Bifunctional methacryloyl-norbornene gelatin chemistry enables tunable bioinks for soft tissue engineering via digital light processing

Photocrosslinkable gelatin derivatives are promising bioinks for soft tissue engineering, but their use in cell-laden digital light processing (DLP) requires a balance between tunable mechanics, printability and cytocompatibility. Here, we report a small library of photocrosslinkable gelatin-based precursor formulations for cell-laden DLP, with the broader aim of generating a versatile platform for soft tissue engineering rather than a formulation restricted to one tissue model. A bifunctional methacryloyl-norbornene gelatin (GelMANB) was developed to combine methacryloyl chain-growth polymerisation with norbornene-mediated thiol-ene crosslinking and was benchmarked against gelatin methacryloyl (GelMA). GelMANB formulations containing different thiolated crosslinkers were evaluated to determine the influence of crosslinking chemistry as well as polymer concentration on network formation and physico-chemical properties. Thiol-ene formulations enabled broad tuning of hydrogel stiffness and exhibited rapid photocrosslinking, while crosslinker selection further influenced swelling and tensile behaviour. Selected GelMANB/dithiothreitol (GelMANB/DTT) and GelMANB/thiolated gelatin (GelMANB/GelSH) formulations were subsequently processed via DLP alongside GelMA. Optimised exposure conditions enabled reproducible fabrication of porous scaffolds that retained dimensional stability under osmotic pressures relevant to several soft tissues. Following cell-laden printing, human foreskin fibroblasts remained viable after seven days, reaching 95.0{+/-}5.9% viability in GelMANB/DTT and 94.9{+/-}2.7% in GelMANB/GelSH, compared with 87.2{+/-}6.0% in GelMA. In 2-mm-thick hydrogel discs, GelMANB/GelSH supported the most sustained fibroblast elongation, reaching 30.9{+/-}6.3% elongated cells at day 7, although elongated cells were mainly confined to the outer surface layers. Porous scaffolds with 400 m struts and 1.3 mm pores reduced the characteristic hydrogel thickness and enhanced elongated morphology across all formulations, highlighting GelMANB as a modular platform for cell-laden soft tissue biofabrication.