Strontium-substituted bioactive glass coatings for bone tissue engineering

Abstract

control 0%Sr 10%Sr 50%Sr % Strontium Substitution N or m al is ed M TT A ct iv ity Day1 Day 7 Day14    Strontiumsubstituted Bioactive Glass Coatings for Bone Tissue Engineering Nasrin Lotfibakhshaiesh , Eileen Gentleman, Robert G Hill, Molly M Stevens Corresponding Author: m.stevens@imperial.ac.uk Department of Materials & Institute of Biomedical Engineering, Imperial College, London, UK Barts and the London School of Medicine and Dentistry, Queen Mary, University of London, UK Introduction Metallic prosthetic implants are widely used to treat joint and skeletal injuries. However, some implants can fail because the metal alloys used do not bond with bone. Bioactive glass (BG) coatings may offer a solution to this problem as they form a strong bond with living tissue and have the added benefit that their dissolution ions stimulate cell activity. Strontium ranelate, a drug used to treat and prevent osteoporosis works via the action of Sr ions which stimulate the formation of new bone and prevent osteoclast-mediated resorbtion. Sr can be substituted for calcium in BGs creating a material that may combine the bone remodelling benefits of Sr ions with the well-established bone stimulatory action of bioactive glass. The aim of this study is to develop Sr containing BG coatings on metallic surfaces to bond to an implant as an effective biomaterial choice for a range of bone regeneration therapies. Materials and Methods Bioactive glasses in the system: SiO2-MgONa2O-K2O-ZnO-P2O5-CaO with 0, 10, and 50 of the Ca being replaced by Sr were prepared by a melt-quench route. A degradation study was carried out on <38μm glass powders in simulated body fluids. Silicon [Si], Phosphorus [P], Calcium [Ca] and Sr were checked at different time periods: 10, 30, 60, 120, 240 and 480 min. Produced glasses were combined with RPMI media on a roller for 4 hours at 37°C and then passed through a 0.2 μm filter. This media was then supplemented with 10% foetal bovine serum, 2mM L-glutamine and 1% penicillin/ streptomycin. The human osteosarcoma cell line, Saos-2, was seeded (30,000 cells/cm) in Sr substituted medium and cultured for up to 28 days. On days 1, 7 and 14 post-planting cell metabolic activity was measured using the tetrazole MTT. BGs were coated on to the surface of Ti6AL4V coupons and were sterilised under UV light both side. 10,000 Saos-2 cells/cm2 were seeded on BG coatings and viability was assessed after 1, 7 and 14 days with a Live/Dead stain. Results Glass dissolution leads to a rise of all the ion concentrations in solution. When [Si] hits the solubility limit, [P] declines. At this point a silica gel layer will start to form on the surface and this might be expected to promote nucleation of HCA consuming the P.[Ca] follows the [P] decrease in low Ca content glasses but decreases then rises in high Ca content glasses. Finally, Sr increases the overall concentration of ions in solution. MTT activity (Fig.1) increased in all samples with time in culture until 14 days. Saos2 cultured treated with Sr-substituted BGs had higher MTT activities than controls. Live/Dead staining showed that cells were alive on all coating materials.