Applications of biomaterials for immunosuppression in tissue repair and regeneration

Immunomodulatory bioadhesive technologies

Bioadhesives have found significant use in medicine and engineering, particularly for wound care, tissue engineering, and surgical applications. Compared to traditional wound closure methods such as sutures and staples, bioadhesives offer advantages, including reduced tissue damage, enhanced healing, and ease of implementation. Recent progress highlights the synergy of bioadhesives and immunoengineering strategies, leading to immunomodulatory bioadhesives capable of modulating immune responses at local sites where bioadhesives are applied. They foster favorable therapeutic outcomes such as reduced inflammation in wounds and implants or enhanced local immune responses to improve cancer therapy efficacy. The dual functionalities of bioadhesion and immunomodulation benefit wound management, tissue regeneration, implantable medical devices, and post-surgical cancer management. This review delves into the interplay between bioadhesion and immunomodulation, highlighting the mechanobiological coupling involved. Key areas of focus include the modulation of immune responses through chemical and physical strategies, as well as the application of these bioadhesives in wound healing and cancer treatment. Discussed are remaining challenges such as achieving long-term stability and effectiveness, necessitating further research to fully harness the clinical potential of immunomodulatory bioadhesives.

Immunomodulatory Effects of Symplectoteuthis oualaniensis Protamine and Its PEG Derivative on Macrophages: Involvement of PI3K/Akt Signaling, Redox Regulation, and Cell Cycle Modulation

Protamine is a promising marine-derived bioactive compound that is highly arginine-rich and has demonstrated unique advantages in medical and biological research. This study, for the first time, investigates the molecular mechanisms underlying the immunomodulatory effects of Salmon Protamine Sulfate (SPS), Symplectoteuthis oualaniensis Protamine (SOP), and its polyethylene glycol (PEG) derivative (SOP-PEG) on RAW264.7 macrophages. The results demonstrate that both SOP and SOP-PEG significantly enhance the proliferation of RAW264.7 cells by promoting the secretion of pro-inflammatory cytokines and nitric oxide (NO), increasing ROS production, and improving antioxidant capacity, in comparison to SPS. Elevated ROS levels play a crucial role in enhancing macrophage immune activity, while the enhanced antioxidant defense mechanisms help maintain redox homeostasis and protect against oxidative stress-induced cellular damage. A Western blot analysis reveals that SOP and SOP-PEG notably regulate the expression of key proteins associated with the PI3K/Akt signaling pathway and anti-apoptotic mechanisms. Furthermore, a flow cytometry analysis indicates a significant increase in the G2/M-phase cell population in the treatment groups, which is corroborated by Western blot data showing alterations in critical regulatory proteins. Notably, SOP-PEG exhibits the strongest effects in regulating macrophage immune activity, which can be attributed to the enhanced stability and prolonged bioactivity resulting from the PEGylation of SOP. This comprehensive study reveals how SOP and SOP-PEG enhance macrophage immune function through multiple mechanisms, including PI3K/Akt activation, redox regulation, and cell cycle modulation. It provides valuable insights and a theoretical foundation for their potential applications in immunotherapy and immune regulation.

Modulation of biomaterial-induced foreign body response by regulating the differentiation and migration of Treg cells through the CXCL12-CXCR4/7 axis

Tissue exposure to implanted biomaterials triggers a foreign body response (FBR), which is a stepwise immunological process involving innate immune cells and tissue repair cells. Although the regulatory T (Treg) cells play a crucial role in inflammation and tissue repair, their function in the process of FBR has not been well investigated. In this study, as titanium (Ti) exhibits better biocompatibility and induces milder FBR than polymethyl methacrylate (PMMA), we analyzed the characteristics of Treg cells during FBR caused by the two types of biomaterials. In a rat femur implantation model, we found that the number of Treg cells around titanium implants was much more than that in the PMMA-implanted group. Meanwhile, the expression of CXCR4 in tissues around Ti implants was significantly higher, and the expression of CXCR7 was lower. When co-cultured with biomaterials and macrophages, the differentiation and migration of Treg cells in the Ti-implanted group were promoted, and this effect could be modulated by CXCR4/7 inhibitors. Moreover, targeting CXCR4/7 influenced the amount of Treg cells in vivo and then reversed the FBR induced by PMMA or Ti implants. In summary, our findings revealed the role of CXCR4/CXCR7 in regulating the migration and differentiation of Treg cells during FBR and suggested that the CXCL12-CXCR4/CXCR7 axis may serve as a potential therapeutic target for immunomodulating foreign body response.

Advances in the application and research of biomaterials in promoting bone repair and regeneration through immune modulation

With the ongoing development of osteoimmunology, increasing evidence indicates that the local immune microenvironment plays a critical role in various stages of bone formation. Consequently, modulating the immune inflammatory response triggered by biomaterials to foster a more favorable immune microenvironment for bone regeneration has emerged as a novel strategy in bone tissue engineering. This review first examines the roles of various immune cells in bone tissue injury and repair. Then, the contributions of different biomaterials, including metals, bioceramics, and polymers, in promoting osteogenesis through immune regulation, as well as their future development directions, are discussed. Finally, various design strategies, such as modifying the physicochemical properties of biomaterials and integrating bioactive substances, to optimize material design and create an immune environment conducive to bone formation, are explored. In summary, this review comprehensively covers strategies and approaches for promoting bone tissue regeneration through immune modulation. It offers a thorough understanding of current research trends in biomaterial-based immune regulation, serving as a theoretical reference for the further development and clinical application of biomaterials in bone tissue engineering.

