Bioactive Pore-Forming Bone Adhesives Facilitating Cell Ingrowth for Fracture Healing

Overcoming the Dilemma of In Vivo Stable Adhesion and Sustained Degradation by the Molecular Design of Polyurethane Adhesives for Bone Fracture Repair

Bone adhesive is a promising candidate to revolutionize the clinical treatment of bone repairs. However, several drawbacks have limited its further clinical application, such as unreliable wet adhesive performance leading to fixation failure and poor biodegradability inhibiting bone tissue growth. By incorporating catechol groups and disulfide bonds into polyurethane (PU) molecules, an injectable and porous PU adhesive is developed with both superior wet adhesion and biodegradability to facilitate the reduction and fixation of comminuted fractures and the subsequent regeneration of bone tissue. The bone adhesive can be cured within a reasonable time acceptable to a surgeon, and then the wet bone adhesive strength is near 1.30 MPa in 1 h. Finally, the wet adhesive strength to the cortical bone will achieve about 1.70 MPa, which is also five times more than nonresorbable poly(methyl methacrylate) bone cement. Besides, the cell culture experiments also indicate that the adhesives show excellent biocompatibility and osteogenic ability in vitro. Especially, it can degrade in vivo gradually and promote fracture healing in the rabbit iliac fracture model. These results demonstrate that this ingenious bone adhesive exhibits great potential in the treatment of comminuted fractures, providing fresh insights into the development of clinically applicable bone adhesives.

Intelligent Vascularized 3D/4D/5D/6D-Printed Tissue Scaffolds

Blood vessels are essential for nutrient and oxygen delivery and waste removal. Scaffold-repairing materials with functional vascular networks are widely used in bone tissue engineering. Additive manufacturing is a manufacturing technology that creates three-dimensional solids by stacking substances layer by layer, mainly including but not limited to 3D printing, but also 4D printing, 5D printing and 6D printing. It can be effectively combined with vascularization to meet the needs of vascularized tissue scaffolds by precisely tuning the mechanical structure and biological properties of smart vascular scaffolds. Herein, the development of neovascularization to vascularization to bone tissue engineering is systematically discussed in terms of the importance of vascularization to the tissue. Additionally, the research progress and future prospects of vascularized 3D printed scaffold materials are highlighted and presented in four categories: functional vascularized 3D printed scaffolds, cell-based vascularized 3D printed scaffolds, vascularized 3D printed scaffolds loaded with specific carriers and bionic vascularized 3D printed scaffolds. Finally, a brief review of vascularized additive manufacturing-tissue scaffolds in related tissues such as the vascular tissue engineering, cardiovascular system, skeletal muscle, soft tissue and a discussion of the challenges and development efforts leading to significant advances in intelligent vascularized tissue regeneration is presented.

A pH-neutral bioactive glass empowered gelatin-chitosan-sodium phytate composite scaffold for skull defect repair

The ideal skull defect repairing material should have good biocompatibility and mechanical properties, and contribute to osteogenesis. In this study, we designed and fabricated biodegradable, bioactive and mechanically robust porous scaffolds composed completely of biological materials. We used a gelatin-chitosan blend as the matrix, sodium phytate instead of toxic glutaraldehyde for cross-linking, and the pH-neutral bioactive glass (PSC) to improve biological activity and mechanical properties. The chitosan-gelatin-30%PSC/sodium phytate composite scaffold avoided the problems of high toxicity in conventional cross-linking agents with glutaraldehyde, the poor mechanical support of the pure chitosan or gelatin scaffold, and the mismatch of the degradation rate with bone repair, becoming a promising new candidate for skull defect repair.

Double-Cross-Linked Hydrogel with Long-Lasting Underwater Adhesion: Enhancement of Maxillofacial In Situ and Onlay Bone Retention

Bone retention is a usual clinical problem existing in a lot of maxillofacial surgeries involving bone reconstruction and bone transplantation, which puts forward the requirements for bone adhesives that are stable, durable, biosafe, and biodegradable in wet environment. To relieve the suffering of patients during maxillofacial surgery with one-step operation and satisfying repair, herein, we developed a double-cross-linked A-O hydrogel named by its two components: [(3-Aminopropyl) methacrylamide]-co-{[Tris(hydroxymethyl) methyl] acrylamide} and oxidated methylcellulose. With excellent bone adhesion ability, it can maintain long-lasting stable underwater bone adhesion for over 14 days, holding a maximum adhesion strength of 2.32 MPa. Schiff-base reaction and high-density hydrogen bonds endow the hydrogel with strong cohesion and adhesion performance as well as maneuverable properties such as easy formation and injectability. A-O hydrogel not only presents rarely reported long-lasting underwater adhesion of hard tissue but also owns inherent biocompatibility and biodegradation properties with a porous structure that facilitates the survival of bone graft. Compared to the commercial cyanoacrylate adhesive (3 M Vetbond Tissue Adhesive), the A-O hydrogel is confirmed to be safer, more stable, and more effective in calvarial in situ bone retention model and onlay bone retention model of rat, providing a practical solution for the everyday scenario of clinical bone retention.

A Review on Polymers for Biomedical Applications on Hard and Soft Tissues and Prosthetic Limbs

In the past decades, there has been a significant increase in the use of polymers for biomedical applications. The global medical polymer market size was valued at USD 19.92 billion in 2022 and is expected to grow at a CAGR of 8.0% from 2023 to 2030 despite some limitations, such as cost (financial limitation), strength compared to metal plates for bone fracture, design optimization and incorporation of reinforcement. Recently, this increase has been more pronounced due to important advances in synthesis and modification techniques for the design of novel biomaterials and their behavior in vitro and in vivo. Also, modern medicine allows the use of less invasive surgeries and faster surgical sutures. Besides their use in the human body, polymer biomedical materials must have desired physical, chemical, biological, biomechanical, and degradation properties. This review summarizes the use of polymers for biomedical applications, mainly focusing on hard and soft tissues, prosthetic limbs, dental applications, and bone fracture repair. The main properties, gaps, and trends are discussed.

