Developing a pro-regenerative biomaterial scaffold microenvironment requires T helper 2 cells

Distinct impacts of aging on the immune responses to extracellular matrix-based versus synthetic biomaterials

All implanted materials inevitably trigger an acute inflammatory response. The long-term outcome, however, is dependent on the trajectory of this response. This study investigates the effects of aging on the immune response to two commercially available biomaterials. Extracellular matrix-based urinary bladder matrix (UBM) and synthetic polypropylene mesh (PPM) were implanted in young (4 months) and aged (18 months) C57BL/6J mice. Overall, PPM led to a sustained inflammatory response regardless of the age of the mice. In contrast, UBM induced an initial inflammatory response that matured into a pro-regenerative/remodeling response with time, though aged mice exhibited a delayed resolution of inflammation. The PPM-induced response was predominantly pro-inflammatory with consistently higher M1-like macrophage phenotype, whereas the response to UBM was characterized by an anti-inflammatory M2-like phenotype, especially in young mice. RNA sequencing revealed marked age-related differences in gene transcription. At day 7 post-implantation, the young mice with UBM showed a robust upregulation of both pro- and anti-inflammatory pathways as compared to young mice implanted with PPM, however, by day 14, the gene expression profile transitioned into an anti-inflammatory profile. Intriguingly, in aged mice, the response to UBM was distinct with consistent downregulation of inflammatory genes compared to PPM, while the response to PPM in both young and aged animals was largely consistent. Upstream analysis identified cytokines as key drivers of the host response, with IL-4 and IL-13 in young mice, and TNF-α and IL-1β driving chronic inflammation in aged mice. These findings highlight the importance of host age in biomaterial outcome, and the potential of ECM-based materials to mount a favorable response even in the presence of age-related immune dysregulation.

The paradigm shifts of periodontal regeneration strategy: From reparative manipulation to developmental engineering

Ideal periodontal regeneration requires the integration of alveolar bone, periodontal ligament, and cementum, along with Sharpey's fibers for occlusal force resistance. However, physiological regeneration remains rare due to its intricate structure, making clinical regeneration a challenge. Periodontal ligament stem cells (PDLSCs), first isolated in 2004, hold the key to multi-directional differentiation into cementoblasts, fibroblasts, and osteoblasts. While traditional therapies like guided tissue regeneration (GTR) aim to activate PDLSCs, clinical outcomes are inconsistent, suggesting the need for additional strategies to enhance PDLSCs' functions. Advancements in molecular biotechnology have introduced the use of recombinant growth factors for tissue regeneration. However, maintaining their efficacy requires high doses, posing cost and safety issues. Multi-layered scaffolds combined with cell sheet technology offer new insights, but face production, ethical, and survival challenges. Immune regulation plays a crucial role in PDLSC-mediated regeneration. The concept of "coagulo-immunomodulation" has emerged, emphasizing the coupling of blood coagulation and immune responses for periodontal regeneration. Despite its potential, the clinical translation of immune-based strategies remains elusive. The "developmental engineering" approach, which mimics developmental events using embryonic-stage cells and microenvironments, shows promise. Our research group has made initial strides, indicating its potential as a viable solution for periodontal complex regeneration. However, further clinical trials and considerations are needed for successful clinical application. This review aims to summarize the strategic transitions in the development of periodontal regenerative materials and to propose prospective avenues for future development.

Micropore structure engineering of injectable granular hydrogels via controlled liquid-liquid phase separation facilitates regenerative wound healing in mice and pigs

Biomaterials can play a crucial role in facilitating tissue regeneration, but their application is often limited by that they induce scarring rather than complete tissue restoration. Hydrogels with microporous architectures, engineered via 3D printing techniques or particle packing (granular hydrogels), have shown promise in providing a conducive microenvironment for cellular infiltration and favorable immune response. Nonetheless, there is a notably lacking in studies that demonstrate scarless regeneration solely through pore structure engineering. In this study, we demonstrate that optimizing micropore structure of injectable granular hydrogels via controlled liquid-liquid phase separation facilitates scarless wound healing. The building block particles are fabricated by precisely controlling the separation kinetics of two immiscible aqueous phases (gelling and porogenic) and timely arresting phase separation, to generate bicontinuous, hollow or closed porous structure. Employing a murine model, we reveal that the optimized pore structure significantly facilitates mature vascular network boosts pro-regenerative macrophage polarization (M2/M1) and CD4+/Foxp3+ regulatory T cells, culminating in scarless skin regeneration enriched with hair follicles. Moreover, our hydrogels outperform the clinical gold-standard collagen/proteoglycan scaffolds in a porcine model, showcasing superior cell infiltration, epidermal integration, and dermal regeneration. Micropore structure engineering of biomaterials presents a promising and biologics free pathway for tissue regeneration.

Crosstalk between T cells and fibroblasts in biomaterial-mediated fibrosis

Biomaterial implants are a critical aspect of our medical therapies and biomedical research and come in various forms: stents, implantable glucose sensors, orthopedic implants, silicone implants, drug delivery systems, and tissue engineered scaffolds. Their implantation triggers a series of biological responses that often times lead to the foreign body response and subsequent fibrotic encapsulation, a dense ECM-rich capsule that isolates the biomaterial and renders it ineffective. These responses lead to the failure of biomaterials and is a major hurdle to overcome and in promoting their success. Much attention has been given to macrophage populations for the inflammatory component of these responses to biomaterials but recent work has identified an important role of T cells and their ability to modulate fibroblast activity and vice versa. In this review, we focus on T cell-fibroblast crosstalk by exploring T cell subsets, critical signaling pathways, and fibroblast populations that have been shown to dictate biomaterial-mediated fibrosis. We then highlight emerging technologies and model systems that enable new insights and avenues to T cell-fibroblast crosstalk that will improve biomaterial outcomes.

Murine gut microbiota dysbiosis via enteric infection modulates the foreign body response to a distal biomaterial implant

The gut microbiota influences systemic immunity and the function of distal tissues, including the brain, liver, skin, lung, and muscle. However, the role of the gut microbiota in the foreign body response and fibrosis is largely unexplored. To investigate this connection, we perturbed the homeostasis of the murine gut microbiota via infection with the pathogenic bacterial species enterotoxigenic Bacteroides fragilis (ETBF) and implanted particulate material (mean particle size <600 μm) of the synthetic polymer polycaprolactone (PCL) into a distal muscle injury. ETBF infection in mice led to increased neutrophil and γδ T cell infiltration into the PCL implant site. ETBF infection alone promoted systemic inflammation, increased levels of neutrophils in lymphoid tissues, and altered skeletal muscle gene expression. At the PCL implant site, we found significant changes in the transcriptome of sorted stromal cells between infected and control mice, including differences related to ECM components such as proteoglycans and glycosaminoglycans. However, we did not observe ETBF-induced differences in fibrosis levels. These results demonstrate the ability of the gut microbiota to mediate long-distance effects such as immune and stromal responses to a distal biomaterial implant.

Functionalization of viscoelastic gels with decellularized extracellular matrix microparticles enhances tissue adhesion, cell spreading, and tissue regeneration

The natural extracellular matrix (ECM) is viscoelastic and fibrous, which are crucial characteristics for controlling cellular responses. In contrast, synthetic gels are mostly elastic and less effective at promoting mechanotransduction. Thus, the design of gels that provide mechanical and biochemical cues for tissue regeneration needs to be explored. In this study, we aimed to develop viscoelastic gels functionalized with decellularized ECM (dECM) microparticles for tissue regeneration. The incorporation of dECM microparticles into gels improved not only the tissue adhesive properties of the gels but also their viscoelasticity. The modulation of the mechanical properties of the gels elicited cell adhesion and spreading. Moreover, the functionalization of viscoelastic gels with dECM microparticles promoted tissue regeneration in volumetric muscle-loss models. This approach would be a powerful method because functional scaffolds with sufficient mechanical and biological properties facilitate tissue regeneration.

