Biohydrogels, composed of naturally occurring biopolymers are typically preferred over their synthetic analogues in bioapplications thanks to their biocompatibility, bioactivity, mechanical or degradation properties. Shaping biohydrogels on the single-cell length scales (micrometers) is a key ability needed to create bioequivalent artificial cell/tissue constructs and cannot be achieved with current methods. This work introduces a method for photolithographic synthesis of arbitrarily shaped microgels composed purely of a biopolymer of choice. The biopolymer is mixed with a sacrificial photocrosslinkable polymer, and the mixture is photocrosslinked in a lithographic process, yielding anisotropic microgels with the biopolymer entrapped in the network. Subsequent ionic or covalent biopolymer crosslinking followed by template cleavage yields a microgel composed purely of a biopolymer with the 3D shape dictated by the photocrosslinking process. Method feasibility is demonstrated with two model polysaccharide biopolymers (alginate, chitosan) using suitable crosslinking methods. Next, alginate microgels were used as microtaggants on a pharmaceutical oral solid dose formulation to prevent its counterfeiting. Since the alginate is approved as an additive in the food and pharmaceutical industries, the presented tagging system can be implemented in practical use much easier than systems comprising synthetic polymers. @en

A controlled synthesis of polymeric particles is becoming increasingly important because of emerging applications ranging from medical diagnostics to self-assembly. Centrifugal synthesis of hydrogel microparticles is a promising method, combining rapid particle synthesis and the ease of manufacturing with readily available laboratory equipment. This method utilizes centrifugal forces to extrude an aqueous polymer solution, sodium alginate (NaALG) through a nozzle. The extruded solution forms droplets that quickly cross-link upon contact with aqueous calcium chloride (CaCl2) solution to form hydrogel particles. The size distribution of hydrogel particles is dictated by the pinch-off behavior of the extruded solution through a balance of inertial, viscous, and surface tension stresses. We identify the parameters dictating the particle size and provide a numerical correlation predicting the average particle size. Furthermore, we create a phase map identifying different pinch-off regimes (dripping without satellites, dripping with satellites, and jetting), explaining the corresponding particle size distributions, and present scaling arguments predicting the transition between regimes. By shedding light on the underlying physics, this study enables the rational design and operation of particle synthesis by centrifugal forces.@en