Novel biomimetic macromolecules system for highly efficient lubrication, ROS scavenging and osteoarthritis treatment.

The early stages of osteoarthritis (OA) in the joints are typically characterized by two key factors: the dysfunction of articular cartilage lubrication and inflammation resulting from the excessive production of reactive oxygen species (ROS). Synthetic injectable macromolecular materials present great potential for preventing the progression of early OA. In this study, to mimic the excellent lubricity of brush-like aggregates found in natural synovial fluid, we develop a novel macromolecular biolubricant (CS-PS-DA) by integrating adhesion and hydration groups onto backbone of natural biomacromolecules. CS-PS-DA exhibits a strong affinity for cartilage surfaces, enabling the formation of a stable lubrication layer at the sliding interface of degraded cartilages to restore joint lubrication performance. In vitro results from ROS scavenging and anti-inflammatory experiments indicate the great advantage of CS-PS-DA to decrease the levels of proinflammatory cytokines by inhibiting ROS overproduction. Finally, in vivo rats OA model demonstrates that intra-cavitary injection of CS-PS-DA could effectively resist cartilage wear and mitigated inflammation in the joints. This novel biolubricant provides a new and timely strategy for the treatment of OA.

Design of Stretchable and Conductive Self-Adhesive Hydrogels as Flexible Sensors by Guar-Gum-Enabled Dynamic Interactions.

The limited elasticity and inadequate bonding of hydrogels made from guar gum (GG) significantly hinder their widespread implementation in personalized wearable flexible electronics. In this study, we devise GG-based self-adhesive hydrogels by creating an interpenetrating network of GG cross-linked with acrylic, 4-vinylphenylboronic acid, and Ca2+. With the leverage of the dynamic interactions (hydrogen bonds, borate ester bonds, and coordination bonds) between -OH in GG and monomers, the hydrogel exhibits a high stretchability of 700%, superior mechanical stress of 110 kPa, and robust adherence to several substrates. The adhesion strength of 54 kPa on porcine skin is obtained. Furthermore, the self-adhesive hydrogel possesses stable conductivity, an elevated gauge factor (GF), and commendable durability. It can be affixed to the human body as a strain sensor to obtain precise monitoring of human movement behavior. Our research offers possibilities for the development of GG-based hydrogels and applications in wearable electronics and medical monitoring.

Bioinspired Interfacial Friction Control: From Chemistry to Structures to Mechanics.

Organisms in nature have evolved a variety of surfaces with different tribological properties to adapt to the environment. By studying, understanding, and summarizing the friction and lubrication regulation phenomena of typical surfaces in nature, researchers have proposed various biomimetic friction regulation theories and methods to guide the development of new lubrication materials and lubrication systems. The design strategies for biomimetic friction/lubrication materials and systems mainly include the chemistry, surface structure, and mechanics. With the deepening understanding of the mechanism of biomimetic lubrication and the increasing application requirements, the design strategy of multi-strategy coupling has gradually become the center of attention for researchers. This paper focuses on the interfacial chemistry, surface structure, and surface mechanics of a single regulatory strategy and multi-strategy coupling approach. Based on the common biological friction regulation mechanism in nature, this paper reviews the research progress on biomimetic friction/lubrication materials in recent years, discusses and analyzes the single and coupled design strategies as well as their advantages and disadvantages, and describes the design concepts, working mechanisms, application prospects, and current problems of such materials. Finally, the development direction of biomimetic friction lubrication materials is prospected.

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.

Functional Zwitterionic Polyurethanes: State-of-the-Art Review.