Effect of 3D-Printed Polycaprolactone Scaffold With Powdery/Smooth Micromorphology on Local Immune Environments

Selective laser sintering (SLS) has become a viable approach for producing biodegradable medical implants in various clinical applications. The resulting scaffolds typically exhibit a powdery microstructure, which may potentially impact the behavior of immune cells and immune responses in surrounding tissues. However, limited research has been conducted to understand the effect of surface morphology in SLS-fabricated scaffolds on local immune environments. This study aims to compare the effect of SLS-fabricated polycaprolactone (PCL) scaffolds with powdery and smooth surface morphologies on immune-related biological responses. Compared with those on the powdery micromorphology, RAW264.7 macrophages displayed greater dispersion and adopted a spread and elongated morphology on the scaffolds with smooth surface. The expression levels of arginase-1 and CD206 were found to be upregulated in macrophages adhering to the PCL scaffolds with smooth surface, accompanied by an augmented secretion of anti-inflammatory cytokines TGF-β and IL-10. Conversely, there was a decrease in the secretion of pro-inflammatory cytokines TNF-α and IL-12. When implanted in vivo, the SLS-derived scaffolds were completely covered by host tissues, Withing increased collagen deposition, indicating good histocompatibility. At 1-week post-implantation, there was a significantly higher presence of M2-type macrophages surrounding the scaffold compared to M1 macrophages in both groups. By 3 weeks post-implantation, the overall level of macrophages had decreased in both groups. However, a significant higher level of M1 macrophages were observed in the powdery scaffold group. At the same time, the number of neutrophils around the powder scaffold increased significantly, demonstrating long-term local inflammatory responses. The results suggested that post-treated scaffolds with smooth surfaces can effectively reduce local inflammation, making them more suitable for clinical implantation.

The Combination of Bioactive Herbal Compounds with Biomaterials for Regenerative Medicine

Regenerative medicine aims to restore the function of diseased or damaged tissues and organs by cell therapy, gene therapy, and tissue engineering, along with the adjunctive application of bioactive molecules. Traditional bioactive molecules, such as growth factors and cytokines, have shown great potential in the regulation of cellular and tissue behavior, but have the disadvantages of limited source, high cost, short half-life, and side effects. In recent years, herbal compounds extracted from natural plants/herbs have gained increasing attention. This is not only because herbal compounds are easily obtained, inexpensive, mostly safe, and reliable, but also owing to their excellent effects, including anti-inflammatory, antibacterial, antioxidative, proangiogenic behavior and ability to promote stem cell differentiation. Such effects also play important roles in the processes related to tissue regeneration. Furthermore, the moieties of the herbal compounds can form physical or chemical bonds with the scaffolds, which contributes to improved mechanical strength and stability of the scaffolds. Thus, the incorporation of herbal compounds as bioactive molecules in biomaterials is a promising direction for future regenerative medicine applications. Herein, an overview on the use of bioactive herbal compounds combined with different biomaterial scaffolds for regenerative medicine application is presented. We first introduce the classification, structures, and properties of different herbal bioactive components and then provide a comprehensive survey on the use of bioactive herbal compounds to engineer scaffolds for tissue repair/regeneration of skin, cartilage, bone, neural, and heart tissues. Finally, we highlight the challenges and prospects for the future development of herbal scaffolds toward clinical translation. Overall, it is believed that the combination of bioactive herbal compounds with biomaterials could be a promising perspective for the next generation of regenerative medicine. Impact statement This article reviews the combination of bioactive herbal compounds with biomaterials in the promotion of skin, cartilage, bone, neural, and heart regeneration, due to the anti-inflammatory, antibacterial, antioxidative, and proangiogenic effects of the herbal compounds, but also their effects on the improvement of mechanic strength and stability of biomaterial scaffolds. This review provides a promising direction for the next generation of tissue engineering and regenerative medicine.

Clinical management and innovation in fracture non-union

INTRODUCTION

With the introduction and continuous improvement in operative fracture fixation, even the most severe bone fractures can be treated with a high rate of successful healing. However, healing complications can occur and when healing fails over prolonged time, the outcome is termed a fracture non-union. Non-union is generally believed to develop due to inadequate fixation, underlying host-related factors, or infection. Despite the advancements in fracture fixation and infection management, there is still a clear need for earlier diagnosis, improved prediction of healing outcomes and innovation in the treatment of non-union.

AREAS COVERED

This review provides a detailed description of non-union from a clinical perspective, including the state of the art in diagnosis, treatment, and currently available biomaterials and orthobiologics.Subsequently, recent translational development from the biological, mechanical, and infection research fields are presented, including the latest in smart implants, osteoinductive materials, and in silico modeling.

