MECHANISMS AND STRUCTURE OF THE BOND BETWEEN BONE AND HYDROXYAPATITE CERAMICS

Two assays were carried out to investigate the postulates that dissolu tion/reprecipitation phenomena and epitaxis are involved in the format ion of the bond between sintered hydroxyapatite (HA) and bone. HA was exposed to a physiologic solution and the ions going into solution qua ntified using inductively coupled plasma (ICP) emission spectroscopy. The HA was retrieved and examined using scanning electron microscopy ( SEM). In the second assay, HA was implanted into Alsatian femura. Foll owing retrieval, specimens were prepared and studied with SEM, at magn ifications usually reserved for transmission electron microscopy (TEM) . In vitro the HA surface composition appeared to shift to the acidic (calcium-deficient) direction. The HA surfaces in both assays underwen t a dissolution/reprecipitation degradation of varying severity, formi ng a recrystallization layer of spherocrystallites. Two modes of bone bonding to implanted HA were identified: (1) bone tissue components bo nded to HA via a recrystallization zone similar in structure to the re precipitation layer in the corrosion assay, and (2) bone tissue compon ents bonded directly to HA crystals with no morphologically discernibl e signs of dissolution embarrassment. The formation of the bone/HA bon d seems to involve dissolution/reprecipitation phenomena. What is beli eved to be the first morphological evidence of epitaxial growth involv ement in the formation of this bond is presented. (C) 1993 John Wiley & Sons, Inc.