Immunomodulatory properties of graphene oxide for osteogenesis and angiogenesis

Applications of Graphene Family Nanomaterials in Regenerative Medicine: Recent Advances, Challenges, and Future Perspectives

Graphene family nanomaterials (GFNs) have attracted considerable attention in diverse fields from engineering and electronics to biomedical applications because of their distinctive physicochemical properties such as large specific surface area, high mechanical strength, and favorable hydrophilic nature. Moreover, GFNs have demonstrated the ability to create an anti-inflammatory environment and exhibit antibacterial effects. Consequently, these materials hold immense potential in facilitating cell adhesion, proliferation, and differentiation, further promoting the repair and regeneration of various tissues, including bone, nerve, oral, myocardial, and vascular tissues. Note that challenges still persist in current applications, including concerns regarding biosecurity risks, inadequate adhesion performance, and unsuitable degradability as matrix materials. This review provides a comprehensive overview of current advancements in the utilization of GFNs in regenerative medicine, as well as their molecular mechanism and signaling targets in facilitating tissue repair and regeneration. Future research prospects for GFNs, such as potential in promoting ocular tissue regeneration, are also discussed in details. We hope to offer a valuable reference for the clinical application of GFNs in the treatment of bone defects, nerve damage, periodontitis, and atherosclerosis.

TPG-functionalized PLGA/PCL nanofiber membrane facilitates periodontal tissue regeneration by modulating macrophages polarization via suppressing PI3K/AKT and NF-κB signaling pathways

Traditional fibrous membranes employed in guided tissue regeneration (GTR) in the treatment of periodontitis have limitations of bioactive and immunomodulatory properties. We fabricated a novel nTPG/PLGA/PCL fibrous membrane by electrospinning which exhibit excellent hydrophilicity, mechanical properties and biocompatibility. In addition, we investigated its regulatory effect on polarization of macrophages and facilitating the regeneration of periodontal tissue both in vivo and in vitro. These findings showed the 0.5%TPG/PLGA/PCL may inhibit the polarization of RAW 264.7 into M1 phenotype by suppressing the PI3K/AKT and NF-κB signaling pathways. Furthermore, it directly up-regulated the expression of cementoblastic differentiation markers (CEMP-1 and CAP) in periodontal ligament stem cells (hPDLSCs), and indirectly up-regulated the expression of cementoblastic (CEMP-1 and CAP) and osteoblastic (ALP, RUNX2, COL-1, and OCN) differentiation markers by inhibiting the polarization of M1 macrophage. Upon implantation into a periodontal bone defect rats model, histological assessment revealed that the 0.5%TPG/PLGA/PCL membrane could regenerate oriented collagen fibers and structurally intact epithelium. Micro-CT (BV/TV) and the expression of immunohistochemical markers (OCN, RUNX-2, COL-1, and BMP-2) ultimately exhibited satisfactory regeneration of alveolar bone, periodontal ligament. Overall, 0.5%TPG/PLGA/PCL did not only directly promote osteogenic effects on hPDLSCs, but also indirectly facilitated cementoblastic and osteogenic differentiation through its immunomodulatory effects on macrophages. These findings provide a novel perspective for the development of materials for periodontal tissue regeneration.

Naringin and graphene oxide incorporated Moringa oleifera gum/poly(vinyl) alcohol patch for enhanced wound healing

Patients and healthcare systems stand to gain much from the use of substances that can accelerate wound healing. In this research work, a polymeric patch was fabricated using polymers like poly (vinyl alcohol) (PVA) and Moringa oleifera gum (MO) incorporated with graphene oxide (GO) and naringin (Nar) (drug). This study determined the impact of using PVA/MO/GO/Nar polymeric patch on wound healing via in vitro and in vivo investigations. Graphene oxide was synthesized by modified Hummer's method. The synthesized sample was characterized using XRD, FT-IR, RAMAN Spectroscopy, FESEM and HRTEM. Antibacterial analysis of the GO on four different bacteria was studied through well diffusion, colony count, growth curve and biofilm assay. Biocompatibility was analysed by haemolysis assay. The morphology, antibacterial activity, haemolysis assay, swelling, degradation, porosity, water vapour transmission rate, drug release, blood pump model, in-vitro scratch assay and MTT assay were analysed for the fabricated polymeric patches under in-vitro condition. The PVA/MO/GO/Nar patch has shown enhanced wound healing in in-vivo wound healing experiments on albino Wistar rats.

A study on the therapeutic potential of graphene titanate nanocomposite for treating chemically induced arthritis in rats

Nanotechnology holds substantial promise in the innovative therapies for rheumatoid arthritis (RA). The current study was designed to synthesize and characterize a new graphene titanate nanocomposite (GTNc) and explore its anti-arthritic, anti-inflammatory, and antioxidant potencies against Complete Freund's adjuvant (CFA)-induced arthritis in rats, as well as investigate the underlying molecular mechanisms. Our characterization methods included XRD, FT-IR, SEM, EDX, zeta potential, practical size, and XRF to characterize the novel GTNc. Our findings revealed that arthritic rats treated with GTNc exhibited lower levels of RF, CRP, IL-1β, TNF-α, IL-17, and ADAMTS-5, and higher levels of IL-4 and TIMP-3. In arthritic rats, GTNc reduced LPO levels while increasing GSH content and GST antioxidant activity. Additionally, GTNc decreased the expression of the TGF-β mRNA gene in arthritic rats. Histopathological investigation showed that GTNc reduced inflammatory cell infiltration, cartilage degradation, and bone destruction in joint injuries caused by CFA in the arthritic rats. Collectively, the anti-arthritic, anti-inflammatory, and antioxidant properties of GTNc appear promising for future arthritis treatments and bone disability research.

Graphene Oxide Functionalized Gelatin Methacryloyl Microgel for Enhanced Biomimetic Mineralization and in situ Bone Repair

Introduction

The formation of bone-like apatite (Ap) on natural polymers through biomimetic mineralization using simulated body fluid (SBF) can improve osteoconductivity and biocompatibility, while lowering immunological rejection. Nonetheless, the coating efficiency of the bone-like Ap layer on natural polymers requires improvement. Carbonyls (-COOH) and hydroxyls (-OH) are abundant in graphene oxide (GO), which may offer more active sites for biomimetic mineralization and promote the proliferation of rat bone marrow stromal cells (BMSCs).

Methods

In this study, gelatin methacryloyl (GelMA) microgels were infused with GO (0, 0.5, 1, and 2 mg/mL) and embedded into microgels in SBF for 1, 7, and 14 days. Systematic in vitro and in vivo experiments were performed to evaluate the structure of the microgel and its effect on cell proliferation and ability to repair bone defects in rats.

Results

The resulting GO-GelMA-Ap microgels displayed a porous, interconnected structure with uniformly coated surfaces in bone-like Ap, and the Ca/P ratio of the 1 mg/mL GO-GelMA-Ap group was comparable to that of natural bone tissue. Moreover, the 1 mg/mL GO-GelMA-Ap group exhibited a greater Ap abundance, enhanced proliferation of BMSCs in vitro and increased bone formation in vivo compared to the GelMA-Ap group.

Discussion

Overall, this study offers a novel method for incorporating GO into microgels for bone tissue engineering to promote biomimetic mineralization.

Carbon Nanomaterial-Based Hydrogels as Scaffolds in Tissue Engineering: A Comprehensive Review

Carbon-based nanomaterials (CBNs) are a category of nanomaterials with various systems based on combinations of sp2 and sp3 hybridized carbon bonds, morphologies, and functional groups. CBNs can exhibit distinguished properties such as high mechanical strength, chemical stability, high electrical conductivity, and biocompatibility. These desirable physicochemical properties have triggered their uses in many fields, including biomedical applications. In this review, we specifically focus on applying CBNs as scaffolds in tissue engineering, a therapeutic approach whereby CBNs can act for the regeneration or replacement of damaged tissue. Here, an overview of the structures and properties of different CBNs will first be provided. We will then discuss state-of-the-art advancements of CBNs and hydrogels as scaffolds for regenerating various types of human tissues. Finally, a perspective of future potentials and challenges in this field will be presented. Since this is a very rapidly growing field, we expect that this review will promote interdisciplinary efforts in developing effective tissue regeneration scaffolds for clinical applications.

