Given the alarmingly increasing rates of glaucoma worldwide and the lack of satisfactory treatments, there is a dire need to explore more feasible treatment options. Magnesium (Mg) is an essential element in maintaining the functional and structural integrity of vital ocular tissues, but Mg and its alloys are rarely mentioned in ophthalmic applications. Our previous research found that hydroxyapatite-coated Mg (Mg@HA) shows the best biocompatibility and bioactivity, and exhibits the effect of inhibiting fibrosis after filtration surgery in the rabbit model, which is expected to be a promising material for glaucoma drainage device. In this study, we further demonstrated the anti-fibrosis effect of Mg@HA from the molecular signal level and the efficacy of implantation in the rabbit filtration surgery model. In vitro experiments showed the surface modification of Mg affects the adhesion behavior and the reorganization of cytoskeleton of Human Western blot analysis and immunofluorescence found that Mg@HA regulates the adhesion and motility of human Tenon’s capsule fibroblasts mainly by down-regulating the phosphorylation of Smad2 and Smad3 in the canonical transforming growth factor-beta (TGF - β) signaling pathway. By observing and recording the condition of filtering blebs and intraocular pressure after surgery, the effectiveness of Mg@HA applied in the rabbit filtration surgery model was further evaluated. In conclusion, the application of hydroxyapatite-coated Mg in the eye has good biocompatibility and has the potential to resist postoperative glaucoma filtration fibrosis, which may be mediated by the regulation of the TGFβ/Smad signaling pathway.

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.