Synthesis, test, calibration and modeling of a temperature-actuated hydrogel bilayer

Abstract

Smart structures such as temperature-sensitive actuators made of soft hydrogels can be useful for designing biomedical devices. In this study, free swelling and force generation behavior of a bilayer actuator based on thermo-sensitive poly(N-isopropylacrylamide) (PNIPAM) hydrogel and an elastomer under various loading profiles has been investigated. The thermo-sensitive hydrogel was synthesized by redox-initiated radical polymerization. We then prepared a bilayer actuator made of temperature-sensitive PNIPAM hydrogel, and examined its behavior under different loading conditions such as free swelling and force generation to study different aspects of the response of the hydrogel, including homogeneous free swelling and confined swelling using two approaches for (monolayer) hydrogel. Experiments on free swelling and force generation swelling of the bilayer actuator were also performed. After implementing an appropriate hydrogel constitutive model within a finite element framework, material parameters (of both the hydrogel and an elastomer) required in fabrication of the bilayer were calibrated. Using these calibrated material parameters, the same test conditions were simulated, and the numerical results were compared to those of experiments; a good agreement was observed between the experimental tests and numerical outcomes. The results show that the material model parameters are reliable, and the finite element method can be used for designing more complicated structures based on thermo-sensitive hydrogels.

Fluidic Infiltrative Assembly of 3D Hydrogel with Heterogeneous Composition and Function

“…Thermo-responsive hydrogel bilayers incorporating PNIPAAm as its thermosensitive element have been previously reported in literature and are generated by either forming one layer on top of another after complete gelation of the former or by adhering two layers together using an adhesive. [65][66][67][68][69] These bilayers are often employed as actuators in solutions that bend as the temperature exceeds the LCST of PNIPAAm. The PNIPAAm-co-PAAm-co-RHO precursor had a lower density than the PAAm-co-FOA precursor so we designed the mold such that the less dense precursor could enter from above and the denser precursor could enter from below (Figure 4c ii).…”

Dynamic, Viscoelasticity-Driven Shape Change of Elastomer Bilayers

“…The polymer layers are typically hydrogels where the active layer swells more than the passive layer resulting in bending toward the passive layer. The swelling can be solvent (i.e., water)-, temperature-, pH-, electric-field- or ionic strength-induced. − Folding into more sophisticated final shapes can be achieved via photopatterning, lithography, or 3D printing (for 4D printing). − Seedpod-like twisting has also been mimicked by imparting orientational order into polymer and elastomeric bilayers to generate solvent − - or temperature − -induced twisting, as well as pH-, ionic strength-, and light-induced shape change. Some highly engineered materials can respond to multiple stimuli such as temperature and solvent, photothermal or electro-thermal, and UV light, NIR, solar, and heat .…”

Effect of sodium chloride on the enhanced performance of chitosan-based ion actuator

“…In recent years, the researchers found that the actuate membrane materials including sodium alginate [8] , cellulose, chitosan [9][10][11][12] . Due to their unique three-dimensional network structure and ability to retain a large amount of water, ion actuator had a wide range of applications in hydrogel arti cial muscles [13] including biomedical applications, drug carriers [14][15] , biosensors [16] , medical devices [17] , tissue engineering [18] , separation systems [19][20] , micro uidic systems [21] , microvalves [22] and actuator [23][24] . Chitosan (CS) was a product of natural chitin.…”