Graphene-Based Material-Mediated Immunomodulation in Tissue Engineering and Regeneration: Mechanism and Significance

Tissue engineering and regenerative medicine hold promise for improving or even restoring the function of damaged organs. Graphene-based materials (GBMs) have become a key player in biomaterials applied to tissue engineering and regenerative medicine. A series of cellular and molecular events, which affect the outcome of tissue regeneration, occur after GBMs are implanted into the body. The immunomodulatory function of GBMs is considered to be a key factor influencing tissue regeneration. This review introduces the applications of GBMs in bone, neural, skin, and cardiovascular tissue engineering, emphasizing that the immunomodulatory functions of GBMs significantly improve tissue regeneration. This review focuses on summarizing and discussing the mechanisms by which GBMs mediate the sequential regulation of the innate immune cell inflammatory response. During the process of tissue healing, multiple immune responses, such as the inflammatory response, foreign body reaction, tissue fibrosis, and biodegradation of GBMs, are interrelated and influential. We discuss the regulation of these immune responses by GBMs, as well as the immune cells and related immunomodulatory mechanisms involved. Finally, we summarize the limitations in the immunomodulatory strategies of GBMs and ideas for optimizing GBM applications in tissue engineering. This review demonstrates the significance and related mechanism of the immunomodulatory function of GBM application in tissue engineering; more importantly, it contributes insights into the design of GBMs to enhance wound healing and tissue regeneration in tissue engineering.

Injectable hydrogel based on silk fibroin/carboxymethyl cellulose/agarose containing polydopamine functionalized graphene oxide with conductivity, hemostasis, antibacterial, and anti-oxidant properties for full-thickness burn healing

Overcoming bacterial infections and promoting wound healing are significant challenges in clinical practice and fundamental research. This study developed a series of enzymatic crosslinking injectable hydrogels based on silk fibroin (SF), carboxymethyl cellulose (CMC), and agarose, with the addition of polydopamine functionalized graphene oxide (GO@PDA) to endow the hydrogel with suitable conductivity and antimicrobial activity. The hydrogels exhibited suitable gelation time, stable mechanical and rheological properties, high water absorbency, and hemostatic properties. Biocompatibility was also confirmed through various assays. After loading the antibiotic vancomycin hydrochloride, the hydrogels showed sustained release and good antibacterial activity against methicillin-resistant Staphylococcus aureus (MRSA). The fast gelation time and desirable tissue-covering ability of the hydrogels allowed for a good hemostatic effect in a rat liver trauma model. In a rat full-thickness burn wound model, the hydrogels exhibited an excellent treatment effect, leading to significantly enhanced wound closure, collagen deposition, and granulation tissue formation, as well as neovascularization and anti-inflammatory effects. In conclusion, the antibacterial electroactive injectable hydrogel dressing, with its multifunctional properties, significantly promoted the in vivo wound healing process, making it an excellent candidate for full-thickness skin wound healing.

Interaction between Mesenchymal Stem Cells and Immune Cells during Bone Injury Repair

Fractures are the most common large organ trauma in humans. The initial inflammatory response promotes bone healing during the initial post-fracture phase, but chronic and persistent inflammation due to infection or other factors does not contribute to the healing process. The precise mechanisms by which immune cells and their cytokines are regulated in bone healing remain unclear. The use of mesenchymal stem cells (MSCs) for cellular therapy of bone injuries is a novel clinical treatment approach. Bone progenitor MSCs not only differentiate into bone, but also interact with the immune system to promote the healing process. We review in vitro and in vivo studies on the role of the immune system and bone marrow MSCs in bone healing and their interactions. A deeper understanding of this paradigm may provide clues to potential therapeutic targets in the healing process, thereby improving the reliability and safety of clinical applications of MSCs to promote bone healing.

Feather keratin-montmorillonite nanocomposite hydrogel promotes bone regeneration by stimulating the osteogenic differentiation of endogenous stem cells

Bone defects caused by bone trauma, infection, surgery, or other systemic diseases remain a severe challenge for the medical field. To address this clinical problem, different hydrogels were exploited to promote bone tissue regrowth and regeneration. Keratins are natural fibrous proteins found in wool, hair, horns, nails, and feather. Due to their unique characteristics of outstanding biocompatibility, great biodegradability, and hydrophilic, keratins have been widely applicated in different fields. In our study, the feather keratin-montmorillonite nanocomposite hydrogels that consist of keratin hydrogels serving as the scaffold support to accommodate endogenous stem cells and montmorillonite is synthesized. The introduction of montmorillonite greatly improves the osteogenic effect of the keratin hydrogels via bone morphogenetic protein 2 (BMP-2)/phosphorylated small mothers against decapentaplegic homolog 1/5/8 (p-SMAD 1/5/8)/runt-related transcription factor 2 (RUNX2) expression. Moreover, the incorporation of montmorillonite into hydrogels can improve the mechanical properties and bioactivity of the hydrogels. The morphology of feather keratin-montmorillonite nanocomposite hydrogels was shown by scanning electron microscopy (SEM) to have an interconnected porous structure. The incorporation of montmorillonite into the keratin hydrogels was confirmed by the energy dispersive spectrum (EDS). We prove that the feather keratin-montmorillonite nanocomposite hydrogels enhance the osteogenic differentiation of BMSCs. Furthermore, micro-CT and histological analysis of rat cranial bone defect demonstrated that feather keratin-montmorillonite nanocomposite hydrogels dramatically stimulated bone regeneration in vivo. Collectively, feather keratin-montmorillonite nanocomposite hydrogels can regulate BMP/SMAD signaling pathway to stimulate osteogenic differentiation of endogenous stem cells and promote bone defect healing, indicating their promising candidate in bone tissue engineering.

Repair of critical-sized bone defects in rabbit femurs using graphitic carbon nitride (g-C3N4) and graphene oxide (GO) nanomaterials

Various biomaterials have been evaluated to enhance bone formation in critical-sized bone defects; however, the ideal scaffold is still missing. The objective of this study was to investigate the in vitro and in vivo regenerative capacity of graphitic carbon nitride (g-C₃N₄) and graphene oxide (GO) nanomaterials to stimulate critical-sized bone defect regeneration. The in vitro cytotoxicity and hemocompatibility of g-C₃N₄ and GO were evaluated, and their potential to induce the in vitro osteogenesis of human fetal osteoblast (hFOB) cells was assessed using qPCR. Then, bone defect in femoral condyles was created in rabbits and left empty as control or filled with either g-C₃N₄ or GO. The osteogenesis of the different implanted scaffolds was evaluated after 4, 8, and 12 weeks of surgery using X-ray, computed tomography (CT), macro/microscopic examinations, and qPCR analysis of osteocalcin (OC) and osteopontin (OP) expressions. Both materials displayed good cell viability and hemocompatibility with enhanced collagen type-I (Col-I), OC, and OP expressions of the hFOB cells. Compared to the control group, the bone healing process in g-C₃N₄ and GO groups was promoted in vivo. Moreover, complete healing of the bone defect was observed radiologically and grossly in g-C₃N₄ implanted group. Additionally, g-C₃N₄ implanted group showed higher percentages of osteoid tissue, mature collagen, biodegradation, and expressions of OC and OP. In conclusion, our results revealed that g-C₃N₄ and GO nanomaterials could induce osteogenesis in critical-sized bone defects.

Effect of graphene-oxide-modified osteon-like concentric microgrooved surface on the osteoclastic differentiation of macrophages

OBJECTIVES

This study aimed to investigate the effect of new biomimetic micro/nano surfaces on the osteoclastic differentiation of RAW264.7 macrophages by simulating natural osteons for the design of concentric circular structures and modifying graphene oxide (GO).

METHODS

The groups were divided into smooth titanium surface group (SS), concentric microgrooved titanium surface group (CMS), and microgroove modified with GO group (GO-CMS). The physicochemical properties of the material surfaces were studied using scanning electron microscopy (SEM), contact-angle measurement, atomic force microscopy, X-ray photoelectron spectroscopy analysis, and Raman spectroscopy. The effect of the modified material surface on the cell biological behavior of RAW264.7 was investigated by cell-activity assay, SEM, and laser confocal microscopy. The effect on the osteoclastic differentiation of macrophages was investiga-ted by tartrate-resistant acid phosphatase (TRAP) immunofluorescence staining and quantitative real-time polymerase chain reaction (qRT-PCR) experiments.

