High phosphate strontium containing bioactive glass coatings for bone tissue engineering

• Main Author: Lotfibakhshaiesh, Nasrin
• Other Authors: Stevens, Molly ; Hill, Robert
• Published: Imperial College London 2011
• Subjects: 617
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.539245

The need for prosthetic joint implants continues to grow, but many implants fail and require revision surgery, mainly due to non-bonding to bone. Currently many metal prostheses are coated with hydroxyapatite (HA), often giving rise to ceramic particles leading to wear of the prosthesis surface. This thesis describes the development of bioactive glass (BG) coatings for metallic implants to improve the bone-implant bond, enable better osseointegration, and improve implant lifespan. Strontium was substituted for calcium in two series of melt-derived BG based on the SiO2-MgONa2O- K2O-ZnO-P2O5-CaO system. In the first series, 0, 10, 25, 50, 75 and 100% of the CaO was replaced by SrO; and in the second series 10% of the CaO was replaced by SrO and the P2O5 content was varied between 1.07 and 6.42 mol%. Ti alloy coupons were surface coated with BG by enamelling technique. The structural and physical properties of the glasses and glass coatings were investigated by differential scanning calorimetry (DSC), X-ray diffraction (XRD), nuclear magnetic resonance (NMR), Fourier-transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). Amorphous coatings showed good adhesion to the Ti alloy with the exception of the 100% Srsubstituted coating. The mixed calcium/strontium glasses exhibited a larger processing window; temperature difference between glass transition and onset of crystallization temperature; favouring the production of amorphous well sintered coatings. Dissolution profiles and bioactivity of the produced glasses were investigated by inductively coupled plasma-optical emission spectroscopy (ICP-OES), XRD, NMR and FTIR. Increasing the P2O5 content of the Sr-substituted glasses aided the formation of the hydroxycarbonate apatite (HCA) layer in SBF. 31P and 29Si NMR showed that the glasses were phase separated with a predominantly Q2 silicate structure co-existing with phosphorus in a predominantly Q0 orthophosphate environment. The Q2 silicate structure in the network did not change with substitution of SrO for CaO. LIVE/DEAD staining of human osteosarcoma cells (Saos-2) seeded onto BG coatings indicated that the coatings were not cytotoxic. SEM imaging showed that the cells attached and spread over the coating surface. The degree of osseointegration of the high-phosphate Sr-contatining (50% of the CaO replaced by SrO) BG-coated implants were compared with HA-coated implants up to 24 weeks which were inserted into lapine long bones (distal femur, proximal tibia). High-phosphate Sr-containing BGcoated implants demonstrated superior mechanical fixation and increased peri-implant bone formation compared to HA-coated implants. The results presented in this thesis demonstrate the potential of Srsubstituted BGs with high-phosphate content for the coating of metallic joint implants.