Organic interfacial film is of great interest for biological applications, because the formed film, containing tailor-made functional group, could fine-tune intrinsic interfacial properties such as biomolecular adsorptions and cell-adhesion characteristics as well as mechanical rigidity, permeability, and wettability. Due to its potential abilities, the formation of organic interfacial film has been attempted for biomedical device technology, biosensor and bioelectronics, and cell encapsulation. Among a variety of biological applications, cell encapsulation with organic interfacial film provides chemical tools for endowing living cells, in a programmed fashion, with exogenous properties that are neither innate nor naturally achievable, such as UV filtration and immunogenic shielding, as well as enhanced tolerance in vitro against lethal factors in real-life settings. So it promises various practical applications, such as whole-cell catalysis and sensors, cell therapy, tissue engineering, probiotic packaging, and provides a basic platform for studying cellular differentiation and communications.
Many different materials have been utilized as a cell-encapsulation material with proper choice of synthetic strategies. For successful cell encapsulation, living cells should be encapsulated with cytocompatible materials under mild conditions. Conventional cell encapsulation with organic interfacial film is usually based on layer-by-layer (LbL) assembly of polyelectrolytes. However, laborious and multistep process has been one of major challenges in the LbL-based cell encapsulation, because repeated purification and concentration steps are required during LbL assembly. Since polyphenolic chemistry (e.g. catechol/pyrogallol chemistry) was introduced in substrate-independent coating, it has been succeeded to simply form organic film on solid substrate under mild condition. So, based on the polyphenolic chemistry, one-pot formation of organic film at various interface is also feasible and, by extension, applied to cell encapsulation.
In this thesis, organic interfacial films, composed of polyphenolics, were formed for cell encapsulation, and could be categorized as follows. (1) Polydopamine thin film at hydrogel-water interface: cytoprotective alginate/polydopamine core/shell microbeads; in this part, the alginate/polydopamine core/shell microbeads were developed by forming the polydopamine film at hydrogel-water interface. Although alginate hydrogel beads swell uncontrollably and are physicochemically labile, the resulting alginate/polydopamine core/shell microbeads were mechanically tough, prevented gel swelling and cell leakage, and increased resistance against enzymatic attack and UV-C irradiation. (2) Polydopamine thin film at hydrogel-water interface: control of cell growth in alginate/polydopamine core/shell microbeads; cell encapsulation not only protects cells from harmful environments by physically isolating them from the outside media, but also has the potential to tailor the release profile of the encapsulated cells. However, the microbial release has not yet been controlled tightly, leading to undesired detrimental exposure of microorganisms to the outside. This challenge could be simply solved by forming ultrathin but robust polydopamine film at hydrogel-water interface. The alginate/polydopamine core/shell microbeads effectively suppressed the microbial growth rate, while maintaining the cell viability, resulting in controlling cell release. (3) Ferric ion-tannic acid metal-organic complex thin film at interfaces through biphasic supramolecular self-assembly: novel chemical strategy for cell encapsulation; in this case, the interfacial supramolecular self-assembly and film formation of ferric ions and tannic acid in biphasic systems was reported, where ferric ion and tannic acid come into immiscible phases. Its versatility is demonstrated with various biphasic systems: hollow microcapsules, encasing microbial or mammalian cells, are generated at the water-oil interface in a microfluidic device; a cytoprotective ferric ion-tannic acid film was formed at hydrogel-water interface for probiotic encapsulation; a pericellular ferric ion-tannic acid shell forms on individual Saccharomyces cerevisiae. The formation of organic interfacial film for cell encapsulation will advance chemical manipulability of living cells and also suggest a simple but versatile structural motif in materials science.