Renatured hydrogel painting

Inspired by lubricin: a tailored cartilage-armor with durable lubricity and autophagy-activated antioxidation for targeted therapy of osteoarthritis

Osteoarthritis (OA), which disables articular cartilage, affects millions of people. The self-healing capacity is inhibited by internal oxidative stress and external lubrication deficiency and enzymatic degradation. To overcome these challenges, a tailored cartilage-armor is designed to ameliorate the inflamed cartilage, which is implemented by a novel collagen type II (Col II)-binding peptide conjugated zwitterionic polymer (PSB-b-PColBP, PSP). By mimicking natural lubricin, PSP specifically targets the cartilage surface and forms an in situ hydration armor. This engineered cartilage-armor can prevent enzymatic cartilage degradation (nearly 100% resistance to catabolic enzymes) and provide durable lubrication properties (COF < 0.013 for 500 cycles). An autophagy-activation process, absent in previous biomimetic lubricants, enhances the enzymatic activity of the tailored cartilage-armor, offering effective anti-oxidant properties to suppress oxidative stress. By inhibiting the PI3K-Akt/NF-κB signaling pathway, chondrocytes protected by the tailored armor can secrete a cartilage matrix even in inflammatory microenvironments. In OA rat models, osteophyte formation and the inflammatory response have been inhibited by the cartilage-armor, demonstrating a therapeutic effect comparable to most drug-loaded systems. This study underscores the potential of tailoring cartilage-armor with the cartilage targeting and autophagy-activating properties in integrating offensive-defensive mechanisms for cartilage remodeling. This represents an alternative strategy for clinical OA therapy.

A Nature-Derived, Hetero-Structured, Pro-Healing Bioadhesive Patch for High-Performance Sealing of Wet Tissues

Tissue adhesives are promising alternatives to sutures and staples to achieve wound closure and hemostasis. However, they often do not work well on tissues that are soaked in blood or other biological fluids, and organs that are typically exposed to a variety of harsh environments such as different pH values, nonhomogeneous distortions, continuous expansions and contractions, or high pressures. In this study, a nature-derived multilayered hetero-bioadhesive patch (skin secretion of Andrias davidianus (SSAD)-Patch) based on hydrophilic/hydrophobic pro-healing bioadhesives derived from the SSAD is developed, which is designed to form pressure-triggered strong adhesion with wet tissues. The SSAD-Patch is successfully applied for the sealing and healing of tissue defects within 10 s in diverse extreme injury scenarios in vivo including rat stomach perforation, small intestine perforation, fetal membrane defect, porcine carotid artery incision, and lung lobe laceration. The findings reveal a promising new type of self-adhesive regenerative SSAD-Patch, which is potentially adaptable to broad applications (under different pH values and air or liquid pressures) in sutureless wound sealing and healing.

Structuring and Shaping of Mechanically Robust and Functional Hydrogels toward Wearable and Implantable Applications

Hydrogels possess unique features such as softness, wetness, responsiveness, and biocompatibility, making them highly suitable for biointegrated applications that have close interactions with living organisms. However, conventional man-made hydrogels are usually soft and brittle, making them inferior to the mechanically robust biological hydrogels. To ensure reliable and durable operation of biointegrated wearable and implantable devices, mechanical matching and shape adaptivity of hydrogels to tissues and organs are essential. Recent advances in polymer science and processing technologies have enabled mechanical engineering and shaping of hydrogels for various biointegrated applications. In this review, polymer network structuring strategies at micro/nanoscales for toughening hydrogels are summarized, and representative mechanical functionalities that exist in biological materials but are not easily achieved in synthetic hydrogels are further discussed. Three categories of processing technologies, namely, 3D printing, spinning, and coating for fabrication of tough hydrogel constructs with complex shapes are reviewed, and the corresponding hydrogel toughening strategies are also highlighted. These developments enable adaptive fabrication of mechanically robust and functional hydrogel devices, and promote application of hydrogels in the fields of biomedical engineering, bioelectronics, and soft robotics.

