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

Abstract

pH-responsive hydrogels are recognized as versatile sensors and actuators due to their unique time-dependent properties. Specifically, pH-sensitive hydrogel-based bilayers exhibit remarkable bending capabilities when exposed to pH-triggered swelling. This study introduces a semi-analytical technique that combines non-linear solid mechanics with ionic species transport to investigate the bending behavior of such bilayers. The technique is validated through numerical simulations, exploring the influence of kinetic and geometric properties on bilayer behavior. The results highlight the significance of the interfacial region, particularly in configurations with lower hydrogel geometric ratios, which are susceptible to rupture. The study also uncovers the benefits of a lower hydrogel layer ratio in improving the swelling rate and final deflection, with a stronger effect observed in the presence of a buffer solution. Additionally, the compressibility of the elastomer contributes to the durability of the final bent shape. These findings enhance our understanding of pH-sensitive hydrogel-based bilayers and offer valuable insights for their design and optimization in diverse applications.

Evaluation of Alginate Hydrogel Microstrands for Stromal Cell Encapsulation and Maintenance

“…Using the SiS technique, we could easily and reproducibly fabricate alginate hydrogel microstrands with diameters of around 200 µm, whose swelling properties remained relatively constant during 7 days of incubation with DMEM, evidenced by their mass swelling ratio and connective porosity. In the future, the chemo-mechanical model [106,107] can be used to better understand the swelling behavior and mechanical properties of these alginate hydrogel microstrands.…”

Dynamic, Viscoelasticity-Driven Shape Change of Elastomer Bilayers

“…55 The main drawback of these stimulus-sensitive designs is that faster temporal responses require thinner bilayers due to the diffusion limit of heat or solvent as well as the penetration depth of light and modeling can help predict, which parameters to vary to hasten swelling. 56 One way to overcome the diffusion limitation is to use a strain-induced stimulus or "mechanical programming", which has been applied to bilayers with fiber orientation variation between the two layers similar to the seedpod. 57 Systems that respond to an applied deformation do not necessarily need to be of limited size.…”

“…An interesting variant is a system with cross-sectional heterogeneity like the cucumber tendril and the ability to preferentially align fibers to affect helical pitch like the seedpod . The main drawback of these stimulus-sensitive designs is that faster temporal responses require thinner bilayers due to the diffusion limit of heat or solvent as well as the penetration depth of light and modeling can help predict, which parameters to vary to hasten swelling …”

Semi-analytical modeling of electro-strictive behavior in dielectric elastomer tube actuators

“…Soft actuators and sensors represent a groundbreaking field in modern engineering, with the ability to respond to various stimuli, including temperature [1,2], chemical triggers [3,4], and electric signals [5][6][7][8][9]. Dielectric actuators have emerged as a crucial player, driving many recent engineering marvels.…”