Light‐Induced Swelling‐Responsive Conductive,Adhesive, and Stretchable Wireless Film Hydrogel as Electronic Artificial Skin

Light‐induced wireless soft electronic skin hydrogels with excellent mechanical and electronic properties are important for several applications, such as soft robotics and intelligent wearable devices. Precise control of reversible stretchability and capacitive properties depending on intermolecular interaction and surface characteristics remains a challenge. Here, a thin‐film hydrogel is designed based on titanium oxide (TiO₂) polydopamine–perfluorosilica carbon dot‐conjugated chitosan–polyvinyl alcohol‐loaded tannic acid with controllable hydrophobic–hydrophilic transition in the presence of UV–vis light irradiation. The shifting of surface wettability from hydrophobic to hydrophilic by irradiation affects thin‐film water permeability and swelling ratio. This allows the penetration of water into the matrix to change its mechanical strength, electronic properties, and adhesive behavior. Specifically, the hydrogel displays mechanical strain as high as 278% in response to light stimuli and demonstrates the ability to regain its initial state determining the elasticity of the fabricated material. Moreover, the thin‐film hydrogel shows an increase in conductivity to 1.096 × 10^?3 and 1.026 × 10^?3 S cm^?1 when irradiated with UV and visible light, respectively. The hydrogel exhibits capacitive reversibility that follows finger motion which can be identified directly or remotely using wireless connection, indicative of its possible applications as an artificial electronic skin.     

Skin-Inspired Double-Hydrophobic-Coating Encapsulated Hydrogels with Enhanced Water Retention Capacity

Traditional hydrogels always lose their flexibility and functions in dry environments because the internal water inevitably undergoes evaporation. In this study, a skin-inspired, facile, and versatile strategy for developing encapsulated hydrogels with excellent water retention capacity through a double-hydrophobic coating is proposed. The robust double-layer coating, which integrates a hydrophobic polymer coating with a hydrophobic oil layer simultaneously, can provide a barrier to prevent the evaporation of water. To overcome the weak interfacial strength between the hydrophilic hydrogel surface and the double-hydrophobic coating, (3-aminopropyl) triethoxysilane (APTES) is utilized as a chemical binding agent. Furthermore, the overall mechanical properties of the bulk hydrogel are not significantly affected, because the coating is only anchored to the surface and its thickness is much lower than that of the native hydrogel. Moreover, it is demonstrated that this proposed strategy particularly holds the capability of encapsulating various types and different shapes of hydrogels, leading to enhanced stability and a prolonged lifetime in air. Therefore, the proposed technology provides new insights for multifarious surface functionalization of hydrogel and broadens the range of hydrogel applications.     

Thermoresponsive Shape‐Memory Hydrogel Actuators Made by Phototriggered Click Chemistry

This article describes the design and synthesis of a new series of hydrogel membranes composed of trialkyne derivatives of glycerol ethoxylate and bisphenol A diazide (BA‐diazide) or diazide‐terminated PEG600 monomer via a Cu(I)‐catalyzed photoclick reaction. The water‐swollen hydrogel membranes display thermoresponsive actuation and their lower critical solution temperature (LCST) values are determined by differential scanning calorimetry. Glycerol ethoxylate moiety serves as the thermoresponsive component and hydrophilic part, while the azide‐based component acts as the hydrophobic comonomer and most likely provides a critical hydrophobic/hydrophilic balance contributing also to the significant mechanical strength of the membranes. These hydrogels exhibit a reversible shape‐memory effect in response to temperature through a defined phase transition. The swelling and deswelling behavior of the membranes are systematically examined. Due to the click nature of the reaction, easy availability of azide and alkyne functional‐monomers, and the polymer architecture, the glass transition temperature (T_g) is easily controlled through monomer design and crosslink density by varying the feed ratio of different monomers. The mechanical properties of the membranes are studied by universal tensile testing measurements. Moreover, the hydrogels show the ability to absorb a dye and release it in a controlled manner by applying heat below and above the LCST.     

