Programming hydrogel adhesion with engineered polymer network topology

A Microphase Separation-Driven Supramolecular Tissue Adhesive with Instantaneous Dry/Wet Adhesion, Alcohol-Triggered Debonding, and Antibacterial Hemostasis

Tissue adhesives are promising materials for expeditious hemorrhage control, while it remains a grand challenge to engineer a superior formulation with instantaneous adhesion, on-demand debonding, and the integration of multiple desirable properties such as antibacterial and hemostatic capabilities. Herein, a multifunctional supramolecular tissue adhesive based on guanidinium-modified polydimethylsiloxane (PDMS) is introduced, driven by a reversible microphase separation mechanism. By optimizing the content of guanidinium ions, precise control over cohesive strength, adhesion, and wettability is achieved, resulting in strong instantaneous adhesion under both dry and wet conditions. Notably, the supramolecular nature of the adhesive allows for convenient on-demand removal using medical-grade alcohol, offering a critical advantage for easy debonding. Additionally, the adhesive exhibits remarkable antimicrobial properties while maintaining excellent biocompatibility and hemocompatibility. Its underwater injectability supports minimally invasive surgical procedures. Furthermore, the adhesive's ability to incorporate solid particles enhances its versatility, particularly for the development of drug-embedded bioadhesives. This work addresses key challenges in tissue adhesive design via a microphase separation-driven working principle, thereby opening promising new avenues for the development of advanced bioadhesives with tailored properties and enhanced surgical and wound care outcomes.

Ultrasound Cavitation Enables Rapid, Initiator-Free Fabrication of Tough Anti-Freezing Hydrogels

Hydrogels are often synthesized with thermal or photo-initiated gelation, leaving alternative energy sources less explored. While ultrasound has been used for polymer synthesis and mechanochemistry, its application through cavitation for hydrogel synthesis as a constructive force is rare, and the underlying sonochemical mechanisms are poorly understood. Here, the application and mechanism of ultrasound cavitation for rapid, initiator-free, and oxygen-tolerant fabrication of tough anti-freezing hydrogels is reported. By incorporating polyol solvents and interpenetrating polymers into the gelling solution, radical generation is amplified and network formation is enhanced. Using tough polyacrylamide-alginate hydrogels as a model system, rapid gelation (as fast as 2 minutes) and high fracture toughness (up to 600 J m- 2) is demonstrated. By varying ultrasound intensity, crosslinker-to-monomer ratio, and glycerol concentration, the synthesis-structure-property relation is established for the resulting sonogels and the underlying mechanism is uncovered using combined molecular, optical, and mechanical testing techniques. The coupling of gelation and convection under ultrasound results in sonogels with unique structural and mechanical properties. Additionally, the fabrication of hydrogel constructs is demonstrated using both non-focused and high-intensity focused ultrasound. This work establishes a foundation for ultrasound-driven sono-fabrication and highlights new avenues in soft materials, advanced manufacturing, bioadhesives, and tissue engineering.

An electroadhesive hydrogel interface prolongs porcine gastrointestinal mucosal theranostics

Establishing a robust and intimate mucosal interface that allows medical devices to remain within lumen-confined organs for extended periods has valuable applications, particularly for gastrointestinal theranostics. Here, we report the development of an electroadhesive hydrogel interface for robust and prolonged mucosal retention after electrical activation (e-GLUE). The e-GLUE device is composed of cationic polymers interpenetrated within a tough hydrogel matrix. An e-GLUE electrode design eliminated the need for invasive submucosal placement of ground electrodes for electrical stimulation during endoscopic delivery. With an electrical stimulation treatment of about 1 minute, the cationic polymers diffuse and interact with polyanionic proteins that have a relatively slow cellular turnover rate in the deep mucosal tissue. This mucosal adhesion mechanism increased the adhesion energy of hydrogels on the mucosa by up to 30-fold and enabled in vivo gastric retention of e-GLUE devices in a pig stomach for up to 30 days. The adhesion strength was modulated by polycationic chain length, electrical stimulation time, gel thickness, cross-linking density, voltage amplitude, polycation concentration, and perimeter-to-area ratio of the electrode assembly. In porcine studies, e-GLUE demonstrated rapid mucosal adhesion in the presence of luminal fluid and mucus exposure. In proof-of-concept studies, we demonstrated e-GLUE applications for mucosal hemostasis, sustained local delivery of therapeutics, and intimate biosensing in the gastrointestinal tract, which is an ongoing clinical challenge for commercially available alternatives, such as endoclips and mucoadhesive. The e-GLUE platform could enable theranostic applications across a range of digestive diseases, including recurrent gastrointestinal bleeding and inflammatory bowel disease.

