Microstructural investigations of strain-related collagen mineralization.

Distraction osteogenesis in rabbit mandibles after osteotomy can be used as an experimental model to study the microstructural features of mineralization of callus under defined mechanical loads. Our aim was to study the relation between the micromotions in the gap and the resulting features of mineralization of the matrix. We found that assembly of collagen and formation of crystals depended on the magnitude of the mechanical stress applied. At physiological bone strains (2000 microstrains), the callus had collagen type I in a mature bone-like extracellular arrangement, whereas at 20000 microstrains bundles were orientated predominantly towards the tension vector. Maximum loads (200000 microstrains) resulted in disorganized assembly of the collagen. Quantitative energy-dispersive analysis by X-rays confirmed that high strains were associated with substantially lower concentrations of calcium and phosphate. In contrast to bone-like apatitic formation of crystals at physiological strains, significantly fewer but larger crystals were detected by electron diffraction analysis in samples exposed to high strains. We suggest that mechanical stress regulates the assembly and mineralization of collagen during distraction osteogenesis.