysis showed that the area fraction of newly formed bone was significantly increased for TCP containing fibres compared to pure PLGA. PLGA and PLGA/TCP treated defects resulted in the formation of a spongiosa-like bone tissue. In a next step, this implant material was made antibacterial  (tested in vitro using E. coli) by using 1-2 nm silver containing TCP nanoparticles and further tested in the femur of sheep. The results suggest application in non-load bearing bone defects of lesions with high exposure to microorganisms, for example in dental surgery. Injectable bone cements Another promising application for amorphous TCP is the application as an injectable bone cement (Figure 2). A comparison to micron-sized α-TCP  showed that the amorphous TCP hardened within 7 ? 15 minutes. Most promising results (resorption rate and new bone formation, histology, etc.) are given in an in vivo study in the femur of sheep. Figure 1: (a) Scanning electron microscopy images of PLGA/TCP nanocomposites after 2 days in vitro biomineralization. (b) Electrospun cotton wool-like scaffolds can be easily applied during surgical procedure. Figure 2: (a) Injectable bone cement consisting of amorphous TCP / α-TCP. (b) Nanosized crystals of apatite are formed after setting. References  M. Simonet, O.D. Schneider, P. Neuenschwander, W.J. Stark, Polym. Eng. Sci., 2007, 47(12), 2020-6.  O.D. Schneider, S. Loher, T.J. Brunner, L. Uebersax, M. Simonet, R.N. Grass, H.P. Merkle, W.J. Stark, J. Biomed Mater Res B, 2007, 84B(2), 350-62.  O.D. Schneider, F. Weber, T.J. Brunner, S. Loher, M. Ehrbar, P.R. Schmidlin, W.J. Stark, Acta Biomater., 2009, 5 ,1775-1784.  O.D. Schneider, S. Loher, T.J. Brunner, P. Schmidlin, W.J. Stark, J. Mater. Chem., 2008, 18, 2679-84.  T.J. Brunner, M. Bohner, C. Dora, C. Gerber, W.J. Stark, J. Biomed. Mater. Res., 2007, 83B(2), 400-7.