Material stiffness influences the polarization state, function and migration mode of macrophages

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.

Controllable fabrication of silk fibroin porous scaffolds and their regulation on cellular behaviours

With the continuous advancement of biomechanics and cell biology, the importance of substrate materials in regulating cell growth, movement, differentiation, apoptosis, gene expression, adhesion, and signal transduction has been increasingly recognized. Silk fibroin (SF) porous scaffolds, owing to their excellent biocompatibility, controllable biodegradability, and ability to effectively simulate the in vivo microenvironment, have been demonstrated to possess broad application prospects in the field of tissue engineering. However, traditional preparation methods for SF porous scaffolds have been found to exhibit poor control over pore size and mechanical properties, and a trade-off between pore size and mechanical performance has often been observed, which has limited their practical application to some extent. A method termed "alcohol addition-freezing method" for preparing SF porous scaffolds was previously developed by our research group, and herein, this method was further extended by adjusting three parameters: the concentration of SF, the concentration of the denaturant n-butanol, and the freezing temperature. Through this approach, controllable preparation of SF porous scaffolds was successfully achieved, resulting in a series of scaffolds with varying pore sizes and compressive moduli. Notably, unidirectional regulation of scaffold pore size and mechanical properties was accomplished, meaning that scaffolds with the same pore size could be designed to exhibit different mechanical properties, and vice versa. Based on this, macrophages, fibroblasts, and bone marrow mesenchymal stem cells (BMSCs), which are frequently involved in tissue engineering scaffold research, were selected to investigate the effects of scaffold pore size and stiffness (represented by compressive modulus) on their biological behaviors. In vitro cell experiments demonstrated that these cells exhibit different biological response in those SF scaffolds with different pore size and stiffness. In summary, the preparation method for SF scaffolds employed in this study has not only addressed the limitations of traditional methods in unidirectionally regulating the physical properties of SF porous scaffolds but has also provided a novel strategy and approach for controlling the microenvironment of cell growth in regenerative medicine, which is considered to hold significant scientific and practical value.

Integration of mechanics and immunology: Perspective for understanding fibrotic disease mechanisms and innovating therapeutic strategies

The treatment of fibrotic diseases has long posed a medical challenge due to the complex mechanisms underlying their occurrence and progression. Emerging evidence suggests that fibrosis development is influenced not only by biochemical factors but also by the activation of mechanotransduction in response to mechanical stimuli. Mechanoimmunology, an interdisciplinary field that examines how the immune system is influenced by physical forces and mechanical environments, has recently demonstrated significant importance and considerable potential for application in the study of fibrotic diseases. While the mechanisms by which biochemical signals regulate the immune system have been extensively explored, the progression of fibrosis is often impacted by both immune dysregulation and mechanical changes. During fibrosis, immune cells encounter strong mechanical stimuli, such as stiffer substrates and altered viscoelasticity, which activate their own mechanotransduction pathways and subsequently influence fibrosis progression. Targeting the mechanosensation of immune cells to enhance or inhibit their mechanoreception and mechanotransduction, thereby enhancing the anti-fibrotic role they play in the fibrotic process, could help innovate therapeutic strategies for fibrotic diseases. STATEMENT OF SIGNIFICANCE: Fibrotic disease progression is often associated with dysregulation of both tissue mechanical properties and immune responses. The fibrotic microenvironment's altered mechanical properties both result from and drive fibrosis, while immune cells actively sense and respond to these mechanical cues through mechanotransduction pathways. Emerging mechanoimmunology research highlights how mechanical stimuli influence immune cell behavior, yet the precise regulatory mechanisms remain unclear. This review examines mechanical communication in fibrosis, focusing on immune cells' mechanosensing capabilities and their role in disease progression, which helps to enhance our understanding of the pathogenesis of fibrosis and inform innovative strategies to open up mechano-immune pathways targeting fibrosis therapy.

Stimulation of macrophage cell lines confined with silica and/or silicon particles and embedded in structured collagen gels

Macrophages encapsulated in composite gels are subjected to a three-dimensional (3D) microenvironment and material-related stimuli that allow modulation of their phenotypes. Herein, 3D collagen fibrillar networks structured with di- or tri-functionalized oligourethanes, including Si-O or Si-Si particles confined therein, are compared regarding their physicochemical properties and material-guided macrophage activation. Gelation kinetics, degradation/swelling, and rheometric results demonstrated that the properties of the composite gels depend on the oligourethane functionalization number (derived from diols/triols and L-Lysine diisocyanate, LDI) and silica incorporation. Human or murine macrophages seeded or encapsulated in the composite gels showed good viability and the adoption of an anti-inflammatory phenotype in response to the silica in the composite gel, showing accelerated gelation when cell culture components are present in the liquid precursors. An increase in cell viability proportional to the storage modulus was observed. ELISA tests strongly suggest that the Si-Si nanoparticles in the composites can antagonize the pro-inflammatory stimulation with lipopolysaccharides (LPS) and interferon-gamma (IFNγ), even promoting an anti-inflammatory response in embedded cells after 24 h. Silicon-doped and crosslinked collagen gels have good potential to modulate macrophage inflammatory response, serving as a 3D immunomodulatory scaffold.

Machine learning-based label-free macrophage phenotyping in immune-material interactions

The rapid advancement of implantable biomedical materials necessitates a comprehensive understanding of macrophage interactions to optimize implant immunocompatibility. Macrophages, key immune regulators, exhibit phenotypic plasticity by polarizing into pro-inflammatory (M1) or anti-inflammatory (M2) subtypes. Conventional phenotyping techniques, such as flow cytometry and immunostaining, provide insights but have limitations related to fixation and endpoint analysis. This study presents a high-throughput, label-free macrophage phenotyping approach integrating AI-driven image classification with quantitative phase imaging (QPI). THP-1-derived macrophages were differentiated into M0, M1, M2a, and M2c phenotypes, and their morphological and refractive index properties were analyzed using QPI. Although QPI alone could not fully distinguish phenotypes, deep learning models, including GoogLeNet, ShuffleNet, VGG-16, and ResNet-18, were evaluated, with ResNet-18 achieving over 90% accuracy. Additionally, macrophage responses to collagen coatings (types I, III, and IV) were assessed using machine learning-based phenotyping and cytokine profiling. Collagen I induced an M1 response, collagen III supported a balanced M1/M2 profile, and collagen IV promoted a controlled immune environment. These findings demonstrate the potential of AI-driven QPI as a non-invasive tool for macrophage characterization, offering insights into biomaterial immunocompatibility and informing implant design strategies.

A crosstalk between adhesion and phagocytosis integrates macrophage functions into their microenvironment

Phagocytosis is the process of actin-dependent internalization and degradation of large particles. Macrophages, which are professional phagocytes, are present in all tissues and are, thus, exposed to environments with different mechanical properties. How mechanical cues from macrophages' environment affect their ability to phagocytose and, in turn, how phagocytosis influences how phagocytic cells interact with their environment remain poorly understood. We found that the ability of macrophages to perform phagocytosis varied with the substrate stiffness. Using live traction force microscopy, we showed that phagocytosing macrophages applied more dynamic traction forces to their substrate. In addition, integrin-mediated phagocytosis triggered a transient loss of podosomes that was associated with decreased degradation of the extracellular matrix, concomitantly with RhoA activation and F-actin recruitment at phagocytic cups. Overall, these results highlight a crosstalk between macrophage phagocytosis and cell adhesion. Mechanical properties of the microenvironment influence phagocytosis, which, in turn, impacts how macrophages interact with their surroundings.

