Preparation And Characterization Of Porous Titanium Coated With TGF-β₁ Loaded Gelatin Microspheres

Objective:Effects of process parameters on the preparation of porous titanium coated with TGF-β₁ loaded gelatin microspheres were systematically studied by using orthogonal arrays design and statistical analysis method.The characterization of porous titanium coated with TGF-β₁ loaded gelatin microspheres was explored.Material and method:Porous titanium implants were prepared by metal injection molding.Gelatin microspheres were prepared by improved emulsified cold condensation method and loaded with TGF-β₁ by swelling in aqueous TGF-β₁ solution.The process parameters of microspheres preparation were optimized by using orthogonal arrays design.The morphology of the microspheres were observe with scanning electron microscopic(SEM).The encapsulation rate,drug content were test with TGF-β₁ ELISA kit.The porous titanium implants were coated with TGF-β₁ loaded gelatin microspheres,drug release kinetics of coating was explored.MTT assay method was used to evaluate the cytotoxicity of coating to the rat fibroblast cells L929.Result:Porous titanium implants were produced by MIM,which microstructure characters were 60%porosity with cross-connection pore structure and pore size range of 50-300μm.The compression yield strength was 49.29Mpa,and elastic modulus was 5.8GP.Orthogonal experiment indicated that gelatin concentration,stirring speed and crosslinking time had remarkable effect on size of gelatin microspheres(P＜0.05),however,cross linking agent had no distinguished influence on the diameter(P＞0.05).The size of gelatin microspheres decreased as gelatin concentration decreased.The size decreased as stirring speed and crosslinking time increased.The size of gelatin microspheres were 21.42±3.67μm in average.The drug content was(0.91±0.02)ng/mg,and encapsulation rate was(91.41±1.82)%.The porous titanium implants were pretreated by 5wt%gelatin and coated with 10mg/ml,20mg/ml,30mg/ml TGF-β₁ loaded gelatin microspheres. Results indicated that there was less microspheres in the pores of sample coated with 10mg/ml gelatin microspheres,and the pore structure of implants were blocked by microspheres in 30mg/ml group.But the TGF-β₁ loaded gelatin microspheres in pores of implant coated with 20mg/ml were appropriate.In vitro,20%of TGF-β₁ released from gelatin microspheres coating in 24h and releasing rat gradually decreased and became stable as time increased.Finally,(94.2±3.4)%of TGF-β₁ were released during 14 days.The MTT test showed the leaching liquor with 100%,50%,10%concentrations of porous titanium coated with gelatin microspheres was nontoxic to L929.Conclusion:The optimized preparation parameters of microspheres were as followings:gelatin concentration 10wt%,stirring speed 800rpm, cross linking agent 0.1ml,and crosslinking time 2h.The porous titanium implants could be coated with 5wt%gelatin and 20mg/ml TGF-β₁ loaded gelatin microspheres,and the structure of pores were kept completely. Porous titanium coated with gelatin microspheres was nontoxic to fibroblast cells L929.In vitro,TGF-β₁ could be released for 14 days probably to promote earlier osseointegration of implant-bone interface.