Immunomodulatory multifunctional janus collagen-based membrane for advanced bone regeneration

Guided bone regeneration (GBR) is a standard therapy for treating bone defects, with collagen-based barrier membranes widely used clinically. However, these membranes face challenges like poor mechanical properties, early bacterial invasion and immunomodulation deficiency, potentially risking GBR failure. Orchestrating macrophage activation and controlling their M1 or M2 polarization are effective strategies for bone repair. Here, we present a Janus collagen-based barrier membrane with immunomodulation. The porous layer promotes direct osteogenic differentiation and inward growth of osteoblasts. The dense layer prevents invasion of soft tissue into bone defects and protects bone defects from bacterial infection. The membrane also enhances rat bone marrow-derived mesenchymal stem cell infiltration, proliferation, and osteogenic differentiation by regulating the immune microenvironment, demonstrating superior bone regeneration compared to the commercial Bio-Gide® membrane. Overall, the Janus collagen-based membrane reduces tissue inflammation and fosters an osteoimmune environment conducive to new bone formation, offering effective material design for advanced GBR technology.

Cell-Instructive Biomaterials with Native-Like Biochemical Complexity

Biochemical signals in native tissue microenvironments instruct cell behavior during many biological processes ranging from developmental morphogenesis and tissue regeneration to tumor metastasis and disease progression. The detection and characterization of these signals using spatial and highly resolved quantitative methods have revealed their existence as matricellular proteins in the matrisome, some of which are bound to the extracellular matrix while others are freely diffusing. Including these biochemical signals in engineered biomaterials can impart enhanced functionality and native-like complexity, ultimately benefiting efforts to understand, model, and treat various diseases. In this review, we discuss advances in characterizing, mimicking, and harnessing biochemical signals in developing advanced engineered biomaterials. An overview of the diverse forms in which these biochemical signals exist and their effects on intracellular signal transduction is also provided. Finally, we highlight the application of biochemically complex biomaterials in the three broadly defined areas of tissue regeneration, immunoengineering, and organoid morphogenesis.

Modulating biomechanical and integrating biochemical cues to foster adaptive remodeling of tissue engineered matrices for cardiovascular implants

Cardiovascular disease remains one of the leading causes of mortality in the Western world. Congenital heart disease affects nearly 1 % of newborns, with approximately one-fourth requiring reconstructive surgery during their lifetime. Current cardiovascular replacement options have significant limitations. Their inability to grow poses particular challenges for pediatric patients. Tissue Engineered Matrix (TEM)-based in situ constructs, with their self-repair and growth potential, offer a promising solution to overcome the limitations of current clinically used replacement options. Various functionalization strategies, involving the integration of biomechanical or biochemical components to enhance biocompatibility, have been developed for Tissue Engineered Vascular Grafts (TEVG) and Tissue Engineered Heart Valves (TEHV) to foster their capacity for in vivo remodeling. In this review, we present the current state of clinical translation for TEVG and TEHV, and provide a comprehensive overview of biomechanical and biochemical functionalization strategies for TEVG and TEHV. We discuss the rationale for functionalization, the implementation of functionalization cues in TEM-based TEVG and TEHV, and the interrelatedness of biomechanical and biochemical cues in the in vivo response. Finally, we address the challenges associated with functionalization and discuss how interdisciplinary research, especially when combined with in silico models, could enhance the translation of these strategies into clinical applications. STATEMENT OF SIGNIFICANCE: Cardiovascular disease remains one of the leading causes of mortality, with current replacements being unable to grow and regenerate. In this review, we present the current state of clinical translation for tissue engineered vascular grafts (TEVG) and heart valves (TEHV). Particularly, we discuss the rationale and implementation for functionalization cues in tissue engineered matrix-based TEVGs and TEHVs, and for the first time we introduce the interrelatedness of biomechanical and biochemical cues in the in-vivo response. These insights pave the way for next-generation cardiovascular implants that promise better durability, biocompatibility, and growth potential. Finally, we address the challenges associated with functionalization and discuss how interdisciplinary research, especially when combined with in silico models, could enhance the translation of these strategies into clinical applications .

Bioengineered Constructs as a Tissue Engineering-Based Therapy for Volumetric Muscle Loss

Severe skeletal muscle injuries involving substantial tissue loss can significantly impair muscle strength and functionality, reducing the quality of life for affected individuals. Such injuries, termed volumetric muscle loss, require extensive clinical intervention, as the body's innate healing mechanisms are insufficient to regenerate functional muscle. The current standard of care primarily involves autologous muscle tissue transfer, with some consideration of acellular synthetic constructs. However, both approaches have limited therapeutic efficacy, presenting challenges such as donor-site morbidity, infection risks, and suboptimal functional recovery. Over the past decade, skeletal muscle tissue engineering (SMTE) has emerged as a promising strategy for regenerating functional muscle through bioengineered constructs. Advanced biofabrication techniques, including bioprinting, have further enabled the development of synthetic constructs that closely mimic native muscle architecture. Given these advancements, a critical review of recent therapeutic strategies, their achievements, and limitations is necessary. This review examines the spectrum of bioengineered constructs developed from various biomaterials and evaluates their therapeutic potential. Special emphasis is placed on 3D bioprinting strategies and their role in creating physiologically relevant constructs for functional muscle restoration. In addition, the integration of machine learning in optimizing construct design, predicting cellular behavior, and enhancing tissue integration is discussed. The review indicates that despite significant progress in SMTE, key challenges remain, including replicating the complex structural organization of muscle tissue, minimizing fibrosis, and achieving vascularization and innervation to regenerate functional, strengthened muscle. Future research should address these barriers while prioritizing the development of translational, clinically relevant regenerative constructs. In addition, efforts should focus on advancing scalable, construct-based regenerative treatments that are readily available at the point of care and easily managed in surgical settings.

Bioelectronics hydrogels for implantable cardiac and brain disease medical treatment application

Hydrogel-based bioelectronic systems offer significant benefits for point-of-care diagnosis, treatment of cardiac and cerebral disease, surgical procedures, and other medical applications, ushering in a new era of advancements in medical technology. Progress in hydrogel-based bioelectronics has advanced from basic instrument and sensing capabilities to sophisticated multimodal perceptions and feedback systems. Addressing challenges related to immune responses and inflammation regulation after implantation, physiological dynamic mechanism, biological toxicology as well as device size, power consumption, stability, and signal conversion is crucial for the practical implementation of hydrogel-based bioelectronics in medical implants. Therefore, further exploration of hydrogel-based bioelectronics is imperative, and a comprehensive review is necessary to steer the development of these technologies for use in implantable therapies for cardiac and brain/neural conditions. In this review, a concise overview is provided on the fundamental principles underlying ionic electronic and ionic bioelectronic mechanisms. Additionally, a comprehensive examination is conducted on various bioelectronic materials integrated within hydrogels for applications in implantable medical treatments. The analysis encompasses a detailed discussion on the representative structures and physical attributes of hydrogels. This includes an exploration of their intrinsic properties such as mechanical strength, dynamic capabilities, shape-memory features, stability, stretchability, and water retention characteristics. Moreover, the discussion extends to properties related to interactions with tissues or the environment, such as adhesiveness, responsiveness, and degradability. The intricate relationships between the structure and properties of hydrogels are thoroughly examined, along with an elucidation of how these properties influence their applications in implantable medical treatments. The review also delves into the processing techniques and characterization methods employed for hydrogels. Furthermore, recent breakthroughs in the applications of hydrogels are logically explored, covering aspects such as materials, structure, properties, functions, fabrication procedures, and hybridization with other materials. Finally, the review concludes by outlining the future prospects and challenges associated with hydrogels-based bioelectronics systems.

