Bone microstructure by collagenase etching

A novel technique has been developed for microstructural studies of bone. The spatial organizations of the mineral and collagen fibres in bone have been a matter of discussion for some time, with numerous diverse observations arising from various preparative techniques. In this latest investigation details of the mineral structure are clearly revealed in the SEM by treating a cut and polished surface of bone with collagenase to remove the major organic component. This new procedure has minimal effect on the mineral and hence reveals microstructural detail which is far closer to that in vivo than in previous investigations. This paper concentrates on two aspects of the studies, namely the detailed morphology of the mineral component and the arrangement of the collagen fibres in the osteons of compact bone. Firstly, the mineral component is revealed as comprising 'crystallites' (approximately 20 nm diam.) which aggregate to form larger contiguous 'spheroidal particles' (approximately 100 nm diam.), which in turn form 'granules' (approximately 500 nm diam.). Secondly, the regions from which collagen fibres have been removed are clearly revealed, showing that within an osteon, alternating lamellae have collagen fibres oriented approximately parallel to and circumferential to the Haversian canal respectively.