EXPERT OPINION

The first challenge for future innovations is to refine and to identify new clinical factors for the proper definition, diagnosis, and treatment of non-union. However, integration of in vitro, in vivo, and in silico research will enable a comprehensive understanding of non-union causes and correlations, leading to the development of more effective treatments.

Macrophage plasticity: signaling pathways, tissue repair, and regeneration

Macrophages are versatile immune cells with remarkable plasticity, enabling them to adapt to diverse tissue microenvironments and perform various functions. Traditionally categorized into classically activated (M1) and alternatively activated (M2) phenotypes, recent advances have revealed a spectrum of macrophage activation states that extend beyond this dichotomy. The complex interplay of signaling pathways, transcriptional regulators, and epigenetic modifications orchestrates macrophage polarization, allowing them to respond to various stimuli dynamically. Here, we provide a comprehensive overview of the signaling cascades governing macrophage plasticity, focusing on the roles of Toll-like receptors, signal transducer and activator of transcription proteins, nuclear receptors, and microRNAs. We also discuss the emerging concepts of macrophage metabolic reprogramming and trained immunity, contributing to their functional adaptability. Macrophage plasticity plays a pivotal role in tissue repair and regeneration, with macrophages coordinating inflammation, angiogenesis, and matrix remodeling to restore tissue homeostasis. By harnessing the potential of macrophage plasticity, novel therapeutic strategies targeting macrophage polarization could be developed for various diseases, including chronic wounds, fibrotic disorders, and inflammatory conditions. Ultimately, a deeper understanding of the molecular mechanisms underpinning macrophage plasticity will pave the way for innovative regenerative medicine and tissue engineering approaches.

Immune-microenvironment modulatory polyurethane-hyaluronic acid hybrid hydrogel scaffolds for diabetic wound treatment

The healing of wounds in diabetic patients is a huge challenge issue in clinical medicine due to the disordered immune. Recruiting endogenous cells to play a role in the early stage and timely reducing inflammation to promote healing in the middle or late of injuring are both prerequisites for effective treatment. Here, inspired by natural extracellular matrix, three-dimensional porous polyurethane-hyaluronic acid hybrid hydrogel scaffolds (PUHA) were prepared to repair diabetic wound through activate cell immunity by moderate foreign body reaction, provide cell adhesion growth extracellular matrix of hyaluronic acid (HA) and exhibit anti-inflammatory effect of polyurethane (PU). The interaction between PU and HA alters the compact PU hydrogel into macroporous PUHA hydrogel scaffolds with super-swelling, elastic mechanical properties, and controllable degradation, which are suitable for endogenous cells infiltration, growth and immune activation. Additionally, incorporating with RGD, PUHA hydrogel scaffolds with bioactive physicochemical features can evidently reduce the inflammation and modulate the polarization of macrophage apparently both in vitro and in vivo, mainly through downregulation of cytokine-cytokine receptor interaction genes, leading to reprogramming immune-microenvironment and rapid diabetic wound healing. This method of gathering cells initially and intervening immune-microenvironment in time provides an expected way to design biomaterials for chronic wound healing.

Interactions of Cells and Biomaterials for Nerve Tissue Engineering: Polymers and Fabrication

Neural injuries affect millions globally, significantly impacting their quality of life. The inability of these injuries to heal, limited ability to regenerate, and the lack of available treatments make regenerative medicine and tissue engineering a promising field of research for developing methods for nerve repair. This review evaluates the use of natural and synthetic polymers, and the fabrication methods applied that influence a cell's behavior. Methods include cross-linking hydrogels, incorporation of nanoparticles, and 3D printing with and without live cells. The endogenous cells within the injured area and any exogenous cells seeded on the polymer construct play a vital role in regulating healthy neural activity. This review evaluates the body's local and systemic reactions to the implanted materials. Although numerous variables are involved, many of these materials and methods have exhibited the potential to provide a biomaterial environment that promotes biocompatibility and the regeneration of a physical and functional nerve. Future studies may evaluate advanced methods for modifying material properties and characterizing the tissue-biomaterial interface for clinical applications.

Wound healing strategies based on nanoparticles incorporated in hydrogel wound patches

The intricate, tightly controlled mechanism of wound healing that is a vital physiological mechanism is essential to maintaining the skin's natural barrier function. Numerous studies have focused on wound healing as it is a massive burden on the healthcare system. Wound repair is a complicated process with various cell types and microenvironment conditions. In wound healing studies, novel therapeutic approaches have been proposed to deliver an effective treatment. Nanoparticle-based materials are preferred due to their antibacterial activity, biocompatibility, and increased mechanical strength in wound healing. They can be divided into six main groups: metal NPs, ceramic NPs, polymer NPs, self-assembled NPs, composite NPs, and nanoparticle-loaded hydrogels. Each group shows several advantages and disadvantages, and which material will be used depends on the type, depth, and area of the wound. Better wound care/healing techniques are now possible, thanks to the development of wound healing strategies based on these materials, which mimic the extracellular matrix (ECM) microenvironment of the wound. Bearing this in mind, here we reviewed current studies on which NPs have been used in wound healing and how this strategy has become a key biotechnological procedure to treat skin infections and wounds.