Modulating Neutrophil Extracellular Trap Formation In Vivo with Locoregional Precision Using Differently Charged Self-Assembled Hydrogels

Neutrophil extracellular traps (NETs) are DNA networks released by neutrophils, first described as a defense response against pathogens but have since been associated with numerous inflammatory diseases. Diverse physical material properties have been shown to promote NET formation. Herein, we report the discovery that the charge of self-assembled peptide hydrogels predictably modulates the formation of NETs in vivo within the implanted material. Positively charged gels induce rapid NET release, whereas negatively charged gels do not. This differential immune response to our self-assembled peptide gels enabled the development of a material platform that allows rheostat-like modulation over the degree of NET formation with anatomical and locoregional control.

Endotoxin, not DNA, determines the host response and tissue regeneration behavior of acellular biologic scaffolds

Established quantitative standards for assessing decellularization of biologic scaffolds based on residual DNA levels have been well-documented and widely acknowledged. However, post-implantation complications, such as fever and seroma, are commonly observed which negatively impact clinical outcomes. The presence of cellular debris following decellularization or using source tissues that are naturally high in endotoxin may contribute to the host response to a biologic scaffold. In the study, several multi-step decellularization methods were used to decellularize small intestinal submucosa (SIS) to obtain materials with three distinct levels of residual DNA, lipid residues, and endogenous endotoxin. The potential influence of these residual components on macrophage and lymphocyte polarization in vitro, as well as on the host inflammatory response in vivo post intra-abdominal implantation or abdominal wall defect repair in rats, was assessed. Urinary bladder matrix (UBM) meeting established decellularization criteria and naturally devoid of endotoxin was utilized as a control. The presence of endogenous endotoxin in SIS-ECM resulted in notable changes in macrophage phenotype. SIS-ECM samples with endotoxin levels below FDA limits still upregulated pro-inflammatory factors in vitro. Conversely, SIS with minimal endotoxin content and UBM controls prompted a shift towards a pro-remodeling M2 phenotype, fostering constructive tissue remodeling in a rodent model of abdominal wall defects, irrespective of DNA content. These findings suggest that endotoxin may be a crucial factor influencing biologic scaffolds that are not fully accounted by current decellularization standards. STATEMENT OF SIGNIFICANCE: Clinically utilized decellularized biologic scaffolds that meet the established quantitative standards still suffer problems in high incidence of inflammatory complications, including fever and seroma. In this study, we confirmed that endotoxin, rather than residual DNA, is the crucial factor influencing host responses and regenerative outcomes. Tissue sources and decellularization processes are critical for reducing endotoxin levels and attenuating immuno-inflammatory complications. These findings enhance the evaluation of ECM scaffold performance for clinical application, thereby facilitating improved preparation and utilization for tissue defect repairs.

Guidance for evaluating biomaterials' properties and biological potential for dental pulp tissue engineering and regeneration research

BACKGROUND

Dental pulp regeneration is a complex and advancing field that requires biomaterials capable of supporting the pulp's diverse functions, including immune defense, sensory perception, vascularization, and reparative dentinogenesis. Regeneration involves orchestrating the formation of soft connective tissues, neurons, blood vessels, and mineralized structures, necessitating materials with tailored biological and mechanical properties. Numerous biomaterials have entered clinical practice, while others are being developed for tissue engineering applications. The composition and a broad range of material properties, such as surface characteristics, degradation rate, and mechanical strength, significantly influence cellular behavior and tissue outcomes. This underscores the importance of employing robust evaluation methods and ensuring precise and comprehensive reporting of findings to advance research and clinical translation.

AIMS

This article aims to present the biological foundations of dental pulp tissue engineering alongside potential testing methodologies and their advantages and limitations. It provides guidance for developing research protocols to evaluate the properties of biomaterials and their influences on cell and tissue behavior, supporting progress toward effective dental pulp regeneration strategies.

Nanocapsuled Neutrophil Extracellular Trap Scavenger Combating Chronic Infectious Bone Destruction Diseases

Chronic infectious bone destruction diseases, such as periodontitis, pose a significant global health challenge. Repairing the bone loss caused by these chronic infections remains challenging. In addition to pathogen removal, regulating host immunity is imperative. The retention of neutrophil extracellular traps (NETs) in chronic infectious niches is found to be a barrier to inflammation resolution. However, whether ruining the existing NETs within the local infectious bone lesions can contribute to inflammation resolve and bone repair remains understudied. Herein, a nanocapsuled delivery system that scavenges NETs dual-responsively to near-infrared light as a switch and to NETs themselves as a microenvironment sensor is designed. Besides, the photothermal and photodynamic effects endow the nanocapsules with antibacterial properties. Together with the ability to clear NETs, these features facilitate the restoration of the normal host response. The immunocorrective properties and inherent pro-osteogenic effects finally promote local bone repair. Together, the NET scavenging nanocapsules address the challenge of impaired bone repair in chronic infections due to biased host response caused by excessive NETs. This study provides new concepts and strategies for repairing bone destruction attributable to chronic infections via correcting biased host responses in chronic infectious diseases.

Biomaterial-Based Regenerative Strategies for Volumetric Muscle Loss: Challenges and Solutions

Significance: Volumetric muscle loss (VML) is caused by the loss of significant amounts of skeletal muscle tissue. VML cannot be repaired by intrinsic regenerative processes, resulting in permanent loss of muscle function and disability. Current rehabilitative-focused treatment strategies lack efficacy and do not restore muscle function, indicating the need for the development of effective regenerative strategies. Recent Advances: Recent developments implicate biomaterial-based approaches for promoting muscle repair and functional restoration post-VML. Specifically, bioscaffolds transplanted in the injury site have been utilized to mimic endogenous cues of the ablated tissue to promote myogenic pathways, increase neo-myofiber synthesis, and ultimately restore contractile function to the injured unit. Critical Issues: Despite the development and preclinical testing of various biomaterial-based regenerative strategies, effective therapies for patients are not available. The unique challenges posed for biomaterial-based treatments of VML injuries, including its scalability and clinical applicability beyond small-animal models, impede progress. Furthermore, production of tissue-engineered constructs is technically demanding, with reproducibility issues at scale and complexities in achieving vascularization and innervation of large constructs. Future Directions: Biomaterial-based regenerative strategies designed to comprehensively address the pathophysiology of VML are needed. Considerations for clinical translation, including scalability and regulatory compliance, should also be considered when developing such strategies. In addition, an integrated approach that combines regenerative and rehabilitative strategies is essential for ensuring functional improvement.

A Sr@Ag-based spatiotemporal and step-release scaffold against chronic osteomyelitis, fabricated by coaxial 3D-printing

Chronic osteomyelitis (OM) represents a severe and persistent infectious bone disease. Effective treatment requires controlled anti-inflammatory releases and bone regeneration across disease phases. A Sr@Ag-based scaffold was successfully printed, featuring micron-scale coaxial fibers containing Ag-doped hydroxyapatite (HA) in the outer layer of PLLA and Sr-doped HA in the inner layer of PLLA, facilitating the spatiotemporal and sequential release of Ag and Sr ions during OM treatment. Most antibacterial agent (Ag) was released during the first 20 days, followed by a slow-release plateau over the next 40 days in phosphate-buffered saline solution (PBS). Meanwhile, the pro-angiogenic agent (Sr) was released in minimal amounts during the initial 20 days, followed by a rapid and considerable release in the following 40 days. The coaxial design effectively inhibited the growth of Staphylococcus aureus and Escherichia coli while preserving the viability of bone cells. The ion-based scaffold exhibited broad-spectrum antibacterial effects and enhanced bone-regenerating gene expression in a complex air-bacteria environment. The Sr@Ag-based coaxial scaffold demonstrated effective antibacterial activity during the early stage and exhibited excellent non-toxic bone regeneration results during the middle and late stages in vivo. This work offered a promising treatment strategy through sequential anti-inflammatory and pro-osteogenic effects for infectious bone-defect diseases.

