Tough Bonding of PVA Hydrogel-on-Textured Titanium Alloy with Varying Texture Densities in Swollen State.

Cartilage defects in large joints are a common occurrence in numerous degenerative diseases, especially in osteoarthritis. The hydrogel-on-metal composite has emerged as a potential candidate material, as hydrogels, to some extent, replicate the composition of human articular cartilage consisting of collagen fibers and proteoglycans. However, achieving tough bonding between the hydrogel and titanium alloy remains a significant challenge due to the swelling of the hydrogel in a liquid medium. This swelling results in reduced interfacial toughness between the hydrogel and titanium alloy, limiting its potential clinical applications. Herein, our approach aimed to achieve durable bonding between a hydrogel and a titanium alloy composite in a swollen state by modifying the surface texture of the titanium alloy. Various textures, including circular and triangular patterns, with dimple densities ranging from 10 to 40%, were created on the surface of the titanium alloy. Subsequently, poly(vinyl alcohol) (PVA) hydrogel was deposited onto the textured titanium alloy using a casting-drying method. Our findings revealed that PVA hydrogel on the textured titanium alloy with a 30% texture density exhibited the highest interfacial toughness in the swollen state, measuring at 1300 J m-2 after reaching equilibrium swelling in deionized water, which is a more than 2-fold increase compared to the hydrogel on a smooth substrate. Furthermore, we conducted an analysis of the morphologies of the detached hydrogel from the textured titanium alloy after various swelling durations. The results indicated that interfacial toughness could be enhanced through mechanical interlocking, facilitated by the expanded volume of the hydrogel protrusions as the swelling time increased. Collectively, our study demonstrates the feasibility of achieving tough bonding between a hydrogel and a metal substrate in a liquid environment. This research opens up promising avenues for designing soft/hard heterogeneous materials with strong adhesive properties.

In vitro drug release and cartilage interface lubrication properties of biomimetic polymers.

Osteoarthritis is a degenerative disease that is widely found in the elderly population, with a trend towards a younger age group in recent years. In the early stages of arthritis, patients are treated with hyaluronic acid injections and anti-inflammatory drugs. However, it has been found that hyaluronic acid can only play a supportive role and does not have a lubricating effect, and due to the absence of blood vessels, nerves, and lymphatic vessels in the articular cartilage, the oral anti-inflammatory drugs cannot reach the interface of the inflammatory joints adequately, and the drug utilisation rate is low. Herein, we designed and prepared a brush-like bionic lubricant for joint lubrication and drug loading. The poly(2-methyl-2-oxazoline) branched chain was grafted onto the hyaluronic acid main chain by ring-opening polymerisation and graft polymerisation to form a brush-like bionic lubricin containing multiple hydrophilic groups, which was self-assembled to encapsulate the drug by using its multi-branched special structure for drug loading. The friction behaviour tests on the articular cartilage surface showed that the prepared bionic lubricin has excellent lubrication effect, with a minimum friction coefficient of 0.036 close to the lubrication effect of natural synovial fluid, which is mainly due to the hydrophilic groups on its molecular chain that can adsorb the water molecules and form a hydration layer at the cartilage interface, which plays the role of hydration lubrication. In addition, in vitro drug release studies showed that the synthesised drug-loading biomimetic lubricin had a certain drug release capacity, and the maximum drug release rate could reach 77.8 % at 72 h. The synthesis of this bionic lubricant with dual functions of lubrication and drug release provides a new idea for the treatment of osteoarthritis.

A lubricant and adhesive hydrogel cross-linked from hyaluronic acid and chitosan for articular cartilage regeneration.

Trauma-induced articular cartilage damages are common in clinical practice. Hydrogels have been used to fill the cartilage defects and act as extracellular matrices for cell migration and tissue regeneration. Lubrication and stability of the filler materials are essential to achieve a satisfying healing effect in cartilage regeneration. However, conventional hydrogels failed to provide a lubricous effect, or could not anchor to the wound to maintain a stable curing effect. Herein, we fabricated dually cross-linked hydrogels using oxidized hyaluronic acid (OHA) and N-(2-hydroxypropyl)-3-trimethylammonium chitosan chloride (HTCC) methacrylate (HTCCMA). The OHA/HTCCMA hydrogels, which were dynamically cross-linked and then covalently cross-linked by photo-irradiation, showed appropriate rheological properties and self-healing capability. The hydrogels exhibited moderate and stable tissue adhesion property due to formation of dynamic covalent bonds with the cartilage surface. The coefficient of friction values were 0.065 and 0.078 for the dynamically cross-linked and double-cross-linked hydrogels, respectively, demonstrating superior lubrication. In vitro studies showed that the hydrogels had good antibacterial ability and promoted cell proliferation. In vivo studies confirmed that the hydrogels were biocompatible and biodegradable, and exhibited a robust regenerating ability for articular cartilage. This lubricant-adhesive hydrogel is expected to be promising for the treatment of joint injuries as well as regeneration.