RESULTS

Macrophages were arranged in concentric circles along the microgrooves, and after modification with GO, the oxygen-containing groups on the surface of the material increased and hydrophilicity increased. Osteoclasts in the GO-CMS group were small in size and number and had the lowest TRAP expression. Although it promoted the proliferation of macrophages in the GO-CMS group, the expression of osteoclastic differentiation-related genes was lower than that in the SS group, and the difference was statistically significant (P<0.05).

CONCLUSIONS

Concentric circular microgrooves restricted the fusion of osteoclasts and the formation of sealing zones. Osteomimetic concentric microgrooves modified with GO inhibited the osteoclastic differentiation of RAW 264.7 macrophages.

Graphene Oxide/RhPTH(1-34)/Polylactide Composite Nanofibrous Scaffold for Bone Tissue Engineering

Polylactide (PLA) is one of the most promising polymers that has been widely used for the repair of damaged tissues due to its biocompatibility and biodegradability. PLA composites with multiple properties, such as mechanical properties and osteogenesis, have been widely investigated. Herein, PLA/graphene oxide (GO)/parathyroid hormone (rhPTH(1-34)) nanofiber membranes were prepared using a solution electrospinning method. The tensile strength of the PLA/GO/rhPTH(1-34) membranes was 2.64 MPa, nearly 110% higher than that of a pure PLA sample (1.26 MPa). The biocompatibility and osteogenic differentiation test demonstrated that the addition of GO did not markedly affect the biocompatibility of PLA, and the alkaline phosphatase activity of PLA/GO/rhPTH(1-34) membranes was about 2.3-times that of PLA. These results imply that the PLA/GO/rhPTH(1-34) composite membrane may be a candidate material for bone tissue engineering.

Polarization Behavior of Bone Macrophage as Well as Associated Osteoimmunity in Glucocorticoid-Induced Osteonecrosis of the Femoral Head

Glucocorticoid-induced osteonecrosis of the femoral head (GIONFH) is a disabling disease with high mortality in China but the detailed molecular and cellular mechanisms remain to be investigated. Macrophages are considered the key cells in osteoimmunology, and the cross-talk between bone macrophages and other cells in the microenvironment is involved in maintaining bone homeostasis. M1 polarized macrophages launch a chronic inflammatory response and secrete a broad spectrum of cytokines (eg, TNF-α, IL-6 and IL-1β) and chemokines to initiate a chronic inflammatory state in GIONFH. M2 macrophage is the alternatively activated anti-inflammatory type distributed mainly in the perivascular area of the necrotic femoral head. In the development of GIONFH, injured bone vascular endothelial cells and necrotic bone activate the TLR4/NF-κB signal pathway, promote dimerization of PKM2 and subsequently enhance the production of HIF-1, inducing metabolic transformation of macrophage to the M1 phenotype. Considering these findings, putative interventions by local chemokine regulation to correct the imbalance between M1/M2 polarized macrophages by switching macrophages to an M2 phenotype, or inhibiting the adoption of an M1 phenotype appear to be plausible regimens for preventing or intervening GIONFH in the early stage. However, these results were mainly obtained by in vitro tissue or experimental animal model. Further studies to completely elucidate the alterations of the M1/M2 macrophage polarization and functions of macrophages in glucocorticoid-induced osteonecrosis of the femoral head are imperative.

Electrospun naringin-loaded microsphere/sucrose acetate isobutyrate system promotes macrophage polarization toward M2 and facilitates osteoporotic bone defect repair

Repairing osteoporotic bone defects is still a major clinical challenge. Recent studies have revealed that immune response is also essential in osteogenesis. The intrinsic inflammatory response of the host, especially the M1/M2 polarization status and inflammatory secretory function of macrophages, can directly affect osteogenic differentiation. Therefore, in this study, an electrospun naringin-loaded microspheres/sucrose acetate isobutyrate (Ng-m-SAIB) system was constructed to investigate its effect on the polarization of macrophage and osteoporotic bone defects. The results of both in vitro and in vivo experiments showed that Ng-m-SAIB had good biocompatibility and could promote the polarization of macrophage toward M2, thereby forming a favorable microenvironment for osteogenesis. The animal experiments also showed that Ng-m-SAIB could promote the osteogenesis of critical size defects in the skull of the osteoporotic model mouse (the senescence-accelerated mouse-strain P6). Together, these results collectively suggested that Ng-m-SAIB might be a promising biomaterial to treat osteoporotic bone defects with favorable osteo-immunomodulatory effects.

Recent advances in 2D material-based phototherapy

Phototherapy, which generally refers to photothermal therapy (PTT) and photodynamic therapy (PDT), has received significant attention over the past few years since it is non-invasive, has effective selectivity, and has few side effects. As a result, it has become a promising alternative to traditional clinical treatments. At present, two-dimensional materials (2D materials) have proven to be at the forefront of the development of advanced nanomaterials due to their ultrathin structures and fascinating optical properties. As a result, much work has been put into developing phototherapy platforms based on 2D materials. This review summarizes the current developments in 2D materials beyond graphene for phototherapy, focusing on the novel approaches of PTT and PDT. New methods are being developed to go above and beyond conventional treatment to fully use the potential of 2D materials. Additionally, the efficacy of cutting-edge phototherapy is assessed, and the existing difficulties and future prospects of 2D materials for phototherapy are covered.

Graphene Oxide-Modified Concentric Microgrooved Titanium Surfaces for the Dual Effects of Osteogenesis and Antiosteoclastogenesis

Surface modification is an effective method to resolve the biocompatibility, mechanical, and functional issues of various titanium implant materials. Therefore, many researchers have modified the implant surface to promote the osseointegration of the implant and improve the implant survival rate. In this study, we used photolithography to construct concentric microgrooves with widths of 10 μm and depths of 10 μm, to produce an osteon-mimetic concentric microgrooved titanium surface that was further modified with graphene oxide by silanization (GO-CMS). The modified surface had great biocompatibility and promoted the proliferation of bone marrow-derived mesenchymal stem cells (BMSCs) and RAW264.7 macrophages. The concentric microgrooves on the titanium surface guided cell migration, altered actin cytoskeleton, and caused the cells to arrange in concentric circles. The titanium surface of the GO-modified osteon-mimetic concentric microgrooves promoted the osteogenic differentiation of BMSCs and inhibited the osteoclastogenic differentiation of RAW264.7 cells. Subsequently, we constructed an indirect coculture system and found that RAW264.7 cells cultured on a GO-CMS material surface in a BMSC-conditioned medium (BCM) decreased receptor activator of nuclear factor-κB ligand (RANKL) secretion and increased OPG secretion and also that the BCM inhibited osteoclastogenic differentiation. Additionally, the secretion of OSM increased in BMSCs cultured in RAW264.7-conditioned medium (RCM) in the GO-CMS group, which in turn promoted the osteogenic differentiation of BMSCs. In conclusion, the titanium surface of GO-modified osteon-mimetic concentric microgrooves had dual effects of osteogenesis and antiosteoclastogenesis under single and coculture conditions, which is beneficial for implant osseointegration and is a promising method for the future direction of surface modifications of implants.

The crosstalk between macrophages and bone marrow mesenchymal stem cells in bone healing

Bone injury plagues millions of patients worldwide every year, and it demands a heavy portion of expense from the public medical insurance system. At present, orthopedists think that autologous bone transplantation is the gold standard for treating large-scale bone defects. However, this method has significant limitations, which means that parts of patients cannot obtain a satisfactory prognosis. Therefore, a basic study on new therapeutic methods is urgently needed. The in-depth research on crosstalk between macrophages (Mϕs) and bone marrow mesenchymal stem cells (BMSCs) suggests that there is a close relationship between inflammation and regeneration. The in-depth understanding of the crosstalk between Mϕs and BMSCs is helpful to amplify the efficacy of stem cell-based treatment for bone injury. Only in the suitable inflammatory microenvironment can the damaged tissues containing stem cells obtain satisfactory healing outcomes. The excessive tissue inflammation and lack of stem cells make the transplantation of biomaterials necessary. We can expect that the crosstalk between Mϕs and BMSCs and biomaterials will become the mainstream to explore new methods for bone injury in the future. This review mainly summarizes the research on the crosstalk between Mϕs and BMSCs and also briefly describes the effects of biomaterials and aging on cell transplantation therapy.

