Injectable muscle-adhesive antioxidant conductive photothermal bioactive nanomatrix for efficiently promoting full-thickness skeletal muscle regeneration

Bletilla Striata polysaccharides thermosensitive gel for photothermal treatment of bacterial infection

Skin is the most important defense shield which touched external environment directly. Effectively clearing microbes in infected wound via non-antibiotic therapy is crucial for the promotion of recovery in complex biological environments, and the wound healing is a crucial process after sterilization to avoid superinfection. Herein, a kind of Prussian blue-based photothermal responsive gel, Bletilla striata polysaccharide-mingled, isatin-functionalized Prussian blue gel (PB-ISA/BSP gel) was reported for effective treatment of bacterial infection and wound healing. The introduction of effective components of traditional Chinese medicine (TCM), isatin (ISA), enhanced the efficiency of sterilization synergistically. Furthermore, the process of wound healing was promoted by Bletilla striata polysaccharides (BSP). PB-ISA@BSP had a considerable antibacterial rate with 98.5 % under an 808 nm laser for 10 min in vitro. Besides, PB-ISA/BSP gel showed an effective antibacterial efficacy in vivo and a fast wound healing rate as well. The as-prepared functional particles can invade and destroy bacteria membrane to kill microbes. This work highlights that PB-ISA/BSP gel is a promising antibacterial agent based on synergistically enhanced photothermal effect and wound healing promotion ability and provides inspiration for future therapy based on the synergy between photothermal agent and active components in TCM.

Injectable tissue prosthesis for instantaneous closed-loop rehabilitation

To construct tissue-like prosthetic materials, soft electroactive hydrogels are the best candidate owing to their physiological mechanical modulus, low electrical resistance and bidirectional stimulating and recording capability of electrophysiological signals from biological tissues1,2. Nevertheless, until now, bioelectronic devices for such prostheses have been patch type, which cannot be applied onto rough, narrow or deep tissue surfaces3-5. Here we present an injectable tissue prosthesis with instantaneous bidirectional electrical conduction in the neuromuscular system. The soft and injectable prosthesis is composed of a biocompatible hydrogel with unique phenylborate-mediated multiple crosslinking, such as irreversible yet freely rearrangeable biphenyl bonds and reversible coordinate bonds with conductive gold nanoparticles formed in situ by cross-coupling. Closed-loop robot-assisted rehabilitation by injecting this prosthetic material is successfully demonstrated in the early stage of severe muscle injury in rats, and accelerated tissue repair is achieved in the later stage.

Designing self-healing hydrogels for biomedical applications

Self-healing hydrogels have emerged as the most promising alternatives to conventional brittle hydrogels used in the biomedical field due to the features of long-term stability and durability. However, the incompatibility between the fast self-healing property and enough mechanical strength of hydrogels remains a challenge. Therefore, hydrogels that possess not only mechanical toughness but also autonomous self-healing capacity are sought after. This review presents a comprehensive summary of the latest self-healing mechanisms. Specifically, we review various systems based on dynamic bonds, ranging from dynamic covalent bonds to non-covalent bonds. Additionally, this review presents different characterization methods for self-healing hydrogels, and also highlights their potential applications in the biomedical field, such as tissue engineering, drug delivery, cell therapy, and wound dressing. Furthermore, this review aims to provide valuable guidance for constructing diverse self-healing hydrogels with tailored functions.

Nanoenzyme-Reinforced Multifunctional Scaffold Based on Ti3C2Tx MXene Nanosheets for Promoting Structure-Functional Skeletal Muscle Regeneration via Electroactivity and Microenvironment Management

The completed volumetric muscle loss (VML) regeneration remains a challenge due to the limited myogenic differentiation as well as the oxidative, inflammatory, and hypoxic microenvironment. Herein, a 2D Ti3C2Tx MXene@MnO2 nanocomposite with conductivity and microenvironment remodeling was fabricated and applied in developing a multifunctional hydrogel (FME) scaffold to simultaneously conquer these hurdles. Among them, Ti3C2Tx MXene with electroconductive ability remarkably promotes myogenic differentiation via enhancing the myotube formation and upregulating the relative expression of the myosin heavy chain (MHC) protein and myogenic genes (MyoD and MyoG) in myogenesis. The MnO2 nanoenzyme-reinforced Ti3C2Tx MXene significantly reshapes the hostile microenvironment by eliminating reactive oxygen species (ROS), regulating macrophage polarization from M1 to M2 and continuously supplying O2. Together, the FME hydrogel as a bioactive multifunctional scaffold significantly accelerates structure-functional VML regeneration in vivo and represents a multipronged strategy for the VML regeneration via electroactivity and microenvironment management.

