Mechanics of inhomogeneous large deformation of photo-thermal sensitive hydrogels

Abstract

a b s t r a c tA polymer network can imbibe copious amounts of solvent and swell, the resulting state is known as a gel. Depending on its constituents, a gel is able to deform under the influence of various external stimuli, such as temperature, pH-value and light. In this work, we investigate the photo-thermal mechanics of deformation of temperature sensitive hydrogels impregnated with light-absorbing nano-particles. The field theory of photo-thermal sensitive gels is developed by incorporating effects of photochemical heating into the thermodynamic theory of neutral and temperature sensitive hydrogels. This is achieved by considering the equilibrium thermodynamics of a swelling gel through a variational approach. The phase transition phenomenon of these gels, and the factors affecting their deformations, are studied. To facilitate the simulation of large inhomogeneous deformations subjected to geometrical constraints, a finite element model is developed using a user-defined subroutine in ABAQUS, and by modeling the gel as a hyperelastic material. This numerical approach is validated through case studies involving gels undergoing phase coexistence and buckling when exposed to irradiation of varying intensities, and as a microvalve in microfluidic application.

Stimulus-active polymer actuators for next-generation microfluidic devices

“…Nanocomposites of elastin-like polypeptides and graphene sheets have been developed and feature response times in the order of seconds or even less and improved control over the location of actuation [119]. In [120], the photothermal deformation mechanics of a temperature-sensitive hydrogel impregnated with light-absorbing nanoparticles was studied theoretically by considering the equilibrium thermodynamics of a swelling gel using a variational approach; additionally a case study in which the composite was employed as a microvalve was presented. Jadhav et al [121] used a composite of PNIPAAm and polypyrrole (PPy) nanoparticles to realize a photoresponsive microvalve for remote actuation with NIR-laser irradiation for flow control in microfluidic devices.…”

Constitutive modeling for polymer hydrogels: A new perspective and applications to anisotropic hydrogels in free swelling

“…(48) and (49) One feasible case is that the two families of fibers are coincident, which, for convenience, 28 takes the form, 29 where φ denoting the initial angle between the two families of fibers. This case, in physics,…”

“…One 45 choice is to reinforce the traditional single-network hydrogels in specific directions with 46 specific materials, such as inorganic clay (Haraguchi et al, 2005), woven rough knitted 47 fabrics (Young et al, 1998), cellulose nano-fibers (Osorio-Madrazo et al, 2012). The 48 reinforced phase plays roles in producing the anisotropic mechanical property and improving 49 the toughness and strength of the material. The synthesized hydrogels show a broad range of 50 mechanical properties that could mimic the toughness and anisotropy of biological tissues, 51 M A N U S C R I P T A C C E P T E D ACCEPTED MANUSCRIPT such as porcine heart valves (Mohammadi, 2011) and aorta and heart valve leaflets (Millon 1 and Wan, 2006).…”

Study of swelling behavior of temperature sensitive hydrogels considering inextensibility of network

“…Smart hydrogels composed of covalently cross-linked polymeric network which can response to environmental stimuli such as temperature [1][2][3], pH [4][5][6], mechanical load [7,8], ionic and salt concentration [9,10], light [11][12][13] and electric field [14,15] and can imbibe large amount of water and experience a large deformation. These materials can be used as sensor and actuator simultaneously.…”