Substrate stiffness modulates bone marrow-derived macrophage polarization through NF-κB signaling pathway

Stiffness sensing via Piezo1 enhances macrophage efferocytosis and promotes the resolution of liver fibrosis

Tissue stiffening is a predominant feature of fibrotic disorders, but the response of macrophages to changes in tissue stiffness and cellular context in fibrotic diseases remains unclear. Here, we found that the mechanosensitive ion channel Piezo1 was up-regulated in hepatic fibrosis. Macrophages lacking Piezo1 showed sustained inflammation and impaired spontaneous resolution of early liver fibrosis. Further analysis revealed an impairment of clearance of apoptotic cells by macrophages in the fibrotic liver. Macrophages showed enhanced efferocytosis when cultured on rigid substrates but not soft ones, suggesting stiffness-dependent efferocytosis of macrophages required Piezo1 activation. Besides, Piezo1 was involved in the efficient acidification of the engulfed cargo in the phagolysosomes and affected the subsequent expression of anti-inflammation genes after efferocytosis. Pharmacological activation of Piezo1 increased the efferocytosis capacity of macrophages and accelerated the resolution of inflammation and fibrosis. Our study supports the antifibrotic role of Piezo1-mediated mechanical sensation in liver fibrosis, suggesting that targeting PIEZO1 to enhance macrophage efferocytosis could induce fibrosis regression.

Mechanical and Functional Responses in Astrocytes under Alternating Deformation Modes Using Magneto-Active Substrates

This work introduces NeoMag, a system designed to enhance cell mechanics assays in substrate deformation studies. NeoMag uses multidomain magneto-active materials to mechanically actuate the substrate, transmitting reversible mechanical cues to cells. The system boasts full flexibility in alternating loading substrate deformation modes, seamlessly adapting to both upright and inverted microscopes. The multidomain substrates facilitate mechanobiology assays on 2D and 3D cultures. The integration of the system with nanoindenters allows for precise evaluation of cellular mechanical properties under varying substrate deformation modes. The system is used to study the impact of substrate deformation on astrocytes, simulating mechanical conditions akin to traumatic brain injury and ischemic stroke. The results reveal local heterogeneous changes in astrocyte stiffness, influenced by the orientation of subcellular regions relative to substrate strain. These stiffness variations, exceeding 50% in stiffening and softening, and local deformations significantly alter calcium dynamics. Furthermore, sustained deformations induce actin network reorganization and activate Piezo1 channels, leading to an initial increase followed by a long-term inhibition of calcium events. Conversely, fast and dynamic deformations transiently activate Piezo1 channels and disrupt the actin network, causing long-term cell softening. These findings unveil mechanical and functional alterations in astrocytes during substrate deformation, illustrating the multiple opportunities this technology offers.

A sequential macrophage activation strategy for bone regeneration: A micro/nano strontium-releasing composite scaffold loaded with lipopolysaccharide

Effective tissue repair relies on the orchestration of different macrophage phenotypes, both the M2 phenotype (promotes tissue repair) and M1 phenotype (pro-inflammatory) deserve attention. In this study, we propose a sequential immune activation strategy to mediate bone regeneration, by loading lipopolysaccharide (LPS) onto the surface of a strontium (Sr) ions -contained composite scaffold, which was fabricated by combining Sr-doped micro/nano-hydroxyapatite (HA) and dual degradable matrices of polycaprolactone (PCL) and poly (lactic-co-glycolic acid) (PLGA). Our strategy involves the sequential release of LPS to promote macrophage homing and induce the expression of the pro-inflammatory M1 phenotype, followed by the release of Sr ions to suppress inflammation. In vitro and in vivo experiments demonstrated that, the appropriate pro-inflammatory effects at the initial stage of implantation, along with the anti-inflammatory effects at the later stage, as well as the structural stability of the scaffolds conferred by the composition, can synergistically promote the regeneration and repair of bone defects.

Exploring the Link Between Autophagy-Lysosomal Dysfunction and Early Heterotopic Ossification in Tendons

Heterotopic ossification (HO), the pathological formation of bone within soft tissues such as tendon and muscle, is a notable complication resulting from severe injury. While soft tissue injury is necessary for HO development, the specific molecular pathology responsible for trauma-induced HO remains a mystery. The previous study detected abnormal autophagy function in the early stages of tendon HO. Nevertheless, it remains to be determined whether autophagy governs the process of HO generation. Here, trauma-induced tendon HO model is used to investigate the relationship between autophagy and tendon calcification. In the early stages of tenotomy, it is observed that autophagic flux is significantly impaired and that blocking autophagic flux promoted the development of more rampant calcification. Moreover, Gt(ROSA)26sor transgenic mouse model experiments disclosed lysosomal acid dysfunction as chief reason behind impaired autophagic flux. Stimulating V-ATPase activity reinstated both lysosomal acid functioning and autophagic flux, thereby reversing tendon HO. This present study demonstrates that autophagy-lysosomal dysfunction triggers HO in the stages of tendon injury, with potential therapeutic targeting implications for HO.

Engineering Biomaterials to Model Immune-Tumor Interactions In Vitro

Engineered biomaterial scaffolds are becoming more prominent in research laboratories to study drug efficacy for oncological applications in vitro, but do they have a place in pharmaceutical drug screening pipelines? The low efficacy of cancer drugs in phase II/III clinical trials suggests that there are critical mechanisms not properly accounted for in the pre-clinical evaluation of drug candidates. Immune cells associated with the tumor may account for some of these failures given recent successes with cancer immunotherapies; however, there are few representative platforms to study immune cells in the context of cancer as traditional 2D culture is typically monocultures and humanized animal models have a weakened immune composition. Biomaterials that replicate tumor microenvironmental cues may provide a more relevant model with greater in vitro complexity. In this review, the authors explore the pertinent microenvironmental cues that drive tumor progression in the context of the immune system, discuss how these cues can be incorporated into hydrogel design to culture immune cells, and describe progress toward precision oncological drug screening with engineered tissues.