The Regenerative Marriage Between High-Density Platelet-Rich Plasma and Adipose Tissue

The use of autologous biological preparations (ABPs) and their combinations fills the void in healthcare treatment options that exists between surgical procedures, like plastic reconstructive, cosmetic, and orthopedic surgeries; non-surgical musculoskeletal biological procedures; and current pharmaceutical treatments. ABPs, including high-density platelet-rich plasma (HD-PRP), bone marrow aspirate concentrates (BMACs), and adipose tissue preparations, with their unique stromal vascular fractions (SVFs), can play important roles in tissue regeneration and repair processes. They can be easily and safely prepared at the point of care. Healthcare professionals can employ ABPs to mimic the classical wound healing cascade, initiate the angiogenesis cascade, and induce tissue regenerative pathways, aiming to restore the integrity and function of damaged tissues. In this review, we will address combining autologous HD-PRP with adipose tissue, in particular the tissue stromal vascular fraction (t-SVF), as we believe that this biocellular combination demonstrates a synergistic effect, where the HD-PRP constituents enhance the regenerative potential of t-SVF and its adipose-derived mesenchymal stem cells (AD-MSCs) and pericytes, leading to improved functional tissue repair, tissue regeneration, and wound healing in variety of clinical applications. We will address some relevant platelet bio-physiological aspects, since these properties contribute to the synergistic effects of combining HD-PRP with t-SVF, promoting overall better outcomes in chronic inflammatory conditions, soft tissue repair, and tissue rejuvenation.

Effects of injury size on local and systemic immune cell dynamics in volumetric muscle loss

We took a systems approach to the analysis of macrophage phenotype in regenerative and fibrotic volumetric muscle loss outcomes in mice together with analysis of systemic inflammation and of other leukocytes in the muscle, spleen, and bone marrow. Differences in expression of macrophage phenotype markers occurred as early as day 1, persisted to at least day 28, and were associated with increased numbers of leukocytes in the muscle and bone marrow, increased pro-inflammatory marker expression in splenic macrophages, and changes in the levels of pro-inflammatory cytokines in the blood. The most prominent differences were in muscle neutrophils, which were much more abundant in fibrotic outcomes compared to regenerative outcomes at day 1 after injury. However, neutrophil depletion had little to no effect on macrophage phenotype or on muscle repair outcomes. Together, these results suggest that the entire system of immune cell interactions must be considered to improve muscle repair outcomes.

Engineered Strategies to Interfere with Macrophage Fate in Myocardial Infarction

Myocardial infarction (MI), a severe cardiovascular condition, is typically triggered by coronary artery disease, resulting in ischemic damage and the subsequent necrosis of the myocardium. Macrophages, known for their remarkable plasticity, are capable of exhibiting a range of phenotypes and functions as they react to diverse stimuli within their local microenvironment. In recent years, there has been an increasing number of studies on the regulation of macrophage behavior based on tissue engineering strategies, and its regulatory mechanisms deserve further investigation. This review first summarizes the effects of key regulatory factors of engineered biomaterials (including bioactive molecules, conductivity, and some microenvironmental factors) on macrophage behavior, then explores specific methods for inducing macrophage behavior through tissue engineering materials to promote myocardial repair, and summarizes the role of macrophage-host cell crosstalk in regulating inflammation, vascularization, and tissue remodeling. Finally, we propose some future challenges in regulating macrophage-material interactions and tailoring personalized biomaterials to guide macrophage phenotypes.

Eosinophils Respond to Extracellular Matrix Treated Muscle Injuries but are Not Required for Macrophage Polarization

The immune response to decellularized extracellular matrix (ECM) muscle injury is characterized by Th2 T cells, Tregs, M2-like macrophages, and an abundance of eosinophils. Eosinophils have previously been described as mediators of muscle regeneration but inhibit skin wound healing. In addition to response to wounding, a large number of eosinophils respond to biomaterial-treated muscle injury, specifically in response to decellularized ECM. ECM treatment of muscle wounds has been associated with positive outcomes in tissue regeneration, but the detailed mechanisms of action are still being evaluated. Here, this work investigates the role of these eosinophils in terms of their immunologic phenotype and subsequent effect on the local tissue microenvironment. These cells have a mixed phenotype showing both type-2 and regulatory gene upregulation and but are not required for macrophage polarization. Beyond the local tissue, ECM treatment is seen to induce a transient flux of eosinophils to the lungs but prevented a trauma-associated neutrophilia in the lungs of injured mice. This work believes this local and systemic immunomodulation contributes to the regenerative effects of the material and such distal tissue effects should be considered in therapeutic design and implementation.

Immunometabolic Approaches Mitigating Foreign Body Response and Transcriptome Characterization of the Foreign Body Capsule

Directing immunometabolism presents new opportunities to modulate key cell types associated with the formation of foreign body response (FBR) capsule. Contrasting approaches directing immunometabolism are investigated to mitigate FBR: a broadly suppressive metabolic inhibitor (MI) cocktail comprised of 2-deoxyglucose (2-DG), metformin, and 6-diazo-5-oxo-l-norleucine (DON) with daily systemic dosing regimen, and local weekly injection of the more narrowly focused tryptophan catabolizing IDO-Gal3 fusion protein. Treatments significantly decrease FBR capsule formed around subcutaneously implanted cellulose disks. MI cocktail results in a substantially thinner FBR capsule (40% of control), while weekly local injection of IDO-Gal3 also results in a thinner FBR capsule (69% of control). RNA-sequencing capsule transcripts reveal MI cocktail promotes quiescence, with decreased antigen processing and presentation, T helper subset differentiation, and cytokine-cytokine receptor pathway. IDO-Gal3 promotes pro-regenerative, alternatively activated M2-like macrophages and T helper 2 cells, with increased expression of type 2 response-associated genes (Il4, Il13, Arg1, Mrc1, Chil3, Gata3). IDO-Gal3 decreases pro-inflammatory innate sensing pathways, and C-type lectin receptor, NOD-like receptor, RIG-I-like receptor, and Toll-like receptor signaling. This work helps define key gene targets and pathways concomitantly regulated in the FBR capsule during immunometabolic modulation compared to control FBR capsule.

Role of macrophage polarization in diabetic foot ulcer healing: A bibliometric study

BACKGROUND

Diabetic foot ulcers (DFUs) are a significant contributor to disability and mortality in diabetic patients. Macrophage polarization and functional regulation are promising areas of research and show therapeutic potential in the field of DFU healing. However, the complex mechanism, the difficulty in clinical translation, and the large heterogeneity present significant challenges. Hence, this study was to comprehensively analyze the publication status and trends of studies on macrophage polarization and DFU healing.

AIM

To examine the relevant literature on macrophage polarization in DFU healing.

METHODS

A bibliometric analysis was conducted using the Web of Science database. Relevant literature was retrieved from the Web of Science Core Collection database between 2013 to 2023 using literature visualization and analysis software (VOSviewer and CiteSpace) and bibliometric online platforms. The obtained literature was then subjected to visualization and analysis of different countries/regions, institutions, journals, authors, and keywords to reveal the research's major trends and focus.

RESULTS

The number of publications on the role of macrophage polarization in DFU healing increased rapidly from 2013 to 2023, especially in the latter period. Chinese researchers were the most prolific in this field, with 217 publications, while American researchers had been engaged in this field for a longer period. Qian Tan of Nanjing Drum Tower Hospital and Qian Ding of Nanjing University were the first to publish in this field. Shanghai Jiao Tong University was the institution with the most publications (27). The keywords "bone marrow", "adjustment, replacement, response, tissue repair", and "activation, repair, differentiation" appeared more frequently. The study of macrophage polarization in DFU healing focused on the regulatory mechanism, gene expression, and other aspects.

CONCLUSION

This study through the bibliometric method reveals the research trends and development trends in this field of macrophage polarization in DFU healing from 2013 to 2023 in the Web of Science Core Collection database. The key hotspots in this field mainly include the regulation of macrophage activation, gene expression, wound tissue repair, and new wound materials. This study provides references for future research directions.

