A novel microencapsulation system : preparation and characterization of genipin cross-linked alginate-chitosan microcapsules for live cell oral delivery and other applications

Oral therapy utilizing artificial cell microencapsulation has shown promise in the treatment of many diseases. The key requirements of microcapsules for such applications include biocompatibility, mechanical stability, permeability and resistance to the human gastrointestinal (GI) environment. In particular, preservation of structural integrity is crucial when live genetically engineered cells are used. One of the main obstacles in the progress of this strategy is attaining biocompatible and stable microcapsules.This thesis aims to develop a suitable microcapsule system, the genipin crosslinked alginate-chitosan (GCAC) microcapsule, for live cell oral delivery. The preparation procedure, including calcium-alginate ionotropic gelation, coacervative chitosan coating and covalent cross-linking by genipin, was established and optimized. Control factors affecting the formation of microcapsule membrane were identified. The structural and physical characteristics of GCAC microcapsules, such as mechanical stability, swelling characteristics, permeability, controlled release, degradation, and others were investigated and compared with earlier established microcapsule systems including alginate-chitosan and alginate-poly-L-lysine-alginate (APA). In addition, live cell oral delivery features were evaluated with a computer controlled dynamic simulated human GI model using genetically engineered Lactobacillus plantarum 80 cells as an example.Results show that by incorporating genipin, a new class of GCAC microcapsule system can be formulated. Results also show that covalent cross-linking by genipin considerably enhanced the microcapsule stability and durability while maintaining permeability similar to that of the APA membrane. The GCAC membrane possessed strong resistance to structural degradation and GI impediments, while providing a favorable microenvironment for cell proliferation and survival in harsh GI conditions.In addition, this research found that the fluorogenic attributes of genipin can be exploited to characterize the microcapsule membrane by confocal laser scanning microscopy. A simple, in situ, and non-destructive approach was established and extended to assess other microcapsule systems. Rapid determination of coating material distribution, binding intensity, and membrane thickness on a routine basis was achieved using this novel and superior method.This work highlights the immense potential of the novel genipin cross-linked alginate-chitosan microcapsule as an oral delivery vehicle for live therapeutic cells and other important applications. Further studies will investigate its full potential for artificial cell oral therapy