Advances and Prospects in Materials for Craniofacial Bone Reconstruction

The craniofacial region is composed of 23 bones, which provide crucial function in keeping the normal position of brain and eyeballs, aesthetics of the craniofacial complex, facial movements, and visual function. Given the complex geometry and architecture, craniofacial bone defects not only affect the normal craniofacial structure but also may result in severe craniofacial dysfunction. Therefore, the exploration of rapid, precise, and effective reconstruction of craniofacial bone defects is urgent. Recently, developments in advanced bone tissue engineering bring new hope for the ideal reconstruction of the craniofacial bone defects. This report, presenting a first-time comprehensive review of recent advances of biomaterials in craniofacial bone tissue engineering, overviews the modification of traditional biomaterials and development of advanced biomaterials applying to craniofacial reconstruction. Challenges and perspectives of biomaterial development in craniofacial fields are discussed in the end.

Biodegradable Implants for Internal Fixation of Fractures and Accelerated Bone Regeneration

Bone fractures have always been a burden to patients due to their common occurrence and severe complications. Traditionally, operative treatments have been widely used in the clinic for implanting, despite the fact that they can only achieve bone fixation with limited stability and pose no effect on promoting tissue growth. In addition, the nondegradable implants usually need a secondary surgery for implant removal, otherwise they may block the regeneration of bones resulting in bone nonunion. To overcome the low degradability of implants and avoid multiple surgeries, tissue engineers have investigated various biodegradable materials for bone regeneration, whereas the significance of stability of long-term bone fixation tends to be neglected during this process. Combining the traditional orthopedic implantation surgeries and emerging tissue engineering, we believe that both bone fixation and bone regeneration are indispensable factors for a successful bone repair. Herein, we define such a novel idea as bone regenerative fixation (BRF), which should be the main future development trend of biodegradable materials.

The marriage of immunomodulatory, angiogenic, and osteogenic capabilities in a piezoelectric hydrogel tissue engineering scaffold for military medicine

BACKGROUND

Most bone-related injuries to grassroots troops are caused by training or accidental injuries. To establish preventive measures to reduce all kinds of trauma and improve the combat effectiveness of grassroots troops, it is imperative to develop new strategies and scaffolds to promote bone regeneration.

METHODS

In this study, a porous piezoelectric hydrogel bone scaffold was fabricated by incorporating polydopamine (PDA)-modified ceramic hydroxyapatite (PDA-hydroxyapatite, PHA) and PDA-modified barium titanate (PDA-BaTiO₃, PBT) nanoparticles into a chitosan/gelatin (Cs/Gel) matrix. The physical and chemical properties of the Cs/Gel/PHA scaffold with 0-10 wt% PBT were analyzed. Cell and animal experiments were performed to characterize the immunomodulatory, angiogenic, and osteogenic capabilities of the piezoelectric hydrogel scaffold in vitro and in vivo.

RESULTS

The incorporation of BaTiO₃ into the scaffold improved its mechanical properties and increased self-generated electricity. Due to their endogenous piezoelectric stimulation and bioactive constituents, the as-prepared Cs/Gel/PHA/PBT hydrogels exhibited cytocompatibility as well as immunomodulatory, angiogenic, and osteogenic capabilities; they not only effectively induced macrophage polarization to M2 phenotype but also promoted the migration, tube formation, and angiogenic differentiation of human umbilical vein endothelial cells (HUVECs) and facilitated the migration, osteo-differentiation, and extracellular matrix (ECM) mineralization of MC3T3-E1 cells. The in vivo evaluations showed that these piezoelectric hydrogels with versatile capabilities significantly facilitated new bone formation in a rat large-sized cranial injury model. The underlying molecular mechanism can be partly attributed to the immunomodulation of the Cs/Gel/PHA/PBT hydrogels as shown via transcriptome sequencing analysis, and the PI3K/Akt signaling axis plays an important role in regulating macrophage M2 polarization.

CONCLUSION

The piezoelectric Cs/Gel/PHA/PBT hydrogels developed here with favorable immunomodulation, angiogenesis, and osteogenesis functions may be used as a substitute in periosteum injuries, thereby offering the novel strategy of applying piezoelectric stimulation in bone tissue engineering for the enhancement of combat effectiveness in grassroots troops.

A Mechanically Reinforced Super Bone Glue Makes a Leap in Hard Tissue Strong Adhesion and Augmented Bone Regeneration

Existing bone tissue engineering strategies aim to achieve minimize surgical trauma, stabilize the injured area, and establish a dynamic osteogenic microenvironment. The cutting-edge bone glue developed in this study satisfies these criteria. Inspired by the excellent adhesive properties of mussels, herein, a super osteogenic glue (L-DPZ) that integrates poly(vinyl alcohol), L-dopa amino acid, and zeolitic imidazolate framework-8 characterized by catechol-metal coordination is used to successfully adhere to hard tissue with a maximum adhesive strength of 10 MPa, which is much higher than those of commercial and previously reported bone glues. The stable hard tissue adhesion also enables it to adhere strongly to luxated or broken teeth, Bio-Oss (a typical bone graft material), and splice fragments from comminuted fractures of the rabbit femur. Then, it is testified that the L-DPZ hydrogels exhibit satisfactory biocompatibility, stable degradability, and osteogenic ability in vitro. Moreover, the ability to anchor Bio-Oss and sustained osteogenesis of L-DPZ result in satisfactory healing in calvarial bone defect models in rabbits, as observed by increased bone thickness and the ingrowth of new bone tissue. These results are expected to demonstrate solutions to clinical dilemmas such as comminuted bone fracture fixation, bone defect reconstruction, and teeth dislocation replantation.

Recent Tissue Engineering Approaches to Mimicking the Extracellular Matrix Structure for Skin Regeneration

Inducing tissue regeneration in many skin defects, such as large traumatic wounds, burns, other physicochemical wounds, bedsores, and chronic diabetic ulcers, has become an important clinical issue in recent years. Cultured cell sheets and scaffolds containing growth factors are already in use but have yet to restore normal skin tissue structure and function. Many tissue engineering materials that focus on the regeneration process of living tissues have been developed for the more versatile and rapid initiation of treatment. Since the discovery that cells recognize the chemical-physical properties of their surrounding environment, there has been a great deal of work on mimicking the composition of the extracellular matrix (ECM) and its three-dimensional network structure. Approaches have used ECM constituent proteins as well as morphological processing methods, such as fiber sheets, sponges, and meshes. This review summarizes material design strategies in tissue engineering fields, ranging from the morphology of existing dressings and ECM structures to cellular-level microstructure mimicry, and explores directions for future approaches to precision skin tissue regeneration.

