Preparation And In Vivo Study Of Selective Laser Sintering 3D Printed Titanium Alloy Implants

Objective:The Ti6Al4 V titanium alloy 3D printed implant(TC4 implant),whose precision and surface morphology were analyzed,was prepared.Also,the performance of TC4 implant osseointegration was explored by in vivo experiments,which provided a theoretical basis for clinical application of 3D printed implants.Methods:1.Modeling and sample preparation of TC4 implants: the implant model,based on Straumann implant,was established by using the 3D scanning technology,and the Selective Laser Sintering(SLS)technology was used to produce the TC4 implant,then the precision measurement and error analysis were completed.By using Scanning Electron microscope(SEM)and Energy Dispersive X-Ray spectroscopy(EDS),the surface topography of TC4 implants were compared with Straumann implants.2.In vivo study of osseointegration performance of TC4 implants: TC4 implants were used as experimental group(TC4 implant group),when Straumann implants were taken as control group(Straumann implant group).Six rabbits were used to establish a bilateral femoral implant model.One TC4 implant and one Straumann implant were implanted in each femur(12 TC4 implants and 12 Straumann implants were implanted).The animals were sacrificed at 2 weeks,4 weeks,and 8 weeks after operation,and gross specimens were observed.The distribution of osteoblasts,new and old bone formation interface,collagen fibers and bone tissue maturation were observed by HE staining,toluidine blue staining,Masson staining,and methylene blue-acid red staining,and combined with postoperative SEM and EDS to evaluate the difference in osseointegration performance between TC4 implants and Straumann implants.Results:1.3D scanning technology combined with SLS technology can produce TC4 implants with complete structure and rough surface.The results of error analysis showed that there were no statistically significant differences between the TC4 implants and the final models in three main shape characteristics,body width(p=0.308),maximum diameter of the implant neck(p=0.111)and pitch of the screw(p=0.259).SEM showed that there were no obvious structural defects on the surface of TC4 implants,and the connected pore structure was scattered between the dense lamellar structure,while Straumann implant had a uniform distribution of tiny pore structure on the surface.EDS showed that the main metal components of TC4 implant were Ti and Al,followed by a small amount of V and trace Fe,which were basically consistent with the powder raw materials.2.Within 72 hours after operation,the experimental animals were slightly in poorly mental state,and gradually returned to normal with usual diet and activities after 72 hours.At each observation time point(2 weeks,4 weeks and 8 weeks after surgery),gross specimens showed that there was no implant loosening or displacement in the TC4 group and the Straumann group,and the implant was firmly combined with bone tissue.3.HE staining showed that no obvious infiltration of inflammatory cell was observed around the implants in the TC4 group and the Straumann group at 2,4 and 8 weeks after surgery.At 2 weeks after surgery,trachychromatic and monostratal osteoblasts were observed on the implant-bone interface between two groups,and the number of osteoblasts in the TC4 group was slightly less than that in the Straumann group.At 4 weeks after surgery,new osteoid formation was observed in both the TC4 group and the Straumann group.At 8 weeks,both groups had formed new bone with a certain thickness at the implant-bone interface,and relatively maturing bone units were discovered in the new bone tissue of Straumann group.4.Masson staining showed that at 2 weeks after operation,dark red and completely-mineralized primitive bone-tissues were observed in the bone tissues of the TC4 and Straumann groups close to the implant,and the bone units were clearly displayed.At 4 weeks after surgery,there were different degrees of formation of new collagen fibers in the surrounding tissues of the implants in both groups.A large quantity of newly-formed and blue-stained collagen fibers were scattered among the development of relatively mature bone tissues with red dots.At 8 weeks after surgery,both two groups showed consistent red-blue staining results.5.Toluidine blue staining showed that at 2 weeks after surgery,the subjects of two groups discovered osteoblasts arranged linearly at the edge of the bone tissue of the implant,whose nucleus deeply stained and the cytoplasm was light blue.At 4 weeks after operation,the two groups were observed to have light staining of new collagen fibers around the implants,which were not neatly arranged.At 8 weeks after surgery,both the TC4 group and the Straumann group showed the formation of new bone with light-blue and continuous structure,containing a large number of bone cells.Also,the boundaries between the new bone and the mineralized bone were clear.6.Methylene blue-acid fuchsin staining showed that 2 weeks after surgery,the TC4 group and the Straumann group still displayed the aggregate behavior of osteoblasts around the implant,and the Straumann group was slightly better than the TC4 group.At 4 weeks after operation,newborn and reddened osteoid structures were observed between the implant and the mineralized bone in the two group.At 8 weeks after surgery,the formation of new bone with a certain degree of calcification was observed on the surface of implants in both groups,appearing a dark red color.7.SEM,at 8 weeks after surgery,presented that the surface structure of TC4 implant was basically consistent with before.EDS revealed that in addition to Ti,Al,V,Fe,C,O and other elements,Ca,Mg and Si were still scattered on the surface of TC4 implants.Conclusion:1.3D-scanning technology combined with SLS technology can produce high-precision TC4 implants with complete structure and rough surface morphology.2.3D-printed TC4 implants have good structural stability and biocompatibility,which can achieve similar osseointegration properties to Straumann implants in vivo,it provides a theoretical basis for the promotion and application of 3D printed TC4 implants.But early osteoconduction and later new bone calcification levels are somewhat different from Straumann implants.This difference can be reduced by surface activation treatment or microscopic morphology improvement of 3D printed TC4 implants,but this remains to be further studied by subsequent experiments.