Multicore-Shell PNIPAm-co-PEGMa Microcapsules for Cell Encapsulation

The overall goal of this study was to fabricate multifunctional core-shell microcapsules with biological cells encapsulated within the polymer shell. Biocompatible temperature responsive microcapsules comprised of silicone oil droplets (multicores) and yeast cells embedded in a polymer matrix (shell) were prepared using a novel micro-array approach. The cross-linked polymer shell and silicone multicores were formed in situ via photopolymerization of either poly(N-isopropylacryamide) (PNIPAm) or PNIPArn, copolymerized with poly(ethylene glycol monomethyl ether monomethacrylate) (PEGMa) within the droplets of an oil-in-water-in-oil double emulsion. An optimized recipe yielded a multicore-shell morphology, which was characterized by optical and laser scanning confocal microscopy (LSCM) and theoretically confirmed by spreading coefficient calculations. Spreading coefficients were calculated from interfacial tension and contact angle measurements as well as from the determination of the Hamaker constants and the pair potential energies. The effects of the presence of PEGMa, its molecular weight (M-n 300 and 1100 g/mol), and concentration (10, 20, and 30 wt %) were also investigated, and they were found not to significantly alter the morphology of the microcapsules. They were found, however, to significantly improve the viability of the yeast cells, which were encapsulated within PNIPAm-based microcapsules by direct incorporation into the monomer solutions, prior to polymerization. Under LSCM, the fluorescence staining for live and dead cells showed a 30% viability of yeast cells entrapped within the PNIPAm matrix after 45 min of photopolymerization, but an improvement to 60% viability in the presence of PEGMa. The thermoresponsive behavior of the microcapsules allows the silicone oil cores to be irreversibly ejected, and so the role of the silicone oil is 2-fold. It facilitates multifunctionality in the microcapsule by first being used as a template to obtain the desired core-shell morphology, and second it can act as an encapsulant for oil-soluble drugs. It was shown that the encapsulated oil droplets were expelled above the volume phase transition temperature of the polymer, while the collapsed microcapsule remained intact. When these microcapsules were reswollen with an aqueous solution, it was observed that the hollow compartments refilled. In principle, these hollow-core microcapsules could then be filled with water-soluble drugs that could be delivered in vivo in response to temperature.