Bioinspired Piezoelectric Periosteum to Augment Bone Regeneration via Synergistic Immunomodulation and Osteogenesis

Ideal periosteum materials are required to participate in a sequence of bone repair-related physiological events, including the initial immune response, endogenous stem cell recruitment, angiogenesis, and osteogenesis. However, conventional tissue-engineered periosteal materials have difficulty achieving these functions by simply mimicking the periosteum via structural design or by loading exogenous stem cells, cytokines, or growth factors. Herein, we present a novel biomimetic periosteum preparation strategy to comprehensively enhance the bone regeneration effect using functionalized piezoelectric materials. The resulting biomimetic periosteum possessing an excellent piezoelectric effect and improved physicochemical properties was prepared using a biocompatible and biodegradable poly(3-hydroxybutyric acid-co-3-hydrovaleric acid) (PHBV) polymer matrix, antioxidized polydopamine-modified hydroxyapatite (PHA), and barium titanate (PBT), which were further incorporated into the polymer matrix to fabricate a multifunctional piezoelectric periosteum by a simple one-step spin-coating method. The addition of PHA and PBT dramatically enhanced the physicochemical properties and biological functions of the piezoelectric periosteum, resulting in improved surface hydrophilicity and roughness, enhanced mechanical performance, tunable degradation behavior, and stable and desired endogenous electrical stimulations, which is conducive to accelerating bone regeneration. Benefiting from endogenous piezoelectric stimulation and bioactive components, the as-fabricated biomimetic periosteum demonstrated favorable biocompatibility, osteogenic activity, and immunomodulatory functions in vitro, which not only promoted adhesion, proliferation, and spreading as well as osteogenesis of mesenchymal stem cells (MSCs) but also effectively induced M2 macrophage polarization, thereby suppressing reactive oxygen species (ROS)-induced inflammatory reactions. Through in vivo experiments, the biomimetic periosteum with endogenous piezoelectric stimulation synergistically accelerated the formation of new bone in a rat critical-sized cranial defect model. The whole defect was almost completely covered by new bone at 8 weeks post treatment, with a thickness close to that of the host bone. Collectively, with its favorable immunomodulatory and osteogenic properties, the biomimetic periosteum developed here represents a novel method to rapidly regenerate bone tissue using piezoelectric stimulation.

Multifunctional Bioinspired Bredigite-Modified Adhesive for Bone Fracture Healing

Despite recent advances in bone adhesives applied for full median sternotomy, the regeneration of bone defects has remained challenging since the healing process is hampered by poor adhesiveness, limited bioactivity, and lack of antibacterial functions. Bioinspired adhesives by marine organisms provide a novel concept to circumvent these problems. Herein, a dual cross-link strategy is employed in designing a multifaceted bioinspired adhesive consisting of a catechol amine-functionalized hyperbranched polymer (polydopamine-co-acrylate, PDA), bredigite (BR) nanoparticles, and Fe³⁺ ions. The hybrid adhesives exhibit strong adhesion to various substrates such as poly(methyl methacrylate), glass, bone, and skin tissues through synergy between irreversible covalent and reversible noncovalent cross-linking, depending on the BR content. Noticeably, the adhesion strength of hybrid adhesives containing 2 wt % BR nanoparticles to bone tissues is 2.3 ± 0.8 MPa, which is about 3 times higher than that of pure PDA adhesives. We also demonstrate that these hybrid adhesives not only are bioactive and accelerate in vitro bone-like apatite formation but also exhibit antibacterial properties against Staphylococcus aureus, depending on the BR concentration. Furthermore, the superior cellular responses in contact with hybrid adhesives, including improved human osteosarcoma MG63 cell spreading and osteogenic differentiation, are achieved owing to the appropriate ion release and flexibility of the cross-linked double-network adhesive. In summary, multifunctional hybrid PDA/BR adhesives with appreciable osteoconductive, mechanical, and antibacterial properties represent the potential applications for median sternotomy surgery as a bone tissue adhesive.

Periodontal bone regeneration with a degradable thermoplastic HA/PLCL bone graft

Strategic bone grafts are required to regenerate periodontal bone defects owing to limited self-healing. Current bioceramic particle or deproteinized bovine bone (DBB) products are not able to ideally meet clinical requirements, such as insufficient operability and slow degradation rates. Herein, a strong-interacted bone graft was designed and synthesized by modifying hydroxyapatite (HA) with a lactide-caprolactone copolymer (PLCL) to improve component homogeneity and mechanical properties. The physical-chemical analysis indicated that HA particles were homogenously distributed in HA/PLCL bone grafts, possessed outstanding thermoplasticity, and facilitated clinic operability and initial mechanical support. The in vitro study suggested that HA/PLCL bone graft degraded in a spatiotemporal model. Micropores were formed on the non-porous surface at the beginning, and interconnected porous structures were gradually generated. Furthermore, HA/PLCL bone grafts exhibited excellent biocompatibility and osteogenic ability as revealed in vitro cell culture and in vivo animal experiments. When applied to rat periodontal bone defects, the HA/PLCL bone graft showed a non-inferior bone regeneration compared to the commercial DBB. This study proposes a potential bone graft for periodontal bone repair with thermoplastic, spatiotemporal degraded, and osteogenic characteristics.