Hybrid Shear-Thinning Hydrogel Integrating Hyaluronic Acid with ROS-Responsive Nanoparticles

Nanoparticle (NP) supra-assembly offers unique opportunities to tune macroscopic hydrogels’ mechanical strength, material degradation, and drug delivery properties. Here, synthetic, reactive oxygen species (ROS)-responsive NPs are physically cross-linked with hyaluronic acid (HA) through guest-host chemistry to create shear-thinning NP/HA hydrogels. A library of triblock copolymers composed of poly(propylene sulfide)-b-poly(N,N-dimethylacrylamide)-b-poly(N,N-dimethylacrylamide-co-N-(1-adamantyl)acrylamide) are synthesized with varied triblock architectures and adamantane grafting densities and then self-assembled into NPs displaying adamantane on their surface. Self-assembled NPs are mixed with β-cyclodextrin grafted HA to yield eighteen NP/HA hydrogel formulations. The NP/HA hydrogel platform demonstrates superior mechanical strength to HA-only hydrogels, susceptibility to oxidative/enzymatic degradation, and inherent cell-protective, antioxidant function. The performance of NP/HA hydrogels is shown to be affected by triblock architecture, guest/host grafting densities, and HA composition. In particular, the length of the hydrophilic second block and adamantane grafting density of self-assembled NPs significantly impacts hydrogel mechanical properties and shear-thinning behavior, while ROS-reactivity of poly(propylene sulfide) protects cells from cytotoxic ROS and reduces oxidative degradation of HA compared to HA-only hydrogels. This study provides insight into polymer structure-function considerations for designing hybrid NP/HA hydrogels and identifies antioxidant, shear-thinning hydrogels as promising injectable delivery platforms for small molecule drugs and therapeutic cells.     

Hydration-Induced Void-Containing Hydrogels for Encapsulation and Sustained Release of Small Hydrophilic Molecules

Efficient encapsulation and sustained release of small hydrophilic molecules from traditional hydrogel systems are challenging due to the large mesh size of 3D networks and high water content. Furthermore, the encapsulated molecules are prone to early release from the hydrogel prior to use, resulting in a short shelf life of the formulation. Here, a hydration-induced void-containing hydrogel (HVH) based on hyperbranched polyglycerol-poly(propylene oxide)-hyperbranched polyglycerol (HPG-PPG-HPG) as a robust and efficient delivery system is presented for small hydrophilic molecules. Specifically, after the HPG-PPG-HPG is incubated overnight at 4 °C in the drug solution, it is hydrated into a hydrogel containing micron-sized voids, which can encapsulate hydrophilic drugs and achieve 100% drug encapsulation efficiency. In addition, the voids are surrounded by a densely packed polymer matrix, which restricts drug transport to achieve sustained drug release. The hydrogel/drug formulation can be stored for several months without changing the drug encapsulation and release properties. HVH hydrogels are injectable due to shear thinning properties. In rats, a single injection of the HPG-PPG-HPG hydrogel containing 8 µg of tetrodotoxin (TTX) produces sciatic nerve block lasting up to 10 h without any TTX-related systemic toxicity nor local toxicity to nerves and muscles.     

Facile One‐Step Micropatterning Using Photodegradable Gelatin Hydrogels for Improved Cardiomyocyte Organization and Alignment

Hydrogels are often employed as temporary platforms for cell proliferation and tissue organization in vitro. Researchers have incorporated photodegradable (PD) moieties into synthetic polymeric hydrogels as a means of achieving spatiotemporal control over material properties. In this study protein‐based PD hydrogels composed of methacrylated gelatin and a crosslinker containing o‐nitrobenzyl ester groups are developed. The hydrogels are able to degrade rapidly and specifically in response to UV light and can be photopatterned to a variety of shapes and dimensions in a one‐step process. Micropatterned PD hydrogels are shown to improve cell distribution, alignment, and beating regularity of cultured neonatal rat cardiomyocytes. Overall this work introduces a new class of PD hydrogel based on natural and biofunctional polymers as cell culture substrates for improving cellular organization and function.     

