A Biomimetic Bilayer Hydrogel Actuator Based on Thermoresponsive Gelatin Methacryloyl–Poly(N-isopropylacrylamide) Hydrogel with Three-Dimensional Printability

Abstract

Development of hydrogel-based actuators with programmable deformation is an important topic that arouses much attention in fundamental and applied research. Most of these actuators are nonbiodegradable or work under nonphysiological conditions. Herein, a temperature-responsive and biodegradable gelatin methacryloyl (GelMA)−poly(N-isopropylacrylamide) hydrogel (i.e., GN hydrogel) network was explored as the active layer of a bilayer actuator. Small-angle X-ray scattering (SAXS) revealed that the GN hydrogel formed a mesoglobular structure (∼230 Å) upon a thermally induced phase transition. Rheological data supported that the GN hydrogel possessed 3D printability and tunable mechanical properties. A bilayer hydrogel actuator composed of active GN and passive GelMA layers was optimized by varying the layer thickness and compositions to achieve large, reproducible, and anisotropic bending with a curvature of ∼5.5 cm −1 . Different patterns of the active layer were designed for actuation in programmable control. The 3D printed GN hydrogel constructs showed significant volume reduction (∼25−60% depending on construct design) at 37 °C with the resolution enhanced by the thermo-triggered actuation, while they were able to fully reswell at room temperature. A more intricate 3D printed butterfly actuator demonstrated the ability to mimic the wing movement through thermoresponsiveness. Furthermore, myoblasts laden in the GN hydrogel exhibited significant proliferation of ∼376% in 14 days. This study provides a new fabrication approach for developing biomimetic devices, artificial muscles, and soft robotics for biomedical applications.

Sustainable Robots 4D Printing

“…Reproduced with permission. [ 76 ] Copyright 2023, American Chemical Society. c) Soft strain sensor made of nanocellulose/nanochitin self‐healing hydrogel.…”

“…Huang et al [ 76 ] used GelMA and poly(N‐isopropyl acrylamide) hydrogel to create a temperature‐responsive and biodegradable hydrogel‐based actuator employing the bioprinting method. The actuator is capable of programmable deformation and has potential applications in biomimetic devices, artificial muscles, and soft robotics for biomedical purposes.…”

“…Regarding their applicability, biodegradable 3D/4D printed soft actuators are utilized in many fields, such as agriculture, [ 60 ] biomedicine, [ 61–93 ] micro positioning, [ 67,79,94–97 ] smart surgical instruments, [ 64,98–101 ] soft rehabilitation devices, [ 98,102,103 ] drug delivery microswimmers, [ 64,67,68,70,72,73,77,84,85,88,94,34,104–108 ] sustainable electronics devices, [ 109–111 ] soft smart fabrics, [ 64 ] muscle tissue membranes, [ 65,76,89,94,96,112,113 ] in‐vivo robotics, [ 67,74,83,86,89–91,93,99–101 ] wearable devices, [ 95,103,111,114–118 ] soft smart prosthetics, [ 114 ] bionic devices, [ 69,72,73,114 ] aeronautics, [ 119,120 ] health monitoring equipment, [ 111,118 ] edible robots, [ 121 ] biomimetic scaffolds, [ 30,62,76,97,115,122,123 ] environmental monitoring equipment, […”

4D-Printed Hydrogel Actuators through Diffusion-Path Architecture Design

“…Hydrogels possess unique properties, including high water content and biocompatibility, which make them highly versatile for a wide range of applications. One notable use is in the development of hydrogel actuators that exhibit stimuli-responsive behavior, allowing for precise control over their shape and size. – This capability enables programmable and dynamic motion, leading to the widespread adoption of hydrogel actuators in diverse fields, such as soft robotics, biomedical devices, energy harvesting, and environmental sensing. – Hydrogel actuation typically involves volumetric changes caused by structural inhomogeneity triggered by external stimuli such as temperature, pH, or light. The popular choice for hydrogel actuators is the bilayer design, consisting of an active layer and an inert layer, each exhibiting a distinct response to the stimulus. – The asymmetric volume expansion of these layers generates internal stress at the interface, resulting in a physical movement or deformation.…”

An Anisotropic Hydrogel by Programmable Ionic Crosslinking for Sequential Two-Stage Actuation under Single Stimulus

“…This is far from the deformation of natural organisms, such as the Venus flytrap [ 19 ], mimosa [ 20 ], and fern sporangia [ 21 ], etc., in response to an emergency. Bi-layer hydrogel actuators integrate different or even contrary functions on two sides [ 22 , 23 , 24 , 25 , 26 ], enabling simple unidirectional or bidirectional bending. The shape transformation driving force arises from the local asymmetric volume change caused by an imbalance in internal stress, especially at the interface.…”