ECM-inspired calcium/zinc laden cellulose scaffold for enhanced bone regeneration

Cellulose-based polymer scaffolds are highly diverse for designing and fabricating artificial bone substitutes. However, realizing the multi-biological functions of cellulose-based scaffolds has long been challenging. In this work, inspired by the structure and function of the extracellular matrix (ECM) of bone, we developed a novel yet feasible strategy to prepare ECM-like scaffolds with hybrid calcium/zinc mineralization. The 3D porous structure was formed via selective oxidation and freeze drying of bacterial cellulose. Following the principle of electrostatic interaction, calcium/zinc hybrid hydroxyapatite nucleated, crystallized, and precipitated on the 3D scaffold in simulated physiological conditions, which was well confirmed by morphology and composition analysis. Compared with alternative scaffold cohorts, this hybrid ion-loaded cellulose scaffold exhibited a pronounced elevation in alkaline phosphatase (ALP) activity, osteogenic gene expression, and cranial defect regeneration. Notably, the hybrid ion-loaded cellulose scaffold effectively fostered an M2 macrophage milieu and had a strong immune effect in vivo. In summary, this study developed a hybrid multifunctional cellulose-based scaffold that appropriately simulates the ECM to regulate immunomodulatory and osteogenic differentiation, setting a measure for artificial bone substitutes.

Modulating extracellular matrix stiffness: a strategic approach to boost cancer immunotherapy

The interplay between extracellular matrix (ECM) stiffness and the tumor microenvironment is increasingly recognized as a critical factor in cancer progression and the efficacy of immunotherapy. This review comprehensively discusses the key factors regulating ECM remodeling, including the activation of cancer-associated fibroblasts and the accumulation and crosslinking of ECM proteins. Furthermore, it provides a detailed exploration of how ECM stiffness influences the behaviors of both tumor and immune cells. Significantly, the impact of ECM stiffness on the response to various immunotherapy strategies, such as immune checkpoint blockade, adoptive cell therapy, oncolytic virus therapy, and therapeutic cancer vaccines, is thoroughly examined. The review also addresses the challenges in translating research findings into clinical practice, highlighting the need for more precise biomaterials that accurately mimic the ECM and the development of novel therapeutic strategies. The insights offered aim to guide future research, with the potential to enhance the effectiveness of cancer immunotherapy modalities.

Application of Cinnamomum burmannii Essential Oil in Promoting Wound Healing

Skin wounds, leading to infections and death, have a huge negative impact on healthcare systems around the world. Antibacterial therapy and the suppression of excessive inflammation help wounds heal. To date, the application of wound dressings, biologics and biomaterials (hydrogels, epidermal growth factor, stem cells, etc.) is limited due to their difficult and expensive preparation process. Cinnamomum burmannii (Nees & T. Nees) Blume is an herb in traditional medicine, and its essential oil is rich in D-borneol, with antibacterial and anti-inflammatory effects. However, it is not clear whether Cinnamomum burmannii essential oil has the function of promoting wound healing. This study analyzed 32 main components and their relative contents of essential oil using GC-MS. Then, network pharmacology was used to predict the possible targets of this essential oil in wound healing. We first proved this essential oil's effects in vitro and in vivo. Cinnamomum burmannii essential oil could not only promote the proliferation and migration of skin stromal cells, but also promote M2-type polarization of macrophages while inhibiting the expression of pro-inflammatory cytokines. This study explored the possible mechanism by which Cinnamomum burmannii essential oil promotes wound healing, providing a cheap and effective strategy for promoting wound healing.

Anti-Acidification and Immune Regulation by Nano-Ceria-Loaded Mg-Al Layered Double Hydroxide for Rheumatoid Arthritis Therapy

Rheumatoid arthritis (RA) is a chronic autoimmune disease featuring an abnormal immune microenvironment and resultant accumulation of hydrogen ions (H+ ) produced by activated osteoclasts (OCs). Currently, clinic RA therapy can hardly achieve sustained or efficient therapeutic outcomes due to the failures in generating sufficient immune modulation and manipulating the accumulation of H+ that deteriorates bone damage. Herein, a highly effective immune modulatory nanocatalytic platform, nanoceria-loaded magnesium aluminum layered double hydroxide (LDH-CeO2 ), is proposed for enhanced immune modulation based on acid neutralization and metal ion inherent bioactivity. Specifically, the mild alkaline LDH initiates significant M2 repolarization of macrophages triggered by the elevated antioxidation effect of CeO2 via neutralizing excessive H+ in RA microenvironment, thus resulting in the efficient recruitment of regulatory T cell (Treg) and suppressions on T helper 17 cell (Th 17) and plasma cells. Moreover, the osteogenic activity is stimulated by the Mg ion released from LDH, thereby promoting the damaged bone healing. The encouraging therapeutic outcomes in adjuvant-induced RA model mice demonstrate the high feasibility of such a therapeutic concept, which provides a novel and efficient RA therapeutic modality by the immune modulatory and bone-repairing effects of inorganic nanocatalytic material.

Regulating Chondro-Bone Metabolism for Treatment of Osteoarthritis via High-Permeability Micro/Nano Hydrogel Microspheres

Destruction of cartilage due to the abnormal remodeling of subchondral bone (SB) leads to osteoarthritis (OA), and restoring chondro-bone metabolic homeostasis is the key to the treatment of OA. However, traditional intra-articular injections for the treatment of OA cannot directly break through the cartilage barrier to reach SB. In this study, the hydrothermal method is used to synthesize ultra-small size (≈5 nm) selenium-doped carbon quantum dots (Se-CQDs, SC), which conjugated with triphenylphosphine (TPP) to create TPP-Se-CQDs (SCT). Further, SCT is dynamically complexed with hyaluronic acid modified with aldehyde and methacrylic anhydride (AHAMA) to construct highly permeable micro/nano hydrogel microspheres (SCT@AHAMA) for restoring chondro-bone metabolic homeostasis. In vitro experiments confirmed that the selenium atoms scavenged reactive oxygen species (ROS) from the mitochondria of mononuclear macrophages, inhibited osteoclast differentiation and function, and suppressed early chondrocyte apoptosis to maintain a balance between cartilage matrix synthesis and catabolism. In vivo experiments further demonstrated that the delivery system inhibited osteoclastogenesis and H-vessel invasion, thereby regulating the initiation and process of abnormal bone remodeling and inhibiting cartilage degeneration in SB. In conclusion, the micro/nano hydrogel microspheres based on ultra-small quantum dots facilitate the efficient penetration of articular SB and regulate chondro-bone metabolism for OA treatment.