Engineering multifunctional bioactive citrate-based biomaterials for tissue engineering

Developing bioactive biomaterials with highly controlled functions is crucial to enhancing their applications in regenerative medicine. Citrate-based polymers are the few bioactive polymer biomaterials used in biomedicine because of their facile synthesis, controllable structure, biocompatibility, biomimetic viscoelastic mechanical behavior, and functional groups available for modification. In recent years, various multifunctional designs and biomedical applications, including cardiovascular, orthopedic, muscle tissue, skin tissue, nerve and spinal cord, bioimaging, and drug or gene delivery based on citrate-based polymers, have been extensively studied, and many of them have good clinical application potential. In this review, we summarize recent progress in the multifunctional design and biomedical applications of citrate-based polymers. We also discuss the further development of multifunctional citrate-based polymers with tailored properties to meet the requirements of various biomedical applications.

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Multifunctional bioactive citrate-based biomaterials have broad applications in regenerative medicine.

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Recent advances in multifunctional design and biomedical applications of citate-based polymers are summarized.

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Future challenge of citrate-based polymers in various biomedical applications are discussed.

On-Demand Removable Self-Healing and pH-Responsive Europium-Releasing Adhesive Dressing Enables Inflammatory Microenvironment Modulation and Angiogenesis for Diabetic Wound Healing

Current diabetic wound treatments remain unsatisfactory due to the lack of a comprehensive strategy that can integrate strong applicability (tissue adhesiveness, shape adaptability, fast self-healability, and facile dressing change) with the initiation and smooth connection of the cascade wound healing processes. Herein, benefiting from the multifaceted bonding ability of tannic acid to metal ions and various polymers, a family of tannin-europium coordination complex crosslinked citrate-based mussel-inspired bioadhesives (TE-CMBAs) are specially developed for diabetic wound healing. TE-CMBAs can gel instantly (< 60 s), possess favorable shape-adaptability, considerable mechanical strengths, high elasticity, considerable wet tissue adhesiveness (≈40 kPa), favorable photothermal antimicrobial activity, excellent anti-oxidant activity, biocompatibility, and angiogenetic property. The reversible hydrogen bond crosslinking and sensitive metal-phenolic coordination also confers TE-CMBAs with self-healability, pH-responsive europium ion and TA releasing properties and on-demand removability upon mixing with borax solution, enabling convenient painless dressing change and the smooth connection of inflammatory microenvironment modulation, angiogenesis promotion, and effective extracellular matrix production leveraging the acidic pH condition of diabetic wounds. This adhesive dressing provides a comprehensive regenerative strategy for diabetic wound management and can be extended to other complicated tissue healing scenarios.

A critical review on polydopamine surface-modified scaffolds in musculoskeletal regeneration

Increasing concern about age-related diseases, particularly musculoskeletal injuries and orthopedic conditions, highlights the need for strategies such as tissue engineering to address them. Surface modification has been developed to create pro-healing interfaces, personalize scaffolds and provide novel medicines. Polydopamine, a mussel-inspired adhesive polymer with highly reactive functional groups that adhere to nearly all substrates, has gained attention in surface modification strategies for biomaterials. Polydopamine was primarily developed to modify surfaces, but its effectiveness has opened up promising approaches for further applications in bioengineering as carriers and nanoparticles. This review focuses on the recent discoveries of the role of polydopamine as a surface coating material, with focus on the properties that make it suitable for tackling musculoskeletal disorders. We report the evolution of using it in research, and discuss papers involving the progress of this field. The current research on the role of polydopamine in bone, cartilage, muscle, nerve, and tendon regeneration is discussed, thus giving comprehensive overview about the function of polydopamine both in-vitro and in-vivo. Finally, the report concludes presenting the critical challenges that must be addressed for the clinical translation of this biomaterial while exploring future perspectives and research opportunities in this area.

The effects of process parameters on polydopamine coatings employed in tissue engineering applications

The biomaterials’ success within the tissue engineering field is hinged on the capability to regulate tissue and cell responses, comprising cellular adhesion, as well as repair and immune processes’ induction. In an attempt to enhance and fulfill these biomaterials’ functions, scholars have been inspired by nature; in this regard, surface modification via coating the biomaterials with polydopamine is one of the most successful inspirations endowing the biomaterials with surface adhesive properties. By employing this approach, favorable results have been achieved in various tissue engineering-related experiments, a significant one of which is the more rapid cellular growth observed on the polydopamine-coated substrates compared to the untreated ones; nonetheless, some considerations regarding polydopamine-coated surfaces should be taken into account to control the ultimate outcomes. In this mini-review, the importance of coatings in the tissue engineering field, the different types of surfaces requiring coatings, the significance of polydopamine coatings, critical factors affecting the result of the coating procedure, and recent investigations concerning applications of polydopamine-coated biomaterials in tissue engineering are thoroughly discussed.

