Surface Modification Of 3D Printed Porous Structure Titanium Implants

With the development of 3D printed technology,3D printed titanium implants have received extensive attention and application in the field of biomedical implants.However,the bio-inert surface of 3D printed titanium implant has an extremely negative effect on osseointegration,which could contribute to the long healing time and high failure rates of operations.Therefore,it is necessary to carry out surface modification treatment,so that the 3D printed titanium implant can be better applied to living organisms.In this study,3D printed technology was used to prepare porous pure titanium biomedical materials.The surface pretreatment and surface modification treatment of 3D printed porous pure titanium were carried out.Scanning electron microscopy?SEM?,X-ray photoelectron spectroscopy?XPS?,X-ray energy spectrometer?EDS?,contact angle measuring instrument,X-ray diffractometer?XRD?and other test methods for surface morphology,composition,surface wettability,etc.were characterized and analyzed.The biomineralization properties of different samples surface were studied by in vitro biomimetic experiments.The effects of different surfaces and related mechanisms were analyzed.Through the investigation of the influence of pure titanium powder for 3D printed,porous titanium samples and different surface pretreatment methods on the surface of the sample.The results show that the porosity of porous titanium implants prepared by 3D printed technology is 64.21%,which meets the design requirements,and the elastic modulus was 1.8±0.24 GPa,close to cancellous bone?0.1-0.5 GPa?and cortical bone?12-18 GPa?,which was more suitable for biomedical implants.By acid etching,acid etching and annealing,acid etching and alkali etching,acid etching and hydrothermal treatment the unfused metal powder on the surface of 3D printed pure titanium sample were removed efficiently,and the surface morphology were changed,hole formation of micro-nano structures with different degrees of surface on each sample surface.The surface pretreatment of the dense titanium samples under the same 3D printed conditions was carried out under the same conditions,and the contact angle test was carried out.The results showed that the surface contact angles of the samples were 49.54°,48.63°,16.61°and 5.53°,respectively.Compared with the sample surface contact angle of 79.05°without any treatment,the surface wettability of the sample after the pretreatment was improved,showing better hydrophilicity or even super hydrophilicity.Acid etching was used as a pretreatment process before 3D printed porous titanium modification,and the surface was further modified by biochemistry surface treatment method,in which polydopamine?PDA?was used as a transition layer to further graft bioactive macromolecular casein phosphopeptide?CPP?,preparation of PDA-CPP composite bioactive coating on porous titanium surface with complex structure.The results show that the immersion method can successfully prepare the PDA-CPP composite coating on the surface,and the surface wettability was improved by the modification of the bioactive coating,the surface contact angle of the PDA modified sample was36.16°,the surface contact angle of the sample modified by PDA-CPP composite bioactive coating was 23.54°.In vitro biomimetic mineralization showed that the surface mineralization performance of the modified bioactive coating was significantly improved,since phenolic hydroxyl groups in PDA can interact with calcium,and phosphoserine groups of CPP chelate calcium to form soluble substances,which increase the concentration of calcium ions,both of them provide more nucleation sites for hydroxyapatite,strengthened interface bonding.The mineralized porous structural scaffold is also wrapped by the hydroxyapatite layer which indicated that the modification of the PDA-CPP bioactive coating was not limited by structure and shape of implants.The pretreated surface of porous titanium was activated by phytic acid?PA?and calcium hydroxide solution.The surface of porous titanium was successfully introduced into calcium and phosphorus by immersed with one-step method and two-step method respectively.The results show that the surface wettability of activated surface was improved due to the presence of calcium,phosphorus and hydroxyl groups,the surface contact angles of the sample after one-step and two-step treatment were 21.04°and 22.92°,respectively.The results of in vitro biomimetic mineralization indicated that the surface of PA/Ca?OH?₂ by one-step treatment and the surface of PA+Ca?OH?₂ by two-step method could accelerate the deposition of hydroxyapatite on the activated surface.Because the calcium and phosphorus on the activated surface interact with the ions in the simulated body fluid,and the nucleation of hydroxyapatite on the surface could be promoted.The biomineralization performance of PA+Ca?OH?₂ surface was better than PA/Ca?OH?₂,which due to the increase of Ca²⁺and hydroxyl on PA+Ca?OH?₂ surface,and the calcium with good biological and chemical properties also improved the formation ability of hydroxyapatite on the surface.