ABSTRACT CORNEA ENGINEERING ON BIODEGRADABLE POLYESTERS Zorlutuna, Pinar M. Sc., Department of Biotechnology Supervisor: Prof. Vasif Hasirci Co-Supervisor: Asst. Prof. AySen Tezcaner January 2005, 66 pages Cornea is the outermost layer of the eye and has an important role in vision. Damage of cornea due to injuries or infections could lead to blindness lowering the quality of life of the patient severely. In such cases, transplantation or artificial corneas have been used for treatment but both had drawbacks. The novel approach for corneal replacements is the tissue engineering of the cornea, a promising method which would be free of these drawbacks, if successful. In this study, carriers for tissue engineering of the cornea were designed and tested in vitro. Blends of biodegradable and biocompatible polyesters of natural (PHBV8) and synthetic (PLLA) origin were used to construct these carriers. For the epithelial layer of the cornea, PLLA-PHBV8 micropatterned films were prepared with solvent casting and seeded with D407 (retinal pigment epithelial) cells. In order to achieve proper cell growth, the films were coated with fibronectin. For the stromal layer of the cornea, highly porous foams of PLLA-PHBV8 were prepared by lyophilization and seeded with 3T3 cells (fibroblasts). A new approach was developed to create a combination of the film and the foam to obtain a surface patterned, 3 dimensional cell carrier. These carriers were seeded with Saos-2 cells (osteosarcoma cells) in the preliminary optimization studies and with D407 and 3T3 cells in further studies. The cell numbers on the carriers were quantified by using MTS assay (non-radioactive cell proliferation assay) and the cell proliferation on polymeric carriers was significantly higher than that of control (Tissue culture polystyrene) by the day 14. Characterization of these cells and the carrier was done using a variety of microscopic methods. The micrographs showed that the foam had a highly porous structure and the pores were interconnected. 3T3 cells were found to be distributed quite homogeneously at the seeding site, but due to the high thickness of the foam, the cells could not sufficiently populate the core (central parts of the foam) during the given incubation time. The micropatterned film allowed multilayer formation of D407 cells. The functionality of the cells seeded on the carriers was examined by immunohistochemistry. These analyses proved that the cells retained their phenotype during culturing. D407 cells formed tight junctions characteristic of epithelial cells, and 3T3 cells deposited collagen type I into the foams. Based on the results, it can be concluded that the 3-D PLLA-PHBV8 construct with surface patterns have a serious potential for use as a tissue engineering carrier for the reconstruction of the cornea. Key words: Tissue engineering, cornea, polymeric carrier, biodegradable, polyester.

It is estimated that 90% of new chemical entities in development pipelines exhibit poor aqueous solubility. For compounds not limited by biological membrane permeability, this poor aqueous solubility is the limiting factor in bioavailability. Therefore, the formulation of such drugs has primarily been centered on improving dissolution properties. Traditional approaches for overcoming poor aqueous solubility include salt formation of the active ingredient, complexation, the use of surface active agents, formulation into oil based systems, particle size reduction, or a combination of these methods. More recently amorphous solid dispersions have been explored. Currently, the drug loading within solid dispersions is limited resulting in large quantities of the formulation being required for a therapeutically relevant dose. In the frame of the work herein, Thin Film Freezing was utilized to generate high drug loaded amorphous solid dispersions of the poorly water soluble drug phenytoin utilizing a hydrophilic polymer or an amphiphilic graft copolymer for system stabilization. Additionally a new solvent removal technique, atmospheric freeze drying, was investigated for removal of the solvents used during Thin Film Freezing. The Thin Film Freezing materials were subsequently incorporated into a polymeric carrier for solid dispersion formulation by a novel fusion production technique termed Kinetisol® dispersing. Studies of the solid dispersions produced by Thin Film Freezing revealed an amorphous system had been obtained for both stabilizing polymers. The formulation containing a hydrophilic carrier was capable of achieving supersaturation. Conversely, the amphiphilic graft copolymer demonstrated a phenytoin-polymer interaction resulting in poor dissolution. Atmospheric freeze drying of the Thin Film Freezing product demonstrated that the alternative drying technique generated powders with significantly improved handling properties as a result of reduced electrostatic interactions due to the increased pore size, reduced surface area, larger particle size, and higher, though acceptable, residual solvent levels. The use of Thin Film Freezing powders during Kinetisol Dispersing resulted in a single phase amorphous system while solid dispersions produced from physical mixtures of bulk materials were amorphous two-phase systems. This indicates that the use of amorphous drug compositions during solid dispersion production may increase drug loading in the final system while remaining single phase in nature. / text