Physikochemische und biologische Charakterisierung von texturiertem Silikon als Grundlage für die Entwicklung eines Retina-Patchs
Retinal detachment (RD) and proliferative vitreoretinopathy (PVR) are serious eye diseases and lead to visual lost and blindness. They are caused by retinal breaks and foramina. The consequence is that the neurosensoric retina detaches from retinal pigment epithelium. Retina-Patchs in form of open-porous foils of polydimethylsiloxane (PDMS) could be a new possibility for closing the retinal breaks. It is intended that the Retina-Patch will be placed epiretinally at the retinal break and be fixed by proliferation of Müller cells (glial cells) located in the retina in the pores of the Retina-Patch. In this study, it was investigated whether textured silicone (TS) complies with the basic requirements to use it for the development of the ophthalomologic product Retina-Patch. Textured silicone is manufactured by the company Polytech-Silimed (Dieburg, D) in large-scale amount for the production of silicone-textured mamma implants. Samples of this material were provided by the company for this study. The textured silicone is characterized by non-porous and a porous side. The experimental part of this study worked on the physico-chemical and of TS and the growth of glial cells on this material in vitro. In detail, the micro structure of the surface texture, the hydrophilization of TS through surface modification, and the covalent protein immobilization were investigated. Furthermore, the cell growth behavior of glial cells were analyzed with the model of the cell line U373 (humane astrocytes). A further focus of this study was the investigation of the influence of anionic functionalization on the cell growth with the cell lines U373 and L929 (mice fibroblasts). The surface texture of TS is characterized by a big amount of pores. The pore size varies between 37 and 518 µm. The mean of the pore size is 84 µm. Small pores (60-90 µm) are most frequent. The inhomogeneity of the pore size distribution is caused by the manufacturing process. With contact angle measuring, the stability of the hydrophilization of TS through surface modification was proved. Graft co-polymerization with allylamine and functionalization with carboxyl groups are the only modification methods to hydrophilize TS longterm. The long-term stability of the hydrophilization through COOH-functionalization is only maintained under storing in water. Plasma treatment with oxygen plasma and anionic functionalization did not hydrophilize TS. Plasmasterilization with hydrogenperoxide plasma increased the hydrophobicity of TS. The influence of surface modification on the proteinadsorption of TS is proved. On plasma modified TS, a protein amount significantly higher than on unmodified resp. Aminfunctionalized TS is adsorbed. With EDC/NHS method, BSA could be covalently immobilized on TS functionalized with carboxyl groups (18,1 molecules/10 nm²). With cross-linking, a 1,64-fold higher protein amount could be immobilized. The density of carboxyl groups was 850 molecules/10 nm². The in vitro growth of glial cells (U373 cells) as model cells for a part of the retinal cell population on textured silicone was influenced by sterilization, pore size, and protein type. Plasmasterilization increased significantly cell density and physiologic activity in contrast to steam sterilization. Furthermore, glial cells grew in larger pores (> 50 µm) with the whole cell body and were physiologically active with these pores. In smaller pores, the glial cells proliferated only with the pseudopodes. In addition, BSA coating increased significantly the physiological activity of U373 cells in long-term in contrast to collagen I coating. In vitro studies demonstrated the increasing of cell density and cell spreading of U373 and L929 cells on PDMS after anionic functionalization. Low degrees of functionalization (25-50%) increased significantly the cell density in contrast to high degrees (100%). Furthermore, the cell spreading decreased with increasing functionalization degree. The results of this study demonstrate in vitro that textured silicone can be fixed epiretinally by glial cells. This is the fundament for the development of the ophthalmologic application retina-patch. The digression to the project retina-stimulator demonstrates that the epiretinal fixation of laserperforated silicone foils by tissue ingrowth in the pores of the foils is successfull in vivo on the animal model rabbit. This result has to be verified with textured silicone in future investigation. The use of textured silicone in other applications (e. g. drug delivery system) has to be considered in further development, too.
info:eu-repo/classification/ddc/610, Tissue Engineering, Scaffold attached region, Oberflächenbehandlung, Implantatwerkstoff, Augenkrankheit, Netzhaut, Medizin, Retina-Patch, surface modification, retinal detachment
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