Near-infrared responsive shape memory hydrogels with programmable and complex shape-morphing

In this work,semi-crystalline nanocomposite hydrogels(i.e.,PAAmA_(11)A/GO gels)were synthesized by micellar copolymerization of acrylamide and N-acryloyl-11-aminoundecanoic acid(A_(11)A)in the presence of a large amount of sodium dodecyl sulfonate(SDS)micelles and GO nanosheets.The resulting hydrogels(SMHs)not only demonstrated high strength and high toughness,but also exhibited good shape memory property.Because of near-infrared(NIR)light absorbability of GO nanosheets,shape recovery and shape of PAAmA_(11)A/GO gels could be tuned by NIR irradiation.Moreover,bilayer hydrogels and trilayer hydrogels were also fabricated by the integration of shape-memorized PAAmA_(11)A/GO gel and elastic hydrophobic associated hydrogel(E-gel).Based on the NIR-responsive shape memory property and layered structure,shape deformation of bilayer hydrogels and trilayer hydrogels was rather different from the single PAAmA_(11)A/GO gel.Each kind of gel structure exhibited diverse and complex shapes via programmable NIR irradiation.More importantly,the shape morphing of NIR-SMHs-based hydrogels could mimic the hand and flower and be used as actuators.

Cold-induced shape memory hydrogels for strong and programmable artificial muscles

Thermo-responsive shape memory hydrogels generally achieve shape fixation at low temperatures,and shape recovery at high temperatures.However,these hydrogels usually suffer from poor mechanical properties.Herein,we present a unique poly(acrylic acid)/calcium acetate shape memory hydrogel with cold-induced shape recovery performances as ultrastrong artificial muscles.Since the acetate groups could form aggregate at high temperatures and thus induce the association of the hydrogel network,the hydrogel can be fixed into a temporary shape upon heating and recover to its original shape in a cold environment.Moreover,a programmable shape recovery process is realized by adjusting the shape fixing time.In addition,the unique shape memory process enables the application demonstration as bio-inspired artificial muscles with an ultrahigh work density of45.2 kJ m^(-3),higher than that of biological muscles(~8 kJ m^(-3)).

4D Printing:History and Recent Progress

4D printing has attracted great interest since the concept was introduced in 2012. The past 5 years have witnessed rapid advances in both 4D printing processes and materials. Unlike 3D printing, 4D printing allows the printed part to change its shape and function with time in response to change in external conditions such as temperature, light, electricity, and water. In this review, we first overview the history of 4D printing and discuss its definition. We then summarize recent technological advances in 4D printing with focuses on methods, materials, and their intrinsic links. Finally, we discuss potential applications and offer perspectives for this exciting new field.

Bioinspired Adaptive Gel Materials with Synergistic Heterostructures

In nature, many biological soft tissues with synergistic heterostructures, such as sea cucumbers, skeletal muscles and cartilages, exhibit high functionality to adapt to complex environments. In artificial soft materials, hydrogels are similar to biological soft tissues due to the unique integration of ＂soft and wet＂ properties and elastic characteristics. However, currently hydrogel materials lack their necessary adaptability, including narrow working temperature windows and uncontrollable mechanics, thus restrict their engineering application in complex environments. Inspired by abovementionedbiological soft tissues, researchers have increasingly developed heterostructural gel materials as functional soft materials with high adaptability to various mechanical and environmental conditions. This article summarizes our recent work on high-performance adaptive gel materials with synergistic heterostructures, including the critical design criteria and the state-of-the-art fabrication strategies of our gel materials. The functional adaptation properties of these heterostructural gel materials are also presented in details, including temperature, wettability, mechanical and shape adaption.