Tribomechanical Properties of PVA/Nomex® Composite Hydrogels for Articular Cartilage Repair

Due to the increasing prevalence of articular cartilage diseases and limitations faced by current therapeutic methodologies, there is an unmet need for new materials to replace damaged cartilage. In this work, poly(vinyl alcohol) (PVA) hydrogels were reinforced with different amounts of Nomex® (known for its high mechanical toughness, flexibility, and resilience) and sterilized by gamma irradiation. Samples were studied concerning morphology, chemical structure, thermal behavior, water content, wettability, mechanical properties, and rheological and tribological behavior. Overall, it was found that the incorporation of aramid nanostructures improved the hydrogel's mechanical performance, likely due to the reinforcement's intrinsic strength and hydrogen bonding to PVA chains. Additionally, the sterilization of the materials also led to superior mechanical properties, possibly related to the increased crosslinking density through the hydrogen bonding caused by the irradiation. The water content, wettability, and tribological performance of PVA hydrogels were not compromised by either the reinforcement or the sterilization process. The best-performing composite, containing 1.5% wt. of Nomex®, did not induce cytotoxicity in human chondrocytes. Plugs of this hydrogel were inserted in porcine femoral heads and tested in an anatomical hip simulator. No significant changes were observed in the hydrogel or cartilage, demonstrating the material's potential to be used in cartilage replacement.

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.

Review of two-dimensional nanomaterials in tribology: Recent developments, challenges and prospects

From our ordinary lives to various mechanical systems, friction and wear are often unavoidable phenomena that are heavily responsible for excessive expenditures of nonrenewable energy, the damages and failures of system movement components, as well as immense economic losses. Thus, achieving low friction and high anti-wear performance is critical for minimization of these adverse factors. Two-dimensional (2D) nanomaterials, including transition metal dichalcogenides, single elements, transition metal carbides, nitrides and carbonitrides, hexagonal boron nitride, and metal-organic frameworks have attracted remarkable interests in friction and wear reduction of various applications, owing to their atomic-thin planar morphologies and tribological potential. In this paper, we systematically review the current tribological progress on 2D nanomaterials when used as lubricant additives, reinforcement phases in the coatings and bulk materials, or a major component of superlubricity system. Additionally, the conclusions and prospects on 2D nanomaterials with the existing drawbacks, challenges and future direction in such tribological fields are briefly provided. Finally, we sincerely hope such a review will offer valuable lights for 2D nanomaterial-related researches dedicated on tribology in the future.

Super-Strong Hydrogel Composites Reinforced with PBO Nanofibers for Cartilage Replacement

Cartilage replacement materials exhibiting a set of demanding properties such as high water content, high mechanical stiffness, low friction, and excellent biocompatibility are quite difficult to achieve. Here, poly(p-phenylene-2,6-benzobisoxazole) (PBO) nanofibers are combined with polyvinyl alcohol (PVA) to form a super-strong structure with a performance that surpasses the vast majority of previously existing hydrogels. PVA-PBO composites with water contents in the 59-76% range exhibit tensile and compressive moduli reaching 20.3 and 4.5 MPa, respectively, and a coefficient of friction below 0.08. Further, they are biocompatible and support the viability of chondrocytes for 1 week, with significant improvements in cell adhesion, proliferation, and differentiation compared to PVA. The new composites can be safely sterilized by steam heat or gamma radiation without compromising their integrity and overall performance. In addition, they show potential to be used as local delivery platforms for anti-inflammatory drugs. These attractive features make PVA-PBO composites highly competitive engineered materials with remarkable potential for use in the design of load-bearing tissues. Complementary work has also revealed that these composites will be interesting alternatives in other industrial fields where high thermal and mechanical resistance are essential requirements, or which can take advantage of the pH responsiveness functionality.

2D Nanomaterials for Tissue Engineering and Regenerative Nanomedicines: Recent Advances and Future Challenges

Regenerative medicine has become one of the hottest research topics in medical science that provides a promising way for repairing tissue defects in the human body. Due to their excellent physicochemical properties, the application of 2D nanomaterials in regenerative medicine has gradually developed and has been attracting a wide range of research interests in recent years. In particular, graphene and its derivatives, black phosphorus, and transition metal dichalcogenides are applied in all the aspects of tissue engineering to replace or restore tissues. This review focuses on the latest advances in the application of 2D-nanomaterial-based hydrogels, nanosheets, or scaffolds that are engineered to repair skin, bone, and cartilage tissues. Reviews on other applications, including cardiac muscle regeneration, skeletal muscle repair, nerve regeneration, brain disease treatment, and spinal cord healing are also provided. The challenges and prospects of applications of 2D nanomaterials in regenerative medicine are discussed.