Matrix stiffness affects tumor-associated macrophage functional polarization and its potential in tumor therapy

The extracellular matrix (ECM) plays critical roles in cytoskeletal support, biomechanical transduction and biochemical signal transformation. Tumor-associated macrophage (TAM) function is regulated by matrix stiffness in solid tumors and is often associated with poor prognosis. ECM stiffness-induced mechanical cues can activate cell membrane mechanoreceptors and corresponding mechanotransducers in the cytoplasm, modulating the phenotype of TAMs. Currently, tuning TAM polarization through matrix stiffness-induced mechanical stimulation has received increasing attention, whereas its effect on TAM fate has rarely been summarized. A better understanding of the relationship between matrix stiffness and macrophage function will contribute to the development of new strategies for cancer therapy. In this review, we first introduced the overall relationship between macrophage polarization and matrix stiffness, analyzed the changes in mechanoreceptors and mechanotransducers mediated by matrix stiffness on macrophage function and tumor progression, and finally summarized the effects of targeting ECM stiffness on tumor prognosis to provide insight into this new field.

Shish-kebab structure fiber with nano and micro diameter regulate macrophage polarization for anti-inflammatory and bone differentiation

Biopolymer grafts often have limited biocompatibility, triggering excessive inflammatory responses similar to foreign bodies. Macrophage phenotype shifts are pivotal in the inflammatory response and graft success. The effects of the morphology and physical attributes of the material itself on macrophage polarization should be the focus. In this study, we prepared electrospun fibers with diverse diameters and formed a shish-kebab (SK) structure on the material surface by solution-induced crystallization, forming electrospun fiber scaffolds with diverse pore sizes and roughness. In vitro cell culture experiments demonstrated that SK structure fibers could regulate macrophage differentiation toward M2 phenotype, and the results of in vitro simulation of in vivo tissue reconstruction by the microenvironment demonstrated that the paracrine role of M2 phenotype macrophages could promote bone marrow mesenchymal stem cells (BMSCs) to differentiate into osteoblasts. In rats implanted with a subcutaneous SK-structured fiber scaffold, the large-pore size and low-stiffness SK fiber scaffolds demonstrated superior immune performance, less macrophage aggregation, and easier differentiation to the anti-inflammatory M2 phenotype. Large pore sizes and low-stiffness SK fiber scaffolds guide the morphological design of biological scaffolds implanted in vivo, which is expected to be an effective strategy for reducing inflammation when applied to graft materials in clinical settings.

Emerging advances in hydrogel-based therapeutic strategies for tissue regeneration

Significant developments in cell therapy and biomaterial science have broadened the therapeutic landscape of tissue regeneration. Tissue damage is a complex biological process in which different types of cells play a specific role in repairing damaged tissues and growth factors strictly regulate the activity of these cells. Hydrogels have become promising biomaterials for tissue regeneration if appropriate materials are selected and the hydrogel properties are well-regulated. Importantly, they can be used as carriers for living cells and growth factors due to the high water-holding capacity, high permeability, and good biocompatibility of hydrogels. Cell-loaded hydrogels can play an essential role in treating damaged tissues and open new avenues for cell therapy. There is ample evidence substantiating the ability of hydrogels to facilitate the delivery of cells (stem cell, macrophage, chondrocyte, and osteoblast) and growth factors (bone morphogenetic protein, transforming growth factor, vascular endothelial growth factor and fibroblast growth factor). This paper reviewed the latest advances in hydrogels loaded with cells or growth factors to promote the reconstruction of tissues. Furthermore, we discussed the shortcomings of the application of hydrogels in tissue engineering to promote their further development.

Exploring the Role of Spatial Confinement in Immune Cell Recruitment and Regeneration of Skin Wounds

Microporous annealed particle (MAP) scaffolds are injectable granular materials comprised of micron sized hydrogel particles (microgels). The diameter of these microgels directly determines the size of the interconnected void space between particles where infiltrating or encapsulated cells reside. This tunable porosity allows the authors to use MAP scaffolds to study the impact of spatial confinement (SC) on both cellular behaviors and the host response to biomaterials. Despite previous studies showing that pore size and SC influence cellular phenotypes, including mitigating macrophage inflammatory response, there is still a gap in knowledge regarding how SC within a biomaterial modulates immune cell recruitment in vivo in wounds and implants. Thus, the immune cell profile within confined and unconfined biomaterials is studied using small (40 µm), medium (70 µm), and large (130 µm) diameter spherical microgels, respectively. This work uncovered that MAP scaffolds impart regenerative wound healing with an IgG1-biased Th2 response. MAP scaffolds made with large microgels promote a balanced pro-regenerative macrophage response, resulting in enhanced wound healing with mature collagen regeneration and reduced inflammation levels.

Recent advances in immunomodulatory hydrogels biomaterials for bone tissue regeneration

There is a high incidence of fractures in clinical practice and therapy. The repairment of critical size defects in the skeletal system remains a huge challenge for surgeons and researchers, which can be overcame by the application of bone tissue-engineered biomaterials. An increasing number of investigations have revealed that the immune system plays a vital role in the repair of bone defects, especially macrophages, which can modulate the integration of biomaterials and bone regeneration in multiple ways. Therefore, it has become increasingly important in regenerative medicine to regulate macrophage polarization to prevent inflammation caused by biomaterial implantation. Recent studies have stressed the importance of hydrogel-based modifications and the incorporation of various cellular and molecular signals for regulating immune responses to promote bone tissue regeneration and integrate biomaterials. In this review, we first elaborate briefly on the described the general physiological mechanism and process of bone tissue regeneration. Then, we summarized the immunomodulatory role macrophages play in bone repair. In addition, the role of hydrogel-based immune modification targeting macrophage modulation in accelerating and enhancing bone tissue regeneration was also discussed. Finally, we highlighted future directions and research strategies related to hydrogel optimization for the regulation of the immune response during bone regeneration and healing.