Emerging roles of mechanically activated ion channels in autoimmune disease

Mechanically activated (MA) ion channels have rapidly gained prominence as vital conduits bridging aberrant mechanical cues in tissues with the dysregulated immune responses at the core of autoimmune diseases. Once regarded as peripheral players in inflammation, these channels, exemplified by PIEZO1, TRPV4, and specific K2P family members, now play a central role in modulating T-cell effector functions, B- cell activation and the activity of macrophages and dendritic cells. Their gating is intimately tied to physical distortions such as increased tissue stiffness, osmotic imbalances, or fluid shear, triggering a cascade of ionic fluxes that elevate proinflammatory signaling and drive tissue-destructive loops. Recognition of these channels as central mediators of mechanical stress-induced inflammation responses in autoimmune pathogenesis is rapidly expanding. In parallel, the emerging therapeutic strategies aim to restrain overactive mechanosensors or selectively harness them in affected tissues. Small molecules, peptide blockers, and gene-targeting approaches show preclinical promise, although off-target effects and the broader homeostatic roles of these channels warrant caution. This review explores how integrating mechanobiological concepts with established immunological paradigms enables a more detailed understanding of autoimmune pathogenesis. By elucidating how mechanical forces potentiate or dampen pathological immunity, we propose innovative strategies that exploit mechanosensitivity to recalibrate immune responses across a spectrum of autoimmune conditions.

The osteoinductive and osseointegration properties of decellularized extracellular matrix bone derived from different sites

Aims

This study aimed to examine the differences in bone induction and osseointegration performance of acellular extracellular matrix bone at different sites.

Methods

We decellularized bone from bovine epiphysis near the marrow cavity (NMC), the middle of the cancellous bone (MCB), and near the cartilage (NC). The characterization, physicochemical properties, and effectiveness of the decellularization process of decellularized extracellular matrix (dECM) were analyzed. The proliferation, adhesion, seeding efficiency, and osteogenic differentiation properties of bone marrow mesenchymal stem cells (BMSCs) on decellularized extracellular matrix were investigated. The osteogenicity and osteointegration of dECM from different sources were verified in vivo by animal experiments, and the compatibility of dECM in vivo was also verified.

Results

The NC group had the most significant compressive properties, where the compressive strength was about 1.62 times higher than that of the MCB group (p = 0.022) and 1.34 times higher than that of the NMC group (p < 0.001). dECM scaffolds had good histocompatibility and supported the adhesion and proliferation of BMSCs. In vitro, compared with the remaining two groups, the MCB group significantly upregulated the expression of osteogenic genes (alkaline phosphatase (ALP), runt-related transcription factor 2 (RUNX2), osteopontin (OPN), collagen type 1 (COL1), and bone morphogenetic protein 2 (BMP2)) and marker proteins (ALP, BMP2), whereas the NC group showed the weakest osteoinductive properties. In vivo, we confirmed that the MCB group possessed the most significant osteogenic and osseointegrative properties, followed by the NMC group, and the NC group proved to be the weakest. In particular, the MCB group possessed the ability to endogenously immunomodulate macrophage M1 phenotype to M2 phenotype polarization, creating the most favourable immune microenvironment for osteogenesis.

Conclusion

Our data indicated that the xenogenic dECM scaffolds in MCB position possess the most significant biocompatibility and in vitro and in vivo induced osteogenesis and osseointegration properties. This study provides a more complete basis for the selection of dECM scaffolds in bone defect repair. In future studies of dECM composites applied to bone tissue engineering (BTE), utilizing the middle part of cancellous bone may be the best solution.

Epithelial-mesenchymal transition orchestrates tumor microenvironment: current perceptions and challenges

The epithelial-mesenchymal transition (EMT) is a critical process in cancer progression, facilitating tumor cells to develop invasive traits and augmenting their migratory capabilities. EMT is primed by tumor microenvironment (TME)-derived signals, whereupon cancer cells undergoing EMT in turn remodel the TME, thereby modulating tumor progression and therapeutic response. This review discusses the mechanisms by which EMT coordinates TME dynamics, including secretion of soluble factors, direct cell contact, release of exosomes and enzymes, as well as metabolic reprogramming. Recent evidence also indicates that cells undergoing EMT may differentiate into cancer-associated fibroblasts, thereby establishing themselves as functional constituents of the TME. Elucidating the relationship between EMT and the TME offers novel perspectives for therapeutic strategies to enhance cancer treatment efficacy. Although EMT-directed therapies present significant therapeutic potential, the current lack of effective targeting approaches-attributable to EMT complexity and its microenvironmental context dependency-underscores the necessity for mechanistic investigations and translational clinical validation.

Mechanosensing alters platelet migration

Platelets have long been established as a safeguard of our vascular system. Recently, haptotactic platelet migration has been discovered as a part of the immune response. In addition, platelets exhibit mechanosensing properties, changing their behavior in response to the stiffness of the underlying substrate. However, the influence of substrate stiffness on platelet migration behavior remains elusive. Here, we investigated the migration of platelets on fibrinogen-coated polydimethylsiloxane (PDMS) substrates with different stiffnesses. Using phase-contrast and fluorescence microscopy as well as a deep-learning neural network, we tracked single migrating platelets and measured their migration distance and velocity. We found that platelets migrated on stiff PDMS substrates (E = 2 MPa), while they did not migrate on soft PDMS substrates (E = 5 kPa). Platelets migrated also on PDMS substrates with intermediate stiffness (E = 100 kPa), but their velocity and the fraction of migrating platelets were diminished compared to platelets on stiff PDMS substrates. The straightness of platelet migration, however, was not significantly influenced by substrate stiffness. We used scanning ion conductance microscopy (SICM) to image the three-dimensional shape of migrating platelets, finding that platelets on soft substrates did not show the polarization and shape change associated with migration. Furthermore, the fibrinogen density gradient, which is generated by migrating platelets, was reduced for platelets on soft substrates. Our work demonstrates that substrate stiffness, and thus platelet mechanosensing, influences platelet migration. Substrate stiffness for optimal platelet migration is quite high (>100 kPa) in comparison to other cell types, with possible implications on platelet behavior in inflammatory and injured tissue. STATEMENT OF SIGNIFICANCE: Platelets can feel and react to the stiffness of their surroundings - a process called mechanosensation. Additionally, platelets migrate via substrate-bound fibrinogen as part of the innate immune response during injury or inflammation. It has been shown that the migration of immune cells is influenced by the stiffness of the underlying substrate, but the effect of substrate stiffness on the migration of platelets has not yet been investigated. Using differently stiff substrates made from PDMS, we show that substrate stiffness affects platelet migration. Stiff substrates facilitate fast and frequent platelet migration with a strong platelet shape anisotropy and a strong fibrinogen removal while soft substrates inhibit platelet migration. These findings highlight the influence of the stiffness of the surrounding tissue on the platelet immune response, possibly enhancing platelet migration in inflamed tissue.

Biomaterial scaffold stiffness influences the foreign body reaction, tissue stiffness, angiogenesis and neuroregeneration in spinal cord injury

Biomaterial scaffold engineering presents great potential in promoting axonal regrowth after spinal cord injury (SCI), yet persistent challenges remain, including the surrounding host foreign body reaction and improper host-implant integration. Recent advances in mechanobiology spark interest in optimizing the mechanical properties of biomaterial scaffolds to alleviate the foreign body reaction and facilitate seamless integration. The impact of scaffold stiffness on injured spinal cords has not been thoroughly investigated. Herein, we introduce stiffness-varied alginate anisotropic capillary hydrogel scaffolds implanted into adult rat C5 spinal cords post-lateral hemisection. Four weeks post-implantation, scaffolds with a stiffness approaching that of the spinal cord effectively minimize the host foreign body reaction via yes-associated protein (YAP) nuclear translocation. Concurrently, the softest scaffolds maximize cell infiltration and angiogenesis, fostering significant axonal regrowth but limiting the rostral-caudal linear growth. Furthermore, as measured by atomic force microscopy (AFM), the surrounding spinal cord softens when in contact with the stiffest scaffold while maintaining a physiological level in contact with the softest one. In conclusion, our findings underscore the pivotal role of stiffness in scaffold engineering for SCI in vivo, paving the way for the optimal development of efficacious biomaterial scaffolds for tissue engineering in the central nervous system.

