| In recent years, magnesium (Mg) alloys and cobalt-chromium (Co-Cr) alloyhave attracted much attention as potential biomaterials due to their excellentmechanical properties and especially biocompatibility as metallic materials. Inthe present study, surface modification of Mg alloy and Co-Cr alloy to developbiological functional coating as implants could be good applications as bonefixation materials, coronary Stent, vascular coupler and drug release system ofdrug-eluting stent. All these character match the practical needs of biomedicalimplant materials.For the bone fixation biomaterials, a Mg alloy surface coating is used toadjust the biodegradation rate and improve the biocompatibility. A dense anduniform Ca-P coating was successfully prepared on Mg substrate by SCSimmersion to improve the surface bioactivity of the metal substrate, especiallyreduce the biodegradation rate. Through8weeks implantation in vivo, coatedsample provided an obvious slower biodegradation rate than naked samples,which is the same result to that in vitro. The reaction on the surface of the Mgimplant between Mg alloy and body fluid results in the formation of aMg-containing calcium phosphate biodegradation layer, which contributesmainly to the fast deposition rate of biological calcium phosphate and fastformation of new bone around Mg implants. Additionally, serum Mgmeasurement shows that biodegradation of Mg did not cause disorder increase inserum Mg after8weeks post implantation. The above results indicated that Mgalloy coating system is well qualified as orthopedic biodegradable materials.Otherwise, Ca-P coating has been obtained by the method of IBAD and apost-treatment process. The width of the mixed interface between the Ca-Pcoating and Mg substrate in the samples is2μm, which can improve the bondingstrength. Compared the naked substrate sample and the coated samples, thepercentage increases of hardness and elastic modulus induced by coating aremore than77.5%and55.7%, respectively. In addition, in the test of degradation,the mass loss of coated samples is just one fifth of that of naked samples on the15day, which indicate the Ca-P coating decrease the degradation rate significantly. Accordingly, biological functional Mg alloy surface coatingwould be a longer longevity of orthopedic implants with appropriate degradationrate in bone repair.For the coupler and stent, CN coating by IBAD, DLC films by RFPACVDand TiO2coating by IBAD were successfully deposited on the Mg alloy. The CN,DLC and TiO2coated Mg alloy improve mechanical characterization, improvedthe roughness of naked substrate, develop the wettability and superficial energyand decrease degradation rate. Due to the forming of biological functional Mgalloy surface coating, the superior biocompatibility, corrosion reducing of theMg alloy substrate and unusual desirable properties as a good candidate forcoronary and vascular application.A completely new concept is biomimetic apatite with sirolimus to create anabsorbable drug eluting system, which in turn can serve as a drug reservoir. Therelease of sirolimus is controllable because of immobilization of sirolimusduring the process of biomimetic apatite forming. We here describe thecharacteristic, mechanisms and drug release in vitro of new drug-eluting systemin comparison to conventional system equivalent. Nano-structured calciumphosphate coating was formed on the Co-Cr alloy. By dropping sirolimus in themethylene chloride solution, the sirolimus could be immobilized in the newlyformed apatite layer. The results showed that a uniform apatite incorporatedwith sirolimus was observed on Co-Cr alloy. HPLC based drug release kineticsrevealed it is a linear drug-eluting system. The diminished inhibition of vascularsmooth muscle cell proliferation may improve arterial healing and contribute tothe safety profile of the stent. |
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