The Experimental Study Of A Special Hydrogel Orbital Implant (PHEMA And MMA)

Objective To investigate the biocompatibility of hydrogel orbital implant experimentally and the rate of vascular izat ion of the implant to form the foundation for its clinical applications.Methods The implant was made of copolymerized 2-hydroxyethyl methacryate (HEMA) with methl methacrylate (MMA). Several experiments have been carried out to evaluate the properties of the implants such as SEM, TGA(Thermogravimetric analysis), subcutaneous implantation in rabbits and compress experiment, ect. We took three experiments by using three different surgical methods. Experiment one :thirty-two hydrogel orbital implants were implanted into the right orbit of 32 New Zealand albino rabbits. The vascularization of the implants was evaluated by SPECT and light microscopy, immunohistochemistry, SEM, TEM (2, 4, 8,12 and 24 weeks after implantation) .Experiment two: thirty hydrogel orbital implants were implanted into the right orbits of 30 New Zealand albino rabbits with sclera wrapping. The vascularization of the implants was evaluated by SPECT and light microscopy.Experiment three: fifteen hydrogel orbital implants were implanted into the right orbit of 15 New Zealand albino rabbits in combination of sclera wrapping with cornea. The vascularization of the implants was evaluated by SPECT and light microscopy.Results MMA denaturative PHEMA had good extensibility with its volume expansive rate of 1. 2. The aperture ratio was 72. 1%. The SEM results showed that the orbital implant had the through-hole structure and the size of aperture was about 500um. TGA photos showed that the salts were wiped off completely. The compress strength of the materials increased with the volume ratio of MMA monomer in mixture and the suitable volume ratios were in the range from 25% to 35%. The copolymerization is useful to improve the compress properties of the polymer. All rabbits healed well after the implantation expect 1 rabbit had conjunction fissuration in experiment one . Incidence of short-term complications was 3. 1% and that of long-term complication was zero. SPECT examination showed that radiotracer gradually concertrated in the hydrogel orbital implants in vivo with time. By light microscopy, f ibrovascular tissue invaded the pores of the implant at 2 weeks and it went deeper from 4 to 8 weeks. Almost all implants were fullyvascularized after 12weeks, with relatively mild inflammatory reaction. Immunohistochemistry examination also showed the growth of fibrovascular tissue . Compared with the methods of implantation either by scleral wrapping or combination of scleral wrapping with auto-cornea , the method of implanting MMA denaturative PHEMA directly into orbital cavity showed faster vascularization. There were no significant differences in the incidence of complications of three methods, but the method with reserved cornea had a number of advantages such as small incision and simple operation process.Conclusion The aperture ratio of MMA denaturative PHEMA is above 70%, and it has steady quality, good histocompatibility and no reject reaction. Its porous structure is suitable for the ingrowing of fibrous vascular tissues. The full vascularization of the 14mm implants needs only 12 weeks. The soft and compressible implant make the surgery easier and safe and faster. The post-operation complication are rare and manageable. So, MMA denaturative PHEMA is a good material for the orbital implants, which are suitable for the clinical application.