Elimination of methicillin-resistant Staphylococcus aureus biofilms on titanium implants via photothermally-triggered nitric oxide and immunotherapy for enhanced osseointegration

BACKGROUND

Treatment of methicillin-resistant Staphylococcus aureus (MRSA) biofilm infections in implant placement surgery is limited by the lack of antimicrobial activity of titanium (Ti) implants. There is a need to explore more effective approaches for the treatment of MRSA biofilm infections.

METHODS

Herein, an interfacial functionalization strategy is proposed by the integration of mesoporous polydopamine nanoparticles (PDA), nitric oxide (NO) release donor sodium nitroprusside (SNP) and osteogenic growth peptide (OGP) onto Ti implants, denoted as Ti-PDA@SNP-OGP. The physical and chemical properties of Ti-PDA@SNP-OGP were assessed by scanning electron microscopy, X-ray photoelectron spectroscope, water contact angle, photothermal property and NO release behavior. The synergistic antibacterial effect and elimination of the MRSA biofilms were evaluated by 2',7'-dichlorofluorescein diacetate probe, 1-N-phenylnaphthylamine assay, adenosine triphosphate intensity, o-nitrophenyl-β-D-galactopyranoside hydrolysis activity, bicinchoninic acid leakage. Fluorescence staining, assays for alkaline phosphatase activity, collagen secretion and extracellular matrix mineralization, quantitative real‑time reverse transcription‑polymerase chain reaction, and enzyme-linked immunosorbent assay (ELISA) were used to evaluate the inflammatory response and osteogenic ability in bone marrow stromal cells (MSCs), RAW264.7 cells and their co-culture system. Giemsa staining, ELISA, micro-CT, hematoxylin and eosin, Masson's trichrome and immunohistochemistry staining were used to evaluate the eradication of MRSA biofilms, inhibition of inflammatory response, and promotion of osseointegration of Ti-PDA@SNP-OGP in vivo.

RESULTS

Ti-PDA@SNP-OGP displayed a synergistic photothermal and NO-dependent antibacterial effect against MRSA following near-infrared light irradiation, and effectively eliminated the formed MRSA biofilms by inducing reactive oxygen species (ROS)-mediated oxidative stress, destroying bacterial membrane integrity and causing leakage of intracellular components (P < 0.01). In vitro experiments revealed that Ti-PDA@SNP-OGP not only facilitated osteogenic differentiation of MSCs, but also promoted the polarization of pro-inflammatory M1 macrophages to the anti-inflammatory M2-phenotype (P < 0.05 or P < 0.01). The favorable osteo-immune microenvironment further facilitated osteogenesis of MSCs and the anti-inflammation of RAW264.7 cells via multiple paracrine signaling pathways (P < 0.01). In vivo evaluation confirmed the aforementioned results and revealed that Ti-PDA@SNP-OGP induced ameliorative osseointegration in an MRSA-infected femoral defect implantation model (P < 0.01).

CONCLUSIONS

These findings suggest that Ti-PDA@SNP-OGP is a promising multi-functional material for the high-efficient treatment of MRSA infections in implant replacement surgeries.

Dually Crosslinked Copper-Poly(tannic acid) Nanoparticles with Microenvironment-Responsiveness for Infected Wound Treatment

Reducing the burden of death due to wound infection is an urgent global public health priority. Metal-phenolic networks (MPNs) have received widespread attention in antimicrobial infections due to their facile synthesis process, excellent biocompatibility, and antimicrobial properties brought about by polyphenols and metal ions. However, typical therapeutic MPNs show rapid release of metal ions due to their poor solution stability, impeding long-acting efficacy in multiple wound healing stages. To address these issues, copper-poly (tannic acid) nanoparticles (Cu-PTA NPs): robust (dually crosslinked), microenvironment-responsive, antibacterial, antioxidative, and anti-inflammatory are prepared, which hierarchically modulate the infected wound healing process. Covalently polymerized via phenol-formaldehyde condensation and crosslinked with bioactive Cu²⁺ , reactive polyphenols are preserved, and Cu²⁺ is efficiently entrapped in the PTA scaffold. The proposed strategy relieves the systemic toxicity, and only high reactive oxygen species (ROS)level as stimuli can "turn on" the catalytic activity of Cu²⁺ to implement antibacterial therapy specifically in an infected wound. Systematic tissue regeneration assessment on the infected full-thickness skin wounds of rats demonstrates enhanced wound healing rate. Cu-PTA NPs enables the direct application in infected wound and exertion of long-acting healing efficacy. This synergetic therapy strategy will pave the way for more complicated infections and inflammatory diseases.

