INVESTIGATION OF A NOVEL MICROCAPSULE MEMBRANE INTEGRATING POLYETHYLENE GLYCOL TO ALGINATE, POLY-L-LYSINE AND CHITOSAN MICROCAPSULES FOR THE APPLICATION OF LIVER CELL TRANSPLANTATION

Abstract

P668 Aims: Liver transplantation is the main form of therapy for most liver diseases. A major drawback to transplantation is the lack of donors and continuous requirement of immunosuppressants. Microencapsulation is an emerging technology which can be used to entrap isolated hepatocytes for cell transplanation as an alternative treatment to several liver diseases. One of the limiting factors in the progress of such therapy is attaining a biocompatible polymer enabling the long-term entrapment and growth of the hepatocytes without causing adverse host immune responses. Presently the most commonly studied membranes are the alginate-poly-l-lysine-alginate (APA) and alginate-chitosan (AC) microcapsules, however there remain limitations associated with these membranes. In the current study, improvements to the biocompatibility and stability of these membranes are investigated by the addition of a polyethylene glycol (PEG) coating and the potential of a novel membrane combining alginate, poly-l-lysine, chitosan and PEG is studied with the objective of proposing a membrane most suitable for cell entrapment. Methods: Five different microcapsules were prepared including APA, APA with PEG, AC, AC with PEG and the novel alginate-chitosan-PEG-PLL-alginate (ACPPA) microcapsule. Mechanical strength of the capsules were assessed using an osmotic pressure test and a rotational stress test. A fluorescence reader (FLx800) was used to detect permeability of dextran through the membranes. Morphological studies on capsule integrity in serum was observed microscopically. Cytotoxicity tests were perfomed by encapsulating Human HepG2 cells and performing an MTT calorimetric assay for monitroing metabolic activity. Further studies on immuno protection using macrophages and cryopreservation potential are also to be investigated. Results: Microcapsules of approximately 400+/-30μm were prepared. Stability tests, using osmotic pressure techniques, reveal the addition of PEG resulted in an increase in mechanical stability of both APA and AC capsules by over 50%. The rotational stress test indicate the novel membrane formulation to exhibit mechanical strength similar to APA membranes and greater than the AC, ACPEG and APPEG microcapsules. The ACPPA membrane was found to retain integrity in FBS. Cytotoxicity tests using human HepG2 cells indicate low viability of AC membranes however, positive MTT was observed for the remaining 4 membranes studied which implies that the addition of PEG can support cellular growth. Conclusions: Results support previous studies which indicate PEG may improve biocompatibility of polymers. The integration of PEG to microcapsules enhances mechanical strength and supports the proliferation of liver cells. This study confirms that the novel membrane combining PLL, chitosan and PEG shows similar mechanical properties as APA capsules. As previous studies indicate that APA encapsulated cells can result in cell growth and protein adhesion to the membrane surface, the new membrane may be an alternative biomaterial for microencapsulation cell therapy.