Recent advancements in bioengineering and medical devices have been greatly influenced and dominated by synthetic polymers, particularly polyurethanes (PUs). PUs offer customizable mechanical properties and long-term stability, but their inherent hydrophobic nature poses challenges in practically biological application processes, such as interface high friction, strong protein adsorption, and thrombosis. To address these issues, surface modifications of PUs for generating functionally hydrophilic layers have received widespread attention, but the durability of generated surface functionality is poor due to irreversible mechanical wear or biodegradation. As a result, numerous researchers have investigated bulk modification techniques to incorporate zwitterionic polymers or groups onto the main or side chains of PUs, thereby improving their hydrophilicity and biocompatibility. This comprehensive review presents an extensive overview of notable zwitterionic PUs (ZPUs), including those based on phosphorylcholine, sulfobetaine, and carboxybetaine. The review explores their wide range of biomedical applications, from blood-contacting devices to antibacterial coatings, fouling-resistant marine coatings, separation membranes, lubricated surfaces, and shape memory and self-healing materials. Lastly, the review summarizes the challenges and future prospects of ZPUs in biological applications.

Microgel-Modified Bilayered Hydrogels Dramatically Boosting Load-Bearing and Lubrication.

Hydrogel-based articular cartilage replacement materials are promising candidates for their potential to provide both high load-bearing capacity and low friction performance, similar to natural cartilage. Nevertheless, the design of these materials presents a significant challenge in reconciling the conflicting demands of the load-bearing capacity and lubrication. Despite extensive research in this area, there is still room for improvement in the creation of hydrogel-based materials that effectively meet these demands. Herein, a facile strategy is provided to realize simultaneously high load-bearing and low friction properties on the proposed hydrogel by modifying the surface of mechanically strong annealled PVA-PAAc hydrogel with a high hydration potential PAAm-co-PAMPS microgel. Consequently, a bilayer hydrogel with a porous surface and a compact substrate has been obtained. Compressive experiments confirmed that the bilayer hydrogel exhibited excellent mechanical strength with a compressive strength of 32.23 MPa at 90% strain. A high load-bearing (applied load up to 30 N), extremely low friction coefficiency (0.01-0.05) and excellent wear resistance (COF low to 0.03 after a 4 h test at 10 N using a steel ball as the contact pair) are successfully achieved. These findings provide new perspectives for the design of articular cartilage materials.

Bioinspired simultaneous regulation in fluorescence of AIEgen-embedded hydrogels.

The development of stimuli-responsive functional fluorescent hydrogels is of great significance for the realization of artificial intelligence. In the present work, we design and synthesize a stimulus-responsive hydrogel embedded with an aggregation-induced emission (AIE) monomer, in which the fluorescence brightness and intensity can be tuned. The hydrogel embedded with tetraphenylethene-grafted-poly[3-sulfopropyl methacrylate potassium salt] (TPE-PSPMA) as the functional element is prepared by the radical polymerization method. Among them, the TPE core exhibits adaptive fluorescence ability through the AIE effect, while the PSPMA chain provides tunable hydrophilic properties under an external stimulus. The effect of different cationic surfactants with different lengths of hydrophobic tails on the fluorescence properties of TPE-PSPMA in solution is systematically investigated. With cationic surfactants, such as cetyltrimethylammonium bromide (CTAB), the fluorescence intensity is gradually tuned from 1059 to 4623. And the fluorescence intensities increase with the growth of hydrophobic tails of surfactants, which results from hydrophobicity-induced electrostatic interactions among surfactants and polymer chains. Furthermore, an obvious tunable fluorescence feature of hydrogel copolymerized TPE-PSPMA is realized, resulting from the change of brightness and the dynamic increase of fluorescence intensity (from 1031 to 3138) for the hydrogel immersed in CTAB solution with different soaking times. Such a typical fluorescence-regulated behavior can be attributed to the AIE of the TPE-PSPMA chain and the electrostatic interaction between the surfactant and the anionic polymer chain. The designed TPE-PSPMA-based hydrogel is responsive to stimuli, inspiring the development of intelligent systems such as soft robots and smart wearables.

Water-assisted strong underwater adhesion via interfacial water removal and self-adaptive gelation.