Improved Interfacial Interactions of Dip Coatings by In Situ Introducing Silica to Enhance Corrosion Resistance and Metal Bonding Strength.

Corrosion is an irreversible phenomenon in nature that has been a major source of metal degradation. We herein provide a unique approach for embedding nanoparticles into epoxy resins via hydrogen bonding adsorption of in situ hydrophilic silica. Based on this adsorption action, a super-anticorrosive epoxy-based Teflon (MEP-PTFE) coating for usage on metals such as aluminum alloys was developed utilizing one-step dip coating, with promising engineering and public applications. It should be noted that the binding strength between the resultant MEP-PTFE coating and the substrate was 13.5 N. This coating had an impedance modulus of over 8 × 109 Ω·cm2 at 0.01 Hz and an impressive corrosion inhibition efficiency of 99.999%. The anticorrosion barrier from the diffusion control to the charge transfer control was revealed for the future good design of resin matrix coatings with excellent corrosion resistance.

Silver/Polypyrrole-Functionalized Polyurethane Foam Embedded Phase Change Materials for Thermal Energy Harvesting.

Conversion of solar energy into thermal energy stored in phase change materials (PCMs) can effectively relieve the energy dilemma and improve energy utilization efficiency. However, facile fabrication of form-stable PCMs (FSPCMs) to achieve simultaneously energetic solar-thermal, conversion and storage remains a formidable challenge. Herein, we report a desirable solar-thermal energy conversion and storage system that utilizes paraffin (PW) as energy-storage units, the silver/polypyrrole-functionalized polyurethane (PU) foam as the cage and energy conversion platform to restrain the fluidity of the melting paraffin and achieve high solar-thermal energy conversion efficiency (93.7%) simultaneously. The obtained FSPCMs possess high thermal energy storage density (187.4 J/g) and an excellent leak-proof property. In addition, 200 accelerated solar-thermal energy conversion-cycling tests demonstrated that the resultant FSPCMs had excellent cycling durability and reversible solar-thermal energy conversion ability, which offered a potential possibility in the field of solar energy utilization technology.

A tannic acid-reinforced PEEK-hydrogel composite material with good biotribological and self-healing properties for artificial joints.

Polyetheretherketone (PEEK) is widely considered as a promising material for joint implants but it still has limitations involving high friction and wear. To mimic the cartilage-subchondral bone structure in natural joints, a polyvinyl alcohol (PVA) hydrogel layer was fabricated on the PEEK substrate to provide a lubrication mechanism. In addition, tannic acid was applied to form dynamic hydrogen bonds with PVA molecules, for the purpose of strengthening the hydrogel layer and endowing it with self-healing ability. Our experimental results demonstrated that the prepared PEEK-hydrogel composite exhibited good biotribological performance with a low average friction coefficient around 0.06 and little wear after the friction test. It also could repair the scratch made by a blade spontaneously at room temperature taking advantage of the reversibility of the hydrogen bonds. The influence of the properties of the PVA hydrogel and the concentration of tannic acid on the frictional and self-healing behavior of the composite structure was investigated and the internal mechanism was discussed. This work presents a facile method to fabricate a PEEK-hydrogel composite possessing outstanding tribological properties and self-healing capacity simultaneously, hopefully promoting its potential in producing artificial joints.

Bio-inspired surface modification of PEEK through the dual cross-linked hydrogel layers.

The biocompatible high-performance material PEEK (polyetheretherketone) is an attractive implant material, however, its hydrophobicity and high friction coefficients severely hinder its biomedical applications. Thus, it is inferred from the recent advances in surface modification technology, achieving the biomimetic natural joint lubrication systems on PEEK still remains a challenge. In view of the above, herein we proposed a novel two-step strategy to fabricate a "soft (dual cross-linked hydrogel) layer-hard (PEEK) substrate" texture that mimics the structure and function of soft cartilage on the hard basal bone in joints. At first, a layer of acrylic acid-co-acryl amide (AA-AM) hydrogel is anchored to the PEEK substrate through UV-initiated polymerization. In the second step, hydrogel coated PEEK substrate is immersed in ferric nitrate solution to create the secondary cross-linkage between Fe3+ and -COOH groups in the hydrogel. As a result, the consequential top-coat hydrogel layer not only transforms the surface wettability (hydrophobic to hydrophilic) but also provides scratch resistance to the underlying PEEK substrate. The modified specimens display low friction coefficients in water under different load conditions. In addition, the obtained surface exhibits a certain self-repairing ability due to its unique physically reversible network structure. Therefore, this work provides a promising strategy for broadening the use of PEEK in orthopedic implants.