Interfacing Perforated Eardrums with Graphene-Based Membranes for Broadband Hearing Recovery

Eardrum perforation and associated hearing loss is a global health problem. Grafting perforated eardrum with autologous tissues in clinic can restore low-frequency hearing but often leaves poor recovery of high-frequency hearing. In this study, the potential of incorporating a thin multilayered graphene membrane (MGM) into the eardrum for broadband hearing recovery in rats is examined. The MGM shows good biocompatibility and biostability to promote the growth of eardrum cells in a regulated manner with little sign of tissue rejection and inflammatory response. After three weeks of implantation, the MGM is found to be encapsulated by a thin layer of newly grown tissue on both sides without a significant folded overgrowth that is often seen in natural healing. The perforation is well sealed, and broadband hearing recovery (1-32 kHz) is enabled and maintained for at least 2 months. Mechanical simulations show that the high elastic modulus of MGM and thin thickness of the reconstructed eardrum play a critical role in the recovery of high-frequency hearing. This work demonstrates the promise of the use of MGM as a functional graft for perforated eardrum to recover hearing in the broadband frequency region and suggests a new acoustics-related medical application for graphene-related 2D materials.

The design, construction and application of graphene family composite nanocoating on dental metal surface

Enhancement of the biological and mechanical properties of dental metals is important for accommodation with therapeutic schemes in different stomatological disciplines. Nanocoatings based on graphene family nanomaterials (GFNs) improve the topological structure and physicochemical properties of metal surfaces, endowing them with new properties while maintaining inherent mechanical properties. Nano-composite coatings, composed of GFNs with one or more type of polymer, metal, oxide, and inorganic nonmetallic compound, offer more matching modification schemes to meet multifunctional oral treatment requirements (e.g., anti-bacterial and anti-corrosive activity, osteogenesis and angiogenesis). This review describes recent progress in the development of GFN composite nanocoatings for the modification of dental metals, focus on biological effects in clinical settings. Underlying molecular mechanisms, critical modification schemes, and technical innovation in preparation methods are also discussed. The key parameters of GFN composite nanocoating surface modification are summarized according to effects on cellular responses and antibacterial activity. This review provides a theoretical reference for the optimization of the biological effects and application of GFN composite nanocoatings for dental metals, and the promotion of the environmentally friendly large-scale production of high-quality multifunctional GFN-based nanocoatings in the field of oral science.

Engineering immunomodulatory hydrogels and cell-laden systems towards bone regeneration

The well-known synergetic interplay between the skeletal and immune systems has changed the design of advanced bone tissue engineering strategies. The immune system is essential during the bone lifetime, with macrophages playing multiple roles in bone healing and biomaterial integration. If in the past, the most valuable aspect of implants was to avoid immune responses of the host, nowadays, it is well-established how important are the crosstalks between immune cells and bone-engineered niches for an efficient regenerative process to occur. For that, it is essential to recapitulate the multiphenotypic cellular environment of bone tissue when designing new approaches. Indeed, the lack of osteoimmunomodulatory knowledge may be the explanation for the poor translation of biomaterials into clinical practice. Thus, smarter hydrogels incorporating immunomodulatory bioactive factors, stem cells, and immune cells are being proposed to develop a new generation of bone tissue engineering strategies. This review highlights the power of immune cells to upgrade the development of innovative engineered strategies, mainly focusing on orthopaedic and dental applications.

Titanium Surfaces Modified with Graphene Oxide/Gelatin Composite Coatings for Enhanced Antibacterial Properties and Biological Activities

Titanium alloys have been widely used in orthopedic implants due to their excellent physicochemical properties and good biocompatibility. However, in practice, titanium implants may fail to integrate or develop an implant-centered infection. Because of its excellent mechanical properties, bone integrability, biocompatibility, antibacterial properties, and so on, graphene oxide is increasingly being used in the preparation of composite biomaterials. The percutaneous titanium implants are used as the research object in this project. To solve the integration of implant and tissue, a graphene oxide/gelatin (GO/gel) composite coating was used to optimize the implant surface. Bacterial and cell experiments were used to investigate the antimicrobial activity, biocompatibility, and regulation of macrophage polarization of GO/gel-modified titanium. According to our findings, GO/gel-modified titanium has a good bacteriostatic effect against Staphylococcus aureus. On the modified surface, L929 cells proliferated well and showed no cytotoxicity. Simultaneously, the GO/gel-modified titanium surface could inhibit macrophage adhesion and spread in the early stage of culture and showed a more obvious inflammatory decline in the late stage of culture. These findings implied that GO/gel-modified titanium is advantageous for resistant bacteria and tissue remolding.

Silibinin Can Promote Bone Regeneration of Selenium Hydrogel by Reducing the Oxidative Stress Pathway in Ovariectomized Rats

Osteoporosis-related bone defects are a major public health concern. Considering poor effects of a singular pharmacological treatment, many have sought combination therapies, including local treatment combined with systemic intervention. Based on recent evidence that selenium and silibinin increase bone formation and bone mineral density, it is hypothesized that systemic administration with silibinin plus local treatment with selenium may have an additive effect on bone regeneration in an OVX rat model with bone defects. To verify this hypothesis, 3-month-old ovariectomized Sprague- Dawley rats (n = 10/gp) were intraperitoneally with a dose of 50 mg/kg silibinin with selenium hydrogel scaffolds implanted into femoral metaphysis bone defect. Moreover, the MC3T3-E1 cells were co-cultured with selenium and silibinin, and observed any change of cell viability, ROS, and osteogenic activity. Experiment results show that the cell mineralization and osteogenic activity of silibinin plus selenium (SSe) group is enormously higher than the control (Con) group and selenium (Se) group, while ROS appears to be immensely reduced. Osteogenic protein expressions such as SIRT1, SOD2, RUNX-2 and OC of SSe group are significantly higher than Con group and Se group. Micro-CT and Histological analysis evaluation display that group SSe, compared with Con group and Se group, presents the strongest effect on bone regeneration, bone mineralization and higher expression of SIRT1 and SOD2. RT-qPCR analysis indicates that SSe group manifests increased SIRT1, SOD1, SOD2 and CAT than the Con group and Se group (p < 0.05). Our current study demonstrates that systemic administration with SIL plus local treatment with Se is a scheme for rapid repair of femoral condylar defects, and these effects may be achieved via reducing the oxidative stress pathway.

Controllable graphene oxide-based biocompatible hybrid interface as an anti-fibrotic coating for metallic implants

In tissue engineering, foreign body reactions (FBRs) that may occur after the insertion of medical implants are a considerable challenge. Materials currently used in implants are mainly metals that are non-organic, and the lack of biocompatibility and absence of immune regulations may lead to fibrosis after long periods of implantation. Here, we introduce a highly biocompatible hybrid interface of graphene oxide (GO) and collagen type I (COL-I), where the topological nanostructure can effectively inhibit the differentiation of fibroblasts into myofibroblasts. The structure and roughness of this coating interface can be easily adjusted at the nanoscale level through changes in the GO concentration, thereby effectively inducing the polarization of macrophages to the M1 state without producing excessive amounts of pro-inflammatory factors. Compared to nanomaterials or the extracellular matrix as an anti-fibrotic interface, this hybrid bio-interface has superior mechanical strength, physical structures, and high inflammation. Evidenced by inorganic materials such as glass, titanium, and nitinol, GO-COL shows great potential for use in medical implants and cell-material interfaces.

2D Materials and Primary Human Dendritic Cells: A Comparative Cytotoxicity Study

Human health can be affected by materials indirectly through exposure to the environment or directly through close contact and uptake. With the ever-growing use of 2D materials in many applications such as electronics, medical therapeutics, molecular sensing, and energy storage, it has become more pertinent to investigate their impact on the immune system. Dendritic cells (DCs) are highly important, considering their role as the main link between the innate and the adaptive immune system. By using primary human DCs, it is shown that hexagonal boron nitride (hBN), graphene oxide (GO) and molybdenum disulphide have minimal effects on viability. In particular, it is evidenced that hBN and GO increase DC maturation, while GO leads to the release of reactive oxygen species and pro-inflammatory cytokines. hBN and MoS₂ increase T cell proliferation with and without the presence of DCs. hBN in particular does not show any sign of downstream T cell polarization. The study allows ranking of the three materials in terms of inherent toxicity, providing the following trend: GO > hBN ≈ MoS₂ , with GO the most cytotoxic.