Tunable Dual Temperature-Pressure Sensing and Parameter Self-Separating Based on Ionic Hydrogel via Multisynergistic Network Design

Hydrogel-based wearable sensors have experienced an explosive development, whereas functional integration to mimic the multisignal responsiveness of skin especially for pressure and temperature remained a challenge. Herein, a functional ionic hydrogel-base flexible sensor was successfully prepared by integrating the thermal-sensitive N-isopropylacrylamide (NIPAAm) into another conductive double-network hydrogel based on polyvinyl alcohol-graphene oxide (PVA-GO) and polyacrylic acid-Fe³⁺ (PAA-Fe³⁺). Because of the multisynergistic network design, the triple-network hydrogel was endowed with excellent conductivity (∼170 Ω/mm), mechanical tolerance (1.1 MPa), and rapid recoverability (within 0.5 s), which demonstrated the potential use in pressure monitoring. Moreover, the introduction of a thermal-sensitive network allowed it to capture the changes in the human body temperature accurately simultaneously and to be further developed as a flexible temperature sensor. In particular, the unsynchronization of pressure and temperature strain (straining to stability within 0.5 s and more than 50 s, respectively) caused the two electrical signals to be automatically separated. Intuitive reading of data without involving complex parameter separation calculations allowed the hydrogel to be developed as an integrated dual temperature-pressure-sensitive flexible sensor. In addition, all above properties demonstrated that the as-prepared functional hydrogel could be extended to the practical application in human-machine interactions and personalized multisignal monitoring.

Dye removal by eco-friendly physically cross-linked double network polymer hydrogel beads and their functionalized composites

Hydrogels have attracted large attention in wastewater treatment fields due to their low-cost and good interaction with pollutants, among which novel double network hydrogel is an outstanding class. To expand the application of double network hydrogel in water treatment, in this study, eco-friendly physically cross-linked double network polymer hydrogel beads (DAP) are prepared and studied in depth on the mechanism of Methylene Blue (MB) adsorption; and then the polymer hydrogels are further functionalized by inorganic materials. MB adsorption on DAP favors alkaline condition which is due to the increase of electrostatic attraction and adsorption site, and it reaches equilibrium within 10 hr, which is faster than that of the single network hydrogel beads (SAP). Through thermodynamics study, the process shows to be an exothermic and spontaneous process. The adsorption isotherms are well fitted by Langmuir model, with a maximum monolayer adsorption capacity of 1437.48 mg/g, which is larger than SAP (1255.75 mg/g). After being functionalized with common inorganic materials including activated carbon, Fe₃O₄ and graphene oxide (GO), the composites show to have larger pore sizes and have obvious increases in adsorption capacity especially the one contains GO. Then the composites contains Fe₃O₄ are used as heterogeneous Fenton catalyst which shows to have excellent performance in MB degradation. The results indicate the potential of polymer double network to be functionalized in environmental areas.

Synthesis and response of pineapple peel carboxymethyl cellulose-g-poly (acrylic acid-co-acrylamide)/graphene oxide hydrogels

Developing biomaterials derived from the renewable resources is an effective and sustainable approach to address environmental and resource issues. Herein, hydrogels were synthesized by grafting copolymerization of acrylic acid and acrylamide onto pineapple peel carboxymethyl cellulose with incorporation of graphene oxide (GO). The structure, swelling, and multiple responses to salt, pH and organic solvents were investigated. The incorporation of GO resulted in a higher cross-linking density of the network and thus decreased the swelling ability. Expansion of the hydrogels occurred at high pH, whereas shrinkage occurred at low pH or in salt solutions and organic solvents/water mixtures, exhibiting multiple responses to pH, salt and organic solvents. Moreover, the hydrogels showed a selective adsorption behavior to various dyes and the incorporation of GO enhanced the adsorption performance. The above results may allude several potential applications of the hydrogels, such as adsorption, smart actuators and drug release fields.

