Investigation of the 4th dimension of PEGDA hydrogel architected by Digital Light Processing 3D printing

4D printing enables the fabrication of objects capable of undergoing programmed transformations in response to external stimuli. Among these objects, hydrogels stand out due to their ability to swell or contract depending on water absorption or loss. Although their 4D behaviour has been widely observed, a comprehensive methodology to quantify, model, and programme these deformations is still lacking. The aim of this study is to provide a systematic and thorough methodology for the experimental and numerical characterisation of 4D properties. Poly(ethylene glycol) diacrylate was used as a model monomer, and the influence of the monomer-to-water ratio on the 4D behaviour of hydrogels was investigated. An approach combining experimental characterisation and finite element simulations was developed to link this ratio to the accuracy of the programmed movements. Experimental analyses, including Fourier-transform infrared spectroscopy, scanning electron microscopy, and digital microscopy, allowed the structure and morphology of the objects to be characterised. Finite element simulations, incorporating water diffusion and mechanical stress analysis, enabled precise prediction and programming of deformations. The results demonstrate that optimisation of the monomer-to-water ratio allows control over the accuracy of deformations and affects print quality. This approach provides a comprehensive and reproducible methodological framework for the study and design of 4D objects, offering a structured basis to characterise and programme their transformations.