One-pot preparation and applications of self-healing,self-adhesive PAA-PDMS elastomers

A new family of transparent,biocompatible,self-adhesive,and self-healing elastomer has been developed by a convenient and efficient one-pot reaction between poly(acrylic acid)(PAA)and hydroxyl-terminated polydimethylsiloxane(PDMSOH).The condensation reaction between PAA and PDMS-OH has been confirmed by attenuated total reflection Fourier transform infrared(ATR-FTIR)spectra.The prepared PAA-PDMS elastomers possess robust mechanical strength and strong adhesiveness to human skin,and they have fast self-healing ability at room temperature(in^10 s with the efficiency of 98%).Specifically,strain sensors were fabricated by assembling PAA-PDMS as packaging layers and polyetherimide-reduced graphene oxide(PEI-rGO)as strain-sensing layers.The PAA-PDMS/PEI-rGO sensors are stably and reliably responsive to slight physical deformations,and they can be attached onto skin directly to monitor the body’s motions.Meanwhile,strain sensors can self-heal quickly and completely,and they can be reused for the motion detecting after shallowly scratching the surface.This work provides new opportunities to manufacture high performance self-adhesive and self-healing materials.

Effect of Self-adhesive Resin Cement and Tribochemical Treatment on Bond Strength to Zirconia

Aim To evaluate the interactive effects of different self- adhesive resin cements and tribochemical treatment on bond strength to zirconia. Methodology The following self-adhesive resin cements for bonding two zirconia blocks were evaluated： Maxcem （MA）, Smartcem （SM）, Rely X Unicem Aplicap （UN）, Breeze （BR）, Biscem （BI）, Set （SE）, and Clearfil SA luting （CL）. The specimens were grouped according to conditioning as follows： Group 1, polishing with 600 grit polishing paper; Group 2, silica coating with 110 μm Al2O3 particles which modified with silica; and, Group 3, tribochemical treatment - silica coating ＋ silanization. Specimens were stored in distilled water at 37℃ for 24 hours before testing shear bond strength. Results Silica coating and tribochemical treatment significantly increased the bond strength of the MA, UN, BR, B1, SE and CL to zirconia compared to #600 polishing. For both #600 polished and silica coating treatments, MDP- containing self-adhesive resin cement CL had the highest bond strengths to zirconia. Conclusion Applying silica coating and tribochemical treatment improved the bond strength of self-adhesive resin cement to zirconia, especially for CL.

Self-Healing,Self-Adhesive and Stable Organohydrogel-Based Stretchable Oxygen Sensor with High Performance at Room Temperature

With the advent of the 5G era and the rise of the Internet of Things,various sensors have received unprecedented attention,especially wearable and stretchable sensors in the healthcare field.Here,a stretchable,self-healable,self-adhesive,and room-temperature oxygen sensor with excellent repeatability,a full concentration detection range(0-100%),low theoretical limit of detection(5.7 ppm),high sensitivity(0.2%/ppm),good linearity,excellent temperature,and humidity tolerances is fabricated by using polyacrylamide-chitosan(PAM-CS)double network(DN)organohydrogel as a novel transducing material.The PAM-CS DN organohydrogel is transformed from the PAM-CS composite hydrogel using a facile soaking and solvent replacement strategy.Compared with the pristine hydrogel,the DN organohydrogel displays greatly enhanced mechanical strength,moisture retention,freezing resistance,and sensitivity to oxygen.Notably,applying the tensile strain improves both the sensitivity and response speed of the organohydrogel-based oxygen sensor.Furthermore,the response to the same concentration of oxygen before and after self-healing is basically the same.Importantly,we propose an electrochemical reaction mechanism to explain the positive current shift of the oxygen sensor and corroborate this sensing mechanism through rationally designed experiments.The organohydrogel oxygen sensor is used to monitor human respiration in real-time,verifying the feasibility of its practical application.This work provides ideas for fabricating more stretchable,self-healable,self-adhesive,and high-performance gas sensors using ion-conducting organohydrogels.