Evaluation of 'surgery-friendly' bone scaffold characteristics: 3D printed ductile BG/PCL scaffold with high inorganic content to repair critical bone defects

The repair of irregular and complex critical bone defects remains a challenge in clinical practice. The application of 3D-printed bioceramics particle/polymer composite scaffolds in bone tissue engineering has been widely studied. At present, the inorganic particle content of the composite scaffolds is generally low, resulting in poor osteogenic activity. However, scaffold with high inorganic content are highly brittle, difficult to operate during surgery, and cannot be in close contact with surrounding bones. Therefore, it is of great significance to design a 'surgery-friendly' scaffold with high bioceramic content and good ductility. In this study, we used the solvent method to add high concentration (wt% 70%) bioglass (BG) into polycaprolactone (PCL), and polyethylene glycol was used as plasticizer to prepare 70% BG/PCL composite scaffolds with high ductility using 3D printing technology.In vitroexperiments showed that the scaffold had good mechanical properties: easy extension, easy folding and strong compressive resistance. It also showed good performance in biocompatibility and osteogenic activity. It was further observed that compared with pure BG or PCL implantation, the scaffold with higher BG content could have more new bone tissue appeared after 12 weeks. All these results indicate that 3D-printed 70% BG/PCL scaffolds have great potential for personalized repair of bone defects.

Facile Construction of Hybrid Hydrogels with High Strength and Biocompatibility for Cranial Bone Regeneration

The significant efforts being made towards the utilization of artificial soft materials holds considerable promise for developing tissue engineering scaffolds for bone-related diseases in clinics. However, most of these biomaterials cannot simultaneously satisfy the multiple requirements of high mechanics, good compatibility, and biological osteogenesis. In this study, an osteogenic hybrid hydrogel between the amine-functionalized bioactive glass (ABG) and 4-armed poly(ethylene glycol) succinimidyl glutarate-gelatin network (SGgel) is introduced to flexibly adhere onto the defective tissue and to subsequently guide bone regeneration. Relying on the rapid ammonolysis reaction between amine groups (-NH₂) of gelatin and ABG components and N-hydroxysuccinimide (NHS)-ester of tetra-PEG-SG polymer, the hydrogel networks were formed within seconds, offering a multifunctional performance, including easy injection, favorable biocompatibility, biological and mechanical properties (compressive strength: 4.2 MPa; storage modulus: 10⁴ kPa; adhesive strength: 56 kPa), which could facilitate the stem cell viability, proliferation, migration and differentiation into osteocytes. In addition, the integration between the SGgel network and ABG moieties within a nano-scale level enabled the hybrid hydrogel to form adhesion to tissue, maintain the durable osteogenesis and accelerate bone regeneration. Therefore, a robust approach to the simultaneously satisfying tough adhesion onto the tissue defects and high efficiency for bone regeneration on a mouse skull was achieved, which may represent a promising strategy to design therapeutic scaffolds for tissue engineering in clinical applications.

Selective Polyetheretherketone Implants Combined with Graphene Cause Definitive Cell Adhesion and Osteogenic Differentiation

INTRODUCTION

Polyetheretherketone (PEEK) has good biosafety and chemical stability for bone repair. However, PEEK is biologically inert and cannot promote bone apposition. This study investigated whether graphene-modified PEEK (G-PEEK) could improve cell adhesion and osteogenic differentiation.

METHODS

G-PEEK was prepared by melted blending and was characterized. In vitro, the biocompatibility of G-PPEK and the ability to promote cell adhesion and osteogenic differentiation in rabbit bone marrow mesenchymal stem cells (rBMSCs) were examined using live and dead cell double staining, the cell counting kit-8 (CCK-8) assay, immunofluorescence and quantitative real-time PCR (qRT‒PCR). An in vivo rabbit extra-articular graft-to-bone healing model was established. At 4 and 12 weeks after surgery, CT analysis and histological evaluation were performed.

RESULTS

In vitro, G-PEEK significantly improved the adhesion and proliferation of rBMSCs, with good biocompatibility. In vivo, G-PEEK promoted new bone formation at the site of the bone defect.

CONCLUSION

G-PEEK showed excellent osteogenesis performance, which promises new applications in implant materials.

Bridging wounds: tissue adhesives' essential mechanisms, synthesis and characterization, bioinspired adhesives and future perspectives

Bioadhesives act as a bridge in wound closure by forming an effective interface to protect against liquid and gas leakage and aid the stoppage of bleeding. To their credit, tissue adhesives have made an indelible impact on almost all wound-related surgeries. Their unique properties include minimal damage to tissues, low chance of infection, ease of use and short wound-closure time. In contrast, classic closures, like suturing and stapling, exhibit potential additional complications with long operation times and undesirable inflammatory responses. Although tremendous progress has been made in the development of tissue adhesives, they are not yet ideal. Therefore, highlighting and summarizing existing adhesive designs and synthesis, and comparing the different products will contribute to future development. This review first provides a summary of current commercial traditional tissue adhesives. Then, based on adhesion interaction mechanisms, the tissue adhesives are categorized into three main types: adhesive patches that bind molecularly with tissue, tissue-stitching adhesives based on pre-polymer or precursor solutions, and bioinspired or biomimetic tissue adhesives. Their specific adhesion mechanisms, properties and related applications are discussed. The adhesion mechanisms of commercial traditional adhesives as well as their limitations and shortcomings are also reviewed. Finally, we also discuss the future perspectives of tissue adhesives.

Osteoimmunity-Regulating Biomimetically Hierarchical Scaffold for Augmented Bone Regeneration

Engineering a proper immune response following biomaterial implantation is essential to bone tissue regeneration. Herein, a biomimetically hierarchical scaffold composed of deferoxamine@poly(ε-caprolactone) nanoparticles (DFO@PCL NPs), manganese carbonyl (MnCO) nanosheets, gelatin methacryloyl hydrogel, and a polylactide/hydroxyapatite (HA) matrix is fabricated to augment bone repair by facilitating the balance of the immune system and bone metabolism. First, a 3D printed stiff scaffold with a well-organized gradient structure mimics the cortical and cancellous bone tissues; meanwhile, an inside infusion of a soft hydrogel further endows the scaffold with characteristics of the extracellular matrix. A Fenton-like reaction between MnCO and endogenous hydrogen peroxide generated at the implant-tissue site triggers continuous release of carbon monoxide and Mn²⁺ , thus significantly lessening inflammatory response by upregulating the M2 phenotype of macrophages, which also secretes vascular endothelial growth factor to induce vascular formation. Through activating the hypoxia-inducible factor-1α pathway, Mn²⁺ and DFO@PCL NP further promote angiogenesis. Moreover, DFO inhibits osteoclast differentiation and synergistically collaborates with the osteoinductive activity of HA. Based on amounts of data in vitro and in vivo, strong immunomodulatory, intensive angiogenic, weak osteoclastogenic, and superior osteogenic abilities of such an osteoimmunity-regulating scaffold present a profound effect on improving bone regeneration, which puts forward a worthy base and positive enlightenment for large-scale bone defect repair.

