| Background:Spine fusion has become a routine technique in the field of spine surgery,and has been widely used in the treatment of lumbar spine degeneration,cervical spine instability,intervertebral disc injury and spinal deformity.Generally speaking,the spinal fusion surgery is an effective method to achieve spinal stability and nerve decompression[1].However,it is usually associated with a high incidence of fusion failure and pseudarthrosis(5-35%).Two of the most important factors are bone grafting materials and bone transplantation mode selection[2].The development of spinal surgery has put forward higher requirements for bone implants.With the development of new technologies and new materials,more and more new bone substitutes,which meet the biomechanical characteristics of human body,emerged as the times require[3-8].The ideal bone substitute materials should have the characteristics of bone conduction,bone induction,no immunogenicity,no risk of disease transmission,suitable mechanical strength,cost-effective and easy to use.So far autologous bone is still the best material for intervertebral fusion.However,it is limited by some of the disadvantages of autologous bone,including additional surgical trauma,increased risk of postoperative complications such as infections,hematomas and pain in donor-site,and limited supply of autologous bone[9-12].The use of allogeneic and xenogeneic bone is also likely to bring risks such as immune rejection and bone disease spread[13,14].The calcium-based and polymeric artificial bone substitutes have been plagued by problems such as poor biodegradability,biocompatibility,and biomechanics so as to lead a low fusion rate[15,16].Therefore,a material with good bio compatibility,bone conduction,and even induction of bone ingrowth,which can be used to improve the rate of spinal fusion and bone regeneration,has become a hot research topic.In the past 30 years,it has witnessed a fast development in the medical porous materials which have been substituting solid metals in bone implantation surgeries.Compared with solid implant metals,the porous ones advance in lighter weight,larger contact surfaces,as well as closer mechanic properties to the human bones.Porous tantalum has been proved to be one of the most suitable substitution materials for human bone due to its similar structure and mechanic properties as human bone.Furthermore,tantalum could stimulate cell proliferation,and improve the ability of osteogenesis of human osteoblasts[17].Different types of tantalum interbody fusion implants evolved over time in shape and quality.A new generation of porous tantalum called trabecular metal(TM)came into being,with good bio compatibility,high porosity and bone similar elastic modulus characteristics.Clinically,trabecular metals(porous tantalum)are widely used in avascular necrosis of the femoral head,artificial joints,spinal fusion and other fields[18-25].Especially in the treatment of early avascular necrosis of the femoral head and total hip/knee reconstruction in situations of massive bone defect,remarkable results could be achieved compared with the traditional materials and methods of treatment[19-22,24].Recently,several clinical studies have been undertaken on the use of porous tantalum for spinal interbody fusion[18,25-29].Trabecular metal has been proved effective in obtaining fusion and improving clinical outcome in patients after lumbar interbody fusion[26-29].However,different fusion rates have been reported in anterior cervical interbodyfusion by trabecular metal implants.Lofgren et al.[30]reported that trabecular metal showed a lower fusion rate(69%)than autograft group(92%)after single-level anterior cervical fusion which led to controversial views among spine surgeons.Zardiackas et al.[31]evaluated a porous tantalum biomaterial(Hedrocel)and the results demonstrated a significant variation in the single-cycle mechanical properties of the porous tantalum,which was probably caused by the differences in morphology and processing that resulted in less precisely controlled micro structural parameters.Shimko et al.[32]explored the effect of porosity on the fluid flow characteristics and mechanical properties of trabecular metal,and they concluded that a better understanding of these structure-function relationships was' benefit for enhancing quality of the implant designs.Objective:A biomedical porous tantalum synthesized via three-dimensional knitted wire framework and chemical vapor deposition,was applied to in vitro and in vivo experiments.The purposes of the present study were to evaluate the biocompatibility and osteocompatibility of the novel porous tantalum implant,and to evaluate the efficacy to achieve lumbar interbody fusion by assessing the radiographic and histological performance between the novel porous tantalum implant and autologous bone in a rabbit anterior lumbar fusion model.Methods:A cubic porous tantalum(Ning Xia orient tantalum industry Co.Ltd,Shizuishan,China)synthesized via three-dimensional knitted wire framework and chemical vapor deposition(length,width and height of 2.5-3.0mm;Figure 1a)was used in this study.The porosity was determined by the porous tantalum volumes and their net weights.It was calculated by the equation;porosity(%)=(1-Mporous/MTa)×100%.Here,Mporous was the weight of the porous block(measured)while MTa represented the weight of pure and solid Ta block with the same volume of the corresponding porous one.The morphology of porous tantalum block was further characterized through a Zeiss Ultra Plus field emission scanning electron microscopy(FESEM;Zeiss,Germany).The FESEM was equipped with an energy dispersive spectral(EDS)X-ray detector(Shimadzu,Japan),which could be applied for the element determination through the particle induced X-ray spectra(PIXS;Shimadzu,Japan).An operation voltage of 10 kV was set for the FESEM,which would be enough to excite the M and L electrons of Ta atoms.Bone marrow-derived mesenchymal stem cells(BMSCs)were cultured on porous tantalum implant Scanning electron microscope(SEM)and Cell Counting Kit-8 assay were used to evaluate the cell toxicity and biocompatibility.Twenty-four rabbits were performed discectomy only,discectomy with autologous bone implanted and discectomy with porous tantalum implanted at three levels:L3-L4,L4-L5,and L5-L6 in random order.All the 24 rabbits were randomly sacrificed at the different postoperative times(2 months,4 months,6 months and 12 months;n=6 at each time point).Histological examination and micro-CT scans were done to evaluate the fusion process.Comparison of fusion index scores between groups was analyzed using one way analysis of variance.Other comparisons of numerical variables between groups were made by Student's t-test.Results:All rabbits survived and recovered without any symptoms of nerve injury Radiographic fusion index scores at 12 months postoperatively between autograft and tantalum groups showed no significant difference(2.89±0.32 vs.2.83±0.38,F=2446,P<0.001;Pautograft vs.tantalum=0.709).Cell Counting Kit-8 assay showed no significant difference of absorbance values between the leaching liquor group and control group(1.25±0.06 vs.1.23±0.04,t=-0.644,P=0.545),which indicated the BMSCs proliferation without toxicity.SEM images showed that these cells had irregular shapes with long spindles adhered to the surface of tantalum implant.No implant degradation,wear debris,or osteolysis was observed.Histological results showed solid fusion in the porous tantalum and autologous bone implanted intervertebral spaces.Conclusion:This novel porous tantalum implant showed a good biocompatibility and osteocompatibility,which could be a valid biomaterial for interbody fusion cages. |
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