Robust, Sprayable, and Multifunctional Hydrogel Coating through a Polycation Reinforced (PCR) Surface Bridging Strategy

The sprayable hydrogel coatings that can establish robust adhesion onto diverse materials and devices hold enormous potential; however, a significant challenge persists due to monomer hydration, which impedes even coverage during spraying and induces inadequate adhesion post-gelation. Herein, a polycation-reinforced (PCR) surface bridging strategy is presented to achieve tough and sprayable hydrogel coatings onto diverse materials. The polycations offer superior wettability and instant electrostatic interactions with plasma-treated substrates, facilitating an effective spraying application. This PCR-based hydrogel coatings demonstrate tough adhesion performance to inert PTFE and silicone, including remarkable shear strength (161 ± 49 kPa for PTFE), interfacial toughness (198 ± 27 J m-2 for PTFE), and notable tolerance to cyclic tension (10 000 cycles, 200% strain, silicone). Meanwhile, this method can be applied to various hydrogel formulations, offering diverse functionalities, including underwater adhesion, lubrication, and drug delivery. Furthermore, the PCR concept enables the conformal construction of durable hydrogel coatings onto sophisticated medical devices like cardiovascular stents. Given its simplicity and adaptability, this approach paves an avenue for incorporating hydrogels onto solid surfaces and potentially promotes untapped applications.

Stretchable, Programmable and Magnet-Insensitive Protonic Display Based on Integrated Ionic Circuit

As a new approach to "More than Moore", integrated ionic circuits serve as a possible alternative to traditional electronic circuits, yet the integrated ionic circuit composed of functional ionic elements and ionic connections is still challenging. Herein, a stretchable and transparent ionic display module of the integrated ionic circuit has been successfully prepared and demonstrated by pixelating a proton-responsive hydrogel. It is programmed to excite the hydrogel color change by a Faraday process occurring at the electrode at the specific pixel points, which enables the display of digital information and even color information. Importantly, the display module exhibits stable performance under strong magnetic field conditions (1.7 T). The transparent and stretchable nature of such ionic modules also allows them to be utilized in a broad range of scenarios, which paves the way for integrated ionic circuits.

Surface functionalization of polyurethanes: A critical review

Synthetic polymers, particularly polyurethanes (PUs), have revolutionized bioengineering and biomedical devices due to their customizable mechanical properties and long-term stability. However, the inherent hydrophobic nature of PU surfaces arises common issues such as high friction, strong protein adsorption, and thrombosis, especially in the physiological environment of blood contact. To overcome these issues, researchers have explored various modification techniques to improve the surface biofunctionality of PUs. In this review, we have systematically summarized several typical surface modification methods including surface plasma modification, surface oxidation-induced grafting polymerization, isocyanate-based chemistry coupling, UV-induced surface grafting polymerization, adhesives-assisted attachment strategy, small molecules-bridge grafting, solvent evaporation technique, and hydrogen bonding interaction. Correspondingly, the advantages, limitations, and future prospects of these surface modification methods were discussed. This review provides an important guidance or tool for developing surface functionalized PUs in the fields of bioengineering and medical devices.

Growth of Double-Network Tough Hydrogel Coatings by Surface-Initiated Polymerization

Hydrogel coatings exhibit versatile applications in biomedicine, flexible electronics, and environmental science. However, current coating methods encounter challenges in simultaneously achieving strong interfacial bonding, robust hydrogel coatings, and the ability to coat substrates with controlled thickness. This paper introduces a novel approach to grow a double-network (DN) tough hydrogel coating on various substrates. The process involves initial substrate modification using a silane coupling agent, followed by the deposition of an initiator layer on its surface. Subsequently, the substrate is immersed in a DN hydrogel precursor, where the coating grows under ultraviolet (UV) illumination. Precise control over the coating thickness is achieved by adjusting the UV illumination duration and the initiator quantity. The experimental measurement of adhesion reveals strong bonding between the DN hydrogel coating and diverse substrates, reaching up to 1012.9 J/m2 between the DN hydrogel coating and a glass substrate. The lubricity performance of the DN hydrogel coating is experimentally characterized, which is dependent on the coating thickness, applied pressure, and sliding velocity. The incorporation of 3D printing technology into the current coating method enables the creation of intricate hydrogel coating patterns on a flat substrate. Moreover, the hydrogel coating's versatility is demonstrated through its effective applications in oil-water separation and antifogging glasses, underscoring its wide-ranging potential. The robust DN hydrogel coating method presented here holds promise for advancing hydrogel applications across diverse fields.