Synergistic anti-inflammatory effects of graphene oxide quantum dots and trans-10-hydroxy-2-decenoic acid on LPS-stimulated RAW 264.7 macrophage cells

Graphene oxide quantum dots (GOQDs) have attracted substantial attention in numerous fields due to their unique physicochemical properties. However, their nanotoxicity and potential for use in biomedicine still require further study. In this work, the effects of GOQD and trans- 10-hydroxy-2-decenoic acid (10-HDA) cotreatment on the immune function of macrophages (RAW264.7 cells) were investigated. In particular, LC/MS-based metabolomics was performed to evaluate the effects of GOQDs on the metabolism of LPS-stimulated macrophages. Herein, we fabricated GOQDs with good dispersibility and a uniform size distribution of approximately 7 nm using a polyimide-pyrolyzed carbon film as the working electrode, a high-voltage graphite electrode as the cathode, and H₂O₂ as the oxidant. The GOQDs entered the macrophages and emitted green fluorescence under UV irradiation. Cotreatment with GOQDs and 10-HDA induced RAW 264.7 cell proliferation. GOQDs promoted the anti-inflammatory effect of 10-HDA on LPS-stimulated RAW264.7 cells and attenuated the secretion of TNF-α, IL-6, and IL-1β. The metabolites in RAW264.7 cells treated with GOQDs were significantly different from those in RAW264.7 cells treated with LPS. The enrichment analysis showed that treatment with GOQDs interfered with amino acid metabolism, and lipid metabolism. Our results demonstrate the role of GOQDs in macrophages and provide a basis for their further application in biomedical fields.

Sequential activation of M1 and M2 phenotypes in macrophages by Mg degradation from Ti-Mg alloy for enhanced osteogenesis

BACKGROUND

Even though the modulatory effects of Magnisum (Mg) and its alloys on bone-healing cells have been widely investigated during the last two decades, relatively limited attention has been paid on their inflammation-modulatory properties. Understanding the activation process of macrophages in response to the dynamic degradation process of Mg as well as the relationship between macrophage phenotypes and their osteogenic potential is critical for the design and development of advanced Mg-based or Mg-incorporated biomaterials.

METHODS

In this work, a Ti-0.625 Mg (wt.%) alloy fabricated by mechanical alloying (MA) and subsequent spark plasma sintering (SPS) was employed as a material model to explore the inflammatory response and osteogenic performance in vitro and in vivo by taking pure Ti as the control. The data analysis was performed following Student's t-test.

RESULTS

The results revealed that the macrophages grown on the Ti-0.625 Mg alloy underwent sequential activation of M1 and M2 phenotypes during a culture period of 5 days. The initially increased environmental pH (~ 8.03) was responsible for the activation of M1 macrophages, while accumulated Mg²⁺ within cells contributed to the lateral M2 phenotype activation. Both M1 and M2 macrophages promoted osteoblast-like SaOS-2 cell maturation. In vivo experiment further showed the better anti-inflammatory response, regenerative potentiality and thinner fibrous tissue layer for the Ti-0.625 Mg alloy than pure Ti.

CONCLUSION

The results highlighted the roles of Mg degradation in the Ti-0.625 Mg alloy on the sequential activation of macrophage phenotypes and the importance of modulating M1-to-M2 transition in macrophage phenotypes for the design and development of inflammation-modulatory biomaterials.

3D printed biocompatible graphene oxide, attapulgite, and collagen composite scaffolds for bone regeneration

Tissue-engineered bone material is one of the effective methods to repair bone defects, but the application is restricted in clinical because of the lack of excellent scaffolds that can induce bone regeneration as well as the difficulty in making scaffolds with personalized structures. 3D printing is an emerging technology that can fabricate bespoke 3D scaffolds with precise structure. However, it is challenging to develop the scaffold materials with excellent printability, osteogenesis ability, and mechanical strength. In this study, graphene oxide (GO), attapulgite (ATP), type I collagen (Col I) and polyvinyl alcohol were used as raw materials to prepare composite scaffolds via 3D bioprinting. The composite materials showed excellent printability. The microcosmic architecture and properties was characterized by scanning electron microscopy, Fourier transform infrared and thermal gravimetric analyzer, respectively. To verify the biocompatibility of the scaffolds, the viability, proliferation and osteogenic differentiation of Bone Marrow Stromal Cells (BMSCs) on the scaffolds were assessed by CCK-8, Live/Dead staining and Real-time PCR in vitro. The composited scaffolds were then implanted into the skull defects on rat for bone regeneration. Hematoxylin-eosin staining, Masson staining and immunohistochemistry staining were carried out in vivo to evaluate the regeneration of bone tissue.The results showed that GO/ATP/COL scaffolds have been demonstrated to possess controlled porosity, water absorption, biodegradability and good apatite-mineralization ability. The scaffold consisting of 0.5% GO/ATP/COL have excellent biocompatibility and was able to promote the growth, proliferation and osteogenic differentiation of mouse BMSCs in vitro. Furthermore, the 0.5% GO/ATP/COL scaffolds were also able to promote bone regeneration of in rat skull defects. Our results illustrated that the 3D printed GO/ATP/COL composite scaffolds have good mechanical properties, excellent cytocompatibility for enhanced mouse BMSCs adhesion, proliferation, and osteogenic differentiation. All these advantages made it potential as a promising biomaterial for osteogenic reconstruction.

Development of Graphene-Based Materials in Bone Tissue Engineaering

Bone regeneration-related graphene-based materials (bGBMs) are increasingly attracting attention in tissue engineering due to their special physical and chemical properties. The purpose of this review is to quantitatively analyze mass academic literature in the field of bGBMs through scientometrics software CiteSpace, to demonstrate the rules and trends of bGBMs, thus to analyze and summarize the mechanisms behind the rules, and to provide clues for future research. First, the research status, hotspots, and frontiers of bGBMs are analyzed in an intuitively and vividly visualized way. Next, the extracted important subjects such as fabrication techniques, cytotoxicity, biodegradability, and osteoinductivity of bGBMs are presented, and the different mechanisms, in turn, are also discussed. Finally, photothermal therapy, which is considered an emerging area of application of bGBMs, is also presented. Based on this approach, this work finds that different studies report differing opinions on the biological properties of bGBMS due to the lack of consistency of GBMs preparation. Therefore, it is necessary to establish more standards in fabrication, characterization, and testing for bGBMs to further promote scientific progress and clinical translation.

Extracellular Vesicles Derived from Primed Mesenchymal Stromal Cells Loaded on Biphasic Calcium Phosphate Biomaterial Exhibit Enhanced Macrophage Polarization

Mesenchymal stromal cells (MSC) loaded on biphasic calcium phosphate biomaterial (MSC + BCP) have been used as an advanced therapy medicinal product to treat complex maxillofacial bone defects in patients. Further, MSC-derived extracellular vesicles (EVs) are established vehicles of paracrine factors, supporting inter-cellular communication between MSC and other interacting cell types, such as monocytes/macrophages. However, the information about the immunomodulatory potential of EVs derived from MSC and biomaterial constructs (MSC + BCP:EV) and inflammatory primed constructs (MSCp + BCP:EV) are scarce. Hence, we isolated and characterized EVs from these different systems, and compared their cytokine contents with plastic-adherent MSC-derived EVs (MSC:EV). When EVs from all three MSC systems were added to the primary blood-derived macrophages in vitro, significantly higher numbers of M0 (naive) macrophages shifted to M2-like (anti-inflammatory) by MSCp + BCP:EV treatment. Further, this treatment led to enhanced switching of M1 polarized macrophages to M2 polarized, and conversely, M2 to M1, as evaluated by determining the M1/M2 ratios after treatment. The enhanced macrophage modulation by MSCp + BCP:EV was attributed to their higher immunomodulatory (TNFα, IL1β, IL5), angiogenic (VEGF), and chemokine-rich (RANTES, MCP1, MIP1β) cytokine cargo. In conclusion, we successfully isolated and characterized EVs from MSC + BCP constructs and demonstrated that, depending upon the tissue microenvironment, these EVs contribute towards modulating the macrophage-mediated inflammation and healing responses. The study offers new insights into the use of biomaterial-induced EVs for MSC secretome delivery, as a step towards future ‘cell-free’ bone regenerative therapies.

