Hydrogel presents as foreign material to the host and participates in immune responses which would skew the biofunctions of immunologic loads (antigen and adjuvants) for in-situ DC priming. This study...

Hydrogel microparticles (HMPs) have been widely applied in biological, pharmacologic, and biomedical industries due to their versatility. Particle size is a paramount factor for controlling drug release profiles from HMPs. Conventional fabrication methods such as bulk emulsion, coacervation, and spray drying do not offer a precise size control and high reproducibility, which may compromise the utility of HMPs for controlled release. Here, we report a dropletbased microfluidic synthesis method for the precise fabrication of HMPs. Functionalized polysaccharides/protein fluid mixtures were emulsified into monodisperse droplets in light mineral oil using a flow-focusing device and well mixed in precursor droplets through a serpentine mixing channel before the solidification of HMPs. The homogenized precursor polymers cross-link in the droplets by catalyst-free Michael addition. As a demonstration of the controlled release of a model drug from the HMPs, fluorescein-labeled immunoglobulin G (F-IgG) and bevacizumab were encapsulated in the HMPs of different diameters for measuring its release dynamics over time. The release kinetics of F-IgG from the HMPs was shown to be controllable by altering the particle size while keeping other parameters unchanged. Around 70% of bevacizumab released from DX HMPs was functional. Both HA and DX HMPs showed no cytotoxicity in the HEK293 cell line. We anticipate that this approach could be used as a general method to fabricate HMPs made of hydrophilic polymers for the controlled release of biotherapeutics.

The controlled release of antigen from the injectable depots have been actively pursued to achieve long-lasting immune responses in vaccine development. Nonetheless, subcutaneous depots are often susceptible to foreign body...