Inherent Photodegradability of Polymethacrylate Hydrogels: Straightforward Access to Biocompatible Soft Microstructures

Hydrogels are important functional materials useful for 3D cell culture, tissue engineering, 3D printing, drug delivery, sensors, or soft robotics. The ability to shape hydrogels into defined 3D structures, patterns, or particles is crucial for biomedical applications. Here, the rapid photodegradability of commonly used polymethacrylate hydrogels is demonstrated without the need to incorporate additional photolabile functionalities. Hydrogel degradation depths are quantified with respect to the irradiation time, light intensity, and chemical composition. It can be shown that these parameters can be utilized to control the photodegradation behavior of polymethacrylate hydrogels. The photodegradation kinetics, the change in mechanical properties of polymethacrylate hydrogels upon UV irradiation, as well as the photodegradation products are investigated. This approach is then exploited for microstructuring and patterning of hydrogels including hydrogel gradients as well as for the formation of hydrogel particles and hydrogel arrays of well‐defined shapes. Cell repellent but biocompatible hydrogel microwells are fabricated using this method and used to form arrays of cell spheroids. As this method is based on readily available and commonly used methacrylates and can be conducted using cheap UV light sources, it has vast potential to be applied by laboratories with various backgrounds and for diverse applications.     

Magnetic Hydrogels and Their Potential Biomedical Applications

Hydrogels find widespread applications in biomedical engineering due to their hydrated environment and tunable properties (e.g., mechanical, chemical, biocompatible) similar to the native extracellular matrix (ECM). However, challenges still exist regarding utilizing hydrogels in applications such as engineering 3D tissue constructs and active targeting in drug delivery, due to the lack of controllability, actuation, and quick‐response properties. Recently, magnetic hydrogels have emerged as a novel biocomposite for their active response properties and extended applications. In this review, the state‐of‐the‐art methods for magnetic hydrogel preparation are presented and their advantages and drawbacks in applications are discussed. The applications of magnetic hydrogels in biomedical engineering are also reviewed, including tissue engineering, drug delivery and release, enzyme immobilization, cancer therapy, and soft actuators. Concluding remarks and perspectives for the future development of magnetic hydrogels are addressed.     

Hofmeister Effect‐Assisted One Step Fabrication of Ductile and Strong Gelatin Hydrogels

Hydrogels with high strength and ductility are normally prepared from synthetic polymers, and most protein‐based hydrogels are soft and brittle. Here, a strong, ductile gelatin hydrogel is prepared by simply soaking a virgin gelatin gel in an ammonium sulfate solution. The polymer chains in the covalent, crosslink‐free network can freely move to homogeneously distribute stress, and more importantly, the highly kosmotropic ammonium sulfate ions greatly enhance the hydrophobic interactions and chain bundling within the gelatin gels. As a result, the treated hydrogels have an extraordinary ultimate strength (compressive and tensile strains of over 99% and 500%, respectively, and stresses of 12 and 3 MPa) superior to that of common protein gels. The physical crosslinks introduced by the Hofmeister effect can rapidly absorb energy and sustain large deformations via decrosslinking and dissociation, which result in energy dissipation and antifatigue properties. The effects of the gelatin and (NH₄)₂SO₄ concentrations on the hydrogel mechanics are evaluated, and the possible strengthening mechanism is discussed. The effect of various ions in the Hofmeister series on the gelatin hydrogel is also investigated. Kosmotropic ions enhance the mechanical properties, whereas chaotropic ions soften and dissolve the gel.     

Biodegradable Polymer Crosslinker: Independent Control of Stiffness,Toughness, and Hydrogel Degradation Rate

Hydrogels are being increasingly studied for use in various biomedical applications including drug delivery and tissue engineering. The successful use of a hydrogel in these applications greatly relies on a refined control of the mechanical properties including stiffness, toughness, and the degradation rate. However, it is still challenging to control the hydrogel properties in an independent manner due to the interdependency between hydrogel properties. Here it is hypothesized that a biodegradable polymeric crosslinker would allow for decoupling of the dependency between the properties of various hydrogel materials. This hypothesis is examined using oxidized methacrylic alginate (OMA). The OMA is synthesized by partially oxidizing alginate to generate hydrolytically labile units and conjugating methacrylic groups. It is used to crosslink poly(ethylene glycol) methacrylate and poly(N‐hydroxymethyl acrylamide) to form three‐dimensional hydrogel systems. OMA significantly improves rigidity and toughness of both hydrogels as compared with a small molecule crosslinker, and also controls the degradation rate of hydrogels depending on the oxidation degree, without altering their initial mechanical properties. The protein‐release rate from a hydrogel and subsequent angiogenesis in vivo are thus regulated with the chemical structure of OMA. Overall, the results of this study suggests that the use of OMA as a crosslinker will allow the implantation of a hydrogel in tissue subject to an external mechanical loading with a desired protein‐release profile. The OMA synthesized in this study will be, therefore, highly useful to independently control the mechanical properties and degradation rate of a wide array of hydrogels.     