The role of non-steroidal anti-inflammatory drugs as adjuncts to periodontal treatment and in periodontal regeneration

Periodontitis is the sixth most prevalent chronic disease globally and places significant burdens on societies and economies worldwide. Behavioral modification, risk factor control, coupled with cause-related therapy have been the "gold standard" treatment for managing periodontitis. Given that host inflammatory and immunological responses play critical roles in the pathogenesis of periodontitis and impact treatment responses, several adjunctive strategies aimed at modulating host responses and improving the results of periodontal therapy and maintenance have been proposed. Of the many pharmacological host modulators, we focused on non-steroidal anti-inflammatory drugs (NSAIDs), due to their long history and extensive use in relieving inflammation and pain and reducing platelet aggregation. NSAIDs have been routinely indicated for treating rheumatic fever and osteoarthritis and utilized for the prevention of cardiovascular events. Although several efforts have been made to incorporate NSAIDs into the treatment of periodontitis, their effects on periodontal health remain poorly characterized, and concerns over the risk-benefit ratio were also raised. Moreover, there is emerging evidence highlighting the potential of NSAIDs, especially aspirin, for use in periodontal regeneration. This review summarizes and discusses the use of NSAIDs in various aspects of periodontal therapy and regeneration, demonstrating that the benefits of NSAIDs as adjuncts to conventional periodontal therapy remain controversial. More recent evidence suggests a promising role for NSAIDs in periodontal tissue engineering and regeneration.

Immunomodulatory biomaterials on chemokine signaling in wound healing

Normal wound healing occurs through a careful orchestration of cytokine and chemokine signaling in response to injury. Chemokines are a small family of chemotactic cytokines that are secreted by immune cells in response to injury and are primarily responsible for recruiting appropriate immune cell types to injured tissue at the appropriate time. Dysregulation of chemokine signaling is suspected to contribute to delayed wound healing and chronic wounds in diseased states. Various biomaterials are being used in the development of new therapeutics for wound healing and our understanding of their effects on chemokine signaling is limited. It has been shown that modifications to the physiochemical properties of biomaterials can affect the body's immune reaction. Studying these effects on chemokine expression by various tissues and cell type can help us develop novel biomaterial therapies. In this review, we summarize the current research available on both natural and synthetic biomaterials and their effects on chemokine signaling in wound healing. In our investigation, we conclude that our knowledge of chemokines is still limited and that many in fact share both pro-inflammatory and anti-inflammatory properties. The predominance of either a pro-inflammatory or anti-inflammatory profile is mostly likely dependent on timing after injury and exposure to the biomaterial. More research is needed to better understand the interaction and contribution of biomaterials to chemokine activity in wound healing and their immunomodulatory effects.

Assessment of tricalcium phosphate/titanium dioxide (TCP/TiO2) nanocomposite scaffold compared with bone autograft and hydroxyapatite (HA) on the healing of segmental femur bone defect in rabbits

Bone healing is a tissue process after a surgical operation. Many formulated materials have been designed for improving these procedures. The purpose of this study was to evaluate the effectiveness of nanocomposite tricalcium phosphate scaffolds combined with Titanium dioxide scaffold (TCP/TiO2) for femoral defects regeneration in rabbits. We studied 80 mature male New Zealand white rabbits weighing between 3 and 3.5 kg. Rabbits were subdivided into four groups. Anesthesia was performed before surgical operation by 50 mg/kg Ketamine 10% and 5 mg/kg xylazine 5% intramuscularly. We inducted a 6 × 5 mm diameter cylinder defect on the femur. Animals were separated into four trial groups of 20 animals each. After defecting, the experimental groups include control, autograft, hydroxyapatite, and TCP/TiO2 (received pure nanocomposite TCP/TiO2 material). A pathologist evaluated the sections on days 15, 30, 45, and 60 after surgery. The improvement of new and lamellar bone formation was the best in the nanocomposite TCP/TiO2 group at various point times, especially 60 days after surgery. We found that TCP/TiO2 nanocomposite has a significant improving function in the remodeling of bone in the defect areas. Graphical abstract.

Phosphatidylserine liposome multilayers mediate the M1-to-M2 macrophage polarization to enhance bone tissue regeneration

