Mechanism of Surface Dissolution in Dense Hydroxyapatite

2007

Ann Biomed Eng

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We have been interested in human teeth which consist of hydroxyapatite (HA), but do not degrade for a long time. In order to overcome dissolution and mechanical degradation of man-made HA, biologically derived hydroxyapatite (BHA) ceramics were prepared from human teeth and their dissolving behavior was investigated in distilled water for 3-14 days and compared with an artificial HA made of synthetic HA powder. BHA ceramics were prepared by calcining freshly extracted human teeth at 900 degrees C and followed by sintering at 1200 degrees C for 2 h. All detectable peaks in the artificial HA are identical to HA lattice planes, whereas BHA consisted of a mixture of HA and beta-tricalcium phosphate (TCP). Although the artificial HA was expected to be stable in water, the surface dissolution initiated at grain boundaries followed by generated many separated grains and their associated pores. On the other hand, BHA showed that definite grains considered as beta-TCP were predominantly dissolved and the grains were separated from the matrix leaving pores. In the mean time, the rest region, mainly consisting of HA, did not show any evidence of dissolution. It indicates that BHA showed rather stable grain boundaries and lack of excessive dissolution in liquid environment.

Section: Resultsmentioning

confidence: 96%

Section: Preparation Of Ha From Teethmentioning

confidence: 99%

Dissolution of Human Teeth-Derived Hydroxyapatite

2007

Ann Biomed Eng

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“…Figure 3 shows the microstructures of HA ceramics prepared from lab-produced powder with immersion period. The HA ceramics used in this work consist of monophase hydroxyapatite without any second phases [13]. The relative density of the HA sintered body was 98 % of the theoretical density, showing a nearly fully densified microstructure and smooth surface, as shown in Fig.…”

Section: Resultsmentioning

confidence: 89%

“…In a recent study by the authors [13], evidence of D-tricalcium phosphate (D-TCP) present in the vicinity of grain boundaries was observed by transmission electron microscopy (TEM) accompanied by high-resolution electron microscopy (HREM). In actuality, the quantity D-TCP was exceedingly small and thus was difficult to detect using intensive XRD analysis.…”

Section: Resultsmentioning

confidence: 99%

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Microstructural disintegration in dense hydroxyapatite and hydroxyapatite-coated metal implants

2007

Met. Mater. Int.

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Hydroxyapatite (HA) has been widely used as a coating for orthopedic metal implants. An important concern regarding HA coating is its degradation of the biological milieu. In this study, the microstructure of a retrieved HA-coated acetabular cup implanted for four years after total hip arthroplasty (THA) was investigated by field emission scanning electron microscopy. In order to understand the underlying mechanism of degradation and exfoliation of the HA coating, degradation of phase-pure and dense HA ceramics was also observed by in vitro and in vivo testing. The surface morphology and fracture surfaces of HA ceramics revealed that the dissolution starting at the surface extended inwards resulting in particle loosening and microstructurallevel degradation. The dissolution features of HA ceramics were similar to the case of HA coating. It was found that extensive dissolution of the coating occurred and most of the coating disappeared. The majority of the remaining grains were fractured by the intergranular mode, suggesting that grain boundaries should be predominantly dissolved. These observations may explain the mechanism through which the biological stability of the HA coated layer becomes unexpectedly poor.

Dissolution-resistance of glass-added hydroxyapatite composites

2009

Met. Mater. Int.

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Hydroxyapatite (HA) has generated a great deal of interest as a promising implant material. However, its poor mechanical properties induced by severe dissolution in biological milieu limit medical applications and lead to clinical failure. In this study, HA ceramics with 30PO glass (1.0 wt.% and 2.5 wt.%) were prepared to improve the resistance of monophase HA. The monophase HA sintered body showed microstructural degradation due to grain boundary dissolution in buffered water. However, the dissolution-resistance of HA/glass composites was significantly improved and showed no apparent evidence of dissolution. This suggests that a less soluble glass phase should be placed at grain boundaries to protect HA from dissolution.