High‐Strength,Durable All‐Silk Fibroin Hydrogels with Versatile Processability toward Multifunctional Applications

Hydrogels are the focus of extensive research due to their potential use in fields including biomedical, pharmaceutical, biosensors, and cosmetics. However, the general weak mechanical properties of hydrogels limit their utility. Here, pristine silk fibroin (SF) hydrogels with excellent mechanical properties are generated via a binary‐solvent‐induced conformation transition (BSICT) strategy. In this method, the conformational transition of SF is regulated by moderate binary solvent diffusion and SF/solvent interactions. β‐sheet formation serves as the physical crosslinks that connect disparate protein chains to form continuous 3D hydrogel networks, avoiding complex chemical and/or physical treatments. The Young's modulus of these new BSICT–SF hydrogels can reach up to 6.5 ± 0.2 MPa, tens to hundreds of times higher than that of conventional hydrogels (0.01–0.1 MPa). These new materials fill the “empty soft materials' space” in the elastic modulus/strain Ashby plot. More remarkably, the BSICT–SF hydrogels can be processed into different constructions through different polymer and/or metal‐based processing techniques, such as molding, laser cutting, and machining. Thus, these new hydrogel systems exhibit potential utility in many biomedical and engineering fields.     

Barnacle Cement Proteins-Inspired Tough Hydrogels with Robust,Long-Lasting,and Repeatable Underwater Adhesion

The development of adhesives that can achieve robust and repeatable adhesion to various surfaces underwater is promising; however, this remains a major challenge primarily because the surface hydration layer weakens the interfacial molecular interactions. Herein, a strategy is proposed to develop tough hydrogels that are robust, reusable, and long-lasting for underwater adhesion. Hydrogels from cationic and aromatic monomers with an aromatic-rich composition inspired by the amino acid residuals in barnacle cement proteins are synthesized. The hydrogels are mechanically strong and tough (elastic modulus 0.35 MPa, fracture stress 1.0 MPa, and fracture strain 720%), owing to the interchain π–π and cation–π interactions. In water, the hydrogels firmly adhere to diverse surfaces through interfacial electrostatic and hydrophobic interactions (adhesion strength of 180 kPa), which allows for instant adhesion and reversibility (50 times). Moreover, the hydrogel shows long-lasting adhesion in water for months (100 days). Novel adhesive hydrogels may be useful in many applications, including underwater transfer, water-based devices, underwater repair, and underwater soft robots.     

Bioinspired Reversibly Cross‐linked Hydrogels Comprising Polypeptide Micelles Exhibit Enhanced Mechanical Properties

Noncovalently cross‐linked networks are attractive hydrogel platforms because of their facile fabrication, dynamic behavior, and biocompatibility. The majority of noncovalently cross‐linked hydrogels, however, exhibits poor mechanical properties, which significantly limit their utility in load bearing applications. To address this limitation, hydrogels are presented composed of micelles created from genetically engineered, amphiphilic, elastin‐like polypeptides that contain a relatively large hydrophobic block and a hydrophilic terminus that can be cross‐linked through metal ion coordination. To create the hydrogels, heat is firstly used to trigger the self‐assembly of the polypeptides into monodisperse micelles that display transition metal coordination motifs on their coronae, and subsequently cross‐link the micelles by adding zinc ions. These hydrogels exhibit hierarchical structure, are stable over a large temperature range, and exhibit tunable stiffness, self‐healing, and fatigue resistance. Gels with polypeptide concentration of 10%, w/v, and higher show storage moduli of ≈1 MPa from frequency sweep tests and exhibit self‐healing within minutes. These reversibly cross‐linked, hierarchical hydrogels with enhanced mechanical properties have potential utility in a variety of biomedical applications.     