High-Performance Photopolymerized Poly(vinyl alcohol)/Silica Nanocomposite Hydrogels with Enhanced Cell Adhesion

Poly(vinyl alcohol) (PVA) hydrogels have been considered as promising implants for various soft tissue engineering applications because of their tissue-like viscoelasticity and biocompatibility. However, two critical barriers including lack of sufficient mechanical properties and non-tissue-adhesive characterization limit their application as tissue substitutes. Herein, PVA is methacrylated with ultralow degrees of substitution of methacryloyl groups to produce PVA-glycidyl methacrylate (GMA). Subsequently, the PVA-GMA/methacrylate-functionalized silica nanoparticle (MSi)-based nanocomposite hydrogels are developed via the photopolymerization approach. Interestingly, both PVA-GMA-based hydrogels and PVA-GMA/MSi-based nanocomposite hydrogels exhibit outstanding compressive properties, which cannot be damaged through compressive stress-strain tests in the allowable scope of a tensile tester. Moreover, PVA-GMA/MSi-based nanocomposite hydrogels demonstrate excellent tensile properties compared with neat PVA-GMA-based hydrogels, and 15-, 14-, and 24-fold increase in fracture stress, elastic modulus, and toughness, respectively, is achieved for the PVA-GMA/MSi-based hydrogels with 10 wt % of MSi. These remarkable enhancements can be ascribed to the amount of long and flexible polymer chains of PVA-GMA and the strong interactions between the MSi and PVA-GMA chains. More interestingly, exciting improvements in the cell adhesion can also be successfully achieved by the incorporation of MSi nanoparticles.

Eco-friendly polyvinyl alcohol/carboxymethyl cellulose hydrogels reinforced with graphene oxide and bentonite for enhanced adsorption of methylene blue

Eco-friendly polyvinyl alcohol/carboxymethyl cellulose (isolated from pineapple peel) hydrogels reinforced with graphene oxide and bentonite were prepared as efficient adsorbents for methylene blue (MB). The structure and morphology of the prepared hydrogels were characterized by Fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM), X-ray diffraction (XRD), thermogravimetry (TG) and differential scanning calorimetry (DSC). Introducing graphene oxide and bentonite into the hydrogels evidently enhanced the thermal stability, swelling ability and MB adsorption capacity. The effects of initial concentration of MB, pH, contact time and temperature on MB adsorption capacity of the prepared hydrogels were investigated. Adsorption kinetics and equilibrium adsorption isotherm fitted pseudo-second-order kinetic model and Langmuir isotherm model well, respectively. After introducing graphene oxide and bentonite into the hydrogels, the maximum adsorption capacity calculated from the Langmuir isotherm model reached 172.14 mg/g at 30 °C, obviously higher than the hydrogels prepared without these additions (83.33 mg/g). Furthermore, all the prepared hydrogels also displayed good reusability for the efficient removal of MB. Consequently, the prepared hydrogels could be served as eco-friendly, stable, efficient and reusable adsorbents for anionic dyes in wastewater treatment.

Enhancement of water diffusion and compression performance of crosslinked alginate films with a minuscule amount of graphene oxide

A series of calcium alginate composite hydrogels with several calcium chloride contents ranging from 3 to 18 wt.% with and without 0.1 wt.% of graphene oxide (GO) was prepared in order to study the effect of crosslinking and nanofilling on water diffusion and compression performance. Thus, for high crosslinker contents, these composite hydrogels exhibited ultrafast diffusion of liquid water and excellent compression properties as compared with control (0 wt.% GO and the same crosslinking). These remarkable results are produced due to calcium cations are able to crosslink alginate and also graphene oxide nanosheets to form large crosslinked GO networks inside the calcium alginate hydrogels. Besides, these crosslinked GO/calcium alginate networks present nanochannels, as confirmed by electron microscopy, able to improve significantly water diffusion. Thus, these composite materials are very promising for many industrial applications demanding low-cost hydrogels with improved mechanical and water diffusion properties.

In situ repair of graphene defects and enhancement of its reinforcement effect in polyvinyl alcohol hydrogels

The reactive groups on the edge of graphene defects are activated at a low γ-ray irradiation dose, and the resulting PVA scission chains at the high γ-ray dose link these reactive groups to repair the graphene defects.