EFFECTS OF DEPROTEINIZATION AND ASHING ON SITE-SPECIFIC PROPERTIES OFCORTICAL BONE

Buffered sodium hypochlorite (NaOCl) solution was used to remove selec tively the collagen phase from bovine cortical bone. Changes in the me chanical behaviour and material properties were studied over a wide ra nge of resolution (from 5 mu m to 3 mm) using an integrated combinatio n of experimental techniques. Optical microscopy indicated that timed immersion in NaOCl results in cortical bone specimens that consist of a mineralized tissue core surrounded by a layer of deproteinized or an organic bone. With increased NaOCl treatment, the mechanical behaviour in three-point flexure of the intact specimens became increasingly ch aracteristic of a brittle ceramic material. Localized material propert ies were evaluated using histology, scanning electron microscopy and m icrohardness testing. The site-specific properties and the mineralizat ion of the cores were not significantly affected by the treatment; how ever, the interactions and structural framework of the hydroxyapatite crystallites within the anorganic material were compromised. This dest ruction of crystallite interlocking was not observed in samples in whi ch the organic phase was removed by ashing at 800 degrees C. The ashed samples maintained microhardness values three times those of the blea ched samples. Because of its damaging effects on cortical bone structu ral integrity, the NaOCl treatment did not provide a reasonable means of studying, as a function of the phasic mass fraction, incremental ch anges in bone mechanical behaviour or the relative roles of collagen a nd mineral with in the structural hierarchy.