Intrinsic immunomodulatory hydrogels for chronic inflammation

The immune system plays a pivotal role in maintaining physiological homeostasis and influencing disease processes. Dysregulated immune responses drive chronic inflammation, which in turn results in a range of diseases that are among the leading causes of death globally. Traditional immune interventions, which aim to regulate either insufficient or excessive inflammation, frequently entail lifelong comorbidities and the risk of severe side effects. In this context, intrinsic immunomodulatory hydrogels, designed to precisely control the local immune microenvironment, have recently attracted increasing attention. In particular, these advanced hydrogels not only function as delivery mechanisms but also actively engage in immune modulation, optimizing interactions with the immune system for enhanced tissue repair, thereby providing a sophisticated strategy for managing chronic inflammation. In this tutorial review, we outline key elements of chronic inflammation and subsequently explore the strategic design principles of intrinsic immunomodulatory hydrogels based on these elements. Finally, we examine the challenges and prospects of such immunomodulatory hydrogels, which are expected to inspire further preclinical research and clinical translation in addressing chronic inflammation.

From ductal carcinoma in situ to invasive breast cancer: the prognostic value of the extracellular microenvironment

Ductal carcinoma in situ (DCIS) is a noninvasive breast disease that variably progresses to invasive breast cancer (IBC). Given the unpredictability of this progression, most DCIS patients are aggressively managed similar to IBC patients. Undoubtedly, this treatment paradigm places many DCIS patients at risk of overtreatment and its significant consequences. Historically, prognostic modeling has included the assessment of clinicopathological features and genomic markers. Although these provide valuable insights into tumor biology, they remain insufficient to predict which DCIS patients will progress to IBC. Contemporary work has begun to focus on the microenvironment surrounding the ductal cells for molecular patterns that might predict progression. In this review, extracellular microenvironment alterations occurring with the malignant transformation from DCIS to IBC are detailed. Not only do changes in collagen abundance, organization, and localization mediate the transition to IBC, but also the discrete post-translational regulation of collagen fibers is understood to promote invasion. Other extracellular matrix proteins, such as matrix metalloproteases, decorin, and tenascin C, have been characterized for their role in invasive transformation and further demonstrate the prognostic value of the extracellular matrix. Importantly, these extracellular matrix proteins influence immune cells and fibroblasts toward pro-tumorigenic phenotypes. Thus, the progressive changes in the extracellular microenvironment play a key role in invasion and provide promise for prognostic development.

Biomaterials to regulate tumor extracellular matrix in immunotherapy

The tumor extracellular matrix (ECM) provides physical support and influences tumor development, metastasis, and the tumor microenvironment, creating barriers to immune drug delivery and cell infiltration. Therefore, modulating or degrading the ECM is of significant importance to enhance the efficacy of tumor immunotherapy. This manuscript initially summarizes the main strategies and mechanisms of biomaterials in modulating various components of the ECM, including collagen, fibronectin, hyaluronic acid, and in remodeling the ECM. Subsequently, it discusses the benefits of biomaterials for immunotherapy following ECM modulation, such as promoting the infiltration of drugs and immune cells, regulating immune cell function, and alleviating the immunosuppressive microenvironment. The manuscript also briefly introduces the application of biomaterials that utilize and mimic the ECM for tumor immunotherapy. Finally, it addresses the current challenges and future directions in this field, providing a comprehensive overview of the potential and innovation in leveraging biomaterials to enhance cancer treatment outcomes. Our work will offer a comprehensive overview of ECM modulation strategies and their application in biomaterials to enhance tumor immunotherapy.

Integrated-omics profiling unveils the disparities of host defense to ECM scaffolds during wound healing in aged individuals

Extracellular matrix (ECM) scaffold membranes have exhibited promising potential to better the outcomes of wound healing by creating a regenerative microenvironment around. However, when compared to the application in younger individuals, the performance of the same scaffold membrane in promoting re-epithelialization and collagen deposition was observed dissatisfying in aged mice. To comprehensively explore the mechanisms underlying this age-related disparity, we conducted the integrated analysis, combing single-cell RNA sequencing (scRNA-Seq) with spatial transcriptomics, and elucidated six functionally and spatially distinctive macrophage groups and lymphocytes surrounding the ECM scaffolds. Through intergroup comparative analysis and cell-cell communication, we characterized the dysfunction of Spp1+ macrophages in aged mice impeded the activation of the type Ⅱ immune response, thus inhibiting the repair ability of epidermal cells and fibroblasts around the ECM scaffolds. These findings contribute to a deeper understanding of biomaterial applications in varied physiological contexts, thereby paving the way for the development of precision-based biomaterials tailored specifically for aged individuals in future therapeutic strategies.

Bioactive sucralfate-based microneedles promote wound healing through reprogramming macrophages and protecting endogenous growth factors

Impaired wound healing due to insufficient cell proliferation and angiogenesis is a significant physical and psychological burden to patients worldwide. Therapeutic delivery of exogenous growth factors (GFs) at high doses for wound repair is non-ideal as GFs have poor stability in proteolytic wound environments. Here, we present a two-stage strategy using bioactive sucralfate-based microneedle (SUC-MN) for delivering interleukin-4 (IL-4) to accelerate wound healing. In the first stage, SUC-MN synergistically enhanced the effect of IL-4 through more potent reprogramming of pro-regenerative M2-like macrophages via the JAK-STAT pathway to increase endogenous GF production. In the second stage, sucralfate binds to GFs and sterically disfavors protease degradation to increase bioavailability of GFs. The IL-4/SUC-MN technology accelerated wound healing by 56.6 % and 46.5 % in diabetic mice wounds and porcine wounds compared to their respective untreated controls. Overall, our findings highlight the innovative use of molecular simulations to identify bioactive ingredients and their incorporation into microneedles for promoting wound healing through multiple synergistic mechanisms.

Adaptive immunity of materials: Implications for tissue healing and regeneration

Recent cumulative findings signify the adaptive immunity of materials as a key agenda in tissue healing that can improve regenerative events and outcomes. Modulating immune responses, mainly the recruitment and functions of T and B cells and their further interplay with innate immune cells (e.g., dendritic cells, macrophages) can be orchestrated by materials. For instance, decellularized matrices have been shown to promote muscle healing by inducing T helper 2 (Th2) cell immunity, while synthetic biopolymers exhibit differential effects on B cell responses and fibrosis compared decellularized matrices. We discuss the recent findings on how implantable materials instruct the adaptive immune events and the subsequent tissue healing process. In particular, we dissect the materials' physicochemical properties (shape, size, topology, degradation, rigidity, and matrix dynamic mechanics) to demonstrate the relations of these parameters with the adaptive immune responses in vitro and the underlying biological mechanisms. Furthermore, we present evidence of recent in vivo phenomena, including tissue healing, cancer progression, and fibrosis, wherein biomaterials potentially shape adaptive immune cell functions and in vivo outcomes. Our discussion will help understand the materials-regulated immunology events more deeply, and offer the design rationale of materials with tunable matrix properties for accelerated tissue repair and regeneration.

Regulating the proinflammatory response to composite biomaterials by targeting immunometabolism

Composite biomaterials comprising polylactide (PLA) and hydroxyapatite (HA) are applied in bone, cartilage and dental regenerative medicine, where HA confers osteoconductive properties. However, after surgical implantation, adverse immune responses to these composites can occur, which have been attributed to size and morphology of HA particles. Approaches to effectively modulate these adverse immune responses have not been described. PLA degradation products have been shown to alter immune cell metabolism (immunometabolism), which drives the inflammatory response. Accordingly, to modulate the inflammatory response to composite biomaterials, inhibitors were incorporated into composites comprised of amorphous PLA (aPLA) and HA (aPLA + HA) to regulate glycolytic flux. Inhibition at specific steps in glycolysis reduced proinflammatory (CD86+CD206-) and increased pro-regenerative (CD206+) immune cell populations around implanted aPLA + HA. Notably, neutrophil and dendritic cell (DC) numbers along with proinflammatory monocyte and macrophage populations were decreased, and Arginase 1 expression among DCs was increased. Targeting immunometabolism to control the proinflammatory response to biomaterial composites, thereby creating a pro-regenerative microenvironment, is a significant advance in tissue engineering where immunomodulation enhances osseointegration and angiogenesis, which could lead to improved bone regeneration.