Low Hysteresis Hydrogel Induced by Spatial Confinement

Stress concentration and hysteresis often occur in polymer hydrogels under large deformation, affecting their mechanical properties, and durability. Here, a new spatial confinement gelation strategy is proposed for fabrication of hysteresis-free polymer hydrogels, and stress concentration is avoided. Experimental results and theoretical calculations confirm that the hydratability difference between salts and polymer chains leads to spatial confinement of the polymer chains by control over the ratio of bound to free water. Spatial confinement acts in place of physical cross-linking of polymer chains, which slide to dissipate energy and effectively avoid stress concentration and hysteresis, resulting in ultra-tough hydrogels with fatigue resistance. This is also a universal strategy for preparing polymer hydrogels with different monomers and salts. Taking the prepared PAM-CaCl₂ hydrogel, it displays a hysteresis of only 0.13% during load-unload cycles, even under 1000% strain. This is the lowest value among hydrogels reported to date. Along with excellent fatigue resistance, water retention, antifreeze, and water-assisted healing ability, this hydrogel shows good performance in fatigue resistant capacitive strain sensors. Moreover, a fishtail-shaped PAM-CaCl₂ hydrogel operates as a bionic muscle to drive a bionic fish at a forward speed of 16.3 cm s⁻¹, when a voltage of 0.1 V is applied.     

Stimuli-Responsive Nanocomposite Hydrogels for Biomedical Applications

The complex tissue-specific physiology that is orchestrated from the nano- to the macroscale, in conjugation with the dynamic biophysical/biochemical stimuli underlying biological processes, has inspired the design of sophisticated hydrogels and nanoparticle systems exhibiting stimuli-responsive features. Recently, hydrogels and nanoparticles have been combined in advanced nanocomposite hybrid platforms expanding their range of biomedical applications. The ease and flexibility of attaining modular nanocomposite hydrogel constructs by selecting different classes of nanomaterials/hydrogels, or tuning nanoparticle-hydrogel physicochemical interactions widely expands the range of attainable properties to levels beyond those of traditional platforms. This review showcases the intrinsic ability of hybrid constructs to react to external or internal/physiological stimuli in the scope of developing sophisticated and intelligent systems with application-oriented features. Moreover, nanoparticle-hydrogel platforms are overviewed in the context of encoding stimuli-responsive cascades that recapitulate signaling interplays present in native biosystems. Collectively, recent breakthroughs in the design of stimuli-responsive nanocomposite hydrogels improve their potential for operating as advanced systems in different biomedical applications that benefit from tailored single or multi-responsiveness.     

A Single Component Conducting Polymer Hydrogel as a Scaffold for Tissue Engineering

Conducting polymers (CPs) have exciting potential as scaffolds for tissue engineering, typically applied in regenerative medicine applications. In particular, the electrical properties of CPs has been shown to enhance nerve and muscle cell growth and regeneration. Hydrogels are particularly suitable candidates as scaffolds for tissue engineering because of their hydrated nature, their biocompatibility, and their tissue‐like mechanical properties. This study reports the development of the first single component CP hydrogel that is shown to combine both electro‐properties and hydrogel characteristics. Poly(3‐thiopheneacetic acid) hydrogels were fabricated by covalently crosslinking the polymer with 1,1′‐carbonyldiimidazole (CDI). Their swelling behavior was assessed and shown to display remarkable swelling capabilities (swelling ratios up to 850%). The mechanical properties of the networks were characterized as a function of the crosslinking density and were found to be comparable to those of muscle tissue. Hydrogels were found to be electroactive and conductive at physiological pH. Fibroblast and myoblast cells cultured on the hydrogel substrates were shown to adhere and proliferate. This is the first time that the potential of a single component CP hydrogel has been demonstrated for cell growth, opening the way for the development of new tissue engineering scaffolds.     

Combining Mechanical Tuneability with Function: Biomimetic Fibrous Hydrogels with Nanoparticle Crosslinkers

Fibrous networks of biopolymers possess unique properties: mechanical stability at low concentrations, an extremely porous architecture, and strong stiffening at small deformations. An outstanding challenge is to find methods that allow to tailor the mechanical properties of these bionetworks or their synthetic equivalents without changing the polymer concentration, which simultaneously changes all other hydrogel properties. Here, networks of dilute (0.1 wt.%) fibrous hydrogels are prepared and crosslink them with functional rod-shaped nanoparticles. The crosslinking is observed to induce an architectural change that strongly affects the mechanical properties of the hydrogels with a 40-fold increase in stiffness. The effect is strongest at the lowest polymer and particle concentrations (99.8% water) and is tailorable through tuning the crosslink density. Moreover, the nanoparticle components in the composite offer the opportunity to introduce additional functions; gels with magnetic and conductive properties are reported. However, through the generic crosslinking approach of a fibrous network with decorated nanoparticle crosslinkers as presented in this work, virtually any functionality may be introduced in highly responsive hydrogels, providing a guide to design next generations of multi-functional soft materials.     

