Long-term interleukin-4 release from 3D printable affinity hydrogels promotes M2-like macrophage polarisation <i>in vitro</i>

The biopharmaceutical industry for engineered protein drugs is rapidly increasing in size but there is a lack of controlled release vehicles to enable targeted delivery for regenerative medicine applications. In this study, we used photocrosslinkable 3-sulfopropyl acrylate potassium salt (SPAK)-poly(ethylene glycol) diacrylate (PEGDA) hydrogels to achieve controlled release of lysozyme for 70 days with zero-order release and tuneable release rate. Scaling down hydrogel volume and protein loading concentration to release Transforming growth factor beta-1 (TGF-β1) and Interleukin-4 (IL-4) resulted in low cumulative release, even without SPAK. Increasing PEGDA molecular weight from 4 kDa to 20 kDa improved TGF-β1 release but it still remained below 10% after 10 days. We observed sustained IL-4 release in the therapeutic ng mL^-1 range for 73 days when loading IL-4 to 5% SPAK-10% PEGDA post photocrosslinking. Released IL-4 maintained bioactivity, promoting M2-like polarisation of THP-1 macrophages with day 53 supernatant, modelling long-term immunomodulation <i>in vitro</i>. We manufactured SPAK-PEGDA hydrogels by projection micro stereolithography, in which 3D printed 5% SPAK-10% PEGDA had an increased lysozyme release rate compared to its cast counterpart. 3D printed 5% SPAK-10% PEGDA with porous 3D design had an increased lysozyme release rate compared to a volume matched non-porous design. These findings highlight the potential of SPAK-PEGDA hydrogels for long-term cytokine delivery and show proof-of-concept for manipulating protein release kinetics with 3D printed hydrogel design.