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Bioadhesives such as tissue adhesives, hemostatic agents, and tissue sealants have potential advantages over sutures and staples for wound closure, hemostasis, and integration of implantable devices onto wet tissues. However, existing bioadhesives display several limitations including slow adhesion formation, weak bonding, low biocompatibility, poor mechanical match with tissues, and/or lack of triggerable benign detachment. Here, we report a bioadhesive that can form instant tough adhesion on various wet dynamic tissues and can be benignly detached from the adhered tissues on demand with a biocompatible triggering solution. The adhesion of the bioadhesive relies on the removal of interfacial water from the tissue surface, followed by physical and covalent cross-linking with the tissue surface. The triggerable detachment of the bioadhesive results from the cleavage of bioadhesive’s crosslinks with the tissue surface by the triggering solution. After it is adhered to wet tissues, the bioadhesive becomes a tough hydrogel with mechanical compliance and stretchability comparable with those of soft tissues. We validate in vivo biocompatibility of the bioadhesive and the triggering solution in a rat model and demonstrate potential applications of the bioadhesive with triggerable benign detachment in ex vivo porcine models.

During operations, surgical mesh is commonly fixed on tissues through fasteners such as sutures and staples. Attributes of surgical mesh include biocompatibility, flexibility, strength, and permeability, but sutures and staples may cause stress concentration and tissue damage. Here, we show that the functions of surgical mesh can be significantly broadened by developing a family of materials called hydrogel–mesh composites (HMCs). The HMCs retain all the attributes of surgical mesh and add one more: adhesion to tissues. We fabricate an HMC by soaking a surgical mesh with a precursor, and upon cure, the precursor forms a polymer network of a hydrogel, in macrotopological entanglement with the fibers of the surgical mesh. In a surgery, the HMC is pressed onto a tissue, and the polymers in the hydrogel form covalent bonds with the tissue. To demonstrate the concept, we use a poly(N-isopropylacrylamide) (PNIPAAm)/chitosan hydrogel and a polyethylene terephthalate (PET) surgical mesh. In the presence a bioconjugation agent, the chitosan and the tissue form covalent bonds, and the adhesion energy reaches above 100 J·m−2. At body temperature, PNIPAAm becomes hydrophobic, so that the hydrogel does not swell and the adhesion is stable. Compared with sutured surgical mesh, the HMC distributes force over a large area. In vitro experiments are conducted to study the application of HMCs to wound closure, especially on tissues under high mechanical stress. The performance of HMCs on dynamic living tissues is further investigated in the surgery of a sheep.

Polyacrylic acid (PAA) and its derivatives are commonly used as essential matrices in wound dressings, but their weak wet adhesion restricts the clinical application. To address this issue, a PAA-based coacervate hydrogel with strong wet adhesion capability is fabricated through a facile mixture of PAA copolymers with isoprenyl oxy poly(ethylene glycol) ether and tannic acid (TA). The poly(ethylene glycol) segments on PAA prevent the electrostatic repulsion among the ionized carboxyl groups and absorbed TA to form coacervates. The absorbed TA provides solid adhesion to dry and wet substrates via multifarious interactions, which endows the coacervate with an adhesive strength to skin of 23.4 kPa and 70% adhesion underwater. This coacervate achieves desirable self-healing and extensible properties suitable for frequently moving joints. These investigations prove that the coacervate has strong antibacterial activity, facilitates fibroblast migration, and modulates M1/M2 polarization of macrophages. In vivo hemorrhage experiments further confirm that the coacervate dramatically shortens the hemostatic time from hundreds to tens of seconds. In addition, full-thickness skin defect experiments demonstrate that the coacervate achieves the best therapeutic effect by significantly promoting collagen deposition, angiogenesis, and epithelialization. These results demonstrate that a PAA-based coacervate hydrogel is a promising wound dressing for medical translation.

