Mg:Ca ratio as regulating factor for osteoclastic in vitro resorption of struvite biocements

Bioceramic degradation can occur by both passive dissolution and following active osteoclastic bone remodeling. Key parameters controlling ceramic degradation are the pH-dependent solubility product of the ceramic phase, which alters ion concentrations in physiological solution and hence regulates cell activity. This study investigated the in vitro degradation profiles of various calcium magnesium phosphate ceramics formed at low temperature. The passive resorption was measured by incubating the cement samples in cell culture medium, while active resorption was determined during a surface culture of multinuclear osteoclastic cells derived from RAW 264.7 macrophages. All surfaces showed mostly similar TRAP activities after adding RANKL-factor to stimulate osteoclastogenesis. The active degradation of the materials by osteoclasts was found to be the predominant factor for ceramic dissolution as determined by measuring the ion concentrations of cell culture medium. Here, large sized osteoclasts formed predominantly on ceramics with a Mg:Ca ratio ≥2.0 seemed to be less effective compared to smaller macrophages.