Effect of molecular weight of tyramine-modified hyaluronan on polarization state of THP-1 and peripheral blood mononuclear cells-derived macrophages

The immunomodulatory properties of hyaluronan and its derivatives are key to their use in medicine and tissue engineering. In this work we evaluated the capability of soluble tyramine-modified hyaluronan (THA) synthesized from hyaluronan of two molecular weights (low Mw = 280 kDa and high Mw = 1640 kDa) for polarization of THP-1 and peripheral blood mononuclear cells (PBMCs)-derived macrophages (MΦs). We demonstrate the polarization effects of the supplemented THA by flow cytometry and bead-based multiplex immunoassay for the THP-1 derived MΦs and by semi-automated image analysis from confocal microscopy, immunofluorescent staining utilizing CD68 and CD206 surface markers, RT-qPCR gene expression analysis, as well as using the enzyme-linked immunosorbent assay (ELISA) for PBMCs-derived MΦs. Our data indicate that supplementation with LMW THA drives changes in THP-1 derived MΦs towards a pro-inflammatory M1-like phenotype, whereas supplementation with the HMW THA leads to a more mixed profile with some features of both M1 and M2 phenotypes, suggesting either a heterogeneous population or a transitional state. For cells directly sourced from human patients, PMBCs-derived MΦs, results exhibit a higher degree of variability, pointing out a differential regulation of factors including IL-10 and CD206 between the two cell sources. While human primary cells add to the clinical relevance, donor diversity introduces wider variability in the dataset, preventing drawing strong conclusions. Nevertheless, the MΦs profiles observed in THP-1 derived cells for treatments with LMW and HMW THA are generally consistent with what might be expected for the treatment with non-modified hyaluronans of respective molecular weights, confirming the known association holds true for the chemically tyramine-modified hyaluronan. We stipulate that these responses will provide basis for more accurate in vivo representation and translational immunomodulatory guidance for the use of THA-based biomaterials to a wider biomaterials and tissue engineering communities.

CaMKK2 Regulates Macrophage Polarization Induced by Matrix Stiffness: Implications for Shaping the Immune Response in Stiffened Tissues

Macrophages are essential for immune responses and maintaining tissue homeostasis, exhibiting a wide range of phenotypes depending on their microenvironment. The extracellular matrix (ECM) is a vital component that provides structural support and organization to tissues, with matrix stiffness acting as a key regulator of macrophage behavior. Using physiologically relevant 3D stiffening hydrogel models, it is found that increased matrix stiffness alone promoted macrophage polarization toward a pro-regenerative phenotype, mimicking the effect of interleukin-4(IL-4) in softer matrices. Blocking Calcium/calmodulin-dependent kinase kinase 2 (CaMKK2) selectively inhibited stiffness-induced macrophage polarization without affecting IL-4-driven pro-regenerative pathways. In functional studies, CaMKK2 deletion prevented M2-like/pro-tumoral polarization caused by matrix stiffening, which in turn hindered tumor growth. In a murine wound healing model, loss of CaMKK2 impaired matrix stiffness-mediated macrophage accumulation, ultimately disrupting vascularization. These findings highlight the critical role of CaMKK2 in the macrophage mechanosensitive fate determination and gene expression program, positioning this kinase as a promising therapeutic target to selectively modulate macrophage responses in pathologically stiff tissues.

Long-term digital microfluidic chips for regulating macrophage cellular interactions in inflammation

We introduce a robust multilayer dielectric stack for digital microfluidic chips to withstand the humid conditions of cell culture incubators for at least 60 days. Consisting of a combination of 1 μm polyvinylidene difluoride and 5 μm SU-8 layers, the stack demonstrated high breakdown voltages up to 1600 V and minimal surface currents <30 nA at 100 V. Long-term stability and precision in liquid handling enabled us to study macrophage phenotype modulation, pro-inflammatory response induction in macrophage population with single cell cytokine quantification and testing of a potentially anti-inflammatory drug candidate TCB-2 and its influence on macrophage phenotype, morphology, and cytokine release. The multilayer dielectric stack offers a durable solution for long-term biological assays on digital microfluidic platforms.

Immunomodulation in Bone Tissue Engineering: Recent Advancements in Scaffold Design and Biological Modifications for Enhanced Regeneration

Bone defects, whether caused by trauma, cancer, infectious diseases, or surgery, can significantly impair people's quality of life. Although autografts are the gold standard for treating bone defects, they often fall short in adequately forming bone tissue. The field of bone tissue engineering has made strides in using scaffolds with various biomaterials, stem cells, and growth factors to enhance bone healing. However, some biological structures do not yield satisfactory therapeutic outcomes for new bone formation. Recent studies have shed light on the crucial role of immunomodulation, specifically the interaction between the implanted scaffold and host immune systems, in bone regeneration. Immune cells, particularly macrophages, are pivotal in the inflammatory response, angiogenesis, and osteogenesis. This review delves into the immune system's mechanism toward foreign bodies and the recent advancements in scaffolds' physical and biological properties that foster bone regeneration by modulating macrophage polarization to an anti-inflammatory phenotype and enhancing the osteoimmune microenvironment.

Focus on mechano-immunology: new direction in cancer treatment

The immune response is modulated by a diverse array of signals within the tissue microenvironment, encompassing biochemical factors, mechanical forces, and pressures from adjacent tissues. Furthermore, the extracellular matrix and its constituents significantly influence the function of immune cells. In the case of carcinogenesis, changes in the biophysical properties of tissues can impact the mechanical signals received by immune cells, and these signals c1an be translated into biochemical signals through mechano-transduction pathways. These mechano-transduction pathways have a profound impact on cellular functions, influencing processes such as cell activation, metabolism, proliferation, and migration, etc. Tissue mechanics may undergo temporal changes during the process of carcinogenesis, offering the potential for novel dynamic levels of immune regulation. Here, we review advances in mechanoimmunology in malignancy studies, focusing on how mechanosignals modulate the behaviors of immune cells at the tissue level, thereby triggering an immune response that ultimately influences the development and progression of malignant tumors. Additionally, we have also focused on the development of mechano-immunoengineering systems, with the help of which could help to further understand the response of tumor cells or immune cells to alterations in the microenvironment and may provide new research directions for overcoming immunotherapeutic resistance of malignant tumors.

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.

Critical Role of Nanomaterial Mechanical Properties in Drug Delivery, Nanovaccines and Beyond

Nanomaterials have become essential in the daily lives, finding applications in food, skincare, drugs, and vaccines. Traditionally, the surface chemistry of nanoparticles (NPs) is considered the key factor in determining their interactions with biological systems. However, recent studies have shown that the mechanical properties of nanomaterials are equally important in regulating nano-bio interactions, though they have often been overlooked. Tuning the mechanical properties of nanomaterials and designing them for biomedical applications is thus crucial. This review begins by discussing the various mechanical cues in biological processes, including how viruses and cells adjust their mechanical properties throughout their life cycles. Basic concepts and terminology related to NP mechanical properties are introduced. Next, five different groups of nanomaterials with tunable mechanical properties are explored. The review then examines the impact of NP mechanical properties on their interactions in vitro and in vivo, covering tumor-targeted drug delivery, nanovaccines, and emerging applications such as oral and intranasal drug delivery. Current challenges in the field and perspectives on future developments are also provided.

