Narrow Results

In order to understand the mechanisms of fracture healing, especially the neovascularization of the callus, we have established a closed femoral fracture model in rats. This chapter describes a microangiography technique that has been adopted to investigate temporal changes in the three-dimensional (3D) vasculature of the healing callus. Quantitative evaluation protocols for vessel size distribution, total vessel volume, and volume fraction have also been established for comparative studies.

Nanoindentation is a relatively new technique that can achieve high-resolution characterization of material properties in musculoskeletal tissues. It has been shown to be an effective tool in describing changes in bone mineralization that result from disease and aging by quantifying the material's direct response to mechanical loading. Several studies have shown that the results of nanoindentation are highly sensitive to parameters such as sample preparation, loading protocol, indent location, and sample storage. This chapter describes the techniques for a successful nanoindentation protocol and addresses key technical considerations.

Bone-forming cells first fabricate a highly organized oollagen matrix, osteoid, which subsequently mineralizes. A variety of cell culture systems exist for osteogenic cells, yet none of these is optimal for the well-organized formation of a mineralized matrix. We have generated collagen substrates which have different degrees of fibrillar orientation, and have cultured osteogenic cells on these matrices. Osteoblast-rich cells isolated from 16 day chick embryos were cultured in micro-mass culture on the collagen sheets. Von Kossa-stained sections showed that highly oriented collagen matrix started to calcify in 6-7 days while a random fibrillar matrix did not mineralize even in 21 days. Mineral has been detected only within the collagen matrix with a narrow unmineralized region between the cells and the mineral like osteoid in vivo. The in vitro system described may serve as implantable materials facilitating in situ cell-mediated bone repair ultimately.