Multifunctional 3D sponge-like macroporous cryogel-modified long carbon fiber reinforced polyetheretherketone implant with enhanced vascularization and osseointegration

Long carbon fiber reinforced polyetheretherketone (LCFRPEEK), a newly developed high-performance composite material, is being investigated as a possible orthopedic implant. However, its inability of angiogenesis and osseointegration after implantation makes...

Titanium surface with nanospikes tunes macrophage polarization to produce inhibitory factors for osteoclastogenesis through nanotopographic cues

Definitive prevention of inflammatory osteolysis around peri-implant bone tissue remains unestablished. M1 macrophages play a key role in the host defense against inflammatory osteolysis, and their polarization depends on cell shape. Macrophage polarization is controlled by environmental stimuli, particularly physicochemical cues and hence titanium nanosurface might tune macrophage polarization and function. This study determined whether titanium nanosurfaces with anisotropically patterned nanospikes regulates macrophage polarization for inhibiting osteoclast differentiation of osteoclast precursors. Alkaline-etching treatment with different protocols created two types of titanium nanosurfaces that had anisotropically patterned nanospikes with high or low distribution density, together with superhydrophilicity and the presence of hydroxyl groups. J774A.1 cells (mouse macrophage-like cell line), cultured on both titanium nanosurfaces, exhibited truly circulated shapes and highly expressed M1, but less M2, markers, without loss of viability. M1-like polarization of macrophages on both titanium nanosurfaces was independent of protein-mediated ligand stimulation or titanium surface hydrophilic or chemical status. In contrast, other smooth or micro-roughened titanium surfaces with little or no nanospikes did not activate macrophages under any culture conditions. Macrophage culture supernatants on both titanium nanosurfaces inhibited osteoclast differentiation of RAW264.7 cells (mouse osteoclast precursor cell line), even when co-incubated with osteoclast differentiation factors. The inhibitory effects on osteoclast differentiation tended to be higher in macrophages cultured on titanium nanosurfaces with denser nanospikes. These results showed that titanium nanosurfaces with anisotropically patterned nanospikes tune macrophage polarization for inhibiting osteoclast differentiation of osteoclast precursors, with nanotopographic cues rather than other physicochemical properties. STATEMENT OF SIGNIFICANCE: Peri-implant inflammatory osteolysis is one of the serious issues for dental and orthopedic implants. Macrophage polarization and function are key for prevention of peri-implant inflammatory osteolysis. Macrophage polarization can be regulated by the biomaterial's surface physicochemical properties such as hydrophilicity or topography. However, there was no titanium surface modification to prevent inflammatory osteolysis through immunomodulation. The present study showed for the first time that the titanium nanosurfaces with anisotropically patterned nanospikes, created by the simple alkali-etching treatment polarized macrophages into M1-like type producing the inhibitory factor on osteoclast differentiation. This phenomenon attributed to nanotopographic cues, but not hydrophilicity on the titanium nanosurfaces. This nanotechnology might pave the way to develop the smart implant surface preventing peri-implant inflammatory osteolysis through immunomodulation.

[Methods of improving the mechanical properties of hydrogels and their research progress in bone tissue engineering]

OBJECTIVE

To review the methods of improving the mechanical properties of hydrogels and the research progress in bone tissue engineering.

METHODS

The recent domestic and foreign literature on hydrogels in bone tissue engineering was reviewed, and the methods of improving the mechanical properties of hydrogels and the effect of bone repair in vivo and in vitro were summarized.

RESULTS

Hydrogels are widely used in bone tissue engineering, but their mechanical properties are poor. Improving the mechanical properties of hydrogels can enhance bone repair. The methods of improving the mechanical properties of hydrogels include the construction of dual network structures, inorganic nanoparticle composites, introduction of conductive materials, and fiber network reinforcement. These methods can improve the mechanical properties of hydrogels to various degrees while also demonstrating a significant bone repair impact.

CONCLUSION

The mechanical properties of hydrogels can be effectively improved by modifying the system, components, and fiber structure, and bone repair can be effectively promoted.

Graphene oxide-modified silk fibroin/nanohydroxyapatite scaffold loaded with urine-derived stem cells for immunomodulation and bone regeneration

Background

The invasive and complicated procedures involving the use of traditional stem cells limit their application in bone tissue engineering. Cell-free, tissue-engineered bones often have complex scaffold structures and are usually engineered using several growth factors (GFs), thus leading to costly and difficult preparations. Urine-derived stem cells (USCs), a type of autologous stem cell isolated noninvasively and with minimum cost, are expected to solve the typical problems of using traditional stem cells to engineer bones. In this study, a graphene oxide (GO)-modified silk fibroin (SF)/nanohydroxyapatite (nHA) scaffold loaded with USCs was developed for immunomodulation and bone regeneration.

Methods

The SF/nHA scaffolds were prepared via lyophilization and cross-linked with GO using 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC) and N-hydroxy succinimide (NHS). Scaffolds containing various concentrations of GO were characterized using scanning electron microscopy (SEM), the elastic modulus test, Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectrometer (XPS). Examinations of cell adhesion, proliferation, viability, morphology, alkaline phosphatase activity, and osteogenesis-related gene expression were performed to compare the osteogenesis-related biological behaviors of USCs cultured on the scaffolds. The effect of USC-laden scaffolds on the differentiation of macrophages was tested using ELISA, qRT-PCR, and immunofluorescence staining. Subcutaneous implantations in rats were performed to evaluate the inflammatory response of the USC-laden scaffolds after implantation. The scaffolds loaded with USCs were implanted into a cranial defect model in rats to repair bone defects. Micro-computed tomography (μCT) analyses and histological evaluation were performed to evaluate the bone repair effects.

Results

GO modification enhanced the mechanical properties of the scaffolds. Scaffolds containing less than 0.5% GO had good biocompatibility and promoted USC proliferation and osteogenesis. The scaffolds loaded with USCs induced the M2-type differentiation and inhibited the M1-type differentiation of macrophages. The USC-laden scaffolds containing 0.1% GO exhibited the best capacity for promoting the M2-type differentiation of macrophages and accelerating bone regeneration and almost bridged the site of the rat cranial defects at 12 weeks after surgery.

Conclusions

This composite system has the capacity for immunomodulation and the promotion of bone regeneration and shows promising potential for clinical applications of USC-based, tissue-engineered bones.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-021-02634-w.

Two-Dimensional Nanomaterials for Peripheral Nerve Engineering: Recent Advances and Potential Mechanisms

Peripheral nerve tissues possess the ability to regenerate within artificial nerve scaffolds, however, despite the advance of biomaterials that support nerve regeneration, the functional nerve recovery remains unsatisfactory. Importantly, the incorporation of two-dimensional nanomaterials has shown to significantly improve the therapeutic effect of conventional nerve scaffolds. In this review, we examine whether two-dimensional nanomaterials facilitate angiogenesis and thereby promote peripheral nerve regeneration. First, we summarize the major events occurring after peripheral nerve injury. Second, we discuss that the application of two-dimensional nanomaterials for peripheral nerve regeneration strategies by facilitating the formation of new vessels. Then, we analyze the mechanism that the newly-formed capillaries directionally and metabolically support neuronal regeneration. Finally, we prospect that the two-dimensional nanomaterials should be a potential solution to long range peripheral nerve defect. To further enhance the therapeutic effects of two-dimensional nanomaterial, strategies which help remedy the energy deficiency after peripheral nerve injury could be a viable solution.