Material matters: exploring the interplay between natural biomaterials and host immune system

Biomaterials are widely used for various medical purposes, for instance, implants, tissue engineering, medical devices, and drug delivery systems. Natural biomaterials can be obtained from proteins, carbohydrates, and cell-specific sources. However, when these biomaterials are introduced into the body, they trigger an immune response which may lead to rejection and failure of the implanted device or tissue. The immune system recognizes natural biomaterials as foreign substances and triggers the activation of several immune cells, for instance, macrophages, dendritic cells, and T cells. These cells release pro-inflammatory cytokines and chemokines, which recruit other immune cells to the implantation site. The activation of the immune system can lead to an inflammatory response, which can be beneficial or detrimental, depending on the type of natural biomaterial and the extent of the immune response. These biomaterials can also influence the immune response by modulating the behavior of immune cells. For example, biomaterials with specific surface properties, such as charge and hydrophobicity, can affect the activation and differentiation of immune cells. Additionally, biomaterials can be engineered to release immunomodulatory factors, such as anti-inflammatory cytokines, to promote a tolerogenic immune response. In conclusion, the interaction between biomaterials and the body's immune system is an intricate procedure with potential consequences for the effectiveness of therapeutics and medical devices. A better understanding of this interplay can help to design biomaterials that promote favorable immune responses and minimize adverse reactions.

Macrophages and fibroblasts in foreign body reactions: How mechanical cues drive cell functions?

Biomaterials, when implanted in the human body, can induce a series of cell- and cytokine-related reactions termed foreign body reactions (FBRs). In the progression of FBRs, macrophages regulate inflammation and healing by polarizing to either a pro-inflammatory or pro-healing phenotype and recruit fibroblasts by secreting cytokines. Stimulated by the biomaterials, fibrotic capsule is formed eventually. The implant, along with its newly formed capsule, introduces various mechanical cues that influence cellular functions. Mechanosensing proteins, such as integrins or ion channels, transduce extracellular mechanical signals into cytoplasm biochemical signals in response to mechanical stimuli. Consequently, the morphology, migration mode, function, and polarization state of the cells are affected. Modulated by different intracellular signaling pathways and their crosstalk, the expression of fibrotic genes increases with fibroblast activation and fibroblast to myofibroblast transition under stiff or force stimuli. However, summarized in most current studies, the outcomes of macrophage polarization in the effect of different mechanical cues are inconsistent. The underlying mechanisms should be investigated with more advanced technology and considering more interfering aspects. Further research is needed to determine how to modulate the progression of fibrotic capsule formation in FBR artificially.

Elucidating osseointegration in vivo in 3D printed scaffolds eliciting different foreign body responses

Osseointegration between biomaterial and bone is critical for the clinical success of many orthopaedic and dental implants. However, the mechanisms of in vivo interfacial bonding formation and the role of immune cells in this process remain unclear. In this study, we investigated the bone-scaffold material interfaces in two different 3D printed porous scaffolds (polymer/hydroxyapatite and sintered hydroxyapatite) that elicited different levels of foreign body response (FBR). The polymer/hydroxyapatite composite scaffolds elicited more intensive FBR, which was evidenced by more FBR components, such as macrophages/foreign body giant cells and fibrous tissue, surrounding the material surface. Sintered hydroxyapatite scaffolds showed less intensive FBR compared to the composite scaffolds. The interfacial bonding appeared to form via new bone first forming within the pores of the scaffolds followed by growing towards strut surfaces. In contrast, it was previously thought that bone regeneration starts at biomaterial surfaces via osteogenic stem/progenitor cells first attaching to them. The material-bone interface of the less immunogenic hydroxyapatite scaffolds was heterogenous across all samples, evidenced by the coexistence of osseointegration and FBR components. The presence of FBR components appeared to inhibit osseointegration. Where FBR components were present there was no osseointegration. Our results offer new insight on the in vivo formation of bone-material interface, which highlights the importance of minimizing FBR to facilitate osseointegration for the development of better orthopaedic and dental biomaterials.

Targeting macrophage M1 polarization suppression through PCAF inhibition alleviates autoimmune arthritis via synergistic NF-κB and H3K9Ac blockade

Sustained inflammatory invasion leads to joint damage and progressive disability in several autoimmune rheumatic diseases. In recent decades, targeting M1 macrophage polarization has been suggested as a promising therapeutic strategy for autoimmune arthritis. P300/CBP-associated factor (PCAF) is a histone acetyltransferase (HAT) that exhibits a strong positive relationship with the proinflammatory microenvironment. However, whether PCAF mediates M1 macrophage polarization remains poorly studied, and whether targeting PCAF can protect against autoimmune arthritis in vivo remains unclear. Commonly used drugs can cause serious side effects in patients because of their extensive and nonspecific distribution in the human body. One strategy for overcoming this challenge is to develop drug nanocarriers that target the drug to desirable regions and reduce the fraction of drug that reaches undesirable targets. In this study, we demonstrated that PCAF inhibition could effectively inhibit M1 polarization and alleviate arthritis in mice with collagen-induced arthritis (CIA) via synergistic NF-κB and H3K9Ac blockade. We further designed dextran sulfate (DS)-based nanoparticles (DSNPs) carrying garcinol (a PCAF inhibitor) to specifically target M1 macrophages in inflamed joints of the CIA mouse model via SR-A-SR-A ligand interactions. Compared to free garcinol, garcinol-loaded DSNPs selectively targeted M1 macrophages in inflamed joints and significantly improved therapeutic efficacy in vivo. In summary, our study indicates that targeted PCAF inhibition with nanoparticles might be a promising strategy for treating autoimmune arthritis via M1 macrophage polarization inhibition.