In nearly all cases of underwater adhesion, water molecules typically act as a destroyer. Thus, removing interfacial water from the substrate surfaces is essential for forming super-strong underwater adhesion. However, current methods mainly rely on physical means to dislodge interfacial water, such as absorption, hydrophobic repulsion, or extrusion, which are inefficient in removing obstinate hydrated water at contact interface, resulting in poor adhesion. Herein, we present a unique means of reversing the role of water to assist in realizing a self-strengthening liquid underwater adhesive (SLU-adhesive) that can effectively remove water at contact interface. This is achieved through multiscale physical-chemical coupling methods across millimeter to molecular levels and self-adaptive strengthening of the cohesion during underwater operations. As a result, strong adhesion over 1,600 kPa (compared to ~100 to 1,000 kPa in current state of the art) can be achieved on various materials, including inorganic metal and organic plastic materials, without preloading in different environments such as pure water, a wide range of pH solutions (pH = 3 to 11), and seawater. Intriguingly, SLU-adhesive/photothermal nanoparticles (carbon nanotubes) hybrid materials can significantly reduce the time required for complete curing from 24 h to 40 min using near-infrared laser radiation due to unique thermal-response of the chemical reaction rate. The excellent adhesion property and self-adaptive adhesion procedure allow SLU-adhesive materials to demonstrate great potential for broad applications in underwater sand stabilization, underwater repair, and even adhesion failure detection as a self-reporting adhesive. This concept of "water helper" has potential to advance underwater adhesion and manufacturing strategies.

A Strong and Double-sided Self-Adhesive Hydrogel Sensor.

Flexible self-adhesive hydrogel sensors are attracting considerable concerns in recent years. However, creating a self-adhesive hydrogel sensor with excellent mechanical properties remains to be challenging. Herein, a double-sided self-adhesive hydrogel capable of strain sensor with high strength is demonstrated by penetration strategy. The middle poly(acrylic acid)-polyacrylamide/Fe3+ (PAA-PAM/Fe3+ ) tough layer endows the double-sided self-adhesive hydrogel with high mechanical properties, while the bilateral poly[2-(methacryloyloxy) ethyl]dimethyl-(3-sulfopropyl)ammonium hydroxide-polyacrylamide (PSBMA-PAM) adhesive layers are used to ensure excellent adhesiveness on diverse substrates. The tough layer of the double-sided self-adhesive hydrogel sensor shows a strong interface bonding force against the adhesive layer. The double-sided self-adhesive hydrogel sensor enables excellent adhesiveness on diverse substrates. More importantly, it can accurately detect different strains and human motions as a self-adhesive hydrogel strain sensor. This work manifests a new route of structural design to develop a self-adhesive hydrogel sensor with excellent mechanical properties that is suitable for a wide range of applications.

Biomimetic chitosan nanoparticles with simultaneous water lubricant and anti-inflammatory.

Rheumatoid arthritis (RA) is a chronic inflammatory immune and lubrication dysfunction disease that causes great damage to the joints. Herein, inspired by the unique biochemistry structure and excellent hydration of chondroitin sulfate (CHI) existing in joint system, one kind of novel polysaccharide nanoparticle lubricant, that is chitosan nanoparticles (CS NPs) grafting CHI (CS-CHI), is synthesized by one-step surface chemistry reaction. CHI with negative charges can form hydration layers on the surface of CS NPs, thus improving the lubricity of nanoparticles. Simultaneously, CS-CHI NPs have effective loading and sustained drug release ability for anti-inflammatory drug diclofenac sodium (DS), along with good biocompatibility. Finally, based on a collagen-induced rat RA model, in vitro animals experimental results indicate that the as-synthesized CS-CHI@DS NPs has obvious inhibitory effects on inflammatory factors and can effectively prevent the damaged cartilage from further destruction.

Injectable carboxymethyl chitosan/nanosphere-based hydrogel with dynamic crosslinking network for efficient lubrication and sustained drug release.

