No abstract

While injectable in situ cross-linking collagen hydrogels offer great potential for applying stem cell therapy to regenerate articular cartilage via minimally invasive procedures, the encapsulated cells experience high shear stress during injection, which results in limited cell survival. In this study, surface-modified cellulose nanocrystals (CNCs) have been investigated as green and biocompatible reinforcing agents for collagen hydrogel. Aldehyde-functionalized CNCs (a-CNCs) were produced through a facile one-pot oxidation. A nanocomposite a-CNC/collagen hydrogel cross-linked rapidly by dynamic Schiff base bonds based on a-CNCs and collagen under physiological conditions. The a-CNC/collagen hydrogel exhibited fast shearthinning, self-healing characteristics, and improved elastic modulus compared with CNC/collagen hydrogel without Schiff base bonds. The a-CNC/collagen hydrogel was then investigated for mesenchymal stem cell (MSC) delivery. MSCs encapsulated in the a-CNC/collagen hydrogel showed high cell viability after extrusion in vitro. Subcutaneous injection of MSCs encapsulated in the a-CNC/collagen hydrogel showed improved implant integrity and higher cell retention. The proposed self-healing collagen-based hydrogel would not only protect cells during injection but also fit into the irregular cartilage defect, thus holding promise in delivering MSCs for cartilage regeneration through minimally invasive procedures.

Designing highly efficient and durable electrocatalysts for methanol oxidation reaction (MOR) plays a decisive role in the commercialization of direct methanol fuel cells (DMFCs). Compared with commercial Pt/C catalysts, fine-tuning the electronic structure of electrocatalysts to reduce the adsorption energy of CO while at the same time increasing the adsorption energy of OH is beneficial to improving the activity of MOR. Herein, ultrastable self-supported PtCu nanowires (NWs) with abundant Cu-vacancies have been developed, wherein the CO adsorption energy is weakened by doping of Cu elements and the OH adsorption energy is strengthened by the vacancy defect through dealloying. The well-designed PtCu NWs exhibit an outstanding performance for the MOR, with a specific activity 7.5 times higher than that for the commercial Pt/C catalyst, which transcends most electrocatalysts' performance currently. Moreover, the stability of PtCu electrocatalysts is greatly improved over 1 h owing to a "non-CO" pathway for MOR. Further DMFC tests present a 2 times higher power density than that of commercial Pt/C, and the PtCu integrated DMFC also presents a higher stability for 24 h, transcending most Pt-based anode catalysts of DMFCs.

Mesenchymal stem cell (MSC) chondrogenesis in three-dimensional (3D) culture involves dynamic changes in cytoskeleton architecture during mesenchymal condensation before morphogenesis. However, the mechanism linking dynamic mechanical properties of matrix to cytoskeletal changes during chondrogenesis remains unclear. Here, we investigated how viscoelasticity, a time-dependent mechanical property of collagen hydrogel, coordinates MSC cytoskeleton changes at different stages of chondrogenesis. The viscoelasticity of collagen hydrogel was modulated by controlling the gelling process without chemical cross-linking. In slower-relaxing hydrogels, although a disordered cortical actin promoted early chondrogenic differentiation, persistent myosin hyperactivation resulted in Rho-associated kinase (ROCK)–dependent apoptosis. Meanwhile, faster-relaxing hydrogels promoted cell-matrix interactions and eventually facilitated long-term chondrogenesis with mitigated myosin hyperactivation and cell apoptosis, similar to the effect of ROCK inhibitors. The current work not only reveals how matrix viscoelasticity coordinates MSC chondrogenesis and survival in a ROCK-dependent manner but also highlights viscoelasticity as a design parameter for biomaterials for chondrogenic 3D culture.

Development of high-strength hydrogels has recently attracted ever-increasing attention. In this work, a new design strategy has been proposed to prepare graphene oxide (GO)/polyacrylamide (PAM)/aluminum ion (Al(3+) )-cross-linked carboxymethyl hemicellulose (Al-CMH) nanocomposite hydrogels with very tough and elastic properties. GO/PAM/Al-CMH hydrogels were synthesized by introducing graphene oxide (GO) into PAM/CMH hydrogel, followed by ionic cross-linking of Al(3+) . The nanocomposite hydrogels were characterized by means of FTIR, X-ray diffraction (XRD), and scanning electron microscopy/energy-dispersive X-ray analysis (SEM-EDX) along with their swelling and mechanical properties. The maximum compressive strength and the Young's modulus of GO3.5 /PAM/Al-CMH0.45 hydrogel achieved values of up to 1.12 and 13.27 MPa, increased by approximately 6488 and 18330 % relative to the PAM hydrogel (0.017 and 0.072 MPa). The as-prepared GO/PAM/Al-CMH nanocomposite hydrogels possess high strength and great elasticity giving them potential in bioengineering and drug-delivery system applications.

Cartilage tissue has limited self-regeneration capacity and current treatment methods often result in fibrocartilage formation. Although collagen has shown the ability to induce chondrogenesis of mesenchymal stem cells (MSCs) and...

Lithium‐rich layered oxides (LLOs) are concerned as promising cathode materials for next‐generation lithium‐ion batteries due to their high reversible capacities (larger than 250 mA h g−1). However, LLOs suffer from critical drawbacks, such as irreversible oxygen release, structural degradation, and poor reaction kinetics, which hinder their commercialization. Herein, the local electronic structure is tuned to improve the capacity energy density retention and rate performance of LLOs via gradient Ta5+ doping. As a result, the capacity retention elevates from 73% to above 93%, and the energy density rises from 65% to above 87% for LLO with modification at 1 C after 200 cycles. Besides, the discharge capacity for the Ta5+ doped LLO at 5 C is 155 mA h g−1, while it is only 122 mA h g−1 for bare LLO. Theoretical calculations reveal that Ta5+ doping can effectively increase oxygen vacancy formation energy, thus guaranteeing the structure stability during the electrochemical process, and the density of states results indicate that the electronic conductivity of the LLOs can be boosted significantly at the same time. This strategy of gradient doping provides a new avenue to improve the electrochemical performance of the LLOs by modulating the local structure at the surface.

Metallic Pd is widely recognized as an efficient electrocatalyst for the formic acid oxidation reaction (FAOR), which unfortunately suffers from poor durability owing to Pd dissolution and CO poisoning. The present work describes an effective method to enhance Pd durability by alloying with Cu and Au. Cu could provide surface OH at low potentials to remove poisonous CO for improved CO resistance. Au, the most inert metal, was added to reduce Pd and Cu dissolution. Moreover, alloying with Cu and Au could also modulate the electronic structure of Pd which is just profitable for the FAOR. The constructed PdCuAu with a nanoporous structure exhibits a specific activity of 14.9 mA cm–2 and a Pd mass activity of 6012 A g–1, which is ∼15 times and ∼14 times higher than those of commercial Pd/C. While these two electrocatalysts were used as fuel cell anodes, the maximum power density of the PdCuAu anode (Pd loading 10 μg cm–2) is 93.2 mW cm–2 and the value of the Pd/C anode (Pd loading 1.2 mg cm–2) is 60.3 mW cm–2. The power efficiency of Pd has been notably increased by 185 times in this home-made nanoporous PdCuAu ternary alloy electrocatalyst.