Development of open-source in situ photocrosslinking printhead attachments for extrusion bioprinting of hydrogel matrices

Extrusion-based bioprinting is a well-established biofabrication technique, employed extensively in tissue engineering applications. While advances have been made in improving biomaterials and equipment for greater print fidelity, limitations in extrusion-based bioprinting of photocrosslinkable hydrogels in particular limit printability and construct stability. Thus, in situ photocrosslinking has been investigated for use of low viscosity, photocrosslinkable bioinks. This is achieved through application of target light of a specific wavelength to form crosslinked polymer networks during extrusion. Various in situ photocrosslinking studies have demonstrated the potential of this concept; however, the specificity and compatibility of these in situ photocrosslinking technologies remain unrefined, generally utilising bulk light exposure or bioprinting equipment not readily available within the field. Here, an in situ photocrosslinking system was developed for use with the commercially available BICO CELLINK BioX™ bioprinters when equipped with either standard or temperature controlled print heads. Utilising our open-source, customisable attachment system, available to users via GitHub, we produced high fidelity bioprinted constructs from various photocrosslinkable materials. Ultimately, we demonstrate the effectiveness of this open-source in situ photocrosslinking system for use with cell-laden hydrogel biomaterials, which exhibit improved print fidelity while maintaining high cell viability, validated with rheological characterisation and computational simulations.