Biofabrication Directions in Recapitulating the Immune System-on-a-Chip

Ever since the implementation of microfluidics in the biomedical field, in vitro models have experienced unprecedented progress that has led to a new generation of highly complex miniaturized cell culture platforms, known as Organs-on-a-Chip (OoC). These devices aim to emulate biologically relevant environments, encompassing perfusion and other mechanical and/or biochemical stimuli, to recapitulate key physiological events. While OoCs excel in simulating diverse organ functions, the integration of the immune organs and immune cells, though recent and challenging, is pivotal for a more comprehensive representation of human physiology. This comprehensive review covers the state of the art in the intricate landscape of immune OoC models, shedding light on the pivotal role of biofabrication technologies in bridging the gap between conceptual design and physiological relevance. The multifaceted aspects of immune cell behavior, crosstalk, and immune responses that are aimed to be replicated within microfluidic environments, emphasizing the need for precise biomimicry are explored. Furthermore, the latest breakthroughs and challenges of biofabrication technologies in immune OoC platforms are described, guiding researchers toward a deeper understanding of immune physiology and the development of more accurate and human predictive models for a.o., immune-related disorders, immune development, immune programming, and immune regulation.

Mechanobiological Approach for Intestinal Mucosal Immunology

The intestinal area is composed of diverse cell types that harmonize gut homeostasis, which is influenced by both endogenous and exogenous factors. Notably, the environment of the intestine is exposed to several types of mechanical forces, including shear stress generated by fluid flow, compression and stretch generated by luminal contents and peristaltic waves of the intestine, and stiffness attributed to the extracellular matrix. These forces play critical roles in the regulation of cell proliferation, differentiation, and migration. Many efforts have been made to simulate the actual intestinal environment in vitro. The three-dimensional organoid culture system has emerged as a powerful tool for studying the mechanism of the intestinal epithelial barrier, mimicking rapidly renewing epithelium from intestinal stem cells (ISCs) in vivo. However, many aspects of how mechanical forces, such as shear stress, stiffness, compression, and stretch forces, influence the intestinal area remain unresolved. Here, we review the recent studies elucidating the impact of mechanical forces on intestinal immunity, interaction with the gut microbiome, and intestinal diseases.

Serotonin receptor 5-HT7 modulates inflammatory-associated functions of macrophages

The hormone and neurotransmitter serotonin regulates numerous physiological functions within the central nervous system and in the periphery upon binding to specific receptors. In the periphery, the serotonin receptor 7 (5-HT7R) is expressed on different immune cells including monocytes and macrophages. To investigate the impact of 5-HT7R-mediated signaling on macrophage properties, we used human THP-1 cells and differentiated them into pro-inflammatory M1- and anti-inflammatory M2-like macrophages. Pharmacological 5-HT7R activation with the specific agonist LP-211 especially modulates morphology of M1-like macrophages by increasing the number of rounded cells. Furthermore, 5-HT7R stimulation results in significantly reduced phagocytic and migratory ability of M1-like macrophages. Noteworthy, LP-211 treatment leads to changes in secretory properties of all macrophage types with the highest effects obtained for M0- and M2c-like macrophages. Finally, the importance of 5-HT7R for regulation of phagocytosis was confirmed in human primary CD14+ cells. These results indicate that 5-HT7R activation selectively impairs basic functions of macrophages and might thus be a new access point for the modulation of macrophage responses in the future treatment of inflammatory diseases.

Biomechanics in the tumor microenvironment: from biological functions to potential clinical applications

Immune checkpoint therapies have spearheaded drug innovation over the last decade, propelling cancer treatments toward a new era of precision therapies. Nonetheless, the challenges of low response rates and prevalent drug resistance underscore the imperative for a deeper understanding of the tumor microenvironment (TME) and the pursuit of novel targets. Recent findings have revealed the profound impacts of biomechanical forces within the tumor microenvironment on immune surveillance and tumor progression in both murine models and clinical settings. Furthermore, the pharmacological or genetic manipulation of mechanical checkpoints, such as PIEZO1, DDR1, YAP/TAZ, and TRPV4, has shown remarkable potential in immune activation and eradication of tumors. In this review, we delved into the underlying biomechanical mechanisms and the resulting intricate biological meaning in the TME, focusing mainly on the extracellular matrix, the stiffness of cancer cells, and immune synapses. We also summarized the methodologies employed for biomechanical research and the potential clinical translation derived from current evidence. This comprehensive review of biomechanics will enhance the understanding of the functional role of biomechanical forces and provide basic knowledge for the discovery of novel therapeutic targets.

Innovative Hydrogel Design: Tailoring Immunomodulation for Optimal Chronic Wound Recovery

Despite significant progress in tissue engineering, the full regeneration of chronic wounds persists as a major challenge, with the immune response to tissue damage being a key determinant of the healing process's quality and duration. Post-injury, a crucial aspect is the transition of macrophages from a pro-inflammatory state to an anti-inflammatory. Thus, this alteration in macrophage polarization presents an enticing avenue within the realm of regenerative medicine. Recent advancements have entailed the integration of a myriad of cellular and molecular signals into hydrogel-based constructs, enabling the fine-tuning of immune cell activities during different phases. This discussion explores modern insights into immune cell roles in skin regeneration, underscoring the key role of immune modulation in amplifying the overall efficacy of wounds. Moreover, a comprehensive review is presented on the latest sophisticated technologies employed in the design of immunomodulatory hydrogels to regulate macrophage polarization. Furthermore, the deliberate design of hydrogels to deliver targeted immune stimulation through manipulation of chemistry and cell integration is also emphasized. Moreover, an overview is provided regarding the influence of hydrogel properties on immune traits and tissue regeneration process. Conclusively, the accent is on forthcoming pathways directed toward modulating immune responses in the milieu of chronic healing.

Insights into the mechanisms, regulation, and therapeutic implications of extracellular matrix stiffness in cancer

The tumor microenvironment (TME) is critical for cancer initiation, growth, metastasis, and therapeutic resistance. The extracellular matrix (ECM) is a significant tumor component that serves various functions, including mechanical support, TME regulation, and signal molecule generation. The quantity and cross-linking status of ECM components are crucial factors in tumor development, as they determine tissue stiffness and the interaction between stiff TME and cancer cells, resulting in aberrant mechanotransduction, proliferation, migration, invasion, angiogenesis, immune evasion, and treatment resistance. Therefore, broad knowledge of ECM dysregulation in the TME might aid in developing innovative cancer therapies. This review summarized the available information on major ECM components, their functions, factors that increase and decrease matrix stiffness, and related signaling pathways that interplay between cancer cells and the ECM in TME. Moreover, mechanotransduction alters during tumorogenesis, and current drug therapy based on ECM as targets, as well as future efforts in ECM and cancer, are also discussed.

Beyond Needles: Immunomodulatory Hydrogel-Guided Vaccine Delivery Systems

Vaccines are critical for combating infectious diseases, saving millions of lives worldwide each year. Effective immunization requires precise vaccine delivery to ensure proper antigen transport and robust immune activation. Traditional vaccine delivery systems, however, face significant challenges, including low immunogenicity and undesirable inflammatory reactions, limiting their efficiency. Encapsulating or binding vaccines within biomaterials has emerged as a promising strategy to overcome these limitations. Among biomaterials, hydrogels have gained considerable attention for their biocompatibility, ability to interact with biological systems, and potential to modulate immune responses. Hydrogels offer a materials science-driven approach for targeted vaccine delivery, addressing the shortcomings of conventional methods while enhancing vaccine efficacy. This review examines the potential of hydrogel-based systems to improve immunogenicity and explores their dual role as immunomodulatory adjuvants. Innovative delivery methods, such as microneedles, patches, and inhalable systems, are discussed as minimally invasive alternatives to traditional administration routes. Additionally, this review addresses critical challenges, including safety, scalability, and regulatory considerations, offering insights into hydrogel-guided strategies for eliciting targeted immune responses and advancing global immunization efforts.