Nanogel Encapsulated Hydrogels As Advanced Wound Dressings for the Controlled Delivery of Antibiotics

Biocompatible and degradable dual-delivery gel systems based on hyperbranched dendritic−linear−dendritic copolymers (HBDLDs) is herein conceptualized and accomplished via thiol-ene click chemistry. The elasticity of the hydrogels is tunable by varying the lengths of PEG (2, 6, 10 kDa) or the dry weight percentages (20, 30, 40 wt%), and are found to range from 2–14.7 kPa, comparable to human skin. The co-delivery of antibiotics is achieved, where the hydrophilic drug novobiocin sodium salt (NB) is entrapped within the hydrophilic hydrogel, while the hydrophobic antibiotic ciprofloxacin (CIP) is encapsulated within the dendritic nanogels (DNGs) with hydrophobic cores (DNGs-CIP). The DNGs-CIP with drug loading capacity of 2.83 wt% are then physically entrapped within the hybrid hydrogels through UV curing. The hybrid hydrogels enable the quick release of NB and prolonged released of CIP. In vitro cell infection assays showed that the antibiotic-loaded hybrid hydrogels are able to treat bacterial infections with significant bacterial reduction. Hybrid hydrogel band aids are fabricated and exhibited better antibacterial activity compared with commercial antimicrobial band aids. Remarkably, most hydrogels and hybrid hydrogels show enhanced human dermal cell proliferation and could be degraded into non-toxic constituents, showing great promise as wound dressing materials.     

Complex Tuning of Physical Properties of Hyperbranched Polyglycerol‐Based Bioink for Microfabrication of Cell‐Laden Hydrogels

Microfabrication technology has emerged as a valuable tool for fabricating structures with high resolution and complex architecture for tissue engineering applications. For this purpose, it is imperative to develop “bioink” that can be readily converted to a solid structure by the modus operandi of a chosen apparatus, while optimally supporting the biological functions by tuning their physicochemical properties. Herein, a photocrosslinkable hyperbranched polyglycerol (acrylic hyperbranched glycerol (AHPG)) is developed as a crosslinker to fabricate cell‐laden hydrogels. Due to its hydrophilicity as well as numerous hydroxyl groups for the conjugation of reactive functional groups (e.g., acrylate), the mechanical properties of resulting hydrogels could be controlled in a wide range by tuning both molecular weight and degree of acrylate substitution of AHPG. The control of mechanical properties by AHPG is highly dependent on the type of monomer, due to the hydrophilic/hydrophobic balance of polyglycerol backbone and acrylate as well as the dynamic conformational flexibility based on the molecular weight of polyglycerol. The cell encapsulation studies demonstrate the biocompatibility of the AHPG‐linked hydrogels. Eventually, the AHPG‐based hydrogel precursor solution is employed as a bioink for a digital light processing based printing system to generate cell‐laden microgels with various shapes and sizes for tissue engineering applications.     

A Reversible Adhesive Hydrogel Tape

Due to the existence of hydration layer at interfaces, the weak affinity between hydrogels and most hydrophobic materials routinely generates weak and brittle bonding, which has been a disadvantage of hydrogels when serving as coatings on solid substrates. Herein, a finding of substantial affinity is presented between polyacrylamide-based hydrogels and cellulose acetate (CA) without particular chemical and physical pretreatments. Besides understanding the mechanism behind it, this unusual finding motivates to make reversible adhesive hydrogel tapes. Learning from the commercial Scotch Magic Tape which typically paints a glue layer on polymer films to achieve appropriate adhesion on solid surfaces, the CA backlayer can be easily glued and firmly bonded to arbitrary solid surfaces without affecting the properties of hydrogel layer on the other side. This particular kind of hydrogel tape can be readily scaled up from laboratory synthesis to a roll-to-roll continuous production. Several applications of hydrogel tapes are succeeded in alarming hyperthermia, thermal dissipation, and serving as ultrasonic couplant. In terms of the advantages of low cost, green fabrication, convenient operation, sticky performance and ignorable residues, the hydrogel tape would be one of the desirable choices to be used as one-off healthcare material.