Graphene Particles Interfere with Pro-Inflammatory Polarization of Human Macrophages: Functional and Electrophysiological Evidence

The interaction of two types of fragmented graphene particles (30-160 nm) with human macrophages is studied. Since macrophages have significant phagocytic activity, the incorporation of graphene particles into cells has an effect on the response to functional polarization stimuli, favoring an anti-inflammatory profile. Incubation of macrophages with graphene foam particles, prepared by chemical vapor deposition, and commercially available graphene nanoplatelet particles does not affect cell viability when added at concentrations up to 100 µg mL^-1 ; macrophages exhibit differential quantitative responses to each type of graphene particles. Although both materials elicit similar increases in the release of reactive oxygen species, the impact on the transcriptional regulation associated with the polarization profile is different; graphene nanoplatelets significantly modify this transcriptomic profile. Moreover, these graphene particles differentially affect the motility and phagocytosis of macrophages. After the incorporation of both graphene types into the macrophages, they exhibit specific responses in terms of the mitochondrial oxygen consumption and electrophysiological potassium currents at the cell plasma membrane. These data support the view that the physical structure of the graphene particles has an impact on human macrophage responses, paving the way for the development of new mechanisms to modulate the activity of the immune system.

Application of some graphene derivatives to increase the efficiency of stem cell therapy

Graphene and its derivatives have application potential in many areas such as environmental technology, catalysis, biomedicine, and in particular, stem cell-based differentiation and regenerative therapies. Mesenchymal stem cell transplantation has emerged as a potential therapy for some diseases, such as acute kidney damage, liver failure and myocardial infarction. However, the poor survival of transplanted stem cells in such applications has significantly limited their therapeutic effectiveness. Graphene-based materials can improve the therapeutic efficacy of stem cells as they prevent the death of implanted cells by attaching them prior to implantation and increasing their paracrine secretion. In this review, we will highlight a number of recent studies that have investigated the potential use of graphene or its derivatives in stem cell applications and the prevention of transplanted stem cells from cell death, thereby improving their therapeutic efficacy.

Osteoinductive and antimicrobial mechanisms of graphene-based materials for enhancing bone tissue engineering

Graphene-based materials (GMs) have great application prospects in bone tissue engineering due to their osteoinductive ability and antimicrobial activity. GMs induce osteogenic differentiation through several mechanisms and pathways in bone tissue engineering. First of all, the surface and high hardness of the porous folds of graphene or graphene oxide (GO) can generate mechanical stimulation to initiate a cascade of reactions that promote osteogenic differentiation without any chemical inducers. In addition, change of the extracellular matrix (ECM), regulation of macrophage polarization, the oncostatin M (OSM) signaling pathway, the MAPK signaling pathway, the BMP signaling pathway, the Wnt/β-catenin signaling pathway, and other pathways are involved in GMs' regulation of osteogenesis. In bone tissue engineering, GMs prevent the formation of microbial biofilms mainly through preventing microbial adhesion and killing them. The former is mainly achieved by reducing surface free energy (SFE) and increasing hydrophobicity. The latter mainly includes oxidative stress and photothermal/photodynamic effects. Graphene and its derivatives (GDs) are mainly combined with bioactive ceramic materials, metal materials and macromolecular polymers to play an antimicrobial effect in bone tissue engineering. Concentration, number of layers, and type of GDs often affect the antimicrobial activity of GMs. In this paper, we reviewed relevant osteoinductive and antimicrobial mechanisms of GMs and their applications in bone tissue engineering.

Biomimetic reduced graphene oxide coated collagen scaffold for in situ bone regeneration

A variety of bone-related diseases and injures and limitations of traditional regeneration methods require new tissue substitutes. Tissue engineering and regeneration combined with nanomedicine can provide different natural or synthetic and combined scaffolds with bone mimicking properties for implantation in the injured area. In this study, we synthesized collagen (Col) and reduced graphene oxide coated collagen (Col-rGO) scaffolds, and we evaluated their in vitro and in vivo effects on bone tissue repair. Col and Col-rGO scaffolds were synthesized by chemical crosslinking and freeze-drying methods. The surface topography, and the mechanical and chemical properties of scaffolds were characterized, showing three-dimensional (3D) porous scaffolds and successful coating of rGO on Col. The rGO coating enhanced the mechanical strength of Col-rGO scaffolds to a greater extent than Col scaffolds by 2.8 times. Furthermore, Col-rGO scaffolds confirmed that graphene addition induced no cytotoxic effects and enhanced the viability and proliferation of human bone marrow-derived mesenchymal stem cells (hBMSCs) with 3D adherence and expansion. Finally, scaffold implantation into rabbit cranial bone defects for 12 weeks showed increased bone formation, confirmed by Hematoxylin–Eosin (H&E) and alizarin red staining. Overall, the study showed that rGO coating improves Col scaffold properties and could be a promising implant for bone injuries.

A practical guide for evaluating the osteoimmunomodulatory properties of biomaterials

Biomaterials offer a promising approach to repair bone defects. Whereas traditional studies predominantly focused on optimizing the osteogenic capacity of biomaterials, less focus has been on the immune response elicited by them. However, the immune and skeletal systems extensively interact, a concept which is referred to as 'osteoimmunology'. This realization has fuelled the development of biomaterials with favourable osteoimmunomodulatory (OIM) properties, aiming to modulate the immune response and to support bone regeneration, thereby affecting the success of an implant. Given the plethora of in vitro assays used to evaluate the OIM properties of biomaterials, it may be challenging to select the right methods to produce conclusive results. In this review, we aim to provide a comprehensive and practical guide for researchers interested in studying the OIM properties of biomaterials in vitro. After a concise overview of the concept of osteoimmunology, emphasis is put on the methodologies that are regularly used to evaluate the OIM properties of biomaterials. First, a description of the most commonly used cell types and cell culture media is provided. Second, typical experimental set-ups and their relevant characteristics are discussed. Third, a detailed overview of the generally used methodologies and readouts, including cell type-specific markers and time points of analysis, is given. Finally, we highlight the promise of advanced approaches, namely microarrays, bioreactors and microfluidic-based systems, and the potential that these may offer to the osteoimmunology field. STATEMENT OF SIGNIFICANCE: Osteoimmunology focuses on the connection and communication between the skeletal and immune systems. This interaction has been recognized to play an important role in the clinical success of biomaterials, which has resulted in an increasing amount of research on the osteoimmunomodulatory (OIM) properties of biomaterials. However, the amount of literature makes it challenging to extract the information needed to design experiments from beginning to end, and to compare obtained results to existing work. This article intends to serve as a guide for those aiming to learn more about the commonly used experimental approaches in the field. We cover early-stage choices, such as cell types and experimental set-ups, but also discuss specific assays, including cell markers and time points of analysis.

The Crosstalk between Mesenchymal Stem Cells and Macrophages in Bone Regeneration: A Systematic Review

Bone regeneration is a complex and well-coordinated process that involves crosstalk between immune cells and resident cells in the injury site. Transplantation of mesenchymal stem cells (MSCs) is a promising strategy to enhance bone regeneration. Growing evidence suggests that macrophages have a significant impact on osteogenesis during bone regeneration. However, the precise mechanisms by which macrophage subtypes influence bone regeneration and how MSCs communicate with macrophages have not yet been fully elucidated. In this systematic literature review, we gathered evidence regarding the crosstalk between MSCs and macrophages during bone regeneration. According to the PRISMA protocol, we extracted literature from PubMed and Embase databases by using "mesenchymal stem cells" and "macrophages" and "bone regeneration" as keywords. Thirty-three studies were selected for this review. MSCs isolated from both bone marrow and adipose tissue and both primary macrophages and macrophage cell lines were used in the selected studies. In conclusion, anti-inflammatory macrophages (M2) have significantly more potential to strengthen bone regeneration compared with naïve (M0) and classically activated macrophages (M1). Transplantation of MSCs induced M1-to-M2 transition and transformed the skeletal microenvironment to facilitate bone regeneration in bone fracture and bone defect models. This review highlights the complexity between MSCs and macrophages, providing more insight into the polarized macrophage behavior in this evolving field of osteoimmunology. The results may serve as a useful reference for definite success in MSC-based therapy based on the critical interaction with macrophages.

