Functionalized Hydrogel-Based Wearable Gas and Humidity Sensors

Breathing is an inherent human activity;however,the composition of the air we inhale and gas exhale remains unknown to us.To address this,wearable vapor sensors can help people monitor air composition in real time to avoid underlying risks,and for the early detection and treatment of diseases for home healthcare.Hydrogels with three-dimensional polymer networks and large amounts of water molecules are naturally flexible and stretchable.Functionalized hydrogels are intrinsically conductive,self-healing,self-adhesive,biocompatible,and room-temperature sensitive.Compared with traditional rigid vapor sensors,hydrogel-based gas and humidity sensors can directly fit human skin or clothing,and are more suitable for real-time monitoring of personal health and safety.In this review,current studies on hydrogel-based vapor sensors are investigated.The required properties and optimization methods of wearable hydrogel-based sensors are introduced.Subsequently,existing reports on the response mechanisms of hydrogel-based gas and humidity sensors are summarized.Related works on hydrogel-based vapor sensors for their application in personal health and safety monitoring are presented.Moreover,the potential of hydrogels in the field of vapor sensing is elucidated.Finally,the current research status,challenges,and future trends of hydrogel gas/humidity sensing are discussed.

Functionalized Hydrogels for Articular Cartilage Tissue Engineering

Articular cartilage(AC)is an avascular and flexible connective tissue located on the bone surface in the diarthrodial joints.AC defects are common in the knees of young and physically active individuals.Because of the lack of suitable tissue-engineered artificial matrices,current therapies for AC defects,espe-cially full-thickness AC defects and osteochondral interfaces,fail to replace or regenerate damaged carti-lage adequately.With rapid research and development advancements in AC tissue engineering(ACTE),functionalized hydrogels have emerged as promising cartilage matrix substitutes because of their favor-able biomechanical properties,water content,swelling ability,cytocompatibility,biodegradability,and lubricating behaviors.They can be rationally designed and conveniently tuned to simulate the extracel-lular matrix of cartilage.This article briefly introduces the composition,structure,and function of AC and its defects,followed by a comprehensive review of the exquisite(bio)design and(bio)fabrication of func-tionalized hydrogels for AC repair.Finally,we summarize the challenges encountered in functionalized hydrogel-based strategies for ACTE both in vivo and in vitro and the future directions for clinical translation.

Hydrogel-mediated drug delivery for treating stroke

Stroke is a common disease and is the major cause of death and disability.It occurs and generates devastating neurological deficits when cerebral blood vessel is blocked(ischemic stroke,IS)or ruptured(hemorrhagic stroke,HS).Hydrogel,being biodegradable and biocompatible,have shown attractive advantages in stroke therapy as a new biomaterial with desirable mechanical properties and tunability of structure,owing to special ability to load different cargoes for multiple treatment strategies,such as pharmacotherapy based on drug-delivery systems and cell therapy including mesenchymal stem cells(MSCs)and neural progenitor cells(NPCs)for improving functional outcomes.However,a comprehensive review of the functional hydrogel for treatment of stroke is still lacking.Therefore,in this work,the main pathological mechanisms of stroke including IS and HS are comprehensively described.The benefits of hydrogel for stroke treatment are also summarized regarding the natural advantages and the delivery advantages.Simultaneously,the application development of hydrogel for treatment of stroke is highlighted.Finally,the unique considerations and challenges in the design and application of hydrogel is discussed for treatment of stroke and clinical application in the future.

PREFACE

Hydrogels are classical soft and wet materials that have been extensively studied over the past several decades. Recently, with the development of supramolecular science, nanotechnology and precisely synthetic chemistry, various novel hydrogels have been designed and fabricated, which show emerging applications in tissue engineering, drug delivery, anti-fouling coatings, flexible electronics and soft robotics. Through tailoring their two-dimensional surface structures and three- dimensional networks, unique properties such as ultra-high mechanical strength, responsiveness to various kinds of stimuli, biocompatibility, special wettability and adhesion can be achieved.