Design,Fabrication And Experimental Study Of Bioactive Porous Titanium Alloy Implant

Background The one of the important work of orthopedist is repair the bone defect caused by trauma, bone tumor surgery or bone degenerative diseases surgery. Although autogenous bone graftinghas been considered as the gold-standard for treatment bone defect. However, its application is limited by bone insufficient and donor site morbidity.Therefore,the artificial bone substitute has developed rapidly and widely used in clinically.The ideal artificial bone substitute, especially for load-bearing conditions, should possess both good bioactivity and high mechanical strength. But the biological ceramic and titanium cannot meet the two condition at the same time. Thus developing a new artificial bone substitute with appropriate mechanical properties and good bone-bonding ability is very meaningful.Electron beam melting(EBM) technique can fabricate porous titanium alloy with designed internal structure and make the mechanical properties of porous titanium alloy implant match to bonetissue. Thehydroxyapatite(HA) coating with osteoconduction ability has been conducted by plasma spraying. The HA coated porous titanium alloy fabricated by EBM and plasma spraying possesspotential to become one kind of ideal artificial bone substitute ObjectThe porous titanium alloys implant fabrication by EBM. The surface treatment of the porous titanium alloys implant by plasma spray HA coating.Evaluate the pore size, porosity and mechanical properties of the porous titanium alloy implant fabricated by EBM. Investigate the surface characteristics of the HA coated implant and un-coated implant. Evaluate the bone ingrowth and osseointegration of the HA coated porous titanium alloy implant by animal experiment in vivo. Methods1. The fabrication and characterization: Three-dimensional model of porous titanium alloys implant was designed by Materialise/MagicsTM. Then, the porous titanium alloys implant was fabricated according to the three-dimensional model by EBM system. The pore size, porosity and mechanical properties of the porous titanium alloy implant was characterized.2. The surface treatment: TheHA coating wasprepared by plasma spraying. The surface characteristics measurement with regard to the surface topography and chemical composition by scanning electron microscope(SEM),energy dispersive X-ray spectrometer(EDS) and confocal laser scanning microscope(CLSM).3. Animal experiment in vivo: 6 mature female Small Tail Han sheep were collected for created cylindrical bone defect in the bilateral distal femur.The HA coated porous titanium alloys implants and un-coated porous titanium alloys implants were implanted into the distal femoral bone defects. The samples were retrieved after 2 months and 4 months for X-ray, Micro-CT and histological analyses. The bone ingrowth and osseointegration of the implants were evaluated. ResultMicro-CT analysis indicated that the porous titanium alloys implant possess high porosity(69±5%) and large pore size(514±35μm) with fully interconnected pores. The compression strength and Young’s modulus of the porous titanium alloys implant were 90±2MPa and 3.2±0.3GPa respectively. The SEM and EDS measurement showed the HA coating prepared on the porous titanium alloys implant surface successfully. The surfaceelement composition of HA coated porous titanium alloys implant were Ca, P, O. But the coating of HA coated implant on inner surface was nonuniform. The CLSM revealed the surface roughness of HA coated implant( Ra 8.45±0.80μm) higher than which of un-coated implant(Ra 4.95±1.26μm).The animal experiment showed both two groups implants have good biocompatible and no inflammatory response was observed. After implantation 2months, Micro-CT found the bone volume fraction of HA coated implant(9.32±0.72%)higher than the bone volume fraction of un-coated implant(5.13±1.73%)significantly. After implantation 4 months, the bone volume fraction of HA coated implant was 17.68±3.49% and the bone volume fraction of un-coated implant was 6.29±2.11%, the difference between the two groups were significantly. Histological analysis showed the mineralized bone fraction of two groups were 8.26±0.35%(HA coated implant) and 5.40±1.51%(un-coated implant) respectively after 2 months. After implantation 4 months, mineralized bone fraction of HA coated implant(19.78±1.46%) higher than which of un-coated implant(5.70±0.85%)significantly. In addition, the HA coated implant incorporation with new bone closely and the gaps were observed between interfaceof the un-coated implant andnewly bone tissue. The result revealed that the bone ingrowth and osseointegration of the HA coated porous titanium alloy implant both better than un-coated implant. ConclusionPorous titanium alloy implant fabricated by EBM possesses interconnected pore structure and mechanical properties similar to bone tissue. The HA coating preparation by plasma spray successfully. The HA coated porous titanium alloy implant showed excellent bone ingrowth and osseointegration performance in vivo study. It has great potential as a ideal artificial bone substitute.