Modulation of macrophages by biophysical cues in health and beyond

Macrophages play a key role in tissue development and homeostasis, innate immune defence against microbes or tumours, and restoring homeostasis through tissue regeneration following infection or injury. The ability to adopt such diverse functions is due to their heterogeneous nature, which is driven largely by their developmental origin and their response to signals they encounter from the microenvironment. The most well-characterized signals driving macrophage phenotype and function are biochemical and metabolic. However, the way macrophages sense and respond to their extracellular biophysical environment is becoming increasingly recognized in the field of mechano-immunology. These biophysical cues can be signals from tissue components, such as the composition and charge of extracellular matrix or topography, elasticity, and stiffness of the tissue surrounding cells; and mechanical forces such as shear stress or stretch. Macrophages are important in determining whether a disease resolves or becomes chronic. Ageing and diseases such as cancer or fibrotic disorders are associated with significant changes in the tissue biophysical environment, and this provides signals that integrate with those from biochemical and metabolic stimuli to ultimately dictate the overall function of macrophages. This review provides a brief overview of macrophage polarization, followed by a selection of commonly recognized physiological and applied biophysical stimuli impacting macrophage activity, and the potential signalling mechanisms driving downstream responses. The effects of biophysical cues on macrophages' function in homeostasis and disease and the associated clinical implications are also highlighted.

A Case for Material Stiffness as a Design Parameter in Encapsulated Islet Transplantation

Diabetes is a disease that plagues over 463 million people globally. Approximately 40 million of these patients have type 1 diabetes mellitus (T1DM), and the global incidence is increasing by up to 5% per year. T1DM is where the body's immune system attacks the pancreas, specifically the pancreatic beta cells, with antibodies to prevent insulin production. Although current treatments such as exogenous insulin injections have been successful, exorbitant insulin costs and meticulous administration present the need for alternative long-term solutions to glucose dysregulation caused by diabetes. Encapsulated islet transplantation (EIT) is a tissue-engineered solution to diabetes. Donor islets are encapsulated in a semipermeable hydrogel, allowing the diffusion of oxygen, glucose, and insulin but preventing leukocyte infiltration and antibody access to the transplanted cells. Although successful in small animal models, EIT is still far from commercial use owing to necessary long-term systemic immunosuppressants and consistent immune rejection. Most published research has focused on tailoring the characteristics of the capsule material to promote clinical viability. However, most studies have been limited in scope to biochemical changes. Current mechanobiology studies on the effect of substrate stiffness on the function of leukocytes, especially macrophages-primary foreign body response (FBR) orchestrators, show promise in tailoring a favorable response to tissue-engineered therapies such as EIT. In this review, we explore strategies to improve the clinical viability of EIT. A brief overview of the immune system, the FBR, and current biochemical approaches will be elucidated throughout this exploration. Furthermore, an argument for using substrate stiffness as a capsule design parameter to increase EIT efficacy and clinical viability will be posed.

Mechanosensory feedback loops during chronic inflammation

Epithelial tissues are crucial to maintaining healthy organization and compartmentalization in various organs and act as a first line of defense against infection in barrier organs such as the skin, lungs and intestine. Disruption or injury to these barriers can lead to infiltration of resident or foreign microbes, initiating local inflammation. One often overlooked aspect of this response is local changes in tissue mechanics during inflammation. In this mini-review, we summarize known molecular mechanisms linking disruption of epithelial barrier function to mechanical changes in epithelial tissues. We consider direct mechanisms, such as changes in the secretion of extracellular matrix (ECM)-modulating enzymes by immune cells as well as indirect mechanisms including local activation of fibroblasts. We discuss how these mechanical changes can modulate local immune cell activity and inflammation and perturb epithelial homeostasis, further dysregulating epithelial barrier function. We propose that this two-way relationship between loss of barrier function and altered tissue mechanics can lead to a positive feedback loop that further perpetuates inflammation. We discuss this cycle in the context of several chronic inflammatory diseases, including inflammatory bowel disease (IBD), liver disease and cancer, and we present the modulation of tissue mechanics as a new framework for combating chronic inflammation.

Material Stiffness in Cooperation with Macrophage Paracrine Signals Determines the Tenogenic Differentiation of Mesenchymal Stem Cells

Stiffness is an important physical property of biomaterials that determines stem cell fate. Guiding stem cell differentiation via stiffness modulation has been considered in tissue engineering. However, the mechanism by which material stiffness regulates stem cell differentiation into the tendon lineage remains controversial. Increasing evidence demonstrates that immune cells interact with implanted biomaterials and regulate stem cell behaviors via paracrine signaling; however, the role of this mechanism in tendon differentiation is not clear. In this study, polydimethylsiloxane (PDMS) substrates with different stiffnesses are developed, and the tenogenic differentiation of mesenchymal stem cells (MSCs) exposed to different stiffnesses and macrophage paracrine signals is investigated. The results reveal that lower stiffnesses facilitates tenogenic differentiation of MSCs, while macrophage paracrine signals at these stiffnesses suppress the differentiation. When exposed to these two stimuli, MSCs still exhibit enhanced tendon differentiation, which is further elucidated by global proteomic analysis. Following subcutaneous implantation in rats for 2 weeks, soft biomaterial induces only low inflammation and promotes tendon-like tissue formation. In conclusion, the study demonstrates that soft, rather than stiff, material has a greater potential to guide tenogenic differentiation of stem cells, which provides comprehensive evidence for optimized bioactive scaffold design in tendon tissue engineering.

dECM based dusal-responsive vascular graft with enzyme-controlled adenine release for long-term patency

Rapid occlusion is the culprit leading to implantation failure of biological blood vessels. Although adenosine is a clinical-proven drug to overcome the problem, its short half-life and turbulent burst-release limit its direct application. Thus, a pH/temperature dual-responsive blood vessel possessed controllable long-term adenosine secretion was constructed based on acellular matrix via compact crosslinking by oxidized chondroitin sulfate (OCSA) and functionalized with apyrase and acid phosphatase. These enzymes, as adenosine micro-generators, controlled the adenosine release amount by "real-time-responding" to acidity and temperature of vascular inflammation sites. Additionally, the macrophage phenotype was switched from M1 to M2, and related factors expression proved that adenosine release was effectively regulated with the severity of inflammation. What's more, the ultra-structure for degradation resisting and endothelialization accelerating was also preserved by their "double-crosslinking". Therefore, this work suggested a new feasible strategy providing a bright future of long-term patency for transplanted blood vessels.