Durable hydrogel-based lubricated composite coating with remarkable underwater performances

HYPOTHESIS

Hydrogel coatings have received great attention in the field of such as medical devices, water treatment membranes, flexible electronics, and marine antifouling. However, when it comes to lubrication of hydrogel materials, though it has great potential applications in the field of industrial and medical drag reduction, some restrained properties are urgently needed to overcome for releasing the practical potential.

EXPERIMENTS

Durability of high lubrication was revealed from the sliding test during the long-term storage, as well as the long-distance sliding. Some variables which possibly affect the lubrication performance were examined to demonstrate that excellent lubricity of the coating would not be easily influenced by load, frequency, friction pair and temperature. The microstructure and mechanical characterization of the lubricative coating indicate that the resistance to harsh running conditions is premised on enough hydration extent and robustness. The formulae of Possion ratio and ball-on-disk contact stress which apply to soft matter were used for calculating contact stress values in tribology tests. Anti-swelling and bio-compatibility are also verified.

FINDINGS

This work found a route of achieving superior lubrication and coexisting with stability in lubrication, which can be used for drag reduction in medical devices and shipbuilding industry.

An underwater stable and durable gelatin composite hydrogel coating for biomedical applications

Developing underwater stable and durable hydrogel coatings with drag-reducing, drug release, and antibacterial properties is essential for lots of biomedical applications. However, most hydrogel coatings cannot meet the requirement of underwater stability and versatility, which severely limits their widespread use. In this work, an underwater stable, durable and substrate-independent gelatin composite hydrogel (GMP) coating is developed through covalent crosslinks, where a silane coupling agent with an unsaturated double bond is grafted onto a substrate of co-deposited polydopamine and polyethylenimine. GMP coating can be easily coated onto various medical device surfaces, such as artificial joints, catheters, tracheal tubes and titanium alloys, showing excellent structural stability and mechanical tunability under extreme conditions of ultrasonic treatment for 1 h (400 W of ultrasonic power) or underwater shearing for 14 days (400 rpm). Besides, friction experiment reveals that GMP coating exhibits good lubrication properties (coefficient of friction < 0.003). The drug-loading and bacterial inhibition ring tests show that the GMP coating has a tunable drug release ability with the final releasing ratios of 70-95% by changing the content of poly (ethylene glycol) diacrylate. This work offers a scalable approach of fabricating bio-functional and stable hydrogel coatings, which can be potentially used in biomedical applications.

A Programmable Actuator as Synthetic Earthworm

Natural earthworm with the ability to loosen soils that favors sustainable agriculture has inspired worldwide interest in the design of intelligent actuators. Given the inability to carry heavy loads and uncontrolled deformation, the vast majority of actuators can only perform simple tasks by bending, contraction, or elongation. Herein, a degradable actuator with the ability to deform in desired ways is presented, which successfully mimics the burrowing activities of earthworms to loosen soils with increased soil porosity by digging, grabbing, and lifting the soil when it receives rains. Such a scarifying actuator is made of degradable cellulose acetate and uncrosslinked polyacrylamide via the swelling-photopolymerizing method. The water absorption of polyacrylamide in moisture conditions causes rapid and remarkable bending. Such mechanical bending can be controlled in specific areas of the cellulose acetate film if polyacrylamide is polymerized in a patterned way, so as to generate complicated deformations of the whole cellulose acetate. Patterning polyacrylamide within cellulose acetate is achieved based on reversible surface protection by means of pen writing, rather than the traditional masking techniques. The water-induced deformation of programmable cellulose-based actuators is well preserved in soil, which is appropriate for promoting rain diffusion as well as root breath.

