Project description:Photomechanical nanocomposites embedded with light-absorbing nanoparticles show promising applications in photoresponsive actuations. Near infrared (nIR)-responsive nanocomposites based photomechanical soft actuators can offer lightweight functional and underexploited entry into soft robotics, active optics, drug delivery, etc. A novel graphene-based photomechanical soft actuators, constituted by Polydimethylsiloxane (PDMS)/graphene-nanoplatelets (GNPs) layer (PDMS/GNPs) and pristine PDMS layer, have been constructed. Due to the mismatch of coefficient of thermal expansion of two layers induced by dispersion of GNPs, controllable and reversible bendings response to nIR light irradiation are observed. Interestingly, two different bending behaviors are observed when the nIR light comes from different sides, i.e., a gradual single-step photomechanical bending towards PDMS/GNPs layer when irradiation from PDMS side, while a dual-step bending (finally bending to the PDMS/GNPs side but with an strong and fast backlash at the time of light is on/off) when irradiation from PDMS/GNPs side. The two distinctive photomechanical bending behaviors are investigated in terms of heat transfer and thermal expansion, which reveals that the distinctive bending behaviors can be attributed to the differences in temperature gradients along the thickness when irradiation from different sides. In addition, the versatile photomechanical bending properties will provide alternative way for drug-delivery, soft robotics and microswitches, etc.
Project description:This article presents a soft pneumatic bending actuator using a magnetically assisted bilayer composite composed of silicone polymer and ferromagnetic particles. Bilayer composites were fabricated by mixing ferromagnetic particles to a prepolymer state of silicone in a mold and asymmetrically distributed them by applying a strong non-uniform magnetic field to one side of the mold during the curing process. The biased magnetic field induces sedimentation of the ferromagnetic particles toward one side of the structure. The nonhomogeneous distribution of the particles induces bending of the structure when inflated, as a result of asymmetric stiffness of the composite. The bilayer composites were then characterized with a scanning electron microscopy and thermogravimetric analysis. The bending performance and the axial expansion of the actuator were discussed for manipulation applications in soft robotics and bioengineering. The magnetically assisted manufacturing process for the soft bending actuator is a promising technique for various applications in soft robotics.
Project description:We report multi-responsive and double-folding bilayer hydrogel sheet actuators, whose directional bending response is tuned by modulating the solvent quality and temperature and where locally crosslinked regions, induced by ionoprinting, enable the actuators to invert their bending axis. The sheets are made multi-responsive by combining two stimuli responsive gels that incur opposing and complementary swelling and shrinking responses to the same stimulus. The lower critical solution temperature (LCST) can be tuned to specific temperatures depending on the EtOH concentration, enabling the actuators to change direction isothermally. Higher EtOH concentrations cause upper critical solution temperature (UCST) behavior in the poly(N-isopropylacrylamide) (pNIPAAm) gel networks, which can induce an amplifying effect during bilayer bending. External ionoprints reliably and repeatedly invert the gel bilayer bending axis between water and EtOH. Placing the ionoprint at the gel/gel interface can lead to opposite shape conformations, but with no clear trend in the bending behavior. We hypothesize that this is due to the ionoprint passing through the neutral axis of the bilayer during shrinking in hot water. Finally, we demonstrate the ability of the actuators to achieve shapes unique to the specific external conditions towards developing more responsive and adaptive soft actuator devices.
Project description:Stimuli-responsive hydrogel actuators have attracted tremendous interest in switches and microrobots. Based on N-isopropylacrylamide (NIPAM) monomers with LCST phase separation and photochromic molecule spiropyran which can respond to ultraviolet light and H+, we develop a novel multistimuli-responsive co-polymer anisotropic bilayer hydrogel, which can undergo complex deformation behavior under environmental stimuli. Diverse bending angles were achieved based on inhomogeneous swelling. By controlling the environmental temperature, the bilayer hydrogels achieved bending angles of 83.4° and -162.4° below and above the critical temperature of PNIPAM. Stimulated by ultraviolet light and H+, the bilayer hydrogels showed bending angles of -19.4° and -17.3°, respectively. In addition, we designed a strategy to enhance the mechanical properties of the hydrogel via double network (DN). The mechanical properties and microscopic Fourier transform infrared (micro-FTIR) spectrum showed that the bilayer hydrogel can be well bonded at the interfaces of such bilayers. This work will inspire the design and fabrication of novel soft actuators with synergistic functions.
Project description:Despite its widespread application in targeted drug delivery, soft robotics, and smart screens, magnetic hydrogel still faces challenges from lagging mechanical performance to sluggish response times. In this paper, a methodology of in situ generation of magnetic hydrogel based on 3D printing of poly-N-isopropylacrylamide (PNIPAM) is presented. A temperature-responsive PNIPAM hydrogel was prepared by 3D printing, and Fe2O3 magnetic particles were generated in situ within the PNIPAM network to generate the magnetic hydrogel. By forming uniformly distributed magnetic particles in situ within the polymer network, 3D printing of customized magnetic hydrogel materials was successfully achieved. The bilayer hydrogel structure was designed according to the different swelling ratios of temperature-sensitive hydrogel and magnetic hydrogel. Combined with the excellent mechanical properties of PNIPAM and printable magnetic hydrogel, 4D-printed remote magnetic field triggered shape morphing of bilayers of five-petal flower-shaped hydrogels was presented, and the deformation process was finished within 300 s.
