Degradation and biological properties of Ca-P contained micro-arc oxidation self-sealing coating on pure magnesium for bone fixation

Poor corrosion resistance is one of the main disadvantages for biodegradable magnesium-based metals,especially applied for bone fixation,where there is a high demand of bio-mechanical strength and stability.Surface coating has been proved as an effective method to control the in vivo degradation.In this study a Ca-P self-sealing micro-arc oxidation(MAO)coating was studied to verify its efficacy and biological properties by in vitro and in vivo tests.It was found that the MAO coating could effectively retard the degradation according to immersion and electrochemical tests as well as 3D reconstruction by X-ray tomography after implantation.The MAO coating exhibited no toxicity and could stimulate the new bone formation.Therefore,the Ca-P self-sealing MAO coating could be a potential candidate for application of biodegradable Mg-based implant in bone fixations.

The effect of different coatings on bone response and degradation behavior of porous magnesium-strontium devices in segmental defect regeneration

Regeneration of long-bone segmental defects remains a challenge for orthopedic surgery.Current treatment options often require several revision procedures to maintain acceptable alignment and achieve osseous healing.A novel hollow tubular system utilizing magnesium-strontium(Mg-Sr)alloy with autogenous morselized bone filled inside to repair segmental defects was developed.To improve the corrosion and biocompatible properties,two coatings,Ca-P and Sr-P coatings,were prepared on surface of the implants.Feasibility of applying these coated implants was systematically evaluated in vitro and in vivo,and simultaneously to have a better understanding on the relationship of degradation and bone regeneration on the healing process.According to the in vitro corrosion study by electrochemical measurements,greater corrosion resistance was obtained for Ca-P coated sample,and attributed to the double-layer protective structure.The cytotoxicity and alkaline phosphatase(ALP)assays demonstrated enhanced bioactivity for Sr-P coated group because of the long-lasting release of beneficial Sr^(2+).At 12 weeks post-implantation with Mg-Sr alloy porous device,the segmental defects were effectively repaired with respect to both integrity and continuity.In addition,compared with the Ca-P coated implant,the Sr-P coated implant was more proficient at promoting bone formation and mineralization.In summary,the Sr-P coated implants have bioactive properties and exceptional durability,and promote bone healing that is close to the natural rate,implying their potential application for the regeneration of segmental defects.

One-step electrodeposition synthesis of bisphosphonate loaded magnesium implant:A strategy to modulate drug release for osteoporotic fracture healing

Osteoporotic fracture with increase of aging population became an urgent orthopedic problem.Bisphosphonates were widely recommended as effective clinical treatment drugs.Combination of biodegradable Mg-based implants and merits of bisphosphonates was suggested for osteoporotic fracture healing.Considering the mild and sustained drug release,a novel one-step electrodeposition synthesis of drug loaded coating was proposed in this study.In comparison to conventional soaking method,encapsulated zoledronate coating by one-step electrodeposition method could modulate drug release in first diffusion-controlled and later degradation-controlled manner.The in vitro cell response to zoledronate loaded coating showed enhanced proliferation and osteogenic differentiation of osteoblasts and no significant inhibition on osteoclasts,which could improve bone-forming and decrease bone resorption due to osteoporosis.

Biofunctional magnesium coating of implant materials by physical vapour deposition

The lack of bioactivity of conventional medical materials leads to low osseointegration ability that may result in the occurrence of aseptic loosening in the clinic.To achieve high osseointegration,surface modifications with multiple biofunctions including degradability,osteogenesis,angiogenesis and antibacterial properties are required.However,the functions of conventional bioactive coatings are limited.Thus novel biofunctional magnesium(Mg)coatings are believed to be promising candidates for surface modification of implant materials for use in bone tissue repair.By physical vapour deposition,many previous researchers have deposited Mg coatings with high purity and granular microstructure on titanium alloys,polyetheretherketone,steels,Mg alloys and silicon.It was found that the Mg coatings with high-purity could considerably control the degradation rate in the initial stage of Mg alloy implantation,which is the most important problem for the application of Mg alloy implants.In addition,Mg coating on titanium(Ti)implant materials has been extensively studied both in vitro and in vivo,and the results indicated that their corrosion behaviour and biocompatibility are promising.Mg coatings continuously release Mg ions during the degradation process,and the alkaline environment caused by Mg degradation has obvious antibacterial effects.Meanwhile,the Mg coating has beneficial effects on osteogenesis and osseointegration,and increases the new bone-regenerating ability.Mg coatings also exhibit favourable osteogenic and angiogenic properties in vitro and increased long-term bone formation and early vascularization in vivo.Inhibitory effects of Mg coatings on osteoclasts have also been proven,which play a great role in osteoporotic patients.In addition,in order to obtain more biofunctions,other alloying elements such as copper have been added to the Mg coatings.Thus,Mg-coated Ti acquired biofunctions including degradability,osteogenesis,angiogenesis and antibacterial properties.These novel multi-functional Mg coatings are expected to significantly enhance the long-term safety of bone implants for the benefit of patients.This paper gives a brief review of studies of the microstructure,degradation behaviours and biofunctions of Mg coatings,and directions for future research are also proposed.