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The periosteum, rich in neurovascular networks, bone progenitor cells, and stem cells, is vital for bone repair. Current artificial periosteal materials face challenges in mechanical strength, bacterial infection, and promoting osteogenic differentiation and angiogenesis. To address these issues, we adjusted the electrospinning ratio of poly-ε-caprolactone and chitosan and incorporated Zn doping whitlockite with polydopamine coating into a nanofiber membrane. After a series of characterizations, optimal results were achieved with a poly-ε-caprolactone: chitosan ratio of 8:1 and 5% nanoparticle content. In vitro cell experiments and in vivo calvarial defect models, the sustained release of Mg2+ and Ca2+ promoted vascularization and new bone formation, respectively, while the release of Zn2+ was conducive to antibacterial and cooperated with Mg2+ to promote neurovascularization. Consequently, this antibacterial bionic periosteum with an angiogenesis-neurogenesis coupling effect demonstrates a promising potential for bone repair applications.

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Dynamic covalent bond hydrogels have demonstrated significant application potential in biomedical fields for their dynamic reversibility. However, the contradiction between the stability and dynamics of the hydrogel restricts its application. Here, utilizing silver sulfadiazine (AgSD) as a catalyst, hyaluronic acid-based hydrogels are constructed through imine bond crosslinking and incorporated disulfide bonds within the same crosslinking chain. It is found that AgSD can accelerate the formation of imine crosslinking bonds to improve the stability of hydrogels, thereby shortening the gelation time by ≈36.9 times, enhancing compression strength and adhesion strength by ≈2.4 times and 1.7 times, respectively, while inhibiting swelling and degradation rates to ≈2.1 times and 3.7 times. Besides, AgSD can coordinate with disulfide bonds to enhance the dynamics of hydrogel, enhancing the hydrogel self-healing efficiency by ≈2.3 times while reducing the relaxation time by ≈25.1 times. Significantly, AgSD imparts remarkable antibacterial properties to the hydrogel, thereby effectively facilitating the healing of bacterial infected wounds. Consequently, introducing AgSD enables hydrogels to possess concurrent stability, dynamics, and antibacterial properties. This strategy of regulating hydrogels by introducing AgSD provides a valuable reference for the application of dynamic covalent bonds.

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Osteochondral defect (OCD) regeneration remains challenging because of the hierarchy of the native tissue including both the articular cartilage and the subchondral bone. Constructing an osteochondral scaffold with biomimetic composition, structure, and biological functionality is the key to achieve its high-quality repair. In the present study, an injectable and 3D printable bilayered osteochondral hydrogel based on compositional gradient of methacrylated sodium alginate, gelatin methacryloyl, and ß-tricalcium phosphate (ß-TCP), as well as the biochemical gradient of kartogenin (KGN) in the two well-integrated zones of chondral layer hydrogel (CLH) and osseous layer hydrogel (OLH) is developed. In vitro and subcutaneous in vivo evaluations reveal that apart from the chondrogenesis of the embedded bone mesenchymal stem cells induced by CLH with a high concentration of KGN, a low concentration of KGN with ß-TCP in the OLH synergistically achieves superior osteogenic differentiation by endochondral ossification, instead of the intramembranous ossification using OLH with only ß-TCP. The biomimetic construct leveraging KGN as the only biochemical inducer can facilitate cartilage and subchondral bone restoration in the in vivo osteochondral defect. This one-stone-two-birds strategy opens up a new facile approach for OCD regeneration by exploiting the biological functions of the bioactive drug molecule KGN.

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Partial-thickness cartilage defects (PTCDs) of the articular surface is the most common problem in cartilage degeneration, and also one of the main pathogenesis of osteoarthritis (OA). Due to the lack of a clear diagnosis, the symptoms are often more severe when full-thickness cartilage defect (FTCDs) is present. In contrast to FTCDs and osteochondral defects (OCDs), PTCDs does not injure the subchondral bone, there is no blood supply and bone marrow exudation, and the nearby microenvironment is unsuitable for stem cells adhesion, which completely loses the ability of self-repair. Some clinical studies have shown that partial-thickness cartilage defects is as harmful as full-thickness cartilage defects. Due to the poor effect of conservative treatment, the destructive surgical treatment is not suitable for the treatment of partial-thickness cartilage defects, and the current tissue engineering strategies are not effective, so it is urgent to develop novel strategies or treatment methods to repair PTCDs. In recent years, with the interdisciplinary development of bioscience, mechanics, material science and engineering, many discoveries have been made in the repair of PTCDs. This article reviews the current status and research progress in the treatment of PTCDs from the aspects of diagnosis and modeling of PTCDs, drug therapy, tissue transplantation repair technology and tissue engineering ("bottom-up").

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For the treatment of infected bleeding wounds, we compounded methacrylate anhydride dopamine (DAMA) and Zn-doped whitlockite nanoparticles (Zn-nWH) into methacrylate anhydride quaternized chitosan (QCSMA) to obtain a multifunctional hydrogel dressing (QCSMA/DAMA/Zn-nWH) with hemostasis, disinfection and wound healing promotion. QCSMA/DAMA/Zn-nWH exhibited good adhesion (0.031 MPa) and DPPH scavenging ability (94%), favorable biocompatibility (hemolysis ratio < 2%, no cytotoxicity), and showed a low BCI value (< 13%) in vitro coagulation test and could activate coagulation pathway. In addition, QCSMA/DAMA/Zn-nWH had excellent hemostatic effect (129 ± 22 s, 27 ± 5 mg) in vivo compared with the control (571 ± 15 s, 147 ± 31 mg) and CCS (354 ± 27 s, 110 ± 46 mg). Meanwhile, QCSMA/DAMA/Zn-nWH showed excellent antibacterial properties (> 90% against S. aureus and E. coli) and could promote collagen deposition, reduce inflammatory expression and promote wound healing. All results indicate that these multifunctional hydrogel dressings have great potential in clinical hemostasis and anti-infection healing.

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Hydrogels are widely used as debriding agents on account of providing a moist environment for wound healing, however the lack of mechanical strength, angiogenesis and antibacterial property limits their applications. In this study, we synthesized novel divalent ion cross-liking hydrogels (copper, zinc, strontium and calcium) and compared the mechanical performance, swelling ratio, antibacterial properties and biocompatibility in vitro and vivo. Thereinto, among the four divalent ions cross-linked hydrogels, copper ion crosslinking exhibited the maximum breaking strength, while strontium and zinc ion cross-linked hydrogels exhibited an excellent mechanical strength. In addition, the swelling ratio and pore size of no-ion cross-linked hydrogels was larger than ion cross-kinked hydrogels. In vitro, the improvements on wound healing after hydrogel application were evaluated by histological and molecular assays by detecting VEGF and TGF-ß expression. In vitro and in vivo study results showed that zinc cross-kinked hydrogel had a spectrum of antibacterial activities, cell viability, mechanical strength and the ability of wound closure by promoting fibroblasts migration, vascularization, collagen deposition and the formation of granulation tissue.

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