MICROSTRUCTURE AND MICROMECHANICAL PROPERTIES OF THE MID-DIAPHYSES OFHUMAN FETAL FEMURS

The microstructure, composition and the micromechanical properties acr oss the thickness of femoral mid-diaphyses from 14 to 26 week human fe tuses have been investigated, Scanning electron microscopy and transmi ssion electron microscopy were employed to examine structural changes with maturation, The fetal bones consist of layers of woven bone. From young to old fetuses and from outer to inner bone layers, the collage n fibrils become more cross-linked, densely packed and change from dis ordered to an ordered arrangement. The collagen fibril bundles are als o more preferentially oriented and change from a chiefly circumferenti al to longitudinal direction, The sizes of the apatite crystals also i ncrease with age, The Ca/P ratio remains constant around 1.55 for all the bone layers except the outmost layer which is lower than 1.2, An n ano-indenter was used to evaluate the microhardness and elastic modulu s of each bone layer, The increase of microhardness and elastic modulu s correlates with the maturation of bone, The mechanical properties of the mid-diaphyses of human fetal femurs are anisotropic, which is due to the preferential orientation of collagen fibrils.