Biointegration of collagen hydrogel, as donor corneal substitute, on PMMA for Boston keratoprosthesis

Abstract

Purpose: To improve biointegration and adhesion strength of collagen hydrogel, as human donor corneal substitute, on PMMA for Boston keratoprosthesis.

Methods: PMMA sheets of 25 x 25 x 0.5 mm were surface modified by: oxygen plasma for 5 minutes (referred as plasma group); oxygen plasma followed by hydroxyapatite (HAp) coating (plasma+HAp group); L-3,4-dihydroxyphenylalanine and 11-mercaptoundecanoic acid followed by HAp coating (DOPA+HAp group); or oxygen plasma followed by 5% (3-aminopropyl)triethoxysilane coating (3-APTES group). The modified surfaces were characterized by water contact angle changes, ATR/FTIR and AFM. Bovine collagen type I hydrogel was casted and allowed to gel overnight on the modified surfaces and then subjected to shear adhesion strength tests. Morphology of primary human corneal fibroblasts seeded on the modified PMMA surfaces was assessed by SEM.

Results: ATR/FTIR showed the presence of respective coating on the PMMA surface. Oxygen plasma, plasma+HAp and DOPA+HAp treatment significantly enhanced the surface hydrophilicity of the PMMA (all p<0.05 compared to untreated PMMA). Water contact angle produced by 3-APTES treatment (71.99±0.90^o) was slightly increased relative to that of untreated PMMA (68.43±3.00^o; p=0.09). AFM revealed relatively rough surface after plasma+HAp (RMS = 294.33±38.43 nm) and DOPA+HAp treatment (337.77±109.89 nm), but they are not significantly different (p=0.499). There was a decrease in surface roughness after 3-APTES coating (8.25±1.10 nm) relative to after plasma treatment (18.58±1.19 nm; p<0.001). On SEM, human corneal fibroblasts were able to maintain their normal morphology on all treated surfaces, comparable to cells seeded on cover slips. Plasma+HAp yielded the best shear adhesion strength with collagen hydrogel (179.50 ± 29.99 mN/cm²), followed by DOPA+HAp (159.50 ± 26.56 mN/cm²), 3-APTES (133.25 ± 20.23 mN/cm²) and plasma treatment (114.50±11.68 mN/cm²). All treatments produced significantly better adhesion strength with collagen hydrogel than untreated PMMA (67.25±10.09 mN/cm²; p<0.05).

Conclusions: HAp coating can potentially be used to enhance the interfacial seal between PMMA optical cylinder and collagen hydrogel. Our study also suggests that collagen hydrogel can be used as donor corneal substitute for Boston keratoprosthesis and thereby, reducing our heavy dependence on transplant-grade donor corneas in the future.