Targeting extracellular matrix stiffness for cancer therapy

The physical characteristics of the tumor microenvironment (TME) include solid stress, interstitial fluid pressure, tissue stiffness and microarchitecture. Among them, abnormal changes in tissue stiffness hinder drug delivery, inhibit infiltration of immune killer cells to the tumor site, and contribute to tumor resistance to immunotherapy. Therefore, targeting tissue stiffness to increase the infiltration of drugs and immune cells can offer a powerful support and opportunities to improve the immunotherapy efficacy in solid tumors. In this review, we discuss the mechanical properties of tumors, the impact of a stiff TME on tumor cells and immune cells, and the strategies to modulate tumor mechanics.

Hierarchically Structured Biodegradable Microspheres Promote Therapeutic Angiogenesis

Promoting neovascularization is a prerequisite for many tissue engineering applications and the treatment of cardiovascular disease. Delivery of a pro-angiogenic stimulus via acellular materials offers several benefits over biological therapies but has been hampered by interaction of the implanted material with the innate immune response. However, macrophages, a key component of the innate immune response, release a plurality of soluble factors that can be harnessed to stimulate neovascularization and restore blood flow to damaged tissue. This study investigates the ability of biodegradable poly(D,L-lactic-co-glycolic acid) (PLGA) microspheres to restore tissue perfusion in a hind limb model of ischaemia. Microspheres exhibiting a hierarchical porous structure are associated with an increase in blood flow at day 21 post-implantation compared with solid microspheres composed of the same polymer. This corresponds with an increase in blood vessel density in the surrounding tissue. In vitro simulation of the foreign body response observed demonstrates M2-like macrophages incubated with the porous microspheres secreted increased amounts of vascular endothelial growth factor (VEGF) compared with M1-like macrophages providing a potential mechanism for the increased neovascularization. The results from this study demonstrate implantable biodegradable porous microspheres provide a novel approach for increasing neovascularization that could be exploited for therapeutic applications.

Tailoring surface stiffness to modulate senescent macrophage immunomodulation: Implications for osteo-/angio-genesis in aged bone regeneration

The application of biomaterials in bone regeneration is a prevalent clinical practice. However, its efficacy in elderly patients remains suboptimal, necessitating further advancements. While biomaterial properties are known to orchestrate macrophage (MΦ) polarization and local immune responses, the role of biomaterial cues, specifically stiffness, in directing the senescent macrophage (S-MΦ) is still poorly understood. This study aimed to elucidate the role of substrate stiffness in modulating the immunomodulatory properties of S-MΦ and their role in osteo-immunomodulation. Our results demonstrated that employing collagen-coated polyacrylamide hydrogels with varying stiffness values (18, 76, and 295 kPa) as model materials, the high-stiffness hydrogel (295 kPa) steered S-MΦs towards a pro-inflammatory M1 phenotype, while hydrogels with lower stiffness (18 and 76 kPa) promoted an anti-inflammatory M2 phenotype. The immune microenvironment created by S-MΦs promoted the bioactivities of senescent endothelial cells (S-ECs) and senescent bone marrow mesenchymal stem cells BMSCs (S-BMSCs). Furthermore, the M2 S-MΦs, particularly incubated on the 76 kPa hydrogel matrices, significantly enhanced the ability of angiogenesis of S-ECs and osteogenic differentiation of S-BMSCs, which are crucial and interrelated processes in bone healing. This modulation aided in reducing the accumulation of reactive oxygen species in S-ECs and S-BMSCs, thereby significantly contributing to the repair and regeneration of aged bone tissue.

Novel Injectable Collagen/Glycerol/Pullulan Gel Promotes Osteogenic Differentiation of Mesenchymal Stem Cells and the Repair of Rat Cranial Defects

Bone tissue engineering is a technique that simulates the bone tissue microenvironment by utilizing cells, tissue scaffolds, and growth factors. The collagen hydrogel is a three-dimensional network bionic material that has properties and structures comparable to those of the extracellular matrix (ECM), making it an ideal scaffold and drug delivery system for tissue engineering. The clinical applications of this material are restricted due to its low mechanical strength. In this investigation, a collagen-based gel (atelocollagen/glycerol/pullulan [Col/Gly/Pul] gel) that is moldable and injectable with high adhesive qualities was created by employing a straightforward technique that involved the introduction of Gly and Pul. This study aimed to characterize the internal morphology and chemical composition of the Col/Gly/Pul gel, as well as to verify its osteogenic properties through in vivo and in vitro experiments. When compared to a standard pure Col hydrogel, this material is more adaptable to the complexity of the local environment of bone defects and the apposition of irregularly shaped flaws due to its greater mechanical strength, injectability, and moldability. Overall, the Col/Gly/Pul gel is an implant that shows great potential for the treatment of complex bone defects and the enhancement of bone regeneration.

Immunophenotypic Profile of Adult Glioblastoma IDH-Wildtype Microenvironment: A Cohort Study

Background: Glioblastoma IDH-wildtype (GBM IDH-wt) is the most aggressive brain tumor in adults and is characterized by an immunosuppressive microenvironment. Different factors shaping its tumor microenvironment (TME) regulate tumor progression and treatment response. The aim of this study was to characterize the main immunosuppressive elements of the GBM IDH-wt TME. Methods: Immunohistochemistry for CD3, CD4, CD8, CD163, programmed death ligand 1 (PD-L1) and programmed death 1 (PD1) was performed on surgical tumor specimens from patients diagnosed with GBM IDH-wt, according to the CNS WHO 2021 criteria. The impact of categorical variables on time-dependent outcomes such as overall survival (OS) and progression-free survival (PFS) has been estimated through the Kaplan-Meier method. Results: We included 30 patients (19 males and 11 females), median age of 59.8 years (range 40.2-69.1 years). All patients underwent surgery followed by temozolomide concurrent with and adjuvant to radiotherapy. MGMT was methylated in 14 patients (47%) and unmethylated in 16 patients (53%). The overall absolute percentages of CD4+ lymphocytes, both intratumoral and perivascular, were significantly more represented than CD8+ lymphocytes in the TME (p = 0.02). A low density of CD4+ lymphocytes (≤10%) was found to be a favorable prognostic factor for GBM outcome (p = 0.02). Patients with MGMT methylated and unmethylated tumors exhibited a distinct TME composition, with a significant higher number of perivascular CD8+ lymphocytes (p = 0.002), intratumoral CD8+ lymphocytes (p = 0.0024) and perivascular CD4+ lymphocytes (p = 0.014) in MGMT unmethylated tumors. PD-L1 expression in tumor cell surface was observed in four tumors (13.3%), and PD1 expression in infiltrating T lymphocytes was observed in nine (30%) tumors, with predominantly perivascular distribution. Conclusions: MGMT methylated and unmethylated tumors exhibit different immune profiles, likely reflecting the different biology of these tumors. The expression of PD-L1 in GBM IDH-wt patients is confined to a small subpopulation. While we found a significant association between low CD4+ lymphocyte density (≤10%) and survival, given the small numbers of our cohort, the prognostic value of CD4+ lymphocyte density will need to be validated in large-scale studies.

