The Regeneration of Bone Via Nanoscopic POSS-collagen

Objectives: Polyhedral oligomeric silasesquioxanes (POSS) (Hybrid Plastics Inc. USA) are a new family of chemicals with a diameter of 1.5 nm. Each POSS molecule is comprised of a rigid three-dimentional Si-O-Si cage core. Externally the cage contains organic groups and reactive groups which, in the case of silanol reactive groups, show a high affinity to osteoprogenitor cells. Effects on differentiation of osteoblast and bone induction via POSS have been investigated. Methods: In vitro, cTi disks were coated with 0.1 to 4.5 % of POSS silanol solution inform a methylene chloride solution. Rat bone stroma cells were cultured on the surfaces of the POSS coated Ti discs and compared to uncoated Ti discs. In vivo studies on Wistar rats weighing 300g were also carried out by embedding in bone, collagen (Koken Co Japan) coated with POSS and again compared to untreated collagen. Results: In vitro, after 2 weeks of culturing cell counts between the POSS-coated disks and uncoated disk were similar. However, the bone stroma cells cultured on the POSS-coated discs expressed significantly more osteocalcin than cells cultured on uncoated disks. In vivo, after 4 days connective tissue cells were observed to have accumulated around the POSS-collagen and after 7 days, most of the osteoblast precursor cells were observed to have infiltrated the embedded POSS-collagen. After 2 weeks, new bone was formed at the central portion of the implant site, and within 3 weeks, spongy bone was filled in the bone defect. At 4 weeks, the spongy bone was completely replaced by the compact bone. The control rat population did not show regrowth of bone. Conclusions: In vivo studies support the in vitro findings that POSS silanols can stimulate the differentiation of bone stroma cells and induced bone formation in rat calvaria. Grant-in–Aid for Scientific Research, Kakenhi (C, 20592289)