Multisized Photoannealable Microgels Regulate Cell Spreading, Aggregation, and Macrophage Phenotype through Microporous Void Space

Microgels are an emerging platform for in vitro models and guiding cell fate due to their inherent porosity and tunability. This work describes a light-based technique for rapidly annealing microgels across a range of diameters. Utilizing 8-arm poly(ethylene) glycol-vinyl sulfone, the number of arms available for crosslinking, functionalization, and annealing is stoichiometrically controlled. Small and large microgels are fabricated to explore how microgel diameter impacts void space and the role of porosity on cell spreading, cell aggregation, and macrophage polarization. Mesenchymal stromal cells spread rapidly in both formulations, yet the smaller microgels permit a higher cell density. When seeded with macrophages, the smaller microgels promote an M1 phenotype, while larger microgels promote an M2 phenotype. As another application, the inherent porosity of annealed microgels is leveraged to induce cell aggregation. Finally, the microgels are implanted to examine how different size microgels influence endogenous cell invasion and macrophage polarization. The use of ultraviolet light allows for microgels to be noninvasively injected into a desired mold or wound defect before annealing, and microgels of different properties combined to create a heterogeneous scaffold. This approach is clinically relevant given its tunability and fast annealing time.

Tumor-associated macrophages induce inflammation and drug resistance in a mechanically tunable engineered model of osteosarcoma

The tumor microenvironment is a complex and dynamic ecosystem composed of various physical cues and biochemical signals that facilitate cancer progression, and tumor-associated macrophages are especially of interest as a treatable target due to their diverse pro-tumorigenic functions. Engineered three-dimensional models of tumors more effectively mimic the tumor microenvironment than monolayer cultures and can serve as a platform for investigating specific aspects of tumor biology within a controlled setting. To study the combinatorial effects of tumor-associated macrophages and microenvironment mechanical properties on osteosarcoma, we co-cultured human osteosarcoma cells with macrophages within biomaterials-based bone tumor niches with tunable stiffness. In the first 24 h of direct interaction between the two cell types, macrophages induced an inflammatory environment consisting of high concentrations of tumor necrosis factor alpha (TNFα) and interleukin (IL)-6 within moderately stiff scaffolds. Expression of Yes-associated protein (YAP), but not its homolog, transcriptional activator with PDZ-binding motif (TAZ), in osteosarcoma cells was significantly higher than in macrophages, and co-culture of the two cells slightly upregulated YAP in both cells, although not to a significant degree. Resistance to doxorubicin treatment in osteosarcoma cells was correlated with inflammation in the microenvironment, and signal transducer and activator of transcription 3 (STAT3) inhibition diminished the inflammation-related differences in drug resistance but ultimately did not improve the efficacy of doxorubicin. This work highlights that the biochemical cues conferred by tumor-associated macrophages in osteosarcoma are highly variable, and signals derived from the immune system should be considered in the development and testing of novel drugs for cancer.

Exploring the Role of Spatial Confinement in Immune Cell Recruitment and Regeneration of Skin Wounds

Microporous annealed particle (MAP) scaffolds are injectable granular materials comprised of micron sized hydrogel particles (microgels). The diameter of these microgels directly determines the size of the interconnected void space between particles where infiltrating or encapsulated cells reside. This tunable porosity allows us to use MAP scaffolds to study the impact of spatial confinement (SC) on both cellular behaviors and the host response to biomaterials. Despite previous studies showing that pore size and SC influence cellular phenotypes, including mitigating the macrophage inflammatory response, there is still a gap in knowledge regarding how SC within a biomaterial modulates immune cell recruitment in vivo in wounds and implants. Thus, we studied the immune cell profile within confined and unconfined biomaterials using small (40 μm), medium (70 μm), and large (130 μm) diameter spherical microgels, respectively. We discovered that MAP scaffolds imparted regenerative wound healing with an IgG1-biased Th2 response. MAP scaffolds generated from 130 μm diameter microgels have a median pore size that can accommodate ∼40 µm diameter spheres induced a more balanced pro-regenerative macrophage response and better wound healing outcomes with more mature collagen regeneration and reduced levels of inflammation.

Mechanical homeostasis imbalance in hepatic stellate cells activation and hepatic fibrosis

Chronic liver disease or repeated damage to hepatocytes can give rise to hepatic fibrosis. Hepatic fibrosis (HF) is a pathological process of excessive sedimentation of extracellular matrix (ECM) proteins such as collagens, glycoproteins, and proteoglycans (PGs) in the hepatic parenchyma. Changes in the composition of the ECM lead to the stiffness of the matrix that destroys its inherent mechanical homeostasis, and a mechanical homeostasis imbalance activates hepatic stellate cells (HSCs) into myofibroblasts, which can overproliferate and secrete large amounts of ECM proteins. Excessive ECM proteins are gradually deposited in the Disse gap, and matrix regeneration fails, which further leads to changes in ECM components and an increase in stiffness, forming a vicious cycle. These processes promote the occurrence and development of hepatic fibrosis. In this review, the dynamic process of ECM remodeling of HF and the activation of HSCs into mechanotransduction signaling pathways for myofibroblasts to participate in HF are discussed. These mechanotransduction signaling pathways may have potential therapeutic targets for repairing or reversing fibrosis.

