The influence of Sr doses on the in vitro biocompatibility and in vivo degradability of single-phase Sr-incorporated HAP cement.

In previous studies, we developed a new type of Sr-incorporated hydroxyapatite cement (Sr-HAC), which was shown to have many excellent physiochemical properties, by an ionic cement route (Guo et al., Biomaterials 2005;26:4073-4083). As a further study, the main aims of this article were to examine the Sr-HAC's in vitro biocompatibility, including acute toxicity, hemolytic reaction, pyrogen reaction, and cytoxicity, to evaluate its in vivo degradability during intramuscular and femur implantation, and also to investigate the influence of Sr doses on these properties. The in vitro results show that all of the Sr-HAC samples exhibit satisfactory biocompatibility, and the Sr/(Sr+Ca) molar ratio has an important effect on these properties. For example, the Sr-HAC with a Sr/(Sr+Ca) molar ratio of 5% (5% Sr-HAC) has higher biocompatibility than both the one with a Sr/(Sr+Ca) molar ratio of 10% (10% Sr-HAC) and the Sr-free one. The in vivo results of both the rabbit intramuscular and femur implantation experiments show that the Sr-HAC samples exhibit a much faster degradation rate than the Sr-free one, and that this also depends on the Sr/(Sr+Ca) molar ratio. Specifically, the mean degradation rate of the 10% Sr-HAC increases by an amplitude of 73.9 wt % compared with that of the Sr-free HAC. In addition, the optical transmission photographs show that the Sr doses play an important role on the interface between the implants and the new bone. The energy dispersion X-ray spectrum analysis indicates that there exists a gradient distribution of Sr element in the tight and bioactive interface between the implants and new bone, indicating that the Sr element takes a share in the mineralization of the new bone together with Ca element.