Approach On The Function Of Nanometer TiO₂-coated PMMA Intraocular Lenses

PURPOSE: To compare the surface property of titanium dioxide (TiO₂) -coated polymethyl methacrylate (PMMA) intraocular lens (IOL) and noncoated PMMA IOLs. This may provide basic information for related study and clinical application in the future.METHODS: Ultraviolet A (UVA,λ=365nm, 4W, 382μW /cm2) was used as the excitation light source. The study consisted of two parts. Part One: The attribute of TiO₂/PMMA IOL was represented by means of water contact angle; Human lens epithelial cells(HLECs) adhesion test in vitro: after UVA pre-irradiation for different time (0min, 20min, 40min), the IOLs coated or non-coated with Nano-TiO₂ films were cultured with 2～3×104cells/mL of HLECs for 3 hours. At the end of culture, the number of cells adhering to the surfaces of the IOLs was counted under inversion phase microscope; Cell apoptosis test: after UVA illumination for different time(0 min,20 min,40min),cells were cultured for 5 hours, cell morphous was observed by TUNEL staining under ordinary light microscope and the apoptosis rate was evaluated by Image-Pro Plus analysis software. The surface energy components of the various substrates and HLECs were calculated based on Lifshitz-van del Waals/acid-base approach (LW-AB). The surface free energies obtained were used to calculate the interfacial free energies of adhesion (â–³Fadh ) of cells on various IOLs. Part Two: Platelets adhesion test:after the preparation of platelet rich plasma (PRP) by centrifugation, each IOL with the pre-irradiation for different minutes(0 min,10 min,30min) was cultured with 20μL PRP for 2 hours, then the platelets adhering to the IOL surface were observed with Wright staining and the adhesive rate was assessed by the analysis software; in Sterilization test:after the pre-irradiation of UVA for diffrernt time(0 min,10 min,30min), each IOL was placed under a culture of Staphylococcus aureus (S.A.,1×10⁵ colony forming units [CFU]/mL) or Escherichia coli (E.C.BL21, 1×10⁵ CFU /mL). After Gram staining, the survival percentage of S.A. was evaluated by software. The interfacial free energies of adhesion (â–³Fadh ) of two kinds of bacteria on various IOLs was calculated.RESULTS: The first part of the study showed that as the time of ultraviolet irradiation increased, the contact angle of TiO₂/PMMA IOL grew down apparently(P﹤0.01) comparing with the control group. Cell adhesion test showed that as the pre-irradiation time increased, the number of the adhering cells was significantly lower in the TiO₂-coated IOL group than the noncoated IOL group (P﹤0.01). TUNEL staining showed that most HLECs began apoptosing when exposed to UVA for 20min. The TiO₂/PMMA IOL group had a higher apoptosis rate than PMMA IOL group(P﹤0.01). The second part: As the pre-irradiation time extended, the number of platelets and bacteria sticking on TiO₂/PMMA IOL reduced and the number was notably lesser in the TiO₂-coated IOL group than the noncoated IOL group (P﹤0.01). After UVA pre-irradiation for 30min, platelets and S.A. showed lower adhesive and survival rate on TiO₂/PMMA IOL surface. And Wright and Gram staining showed that both the distribution of platelets and bacteria on TiO₂/PMMA IOL suface were scattered singly, while most were clustered together on the PMMA IOL surface. The facial adhesion free energies of HLECs and bacteria to TiO₂/PMMA IOL were both positive(â–³Fadhï¹¥0), while PMMA IOL were negative. So TiO₂/PMMA IOLs would be more unfavourable for cells and bacteria adhesion from the point of view of thermodynamics.CONCLUSION: (1) The TiO₂/PMMA IOLs coated with nano- TiO₂ thin film were shown to have smaller water contact angle and stronger hydrophilicity. And as the time of UVA irradiation extended, the angle got smaller and the hydrophilicity increased. (2) After UVA irradiation, the adhesion and growth of human lens epithelial cells, platelets, Staphylococcus aureus and Escherichia coli on the surface of TiO₂/PMMA IOL were all suppressed obviously. (3)The computation indicated that the facial adhesion free energy of HLECs, S. aureus and E. coli to TiO₂/PMMA IOLs elevated significantly, resulting an unfavourable intraocular surface for adhesion.