An appropriate immune microenvironment, governed by macrophages, is essential for rapid tissue regeneration after biomaterial implantation. The macrophage phenotypes, M1 (inflammatory) and M2 (anti-inflammatory/healing), exert opposing effects on the repair of various tissues. In this study, a new strategy to promote tissue repair and tissue-to-biomaterial integration by M1-to-M2 macrophage transition using artificial apoptotic cell mimetics (phosphatidylserine liposomes; PSLs) was developed using bone as a model tissue. Titanium was also selected as a model substrate material because it is widely used for dental and orthopedic implants. Titanium implants were functionalized with multilayers via layer-by-layer assembly of cationic protamine and negatively charged PSLs that were chemically stabilized to prevent disruption of lipid bilayers. Samples carrying PSL multilayers could drive M1-type macrophages into M2-biased phenotypes, resulting in a dramatic change in macrophage secretion for tissue regeneration. In a rat femur implantation model, the PSL-multilayer-coated implant displayed augmented de novo bone formation and bone-to-implant integration, associated with an increased M1-to-M2-like phenotypic transition. This triggered the proper generation and activation of bone-forming osteoblasts and bone-resorbing osteoclasts relative to their uncoated counterparts. This study demonstrates the benefit of local M1-to-M2 macrophage polarization induced by PSL-multilayers constructed on implants for potent bone regeneration and bone-to-implant integration. The results of this study may help in the design of new immunomodulatory biomaterials. STATEMENT OF SIGNIFICANCE: Effective strategies for tissue regeneration are essential in the clinical practice. The macrophage phenotypes, M1 (inflammatory) and M2 (anti-inflammatory/healing), exert opposing effects on the repair of various tissues. Artificially produced phosphatidylserine-containing liposomes (PSLs) can induce M2 macrophage polarization by mimicking the inverted plasma membranes of apoptotic cells. This study demonstrates the advantages of local M1-to-M2 macrophage polarization induced by PSL-multilayers constructed on implants for effective bone regeneration and osseointegration (bone-to-implant integration). Mechanistically, M2 macrophages promote osteogenesis but inhibit osteoclastogenesis, and M1 macrophages vice versa. We believe that our study makes a significant contribution to the design of new immunomodulatory biomaterials for regenerative medicine because it is the first to validate the benefit of PSLs for tissue regeneration.

The role of the immune microenvironment in bone, cartilage, and soft tissue regeneration: from mechanism to therapeutic opportunity

Bone, cartilage, and soft tissue regeneration is a complex spatiotemporal process recruiting a variety of cell types, whose activity and interplay must be precisely mediated for effective healing post-injury. Although extensive strides have been made in the understanding of the immune microenvironment processes governing bone, cartilage, and soft tissue regeneration, effective clinical translation of these mechanisms remains a challenge. Regulation of the immune microenvironment is increasingly becoming a favorable target for bone, cartilage, and soft tissue regeneration; therefore, an in-depth understanding of the communication between immune cells and functional tissue cells would be valuable. Herein, we review the regulatory role of the immune microenvironment in the promotion and maintenance of stem cell states in the context of bone, cartilage, and soft tissue repair and regeneration. We discuss the roles of various immune cell subsets in bone, cartilage, and soft tissue repair and regeneration processes and introduce novel strategies, for example, biomaterial-targeting of immune cell activity, aimed at regulating healing. Understanding the mechanisms of the crosstalk between the immune microenvironment and regeneration pathways may shed light on new therapeutic opportunities for enhancing bone, cartilage, and soft tissue regeneration through regulation of the immune microenvironment.

Inflammation-mediated matrix remodeling of extracellular matrix-mimicking biomaterials in tissue engineering and regenerative medicine

Extracellular matrix (ECM)-mimicking biomaterials are considered effective tissue-engineered scaffolds for regenerative medicine because of their biocompatibility, biodegradability, and bioactivity. ECM-mimicking biomaterials preserve natural microstructures and matrix-related bioactive components and undergo continuous matrix remodeling upon transplantation. The interaction between host immune cells and transplanted ECM-mimicking biomaterials has attracted considerable attention in recent years. Transplantation of biomaterials may initiate injuries and early pro-inflammation reactions characterized by infiltration of neutrophils and M1 macrophages. Pro-inflammation reactions may lead to degradation of the transplanted biomaterial and drive the matrix into a fetal-like state. ECM degradation leads to the release of matrix-related bioactive components that act as signals for cell migration, proliferation, and differentiation. In late stages, pro-inflammatory cells fade away, and anti-inflammatory cells emerge, which involves macrophage polarization to the M2 phenotype and leukocyte activation to T helper 2 (Th2) cells. These anti-inflammatory cells interact with each other to facilitate matrix deposition and tissue reconstruction. Deposited ECM molecules serve as vital components of the mature tissue and influence tissue homeostasis. However, dysregulation of matrix remodeling results in several pathological conditions, such as aggressive inflammation, difficult healing, and non-functional fibrosis. In this review, we summarize the characteristics of inflammatory responses in matrix remodeling after transplantation of ECM-mimicking biomaterials. Additionally, we discuss the intrinsic linkages between matrix remodeling and tissue regeneration. STATEMENT OF SIGNIFICANCE: Extracellular matrix (ECM)-mimicking biomaterials are effectively used as scaffolds in tissue engineering and regenerative medicine. However, dysregulation of matrix remodeling can cause various pathological conditions. Here, the review describes the characteristics of inflammatory responses in matrix remodeling after transplantation of ECM-mimicking biomaterials. Additionally, we discuss the intrinsic linkages between matrix remodeling and tissue regeneration. We believe that understanding host immune responses to matrix remodeling of transplanted biomaterials is important for directing effective tissue regeneration of ECM-mimicking biomaterials. Considering the close relationship between immune response and matrix remodeling results, we highlight the need for studies of the effects of clinical characteristics on matrix remodeling of transplanted biomaterials.