Bioinspired soft devices, which possess high adaptability to targeted objects, provide promising solutions for a variety of industrial and medical applications. However, achieving stable and switchable attachment to objects with curved, rough, and irregular surfaces remains difficult, particularly in dry and underwater environments. Here, a highly adaptive soft microstructured switchable adhesion device is presented, which is inspired by the geometric and material characteristics of the tiny denticles on the surface of an octopus sucker. The contact interface of the artificial octopus sucker (AOS) is imprinted with soft, microscale denticles that interact adaptably with highly rough or curved surfaces. Robust and controllable attachment of the AOS with soft microdenticles (AOS‐sm) to dry and wet surfaces with diverse morphologies is achieved, allowing conformal attachment on curved and soft objects with high roughness. In addition, AOS‐sms assembled with an octopus‐arm‐inspired soft actuator demonstrate reliable grasping and the transport of complex polyhedrons, rough objects, and soft, delicate, slippery biological samples. Inspired by the hierarchical structural and material aspects of an octopus sucker, a soft microstructured switchable adhesive device with a high degree of adaptability is developed. Owing to good adaptability provided by a hierarchical structure, this device can be robustly attached to irregular objects and detach almost immediately upon deflation under both dry and wet conditions.

Glue-type bio-adhesives are in high demand for many applications, including hemostasis, wound closure, and integration of bioelectronic devices, due to their injectable ability and in situ adhesion. However, most glue-type bio-adhesives cannot be used for short-term tissue adhesion due to their weak instant cohesion. Here, we show a novel glue-type bio-adhesive based on the phase separation of proteins and polysaccharides by functionalizing polysaccharides with dopa. The bio-adhesive exhibits increased adhesion performance and enhanced phase separation behaviors. Because of the cohesion from phase separation and adhesion from dopa, the bio-adhesive shows excellent instant and long-term adhesion performance for both organic and inorganic substrates. The long-term adhesion strength of the bio-glue on wet tissues reached 1.48 MPa (shear strength), while the interfacial toughness reached ~880 J m−2. Due to the unique phase separation behaviors, the bio-glue can even work normally in aqueous environments. At last, the feasibility of this glue-type bio-adhesive in the adhesion of various visceral tissues in vitro was demonstrated to have excellent biocompatibility. Given the convenience of application, biocompatibility, and robust bio-adhesion, we anticipate the bio-glue may find broad biomedical and clinical applications.

Hydrogels are promising materials for wound protection, but in wet, or underwater environments, the hydration layer and swelling of hydrogels can seriously reduce adhesion and limit their application. In this study, inspired by the structural characteristics of strong barnacle wet adhesion and combined with solvent exchange, a robust wet adhesive hydrogel (CP-Gel) based on chitosan and 2-phenoxyethyl acrylate was obtained by breaking the hydration layer and resisting swelling. As a result, CP-Gel exhibited strong wet adhesion to various interfaces even underwater, adapted to joint movement and skin twisting, resisted sustained rushing water, and sealed damaged organs. More importantly, on-demand detachment and controllable adhesion were achieved by promoting swelling. In addition, CP-Gel with good biosafety significantly promotes seawater-immersed wound healing and is promising for use in water-contact wound care, organ sealing, and marine emergency rescue. [Display omitted] •Robust wet adhesive hydrogel (CP-Gel) is obtained by barnacle-inspired strategy.•On-demand detachment and controllable adhesion of CP-Gel are realized.•CP-Gel significantly promotes seawater-immersed wound healing.•CP-Gel can be used for water-contact wound care, organ sealing and information encryption.