Enhancement of Osteoblast Function through Extracellular Vesicles Derived from Adipose-Derived Stem Cells

Adipose-derived stem cells (ADSCs) are a type of mesenchymal stem cell that is investigated in bone tissue engineering (BTE). Osteoblasts are the main cells responsible for bone formation in vivo and directing ADSCs to form osteoblasts through osteogenesis is a research topic in BTE. In addition to the osteogenesis of ADSCs into osteoblasts, the crosstalk of ADSCs with osteoblasts through the secretion of extracellular vesicles (EVs) may also contribute to bone formation in ADSC-based BTE. We investigated the effect of ADSC-secreted EVs (ADSC-EVs) on osteoblast function. ADSC-EVs (size ≤ 1000 nm) were isolated from the culture supernatant of ADSCs through ultracentrifugation. The ADSC-EVs were observed to be spherical under a transmission electron microscope. The ADSC-EVs were positive for CD9, CD81, and Alix, but β-actin was not detected. ADSC-EV treatment did not change survival but did increase osteoblast proliferation and activity. The 48 most abundant known microRNAs (miRNAs) identified within the ADSC-EVs were selected and then subjected to gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses. The GO analysis revealed that these miRNAs are highly relevant to skeletal system morphogenesis and bone development. The KEGG analysis indicated that these miRNAs may regulate osteoblast function through autophagy or the mitogen-activated protein kinase or Ras-related protein 1 signaling pathway. These results suggest that ADSC-EVs enhance osteoblast function and can contribute to bone regeneration in ADSC-based BTE.

Strong and bioactive bioinspired biomaterials, next generation of bone adhesives

The bone adhesive is a clinical requirement for complicated bone fractures always articulated by surgeons. Applying glue is a quick and easy way to fix broken bones. Adhesives, unlike conventional fixation methods such as wires and sutures, improve healing conditions and reduce postoperative pain by creating a complete connection at the fractured joint. Despite many efforts in the field of bone adhesives, the creation of a successful adhesive with robust adhesion and appropriate bioactivity for the treatment of bone fractures is still in its infancy. Because of the resemblance of the body's humid environment to the underwater environment, in the latest decades, researchers have pursued inspiration from nature to develop strong bioactive adhesives for bone tissue. The aim of this review article is to discuss the recent state of the art in bone adhesives with a specific focus on biomimetic adhesives, their action mechanisms, and upcoming perspective. Firstly, the adhesive biomaterials with specific affinity to bone tissue are introduced and their rational design is studied. Consequently, various types of synthetic and natural bioadhesives for bone tissue are comprehensively overviewed. Then, bioinspired-adhesives are described, highlighting relevant structures and examples of biomimetic adhesives mainly made of DOPA and the complex coacervates inspired by proteins secreted in mussel and sandcastle worms, respectively. Finally, this article overviews the challenges of the current bioadhesives and the future research for the improvement of the properties of biomimetic adhesives for use as bone adhesives.

Biodegradable and Biocompatible Adhesives for the Effective Stabilisation, Repair and Regeneration of Bone

Bone defects and complex fractures present significant challenges for orthopaedic surgeons. Current surgical procedures involve the reconstruction and mechanical stabilisation of complex fractures using metal hardware (i.e., wires, plates and screws). However, these procedures often result in poor healing. An injectable, biocompatible, biodegradable bone adhesive that could glue bone fragments back together would present a highly attractive solution. A bone adhesive that meets the many clinical requirements for such an application has yet to be developed. While synthetic and biological polymer-based adhesives (e.g., cyanoacrylates, PMMA, fibrin, etc.) have been used effectively as bone void fillers, these materials lack biomechanical integrity and demonstrate poor injectability, which limits the clinical effectiveness and potential for minimally invasive delivery. This systematic review summarises conventional approaches and recent developments in the area of bone adhesives for orthopaedic applications. The required properties for successful bone repair adhesives, which include suitable injectability, setting characteristics, mechanical properties, biocompatibility and an ability to promote new bone formation, are highlighted. Finally, the potential to achieve repair of challenging bone voids and fractures as well as the potential of new bioinspired adhesives and the future directions relating to their clinical development are discussed.

Ternary Complex Coacervate of PEG/TA/Gelatin as Reinforced Bioadhesive for Skin Wound Repair

Bioadhesives have attracted more attention in surgery due to their easy operability and abilities of promoting wound closure and tissue healing. However, it is still a great challenge to develop a robust and biocompatible bioadhesive through a facile preparation method. Herein, a ternary complex coacervate comprised of tannic acid (TA), polyethylene glycol (PEG), and gelatin (TPG) is proposed as a novel bioadhesive, which is fabricated by simple physical blending method. The adhesion capacity of TPG was reinforced through programming the cross-linking network of TPG matrix and tailoring the interfacial interactions between matrix and tissue. Curing parameters (pH, temperature, and period) and gelatin content in TPG have crucial impacts on the final comprehensive adhesion performance. The adhesion strength of the optimized formulation, fabricated with 10% (m/m) gelatin (TPG10), was over 3 folds of TPG0 (without gelatin inclusion) after 24 h curing at pH 6 and 37 °C. The mechanism of the reinforced comprehensive adhesion was also investigated, suggesting TA provided tough interfacial adhesion, covalent cross-link of TA-gelatin improved mechanical properties, and the hydrogen bonds mediated dynamic cross-link between TA and PEG enabled the bulk matrix to dissipate energy upon deformation. Furthermore, the additional antibacterial activity, biocompatibility, and suitable degradability endowed TPG10 with desirable wound closure and tissue repairing efficacy on rat skin wound model. Such low-cost, readily prepared, and function-efficient bioadhesive could provide a versatile platform for tissue repair and regeneration.