Diffusion-Limited Processes in Hydrogels with Chosen Applications from Drug Delivery to Electronic Components

Diffusion is one of the key nature processes which plays an important role in respiration, digestion, and nutrient transport in cells. In this regard, the present article aims to review various diffusion approaches used to fabricate different functional materials based on hydrogels, unique examples of materials that control diffusion. They have found applications in fields such as drug encapsulation and delivery, nutrient delivery in agriculture, developing materials for regenerative medicine, and creating stimuli-responsive materials in soft robotics and microrobotics. In addition, mechanisms of release and drug diffusion kinetics as key tools for material design are discussed.

Structurally dynamic self-healable hydrogel cooperatively inhibits intestinal inflammation and promotes mucosal repair for enhanced ulcerative colitis treatment

Hydrogels are a class of biocompatible materials with versatile functions that have been increasing explored for the localized treatment of ulcerative colitis (UC), but various mechanical stimuli may cause premature hydrogel breakage and detachment, impeding their further clinical translation. Here we report a multifunctional mechanically-resilient self-healing hydrogel for effective UC treatment, which is synthesized through the host-guest interaction between dopamine/β-cyclodextrin-modified hyaluronic acid (HA-CD-DA) and amantadine-modified carboxymethyl chitosan (CMCS-AD). The excessive β-CD cavities allow the incorporation of dexamethasone (DEX), while the porous hydrogel network potentiates the encapsulation of basic fibroblast growth factor (bFGF) and L-alanyl-l-glutamine (ALG). DA moieties in HA components allow firm adhesion of the hydrogel to the ulcerative lesions after in-situ implantation, while the reversible host-guest interaction between CD and AD could enhance the persistence of hydrogel. The hydrogel demonstrated favorable biocompatibility and could continuously release DEX to induce M1-to-M2 repolarization of mucosal macrophages through inhibiting the toll-like receptor 4 (TLR4)-nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) axis. Furthermore, the co-delivered bFGF and ALG facilitates the regeneration of ulcerative mucosa and restore its barrier functions to ameliorate UC symptoms. The mechanically resilient hydrogel offers an integrative approach for UC therapy in the clinics.

Strongly adhesive zwitterionic composite hydrogel paints for surgical sutures and blood-contacting devices

Hydrogels show eminent advantages in biomedical and pharmaceutical fields. However, their application as coating materials for biomedical devices is limited by several key challenges, such as lack of universality, weak mechanical strength, and low adhesion to the substrate. Here we report versatile and tough adhesion composite hydrogel paints (CHPs), which consist of zwitterionic copolymers and microgels, both with reactive groups. The CHPs exhibit tunable rheology and thickness, hydrophilicity, biofouling resistance, durability, and convenient fabrication on metal, polymer, and inorganic surfaces with arbitrary shapes. As a proof-of-concept, the CHP-surgical sutures demonstrate exceptional lubrication, drug delivery, anti-infection, and anti-fibrous capsule properties. Moreover, the CHP-PVC tubing effectively prevents thrombus formation in vitro and ex vivo rabbit blood circulation without anticoagulants. This work provides valuable insights for enhancing and developing integrated hydrogel technologies for biomedical devices. STATEMENT OF SIGNIFICANCE: The combination of hydrogel and biomedical devices can enable numerous existing applications in medicine. In this study, inspired by the principle of microgel reinforcement in industrial paints, we propose a simple and versatile zwitterionic composite hydrogel paints (CHPs) strategy, which can be easily applied to diverse substrates with arbitrary shapes by covalent grafting between complementary groups by brush, dip, or spray. The CHPs integrated universality, tough adhesion, mechanical durability, and anti-biofouling properties because of their unique chemical composition and coating structure design. This strategy provides a simple and versatile route for surface modification of biomedical devices.

Exosome inspired photo-triggered gelation hydrogel composite on modulating immune pathogenesis for treating rheumatoid arthritis

Although exosome therapy has been recognized as a promising strategy in the treatment of rheumatoid arthritis (RA), sustained modulation on RA specific pathogenesis and desirable protective effects for attenuating joint destruction still remain challenges. Here, silk fibroin hydrogel encapsulated with olfactory ecto-mesenchymal stem cell-derived exosomes (Exos@SFMA) was photo-crosslinked in situ to yield long-lasting therapeutic effect on modulating the immune microenvironment in RA. This in situ hydrogel system exhibited flexible mechanical properties and excellent biocompatibility for protecting tissue surfaces in joint. Moreover, the promising PD-L1 expression was identified on the exosomes, which potently suppressed Tfh cell polarization via inhibiting the PI3K/AKT pathway. Importantly, Exos@SFMA effectively relieved synovial inflammation and joint destruction by significantly reducing T follicular helper (Tfh) cell response and further suppressing the differentiation of germinal center (GC) B cells into plasma cells. Taken together, this exosome enhanced silk fibroin hydrogel provides an effective strategy for the treatment of RA and other autoimmune diseases.

