Developing an analytical solution for photo-sensitive hydrogel bilayers

Abstract

In this article, a new conceptual design of light-sensitive switches made of a soft bilayer is introduced. The bilayer structure consists of a photothermal-sensitive hydrogel strip attached to another neutral incompressible elastomeric layer. The bilayer is assumed to be initially flat under a uniform light irradiation. Decreasing the light intensity causes the bilayer to bend due to the inhomogeneous swelling of hydrogel layer and results in the switch actuation. To enlighten the actuation mechanism and investigate the influence of various parameters on the switch’s photomechanical response, an analytical method is developed to study the bilayer deformation due to the light-intensity variation under plane-strain condition. Additionally, the finite element analysis of the bilayer is conducted, implementing the relevant constitutive model into a finite element code. The deformation and stress inside the layers are studied both analytically and numerically for several cases. The numerical results verify the accuracy of the presented analytical method in this work. The influence of various material and geometrical parameters including each layer’s modulus, the thickness ratio of the layers, and the aspect ratio of the bilayer is investigated. The analytical method is found to be useful for proper design of the light-sensitive hydrogel-based switches.

Polyvinyl alcohol-poly acrylic acid bilayer oral drug delivery systems: A comparison between thin films and inverse double network bilayers

“…The ability of oral drugs to achieve desired effects is very much dependent on their release, which in turn is dependent on the biomaterials used to deliver the drugs by leveraging the large movements generated by these hydrogels upon stimulation. 2 Depending on the molecular structure of the specific polymers used, stimuli-responsive hydrogels are able to respond to changes in environmental stimuli such as pH, 6 temperature, 7 light 8 or ionic strength 9 with a change in their volume. Further, applications such as oral drug delivery systems benefit from having a bendable structure since such changes in shape potentially provide greater exposed surface area with increased attachment to the mucus layer.…”

“…1–3 Thin films are generally produced using conventional techniques such as photolithography, 4,5 and these bilayer hydrogels have demonstrated an ability to generate large deflections upon stimulation. 2 Depending on their molecular structure, stimulus-responsive hydrogels are able to respond to changes in the pH, 6 temperature, 7 light 8 or ionic strength 9 of the environment with a change in their volume. Through appropriate design of bilayer architecture, 10 these changes in volume may be converted into longitudinal, 11 folding, 12 rolling, 7 twisting 13 and bending movements 6 of the overall hydrogel construct.…”

Antibacterial smart hydrogels: New hope for infectious wound management

“…Under UV radiation, the triphenylmethane leuco dye is ionized into triphenylmethyl cations, and electrostatic repulsion between photogenerated ions causes photoinduced swelling. Light-active chromophores (azobenzene moieties, e.g., trisodium salt of copper chlorophyllin) can be incorporated into the polymer structure to synthesize a visible light hydrogel (e.g., 488 ​nm) [ 108 , 109 ]. The chromophore can absorb applied light, which is then disintegrated as heat, increasing the hydrogel's local temperature.…”

Modeling of photo-thermo-sensitive hydrogels by applying the temperature expansion analogy

“…The work of Nakamura et al (2017) presents also a simple numerical model for the thermodynamic state of a photoresponsive hydrogel with incorporated particles for a temperature increase of the gel induced by strong light. Kargar-Estahbanaty et al (2018) investigated a conceptual design and an analytical solution for light-sensitive bending switches of a soft hydrogel bilayer, based on a modified form of the free energy function and an analytical description of finite bending deformation. Mazaheri et al (2021) presented a 3D constitutive model for photo-thermal sensitive hydrogels based on a free energy decomposition.…”