Biomaterials

Beneficial Defects

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Science  19 Sep 2003:
Vol. 301, Issue 5640, pp. 1633
DOI: 10.1126/science.301.5640.1633a

Although bone is composed of small inorganic crystals, consisting primarily of hydroxyapatite (HA), it is constantly remodeled through processes of dissolution and redeposition. Pure HA has been used as a bone graft, but it has poor rates of reactivity and integration with existing bone when compared with bioactive glasses and glass ceramics. Previous studies had shown that incorporation of Si atoms into the HA increased the bioactivity, and that dissolution processes are enhanced at grain boundaries. Porter et al. studied the dissolution of HA and Si-substituted HA that was implanted into sheep using high-resolution transmission electron microscopy. Pure HA implants showed no change after 6 weeks, with some small voids appearing after 12 weeks, probably at the sites of dislocations. In contrast, samples with both 0.8 and 1.5 weight % Si showed extensive dissolution after 6 weeks. The material loss was found to initiate at grain boundaries and triple junctions (where three grain boundaries meet) and was far more extensive in the more highly substituted HA. In addition to creating more grain boundaries, the Si also leads to the formation of smaller crystals, which dissolve more readily. This in turn leads to an enhanced concentration of ions at the bone-graft interface, thus enhancing the rate of the incorporation of the graft though the precipitation of biological apatite. — MSL

Biomaterials 24, 4609 (2003).

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