An in-situ photocrosslinking microfluidic technique to generate non-spherical, cytocompatible, degradable, monodisperse alginate microgels for chondrocyte encapsulation

Alginate microgels are widely generated by ionic crosslinking methods, but this method has limitations in controlling the microgel degradation and generating non-spherical microgels. By employing oxidized methacrylated alginate (OMA) that is degradable and photocrosslinkable, we have successfully photocrosslinked monodisperse OMA microgels and demonstrated the feasibility to generate discoid alginate microgels. However, several technical issues obstructed our opto-microfluidic method from being a useful technique. Here, we further characterized and optimized this method. Monodisperse discoid OMA microgels with good shape consistency were, for the first time, generated. The curability of OMA microgels was characterized as the macromer concentration varied from 2% to 10%, and the minimum required photoinitiator (VA-086) concentrations were determined. The effects of crosslinking density and the presence of ions in the storage solution on swelling of OMA hydrogels were identified to give insights into accurate controlling of the microgel size. A much quicker degradation rate (within three weeks) compared to ionically crosslinked alginate hydrogels was indirectly identified by quantifying the elastic modulus using atomic force microscopy. The viability of encapsulated chondrocytes in OMA microgels formed by this method was higher than those from other existing methods, demonstrating its favorable cytocompatibility. It was found that the oxygen tension played a critical role in both the curability of microgels and the cytocompatibility of this technique. We also summarize common practical issues and provide related solutions and/or operational suggestions. By this method, OMA microgels are expected to be valuable alternatives to traditional ionically crosslinked alginate microgels in drug delivery, tissue engineering, and single cell analysis areas due to their multiple favorable properties.