Oxygen-Purged Microfluidic Device to Enhance Cell Viability in Photopolymerized PEG Hydrogel Microparticles

Encapsulating cells within biocompatible materials is a widely used strategy for cell delivery and tissue engineering. While cells are commonly suspended within bulk hydrogel-forming solutions during gelation, substantial interest in the microfluidic fabrication of miniaturized cell encapsulation vehicles has more recently emerged. Here, we utilize multiphase microfluidics to encapsulate cells within photopolymerized picoliter-volume water-in-oil droplets at high production rates. The photoinitiated polymerization of polyethylene glycol diacrylate (PEGDA) is used to continuously produce solid particles from aqueous liquid drops containing cells and hydrogel forming solution. It is well understood that this photoinitiated addition reaction is inhibited by oxygen. In contrast to bulk polymerization in which ambient oxygen is rapidly and harmlessly consumed, allowing the polymerization reaction to proceed, photopolymerization within air permeable polydimethylsiloxane (PDMS) microfluidic devices allows oxygen to be replenished by diffusion as it is depleted. This sustained presence of oxygen and the consequential accumulation of peroxy radicals produce a dramatic effect upon both droplet polymerization and post-encapsulation cell viability. In this work we employ a nitrogen microjacketed microfluidic device to purge oxygen from flowing fluids during photopolymerization. By increasing the purging nitrogen pressure, oxygen concentration was attenuated, and increased post-encapsulation cell viability was achieved. A reaction-diffusion model was used to predict the cumulative intradroplet concentration of peroxy radicals, which corresponded directly to post-encapsulation cell viability. The nitrogen-jacketed microfluidic device presented here allows the droplet oxygen concentration to be finely tuned during cell encapsulation, leading to high post-encapsulation cell viability

Targeted, Stimuli-Responsive Delivery of Plasmid DNA and miRNAs Using a Facile Self-Assembled Supramolecular Nanoparticle System

Gene therapy is rapidly regaining traction in terms of research activity and investment across the globe, with clear potential to revolutionize medicine and tissue regeneration. Viral vectors remain the most commonly utilized gene delivery vehicles, due to their high efficiency, however, they are acknowledged to have numerous drawbacks, including limited payload capacity, lack of cell-type specificity, and risk of possible mutations in vivo, hence, patient safety. Synthetic nanoparticle gene delivery systems can offer substantial advantages over viral vectors. They can be utilized as off-the-shelf components to package genetic material, display targeting ligands, and release payloads upon environmental triggers and enable the possibility of programmed cell-specific uptake and transfection. In this study, we have synthesized three functional polymeric building blocks that, in a rapid, facile, tailorable, and stage-wise manner, associate through both electrostatic and noncovalent hydrophobic “host–guest” interactions to form monodisperse self-assembled nanoparticles (SaNP). We show that these SaNPs successfully package significant amounts of microRNA through to plasmid DNA, present desired ligands on their outer surface for targeted receptor-mediated cell-specific uptake and affect efficient translation of packaged plasmids. We confirm that these SaNPs outperform commercially available, gold standard transfection agents in terms of in vitro transfection efficiencies and have very low cytotoxicity. With facile self-assembly and tailorable composition, our SaNP gene delivery system has significant potential in targeted gene therapy applications