After several billions of years, nature still makes decisions on its own to identify, develop, and direct the most effective material for phenomena/challenges faced. Likewise, and inspired by the nature, we learned how to take steps in developing new technologies and materials innovations. Wet and strong adhesion by Mytilidae mussels (among which Mytilus edulis—blue mussel and Mytilus californianus—California mussel are the most well‐known species) has been an inspiration in developing advanced adhesives for the moist condition. The wet adhesion phenomenon is significant in designing tissue adhesives and surgical sealants. However, a deep understanding of engaged chemical moieties, microenvironmental conditions of secreted proteins, and other contributing mechanisms for outstanding wet adhesion mussels are essential for the optimal design of wet glues. In this review, all aspects of wet adhesion of Mytilidae mussels, as well as different strategies needed for designing and fabricating wet adhesives are discussed from a chemistry point of view. Developed muscle‐inspired chemistry is a versatile technique when designing not only wet adhesive, but also, in several more applications, especially in the bioengineering area. The applications of muscle‐inspired biomaterials in various medical applications are summarized for future developments in the field.

Currently, uncontrolled bleeding remains a serious problem in emergency, surgical and battlefield environments. Despite the specific properties of available hemostatic agents, sealants, and adhesives, effective hemostasis under wet and dynamic conditions remains a challenge. In recent years, polymeric hydrogels with excellent hemostatic properties have received much attention because of their adjustable mechanical properties, high porosity, and biocompatibility. In this review, to investigate the role of hydrogels in hemostasis, the mechanisms of hydrogel hemostasis and adhesion are firstly elucidated, the adhesion design strategies of hemostatic hydrogels in wet environments are briefly introduced, and then, based on a comprehensive literature review, the studies and in vivo applications of wet-adhesive hemostatic hydrogels in different environments are summarized, and the improvement directions of such hydrogels in future studies are proposed.

Cellulose-based hydrogels have attracted considerable attention in biomedical engineering. However, existing cellulose-based adhesive hydrogels have several limitations, including poor wet adhesion, average antimicrobial activity and a lack of benign on-demand detachment. Using a dual-crosslinked design strategy, we created a cellulose-based hydrogel (ACCPFM) by combining polymerisable allyl cellulose, carboxymethyl chitosan and the aldehyde-cation copolymer P(FPMA-co-META). Covalent (Schiff base) and non-covalent (electrostatic interaction and hydrogen bonding) crosslinking enhance the mechanical performance of the prepared hydrogel. The introduction of P(FPMA-co-META) into the cellulose network architecture endowed the ACCPFM hydrogel with an impressive antibacterial capacity (bacterial reduction: > 95%). The ACCPFM hydrogel used the hygroscopicity of the hydroxy, carboxyl and cationic moieties to remove interfacial water on the tissue surface and then formed physical and dynamic covalent cross-links with the tissue (shear strength: > 50 kPa, tensile strength: > 70 kPa and interfacial toughness: > 110 J m−2). Notably, due to the dominance of physical and dynamic covalent crosslinking, which transforms timescale-dependent, on-demand detachment was achieved by applying a tailored benign solution (sodium bicarbonate/glycine) at different stages, providing a wider time window and fault-tolerance for the adhesion process. Given the ACCPFM hydrogel’s strong wet adhesion, excellent antimicrobial capability and cytocompatibility, and benign on-demand detachment from tissues, cellulose-based hydrogels are expected to have potential applications in the biomedical field.

Drawing inspiration from the adhesion abilities of a leaf beetle found in nature, we have engineered a switchable adhesion device. The device combines two concepts: The surface tension force from a large number of small liquid bridges can be significant (capillaritybased adhesion) and these contacts can be quickly made or broken with electronic control (switchable). The device grabs or releases a substrate in a fraction of a second via a low-voltage pulse that drives electroosmotic flow. Energy consumption is minimal because both the grabbed and released states are stable equilibria that persist with no energy added to the system. Notably, the device maintains the integrity of an array of hundreds to thousands of distinct interfaces during active reconfiguration from droplets to bridges and back, despite the natural tendency of the liquid toward coalescence. We demonstrate the scaling of adhesion strength with the inverse of liquid contact size. This suggests that strengths approaching those of permanent bonding adhesives are possible as feature size is scaled down. In addition, controllability is fast and efficient because the attachment time and required voltage also scale down favorably. The device features compact size, no solid moving parts, and is made of common materials.