Granular Hydrogels Improve Myogenic Invasion and Repair after Volumetric Muscle Loss

Skeletal muscle injuries including volumetric muscle loss (VML) lead to excessive tissue scarring and permanent functional disability. Despite its high prevalence, there is currently no effective treatment for VML. Bioengineering interventions such as biomaterials that fill the VML defect to support cell and tissue growth are a promising therapeutic strategy. However, traditional biomaterials developed for this purpose lack the pore features needed to support cell infiltration. The present study investigates for the first time, the impact of granular hydrogels on muscle repair - hypothesizing that their flowability will permit conformable filling of the defect site and their inherent porosity will support the invasion of native myogenic cells, leading to effective muscle repair. Small and large microparticle fragments are prepared from photocurable hyaluronic acid polymer via extrusion fragmentation and facile size sorting. In assembled granular hydrogels, particle size and degree of packing significantly influence pore features, rheological behavior, and injectability. Using a mouse model of VML, it is demonstrated that, in contrast to bulk hydrogels, granular hydrogels support early-stage (satellite cell invasion) and late-stage (myofiber regeneration) muscle repair processes. Together, these results highlight the promising potential of injectable and porous granular hydrogels in supporting endogenous repair after severe muscle injury.

Bioresponsive Immunotherapeutic Materials

The human immune system is an interaction network of biological processes, and its dysfunction is closely associated with a wide array of diseases, such as cancer, infectious diseases, tissue damage, and autoimmune diseases. Manipulation of the immune response network in a desired and controlled fashion has been regarded as a promising strategy for maximizing immunotherapeutic efficacy and minimizing side effects. Integration of "smart" bioresponsive materials with immunoactive agents including small molecules, biomacromolecules, and cells can achieve on-demand release of agents at targeted sites to reduce overdose-related toxicity and alleviate off-target effects. This review highlights the design principles of bioresponsive immunotherapeutic materials and discusses the critical roles of controlled release of immunoactive agents from bioresponsive materials in recruiting, housing, and manipulating immune cells for evoking desired immune responses. Challenges and future directions from the perspective of clinical translation are also discussed.

Age-associated Senescent - T Cell Signaling Promotes Type 3 Immunity that Inhibits the Biomaterial Regenerative Response

Aging is associated with immunological changes that compromise response to infections and vaccines, exacerbate inflammatory diseases and can potentially mitigate tissue repair. Even so, age-related changes to the immune response to tissue damage and regenerative medicine therapies remain unknown. Here, it is characterized how aging induces changes in immunological signatures that inhibit tissue repair and therapeutic response to a clinical regenerative biological scaffold derived from extracellular matrix. Signatures of inflammation and interleukin (IL)-17 signaling increased with injury and treatment both locally and regionally in aged animals, and computational analysis uncovered age-associated senescent-T cell communication that promotes type 3 immunity in T cells. Local inhibition of type 3 immune activation using IL17-neutralizing antibodies improves healing and restores therapeutic response to the regenerative biomaterial, promoting muscle repair in older animals. These results provide insights into tissue immune dysregulation that occurs with aging that can be targeted to rejuvenate repair.

Immunometabolic cues recompose and reprogram the microenvironment around implanted biomaterials

Circulating monocytes infiltrate and coordinate immune responses in tissues surrounding implanted biomaterials and in other inflamed tissues. Here we show that immunometabolic cues in the biomaterial microenvironment govern the trafficking of immune cells, including neutrophils and monocytes, in a manner dependent on the chemokine receptor 2 (CCR2) and the C-X3-C motif chemokine receptor 1 (CX3CR1). This affects the composition and activation states of macrophage and dendritic cell populations, ultimately orchestrating the relative composition of pro-inflammatory, transitory and anti-inflammatory CCR2+, CX3CR1+ and CCR2+ CX3CR1+ immune cell populations. In amorphous polylactide implants, modifying immunometabolism by glycolytic inhibition drives a pro-regenerative microenvironment principally by myeloid cells. In crystalline polylactide implants, together with arginase-1-expressing myeloid cells, T helper 2 cells and γδ+ T cells producing interleukin-4 substantially contribute to shaping the metabolically reprogrammed pro-regenerative microenvironment. Our findings inform the premise that local metabolic states regulate inflammatory processes in the biomaterial microenvironment.

Inhalable SPRAY nanoparticles by modular peptide assemblies reverse alveolar inflammation in lethal Gram-negative bacteria infection

Current pharmacotherapy remains futile in acute alveolar inflammation induced by Gram-negative bacteria (GNB), eliciting consequent respiratory failure. The release of lipid polysaccharides after antibiotic treatment and subsequent progress of proinflammatory cascade highlights the necessity to apply effective inflammation management simultaneously. This work describes modular self-assembling peptides for rapid anti-inflammatory programming (SPRAY) to form nanoparticles targeting macrophage specifically, having anti-inflammation and bactericidal functions synchronously. SPRAY nanoparticles accelerate the self-delivery process in macrophages via lysosomal membrane permeabilization, maintaining anti-inflammatory programming in macrophages with efficacy close to T helper 2 cytokines. By pulmonary deposition, SPRAY nanoparticles effectively suppress inflammatory infiltration and promote alveoli regeneration in murine aseptic acute lung injury. Moreover, SPRAY nanoparticles efficiently eradicate multidrug-resistant GNB in alveoli by disrupting bacterial membrane. The universal molecular design of SPRAY nanoparticles provides a robust and clinically unseen local strategy in reverse acute inflammation featured by a high accumulation of proinflammatory cellularity and drug-resistant bacteria.

Decellularized Extracellular Matrix Scaffolds for Soft Tissue Augmentation: From Host-Scaffold Interactions to Bottlenecks in Clinical Translation

Along with a paradigm shift in looking at soft tissue fillers from space-filling to bioactive materials, decellularized extracellular matrix (DEM) fillers have gained more attention considering their superior bioactivity. However, the complex mechanisms that govern the interaction between host tissues and DEMs have been partially understood. This review first covers the mechanisms that determine immunogenicity, angiogenesis and vasculogenesis, and recellularization and remodeling after DEM implantation into host tissue, with a particular focus on related findings from filler materials. Accordingly, the review delves into the dual role of macrophages and their M1/M2 polarization paradigm to form both constructive and destructive immune responses to DEM implants. Moreover, the contribution of macrophages in angiogenesis has been elucidated, which includes but is not limited to the secretion of angiogenic growth factors and extracellular matrix (ECM) remodeling. The findings challenge the traditional view of immune cells as solely destructive entities in biomaterials and indicate their multifaceted roles in tissue regeneration. Furthermore, the review discusses how the compositional factors of DEMs, such as the presence of growth factors and matrikines, can influence angiogenesis, cell fate, and differentiation during the recellularization process. It is also shown that the biomechanical properties of DEMs, including tissue stiffness, modulate cell responses through mechanotransduction pathways, and the structural properties of DEMs, such as scaffold porosity, impact cell-cell and cell-ECM interactions. Finally, we pointed out the current clinical applications, the bottlenecks in the clinical translation of DEM biomaterials into soft tissue fillers, as well as the naïve research areas of the field.

Recombinant humanized type I collagen remodels decidual immune microenvironment at maternal-fetal interface by modulating Th17/Treg imbalance

Disruption of the extracellular matrix and dysregulation of the balance between Th17 and regulatory T cells are recognized as risk factors for recurrent spontaneous abortion (RSA). However, the interaction between matrix components and the Th17/Treg axis remains poorly elucidated. The result of this study revealed that the absence of type I collagen in the decidua is linked to Th17/Treg imbalance in RSA. Furthermore, we discovered that biomaterial recombinant humanized type I collagen (rhCOLI) promoted T cell differentiation into Tregs by inhibition the Notch1/Hes1 signaling pathway and enhanced the immunosuppressive function of Tregs, as indicated by increased secretion level of IL-10 and TGF-β. Importantly, this study is the first to demonstrate that rhCOLI can modulate the Th17/Treg imbalance, reduce embryo resorption rates, reshape the immune microenvironment at the maternal-fetal interface, and improve fertility in an RSA mouse model. Collectively, these findings suggest that type I collagen deficiency may contribute to, rather than result from, RSA, and propose a potential intervention for RSA using rhCOLI.

