Bano, Saira
(2021)
Suspension high velocity oxy fuel thermal spraying for biomedical coatings.
PhD thesis, University of Nottingham.
Abstract
Thermal spraying of bioglasses offers the opportunity to produce coatings for different biomedical applications. The resorption of the coatings can be adjusted by tailoring the chemical composition of the glass and the coating microstructure.
This thesis describes the production of novel bioactive and bioresorbable glass coatings for biomedical applications via an emerging suspension high velocity-oxy fuel (SHVOF) thermal spray.
Bioglass® (45S5) was sprayed at the flame power of 90, 75, 50 and 25 kW by varying fuel (hydrogen) and oxygen flow rates. No coating was obtained at the flame power of 90 kW, and thin coating (< 10 µm) was obtained at 25 kW. Thick (25 ± 3 µm) and uniform coatings were obtained at the flame powers of 50 and 75 kW. The 50 kW coating was 16 ± 2 % porous, while the 75 kW coating was 10 ± 1 % porous. The bioactivity tests of the coatings showed that no hydroxyapatite (HA) was deposited on the surface of 25 kW coating even after seven days of immersion in simulated body fluid (SBF). Whilst, the coatings produced at 50 and 75 kW revealed HA deposition after three days. EDX analysis of the cross-section of the coated samples showed that the 50 kW initial coating thickness reduced from 25 µm to 6 µm after immersion in SBF for 7 days, which means that this microstructure was highly reactive towards SBF and hence behaved like a resorbable coating.
Coatings from two bioactive glasses, namely ICIE16 (48.0 % SiO2, 33.0 % CaO, 6.6 % Na2O, 2.4 % P2O5 and 10.0 % K2O, in wt %.) and 13-93 (53.0 % SiO2, 6.0 % Na2O, 20.0 % CaO, 12.0 % K2O, 5.0 % MgO and 4.0 % P2O5, in wt %) were successfully produced at the flame powers of 50 and 75 kW. For both formulations, thick, porous and less hard coatings were obtained at 50 kW, whilst harder, dense and less thick coatings were obtained at 75 kW. ICIE16 coatings showed more dissolution in SBF than the 13-93 coatings. Moreover, in-vitro cell tests, using MG63 cells, showed good cell attachment and proliferation on the surfaces of the coating, revealing good cytocompatibility.
Resorbable phosphate based glass (PBG), P-40 (40.0 % P2O5, 16.0 % CaO, 24.0 % MgO, 20.0 % Na2O in mol %) was sprayed at 50 and 75 kW flame power. The 75 kW coating was thinner and rougher than the 50 kW coating; both coatings presented globules on the surface. The Raman analysis of the P-40 coatings suggested that the structure of the glass had changed as the concentration of Q2 (2 bridging oxygen)species has been decreased. Whilst, Q1 (1 bridging oxygen) concentration has been increased and Q0 (0 bridging oxygen) species has been formed. Due to these structural alterations, these coatings showed less ion release and mass degradation than those reported in the literature for P-40 thin films and bulk glass.
Ga2O3 doped Bioglass® was manufactured for antimicrobial applications and deposited at 50 kW. Moreover, Ga2O3 and Bioglass® suspensions were co-deposited via a hybrid nozzle at 50 kW to mix them in the flame. Both coatings showed bioactivity as HA was deposited on the surfaces of these coatings after immersion in SBF for 3 days.
In summary, SHVOF thermal spraying has been proven to be an effective and versatile technique to deposit different bioglasses, maintaining their amorphous tetrahedral structure and composition.
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