Physicochemical and nanomechanical behaviour of 3d printed pegda hydrogel structures for tissue engineering applications

Poly(ethylene glycol) diacrylate (PEGDA) hydrogels are well established in tissue engineering and organ-on-chip applications as scaffolds for 3D templates in aqueous environments due to their high water content, biocompatibility and low toxicity. The versatility of PEGDA hydrogels as a platform for cell encapsulation and tissue engineering is attributed to their ability to be modified in various ways, including concentration, molecular weight, and polymerisation technique. Since properties of the PEGDA host material will affect the functionality of the cells and tissues, and vice versa, a key missing feature of the currently developed screening solutions is the lack of proper understanding of the behaviour of the 3D printed PEGDA soft support structures holding living tissues in a dynamic human like tissue microenvironment. Thus, the aim of this research is to demonstrate repeatability and reliability in the measurement of physicochemical and nanomechanical properties of multilayer 3D printed UV crosslinked PEGDA hydrogels for use in organ-on-chip devices. The research offers insights into long term stability of hydrogels through studying how changes in both environmental and printing parameters can be extrapolated to other biomaterials for benefit of other tissue engineering applications. Recent advancements in the use of PEGDA hydrogels for tissue engineering are reviewed, with a focus on bulk cross-linking and 3D printing synthesis methods. Characterisation methods for 3D printed PEGDA hydrogels are also discussed. The current state of development of biomedical applications, particularly in organ on-chip devices, is highlighted. The thermal response of multilayer PEGDA hydrogels made using in-house projection lithography was compared to monolithic hydrogels created through bulk photo-cross-linking. The results indicated that the volume of multilayer PEGDA hydrogels changes in response to the temperature with dimensional change between +10% and -11.5%, and also displaying an anisotropic characteristic where the axial dimensional change was higher than the lateral dimension. The results also confirmed the swelling behaviour to be reversible between 8 and 45 °C. The nanomechanical properties of monolithic and multilayer PEGDA hydrogels fabricated through bulk cross linking and layer-by-layer projection lithography were studied. The findings showed that an increase in the number of layers results variation in axial elastic modulus between 1.69 and 0.67 MPa. Additionally, the research examines the structural heterogeneity of 3D printed hydrogels which is linked to the degree of cross-linking of the printed layers and showed variations in lateral elastic modulus between 2.8 and 11.9 kPa. The results suggest that by controlling the cross linking throughout the 3D printed structure, the surface nanomechanical properties of the hydrogels can be manipulated to direct cell attachment and adhesion in specific regions within the structure, offering potential for future improvement in the reproducibility and reliability of 3D printed hydrogels for tissue engineering and organ-on-chip applications.