Effect of albumin on brushite transformation to hydroxyapatite

Abstract

Brushite (CaHPO(4) x 2H(2)O) is a precursor to hydroxyapatite [HA, Ca(5)(PO(4))(3)OH]. It has been shown that a modified form of brushite, with potassium substituting for calcium at specific sites, demonstrated accelerated transformation to HA when exposed to nonproteinaceous Hanks' balanced aqueous salt solutions (HBSS). The biocompatibility of a transforming material is related to cellular response to the process, which is initiated by protein adsorption. The effect of adsorbed protein on the kinetics and chemistry of brushite transformation to HA, when exposed to HBSS containing bovine serum albumin (BSA), was examined using Fourier transform IR spectroscopy, X-ray diffraction, and energy dispersive spectrometry techniques. The effect of solution pH was also studied. Results show that, in the presence of a protein-free environment, transformation is faster in buffered medium than in nonbuffered medium. Moreover, curve fitting and second derivatives of the IR spectra show that some bands shift depending on whether the brushite transforms in a buffered or nonbuffered medium. Therefore, variation in pH affects both transformation rate and the associated chemistry. The presence of BSA in either buffered or nonbuffered medium retards the transformation in comparison to the corresponding BSA-free medium. The extent of this retardation increases with the increase in bulk concentration of BSA but does not alter the transformation chemistry. This suggests the retardation on the transformation rate is due to BSA adsorption coverage on the calcium phosphate ceramic. This may be due to the shielding of Ca(2+) and PO(4)(-3) sites, preventing their interaction with the HBSS.

Self-Setting Calcium Orthophosphate Formulations

“…Transformation of DCPD into CDHA occurs via two successive processes: dissolution and precipitation [264] and can be retarded by adding magnesium ions to the formulations, thus reducing the possibility of inflammation [4,5]. The aforementioned case of acid deficient formulations [chemical Equation (13)] is the second option, because it reduces the amount of un-reacted acid [259] with an option to consume liberating in chemical Equation (14) H 3 PO 4 by the excess of β-TCP.…”

Self-Setting Calcium Orthophosphate Formulations: Cements, Concretes, Pastes and Putties

“…Transformation of DCPD into CDHA occurs via two successive processes: dissolution and precipitation [235] and can be retarded by adding magnesium ions to the cement paste, thus reducing the possibility of inflammation [197,198]. The aforementioned case of acid deficient formulations of brushite cements (chemical equation (13)) is an alternative, because it reduces the amount of unreacted acid in the cement [230] with an option to consume liberating in chemical equation (14) orthophosphoric acid by the excess of β-TCP.…”

Biologically mediated resorption of brushite cement in vitro

“…Since no compositional differences between the b-TCP-pyrophosphoric acid solution cements aged in serum or PBS were observed in the work reported here, the difference in weight loss in this new pyrophosphate containing brushite cement could be attributed to the difference in the solubility of the cement matrix in different ageing media. The fact that the brushite and dicalcium pyrophosphate dihydrate phases dissolved more rapidly in serum than in PBS is surprising since bovine serum contains 50 and 90 ppm Ca 2+ and similar levels of these ions have been reported to reduce the rate that brushite is dissolved by up to 98% of the rate that brushite dissolves in medium containing no Ca 2+ (such as PBS) [25]. It appeared probable, that another serum component accelerated the rate of dissolution of the brushite and calcium pyrophosphate phases present in the b-TCP-pyrophosphoric acid cement.…”