Integrating Hydrogels and Biomedical Plastics via In Situ Physical Entanglements and Covalent Bonding

Both rigid plastics and soft hydrogels find ample applications in engineering and medicine but bear their own disadvantages that limit their broader applications. Bonding these mechanically dissimilar materials may resolve these limitations, preserve their advantages, and offer new opportunities as biointerfaces. Here, a robust adhesion strategy is proposed to integrate highly entangled tough hydrogels and diverse plastics with high interfacial adhesion energy and strength. Systemic investigations on the effects of hydrogel monomer content and crosslink fraction revealed the significant contributions of both polymer physical entanglements and interfacial covalent bonding. This hybrid engineering strategy also enables the plastic-hydrogel composite to attenuate foreign body response caused by pristine rigid plastics in vivo in mice. This versatile materials engineering approach may be broadly applicable to other polymer-based devices commonly used in regenerative medicine and surgical robotics.

An Environmentally Stable, Biocompatible, and Multilayered Wound Dressing Film with Reversible and Strong Adhesion

Reversible adhesives for wound care improve patient experiences by permitting reuse and minimizing further tissue injury. Existing reversible bandages are vulnerable to water and can undergo unwanted deformation during removal and readdressing procedures. Here, a biocompatible, multilayered, reversible wound dressing film that conforms to skin and is waterproof is designed. The inner layer is capable of instant adhesion to various substrates upon activation of the dynamic boronic ester bonds by water; intermediate hydrogel layer and outer silicone backing layer can enhance the dressing's elasticity and load distribution for adhesion, and the silicone outer layer protects the dressing from exposure to water. The adhesive layer is found to be biocompatible with mouse skin. Skin injuries on the mouse skin heal more rapidly with the film compared to no dressing controls. Evaluations of the film on skin of freshly euthanized minipigs corroborate the findings in the mouse model. The film remains attached to skins without delamination despite subjecting to various degrees of deformation. Exposure to water softens the film to allow removal from the skin without pulling any hair off. The multilayered design considers soft mechanics in each layer and will offer new insights to improve wound dressing performance and patient comfort.

Penetration enhancers strengthen tough hydrogel bioadhesion and modulate locoregional drug delivery

The human body possesses natural barriers, such as skin and mucosa, which limit the effective delivery of therapeutics and integration of medical devices to target tissues. Various strategies have been deployed to breach these barriers mechanically, chemically, or electronically. The development of various penetration enhancers (PEs) offers a promising solution due to their ability to increase tissue permeability using readily available reagents. However, existing PE-mediated delivery methods often rely on weak gel or liquid drug formulations, which are not ideal for sustained local delivery. Hydrogel adhesives that can seamlessly interface biological tissues with controlled drug delivery could potentially resolve these issues. Here, we demonstrate that tough adhesion between drug-laden hydrogels and biological tissue (e.g. skin and tumours) can lead to effective local delivery of drugs deep into targeted tissues by leveraging the enhanced tissue penetration mediated by PEs. The drug release profile of the hydrogel adhesives can be fine-tuned by further engineering the nanocomposite hydrogel matrix to elute chemotherapeutics from 2 weeks to 2 months. Using a 3D tumour spheroid model, we demonstrated that PEs increased the cancer-killing effectiveness of doxorubicin by facilitating its delivery into tumour microtissues. Therefore, the proposed tough bioadhesion and drug delivery strategy modulated by PEs holds promise as a platform technique to develop next-generation wearable and implantable devices for cancer management and regenerative medicine.