Inflammation Responses to Bone Scaffolds under Mechanical Stimuli in Bone Regeneration

Physical stimuli play an important role in one tissue engineering. Mechanical stimuli, such as ultrasound with cyclic loading, are widely used to promote bone osteogenesis; however, the inflammatory response under physical stimuli has not been well studied. In this paper, the signaling pathways related to inflammatory responses in bone tissue engineering are evaluated, and the application of physical stimulation to promote osteogenesis and its related mechanisms are reviewed in detail; in particular, how physical stimulation alleviates inflammatory responses during transplantation when employing a bone scaffolding strategy is discussed. It is concluded that physical stimulation (e.g., ultrasound and cyclic stress) helps to promote osteogenesis while reducing the inflammatory response. In addition, apart from 2D cell culture, more consideration should be given to the mechanical stimuli applied to 3D scaffolds and the effects of different force moduli while evaluating inflammatory responses. This will facilitate the application of physiotherapy in bone tissue engineering.

Hyperglycemic Conditions Enhance the Mechanosensitivity of Proinflammatory RAW264.7 Macrophages

Macrophages are a primary contributor to the orchestration and severity of the foreign body response. As phagocytes and antigen-presenting cells, macrophages engage foreign objects, producing chemokines, degrading enzymes, and proinflammatory cytokines, including tumor necrosis factor-alpha (TNF-α) and interleukin-6 (IL-6). Encapsulated islet transplantation (EIT) is a return of function therapy in which donor insulin-secreting cells are encased in a biomaterial and implanted into a diabetic patient to regulate blood glucose levels. However, the foreign body response by macrophages to the encapsulated islet allograft may cause rejection. Recent studies have shown that substrate stiffness affects macrophage activity, which can inform EIT capsule design. However, due to the dysregulation of glucose maintenance in diabetic patients, varying from normoglycemic to hypoglycemic or hyperglycemic conditions, it is imperative to determine if glucose dysregulation affects macrophage mechanosensitivity to EIT biomaterials. This study explores the relationship between glucose metabolism and mechanosensitivity and the ultimate impact on proinflammatory macrophage function in static hyperglycemic and normoglycemic conditions. Using a 2-dimensional (2D) polyacrylamide model of 3-order magnitude in stiffness, 2, 15, and 274 kPa Young's moduli, the effect of glycemic condition on the mechanosensitive characteristics of unstimulated and proinflammatory RAW264.7 macrophage function in vitro using lipopolysaccharide (LPS) was examined. Hyperglycemic conditions were found to impact macrophage response to substrate stiffness significantly. Notably, TNF-α secretion was significantly reduced as substrate stiffness increased in LPS-stimulated hyperglycemic conditions, whereas normoglycemic macrophages held similar secretion across all stiffnesses. Stiffness-influenced differences in cytokine secretion were also induced in IL-6 secretion by hyperglycemic conditions. Hyperglycemic conditions promoted a biphasic trend in IL-6 cytokine secretion and gene expression by proinflammatory macrophages with significantly decreased production when cultured on 15 kPa compared to production on 2 and 274 kPa. Although hyperglycemic conditions drastically increased IL-10 secretion, stiffness-influenced differences were not shown when compared to the same glycemic condition. Furthermore, under LPS stimulation, lactate secretion had an inverse relationship to TNF-α secretion. However, no significant stiffness-influenced difference was demonstrated in glucose transporter 1 (GLUT1) expression, glucose uptake, or GAPDH. These findings suggest that hyperglycemic conditions enhance the mechanosensitivity of proinflammatory macrophages and should be explored further. Impact statement The work presented increases our understanding of the effect of glycemic condition on macrophage mechanosensitivity related to substrate stiffness. This has ramifications on the design of material-based therapies, such as encapsulated islet transplantation, for type 1 diabetic patients who experience glycemic dysregulation.

BMP-2 functional polypeptides relieve osteolysis via bi-regulating bone formation and resorption coupled with macrophage polarization

Osteolysis caused by wear debris around the prosthesis is the main reason for aseptic loosening. Extending prosthetic service life is still challenging. In this study, we first synthesized a bone morphogenetic protein-2 (BMP-2) functional polypeptide (BMP2pp), and evaluated the effects of BMP2pp on macrophage polarization and impaired osteogenesis caused by titanium (Ti) particles in vitro. Then, we delineated the impact of BMP2pp on bone formation and resorption in a mouse calvarial bone osteolysis model induced by Ti particles. The results showed that BMP2pp not only alleviated the Ti-induced inhibition of osteoblastic differentiation in human placenta-derived mesenchymal stem cells (hPMSCs) but also prevented Ti-induced M1 macrophage polarization and promoted M2 macrophage differentiation in mice. Conditioned medium from BMP2pp-activated macrophages increased the osteogenesis of hPMSCs. The western blot results indicated a significant decrease in the expression of NF-κB inducing kinase (NIK) and phospho-NF-κB p65 in bone marrow-derived macrophages treated with BMP2pp. Furthermore, we clarified the protective effect of BMP2pp on bone formation and the reduction in bone resorption coupled with the immunomodulatory properties of calvarial osteolysis in mice. In summary, BMP2pp ameliorated the Ti-mediated impairment in osteogenic potential of hPMSCs, suppressed the M1 polarization of macrophages by inhibiting the activation of the NF-κB signaling pathway, and ameliorated Ti-induced bone osteolysis. Our research suggests that BMP2pp may be a potential option for treating prosthetic loosening induced by wear debris from prostheses.

Biomaterial scaffolds regulate macrophage activity to accelerate bone regeneration

Bones are important for maintaining motor function and providing support for internal organs. Bone diseases can impose a heavy burden on individuals and society. Although bone has a certain ability to repair itself, it is often difficult to repair itself alone when faced with critical-sized defects, such as severe trauma, surgery, or tumors. There is still a heavy reliance on metal implants and autologous or allogeneic bone grafts for bone defects that are difficult to self-heal. However, these grafts still have problems that are difficult to circumvent, such as metal implants that may require secondary surgical removal, lack of bone graft donors, and immune rejection. The rapid advance in tissue engineering and a better comprehension of the physiological mechanisms of bone regeneration have led to a new focus on promoting endogenous bone self-regeneration through the use of biomaterials as the medium. Although bone regeneration involves a variety of cells and signaling factors, and these complex signaling pathways and mechanisms of interaction have not been fully understood, macrophages undoubtedly play an essential role in bone regeneration. This review summarizes the design strategies that need to be considered for biomaterials to regulate macrophage function in bone regeneration. Subsequently, this review provides an overview of therapeutic strategies for biomaterials to intervene in all stages of bone regeneration by regulating macrophages.

