Experimental Study On Pure Titanium For Implant Materials Fabricated By Laser Rapid Forming Technique

To investigate the feasibility of laser rapid forming titanium(LRF Ti)for medical implant materials,this paper evaluated the mechanical properties, biological safety,biocompatibility and corrosion behavior of LRF Ti according to national standard.PartⅠFabrication of pure titanium specimens by LRF technique and the test of mechanical propertiesPure Ti specimens were fabricated by LRF technique with suitable parameters.The parameters used in the test were:power,2200W;spot diameter, 3mm.The powder was delivered in a gas jet through nozzles coaxially with the laser beam.Powder feeder rate was 4.2g/min.The process was occurred in closed chambers with controlled inert atmospheres(Ar:250L/h, 5-7.5L/min).The layer thickness was 0.5mm.To evaluate the mechanical properties of LRF Ti,the specimens underwent tensile test,microhardness test,chemical composition analysis,microstructure observation and fatigue test.Results:The tensile strength and yield strength of LRF Ti were 475 MPa and 383MPa,they were higher than TA2 respectively according to GB/T 13810-1997.The elongation(27%) was far higher than TA2(18%). The oxygen content of LRF Ti was 0.083% and far below TA1(0.15%) and TA2(0.25%) according to YY0315-1999.The fracture surface of tensile specimens was ductile. Yang's modulus of LRF Ti(103.7GPa) was slightly lower than TA2 (108GPa).The microstructure of LRF Ti was basket -weave structure. The Vickers hardness is 188.4~206.3.The fatigue strength of LRF Ti was 250-275MPa at the end of 107cycles while TA1 and TA2 were 193 and 230 MPa respectively.Conclusion: The LRF Ti specimens fabricated completely were silvery with a smooth surface with low oxygen content. The LRF Ti had better mechanical compatibility and the mechanical properties meet the requirement of pure titanium implant materials.PartⅡBiological safety test of LRF TiBiological tests were carried out to evaluate the biological safety of LRF Ti for biomedical materials according to standards GB/T 16886.5-2002,YY/T 0279-1995,YY/T 0127.1-93 and YY/T 0127.2-93.The biological tests included Cytotoxicity test, oral mucous membrane irritation test ,hemolysis test, acute systemic toxicity test and bone implant test.Results: The cytotoxicity rank of LRF Ti was 0; The oral mucous membrane surround LRF Ti specimens had no pathological reaction and membrane irritation. Hemolysis ratio was 2.68% and fell bellow the standard limits (5% ,YY/T 0127.1-93),LRF Ti didn't result in hemolysis. The animals had no signs of toxicity during 72 hour after injected with the leaching liquor of LRF Ti,the weights of animals had no statistical difference between different test periods compared to controlled group. The animals had no bone absorption near the LRF Ti implants , the implants contacted bone tissue tightly. There were bone lacunas and new osseous tissue formation on the surface of LRF Ti implants. The synapsis of osteoblasts and fibroblasts stretched to the surface of LRF Ti implants. The reacton of bone tissue surrounded LRF Ti implants had no difference with CP Ti implants in vivo.Conclusion: LRF Ti had excellent biological safety and meet the requirement of biological test standard.PartⅢBiocompatibility test of LRF TiCell culture tests in vitro were undertook to evaluate the biocompatibility of LRF Ti. The cell cranium osteoblasts of mouse were used in the experiment. The contact angles and total surface energies of LRF Ti and CP Ti specimens were tested also.Results: The total surface energy of LRF Ti sample was higher than CP Ti sample. The cell growth rate had no statistical difference between LRF Ti and CP Ti samples. The multiplication of LRF Ti specimen was faster than CP Ti specimen with the cultivation time increased. The alkaline phosphatase (ALP) activity were increased consequently. The morphology of osteoblast indicated high activity of osteoblast on the surface of LRF Ti specimen.Conclusion: LRF Ti stimulated osteoblasts multiplication and had favorable biocompatibility. PartⅣThe corrosion behavior of LRF TiElectrochemical test,static immersion test and stress-corrosion test were used to evaluate the corrosion behavior of LRF Ti according to standard. The influence of fluoride and pH value on the corrosion resistance of LRF Ti were also investigated.Results:In artificial saliva,1%lactic acid solution,2%NaF artificial saliva (pH=7) and 2%NaF artificial saliva (pH=3),the amounts of Ti ion released from LRF Ti sample(62ng/ml,302ng/ml,24.7μg/ml and 156.7μg/ml) were lower than CP Ti (66.1ng/ml, 353ng/ml, 33.1μg/ml and 295.7μg/ml) respectively;The corrosion products were Na3TiF6. The greatest amounts of metal ion release were observed in 2% NaF artificial saliva (pH=3). LRF Ti had less corrosion products and pitting corrosion than CP Ti in stress-corrosion test. In artificial saliva, 2%NaF artificial saliva(pH=7) and 2%NaF artificial saliva (pH=3),the free circuit potential (Ecorr) of LRF Ti (-469mV,-925mV and-943mV) were higher than those of CP Ti (-555mV,-943mV and-956mV);the current density of LRF Ti (2.14×10-6 Acm-2,2.65×10-6 Acm-2 and 4.51×10-6 Acm-2) were lower than those of CP Ti (2.18×10-6Acm-2,4.49×10-6Acm-2 and 6.63×10-6Acm-2),the film resistance (2.77×106?cm2,3.41×105?cm2 and 4.3×104?cm2)and transfer resistance (6.71×104?cm2,2028?cm2 and 4.4×103?cm2)of LRF Ti were higher than those of CP Ti(1.42×106?cm2,6.65×104?cm2and16.93?cm2)(236.9?cm2,44.1 ?cm2and 2.56×103?cm2)respectively。Conclusion: Low pH value and fluoride in the solution could accelerate Ti iron release,LRF Ti had better corrosion resistance for long-term implants than CP Ti.