The Art of Reprogramming for Regenerative Medicine

Traditional pharmaceuticals in the forms of small chemical compounds or macromolecules such as proteins or RNAs have provided lifesaving solutions to many acute and chronic conditions to date. However, there are still many unmet medical needs, especially those of degenerative nature. The advent of cell-based therapy holds the promise to meet these challenges. In this review, we highlight a relatively new paradigm for generating or regenerating functional cells for replacement therapy against conditions such as type I diabetes, myocardial infarction, neurodegenerative diseases and liver fibrosis. We focus on the latest progresses in cellular reprogramming for generating diverse functional cell types. We will also discuss the mechanisms involved and conclude with likely general principles underlying reprogramming.

Supramolecular Adhesive Hydrogels for Tissue Engineering Applications

Tissue engineering is a promising and revolutionary strategy to treat patients who suffer the loss or failure of an organ or tissue, with the aim to restore the dysfunctional tissues and enhance life expectancy. Supramolecular adhesive hydrogels are emerging as appealing materials for tissue engineering applications owing to their favorable attributes such as tailorable structure, inherent flexibility, excellent biocompatibility, near-physiological environment, dynamic mechanical strength, and particularly attractive self-adhesiveness. In this review, the key design principles and various supramolecular strategies to construct adhesive hydrogels are comprehensively summarized. Thereafter, the recent research progress regarding their tissue engineering applications, including primarily dermal tissue repair, muscle tissue repair, bone tissue repair, neural tissue repair, vascular tissue repair, oral tissue repair, corneal tissue repair, cardiac tissue repair, fetal membrane repair, hepatic tissue repair, and gastric tissue repair, is systematically highlighted. Finally, the scientific challenges and the remaining opportunities are underlined to show a full picture of the supramolecular adhesive hydrogels. This review is expected to offer comparative views and critical insights to inspire more advanced studies on supramolecular adhesive hydrogels and pave the way for different fields even beyond tissue engineering applications.

Construction of tissue-customized hydrogels from cross-linkable materials for effective tissue regeneration

Hydrogels are prevalent scaffolds for tissue regeneration because of their hierarchical architectures along with outstanding biocompatibility and unique rheological and mechanical properties. For decades, researchers have found that many materials (natural, synthetic, or hybrid) can form hydrogels using different cross-linking strategies. Traditional strategies for fabricating hydrogels include physical, chemical, and enzymatical cross-linking methods. However, due to the diverse characteristics of different tissues/organs to be regenerated, tissue-customized hydrogels need to be developed through precisely controlled processes, making the manufacture of hydrogels reliant on novel cross-linking strategies. Thus, hybrid cross-linkable materials are proposed to tackle this challenge through hybrid cross-linking strategies. Here, different cross-linkable materials and their associated cross-linking strategies are summarized. From the perspective of the major characteristics of the target tissues/organs, we critically analyze how different cross-linking strategies are tailored to fit the regeneration of such tissues and organs. To further advance this field, more appropriate cross-linkable materials and cross-linking strategies should be investigated. In addition, some innovative technologies, such as 3D bioprinting, the internet of medical things (IoMT), and artificial intelligence (AI), are also proposed to improve the development of hydrogels for more efficient tissue regeneration.

3D bioprinting of conductive hydrogel for enhanced myogenic differentiation

Recently, hydrogels have gained enormous interest in three-dimensional (3D) bioprinting toward developing functional substitutes for tissue remolding. However, it is highly challenging to transmit electrical signals to cells due to the limited electrical conductivity of the bioprinted hydrogels. Herein, we demonstrate the 3D bioprinting-assisted fabrication of a conductive hydrogel scaffold based on poly-3,4-ethylene dioxythiophene (PEDOT) nanoparticles (NPs) deposited in gelatin methacryloyl (GelMA) for enhanced myogenic differentiation of mouse myoblasts (C2C12 cells). Initially, PEDOT NPs are dispersed in the hydrogel uniformly to enhance the conductive property of the hydrogel scaffold. Notably, the incorporated PEDOT NPs showed minimal influence on the printing ability of GelMA. Then, C2C12 cells are successfully encapsulated within GelMA/PEDOT conductive hydrogels using 3D extrusion bioprinting. Furthermore, the proliferation, migration and differentiation efficacies of C2C12 cells in the highly conductive GelMA/PEDOT composite scaffolds are demonstrated using various in vitro investigations of live/dead staining, F-actin staining, desmin and myogenin immunofluorescence staining. Finally, the effects of electrical signals on the stimulation of the scaffolds are investigated toward the myogenic differentiation of C2C12 cells and the formation of myotubes in vitro. Collectively, our findings demonstrate that the fabrication of the conductive hydrogels provides a feasible approach for the encapsulation of cells and the regeneration of the muscle tissue.