Effect of Different Pretreatments to Post-space on Bonding Strength of Fiber Posts Luted with a Self-adhesive Resin Cement

The effects of different post-space pretreatments on the retentive force of fiber posts cemented with a self-adhesive resin cement were investigated. Twenty-eight single-canal premolars were obturated by Resilon using warm vertical compaction and treated with distilled water, 2.5% NaOCl, 17% EDTA and 2.5% NaOCI; or 17% EDTA, 2.5% NaOCI, and ultrasonic agitation （U/E/N treatment）. Subsequently, radicular dentin surfaces were observed under scanning electron microscopy （SEM）. RelyX Fiber Posts were cemented in the treated canals by using RelyX U100, and thin-slice push-out test and SEM observation of coronal and apical regions of the specimens were performed. Data were analyzed using two-way ANOVA and Tukey＇s HSD post- hoc tests, and the percentage of failure type was calculated. Ultrasonic/EDTA/NaOC1 irrigation showed the maximum effectiveness in removing the smear layer and debris on the dentin surface. The apical bond strength of the experimental groups was significantly higher than that of the control group （P〈 0.05）. Adhesive failure between cement and dentin was the most common mode of failure. No obvious RDIZ or resin tag was detected. Chemical irrigants facilitated the bonding of these fiber posts, and ultrasonic activation improved retention. Future studies should evaluate the effectiveness of irrigation on fiber post push-out strength in fatigue cycling condition.

Matrine-loaded self-adhesive swelling microneedle for inflammation regulation to improve eczema treatment

Eczema is a common chronic dermatological disease.Conventional treatments exhibit limited efficacy due to fast drug release resulting in short-term relief.Development of a new treatment strategy that enables sustained drug release and longterm maintenance on the skin surface is necessary.A self-adhesive swelling microneedle patch(SDSMNs)was designed and constructed using a two-step casting method.The adhesive substrate was prepared by blending gelatin and dopamine via oxidation of NaIO4,so it could adhere onto the skin surface as well as withstand repeated bending movement without detachment.The swelling needles were fabricated using polyvinyl alcohol(PVA)and polyvinylpyrrolidone(PVP),which could swell by absorbing interstitial fluid and release the drug in a controlled manner.SDSMNs also showed desirable antibacterial activities toward E.coli and S.aureus.The adhesive microneedles loaded with matrine(MAT-SDSMNs),an antiinflammatory Chinese medicine,dramatically relieved eczema symptoms through IL-17 mediated inflammation responses.The use of MAT-SDSMNs significantly decreased the infiltration of inflammation cells and level of inflammatory cytokines,reduced the skin thickness,and increased collagen deposition fraction compared with conventional ointment or subcutaneous injection.The results suggested that MAT-SDSMNs can improve eczema treatment by regulating the local inflammatory microenvironment,providing a simple,self-administered sustainable strategy for eczema treatment.

Self-adhesive and biocompatible dry electrodes with conformal contact to skin for epidermal electrophysiology

Long-term biopotential monitoring requires high-performance biocompatible wearable dry electrodes.But currently,it is challenging to establish a form-preserving fit with the skin,resulting in high interface impedance and motion artifacts.This research aims to present an innovative solution using an all-green organic dry electrode that eliminates the aforementioned challenges.The dry electrode is prepared by introducing biocompatible maltitol into the chosen conductive polymer,poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate).Thanks to the secondary doping and plasticizer effect of maltitol,the dry electrode exhibits good stretchability(62%),strong self-adhesion(0.46 N/cm),high conductivity(102 S/cm),and low Young's modulus(7 MPa).It can always form a conformal contact with the skin even during body movements.Together with good electrical properties,the electrode enables a lower skin contact impedance compared to the current standard Ag/AgCl gel electrode.Consequently,the application of this dry electrode in bioelectrical signal measurement(electromyography,electrocardiography,electroencephalogra-phy)and long-term biopotential monitoring was successfully demonstrated.

Rapid self-healing,self-adhesive,anti-freezing,moisturizing,antibacterial and multi-stimuli-responsive PVA/starch/tea polyphenol-based composite conductive organohydrogel as flexible strain sensor