Doubly crosslinked biodegradable hydrogels based on gellan gum and chitosan for drug delivery and wound dressing.

Biopolymer-based hydrogels with sustained drug release capability and antibacterial activity have exhibited great potential in clinical application in drug delivery and wound healing. In this study, a new type of composite wound dressing hydrogel aiming at avoiding wound infection was developed through embedding drug loaded gellan gum microspheres (GMs) into a doubly crosslinked hydrogel, which was constructed by Schiff-base crosslinking of oxidized gellan gum (OG) (pre-crosslinked by calcium ion) and carboxymethyl chitosan (CMCS). The gelation time, swelling index, degradation rate and mechanical properties of the blank hydrogel was optimized by varying the ratios of CMCS/OG (w/w) with fixed OG/calcium (w/w) ratio. The best overall performance of the hydrogel was obtained when CMCS/OG is 16/7 (w/w), with a 139 s gelation time, swelling index remained above 30 after swelling equilibrium, 100.5% degradation rate on the seventh day, and 8.8 KPa compressive modulus. After being embedded with cargo-loaded GMs, the aforementioned performance of the blank hydrogel was improved, and the sustained release of cargoes (antibacterial drugs, tetracycline hydrochloride and silver sulfadiazine) was observed. Moreover, the excellent antibacterial activity of the composite hydrogel was also demonstrated in vitro. These results support the bioactive composite hydrogel can be employed as a promising injectable scaffold for promoting wound regeneration and drug delivery.

Multilayers of poly(ethyleneimine)/poly(acrylic acid) coatings on Ti6Al4V acting as lubricated polymer-bearing interface.

To achieve an efficient lubricated interface on titanium alloy (Ti6Al4V) alloy, polyelectrolyte multilayer (PEM) polymer coatings, based on poly(ethyleneimine)/poly(acrylic acid) (PEI/PAA), were fabricated on the surface of Ti6Al4V alloy substrates using the layer-by-layer (LbL) assembly technique. Their composition and morphology were confirmed by Fourier-transform infrared/attenuated total reflectance (FTIR/ATR) spectroscopy, X-ray photoelectron spectroscopy, and scanning electron microscopy. The tribological properties were investigated by a ball-on-disk rotating tribometer using deionized water, saline, and calf serum. The results exhibit that (PEI/PAA)*n coatings have the internal cross-linked network and porous structure on the surface. The surface of PEI/PAA coatings-modified Ti6Al4V shows the sufficient wettability. The polymer-bearing interface of (PEI/PAA)*10 exhibits a low friction coefficient, 0.059, for 2 hr, and represents an 88% decline compared with bare Ti6Al4V. Moreover, the wear track on the polymer-bearing interface is superlow. There is no obvious wear volume, which indicates effective wear resistance. The hydrated layer, the cross-linked network structure, and the porous structure of PEM coatings are the main factors for efficient tribological properties. The multilayer PEI/PAA coating shows the potential uses of developing the lubricated-bearing interface on Ti6Al4V alloy.

Superhydrophobic Surface with Stepwise Multilayered Micro- and Nanostructure and an Investigation of Its Corrosion Resistance.

We develop a fluorine-free preparation of the superhydrophobic surface on an aluminum alloy with anticorrosion performance and mechanical robustness. The surface morphology, chemical composition, and water repellency were determined with SEM, CLSM, EDS, FT-IR, TG, and contact-angle measurements, respectively. The aluminum matrix superhydrophobic surface (STA-PDMS-ZnO sample) was able to display excellent repellency to water with a WCA of 152° and a WSA of 2°. The outstanding superhydrophobicity on the as-prepared surface was greatly related to the construction of stepwise multilayered micro- and nanostructure within the superhydrophobic surface. Because of the special surface structure, the mechanical robustness and corrosion resistance of the STA-PDMS-ZnO sample were improved. Notably, the anticorrosion mechanism by air pockets was explained by the comparison of two superhydrophobic surfaces prepared with the same low-surface-energy chemicals. The superhydrophobic surface with a multilayered micro- and nanostructure (STA-PDMS-ZnO sample) showed greater corrosion resistance than the surface coated by superhydrophobic modification (control sample). This is because of the entrapments of numerous air pockets within the aluminum matrix superhydrophobic surface, thus strengthening the corrosion resistance. On the basis of the results, the multidimensional superhydrophobic surface is promising for having a good application future in the field of metal corrosion protection.