Surface Modification And Characterization Of Cornea Repair Materials By Plasma

Chitosan and fluorosilicone acrylates （FSA） have been widely used for cornea repair studyand application. But chitosan’s poor surface hydrophilicity and low surface free energy,together with the lack of cell-recognition sites restrict the adhesion and propagation of cell onits surface. The peculiar molecular structure of FSA makes it a promident material for makingrigid gas permeable contact lens （RGP）. But the surface hydrophobicity makes the lensunwettable for the tears, and the non-polar interaction between the surface unpolar groupswith the tear protein will lead to the surface protein and lipid adsorption. The study focusedon the surface modification and characterization of chitosan membrane and RGP contact lensin order to improve surface hydrophilicity and biological properties by plasma surfacetreatment and graft polymerization.The surface properties of chitosan membrane were characterized by angle-resolved X-rayphotoelectron spectroscopy （XPS）. The results indicated that the polar groups （-OH） onchitosan membrane migrated into the membrane bulk, which made the surface hydrophobicwith low surface free energy. The surface nitrogen mainly exists in the form of–NH₂. The-CONH₂groups on chitosan molecule also distributed into the membrane bulk.In this study, chitosan membranes were surface modified by oxygen and nitrogen plasmarespectively. The surface hydrophilicity of chitosan membrane was greatly improved byoxygen plasma treatment. The mechanism for surface hydrophilicity improvement was thesurface oxidation after plasma treatment and exposure to air. Through this kind of surfaceoxidation, polar groups, such as–OH,-COO, H₂N-C=O were incorporated onto chitosanmembrane surface. The optimal plasma condition for chitosan surface treatment was100Wand60s. Higher plasma power or longer exposure time will bring about surface etching. Noevident morphology change was observed, but surface roughness increased slightly afterplasma treatment. Nitrogen plasma can also improve the surface hydrophilicity of chitosanmembrane. But the effect was not so evident compared with oxygen plasma. The surfacecontact angle decreased to about65°when the plasma power was100W and exposure timewas60s. Some kind of nitrogen can be incorporated onto chitosan membrane surface with theform of O=C-NH₂. The surface oxidation of chitosan membrane after exposing to air was still the main mechanism of surface activitation, which induced the improvement of surfacehydrophilicity and surface free energy.For the ageing effect of plasma treatment, the incorporated polar groups on chitosanmembrane surface will migrated into the membrane bulk gradually. This kind of redistributionof polar groups induced the recovery of surface hydrophobicity. The aging effect of chitosanmembrane after plasma treatment lasted for about10days before the surface contact anglereaching the value of untreated sample.Ar plasma induced surface graft of PEG onto chitosan membrane surface was carried out inthe study. The thickness of the grafted PEG layer was in the order of10nm indicated by XPSresults. The surface graft ratio depends on the monomer concentration and argon plasmacondition. The optimal monomer concentration was10%under the plasma power of100Wand plasma exposure time of60s. Methoxy polyethylene Glycol Monomethacrylate （PEGMA）was more favorable for surface graft of chitosan membrane than Polyethylene GlycolDimethacrylate （PEGDA） for its higher graft ratio under the same condition. The surfacehydrophilicity and surface free energy of chitosan membrane were improved by the graft ofPEGMA on membrane surface. The surface roughness was increased by the grafted PEGchain. The surface modified chitosan membrane has a good protein adsorption property. Andthe human corneal epithelial cell （HCEC） cell adhesion on chitosan membrane surface wasstrengthened.Oxygen, nitrogen and argon plasma were applied in the study for RGP lens surfacetreatment respectively. They all could improve the surface hydrophilicity of RGP lens. Themain reason for the improvement of surface hydrophilicity was the incorporation ofoxygen-containing groups on RGP lens surface. The chemical state of Si was changed fromsilixane （Si-CH3） into hydrophilic Si-O through the broken of Si-C bond. The formation of theinorganic Si-O was the main reason for the surface hydrophilicity improvement. Some C-Obond on RGP surface was also broken by plasma treatment, and transformed into O-C=O,which was another reason for the surface hydrophilicity improvement. Nitrogen plasma canintroduce O=C-NH₂group onto RGP lens surface. The reaction between the radicalsgenerated by plasma treatment and air oxygen was the main mechanism for surface oxidation.And the introduced oxygen was mainly in the state of Si-O. The effect of plasma treatment on surface morphology depends on the plasma power. Compared with oxygen and nitrogenplasma, argon plasma has a more strong influence on surface morphology by surface etching.The optimal condition for plasma treatment is100W and1₂0s. Ar plasma with higher powerwill induced the increase of surface roughness by surface etching.PEGMA can be grafted successfully onto RGP surface through Ar plasma induced graftpolymerization. The thickness of the grafted PEG layer is in the order of several nanometers.The surface graft ratio depends on the monomer concentration. And the graft ratio reaches themaximum when the monomer concentration is10%with water as the solvent. After the graftof PEGMA, the surface hydrophilicity of RGP was improved, and the surface adsorption ofprotein on RGP surface was decreased greatly compared with the untreated sample. Thesurface modified RGP lens showed good cell compatibility.