Nanoindentation Response of 3D Printed PEGDA Hydrogels in a Hydrated Environment

Mohammad Hakim Khalili; Craig J Williams; Christian Micallef; Fabian Duarte-Martinez; Ashfaq Afsar; Rujing Zhang; Sandra Wilson; Eleftheria Dossi; Susan A Impey; Saurav Goel; Adrianus Indrat Aria

doi:10.1021/acsapm.2c01700

Nanoindentation Response of 3D Printed PEGDA Hydrogels in a Hydrated Environment

ACS Appl Polym Mater. 2023 Jan 20;5(2):1180-1190. doi: 10.1021/acsapm.2c01700. eCollection 2023 Feb 10.

Authors

Affiliations

¹ Surface Engineering and Precision Centre, School of Aerospace, Transport and Manufacturing, Cranfield University, Cranfield MK43 0AL, U.K.
² The Henry Royce Institute, Department of Materials, The University of Manchester, Manchester M13 9PL, U.K.
³ School of Chemistry, University of Edinburgh, David Brewster Road, Edinburgh EH9 3FJ, U.K.
⁴ Centre for Defence Chemistry, Cranfield University, Shrivenham, Swindon SN6 8LA, U.K.
⁵ Sophion Bioscience A/S, Baltorpvej 154, 2750 Ballerup, Denmark.
⁶ London South Bank University, 103 Borough Road, London SE1 0AA, U.K.
⁷ University of Petroleum and Energy Studies, Dehradun 248007, India.

Abstract

Hydrogels are commonly used materials in tissue engineering and organ-on-chip devices. This study investigated the nanomechanical properties of monolithic and multilayered poly(ethylene glycol) diacrylate (PEGDA) hydrogels manufactured using bulk polymerization and layer-by-layer projection lithography processes, respectively. An increase in the number of layers (or reduction in layer thickness) from 1 to 8 and further to 60 results in a reduction in the elastic modulus from 5.53 to 1.69 and further to 0.67 MPa, respectively. It was found that a decrease in the number of layers induces a lower creep index (C_IT) in three-dimensional (3D) printed PEGDA hydrogels. This reduction is attributed to mesoscale imperfections that appear as pockets of voids at the interfaces of the multilayered hydrogels attributed to localized regions of unreacted prepolymers, resulting in variations in defect density in the samples examined. An increase in the degree of cross-linking introduced by a higher dosage of ultraviolet (UV) exposure leads to a higher elastic modulus. This implies that the elastic modulus and creep behavior of hydrogels are governed and influenced by the degree of cross-linking and defect density of the layers and interfaces. These findings can guide an optimal manufacturing pathway to obtain the desirable nanomechanical properties in 3D printed PEGDA hydrogels, critical for the performance of living cells and tissues, which can be engineered through control of the fabrication parameters.