Oxygen-Carrying and Antibacterial Fluorinated Nano-Hydroxyapatite Incorporated Hydrogels for Enhanced Bone Regeneration

Insufficient oxygen availability in tissue engineering is one of the major factors for the failure of clinical transplantation. One potential strategy to conquer this limitation is the fabrication of spontaneous and continuous oxygen supplying scaffolds for in situ tissue regeneration. In this work, a versatile fluorine-incorporating hydrogel is designed which can not only timely and continuously supply oxygen for mesenchymal stem cells (MSCs) to overcome deficient oxygen before vascularization in scaffolds, but can present a higher antibacterial capability to avoid bacterial infections. The HAp@PDA-F nanoparticles are first prepared and then incorporated with the quaternized and methacrylated chitosan forming CS/HAp@PDA-F by photo-crosslinking. In vitro results indicate that CS/HAp@PDA-F hydrogel has outstanding mechanical performance, moreover, it also has the oxygen-carrying ability to prolong survival ability, enhance proliferation activity, and preserve osteogenic differentiation potency and promote osteogenic-related genes expression of rat bone mesenchymal stem cells (rBMSCs) under hypoxic environment. Furthermore, the CS/HAp@PDA-F hydrogel can inhibit the growth of Staphylococcus aureus and Escherichia coli, providing a good antibacterial activity. Additionally, in vivo experiments demonstrate higher bone volume and bone mineral density, and more new bone tissue generation in CS/HAp@PDA-F group than in CS/HAp@PDA group. These results indicate that the rational design of fluorinated hydrogel possesses a good clinical application prospect for bone regeneration.

3D Printed Graphene-PLA Scaffolds Promote Cell Alignment and Differentiation

Traumas and chronic damages can hamper the regenerative power of nervous, muscle, and connective tissues. Tissue engineering approaches are promising therapeutic tools, aiming to develop reliable, reproducible, and economically affordable synthetic scaffolds which could provide sufficient biomimetic cues to promote the desired cell behaviour without triggering graft rejection and transplant failure. Here, we used 3D-printing to develop 3D-printed scaffolds based on either PLA or graphene@PLA with a defined pattern. Multiple regeneration strategies require a specific orientation of implanted and recruited cells to perform their function correctly. We tested our scaffolds with induced pluripotent stem cells (iPSC), neuronal-like cells, immortalised fibroblasts and myoblasts. Our results demonstrated that the specific “lines and ridges” 100 µm-scaffold topography is sufficient to promote myoblast and fibroblast cell alignment and orient neurites along with the scaffolds line pattern. Conversely, graphene is critical to promote cells differentiation, as seen by the iPSC commitment to neuroectoderm, and myoblast fusions into multinuclear myotubes achieved by the 100 µm scaffolds containing graphene. This work shows the development of a reliable and economical 3D-printed scaffold with the potential of being used in multiple tissue engineering applications and elucidates how scaffold micro-topography and graphene properties synergistically control cell differentiation.

Functional Macromolecular Adhesives for Bone Fracture Healing

Compared with traditional internal fixation devices, bone adhesives are expected to exhibit remarkable advantages, such as improved fixation of comminuted fractures and maintained spatial location of fractured scattered bone pieces in treating bone injuries. In this review, different bone adhesives are summarized from the aspects of bone tissue engineering, and the applications of bone adhesives are emphasized. The concepts of "liquid scaffold" and "liquid plate" are proposed to summarize two different research directions of bone adhesives. Furthermore, significant advances of bone adhesives in recent years in mechanical strength, osseointegration, osteoconductivity, and osteoinductivity are discussed. We conclude this topic by providing perspectives on the state-of-the-art research progress and future development trends of bone adhesives. We hope this review will provide a comprehensive summary of bone adhesives and inspire more extensive and in-depth research on this subject.

Bone Tumor Suppression in Rabbits by Hyperthermia below the Clinical Safety Limit Using Aligned Magnetic Bone Cement

Demonstrating highly efficient alternating current (AC) magnetic field heating of nanoparticles in physiological environments under clinically safe field parameters has remained a great challenge, hindering clinical applications of magnetic hyperthermia. In this work, exceptionally high loss power of magnetic bone cement under the clinical safety limit of AC field parameters, incorporating direct current field-aligned soft magnetic Zn_0.3 Fe_2.7 O₄ nanoparticles with low concentration, is reported. Under an AC field of 4 kA m^-1 at 430 kHz, the aligned bone cement with 0.2 wt% nanoparticles achieves a temperature increase of 30 °C in 180 s. This amounts to a specific loss power value of 327 W gmetal-1 and an intrinsic loss power of 47 nHm² kg^-1 , which is enhanced by 50-fold compared to randomly oriented samples. The high-performance magnetic bone cement allows for the demonstration of effective hyperthermia suppression of tumor growth in the bone marrow cavity of New Zealand White Rabbits subjected to rapid cooling due to blood circulation, and significant enhancement of survival rate.

Biologically modified implantation as therapeutic bioabsorbable materials for bone defect repair

For decades, researches have concentrated on the mechanical properties, biodegradation, and biocompatibility of implants used in the therapy of large size bone defect. In vivo studies demonstrate that bioabsorbable bone substitute materials can reduce the risk of common symptoms such as inflammation and osteonecrosis caused by bio-inert materials after long-term implantation. Several organic, inorganic, and composite materials have been approved for clinical application, based on their unique characteristics and advantages. Although some artificial bioabsorbable bone substitute materials have been used for years, there are still some disadvantages existing, such as low mechanical strength, high brittleness, and low degradation rate. Therefore, novel bioabsorbable composite materials biomaterials have been developed for bone defect repair. In this review, we provide an overview of the development of artificial bioabsorbable bone substitute materials and highlight the advantages and disadvantages. Furthermore, recent advances in bioabsorbable bone substitute materials used in bone defect repair are outlined. Finally, we discuss current challenges and further developments in the clinical application of bioabsorbable bone substitute materials.