Additive manufacturing of highly entangled polymer networks

Incorporation of polymer chain entanglements within a single network can synergistically improve stiffness and toughness, yet attaining such dense entanglements through vat photopolymerization additive manufacturing [e.g., digital light processing (DLP)] remains elusive. We report a facile strategy that combines light and dark polymerization to allow constituent polymer chains to densely entangle as they form within printed structures. This generalizable approach reaches high monomer conversion at room temperature without the need for additional stimuli, such as light or heat after printing, and enables additive manufacturing of highly entangled hydrogels and elastomers that exhibit fourfold- to sevenfold-higher extension energies in comparison to that of traditional DLP. We used this method to print high-resolution and multimaterial structures with features such as spatially programmed adhesion to wet tissues.

Recent Advances in Wearable Healthcare Devices: From Material to Application

In recent years, the proliferation of wearable healthcare devices has marked a revolutionary shift in the personal health monitoring and management paradigm. These devices, ranging from fitness trackers to advanced biosensors, have not only made healthcare more accessible, but have also transformed the way individuals engage with their health data. By continuously monitoring health signs, from physical-based to biochemical-based such as heart rate and blood glucose levels, wearable technology offers insights into human health, enabling a proactive rather than a reactive approach to healthcare. This shift towards personalized health monitoring empowers individuals with the knowledge and tools to make informed decisions about their lifestyle and medical care, potentially leading to the earlier detection of health issues and more tailored treatment plans. This review presents the fabrication methods of flexible wearable healthcare devices and their applications in medical care. The potential challenges and future prospectives are also discussed.

Enhancing Adhesion of Fibrin-Based Hydrogel to Polythioether Polymer Surfaces

The development of stable (bio)hybrid constructs composed of scaffolds and (bio)matrices is a major challenge in the field of tissue engineering. In the present work, the adhesion of fibrin-based hydrogels to the surface of polythioether-based polymers relevant to the 3D printing of polymer scaffolds produced by thiol-ene click chemistry was investigated. Adhesion properties were characterized by single-lap tensile shear testing. Both the sample preparation and the test method were optimized for the analysis of fibrin gel bonding to the polythioether surface. Our experimental results show that even without further modification, an adhesion between the fibrin hydrogel and polythioether is substantial, with an adhesion strength of 4.9 ± 1.0 kPa. To further improve the bonding, linear functional poly(N-vinylpyrrolidone-co-glycidyl methacrylate) (PVP-co-GMA) copolymers were used that are known for covalently binding to fibrin. The maximum adhesion strength in our study was found to be 18.4 ± 3.4 kPa. The pure PVP-co-GMA copolymers also demonstrate covalent binding to the thiol-ene-based polymers with a maximum adhesion strength of 32.2 ± 2.7 kPa. Therefore, compared to pure fibrin, the presence of copolymer coating both on the polythioether surface and in the fibrin gel led to a significant increase of the adhesion strength by a factor of 1.6.

Instant tough adhesion of polymer networks

Generating strong rapid adhesion between hydrogels has the potential to advance the capabilities of modern medicine and surgery. Current hydrogel adhesion technologies rely primarily on liquid-based diffusion mechanisms and the formation of covalent bonds, requiring prolonged time to generate adhesion. Here, we present a simple and versatile strategy using dry chitosan polymer films to generate instant adhesion between hydrogel-hydrogel and hydrogel-elastomer surfaces. Using this approach we can achieve extremely high adhesive energies (>3,000 J/m2), which are governed by pH change and non-covalent interactions including H-bonding, Van der Waals forces, and bridging polymer entanglement. Potential examples of biomedical applications are presented, including local tissue cooling, vascular sealing, prevention of surgical adhesions, and prevention of hydrogel dehydration. We expect these findings and the simplicity of this approach to have broad implications for adhesion strategies and hydrogel design.