Microfluidic designing of polymeric microcapsules with size-selective permeability

Abstract

Semipermeable microcapsules have a great potential in protection of catalysts, controlled release of drugs, and platform for microcapsule type sensor. However, a method to create such microcapsules with precisely controlled cut-off value and high mechanical stability remains an important challenge. Here in we report three microfluidic approaches to create polymer microcapsules with size-selective permeability.

First approach is to utilize phase separation of homopolymer blends in ultra-thin middle layer of double-emulsion drops. The blend strongly confined in two-dimensional space exhibit local phase separation, instead of global separation. This enables the perforation of microcapsule membrane by selectively removing one of the phase-separated polymeric domains. The resultant monolithic membrane has uniform pores which connect the interior and the exterior of the microcapsules, thereby providing size-selective permeability. The pore size can be precisely tuned by regulating the extent of phase separation

this enables the control of cutoff value for permeation.

Second approach is to employ polymerization-induced phase separation between crosslinked polymer and oil to enhance organic solvent resistance and biocompatibility of the microcapsules. Upon UV illumination on double-emulsion drops whose ultrathin middle layer is composed of photocurable resin and inert oil, the monomers are photopolymerized, which leads to phase separation between the polymerized resin and the oil within the ultrathin shell. Subsequent dissolution of the oil leaves behind regular pores in the polymerized membrane providing size-selective permeability. The degree of phase separation can be further tuned by adjusting the fraction of oil in the shell or the affinity of the oil to the monomers, thereby enabling the control of the cutoff value of permeation.

Finally, I suggest polymerization-induced microphase separation with in situ block polymer formation approach for creating semipermeable microcapsules which has more delicate controllability over size and porosity of porous membrane. Copolymerization of styrene and divinylbenzene (DVB) in the presence of PLA macro-chain transfer agent (PLA-CTA) via reversible addition-fragmentation chain transfer (RAFT) process produced a crosslinked PS-b-PLA precursor with a disordered bicontinuous morphology consisting of PS and PLA microdomains, and PLA etching out of the precursor yielded the desired nanoporous membrane. Pore size is finely controlled by varying molecular weight of PLA block in a range of 5-30 nm.

We introduce three different strategy of fabricating semipermeable microcapsule with controlled permeability. High mechanical stability and chemical resistance of the microcapsules, as well as controllable permeability and high encapsulation efficiency, will provide new opportunity in a wide range of applications.