The typical symptoms of arthritis are inflammation and lubrication deficiency in joints, which increase wear of articular cartilage along with pain of patients. In the present study, one kind of novel macromolecular/microsphere-based injectable hydrogels (CMC-ODex NPs) with dual functionalities of drug release and lubrication, was fabricated via dynamic Schiff base crosslinking network between carboxymethyl chitosan (CMC) and oxidation dextran nanoparticles (ODex NPs). The CMC-ODex NPs hydrogels exhibited typical viscosity-thinning phenomenon at wide range of shear rates and obvious gel-sol transition feature at specific strain. As a result, CMC-ODex NPs hydrogels presented low friction coefficient at the sliding interface of bovine articular cartilages, resulting from the boundary lubrication of hydrogel and the rolling friction effect of ODex NPs. Furthermore, the anti-inflammatory drug (dexamethasone, DXM) encapsulated in ODex NPs exhibited sustainable drug release behavior during the dynamic shearing process, which making CMC-ODex NPs hydrogels possessed good and stable anti-inflammatory effect. CMC-ODex NPs hydrogels was prepared without utilizing any toxic agents, thus demonstrated excellent cytocompatibility. Our experimental results reveal the CMC-ODex NPs hydrogels is promising to be used as functional lubricant for inhibiting the development of arthritis.

Biomimetic chitosan-derived bifunctional lubricant with superior antibacterial and hydration lubrication performances.

The lubrication deficiency in joints is a major cause of osteoarthritis. One of the most commonly used treatment means is to inject artificial lubricants, but there is a potential risk of infection during the injection process. Therefore, developing artificial lubricants with dual functions of friction-reduction and antibacterial is urgent. In this work, a novel polysaccharide-derived lubricant with simultaneous anti-bacteria and water-lubrication properties, called CS-MPC-N, is developed by grafting 2­methacryloyloxylethyl phosphorylcholine (MPC) and nisin peptide onto backbone of chitosan (CS). Compared to the control CS, CS-MPC-N exhibits good lubrication and friction-reduction properties because of its excellent water solubility. Especially, CS-MPC-N shows low friction coefficient (0.03 âˆ¼ 0.05) at the sliding interfaces of artificial joints materials or even natural articular cartilages. Moreover, CS-MPC-N can effectively inhibit the proliferation of Staphylococcus aureu, exhibiting excellent antibacterial effect. This kind of novel polysaccharide-derived lubricant is expected to be used in treating infectious arthritis.

Bioinspired Polysaccharide Derivative with Efficient and Stable Lubrication for Silicon-Based Devices.

It is becoming increasingly important to synthesize efficient biomacromolecule lubricants suitable for medical devices. Even though the development of biomimetic lubricants has made great progress, the current system suitable for hydrophobic silicone-based medical devices is highly limited. In this work, we synthesize one kind of novel polysaccharide-derived macromolecule lubricant of chitosan (CS) grafted polyethylene glycol (PEG) chains and catechol groups (CT) (CS-g-PEG-g-CT). CS-g-PEG-g-CT shows good adsorption ability by applying quantitative analysis of quartz crystal microbalance (QCM), attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR), and confocal fluorescence imaging technique, as well as the typical shear-thinning feature. CS-g-PEG-g-CT exhibits low and stable coefficients of friction (COFs) (0.01-0.02) on polydimethylsiloxane (PDMS) surfaces at a wide range of mass concentrations in diverse media including pure water, physiological saline, and PBS buffer solution and is even tolerant to various normal loads and sliding frequencies for complex pressurizing or shearing environments. Subsequently, systematic surface characterizations are used to verify the dynamic attachment ability of the CS-g-PEG-g-CT lubricant on the loading/shearing process. The lubrication mechanism of CS-g-PEG-g-CT can be attributed to the synergy of strong adsorption from catechol groups to form a uniform assembly layer, excellent hydration effect from PEG chains, and typical shear-thinning feature to dissipate viscous resistance. Surprisingly, CS-g-PEG-g-CT exhibits efficient lubricity on silicone-based commercial contact lenses and catheters. The current macromolecule lubricant demonstrates great real application potential in the fields of medical devices and disease treatments.

Successive Redox-Reaction-Triggered Interface Radical Polymerization for Growing Hydrogel Coatings on Diverse Substrates.