Emerging Biopolymer-Based Bioadhesives

Bioadhesives have been widely used in healthcare and biomedical applications due to their ease-of-operation for wound closure and repair compared to conventional suturing and stapling. However, several challenges remain for developing ideal bioadhesives, such as unsatisfied mechanical properties, non-tunable biodegradability, and limited biological functions. Considering these concerns, naturally derived biopolymers have been considered good candidates for making bioadhesives owing to their ready availability, facile modification, tunable mechanical properties, and desired biocompatibility and biodegradability. Over the past several years, remarkable progress has been made on biopolymer-based adhesives, covering topics from novel materials designs and advanced processing to clinical translation. The developed bioadhesives have been applied for diverse applications, including tissue adhesion, hemostasis, antimicrobial, wound repair/tissue regeneration, and skin-interfaced bioelectronics. Here in this comprehensive review, recent progress on biopolymer-based bioadhesives is summarized with focuses on clinical translations and multifunctional bioadhesives. Furthermore, challenges and opportunities such as weak adhesion strength at the hydrated state, mechanical mismatch with tissues, and unfavorable immune responses are discussed with an aim to facilitate the future development of high-performance biopolymer-based bioadhesives.

Bioinspired Redwood-Like Scaffolds Coordinated by In Situ-Generated Silica-Containing Hybrid Nanocoatings Promote Angiogenesis and Osteogenesis both In Vitro and In Vivo

Inspired by natural redwood and bone, a biomimetic strategy is presented to develop a highly bioactive redwood-like nanocomposite via radial freeze casting of biocompatible hydrogels followed by the in situ coprecipitation of a Si-containing CaP hybrid nanocoating (SCPN). The engineered material displays radially aligned macrochannels and a porous network structure similar to those of natural redwood. In addition to acting as a mechanical reinforcement, introducing SCPNs into the weak redwood-like scaffold yields not only a nanoroughened surface topography, a low swelling ratio, retarded enzymatic degradation, and enhanced protein absorption abilities but also the sustained sequential release of Si and Ca ions, thereby providing essential biophysical and biochemical cues for effective bone regeneration. Benefiting from the redwood-like structures and bioactive SCPNs, the biomimetic materials create a favorable microenvironment for promoting the initial adhesion, spreading, proliferation, and migration of bone marrow-derived mesenchymal stem cells and human umbilical vein endothelial cells. Furthermore, the in vitro and in vivo data showed that the biocompatible redwood-like scaffold with precipitated SCPN can synergistically promote osteogenesis and angiogenesis in their aligned direction. Collectively, this work presents a novel bioinspired redwood-like material with multifunctional properties that provides new insight into bone defect repair.

Capturing Magnesium Ions via Microfluidic Hydrogel Microspheres for Promoting Cancellous Bone Regeneration

Metal ions are important trace elements in the human body, which directly affect the human metabolism and the regeneration of damaged tissues. For instance, the advanced combination of magnesium ions (Mg²⁺) and bone repair materials make the composite materials have the function of promoting vascular repair and enhancing the adhesion of osteoblasts. Herein, inspired by magnets to attract metals, we utilized the coordination reaction of metal ion ligand to construct a bisphosphonate-functionalized injectable hydrogel microsphere (GelMA-BP-Mg) which could promote cancellous bone reconstruction of osteoporotic bone defect via capturing Mg²⁺. By grafting bisphosphonate (BP) on GelMA microspheres, GelMA-BP microspheres could produce powerful Mg²⁺ capture ability and sustained release performance through coordination reaction, while sustained release BP has bone-targeting properties. In the injectable GelMA-BP-Mg microsphere system, the atomic percentage of captured Mg²⁺ was 0.6%, and the captured Mg²⁺ could be effectively released for 18 days. These proved that the composite microspheres could effectively capture Mg²⁺ and provided the basis for the composite microspheres to activate osteoblasts and endothelial cells and inhibit osteoclasts. Both in vivo and in vitro experimental results revealed that the magnet-inspired Mg²⁺-capturing composite microspheres are beneficial to osteogenesis and angiogenesis by stimulating osteoblasts and endothelial cells while restraining osteoclasts, and ultimately effectively promote cancellous bone regeneration. This study could provide some meaningful conceptions for the treatment of osteoporotic bone defects on the basis of metal ions.

A review of biomimetic scaffolds for bone regeneration: Toward a cell-free strategy

In clinical terms, bone grafting currently involves the application of autogenous, allogeneic, or xenogeneic bone grafts, as well as natural or artificially synthesized materials, such as polymers, bioceramics, and other composites. Many of these are associated with limitations. The ideal scaffold for bone tissue engineering should provide mechanical support while promoting osteogenesis, osteoconduction, and even osteoinduction. There are various structural complications and engineering difficulties to be considered. Here, we describe the biomimetic possibilities of the modification of natural or synthetic materials through physical and chemical design to facilitate bone tissue repair. This review summarizes recent progresses in the strategies for constructing biomimetic scaffolds, including ion-functionalized scaffolds, decellularized extracellular matrix scaffolds, and micro- and nano-scale biomimetic scaffold structures, as well as reactive scaffolds induced by physical factors, and other acellular scaffolds. The fabrication techniques for these scaffolds, along with current strategies in clinical bone repair, are described. The developments in each category are discussed in terms of the connection between the scaffold materials and tissue repair, as well as the interactions with endogenous cells. As the advances in bone tissue engineering move toward application in the clinical setting, the demonstration of the therapeutic efficacy of these novel scaffold designs is critical.

Marginal sealing around integral bilayer scaffolds for repairing osteochondral defects based on photocurable silk hydrogels

Osteochondral repair remains a major challenge in current clinical practice despite significant advances in tissue engineering. In particular, the lateral integration of neocartilage into surrounding native cartilage is a difficult and inadequately addressed problem that determines the success of tissue repair. Here, a novel design of an integral bilayer scaffold combined with a photocurable silk sealant for osteochondral repair is reported. First, we fabricated a bilayer silk scaffold with a cartilage layer resembling native cartilage in surface morphology and mechanical strength and a BMP-2-loaded porous subchondral bone layer that facilitated the osteogenic differentiation of BMSCs. Second, a TGF-β3-loaded methacrylated silk fibroin sealant (Sil-MA) exhibiting biocompatibility and good adhesive properties was developed and confirmed to promote chondrocyte migration and differentiation. Importantly, this TGF-β3-loaded Sil-MA hydrogel provided a bridge between the cartilage layer of the scaffold and the surrounding cartilage and then guided new cartilage to grow towards and replace the degraded cartilage layer from the surrounding native cartilage in the early stage of knee repair. Thus, osteochondral regeneration and superior lateral integration were achieved in vivo by using this composite. These results demonstrate that the new approach of marginal sealing around the cartilage layer of bilayer scaffolds with Sil-MA hydrogel has tremendous potential for clinical use in osteochondral regeneration.