Customizable Low-Friction Tough Hydrogels for Potential Cartilage Tissue Engineering by a Rapid Orthogonal Photoreactive 3D-Printing Design

Hydrogels have demonstrated wide applications in tissue engineering, but it is still challenging to develop strong, customizable, low-friction artificial scaffolds. Here, we report a rapid orthogonal photoreactive 3D-printing (ROP3P) strategy to achieve the design of high-performance hydrogels in tens of minutes. The orthogonal ruthenium chemistry enables the formation of multinetworks in hydrogels via phenol-coupling reaction and traditional radical polymerization. Further Ca²⁺-cross-linking treatment greatly improves their mechanical properties (6.4 MPa at a critical strain of 300%) and toughness (10.85 MJ m^-3). The tribological investigation reveals that the high elastic moduli of the as-prepared hydrogels improve their lubrication (∼0.02) and wear-resistance performances. These hydrogels are biocompatible and nontoxic and promote bone marrow mesenchymal stem cell adhesion and propagation. The introduction of 1-hydroxy-3-(acryloylamino)-1,1-propanediylbisphosphonic acid units can greatly enhance their antibacterial property to kill typical Escherichia coli and Staphylococcus aureus. Moreover, the rapid ROP3P can achieve hydrogel preparation in several seconds and is readily compatible with making artificial meniscus scaffolds. The printed meniscus-like materials are mechanically stable and can maintain their shape under long-term gliding tests. It is anticipated that these high-performance customizable low-friction tough hydrogels and the highly efficient ROP3P strategy could promote further development and practical applications of hydrogels in biomimetic tissue engineering, materials chemistry, bioelectronics, and so on.

Stainless Steel Screen Modified with Renatured Xerogel for Efficient and Highly Stable Oil/Water Separation via Gravity

The application of hydrogel coatings to surface-modified metallic materials has gained considerable attention in engineering practice such as water-oil separation. However, the low coating adhesion and poor coating stability restrict its application. In this study, to obtain special wettability and durable filter materials, polyacrylamide (PAM)/sodium alginate (SA) xerogel particles were first prepared and adhered to a stainless steel screen by using an epoxy resin as a linker. Subsequently, the xerogel particles of the screen rehydrates in water to form a PAM-SA double-network hydrogel. The results show that the screen modified by PAM-SA xerogel of 20-30 μm particle size and a linker concentration of 0.1 g/mL resulted in a chimeric structure and subsequently transformed a uniform double-network hydrogel coating in water. According to the experimental results, the rough hydrogel coating exhibits superhydrophilicity and superoleophobicity under water; in particular, it has excellent wear resistance as well as physical and chemical stability. Under gravity-driven action, the PAM-SA-modified screen demonstrates high separation efficiency values of up to 99% in separating a wide range of oil/water mixtures and maintaining a water flux of (2-6) × 10⁴ L·m^-2·h^-1. There was no significant reduction in efficiency of separation and water flux after 10 cycles, indicating that the PAM-SA-modified screen is capable of offering outstanding separation performance and durability. Moreover, the hydrogel-modified screen demonstrated corrosion and swelling resistance in some extreme environments, paving a way for practical applications in water treatment. The novel hydrogel-coating-modified screen with ease of preparation holds great promise for oil/water separation and other engineering applications.

