Hydroxyapatite‐coated magnesium implants with improved in vitro and in vivo biocorrosion, biocompatibility, and bone response

Abstract

Magnesium and its alloys are candidate materials for biodegradable implants; however, excessively rapid corrosion behavior restricts their practical uses in biological systems. For such applications, surface modification is essential, and the use of anticorrosion coatings is considered as a promising avenue. In this study, we coated Mg with hydroxyapatite (HA) in an aqueous solution containing calcium and phosphate sources to improve its in vitro and in vivo biocorrosion resistance, biocompatibility and bone response. A layer of needle-shaped HA crystals was created uniformly on the Mg substrate even when the Mg sample had a complex shape of a screw. In addition, a dense HA-stratum between this layer and the Mg substrate was formed. This HA-coating layer remarkably reduced the corrosion rate of the Mg tested in a simulated body fluid. Moreover, the biological response, including cell attachment, proliferation and differentiation, of the HA-coated samples was enhanced considerably compared to samples without a coating layer. The preliminary in vivo experiments also showed that the biocorrosion of the Mg implant was significantly retarded by HA coating, which resulted in good mechanical stability. In addition, in the case of the HA-coated implants, biodegradation was mitigated, particularly over the first 6 weeks of implantation. This considerably promoted bone growth at the interface between the implant and bone. These results confirmed that HA-coated Mg is a promising material for biomedical implant applications.

Cardiovascular Applications of Magnesium Alloys

“…With impurities as well as alloying or coating elements, it is important to keep in mind the tolerable upper intake levels of these elements in humans so that improved strength or corrosion resistance does not come at the expense of biocompatibility. Pure Mg alloys for biomedical applications have mostly been replaced by other alloys, though some studies still contain pure magnesium, often as a control [102][103][104][105].…”

In vitro degradation behavior and cytocompatibility of biodegradable AZ31 alloy with PEO/HT composite coating

“…The HA coated magnesium substrate showed enhanced corrosion resistance in simulated body fluid [21]. Moreover, the HA coated magnesium samples showed enhanced cytocompatibility and mitigated the in vivo biodegradation of magnesium implant, particularly over the first 6 weeks of implantation, which considerably promoted bone growth at the interface between the implant and bone [22]. However, the fabrication of HA layer by this method on other substrates, such as PEO coating, has been rarely investigated [23].…”

Self-healing property of hydroxyapatite and octacalcium phosphate coatings on pure magnesium and magnesium alloy

“…Calcium phosphate precipitation improved the protectiveness of the coatings; therefore the mass-transfer conditions of the test solution should be controlled, depending on the targeted part of the body. It has been reported that corrosion of uncoated Mg alloys in bone marrow is faster than that in cortical bone and soft tissue [20,39,40]. Kim et al reported that HAp coating prevented corrosion of pure Mg in the bone marrow of rabbit tibias, although calcium phosphate precipitation behaviour on the HAp coating in bone marrow was not examined [20].…”

“…The HAp coating showed good adhesiveness to the Mg alloy substrate under static tensile deformation with 5% elongation and under fatigue loading accompanying 3% cyclic elongation [18]. Kim et al reported that a similar HAp coating on pure Mg gave good corrosion protectiveness, biocompatibility, and bone response in the bone-pericranium pouches of rats and/or in tibial shafts of rabbits [20]. A brushite (dicalcium phosphate dihydrate) coating prolonged the in vivo degradation period of a Mg-Nd-Zn-Zr alloy [21].…”

“…Magnesium and its alloys are suitable for use as orthopaedic implant materials because they are bioabsorbable/biodegradable and therefore do not require surgical removal. They also have high specific strength and low Young's modulus (41)(42)(43)(44)(45) GPa) similar to that of bone (3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20) [1][2][3][4][5].…”