Transient swelling of cylindrical hydrogels under coupled extension-torsion: Analytical and 3D FEM solutions

Abstract

To design more accurate soft sensors and actuators, there is a significant requirement for the application of complicated deformation conditions. Coupled extension-torsion is a type of deformation which may be utilized in the property characterization of materials with complex behavior such as soft hydrogels. Hydrogels with coupled diffusion and large deformation behavior have intricate kinetics which should be studied in detail. In this work, a robust semi-analytical procedure is proposed to capture the transient behavior of cylindrical hydrogels in combined loading of extension and torsion in different conditions. Moreover, the whole problem with the same conditions is simulated in COMSOL-Multiphysics as a verification framework of the proposed semi-analytical procedure, where comparing the results shows a good agreement. The results demonstrate that the transient behavior of the cylindrical hydrogel under coupled extension-torsion is significantly dependent on the rate of the deformation and material properties. Besides, since the hydrogel undergoes a highly nonlinear swelling in this deformation regime, the simulations predict a complicated reaction force and moment. Visualizing the effect of different parameters engaged in the material shows the robust behavior of the proposed semi-analytical procedure, which can be employed in constitutive models’ calibration as well as in the design and optimization of hydrogels structures.

pH-Sensitive Hydrogel Bilayers: Investigation on Transient Swelling-Induced Bending through Analytical and FEM Approaches

“…One of the primary stages in exploring hydrogels involves formulating theories that describe their behavior. The classical theory of swelling established the mechanisms of swelling in neutral hydrogels by applying the widely recognized polymer solution theory, commonly referred to as the Flory-Huggins theory [6]. Furthermore, scientists have investigated the triggers that can prompt swelling behavior in hydrogels.…”

“…Furthermore, scientists have investigated the triggers that can prompt swelling behavior in hydrogels. The primary stimuli include temperature [6], pH [7], magnetic field [8], and light [9]. Examples include Gels 2023, 9, 563 2 of 19 temperature-sensitive hydrogels, such as Poly(ethylene glycol) (PEG) [10], which undergo reversible swelling in response to temperature changes, enabling their use in wound healing and drug delivery applications.…”

“…To gain a thorough understanding of hydrogel behavior and attributes, it is essential to use models of hydrogel swelling. Two swelling models are commonly used: steadystate models [9,12,13] and transient models [6,14]. While steady-state models describe a hydrogel at equilibrium, where its behavior is assumed to be independent of time, this assumption may not always hold for hydrogel swelling.…”

“…The process of diffusion through hydrogel swelling is intricate and dependent on time. As a result, modeling hydrogel behavior at equilibrium may not always effectively capture the characteristics of hydrogel deformation behavior critical to their performance [6]. Studies have recently focused on incorporating hydrogel kinetics into their theories to produce more accurate predictions of time-dependent swelling behavior [6].…”