Review of Flexible Wearable Sensor Devices for Biomedical Application

With the development of cross-fertilisation in various disciplines, flexible wearable sensing technologies have emerged, bringing together many disciplines, such as biomedicine, materials science, control science, and communication technology. Over the past few years, the development of multiple types of flexible wearable devices that are widely used for the detection of human physiological signals has proven that flexible wearable devices have strong biocompatibility and a great potential for further development. These include electronic skin patches, soft robots, bio-batteries, and personalised medical devices. In this review, we present an updated overview of emerging flexible wearable sensor devices for biomedical applications and a comprehensive summary of the research progress and potential of flexible sensors. First, we describe the selection and fabrication of flexible materials and their excellent electrochemical properties. We evaluate the mechanisms by which these sensor devices work, and then we categorise and compare the unique advantages of a variety of sensor devices from the perspective of in vitro and in vivo sensing, as well as some exciting applications in the human body. Finally, we summarise the opportunities and challenges in the field of flexible wearable devices.

Artificial Kidney Capsule Packed with Mesenchymal Stem Cell-Laden Hydrogel for the Treatment of Rhabdomyolysis-Induced Acute Kidney Injury

Acute kidney injury (AKI) has emerged as a major public health problem affecting millions of people worldwide without specific and satisfactory therapies due to the lack of an effective delivery approach. In the past few decades, hydrogels present infinite potential in localized drug delivery, while their poor adhesion to moist tissue and isotropic diffusion character always restrict the therapeutic efficiency and may lead to unwanted side effects. Herein, we proposed a novel therapeutic strategy for AKI via a customizable artificial kidney capsule (AKC) together with a mesenchymal stem cell (MSC)-laden hydrogel. Specifically, an elastic capsule owning an inner chamber with the same size and shape as the kidney is designed and fabricated through three-dimensional (3D) modeling and printing, serving as an outer wrap for kidney and cell-laden hydrogels. According to the in vitro experiment, the excellent biocompatibility of gelatin-based hydrogel ensures viability and proliferation of MSCs. In vivo mice experiments proved that this concept of AKC-assisted kidney drug delivery could efficiently reduce epithelial cell apoptosis and minimize the damage of the renal tubular structure for mice suffering AKI. Such a strategy not only provides a promising alternative in the treatment of AKI but also offers a feasible and versatile approach for the repair and recovery of other organs.

COCu: A Robust Self-Regenerative Hydrogel with Applicability as Both Hydrated Gel Dressing and Dry Suture for Seamless Tissue Fixation and Repair

Self-regenerative hydrogels have recently been developed, and represent a special type of self-healing hydrogels with the ability to restore a dehydrated hydrogel with physical damage. In this study, a self-regenerative hydrogel (COCu) based on two chitosan polymers assembled by slow-released Cu²⁺ is developed. The COCu hydrogel displays an excellent regeneration ability after being dehydrated and fractured. By simple hydration at room temperature, the fragments of the dehydrated gel fuse into one seamless whole, thereby preserving the mechanical properties and functionalities of the original hydrogel. The regeneration process can be conducted repeatedly after different methods of dehydration (natural volatilization, heat drying, lyophilization) and various modes of deconstruction (flakes, powder, lumpy sponge, etc.). Furthermore, the COCu hydrogel provides ultra-stretchability, and it can be stretched into thin (0.01-0.1 mm) filaments, which, when dried (dtCOCu), can be used as suture lines. Moreover, when used as a dry suture, it regenerates into the hydrogel in the presence of the tissue fluid, forming an excellent sealant to immobilize tissues and seamlessly seal wounds. The fast self-regeneration allows for its facile application as both a hydrated gel dressing and dry suture, and offers customized strategies for fixing and repair of different wounds in soft tissues.

WET-Induced Layered Organohydrogel as Bioinspired "Sticky-Slippy Skin" for Robust Underwater Oil-Repellency

Underwater superoleophobic surfaces featuring anti-oil-fouling properties are of great significance in widespread fields. However, their complicated engineering process and weak interfacial adhesion strength with underlying substrates severely hamper these ideal surfaces toward practical applications. Here, a moss-inspired sticky-slippy skin composed of layered organohydrogel is reported through a one-step wetting-enabled-transfer (WET) strategy, which unprecedentedly integrates robust inherent adhesion with durable anti-oil-fouling properties. The sticky organogel layer can be simply attached to various substrates, from metals and plastics to glass, independent of any surface pretreatment. The slippy hydrogel layer enables stable underwater superoleophobicity and ultralow oil adhesion for diverse kinds of oils. The sticky-slippy skin features outstanding comprehensive properties including easy-pasting, anti-swelling/anti-bending, compatibility with commercial adhesives, acid/alkali resistance, environmental friendliness, and substrate universality. The design strategy with integrated functions provides a clue to accelerate the development of bioinspired multifunctional interfacial materials toward real-world applications.