Effects of injury size on local and systemic immune cell dynamics in volumetric muscle loss

We took a systems approach to the analysis of macrophage phenotype in regenerative and fibrotic volumetric muscle loss outcomes in mice together with analysis of systemic inflammation and of other leukocytes in the muscle, spleen, and bone marrow. Macrophage dysfunction in the fibrotic group occurred as early as day 1, persisted to at least day 28, and was associated with increased numbers of leukocytes in the muscle and bone marrow, increased pro-inflammatory marker expression in splenic macrophages, and changes in the levels of pro-inflammatory cytokines in the blood. The most prominent differences were in muscle neutrophils, which were much more abundant in fibrotic outcomes compared to regenerative outcomes at day 1 after injury. However, neutrophil depletion had little to no effect on macrophage phenotype or on muscle repair outcomes. Together, these results suggest that the entire system of immune cell interactions must be considered to improve muscle repair outcomes.

Advances in Nanomedicine and Biomaterials for Endometrial Regeneration: A Comprehensive Review

The endometrium is an extremely important component of the uterus and is crucial for individual health and human reproduction. However, traditional methods still struggle to ideally repair the structure and function of damaged endometrium and restore fertility. Therefore, seeking and developing innovative technologies and materials has the potential to repair and regenerate damaged or diseased endometrium. The emergence and functionalization of various nanomedicine and biomaterials, as well as the proposal and development of regenerative medicine and tissue engineering techniques, have brought great hope for solving these problems. In this review, we will summarize various nanomedicine, biomaterials, and innovative technologies that contribute to endometrial regeneration, including nanoscale exosomes, nanomaterials, stem cell-based materials, naturally sourced biomaterials, chemically synthesized biomaterials, approaches and methods for functionalizing biomaterials, as well as the application of revolutionary new technologies such as organoids, organ-on-chips, artificial intelligence, etc. The diverse design and modification of new biomaterials endow them with new functionalities, such as microstructure or nanostructure, mechanical properties, biological functions, and cellular microenvironment regulation. It will provide new options for the regeneration of endometrium, bring new hope for the reconstruction and recovery of patients' reproductive abilities.

Hydrogel crosslinking modulates macrophages, fibroblasts, and their communication, during wound healing

Biomaterial wound dressings, such as hydrogels, interact with host cells to regulate tissue repair. This study investigates how crosslinking of gelatin-based hydrogels influences immune and stromal cell behavior and wound healing in female mice. We observe that softer, lightly crosslinked hydrogels promote greater cellular infiltration and result in smaller scars compared to stiffer, heavily crosslinked hydrogels. Using single-cell RNA sequencing, we further show that heavily crosslinked hydrogels increase inflammation and lead to the formation of a distinct macrophage subpopulation exhibiting signs of oxidative activity and cell fusion. Conversely, lightly crosslinked hydrogels are more readily taken up by macrophages and integrated within the tissue. The physical properties differentially affect macrophage and fibroblast interactions, with heavily crosslinked hydrogels promoting pro-fibrotic fibroblast activity that drives macrophage fusion through RANKL signaling. These findings suggest that tuning the physical properties of hydrogels can guide cellular responses and improve healing, offering insights for designing better biomaterials for wound treatment.

Novel IL-4/HB-EGF-dependent crosstalk between eosinophils and macrophages controls liver regeneration after ischaemia and reperfusion injury

OBJECTIVE

Previous studies indicate that eosinophils are recruited into the allograft following orthotopic liver transplantation and protect from ischaemia reperfusion (IR) injury. In the current studies, we aim to explore whether their protective function could outlast during liver repair.

DESIGN

Eosinophil-deficient mice and adoptive transfer of bone marrow-derived eosinophils (bmEos) were employed to investigate the effects of eosinophils on tissue repair and regeneration after hepatic IR injury. Aside from exogenous cytokine or neutralising antibody treatments, mechanistic studies made use of a panel of mouse models of eosinophil-specific IL-4/IL-13-deletion, cell-specific IL-4rα-deletion in liver macrophages and hepatocytes and macrophage-specific deletion of heparin-binding epidermal growth factor-like growth factor (hb-egf).

RESULT

We observed that eosinophils persisted over a week following hepatic IR injury. Their peak accumulation coincided with that of hepatocyte proliferation. Functional studies showed that eosinophil deficiency was associated with a dramatic delay in liver repair, which was normalised by the adoptive transfer of bmEos. Mechanistic studies demonstrated that eosinophil-derived IL-4, but not IL-13, was critically involved in the reparative function of these cells. The data further revealed a selective role of macrophage-dependent IL-4 signalling in liver regeneration. Eosinophil-derived IL-4 stimulated macrophages to produce HB-EGF. Moreover, macrophage-specific hb-egf deletion impaired hepatocyte regeneration after IR injury.

CONCLUSION

Together, these studies uncovered an indispensable role of eosinophils in liver repair after acute injury and identified a novel crosstalk between eosinophils and macrophages through the IL-4/HB-EGF axis.

Contribution of Tregs to the promotion of constructive remodeling after decellularized extracellular matrix material implantation

Host remodeling of decellularized extracellular matrix (dECM) material through the appropriate involvement of immune cells is essential for achieving functional organ/tissue regeneration. As many studies have focused on the role of macrophages, only few have evaluated the role of regulatory T cells (Tregs) in dECM remodeling. In this study, we used a mouse model of traumatic muscle injury to determine the role of Tregs in the constructive remodeling of vascular-derived dECM. According to the results, a certain number of Tregs could be recruited after dECM implantation. Notably, using anti-CD25 to reduce the number of Tregs recruited by the dECM was significantly detrimental to material remodeling based on a significant reduction in the number of M2 macrophages. In addition, collagen and elastic fibers, which maintain the integrity and mechanical properties of the material, rapidly degraded during the early stages of implantation. In contrast, the use of CD28-SA antibodies to increase the number of Tregs recruited by dECM promoted constructive remodeling, resulting in a decreased inflammatory response at the material edge, thinning of the surrounding fibrous connective tissue, uniform infiltration of host cells, and significantly improved tissue remodeling scores. The number of M2 macrophages increased whereas that of M1 macrophages decreased. Moreover, Treg-conditioned medium further enhanced material-induced M2 macrophage polarization in vitro. Overall, Treg is an important cell type that influences constructive remodeling of the dECM. Such findings contribute to the design of next-generation biomaterials to optimize the remodeling and regeneration of dECM materials.

Conserved and tissue-specific immune responses to biologic scaffold implantation

Upon implantation into a patient, any biomaterial induces a cascade of immune responses that influences the outcome of that device. This cascade depends upon several factors, including the composition of the material itself and the location in which the material is implanted. There is still significant uncertainty around the role of different tissue microenvironments in the immune response to biomaterials and how that may alter downstream scaffold remodeling and integration. In this study, we present a study evaluating the immune response to decellularized extracellular matrix materials within the intraperitoneal cavity, the subcutaneous space, and in a traumatic skeletal muscle injury microenvironment. All different locations induced robust cellular recruitment, specifically of macrophages and eosinophils. The latter was most prominent in the subcutaneous space. Intraperitoneal implants uniquely recruited B cells that may alter downstream reactivity as adaptive immunity has been strongly implicated in the outcome of scaffold remodeling. These data suggest that the location of tissue implants should be taken together with the composition of the material itself when designing devices for downline therapeutics. STATEMENT OF SIGNIFICANCE: Different tissue locations have unique immune microenvironments, which can influence the immune response to biomaterial implants. By considering the specific immune profiles of the target tissue, researchers can develop implant materials that promote better integration, reduce complications, and improve the overall outcome of the implantation process.