Multi-functional wound dressings based on silicate bioactive materials

Most traditional wound dressings passively offer a protective barrier for the wounds, which lacks the initiative in stimulating tissue regeneration. In addition, cutaneous wound healing is usually accompanied by various complicated conditions, including bacterial infection, skin cancer, and damaged skin appendages, bringing further challenges for wound management in clinic. Therefore, an ideal wound dressing should not only actively stimulate wound healing but also hold multi-functions for solving problems associated with different specific wound conditions. Recent studies have demonstrated that silicate bioceramics and bioglasses are one type of promising materials for the development of wound dressings, as they can actively accelerate wound healing by regulating endothelial cells, dermal fibroblasts, macrophages, and epidermal cells. In particular, silicate-based biomaterials can be further functionalized by specific structural design or doping with functional components, which endow materials with enhanced bioactivities or expanded physicochemical properties such as photothermal, photodynamic, chemodynamic, or imaging properties. The functionalized materials can be used to address wound healing with different demands including but not limited to antibacterial, anticancer, skin appendages regeneration, and wound monitoring. In this review, we summarized the current research on the development of silicate-based multi-functional wound dressings and prospected the development of advanced wound dressings in the future.

Immunoengineering strategies to enhance vascularization and tissue regeneration

Immune cells have emerged as powerful regulators of regenerative as well as pathological processes. The vast majority of regenerative immunoengineering efforts have focused on macrophages; however, growing evidence suggests that other cells of both the innate and adaptive immune system are as important for successful revascularization and tissue repair. Moreover, spatiotemporal regulation of immune cells and their signaling have a significant impact on the regeneration speed and the extent of functional recovery. In this review, we summarize the contribution of different types of immune cells to the healing process and discuss ways to manipulate and control immune cells in favor of vascularization and tissue regeneration. In addition to cell delivery and cell-free therapies using extracellular vesicles, we discuss in situ strategies and engineering approaches to attract specific types of immune cells and modulate their phenotypes. This field is making advances to uncover the extraordinary potential of immune cells and their secretome in the regulation of vascularization and tissue remodeling. Understanding the principles of immunoregulation will help us design advanced immunoengineering platforms to harness their power for tissue regeneration.

Embedding MSCs in Si-HPMC hydrogel decreased MSC-directed host immune response and increased the regenerative potential of macrophages

Embedding mesenchymal stromal cells (MSCs) in biomaterial is a subject of increasing interest in the field of Regenerative Medicine. Speeding up the clinical use of MSCs is dependent on the use of non-syngeneic models in accordance with Good Manufacturing Practices (GMP) requirements and on costs. To this end, in this study, we analyzed the in vivo host immune response following local injection of silanized hydroxypropyl methylcellulose (Si-HPMC)-embedded human MSCs in a rat model developing colorectal damage induced by ionizing radiation. Plasma and lymphocytes from mesenteric lymph nodes were harvested in addition to colonic tissue. We set up tests, using flow cytometry and a live imaging system, to highlight the response to specific antibodies and measure the cytotoxicity of lymphocytes against injected MSCs. We demonstrated that Si-HPMC protects MSCs from specific antibodies production and from apoptosis by lymphocytes. We also observed that Si-HPMC does not modify innate immune response infiltrate in vivo, and that in vitro co-culture of Si-HPMC-embedded MSCs impacts macrophage inflammatory response depending on the microenvironment but, more importantly, increases the macrophage regenerative response through Wnt-family and VEGF gene expression. This study furthers our understanding of the mechanisms involved, with a view to improving the therapeutic benefits of biomaterial-assisted cell therapy by modulating the host immune response. The decrease in specific immune response against injected MSCs protected by Si-HPMC also opens up new possibilities for allogeneic clinical use.

Polyarginine as a simultaneous antimicrobial, immunomodulatory and miRNA delivery agent within polyanionic hydrogels

Implantation of biomedical devices is followed by immune response to the implant, as well as occasionally bacterial, yeast and/or fungal infections. In this context, new implant materials and coatings that deal with medical device-associated complications are required. Antibacterial and anti-inflammatory materials are also required for wound healing applications, especially in diabetic patients with chronic wounds. In this work, we present hyaluronic acid (HA) hydrogels with triple activity: antimicrobial, immunomodulatory and miRNA delivery agent. We demonstrate that polyarginine with a degree of polymerization of 30 (PAR30), which was previously shown to have a prolonged antibacterial activity, decreases inflammatory response of LPS-stimulated macrophages. In addition, PAR30 accelerated fibroblast migration in macrophage/fibroblast co-culture system, suggesting a positive effect on wound healing. Furthermore, PAR30 allowed to load miRNA into HA hydrogels, and then to deliver them into the cells. To our knowledge, this study is the first describing miRNA-loaded hydrogels with antibacterial effect and anti-inflammatory features. Such system can become a tool for the treatment of infected wounds, e.g. diabetic ulcers, as well as for foreign body response modulation. This article is protected by copyright. All rights reserved.