Visible-Light-Mediated Nano-biomineralization of Customizable Tough Hydrogels for Biomimetic Tissue Engineering

Biomineralized tough hydrogels (BTHs) have advanced applications in the fields of soft bioelectronics and biomimetic tissue engineering. But the development of rapid and general photomineralization strategies for one-step fabrication of customizable BTHs is still a challenging task. Here we report a straightforward, low-cost visible-light-mediated nano-biomineralization (VLMNB) strategy via a rational design of a phosphate source and efficient ruthenium photochemistry. Multinetwork tough hydrogels are simultaneously constructed under the same condition. Therefore, BTHs are rapidly prepared in a short time as low as ∼60 s under visible light irradiation. The in situ formation of calcium phosphate particles can improve BTHs' mechanical and biological properties and reduce the friction coefficient with bones. Furthermore, fast biomineralization and solidification processes in these BTHs benefit their injectable and highly flexible customizable design, showing applications of promoting customizable skin repair and bone regeneration.

A Universal Strategy for Growing a Tenacious Hydrogel Coating from a Sticky Initiation Layer

Controllably coating the surfaces of substrates/medical devices with hydrogels exhibits great application potential, but lacks universal techniques. Herein, a new method, namely ultraviolet-triggered surface catalytically initiated radical polymerization (UV-SCIRP) from a sticky initiation layer (SIL) (SIL@UV-SCIRP), is proposed for growing hydrogel coatings. The method involves three key steps: 1) depositing a sticky polydopamine/Fe³⁺ coating on the surface of the substrates-SIL, 2) reducing Fe³⁺ ions to Fe²⁺ ions as active catalysts by UV illumination with the assistance of citric acid, and 3) conducting SCIRP in a monomer solution at room temperature for growing hydrogel coatings. In this manner, practically any substrate's surface (natural or artificial materials) can be modified by hydrogel coatings with controllable thickness and diverse compositions. The hydrogel coatings exhibit good interface bonding with the substrates and enable easy changes in their wettability and lubrication performances. Importantly, this novel method facilitates the smooth growth of uniform hydrogel lubrication coatings on the surface of a range of medical devices with complex geometries. Finally, as a proof-of-concept, the slippery balls coated with hydrogel exhibited smooth movement within the catheter and esophagus. Hence, this method can prove to be a pioneering universal modification tool, especially in surface/interface science and engineering.

Mucosa-Like Conformal Hydrogel Coating for Aqueous Lubrication

Mucosa is a protective and lubricating barrier in biological tissue, which has a great clinical inspiration because of its slippery, soft, and hydrophilic surface. However, mimicking mucosal traits on complex surface remains an enormous challenge. Herein, a novel approach to create mucosa-like conformal hydrogel coating is developed. A thin conformal hydrogel layer mimicking the epithelial layer is obtained by first absorbing micelles, followed by forming covalent interlinks with the polymer substrate via interface-initiated hydrogel polymerization. The resulting coating exhibits uniform thickness (≈15 µm), mucosa-matched compliance (Young's modulus = 1.1 ± 0.1 kPa) and lubrication (coefficients of friction = 0.018 ± 0.003), robust interfacial bonding against peeling (peeling strength = 1218.0 ± 187.9 J m^-2 ), as well as high water absorption capacity. It effectively resists adhesion of proteins and bacteria without compromising biocompatibility. As demonstrated by an in vivo cynomolgus monkey model and clinical trial, applications of the mucosa-like conformal hydrogel coating on the endotracheal tube significantly reduce intubation-related complications, such as invasive stimuli, mucosal lesions, laryngeal edema, inflammation, and postoperative pain. This work offers a promising prototype for surface decoration of biomedical devices and holds great prospects for clinical translation to enable interventional operations with minimally invasive impacts.