Bioinspired Fabrication of Bio-Silica-Based Bone-Substitution Materials

The gold standard for bone reconstruction is the use of autogeneic grafts from various donor regions, since they possess osteoinductive as well as osteoconductive potential. Only a few synthetic materials possess/display properties that allow optimal bone reconstitution. Previously, we showed that the natural product, bio-silica, comprises osteoinductive, and probably also osteoconductive activity. Bio-silica is formed enzymatically via silicatein; this enzyme has been isolated from siliceous sponges and has also been cloned and prepared recombinantly. In the present study, silicatein was encapsulated together with its substrate, sodium metasilicate, in poly(D, L-lactide)/poly(vinyl pyrrolidone)-based microspheres, termed silicatein-and-silica-containing microspheres (SSMs). The deposition of silica and the kinetics of silicatein release from the microspheres are given. Furthermore, SSMs were successfully embedded in a poly(vinyl pyrrolidone)/starch-based matrix, termed plastic-like filler matrix containing silicic acid (PMSA). A blend of SSM and PMSA forms a biocompatible, moldable, and biodegradable functional implant material that hardens at a controlled and clinically suitable rate within approximately 30 min to 6 h to implants that were tightly integrated in artificial defects of rabbit femurs. Until now no toxic reactions caused by the silicatein have been observed in vitro or in vivo. We assume that the data given here contribute to a successful introduction of the silicatein/bio-silica-based implant materials to the field of regenerative medicine.