Biodegradation and biocompatibility of calcium phosphate-coated magnesium in eye environment, in vitro and in vivo

The possible application of magnesium (Mg) in glaucoma surgical treatment has been investigated in our previous work. In this paper, the degradation behavior and biocompatibility of Mg coated with hydroxyapatite (HA) and dicalcium phosphate dihydrate (DCPD) in eye environment were evaluated, and uncoated Mg was used for comparison. It was found that uniform corrosion occurred macroscopically to the coated Mg samples in sodium lactate ringer's injection (SLRI) as well as in the rabbit eyes. In micro-scale, the corrosion was characterized by local cracking and pitting primarily. Mg and calcium (Ca) were incorporated into the surface corrosion products and a multi-layer structure was formed. Compared to other samples, HA-coated Mg slowed down dramatically the alkalinity of the solution and the ion release of the sample, and exhibited the lowest corrosion rate in SLRI, which was about 0.22 mm/a. In terms of biocompatibility, fibroblasts demonstrated high viability in the HA-coated and DCPD-coated Mg groups (p<0.05) in vitro. In vivo, HA-coated Mg was found to show lower inflammatory response and fibrosis than the other groups did, as indicated by hematoxylin-eosin and immunofluorescence staining. During the degrading process of HA-coated Mg in the rabbits' eyes, no inflammation was found in the anterior chamber, lens, and vitreous body. HA-coated Mg was fully biodegraded fifteen weeks post-operation, and the scleral drainage channel (SDC) was formed without obvious scarring. It is concluded that HA-coated Mg implantation is a promising adjunctive procedure to improve the success rate of trabeculectomy.

Statement of significance: Magnesium (Mg) has shown to be a potential biomaterial for ophthalmic implants in our previous work. However, inflammatory response resulted from the low corrosion resistance of Mg is a major concern. It is shown here that Mg coated with different calcium phosphates can improve these properties in varying degrees and keep the scleral drainage channel unobstructed and unscarred. Based on our in vitro and in vivo studies, HA-coated Mg exhibited a better degradation behavior and excellent biocompatibility. The scleral drainage channel still exists and aqueous humor flows out smoothly after the full degradation of the implant. It is concluded that HA-coated Mg is a promising biomaterial to increase the therapeutic efficiency of trabeculectomy for glaucoma.