Magnetically Driven Hydrogel Surfaces for Modulating Macrophage Behavior

During the host response toward implanted biomaterials, macrophages can shift phenotypes rapidly upon changes in their microenvironment within the host tissue. Exploration of this phenomenon can benefit significantly from the development of adequate tools. Creating cell microenvironment alterations on classical hydrogel substrates presents challenges, particularly when integrating them with cell cultivation and monitoring processes. However, having the capability to dynamically manipulate the cell microenvironment on biomaterial surfaces holds significant potential. We introduce magnetically actuated hydrogels (MadSurface) tailored to induce reversible stiffness changes on polyacrylamide hydrogel substrates with embedded magnetic microparticles in a time-controllable manner. Our investigation focused on exploring the potential of magnetic fields and MadSurfaces in dynamically modulating macrophage behavior in a programmable manner. We achieved a consistent modulation by subjecting the MadSurface to a pulsed magnetic field with a frequency of 0.1 Hz and a magnetic field flux density of 50 mT and analyzed exposed cells using flow cytometry and ELISA. At the single-cell level, we identified a subpopulation for which the dynamic stiffness conditions in conjunction with the pulsed magnetic field increased the expression of CD206 in M1-activated THP-1 cells, indicating a consistent shift toward the M2 anti-inflammatory phenotype on MadSurface. At the population level, this effect was mostly hindered in the culture period utilized in this work. The MadSurface approach advances our understanding of the interplay between magnetic field, cell microenvironment alterations, and macrophage behavior.

Augmentation of Tendon and Ligament Repair with Fiber-Reinforced Hydrogel Composites

This review highlights the promise of fiber-reinforced hydrogel composites (FRHCs) for augmenting tendon and ligament repair and regeneration. Composed of reinforcing fibers embedded in a hydrogel, these scaffolds provide both mechanical strength and a conducive microenvironment for biological processes required for connective tissue regeneration. Typical properties of FRHCs are discussed, highlighting their ability to simultaneously fulfill essential mechanical and biological design criteria for a regenerative scaffold. Furthermore, features of FRHCs are described that improve specific biological aspects of tendon healing including mesenchymal progenitor cell recruitment, early polarization to a pro-regenerative immune response, tenogenic differentiation of recruited progenitor cells, and subsequent production of a mature, aligned collagenous matrix. Finally, the review offers a perspective on clinical translation of tendon FRHCs and outlines key directions for future work.

The influence of biophysical niche on tumor-associated macrophages in liver cancer

HCC, the most common type of primary liver cancer, is a leading cause of cancer-related mortality worldwide. Although the advancement of immunotherapies by immune checkpoint inhibitors (ICIs) that target programmed cell death 1 or programmed cell death 1-ligand 1 has revolutionized the treatment for HCC, the majority is still not beneficial. Accumulating evidence has pointed out that the potent immunosuppressive tumor microenvironment in HCC poses a great challenge to ICI therapeutic efficacy. As a key component in tumor microenvironment, tumor-associated macrophages (TAMs) play vital roles in HCC development, progression, and ICI low responsiveness. Mechanistically, TAM can promote cancer invasion and metastasis, angiogenesis, epithelial-mesenchymal transition, maintenance of stemness, and most importantly, immunosuppression. Targeting TAMs, therefore, represents an opportunity to enhance the ICI therapeutic efficacy in patients with HCC. While previous research has primarily focused on biochemical cues influencing macrophages, emerging evidence highlights the critical role of biophysical signals, such as substrate stiffness, topography, and external forces. In this review, we summarize the influence of biophysical characteristics within the tumor microenvironment that regulate the phenotype and function of TAMs in HCC pathogenesis and progression. We also explore the possible mechanisms and discuss the potential of manipulating biophysical cues in regulating TAM for HCC therapy. By gaining a deeper understanding of how macrophages sense and respond to mechanical forces, we may potentially usher in a path toward a curative approach for combinatory cancer immunotherapies.

Acute contact with profibrotic macrophages mechanically activates fibroblasts via αvβ3 integrin-mediated engagement of Piezo1

Fibrosis-excessive scarring after injury-causes >40% of disease-related deaths worldwide. In this misguided repair process, activated fibroblasts drive the destruction of organ architecture by accumulating and contracting extracellular matrix. The resulting stiff scar tissue, in turn, enhances fibroblast contraction-bearing the question of how this positive feedback loop begins. We show that direct contact with profibrotic but not proinflammatory macrophages triggers acute fibroblast contractions. The contractile response depends on αvβ3 integrin expression on macrophages and Piezo1 expression on fibroblasts. The touch of macrophages elevates fibroblast cytosolic calcium within seconds, followed by translocation of the transcription cofactors nuclear factor of activated T cells 1 and Yes-associated protein, which drive fibroblast activation within hours. Intriguingly, macrophages induce mechanical stress in fibroblasts on soft matrix that alone suppresses their spontaneous activation. We propose that acute contact with suitable macrophages mechanically kick-starts fibroblast activation in an otherwise nonpermissive soft environment. The molecular components mediating macrophage-fibroblast mechanotransduction are potential targets for antifibrosis strategies.

Soft hydrogel semiconductors with augmented biointeractive functions

Hydrogels, known for their mechanical and chemical similarity to biological tissues, are widely used in biotechnologies, whereas semiconductors provide advanced electronic and optoelectronic functionalities such as signal amplification, sensing, and photomodulation. Combining semiconducting properties with hydrogel designs can enhance biointeractive functions and intimacy at biointerfaces, but this is challenging owing to the low hydrophilicity of polymer semiconductors. We developed a solvent affinity-induced assembly method that incorporates water-insoluble polymer semiconductors into double-network hydrogels. These semiconductors exhibited tissue-level moduli as soft as 81 kilopascals, stretchability of 150% strain, and charge-carrier mobility up to 1.4 square centimeters per volt per second. When they are interfaced with biological tissues, their tissue-level modulus enables alleviated immune reactions. The hydrogel's high porosity enhances molecular interactions at semiconductor-biofluid interfaces, resulting in photomodulation with higher response and volumetric biosensing with higher sensitivity.

Formation and biological activities of foreign body giant cells in response to biomaterials

The integration of biomaterials in medical applications triggers the foreign body response (FBR), a multi-stage immune reaction characterized by the formation of foreign body giant cells (FBGCs). Originating from the fusion of monocyte/macrophage lineage cells, FBGCs are pivotal participants during tissue-material interactions. This review provides an in-depth examination of the molecular processes during FBGC formation, highlighting signaling pathways and fusion mediators in response to both exogenous and endogenous stimuli. Moreover, a wide range of material-specific characteristics, such as surface chemical and physical properties, has been proven to influence the fusion of macrophages into FBGCs. Multifaceted biological activities of FBGCs are also explored, with emphasis on their phagocytic capabilities and extracellular secretory functions, which profoundly affect the vascularization, degradation, and encapsulation of the biomaterials. This review further elucidates the heterogeneity of FBGCs and their diverse roles during FBR, as demonstrated by their distinct behaviors in response to different materials. By presenting a comprehensive understanding of FBGCs, this review intends to provide strategies and insights into optimizing biocompatibility and the therapeutic potential of biomaterials for enhanced stability and efficacy in clinical applications. STATEMENT OF SIGNIFICANCE: As a hallmark of the foreign body response (FBR), foreign body giant cells (FBGCs) significantly impact the success of implantable biomaterials, potentially leading to complications such as chronic inflammation, fibrosis, and device failure. Understanding the role of FBGCs and modulating their responses are vital for successful material applications. This review provides a comprehensive overview of the molecules and signaling pathways guiding macrophage fusion into FBGCs. By elucidating the physical and chemical properties of materials inducing distinct levels of FBGCs, potential strategies of materials in modulating FBGC formation are investigated. Additionally, the biological activities of FBGCs and their heterogeneity in responses to different material categories in vivo are highlighted in this review, offering crucial insights for improving the biocompatibility and efficacy of biomaterials.

