Densification, phase stability and in vitro biocompatibility property of hydroxyapatite-10 wt% silver composites

Abstract

In this paper, we demonstrate how a simple fabrication route, i.e., pressureless sintering of mechanically mixed powders can be employed to develop hydroxyapatite (HAp, Ca(10)(PO(4))(6)(OH)(2))-silver (Ag) bioceramic composites with superior combination of physical (hardness, toughness), non-cytotoxicity, cytocompatiblity and anti-microbial property. The densification results show that such composites can be sintered at 1200 degrees C for 2 h near to theoretical density (>98% rho(th).) An important observation is that the dissociation of HAp phase can be prevented during sintering up to 1300 degrees C for 2 h in HAp-10 wt% Ag composites. The stability of HAp in presence of silver is discussed in reference to the results obtained using XRD, FTIR and Raman spectroscopy. The hardness values of the composites are comparable (approximately 6.5 GPa) to that of pure HAp, despite of the presence of softer Ag particles. The sintered composites exhibit modest crack growth resistance property and their toughness varies in the range of 0.9-1.2 MPa m(0.5), depending on sintering temperature. For selected samples, the in vitro characterization was performed using mouse fibroblast (L929) and human osteosarcoma (MG63) cell lines. The combination of biochemical assays (MTT, ALP and osteocalcin) confirm that HAp-10 wt% Ag biocomposites have comparable or even better cellular viability, osteogenic differentiation and bone mineralization as well as osteoinduction property. Antibacterial experiments involving gram-negative bacteria, Escherichia coli confirm excellent bactericidal property of HAp-10 wt% Ag composites, sintered using mechanically mixed powders.

A mechanistic study on the antibacterial behavior of silver doped bioceramic

“…3 shows SEM micrograph of the YSZ-Ag sintered at 1400°C for 1 h. Near-equi-axial grains can be seen in close contact with a few voids, suggesting that the sintering process produces a dense compact. Although 10 wt% Ag has been reported to melt and locate to the grain boundaries in sintered hydroxyapatite [23], this cannot be observed in this study since only 0.5 wt% Ag was used. The surface topography of the YSZ-Ag, obtained by AFM, is shown in Fig.…”

“…Comparing the antibacterial ability and mechanism of Ag containing alloys or composites [10,23,32,38,39] most of literatures conclude that Ag + -ions-release causes the bacteria-inhibiting effect. In this study, YSZ-Ag composites exhibited significant inhibiting effect when 0.5 wt% Ag was added.…”

Crystallographic Aspects Regarding the Insertion of Ag+ Ions into a Hydroxyapatite Structure

“…Other studies also demonstrated the formation of this phase for various Ag + concentrations 8,9 . These studies demonstrated that inserting ions of different sizes and charges into HA could compensate for the structural stress caused by inserting a single type of ion.…”

“…(1-y/6)Ca 10 (PO 4 ) 6 (OH) 2 + (x+y)CO 2 + yCaO + yAg (6) After CO 3 2-is released from the HA structure, the excess Ca 2+ tends to form CaO, the inserted silver tends to form metallic silver 8,25 , and the remainder generates a stoichiometric hydroxyapatite. Thus, after calcination, the vibrational modes from OH -groups may be remarkably enhanced because of the better lattice organization and release of CO 3 2-from the structure.…”

Processing and biological evaluation of porous HA/poly(methyl methacrylate) hybrid composite

“…Human osteoblast SaOS2 cell line, procured from ATCC, USA, was used to study the in vitro cytocompatibility of the as-synthesized bioceramics following the standard cell culture protocol, as described in our earlier work [16][17][18]. A plastic disc was used as control and the cell seeded samples were incubated in a CO 2 incubator for 72 h at 37°C.…”