In Situ Synthesized Selenium Nanoparticles-Decorated Bacterial Cellulose/Gelatin Hydrogel with Enhanced Antibacterial, Antioxidant, and Anti-Inflammatory Capabilities for Facilitating Skin Wound Healing

Bacterial-associated wound infection and antibiotic resistance have posed a major burden on patients and health care systems. Thus, developing a novel multifunctional antibiotic-free wound dressing that cannot only effectively prevent wound infection, but also facilitate wound healing is urgently desired. Herein, a series of multifunctional nanocomposite hydrogels with remarkable antibacterial, antioxidant, and anti-inflammatory capabilities, based on bacterial cellulose (BC), gelatin (Gel), and selenium nanoparticles (SeNPs), are constructed for wound healing application. The BC/Gel/SeNPs nanocomposite hydrogels exhibit excellent mechanical properties, good swelling ability, flexibility and biodegradability, and favorable biocompatibility, as well as slow and sustainable release profiles of SeNPs. The decoration of SeNPs endows the hydrogels with superior antioxidant and anti-inflammatory capability, and outstanding antibacterial activity against both common bacteria (E. coli and S. aureus) and their multidrug-resistant counterparts. Furthermore, the BC/Gel/SeNPs hydrogels show an excellent skin wound healing performance in a rat full-thickness defect model, as evidenced by the significantly reduced inflammation, and the notably enhanced wound closure, granulation tissue formation, collagen deposition, angiogenesis, and fibroblast activation and differentiation. This study suggests that the developed multifunctional BC/Gel/SeNPs nanocomposite hydrogel holds a great promise as a wound dressing for preventing wound infection and accelerating skin regeneration in clinic.

Fast photocurable thiol-ene elastomers with tunable biodegradability, mechanical and surface properties enhance myoblast differentiation and contractile function

Biodegradable elastomers are important emerging biomaterials for biomedical applications, particularly in the area of soft-tissue engineering in which scaffolds need to match the physicochemical properties of native tissues. Here, we report novel fast photocurable elastomers with readily tunable mechanical properties, surface wettability, and degradability. These elastomers are prepared by a 5-min UV-irradiation of thiol-ene reaction systems of glycerol tripentenoate (GTP; a triene) or the combination of GTP and 4-pentenyl 4-pentenoate (PP; a diene) with a carefully chosen series of di- or tri-thiols. In the subsequent application study, these elastomers were found to be capable of overcoming delamination of myotubes, a technical bottleneck limiting the in vitro growth of mature functional myofibers. The glycerol-based elastomers supported the proliferation of mouse and human myoblasts, as well as myogenic differentiation into contractile myotubes. More notably, while beating mouse myotubes detached from conventional tissue culture plates, they remain adherent on the elastomer surface. The results suggest that these elastomers as novel biomaterials may provide a promising platform for engineering functional soft tissues with potential applications in regenerative medicine or pharmacological testing.

A Review on Hydrogels with Photothermal Effect in Wound Healing and Bone Tissue Engineering

Photothermal treatment (PTT) is a promising strategy to deal with multidrug-resistant bacteria infection and promote tissue regeneration. Previous studies demonstrated that hyperthermia can effectively inhibit the growth of bacteria, whereas mild heat can promote cell proliferation, further accelerating wound healing and bone regeneration. Especially, hydrogels with photothermal properties could achieve remotely controlled drug release. In this review, we introduce a photothermal agent hybrid in hydrogels for a photothermal effect. We also summarize the potential mechanisms of photothermal hydrogels regarding antibacterial action, angiogenesis, and osteogenesis. Furthermore, recent developments in photothermal hydrogels in wound healing and bone regeneration applications are introduced. Finally, future application of photothermal hydrogels is discussed. Hydrogels with photothermal effects provide a new direction for wound healing and bone regeneration, and this review will give a reference for the tissue engineering.

Current Strategies for the Regeneration of Skeletal Muscle Tissue

Traumatic injuries, tumor resections, and degenerative diseases can damage skeletal muscle and lead to functional impairment and severe disability. Skeletal muscle regeneration is a complex process that depends on various cell types, signaling molecules, architectural cues, and physicochemical properties to be successful. To promote muscle repair and regeneration, various strategies for skeletal muscle tissue engineering have been developed in the last decades. However, there is still a high demand for the development of new methods and materials that promote skeletal muscle repair and functional regeneration to bring approaches closer to therapies in the clinic that structurally and functionally repair muscle. The combination of stem cells, biomaterials, and biomolecules is used to induce skeletal muscle regeneration. In this review, we provide an overview of different cell types used to treat skeletal muscle injury, highlight current strategies in biomaterial-based approaches, the importance of topography for the successful creation of functional striated muscle fibers, and discuss novel methods for muscle regeneration and challenges for their future clinical implementation.