Recent advances in small-scale hydrogel-based robots for adaptive biomedical applications

Small-scale robots,ranging in size from micrometers to centimeters,have gained significant attention in the biomedical field.However,conventional small-scale robots made of rigid materials encounter challenges in adapting themselves to the soft tissues and complicated environments of human body.Compared to the rigid counterpart,small-scale hydrogel-based robots hold great promises due to their tissue-like low modulus,outstanding biocompatibility and accessible stimuli-responsive capabilities.These attributes offer small-scale hydrogel-based robots with multimodal locomotion and reinforced functions,further enhancing the adaptability in manipulation and tasks execution for various biomedical applications.In this review,we present recent advances in small-scale hydrogel-based robots.We first summarize the design principles of small-scale hydrogel-based robots including materials,fabrication techniques and manipulation strategies,then highlighting their upgraded functions and adaptive biomedical applications.Finally,we discuss existing challenges and future perspectives for small-scale hydrogel-based robots.

Editing the Shape Morphing of Monocomponent Natural Polysaccharide Hydrogel Films

Shape-morphing hydrogels can be widely used to develop artificial muscles,reconfigurable biodevices,and soft robotics.However,conventional approaches for developing shape-morphing hydrogels highly rely on composite materials or complex manufacturing techniques,which limit their practical applications.Herein,we develop an unprecedented strategy to edit the shape morphing of monocomponent natural polysaccharide hydrogel films via integrating gradient cross-linking density and geometry effect.Owing to the synergistic effect,the shape morphing of chitosan(CS)hydrogel films with gradient cross-linking density can be facilely edited by changing their geometries(length-to-width ratios or thicknesses).Therefore,helix,short-side rolling,and longside rolling can be easily customized.Furthermore,various complex artificial 3D deformations such as artificial claw,horn,and flower can also be obtained by combining various flat CS hydrogel films with different geometries into one system,which can further demonstrate various shape transformations as triggered by pH.This work offers a simple strategy to construct a monocomponent hydrogel with geometry-directing programmable deformations,which provides universal insights into the design of shape-morphing polymers and will promote their applications in biodevices and soft robotics.

High-performance textile piezoelectric pressure sensor with novel structural hierarchy based on ZnO nanorods array for wearable application

With the increasing demand for smart wearable clothing, the textile piezoelectric pressure sensor (T-PEPS) that can harvest mechanical energy directly has attracted significant attention. However, the current challenge of T-PEPS lies in remaining the outstanding output performance without compromising its wearing comfort. Here, a novel structural hierarchy T-PEPS based on the single-crystalline ZnO nanorods are designed. The T-PEPS is constructed with three layers mode consisting of a polyvinylidene fluoride (PVDF) membrane, the top and bottom layers of conductive rGO polyester (PET) fabrics with self-orientation ZnO nanorods. As a result, the as-fabricated T-PEPS shows low detection limit up to 8.71 Pa, high output voltage to 11.47 V and superior mechanical stability. The sensitivity of the sensor is 0.62 V·kPa−1 in the pressure range of 0–2.25 kPa. Meanwhile, the T-PEPS is employed to detect human movements such as bending/relaxation motion of the wrist, bending/stretching motion of each finger. It is demonstrated that the T-PEPS can be up-scaled to promote the application of wearable sensor platforms and self-powered devices.

Inside-Out 3D Reversible Ion-Triggered Shape-Morphing Hydrogels

Shape morphing is a critical aptitude for the survival of organisms and is determined by anisotropic tissue composition and directional orientation of micro-and nanostructures within cell walls,resulting in diferent swelling behaviors.Recent eforts have been dedicated to mimicking the behaviors that nature has perfected over billions of years.We present a robust strategy for preparing 3D periodically patterned single-component sodium alginate hydrogel sheets cross-linked with Ca^(2+)ions,which can reversibly deform and be retained into various desirable inside-out shapes as triggered by biocompatible ions(Na^(+)/Ca^(2+)).By changing the orientations of the patterned microchannels or triggering with Na^(+)/Ca^(2+)ions,various 3D twisting,tubular,and plantinspired architectures can be facilely programmed.Not only can the transformation recover their initial shapes reversibly,but also it can keep the designated shapes without continuous stimuli.Tese inside-out 3D reversible ion-triggered hydrogel transformations shall inspire more attractive applications in tissue engineering,biomedical devices,and sof robotics felds.

Q[8]/SC[6]A-based framework constructed via OSIQ for metal ion capture

Since the outer surface interaction of Q[n]s (OSIQ, including self-, anion- and aromatic-induced OSIQs) was proposed in 2014, it has become the most important research area in our group to construct various Q[n]-based supramolecular frameworks via the OSIQ strategy. Herein, we report a novel supramolecular framework constructed using cucurbit[8]uril (Q[8]) and 4-sulfocalix[6]arene (SC[6]A). This Q[8]/SC[6]A-based supramolecular framework is a product via the perfect combination of self-, anion- and aromatic-induced OSIQs. This framework has the characteristics of easy preparation and high stability with the most important feature being the sequence selective capture of specific metal cations, such as common alkali- and alkaline earth metal ions, and renewability. Thus, this framework may be used in seawater desalination, potassium ion enrichment, radioactive cesium ion pollution source treatment, Gruinard's treatment or water softening and other applications.

Bioinspired microcone-array-based living biointerfaces: enhancing the anti-inflammatory effect and neuronal network formation

Implantable neural interfaces and systems have attracted much attention due to their broad applications in treating diverse neuropsychiatric disorders.However,obtaining a long-term reliable implant-neural interface is extremely important but remains an urgent challenge due to the resulting acute inflammatory responses.Here,bioinspired microcone-array-based(MA)interfaces have been successfully designed,and their cytocompatibility with neurons and the inflammatory response have been explored.Compared with smooth control samples,MA structures cultured with neuronal cells result in much denser extending neurites,which behave similar to creepers,wrapping tightly around the microcones to form complex and interconnected neuronal networks.After further implantation in mouse brains for 6 weeks,the MA probes(MAPs)significantly reduced glial encapsulation and neuron loss around the implants,suggesting better neuron viability at the implant-neural interfaces than that of smooth probes.This bioinspired strategy for both enhanced glial resistance and neuron network formation via a specific structural design could be a platform technology that not only opens up avenues for next-generation artificial neural networks and brain-machine interfaces but also provides universal approaches to biomedical therapeutics.