Growing lubricating hydrogel coatings in controllable manners on diverse material surfaces demonstrates promising applications. Here, a surface modification method is reported for in situ growing hydrogel coatings onto surfaces of diverse substrates in the absence of UV assistance. It is performed by decorating substrates with a universal mussel-inspired synthetic adhesive with catechol groups. Upon being immersed in reaction solution, these groups can assist substrate bonding and in situ capture and reduce Fe3+ into Fe2+ for decomposing S2 O8 2- into SO4 - ⋅ catalytically at the interface to initiate interface polymerization of monomers. As a result, hydrogel coatings with controllable thickness could be grown on surfaces of arbitrary substrates to change their surface characteristics regardless of materials size, category, geometry and transparency, implying considerable potential in surface engineering.

Toward a Multifunctional Light-Driven Biomimetic Mudskipper-Like Robot for Various Application Scenarios.

The systematicness, flexibility, and complexity of natural biological organisms are a constant stream of inspiration for researchers. Therefore, mimicking the natural intelligence system to develop microrobotics has attracted broad interests. However, developing a multifunctional device for various application scenarios has great challenges. Herein, we present a bionic multifunctional actuation device─a light-driven mudskipper-like actuator that is composed of a porous silicone elastomer and graphene oxide. The actuator exhibits a reversible and well-integrated response to near-infrared (NIR) light due to the photothermal-induced contractile stress in the actuation film, which promotes generation of cyclical and rapid locomotion upon NIR light being switched on and off, such as bending in air and crawling in liquid. Furthermore, through rational device design and modulation of light, the mechanically versatile device can float and swim controllably following a predesigned route at the liquid/air interface. More interestingly, the actuator can jump from liquid medium to air with an extremely short response time (400 ms), a maximum speed of 2 m s-1, and a height of 14.3 cm under the stimulation of near-infrared light. The present work possesses great potential in the applications of bioinspired actuators in various fields, such as microrobots, sensors, and locomotion.

Bioinspired Polysaccharide-Derived Zwitterionic Brush-like Copolymer as an Injectable Biolubricant for Arthritis Treatment.

Developing highly efficient and biocompatible biolubricants for arthritis treatment is extraordinarily demanded. Herein, inspired by the efficient lubrication of synovial joints, a paradigm that combines natural polysaccharide (chitosan) with zwitterionic poly[2-(methacryloyloxy) ethyl phosphorylcholine] (PMPC), to design a series of brush-like Chitosan-g-PMPC copolymers with highly efficient biological lubrication and good biocompatibility is presented. The Chitosan-g-PMPC copolymers are prepared via facile one-step graft polymerization in aqueous medium without using any toxic catalysts and organic solvents. The as-prepared Chitosan-g-PMPC copolymers exhibit very low coefficient of friction (µ < 0.01) on Ti6 Al4 V alloy substrate in both pure water and biological fluids. The superior lubrication is attributed primarily to the hydrated feature of PMPC side chains, interface adsorption of copolymer as well as to the hydrodynamic effect. In vivo experiments confirm that Chitosan-g-PMPC can alleviate the swelling symptom of arthritis and protect the bone and cartilage from destruction. Due to their facile preparation, distinctive lubrication properties, and good biocompatibility, Chitosan-g-PMPC copolymers represent a new type of biomimetic lubricants derived from natural biopolymer for promising arthritis treatment and artificial joint lubrication.

Repeatedly Regenerating Mechanically Robust Polymer Brushes from Persistent Initiator Coating (PIC).

