Stimuli‐responsive hydrogels with programmable shapes produced by defined patterns of particles are of great interest for the fabrication of small‐scale soft actuators and robots. Patterning the particles in the hydrogels during fabrication generally requires external magnetic or electric fields, thus limiting the material choice for the particles. Acoustically driven particle manipulation, however, solely depends on the acoustic impedance difference between the particles and the surrounding fluid, making it a more versatile method to spatially control particles. Here, an approach is reported by combining direct acoustic force to align photothermal particles and photolithography to spatially immobilize these alignments within a temperature‐responsive poly(N‐isopropylacrylamide) hydrogel to trigger shape deformation under temperature change and light exposure. The spatial distribution of particles can be tuned by the power and frequency of the acoustic waves. Specifically, changing the spacing between the particle patterns and position alters the bending curvature and direction of this composite hydrogel sheet, respectively. Moreover, the orientation (i.e., relative angle) of the particle alignments with respect to the long axis of laser‐cut hydrogel strips governs the bending behaviors and the subsequent shape deformation by external stimuli. This acousto‐photolithography provides a means of spatiotemporal programming of the internal heterogeneity of composite polymeric systems.more » « less
- Award ID(s):
- NSF-PAR ID:
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
A vision for soft, autonomous materials entails synthesis of multiple senses in multifunctional materials where material response requires sensitivity to external stimuli. Stimuli-responsive hydrogels are of particular interest for optically induced mechanical response due to the ability to transform external stimuli into large, reversible shape change. Specifically, temperature-responsive hydrogels are broadly used and can be designed to achieve deformation through the photothermal effect as a result of surface plasmonic resonance of gold nanoparticles. Here, a multi-material stimuli-responsive hydrogel network with embedded gold nanoparticles is demonstrated in a unit cell pattern with anisotropic swelling behavior in response to visible light. Reversible, anisotropic swelling leads to bending motion that contributes to the development of soft, autonomous materials.more » « less
Shape morphing of stimuli‐responsive composite hydrogels has received considerable attention in different research fields. Although various multilayer structures with dissimilar materials are studied to achieve shape morphing, combining swellable hydrogel layers with non‐swellable layers results in issues with interface adhesion and structural integrity. In this study, single‐hydrogel‐based bilayer actuators comprising poly(
N‐isopropylacrylamide) (PNIPAM) matrices and graphene oxide (GO)–PNIPAM hinges are presented. Upon temperature rising, the PNIPAM hydrogel acts as the passive layer due to the formation of dense microstructures near the surface (i.e., the skin layer effect), whereas the GO‐PNIPAM hydrogel functions as the active layer, maintaining porous due to structural modification by the presence of GO. Under light exposure, the GO‐PNIPAM hinges experience selective heating due to the photothermal effect of GO. Consequently, the resulting bilayer structures exhibit programmable dual‐responsive 3D shape morphing. Additionally, the folding kinetics of these actuators can be adjusted based on the applied stimulus (temperature changes or light), as they are driven by different mechanisms, the skin layer, or photothermal effects, respectively. Furthermore, the hinge‐based bilayer structures demonstrate walking and steering locomotion by light exposure. This approach can lead to advances in soft robotics, biomimetic systems, and autonomous soft actuators in hydrogel‐based systems.
Non‐spherical stimuli‐responsive polymeric particles have shown critical importance in therapeutic delivery. Herein, pH‐responsive poly(methacrylic acid) (PMAA) cubic hydrogel microparticles are synthesized by crosslinking PMAA layers within PMAA/poly(
N‐vinylpyrrolidone) hydrogen‐bonded multilayers templated on porous inorganic microparticles. This study investigates the effects of template porosity and surface morphology on the PMAA multilayer hydrogel microcube properties. It is found that the hydrogel structure depends on the template's calcination time and temperature. The pH‐triggered PMAA hydrogel cube swelling depends on the hydrogel's internal architecture, either hollow capsule‐like or non‐hollow continuous hydrogels. The loading efficiency of the doxorubicin (DOX) drug inside the microcubes is analyzed by high‐performance liquid chromatography (HPLC), and shows the dependenceof the drug uptake on the network structure and morphology controlled by the template porosity. Varying the template calcination from low (300 °C) to high (1000 °C) temperature results in a 2.5‐fold greater DOX encapsulation by the hydrogel cubes. The effects of hydrogel surface charge on the DOX loading and release are also studied using zeta‐potential measurements. This work provides insight into the effect of structural composition, network morphology, and pH‐induced swelling of the cubical hydrogels and may advance the development of stimuli‐responsive vehicles for targeted anticancer drug delivery.
Stimuli responsive hydrogels that can change shape in response to applied external stimuli are appealing for soft robotics, biomedical devices, drug delivery, and actuators. However, existing 3D printed shape morphing materials are non‐biodegradable, which limits their use in biomedical applications. Here, 3D printed protein‐based hydrogels are developed and applied for programmable structural changes under the action of temperature, pH, or an enzyme. Key to the success of this strategy is the use of methacrylated bovine serum albumin (MA–BSA) as a biodegradable building block to Pickering emulsion gels in the presence of
N‐isopropylacrylamide or 2‐dimethylaminoethyl methacrylate. These shear‐thinning gels are ideal for direct ink write (DIW) 3D printing of multi‐layered stimuli‐responsive hydrogels. While poly( N‐isopropylacrylamide) and poly(dimethylaminoethyl methacrylate) introduce temperature and pH‐responsive properties into the printed objects, a unique feature of this strategy is an enzyme‐triggered shape transformation based on the degradation of the bovine serum albumin network. To highlight this technique, protein‐based hydrogels that reversibly change shape based on environmental temperature and pH are fabricated, and irreversibly altered by enzymatic degradation, which demonstrates the complexity that can be introduced into 4D printed systems.
null (Ed.)Stimuli-responsive hydrogel strain sensors that synergize the advantages of both soft-wet hydrogels and smart functional materials have attracted rapidly increasing interest for exploring the opportunities from material design principles to emerging applications in electronic skins, health monitors, and human–machine interfaces. Stimuli-responsive hydrogel strain sensors possess smart and on-demand ability to specifically recognize various external stimuli and convert them into strain-induced mechanical, thermal, optical, and electrical signals. This review presents an up-to-date summary over the past five years on hydrogel strain sensors from different aspects, including material designs, gelation/fabrication methods, stimuli-responsive principles, and sensing performance. Hydrogel strain sensors are classified into five major categories based on the nature of the stimuli, and representative examples from each category are carefully selected and discussed in terms of structures, response mechanisms, and potential medical applications. Finally, current challenges and future perspectives of hydrogel strain sensors are tentatively proposed to stimulate more and better research in this emerging field.more » « less