A Feasibility Study Of Using Biodegradable Coated Magnesium Material In Glaucoma Filtration Surgery

Background: Glaucoma is the leading cause of irreversible blindness.Filtration surgery still plays a mainstream role of treatment for glaucoma.The last decade has seen the emergence of minimally invasive glaucoma surgery(MIGS),with the most recent utilizing implantable devices.Filtration surgery has undergone various modifications with trabeculectomy no longer being the only choice.The first generation of glaucoma micro-incisional devices has been made of titanium.Since then other non-biodegradable materials have also been introduced.In each case,the presence of a permanent foreign body has been associated with undesirable wound healing responses characterized by fibroblast proliferation and surgical failure.Currently,magnesium materials have attracted much attention as biodegradable implantable materials due to their excellent biodegradable and biocompatibility properties.The goal of the research was to establish a proof of principle for further exploration of this novel material as a potential adjunct to glaucoma surgery.Purpose: To evaluate the vitro and vivo corrosive properties,biocompatibility and anti-proliferative properties of differently coated magnesium in a primary culture of human tenon's capsule fibroblast(HTCFs)and in rabbit glaucoma filtration surgery(GFS).Methods:1.Coated magnesium materials corrosive properties testScanning electron microscope(SEM)morphologies were observed,and ion release,sample weight change,and pH change were investigated by immersion of coated and uncoated pure magnesium samples in balanced salt solution(BSS).2.Effects of coated magnesium on the bio-modulation of HTCFsIn vitro,primary HTCFs were seeded on dicalcium phosphate dihydrate(DCPD),DCPD + stearic acid(DCPD+SA)and hydroxyapatite(HA)disks with glass and titanium disks used as controls.SEM observed images of HTCFs seeded different disks.The MTT and LDH assays were used to determine cellular metabolic activity and cytotoxicity during the logarithmic phase of HTCFs,respectively.The BrdU assay was used to evaluate cellular proliferation.Western blot(WB)was used to assess the expression of alpha-smooth muscle actin(?-SMA).3.The safety and efficacy of coated magnesium application in rabbit glaucoma filtration surgeryIn vivo,New Zealand rabbits underwent a standard primary trabeculectomy with a titanium disk,pure magnesium disk and the three coated magnesium disks(HA,DCPD,DCPD+SA)placed under a scleral flap,the procedure of trabeculectomy alone used as control.0.1ml of aqueous was extracted before the rabbits were euthanized,which was used to analyze the ion concentration of samples.The sections of eye were stained with hematoxylin and eosin(H&E)for histology analysis.Western blot was used to assess the expression of ?-SMA and Collagen-1.Reverse transcription-polymerase chain reaction(RT-PCR)analysis was used to detect ?-SMA and Collagen-1 mRNA in the tissue of rabbit's tenon's.Results:1.Coated magnesium materials corrosive properties testIn corrosive properties test,SEM showed the HA coating was exfoliated from the matrix on day 5,but without any obvious changes on the surface of non-exfoliated areas.The sample weight of the DCPD and DCPD+ SA groups was dramatically reduced during the first 2 days in BSS.The pure magnesium group had higher pH levels compared with other groups.The magnesium concentration in the pure magnesium group was obviously higher than that of other groups.The calcium and phosphorus concentration of the DCPD and DCPD+ SA groups was much higher than that of the HA group.2.Effects of coated magnesium on the bio-modulation of HTCFsIn vitro,the number and shape of HTCFs seeded on different coatings showed less quantity and poor cell morphology.Each type of coated magnesium demonstrated significantly decreased metabolic activity of HTCFs when compared to the controls(P<0.001).DCPD+SA showed higher cytotoxicity than the other coatings but was not statistically different when compared to the controls(P=0.976).Significant inhibition of proliferation was observed with the DCPD+SA coating(P=0.047).The expression of ?-SMA was decreased in the cells when seeded on all of the coated magnesium alloy disks.3.The safety and efficacy of coated magnesium application in rabbit glaucoma filtration surgeryIn vivo,after 60 days following surgery,the rabbits didn't exhibit any complications and adverse effects.No significant difference existed for any of the groups regarding different ion concentrations in the aqueous humor.H&E stain indicated the inflammatory response in the titanium,pure magnesium,DCPD and DCPD+SA treated eyes was more intense than in the trabeculectomy alone and HA groups.Western Blot analysis showed that ?-SMA and collagen-1 expression was significantly lower in the HA,DCPD and DCPD+SA groups compared with controls(P<0.001).The HA group showed lowest level of ?-SMA and collagen-1.RT-PCR analysis showed significantly lower expression of ?-SMA and collagen-1 mRNA(P<0.001)was observed in coated magnesium groups.HA group showed lowest expression.Conclusions: The coating technology effectively reduced the corrosive properties of pure magnesium matrix during the biodegradation.The coated magnesium materials affected the morphology of HTCFs,reduced its metabolic activity and proliferation performance,inhibited the expression of ?-SMA,and had no obvious cytotoxicity.Two months after the operation,no complications and adverse reactions were observed in the anterior and posterior segment of rabbit's eyes.The ions released from materials degradation had no significant effect on the ions concentration in aqueous humor.HA coated magnesium implantation had lower inflammatory response with surrounding tissues,and significantly inhibited the protein and mRNA expression of ?-SMA and Collagen-1.