Effect of naturally derived surgical hemostatic materials on the proliferation of A549 human lung adenocarcinoma cells

Hemostatic materials are generally applied in surgical operations for cancer, but their effects on the growth and recurrence of tumors are unclear. Herein, three commonly used naturally derived hemostatic materials, gelatin sponge, Surgicel (oxidized regenerated cellulose), and biopaper (mixture of sodium hyaluronate and carboxymethyl chitosan), were cocultured with A549 human lung adenocarcinoma cells in vitro. Furthermore, the performance of hemostatic materials and the tumorigenicity of the materials with A549 ​cells were observed after subcutaneous implantation into BALB/c mice. The in vitro results showed that biopaper was dissolved quickly, with the highest cell numbers at 2 and 4 days of culture. Gelatin sponges retained their structure and elicited the least cell infiltration during the 2- to 10-day culture. Surgicel partially dissolved and supported cell growth over time. The in vivo results showed that biopaper degraded rapidly and elicited an acute Th1 lymphocyte reaction at 3 days after implantation, which was decreased at 7 days after implantation. The gelatin sponge resisted degradation and evoked a hybrid M1/M2 macrophage reaction at 7–21 days after implantation, and a protumor M2d subset was confirmed. Surgicel resisted early degradation and caused obvious antitumor M2a macrophage reactions. Mice subjected to subcutaneous implantation of A549 ​cells and hemostatic materials in the gelatin sponge group had the largest tumor volumes and the shortest overall survival (OS), while the Surgicel and the biopaper group had the smallest volumes and the longest OS. Therefore, although gelatin sponges exhibited cytotoxicity to A549 ​cells in vitro, they promoted the growth of A549 ​cells in vivo, which was related to chronic M2d macrophage reaction. Surgicel and biopaper inhibited A549 ​cell growth in vivo, which is associated with chronic M2a macrophage reaction or acute Th1 lymphocyte reaction.

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The gelatin sponge, Surgicel and biopaper had different effects on A549 ​cell growth and proliferation.

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Biopaper degraded rapidly in vivo and elicited an antitumor Th1 lymphocyte reaction at acute inflammatory phase.

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The gelatin sponge resisted degradation and evoked a protumor M2d macrophage reactions.

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Surgicel resisted early degradation and caused obvious antitumor M2a macrophage reactions.

The characterization, cytotoxicity, macrophage response and tissue regeneration of decellularized cartilage in costal cartilage defects

After harvesting multiple costal cartilages, the local defect disrupts the integrity of the chest wall and may lead to obvious thoracic complications, such as local depression and asymmetry of the bilateral thoracic height. Decellularized materials have been used for tissue reconstruction in clinical surgeries. To apply xenogenic decellularized cartilage in costal cartilage defects, porcine-derived auricular and costal cartilage was tested for characterization, cytotoxicity, macrophage response, and tissue regeneration. Most of the DNA and α-Gal were effectively removed, and the collagen was well preserved after the decellularization process. The glycosaminoglycan (GAG) content decreased significantly compared to that in untreated cartilage. The decellularized auricular cartilage had a larger pore size, more pores, and a higher degradation rate than the decellularized costal cartilage. No apparent nuclei or structural damage was observed in the extracellular matrix. The decellularized auricular cartilage had a higher cell proliferation rate and more prominent immunomodulatory effect than the other groups. Two types of decellularized cartilage, particularly decellularized auricular cartilage, promoted the tissue regeneration in the cartilage defect area, combined with noticeable cartilage morphology and increased chondrogenic gene expression. In our research, the functional components and structure of the extracellular matrix were well preserved after the decellularization process. The decellularized cartilage had better biocompatibility and suitable microenvironment for tissue regeneration in the defect area, suggesting its potential application in cartilage repair during the surgery. STATEMENT OF SIGNIFICANCE: Autologous costal cartilage has been widely used in various surgeries, while the cartilage defects after the harvesting of multiple costal cartilages may cause localized chest wall deformities. Decellularized cartilage is an ideal material that could be produced in the factory and applied in surgeries. In this study, both decellularized costal cartilage and auricular cartilage preserved original structure, functional biocompatibility, immunosuppressive effects, and promoted tissue regeneration in the cartilage defect area.

Nanoparticles to Target and Treat Macrophages: The Ockham's Concept?

Nanoparticles are nanomaterials with three external nanoscale dimensions and an average size ranging from 1 to 1000 nm. Nanoparticles have gained notoriety in technological advances due to their tunable physical, chemical, and biological characteristics. However, the administration of functionalized nanoparticles to living beings is still challenging due to the rapid detection and blood and tissue clearance by the mononuclear phagocytic system. The major exponent of this system is the macrophage. Regardless the nanomaterial composition, macrophages can detect and incorporate foreign bodies by phagocytosis. Therefore, the simplest explanation is that any injected nanoparticle will be probably taken up by macrophages. This explains, in part, the natural accumulation of most nanoparticles in the spleen, lymph nodes, and liver (the main organs of the mononuclear phagocytic system). For this reason, recent investigations are devoted to design nanoparticles for specific macrophage targeting in diseased tissues. The aim of this review is to describe current strategies for the design of nanoparticles to target macrophages and to modulate their immunological function involved in different diseases with special emphasis on chronic inflammation, tissue regeneration, and cancer.