Project description:Hydrogels actuators (HAs) that can reversibly respond to stimuli have applications in diverse fields. However, faster response rates and improved control over actuation timing and location are required to fulfill their potential. To address these criteria, we synthesized near-infrared light-driven HAs by interfacing genetically engineered elastin-like polypeptides with reduced-graphene oxide sheets. The resulting nanocomposites exhibited rapid and tunable motions controlled by light position, intensity, and path, including finger-like flexing and crawling. This work demonstrates the ability of rationally designed proteins to be combined with synthetic nanoparticles for the creation of macroscale functional materials.
Project description:Recently, four-dimensional (4D) shape-morphing structures, which can dynamically change shape over time, have attracted much attention in biomedical manufacturing. The 4D printing has the capacity to fabricate dynamic construction conforming to the natural bending of biological tissues, superior to other manufacturing techniques. In this study, we presented a multi-responsive, flexible, and biocompatible 4D-printed bilayer hydrogel based on acrylamide-acrylic acid/cellulose nanocrystal (AAm-AAc/CNC) network. The first layer was first stretched and then formed reversible coordination with Fe3+ to maintain this pre-stretched length; it was later combined with a second layer. The deformation process was actuated by the reduction of Fe3+ to Fe2+ in the first layer which restored it to its initial length. The deformation condition was to immerse the 4D construct in sodium lactate (LA-Na) and then expose it to ultraviolet (UV) light until maximal deformation was realized. The bending degree of this 4D construct can be programmed by modifying the pre-stretched lengths of the first layer. We explored various deformation steps in simple and complex constructs to verify that the 4D bilayer hydrogel can mimic the curved morphology of the intestines. The bilayer hydrogel can also curve in deionized water due to anisotropic volume change yet the response time and maximum bending degree was inferior to deformation in LA-Na and UV light. Finally, we made a 4D-printed bilayer hydrogel stent to test its closure effect for enteroatmospheric fistulas (EAFs) in vitro and in vivo. The results illustrate that the hydrogel plays a role in the temporary closure of EAFs. This study offers an effective method to produce curved structures and expands the potential applications of 4D printing in biomedical fields.
Project description:The emerging field of soft robotics often relies on soft actuators powered by pressurized fluids to obtain a variety of movements. Strategic incorporation of soft actuators can greatly increase the degree of freedom of soft robots thereby bestowing them with a range of movements. Balloon actuators are extensively used to achieve various motions such as bending, twisting, and expanding. A detailed understanding of how material properties and architectural designs of balloon actuators influence their motions will greatly enable the application of these soft actuators. In this study, we developed a framework involving experimental and theoretical analyses, including computational analysis, delineating material and geometrical parameters of balloon actuators to their bending motions. Furthermore, we provide a simple analytical model to predict and control the degree of bending of these actuators. The described analytical tool could be used to predict the actuating function of balloon actuators and thereby help generate optimal actuators for functions which require control over the extent and direction of actuation.
Project description:Hydrogel actuators have shown great promise in underwater robotic applications as they can generate controllable shape transformations upon stimulation due to their ability to absorb and release water reversibly. Herein, a photoresponsive anisotropic hydrogel actuator is developed from poly(N-isopropylacrylamide) (PNIPAM) and gold-decorated carbon nitride (Au/g-C3 N4 ) nanoparticles. Carbon nitride nanoparticles endow hydrogel actuators with photocatalytic properties, while their reorientation and mobility driven by the electrical field provide anisotropic properties to the surrounding network. A variety of light-fueled soft robotic functionalities including controllable and programmable shape-change, gripping, and locomotion is elicited. A responsive flower-like photocatalytic reactor is also fabricated, for water splitting, which maximizes its energy-harvesting efficiency, that is, hydrogen generation rate of 1061.82 µmol g-1 h-1 , and the apparent quantum yield of 8.55% at 400 nm, by facing its light-receiving area adaptively towards the light. The synergy between photoactive and photocatalytic properties of this hydrogel portrays a new perspective for the design of underwater robotic and photocatalytic devices.
Project description:Two-wavelength infrared responsive soft actuators composed of rare-earth-oxide particles composited in a thermoresponsive hydrogel have been constructed. Because Nd2O3 and Yb2O3 particles possess independent narrow infrared adsorption at 808 and 980 nm, respectively, the vicinity of the particles in the gel can be individually heated by irradiation at each adsorption wavelength, inducing a local volume phase transition. The wavelength-selective volume phase transition can be controlled based on the combination of the particles incorporated in the gels and the wavelength of the irradiation laser at the optimized water temperature. Only the alternatively correct combinations successfully induced selective local clouding at the irradiation spots in the gel sheets. The original transparency of the gel was immediately recovered by turning off the light. Furthermore, rod-shaped block gels with Nd2O3 and Yb2O3 particles separately arranged on the left and right sides at the bottom of the rods were prepared to demonstrate wavelength-selective bending motion. The correct light combination caused reversible bending motion of only the side of the rod gel with the corresponding adsorbed particles.