A Solvent-Free and Water-Resistant Dipole-Dipole Interaction-Based Super Adhesive

Water-resistant and high-strength adhesion on different surfaces has attracted considerable attention for decades. However, the adhesion performances of conventional adhesives suffer from deterioration in adhesion performances under water or wet conditions. This work proposes a dipole-dipole interaction strategy for fabricating a solvent-free adhesive that is synthesized via simple one-step copolymerization of dipole monomer acrylonitrile (AN), crosslinker poly(ethylene glycol) diacrylate (PEGDA) with variable length, and a monomer-soluble initiator that initiates room-temperature polymerization. The dipole-dipole interactions from cyan groups in AN concurrently contribute to strong cohesion and adhesion strength in bonding to a wide range of substrates including aluminum, ceramic, glass fiber, epoxy resin, polyethylene terephthalate, wood, and fractured large segmental bone. The adhesion strengths are dependent upon the length of PEGDA, and the shorter PEGDA-crosslinked PAN adhesive demonstrates outstanding water-resistant adhesion spanning pH 2 to pH 10 for 30 days with adhesion strength ranging from 3.31 to 3.97 MPa due to strong dipole-dipole pairing shielding. This dipole-dipole interaction and co-dissolution strategy open a new avenue for creating high-strength water-resistant adhesives for promising applications in engineering and hard-tissue repair.

Robust Underwater Adhesives Based on Dynamic Hydrophilic and Hydrophobic Moieties to Diverse Surfaces

Underwater adhesives (UAs) have promising applications in diverse areas. However, traditional UAs have several drawbacks such as weak and irreversible adhesion behaviors as well as poor performance in biological environments. To address these challenges, we engineered a novel synthetic adhesive based on dynamic hydrophilic and hydrophobic moieties, which shows very strong underwater adhesion strength (30-110 kPa) and debonding energy (20-100 J/m²) to diverse substrates. Interestingly, the UAs could also be switched reversibly and repeatedly by the dynamic exchange of hydrophilic and hydrophobic moieties under alternating temperatures. We also demonstrate the versatile functions and practical value of the UAs for clinical applications as tissue sealants and hemostatic dressing in emergency rescue operations. This general and efficient strategy may be generalized to develop additional next generation UAs for many emerging technological and medical applications.

A New Self-Healing Hydrogel Containing hucMSC-Derived Exosomes Promotes Bone Regeneration

BACKGROUND

Fractures are a medical disease with a high incidence, and about 5-10% of patients need bone transplantation to fill the defect. In this study, we aimed to synthesize a new type of coralline hydroxyapatite (CHA)/silk fibroin (SF)/glycol chitosan (GCS)/difunctionalized polyethylene glycol (DF-PEG) self-healing hydrogel and to evaluate the therapeutic effects of this novel self-healing hydrogel as a human umbilical cord mesenchymal stem cells (hucMSC)-derived exosome carrier on bone defects in SD rat.

METHODS

HucMSCs were isolated from fetal umbilical cord tissue and characterized by surface antigen analysis and pluripotent differentiation in vitro. The cell supernatant after ultracentrifugation was collected to isolate exosomes, which were characterized by transmission electron microscopy and western blot analysis. In vitro cell induction experiments were performed to observe the effects of hucMSC-derived exosomes on the biological behavior of mouse osteoblast progenitor cells (mOPCs) and human umbilical vein endothelial cells (HUVECs). The CHA/SF/GCS/DF-PEG hydrogels were prepared using DF-PEG as the gel factor and then structural and physical properties were characterized. HucMSCs-derived exosomes were added to the hydrogel and their effects were evaluated in SD rats with induced femoral condyle defect. These effects were analyzed by X-ray and micro-CT imaging and H&E, Masson and immunohistochemistry staining.

RESULTS

HucMSC-derived exosomes can promote osteogenic differentiation of mOPCs and promote the proliferation and migration of HUVECs. The CHA/SF/GCS/DF-PEG hydrogel has a high self-healing capacity, perfect surface morphology and the precipitated CHA crystals have a small size and low crystallinity similar to natural bone minerals. The MTT results showed that the hydrogel was non-toxic and have a good biocompatibility. The in vivo studies have shown that the hydrogel containing exosomes could effectively promote healing of rat bone defect. The histological analysis revealed more new bone tissue and morphogenetic protein 2 (BMP-2) in the hydrogel-exosome group. In addition, the hydrogel-exosome group had the highest microvessel density.

CONCLUSION

A self-healing CHA/SF/GCS/DF-PEG hydrogel was successfully prepared. The hydrogel has excellent comprehensive properties and is expected to become a new type of bone graft material. This hydrogel has the effect of promoting bone repair, which is more significant after the addition of hucMSC-derived exosomes.

Regeneration of skeletal system with genipin crosslinked biomaterials

Natural biomaterials, such as collagen, gelatin, and chitosan, are considered as promising candidates for use in tissue regeneration treatment, given their similarity to natural tissues regarding components and structure. Nevertheless, only receiving a crosslinking process can these biomaterials exhibit sufficient strength to bear high tensile loads for use in skeletal system regeneration. Recently, genipin, a natural chemical compound extracted from gardenia fruits, has shown great potential as a reliable crosslinking reagent, which can reconcile the crosslinking effect and biosafety profile simultaneously. In this review, we briefly summarize the genipin extraction process, biosafety, and crosslinking mechanism. Subsequently, the applications of genipin regarding aiding skeletal system regeneration are discussed in detail, including the advances and technological strategies for reconstructing cartilage, bone, intervertebral disc, tendon, and skeletal muscle tissues. Finally, based on the specific pharmacological functions of genipin, its potential applications, such as its use in bioprinting and serving as an antioxidant and anti-tumor agent, and the challenges of genipin in the clinical applications in skeletal system regeneration are also presented.