Probing Nanotopography-Mediated Macrophage Polarization via Integrated Machine Learning and Combinatorial Biophysical Cue Mapping

Inflammatory responses, leading to fibrosis and potential host rejection, significantly hinder the long-term success and widespread adoption of biomedical implants. The ability to control and investigated macrophage inflammatory responses at the implant-macrophage interface would be critical for reducing chronic inflammation and improving tissue integration. Nonetheless, the systematic investigation of how surface topography affects macrophage polarization is typically complicated by the restricted complexity of accessible nanostructures, difficulties in achieving exact control, and biased preselection of experimental parameters. In response to these problems, we developed a large-scale, high-content combinatorial biophysical cue (CBC) array for enabling high-throughput screening (HTS) of the effects of nanotopography on macrophage polarization and subsequent inflammatory processes. Our CBC array, created utilizing the dynamic laser interference lithography (DLIL) technology, contains over 1 million nanotopographies, ranging from nanolines and nanogrids to intricate hierarchical structures with dimensions ranging from 100 nm to several microns. Using machine learning (ML) based on the Gaussian process regression algorithm, we successfully identified certain topographical signals that either repress (pro-M2) or stimulate (pro-M1) macrophage polarization. The upscaling of these nanotopographies for further examination has shown mechanisms such as cytoskeletal remodeling and ROCK-dependent epigenetic activation to be critical to the mechanotransduction pathways regulating macrophage fate. Thus, we have also developed a platform combining advanced DLIL nanofabrication techniques, HTS, ML-driven prediction of nanobio interactions, and mechanotransduction pathway evaluation. In short, our developed platform technology not only improves our ability to investigate and understand nanotopography-regulated macrophage inflammatory responses but also holds great potential for guiding the design of nanostructured coatings for therapeutic biomaterials and biomedical implants.

Cell volume regulation modulates macrophage-related inflammatory responses via JAK/STAT signaling pathways

Cell volume as a characteristic of changes in response to external environmental cues has been shown to control the fate of stem cells. However, its influence on macrophage behavior and macrophage-mediated inflammatory responses have rarely been explored. Herein, through mediating the volume of macrophages by adding polyethylene glycol (PEG), we demonstrated the feasibility of fine-tuning cell volume to regulate macrophage polarization towards anti-inflammatory phenotypes, thereby enabling to reverse macrophage-mediated inflammation response. Specifically, lower the volume of primary macrophages can induce both resting macrophages (M0) and stimulated pro-inflammatory macrophages (M1) to up-regulate the expression of anti-inflammatory factors and down-regulate pro-inflammatory factors. Further mechanistic investigation revealed that macrophage polarization resulting from changing cell volume might be mediated by JAK/STAT signaling pathway evidenced by the transcription sequencing analysis. We further propose to apply this strategy for the treatment of arthritis via direct introduction of PEG into the joint cavity to modulate synovial macrophage-related inflammation. Our preliminary results verified the credibility and effectiveness of this treatment evidenced by the significant inhibition of cartilage destruction and synovitis at early stage. In general, our results suggest that cell volume can be a biophysical regulatory factor to control macrophage polarization and potentially medicate inflammatory response, thereby providing a potential facile and effective therapy for modulating macrophage mediated inflammatory responses. STATEMENT OF SIGNIFICANCE: Cell volume has recently been recognized as a significantly important biophysical signal in regulating cellular functionalities and even steering cell fate. Herein, through mediating the volume of macrophages by adding polyethylene glycol (PEG), we demonstrated the feasibility of fine-tuning cell volume to induce M1 pro-inflammatory macrophages to polarize towards anti-inflammatory M2 phenotype, and this immunomodulatory effect may be mediated by the JAK/STAT signaling pathway. We also proposed the feasible applications of this PEG-induced volume regulation approach towards the treatment of osteoarthritis (OA), wherein our preliminary results implied an effective alleviation of early synovitis. Our study on macrophage polarization mediated by cell volume may open up new pathways for immune regulation through microenvironmental biophysical clues.

Electrospun Fiber Surface Roughness Modulates Human Monocyte-Derived Macrophage Phenotype

Injuries to fibrous connective tissues have very little capacity for self-renewal and exhibit poor healing after injury. Phenotypic shifts in macrophages play a vital role in mediating the healing response, creating an opportunity to design immunomodulatory biomaterials which control macrophage polarization and promote regeneration. In this study, electrospun poly(-caprolactone) fibers with increasing surface roughness (SR) were produced by increasing relative humidity and inducing vapor-induced phase separation during the electrospinning process. The impact of surface roughness on macrophage phenotype was assessed using human monocyte-derived macrophages in vitro and in vivo using B6.Cg-Tg(Csf1r-EGFP)1Hume/J (MacGreen) mice. In vitro experiments showed that macrophages cultured on mesh with increasing SR exhibited decreased release of both pro- and anti-inflammatory cytokines potentially driven by increased protein adsorption and biophysical impacts on the cells. Further, increasing SR led to an increase in the expression of the pro-regenerative cell surface marker CD206 relative to the pro-inflammatory marker CD80. Mesh with increasing SR were implanted subcutaneously in MacGreen mice, again showing an increase in the ratio of cells expressing CD206 to those expressing CD80 visualized by immunofluorescence. SR on implanted biomaterials is sufficient to drive macrophage polarization, demonstrating a simple feature to include in biomaterial design to control innate immunity.

Advances and applications of biomimetic biomaterials for endogenous skin regeneration

Endogenous regeneration is becoming an increasingly important strategy for wound healing as it facilitates skin's own regenerative potential for self-healing, thereby avoiding the risks of immune rejection and exogenous infection. However, currently applied biomaterials for inducing endogenous skin regeneration are simplistic in their structure and function, lacking the ability to accurately mimic the intricate tissue structure and regulate the disordered microenvironment. Novel biomimetic biomaterials with precise structure, chemical composition, and biophysical properties offer a promising avenue for achieving perfect endogenous skin regeneration. Here, we outline the recent advances in biomimetic materials induced endogenous skin regeneration from the aspects of structural and functional mimicry, physiological process regulation, and biophysical property design. Furthermore, novel techniques including in situ reprograming, flexible electronic skin, artificial intelligence, single-cell sequencing, and spatial transcriptomics, which have potential to contribute to the development of biomimetic biomaterials are highlighted. Finally, the prospects and challenges of further research and application of biomimetic biomaterials are discussed. This review provides reference to address the clinical problems of rapid and high-quality skin regeneration.

The effect of compressive force in bone tissue induced by implants of different primary stabilities on macrophage polarization and bone regeneration

Dental implants with different primary stabilities give rise to distinct stress distributions at the implant-bone interface after placement and exert mechanical force on the cells in the bone tissue. This study aimed to investigate whether the mechanical forces in peri-implant bone participate in the body's immune response and influence macrophage polarization. Therefore, an in vivo rat implantation model with different primary implant stabilities was established. The osteoimmune response and macrophage polarization were investigated, and the osseointegration of the implants was evaluated. In an in vitro experiment, an external compressive force was applied to RAW264.7 cells, and the polarization phenotype was observed. MC3T3-E1 cells were cultured in macrophage-conditioned medium to investigate the regulatory effect of the macrophage-secreted cytokines on the osteogenic differentiation of osteoblasts. In vivo experimental results indicated that the primary stability of implants is positively correlated with the mechanical force. The osteoimmune response was significantly amplified by compressive force generated from implants. This compressive force first induced both M1 and M2 macrophage polarization and then accelerated the progression of the transition to M2 macrophages in the bone repair phase. In vitro, compressive force significantly upregulated the M1 and M2 macrophage polarization. In addition, the suppressive effect of macrophages on the osteogenesis of MC3T3 cells was relieved by cytokines secreted by macrophages under compressive force loading, which promoted their osteogenesis. Overall, these results clarify that compressive force from different primary stabilities is an important influencing factor regulating the osteoimmunne response and macrophage polarization in addition to maintaining the implant.