The complexity of application environment stimulates the development of wearable devices based on functional hydrogels.Among all the promising performances,self-healing and self-adhesion properties are ideal for hydrogel sensors,which can guarantee good accuracy,comfort and long service life.However,it is still a challenge to achieve simultaneous self-healing and self-adhesion in different environments(in the air,underwater and at low temperatures).Herein,a feasible new strategy was successfully carried out to prepare a starch-based composite conductive organohydrogel based on the reversible borate ester bonds formed by complexing starch/polyvinyl alcohol(PVA)/tea polyphenol(TP)with borax,and multiple hydrogen-bond interactions among PVA,starch,TP and ethylene glycol(EG).Silver nanoparticles(Ag-NPs),reduced and stabilized by TP,and MWCNTs(multi-walled carbon nanotubes)were introduced into the cross-linking networks to endow the resulting PBSTCE organohydrogel with considerable antibacterial property and conductivity,respectively.The organohydrogel possessed rapid self-healing(HE(self-healing efficiency)=96.07%in 90 s,both in the air and underwater,also at-20℃),considerable self-adhesion(both in the air and underwater,also at-20℃),remarkable stretchability(814%of elongation),anti-freezing(-20℃)and moisture-retention abilities,antibacterial activity,sensitive pH/sugar-responsiveness,and plasticity.The strain sensor formed by the PBSTCE organohydrogel can not only effectively record large-scale human motions(e.g.finger/wrist/elbow bending,walking,etc.),but also accurately capture subtle motion changes(e.g.breathing,chewing,swallowing,speaking,smiling and frowning).Moreover,the self-healed organohydrogel sensor also exhibited almost invariable mechanical,electrical and sensing behaviors.This work demonstrates a feasible strategy to construct multifunctional starch-based organohy-drogels,and promotes their efficient,stable and eco-friendly application as flexible wearable devices.

Bioinspired hybrid patches with self-adhesive hydrogel and piezoelectric nanogenerator for promoting skin wound healing

Wound management is a crucial measure for skin wound healing and is significantly important to maintaining the integrity of skins and their functions.Electrical stimulation at the wound site is a compelling strategy for skin wound repair.However,there has been an urgent need for wearable and point-of-care electrical stimulation devices that have self-adhesive and mechanical properties comparable to wound tissue.Herein,we develop a bioinspired hybrid patch with self-adhesive and piezoelectric nanogenerator(HPSP)for promoting skin wound healing,which is composed of a mussel-inspired hydrogel matrix and a piezoelectric nanogenerator based on aligned electrospun poly(vinylidene fluoride)nanofibers.The device with optimized modulus and permeability for skin wear can self-adhere to the wound site and locally produce a dynamic voltage caused by motion.We show that the HPSP not only promotes fibroblast proliferation and migration in vitro,but also effectively facilitates the collagen deposition,angiogenesis,and re-epithelialization in vivo with the increased expressions of crucial growth factors.The HPSP reduces the wound closure time of full-thickness skin defects by about 1/3,greatly accelerating the healing process.This patch can serve as wearable and real-time electrical stimulation devices,potentially useful in clinical applications of skin wound healing.

Self-adhesive lubricated coating for enhanced bacterial resistance

Limited surface lubrication and bacterial biofilm formation pose great challenges to biomedical implants.Although hydrophilic lubricated coatings and bacterial resistance coatings have been reported,the harsh and tedious synthesis greatly compromises their application,and more importantly,the bacterial resistance property has seldom been investigated in combination with the lubrication property.In this study,bioinspired by the performances of mussel and articular cartilage,we successfully synthesized self-adhesive lubricated coating and simultaneously achieved optimal lubrication and bacterial resistance properties.Additionally,we reported the mechanism of bacterial resistance on the nanoscale by studying the adhesion interactions between biomimetic coating and hydrophilic/hydrophobic tip or living bacteria via atomic force microscopy.In summary,the self-adhesive lubricated coating can effectively enhance lubrication and bacterial resistance performances based on hydration lubrication and hydration repulsion,and represent a universal and facial strategy for surface functionalization of biomedical implants.

An environment-stable hydrogel with skin-matchable performance for human-machine interface

Ionic hydrogel-based sensors have shined a spotlight on wearable electronics.However,the sensitivity and reliability of hydrogel devices are significantly hampered by the weak adhesion of skin-sensor interface as well as inferior temperature tolerance.Here,inspired by the structure and composition of dermis,a novel skin-attachable and environment-stable hydrogel was designed by integrating collagen into the LiCl-containing chemically cross-linked polyacrylamide hydrogel.The hydrogel exhibited skin-like mechanical properties of low modulus,superior stretchability as well as excellent elasticity.Furthermore,the introduction of collagen endowed the hydrogel with robust and seamless interfaces with diverse materials,including the curved skin.As a result,the hydrogel is capable of serving as a human-machine interface for collecting reliable electrocardiography(ECG)signals and discerning various human motions,with high sensitivity(gauge factor=10.7),fast response,negligible hysteresis as well as extensive monitoring range.Notably,the hydrogel that can mimick the temperature-tolerant mechanism of most organisms possesses persistent stabilization of adhesive,conductive,sensory and mechanical performances at subzero or ambient conditions.The skin-inspired strategy paves an effective way for the design of multifunctional materials with potential applications in next-generation electronics.