# Comprehensive Characterisation of Photocurable PEGDA/Gelatine Hydrogels for Extrusion-Based 3D Printing

## TL;DR

This study develops and characterizes photocurable hydrogel inks for 3D printing, showing they can be tuned for mechanical properties and are safe for cell growth after washing.

## Contribution

A novel PEGDA–gelatine–collagen ink formulation with optimized rheology, tuneable stiffness, and low cytotoxicity after washing is introduced.

## Key findings

- The Herschel–Bulkley model best described the inks' flow behavior.
- Washing significantly reduced residual photoinitiator and improved cell viability.
- PeGeCol_10_2 ink enabled high-fidelity printing of large anatomical models.

## Abstract

The development of photocurable hydrogel biomaterial inks with suitable rheology, low cytotoxicity, and tuneable mechanical properties is essential for reliable biofabrication. This study aimed to formulate PEGDA–gelatine–collagen inks using lithium phenyl-2,4,6-trimethylbenzoylphosphinate (LAP) as photoinitiator. Rheological characterisation and flow-model fitting were performed, mechanical stiffness modulation under different light intensities was evaluated, complex structures were printed using direct extrusion and FRESH methodologies, and PEGDA/LAP extractables were quantified by NMR after controlled washing procedures. In vitro assays assessed cell viability and proliferation on the resulting scaffolds. The Herschel–Bulkley model best described the flow behaviour across formulations; while viscoelastic measurements showed that increasing light intensity progressively enhanced hydrogel stiffness, enabling fine control over final mechanical properties. NMR analysis showed that washing removed a substantial fraction of residual LAP, in agreement with the biological findings: fibroblasts failed to survive on unwashed scaffolds but exhibited robust proliferation and recovered their characteristic elongated morphology on washed constructs. Among all inks, PeGeCol_10_2 provided the best combination of shear-thinning behaviour, structural integrity, low residual photoinitiator, and tuneable mechanics. Using this formulation, we successfully printed large anatomical models with high fidelity and excellent handling properties, underscoring its potential for soft-tissue prosthetics and broader tissue-engineering applications.