Basic immunologic study as a foundation for engineered therapeutic development

Bioengineering and drug delivery technologies play an important role in bridging the gap between basic scientific discovery and clinical application of therapeutics. To identify the optimal treatment, the most critical stage is to diagnose the problem. Often these two may occur simultaneously or in parallel, but in this review, we focus on bottom-up approaches in understanding basic immunologic phenomena to develop targeted therapeutics. This can be observed in several fields; here, we will focus on one of the original immunotherapy targets-cancer-and one of the more recent targets-regenerative medicine. By understanding how our immune system responds in processes such as malignancies, wound healing, and medical device implantation, we can isolate therapeutic targets for pharmacologic and bioengineered interventions.

Extracellular matrix-inspired biomaterials for wound healing

Diabetic foot ulcers (DFU) are a debilitating and life-threatening complication of Diabetes Mellitus. Ulceration develops from a combination of associated diabetic complications, including neuropathy, circulatory dysfunction, and repetitive trauma, and they affect approximately 19-34% of patients as a result. The severity and chronic nature of diabetic foot ulcers stems from the disruption to normal wound healing, as a result of the molecular mechanisms which underly diabetic pathophysiology. The current standard-of-care is clinically insufficient to promote healing for many DFU patients, resulting in a high frequency of recurrence and limb amputations. Biomaterial dressings, and in particular those derived from the extracellular matrix (ECM), have emerged as a promising approach for the treatment of DFU. By providing a template for cell infiltration and skin regeneration, ECM-derived biomaterials offer great hope as a treatment for DFU. A range of approaches exist for the development of ECM-derived biomaterials, including the use of purified ECM components, decellularisation and processing of donor/ animal tissues, or the use of in vitro-deposited ECM. This review discusses the development and assessment of ECM-derived biomaterials for the treatment of chronic wounds, as well as the mechanisms of action through which ECM-derived biomaterials stimulate wound healing.

Unraveling and Harnessing the Immune Response at the Cell-Biomaterial Interface for Tissue Engineering Purposes

Biomaterials are defined as "engineered materials" and include a range of natural and synthetic products, designed for their introduction into and interaction with living tissues. Biomaterials are considered prominent tools in regenerative medicine that support the restoration of tissue defects and retain physiologic functionality. Although commonly used in the medical field, these constructs are inherently foreign toward the host and induce an immune response at the material-tissue interface, defined as the foreign body response (FBR). A strong connection between the foreign body response and tissue regeneration is suggested, in which an appropriate amount of immune response and macrophage polarization is necessary to trigger autologous tissue formation. Recent developments in this field have led to the characterization of immunomodulatory traits that optimizes bioactivity, the integration of biomaterials and determines the fate of tissue regeneration. This review addresses a variety of aspects that are involved in steering the inflammatory response, including immune cell interactions, physical characteristics, biochemical cues, and metabolomics. Harnessing the advancing knowledge of the FBR allows for the optimization of biomaterial-based implants, aiming to prevent damage of the implant, improve natural regeneration, and provide the tools for an efficient and successful in vivo implantation.

Immunoengineering Biomaterials for Musculoskeletal Tissue Repair across Lifespan

Musculoskeletal diseases and injuries are among the leading causes of pain and morbidity worldwide. Broad efforts have focused on developing pro-regenerative biomaterials to treat musculoskeletal conditions; however, these approaches have yet to make a significant clinical impact. Recent studies have demonstrated that the immune system is central in orchestrating tissue repair and that targeting pro-regenerative immune responses can improve biomaterial therapeutic outcomes. However, aging is a critical factor negatively affecting musculoskeletal tissue repair and immune function. Hence, understanding how age affects the response to biomaterials is essential for improving musculoskeletal biomaterial therapies. This review focuses on the intersection of the immune system and aging in response to biomaterials for musculoskeletal tissue repair. The article introduces the general impacts of aging on tissue physiology, the immune system, and the response to biomaterials. Then, it explains how the adaptive immune system guides the response to injury and biomaterial implants in cartilage, muscle, and bone and discusses how aging impacts these processes in each tissue type. The review concludes by highlighting future directions for the development and translation of personalized immunomodulatory biomaterials for musculoskeletal tissue repair.

A Thy-1-negative immunofibroblast population emerges as a key determinant of fibrotic outcomes to biomaterials

Fibrosis-associated fibroblasts have been identified across various fibrotic disorders, but not in the context of biomaterials, fibrotic encapsulation, and the foreign body response. In other fibrotic disorders, a fibroblast subpopulation defined by Thy-1 loss is strongly correlated with fibrosis yet we do not know what promotes Thy-1 loss. We have previously shown that Thy-1 is an integrin regulator enabling normal fibroblast mechanosensing, and here, leveraging nonfibrotic microporous annealed particle (MAP) hydrogels versus classical fibrotic bulk hydrogels, we demonstrate that Thy1-/- mice mount a fibrotic response to MAP gels that includes inflammatory signaling. We found that a distinct and cryptic α-smooth muscle actin-positive Thy-1- fibroblast population emerges in response to interleuklin-1β (IL-1β) and tumor necrosis factor-α (TNFα). Furthermore, IL-1β/TNFα-induced Thy-1- fibroblasts consist of two distinct subpopulations that are strongly proinflammatory. These findings illustrate the emergence of a unique proinflammatory, profibrotic fibroblast subpopulation that is central to fibrotic encapsulation of biomaterials.

Navigating the Immunological Crossroads: Mesenchymal Stem/Stromal Cells as Architects of Inflammatory Harmony in Tissue-Engineered Constructs

In the dynamic landscape of tissue engineering, the integration of tissue-engineered constructs (TECs) faces a dual challenge-initiating beneficial inflammation for regeneration while avoiding the perils of prolonged immune activation. As TECs encounter the immediate reaction of the immune system upon implantation, the unique immunomodulatory properties of mesenchymal stem/stromal cells (MSCs) emerge as key navigators. Harnessing the paracrine effects of MSCs, researchers aim to craft a localized microenvironment that not only enhances TEC integration but also holds therapeutic promise for inflammatory-driven pathologies. This review unravels the latest advancements, applications, obstacles, and future prospects surrounding the strategic alliance between MSCs and TECs, shedding light on the immunological symphony that guides the course of regenerative medicine.

In vivo assessment of marine vs bovine origin collagen-based composite scaffolds promoting bone regeneration in a New Zealand rabbit model

The ability of human tissues to self-repair is limited, which motivates the scientific community to explore new and better therapeutic approaches to tissue regeneration. The present manuscript provides a comparative study between a marine-based composite biomaterial, and another composed of well-established counterparts for bone tissue regeneration. Blue shark skin collagen was combined with bioapatite obtained from blue shark's teeth (mColl:BAp), while bovine collagen was combined with synthetic hydroxyapatite (bColl:Ap) to produce 3D composite scaffolds by freeze-drying. Collagens showed similar profiles, while apatite particles differed in their composition, being the marine bioapatite a fluoride-enriched ceramic. The marine-sourced biomaterials presented higher porosities, improved mechanical properties, and slower degradation rates when compared to synthetic apatite-reinforced bovine collagen. The in vivo performance regarding bone tissue regeneration was evaluated in defects created in femoral condyles in New Zealand rabbits twelve weeks post-surgery. Micro-CT results showed that mColl:BAp implanted condyles had a slower degradation and an higher tissue formation (17.9 ± 6.9 %) when compared with bColl:Ap implanted ones (12.9 ± 7.6 %). The histomorphometry analysis provided supporting evidence, confirming the observed trend by quantifying 13.1 ± 7.9 % of new tissue formation for mColl:BAp composites and 10.4 ± 3.2 % for bColl:Ap composites, suggesting the potential use of marine biomaterials for bone regeneration.