In this study, a novel surface initiated polymerization (SIP) method was developed from organic-inorganic hybrid persistent initiator coating (PIC) that embeds initiator molecules into inorganic silica sol-gel layer. Comparing with traditional silane initiator surface that prepared by chemical vapor deposition (CVD) method, the PIC can effectively improve the mechanical stability of initiator that was able to endure ten-thousand times of friction cycles. Besides, it allows polymer grafting from sub-surface and so the grafted brushes, poly 3-sulfopropyl methacrylate potassium salt (pSPMA) on the PIC were also much more wear-resisting than those prepared by the traditional ways. More importantly, the PIC could still trigger new polymerization reaction when the grafted brushes were worn off. In addition, the PIC is universal and can be covered on different substrates including glass, metals and plastics, etc. to realize functionalization of these materials. The approach may pave technological way for the application of surface grafted polymer brushes.

Molecular Engineering Super-Robust Dry/Wet Adhesive with Strong Interface Bonding and Excellent Mechanical Tolerance.

Despite the fact that synthetic adhesives have achieved great progress, achieving robust dry/wet adhesion under harsh operating environments is still challenging. Herein, inspired from the extraordinary adhesion mechanism of nature mussel protein adhesive, the balanced design concept of co-adhesion and interfacial adhesion is proposed to prepare one kind of novel copolymer adhesive of [poly(dopamine methacrylamide-co-methoxethyl acrylate-co-adamantane-1-carboxylic acid 2-(2-methyl-acryloyloxy)-ethyl ester)] [p(DMA-co-MEA-co-AD)], named as super-robust adhesive (SRAD). The SRAD exhibits ultra-high interface bonding strengths in air (∼7.66 MPa) and underwater (∼2.78 MPa) against an iron substrate. Especially, a greatly tough and stable adhesion strength (∼2.11 MPa) can be achieved after immersing the bonded sample in water for half a year. Furthermore, the SRAD demonstrates surprising wet bonding robustness/tolerance even encountering harsh conditions such as fluid shearing, dynamic loading, and cyclic mechanical fretting. The great advantages of SRAD, such as strong interface bonding, stable wet adhesion underwater, and good mechanical tolerance, makes it demonstrate huge application potential in engineering sealants and underwater adhesion.

Bioinspired Design of a Cartilage-like Lubricated Composite with Mechanical Robustness.

Natural articular cartilages show extraordinary tribological performance based on their penetrated surface lubricated biomacromolecules and good mechanical tolerance. Hydrogels are considered to be potential alternatives to cartilages due to their low surface friction and good biocompatibility, although the poor mechanical properties limited their applications. Inspired by the excellent mechanical properties and the remarkable surface lubrication mechanism of natural articular cartilages, one kind of cartilage-like composite material with a lubrication phase (Composite-LP) was developed by chemically grafting a thick hydrophilic polyelectrolyte brush layer onto the subsurface of a three-dimensional manufactured elastomer scaffold-hydrogel composite architecture. The Composite-LP exhibited good load-bearing capacities because of the nondissipation strategy and the stress dispersion mechanism resulting from the elastomer scaffold enhancement. In the presence of the top lubrication layer, the Composite-LP showed superior friction reduction functionality and wear resistance under a dynamic shearing process. This design concept of coupling the non-dissipative mechanism and interface lubrication provides a new avenue for developing cartilage-like hydrogels and soft robots.

Modulus adaptive lubricating prototype inspired by instant muscle hardening mechanism of catfish skin.

In nature, living organisms evolve unique functional components with mechanically adaptive compatibility to cater dynamic change of interface friction/lubrication. This mechanism can be used for developing intelligent artificial lubrication-regulation systems. Inspired by the muscle hardening-triggered lubrication of longsnout catfish, here we report a modulus adaptive lubricating hydrogel prototype consisting of top mucus-like hydrophilic lubricating layer and muscle-like bottom hydrogel that can stiffen via thermal-triggered phase separation. It exhibits instant switch from soft/high frictional state (~0.3 MPa, µ~0.37) to stiff/lubricating state (~120 MPa, µ~0.027) in water upon heating up. Such switchable lubrication is effective for wide range of normal loads and attributed to the modulus-dominated adaptive contact mechanism. As a proof-of-concept, switchable lubricating hydrogel bullets and patches are engineered for realizing controllable interface movements. These important results demonstrate potential applications in the fields of intelligent motion devices and soft robots.