Carbon-Based Nanomaterials: Promising Antiviral Agents to Combat COVID-19 in the Microbial-Resistant Era

Therapeutic options for the highly pathogenic human severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) causing the current pandemic coronavirus disease (COVID-19) are urgently needed. COVID-19 is associated with viral pneumonia and acute respiratory distress syndrome causing significant morbidity and mortality. The proposed treatments for COVID-19 have shown little or no effect in the clinic so far. Additionally, bacterial and fungal pathogens contribute to the SARS-CoV-2-mediated pneumonia disease complex. The antibiotic resistance in pneumonia treatment is increasing at an alarming rate. Therefore, carbon-based nanomaterials (CBNs), such as fullerene, carbon dots, graphene, and their derivatives constitute a promising alternative due to their wide-spectrum antimicrobial activity, biocompatibility, biodegradability, and capacity to induce tissue regeneration. Furthermore, the antimicrobial mode of action is mainly physical (e.g., membrane distortion), characterized by a low risk of antimicrobial resistance. In this Review, we evaluated the literature on the antiviral activity and broad-spectrum antimicrobial properties of CBNs. CBNs had antiviral activity against 13 enveloped positive-sense single-stranded RNA viruses, including SARS-CoV-2. CBNs with low or no toxicity to humans are promising therapeutics against the COVID-19 pneumonia complex with other viruses, bacteria, and fungi, including those that are multidrug-resistant.

Biocompatibility and Angiogenic Effect of Chitosan/Graphene Oxide Hydrogel Scaffolds on EPCs

Angiogenesis in the field of tissue engineering has attracted significant attention. Graphene oxide has become a promising nanomaterial in tissue engineering for its unique biochemical properties. Therefore, herein, a series of chitosan (CS)/graphene oxide (GO) hydrogel scaffolds were synthesized by crosslinking CS and GO at different concentrations (0.1, 0.5, and 1.0 wt.%) using genipin. Compared with the CS hydrogel scaffolds, the CS/GO hydrogel scaffolds have a better network structure and mechanical strength. Then, we used endothelial progenitor cells (EPCs) extracted from human umbilical cord blood and cocultured these EPCs with the as-prepared scaffolds. The scaffolds with 0.1 and 0.5 wt.%GO showed no considerable cytotoxicity, could promote the proliferation of EPCs and tube formation, and upregulated the expressions of CD34, VEGF, MMP9, and SDF-1 in EPCs compared to the case of the scaffold with 1.0 wt.%GO. This study shows that the addition of graphene oxide improves the structure of chitosan hydrogel and enhances the proliferation activity and angiogenic capacity of EPCs.

Enhanced Effect of Polyethyleneimine-Modified Graphene Oxide and Simvastatin on Osteogenic Differentiation of Murine Bone Marrow-Derived Mesenchymal Stem Cells

Statin derivatives traditionally have been used for the treatment of hyperlipidemia, but recent studies have shown their ability to regulate bone metabolism and promote bone growth. In this study, simvastatin (Sim), a new therapeutic candidate for bone regeneration, was combined with graphene oxide (GO), which has recently attracted much interest as a drug delivery method, to produce a compound substance effective for bone regeneration. To create a stable and homogenous complex with Sim, GO was modified with polyethylenimine, and the effect of modification was analyzed using Fourier transform infrared spectroscopy, zeta potential, and cytotoxicity testing. More specifically, the osteogenic differentiation potential expected by the combination of the two effective materials for osteogenic differentiation, GO and Sim, was evaluated in mesenchymal stem cells. Compared with control groups with GO and Sim used separately, the GO/Sim complex showed excellent osteogenic differentiation properties, with especially enhanced effects in the complex containing < 1 μM Sim.

Simvastatin-loaded graphene oxide embedded in polycaprolactone-polyurethane nanofibers for bone tissue engineering applications

Here, the role of simvastatin-loaded graphene oxide embedded in polyurethane-polycaprolactone nanofibers for bone tissue engineering has been investigated. The scaffolds were physicochemically and mechanically characterized, and obtained polymeric composites were used as MG-63 cell culture scaffolds. The addition of graphene oxide-simvastatin to nanofibers generates a homogeneous and uniform microstructure as well as a reduction in fiber diameter. Results of water-scaffolds interaction indicated higher hydrophilicity and absorption capacity as a function of graphene oxide addition. Scaffolds’ mechanical properties and physical stability improved after the addition of graphene oxide. Inducing bioactivity after the addition of simvastatin-loaded graphene oxide terminated its capability for hard tissue engineering application, evidenced by microscopy images and phase characterization. Nanofibrous scaffolds could act as a sustained drug carrier. Using the optimal concentration of graphene oxide-simvastatin is necessary to avoid toxic effects on tissue. Results show that the scaffolds are biocompatible to the MG-63 cell and support alkaline phosphatase activity, illustrating their potential use in bone tissue engineering. Briefly, graphene-simvastatin-incorporated in polymeric nanofibers was developed to increase bioactive components’ synergistic effect to induce more bioactivity and improve physical and mechanical properties as well as in vitro interactions for better results in bone repair.

On the road to smart biomaterials for bone research: definitions, concepts, advances, and outlook

The demand for biomaterials that promote the repair, replacement, or restoration of hard and soft tissues continues to grow as the population ages. Traditionally, smart biomaterials have been thought as those that respond to stimuli. However, the continuous evolution of the field warrants a fresh look at the concept of smartness of biomaterials. This review presents a redefinition of the term "Smart Biomaterial" and discusses recent advances in and applications of smart biomaterials for hard tissue restoration and regeneration. To clarify the use of the term "smart biomaterials", we propose four degrees of smartness according to the level of interaction of the biomaterials with the bio-environment and the biological/cellular responses they elicit, defining these materials as inert, active, responsive, and autonomous. Then, we present an up-to-date survey of applications of smart biomaterials for hard tissues, based on the materials' responses (external and internal stimuli) and their use as immune-modulatory biomaterials. Finally, we discuss the limitations and obstacles to the translation from basic research (bench) to clinical utilization that is required for the development of clinically relevant applications of these technologies.

Co-inspired hydroxyapatite-based scaffolds for vascularized bone regeneration

Hydroxyapatite (HA) is the main inorganic component of human bone. Inspired by nacre and cortical bone, hydroxyapatite-based coil scaffolds were successfully prepared. The scaffolds presented "brick and mortar" multi-layered structure of nacre and multi-layered concentric circular structure of cortical bone. Because of bioactive components and hierarchical structure, the scaffolds possessed good compressive strength (≈95 MPa), flexural strength (≈161 MPa) and toughness (≈1.1 MJ/m³). In addition, they showed improved angiogenesis and osteogenesis in rat and rabbit critical sized bone defect models. By mimicking co-biological systems, this work provided a feasible strategy to optimize the properties of traditional tissue engineering biological materials for vascularized bone regeneration.

Applications of Graphene and Graphene Oxide in Smart Drug/Gene Delivery: Is the World Still Flat?

Graphene, a wonder material, has made far-reaching developments in many different fields such as materials science, electronics, condensed physics, quantum physics, energy systems, etc. Since its discovery in 2004, extensive studies have been done for understanding its physical and chemical properties. Owing to its unique characteristics, it has rapidly became a potential candidate for nano-bio researchers to explore its usage in biomedical applications. In the last decade, remarkable efforts have been devoted to investigating the biomedical utilization of graphene and graphene-based materials, especially in smart drug and gene delivery as well as cancer therapy. Inspired by a great number of successful graphene-based materials integrations into the biomedical area, here we summarize the most recent developments made about graphene applications in biomedicine. In this paper, we review the up-to-date advances of graphene-based materials in drug delivery applications, specifically targeted drug/ gene delivery, delivery of antitumor drugs, controlled and stimuli-responsive drug release, photodynamic therapy applications and optical imaging and theranostics, as well as investigating the future trends and succeeding challenges in this topic to provide an outlook for future researches.

Dental pulp stem cells response on the nanotopography of scaffold to regenerate dentin-pulp complex tissue

The study of regenerative dentistry receives a fast growing interest. The potential ability of the dentin-pulp complex to regenerate is both promising and perplexing. To answer the challenging nature of the dental environment, scientists have developed various combinations of biomaterial scaffolds, stem cells, and incorporation of several growth factors. One of the crucial elements of this tissue engineering plan is the selection and fabrication of scaffolds. However, further findings suggest that cell behavior hugely depends on mechanical signaling. Nanotopography modifies scaffolds to alter cell migration and differentiation. However, to the best of the author's knowledge, there are very few studies addressing the correlation between nanotopography and dentin-pulp complex regeneration. Therefore, this article presents a comprehensive review of these studies and suggests a direction for future developments, particularly in the incorporation of nanotopography design for dentin-pulp complex regeneration.