Chitosan-based biomaterials promote bone regeneration by regulating macrophage fate

The development of various osteogenic biomaterials has not only promoted the development of bone tissue engineering but also provided more possibilities for bone defect repair. However, most previous studies have focused on the interaction of biomaterials on endogenous or exogenous stem cells involved in the bone regeneration process while neglecting the effect of changes in the immune microenvironment of bone defect sites on bone regeneration after biomaterial implantation into the host. With the development of bone immunology, the role of various immune cells, especially macrophages, in bone regeneration has gradually attracted the attention of researchers. An increasing number of studies have begun to target macrophages to better promote bone regeneration by modulating the fate of macrophages in a spatiotemporally ordered manner to mimic the changes in the immune microenvironment of bone defect sites during the natural repair process of bone tissue. Chitosan is one of the most abundant natural polysaccharides in the world. In recent years, various chitosan-based biomaterials have been widely used in macrophage fate modulation and bone regeneration. In this review, we review the interaction between macrophages and scaffold materials, general information about chitosan, the modulation of macrophage fate by chitosan-based biomaterials, and their application in bone regeneration.

Single-Cell Analyses Reveal the Metabolic Heterogeneity and Plasticity of the Tumor Microenvironment during Head and Neck Squamous Cell Carcinoma Progression

Metabolic reprogramming is a hallmark of cancer. In addition to metabolic alterations in the tumor cells, multiple other metabolically active cell types in the tumor microenvironment (TME) contribute to the emergence of a tumor-specific metabolic milieu. Here, we defined the metabolic landscape of the TME during the progression of head and neck squamous cell carcinoma (HNSCC) by performing single-cell RNA sequencing on 26 human patient specimens, including normal tissue, precancerous lesions, early stage cancer, advanced-stage cancer, lymph node metastases, and recurrent tumors. The analysis revealed substantial heterogeneity at the transcriptional, developmental, metabolic, and functional levels in different cell types. SPP1+ macrophages were identified as a protumor and prometastatic macrophage subtype with high fructose and mannose metabolism, which was further substantiated by integrative analysis and validation experiments. An inhibitor of fructose metabolism reduced the proportion of SPP1+ macrophages, reshaped the immunosuppressive TME, and suppressed tumor growth. In conclusion, this work delineated the metabolic landscape of HNSCC at a single-cell resolution and identified fructose metabolism as a key metabolic feature of a protumor macrophage subpopulation. Significance: Fructose and mannose metabolism is a metabolic feature of a protumor and prometastasis macrophage subtype and can be targeted to reprogram macrophages and the microenvironment of head and neck squamous cell carcinoma.

Macrophage-Centric Biomaterials for Bone Regeneration in Diabetes Mellitus: Contemporary Advancements, Challenges, and Future Trajectories

Increased susceptibility to bone fragility and the diminution of bone regenerative capacity are recognized as significant and frequent sequelae of diabetes mellitus. Research has elucidated the pivotal role of macrophages in the pathogenesis and repair of diabetic bone defects. Notwithstanding this, the therapeutic efficacy of traditional interventions remains predominantly inadequate. Concomitant with substantial advancements in tissue engineering in recent epochs, there has been an escalation in the development of biomaterials designed to modulate macrophage activity, thereby augmenting osseous tissue regeneration in the context of hyperglycemia. This review amalgamates insights from extant research and delineates recent progressions in the domain of biomaterials that target macrophages for the regeneration of diabetic bone, whilst also addressing the clinical challenges and envisaging future directions within this field.

Matrix stiffness regulates macrophage polarisation via the Piezo1-YAP signalling axis

Macrophages play a pivotal role in the immunological cascade activated in response to biomedical implants, which predetermine acceptance or rejection of implants by the host via pro- and anti-inflammatory polarisation states. The role of chemical signals in macrophage polarisation is well-established, but how physical cues regulate macrophage function that may play a fundamental role in implant-bone interface, remains poorly understood. Here we find that bone marrow-derived macrophages (BMDM) cultured on polyacrylamide gels of varying stiffness exhibit different polarisation states. BMDM are 'primed' to a pro-inflammatory M1 phenotype on stiff substrates, while to an anti-inflammatory M2 phenotype on soft and medium stiffness substrates. It is further observed that matrix stiffening increases Piezo1 expression, as well as leads to subsequent activation of the mechanotransduction signalling effector YAP, thus favouring M1 polarisation whilst suppressing M2 polarisation. Moreover, upon treatment with YAP inhibitor, we successfully induce macrophage re-polarisation to the M2 state within the implant site microenvironment, which in turn promotes implant osseointegration. Collectively, our present study thus characterises the critical role of the Piezo1-YAP signalling axis in macrophage mechanosensing and stiffness-mediated macrophage polarisation and provides cues for the design of immuno-modulatory biomaterials that can regulate the macrophage phenotype.

Macrophage polarization and its impact on idiopathic pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) is a lung disease that worsens over time, causing fibrosis in the lungs and ultimately resulting in respiratory failure and a high risk of death. Macrophages play a crucial role in the immune system, showing flexibility by transforming into either pro-inflammatory (M1) or anti-inflammatory (M2) macrophages when exposed to different stimuli, ultimately impacting the development of IPF. Recent research has indicated that the polarization of macrophages is crucial in the onset and progression of IPF. M1 macrophages secrete inflammatory cytokines and agents causing early lung damage and fibrosis, while M2 macrophages support tissue healing and fibrosis by releasing anti-inflammatory cytokines. Developing novel treatments for IPF relies on a thorough comprehension of the processes involved in macrophage polarization in IPF. The review outlines the regulation of macrophage polarization and its impact on the development of IPF, with the goal of investigating the possible therapeutic benefits of macrophage polarization in the advancement of IPF.

Single Living Cell "Observation-Analysis" Integrated Platform Decodes Cell Migration Plasticity Orchestrated by Nucleocytoplasmic STAT3

Cell migration requires the interplay among diverse migration patterns. The molecular basis of distinct migration programs is undoubtedly vital but not fully explored. Meanwhile, the lack of tools for investigating spontaneous migratory plasticity in a single living cell also adds to the hindrance. Here, we developed a micro/nanotechnology-enabled single-cell analytical platform to achieve coherent monitoring of spontaneous migratory pattern and signaling molecules. Via the platform, we unveiled a previously unappreciated STAT3 regionalization on the multifunctional regulations of migration. Specifically, nuclear STAT3 is associated with amoeboid migration, while cytoplasmic STAT3 promotes mesenchymal movement. Opposing effects of JAK2 multisite phosphorylation shape its response to STAT3 distribution in a dynamic and antagonistic manner, eventually triggering a reversible amoeboid-mesenchymal transition. Based on the above results, bioinformatics further revealed a possible downstream regulator of nucleocytoplasmic STAT3. Thus, our platform, as an exciting technological advance in single-cell migration research, can provide in-depth mechanism interpretations of tumor metastasis and progression.

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.