Heparin-mimicking polymer-based hydrogel matrix regulates macrophage polarization by controlling cell adhesion

The physicochemical properties of biomaterials influence cell adhesion, shape, and polarization of macrophages. In this study, we aimed to evaluate the polarization of macrophages in terms of the regulation of cell adhesion and how synthetic mimics for heparin and poly(sodium-4-styrenesulfonate) can regulate macrophage polarization by modulating cell shape, focal adhesion, cell traction force, and intracellular tension. Our initial findings showed that macrophages cultured with heparin-mimicking polymer-based hydrogel matrix showed reduced expression of cell adhesion markers such as integrins, vinculin, RhoA, and ROCK1/2 and reduced cell shape, elongation, cell-matrix traction force, and intracellular tension. Furthermore, we observed a significant decrease in cell adhesion in cells cultured on the hydrogel, resulting in the promotion of M1 polarization. These findings offer insights into the important roles of cell-matrix interactions in macrophage polarization and offer a platform for heparin-mimicking polymer-based hydrogel matrices to induce M1 polarization by inducing cell adhesion without classical activators.

Macrophages modulate stiffness-related foreign body responses through plasma membrane deformation

Implants are widely used in medical applications and yet macrophage-mediated foreign body reactions caused by implants severely impact their therapeutic effects. Although the extensive use of multiple surface modifications has been introduced to provide some mitigation of fibrosis, little is known about how macrophages recognize the stiffness of the implant and thus influence cell behaviors. Here, we demonstrated that macrophage stiffness sensing leads to differential inflammatory activation, resulting in different degrees of fibrosis. The potential mechanism for macrophage stiffness sensing in the early adhesion stages tends to involve cell membrane deformations on substrates with different stiffnesses. Combining theory and experiments, we show that macrophages exert traction stress on the substrate through adhesion and altered membrane curvature, leading to the uneven distribution of the curvature-sensing protein Baiap2, resulting in cytoskeleton remodeling and inflammation inhibition. This study introduces a physical model feedback mechanism for early cellular stiffness sensing based on cell membrane deformation, offering perspectives for future material design and targeted therapies.

Platinum-Based TREM2 Inhibitor Suppresses Tumors by Remodeling the Immunosuppressive Microenvironment

Triggering receptor expressed on myeloid cells-2 (TREM2) is a key pro-tumorigenic marker of tumor-infiltrating macrophages, showing potent immunosuppressive activity in tumor microenvironment. A platinum(IV) complex OPA derived from oxaliplatin (OP) and artesunate (ART) exhibited direct cytotoxicity against human colon cancer cells and immunomodulatory activity to inhibit TREM2 on macrophages in vitro and vivo. Furthermore, OPA deterred the tumor growth in mouse models bearing MC38 colorectal tumor by reducing the number of CD206⁺ and CX₃ CR1⁺ immunosuppressive macrophages; it also promoted the expansion and infiltration of immunostimulatory dendritic, cytotoxic T, and natural killer cells. OPA is the first small-molecular TREM2 inhibitor capable of relieving immunosuppressive tumor microenvironment and enhancing chemical anticancer efficiency of a platinum drug, thus showing typical characteristics of a chemoimmunotherapeutic agent.

Sericin/Nano-Hydroxyapatite Hydrogels Based on Graphene Oxide for Effective Bone Regeneration via Immunomodulation and Osteoinduction

Background

Immune responses and osteogenesis differentiation induced by implants are crucial for bone tissue regeneration. Consideration of only one of those properties is not sufficient. To investigate the synergistic actions, we designed alginate/graphene oxide/sericin/nanohydroxyapatite (Alg/GO/Ser/nHAP) nanocomposite hydrogels with both osteoimmunomodulatory and osteoinductive activities. This study aimed to explore the effect of hydrogel with osteoimmunomodulatory properties on promoting osteogenesis of bone marrow stem cells (BMSCs).

Methods

Alg/GO/Ser/nHAP nanocomposite hydrogel was fabricated and was characterized by SEM, FTIR, XRD, stress-strain, rheology, swelling and degradation. After the impact of sericin on M2 macrophage polarization was identified, the BMSCs viability and adhesion were evaluated by CCK8 assay, live/dead staining, cytoskeleton staining. The cell osteogenic differentiation was observed by ALP/ARS staining, immunofluorescence staining, RT-PCR, and Western blotting, respectively. Rat cranial defect model was used to assess osteoimmunomodulatory effects of scaffolds in vivo by micro‑computed tomographic, histological, and immunohistochemical analyses after 8 weeks of healing.

Results

In vitro experiments revealed that the hydrogel presented desirable mechanical strength, stability, porosity, and biocompatibility. Significantly, sericin and nHAP appeared to exert synergistic effects on bone regeneration. Sericin was observed to inhibit the immune response by inducing macrophage M2-type polarization to create a positive osteoimmune microenvironment, contributing to improving osseointegration at the bone-implant interface to promote osteogenesis. However, the osteogenic differentiation in rat BMSCs was further enhanced by combining nHAP and sericin in the nanocomposite hydrogel. Eventually, the hydrogel was implanted into the rat cranial defect model, assisting in the reduction of local inflammation and efficient bone regeneration.

Conclusion

The nanocomposite hydrogel stimulated bone formation by the synergistic effects of immunomodulation of macrophage polarization by sericin and direct osteogenic induction by nHAP, demonstrating that such a scaffold that modulates the osteoimmune microenvironment to promote osteogenesis is a promising approach for the development of bone tissue engineering implants in the future.

Extracellular matrix stiffness-The central cue for skin fibrosis

Skin fibrosis is a physiopathological process featuring the excessive deposition of extracellular matrix (ECM), which is the main architecture that provides structural support and constitutes the microenvironment for various cellular behaviors. Recently, increasing interest has been drawn to the relationship between the mechanical properties of the ECM and the initiation and modulation of skin fibrosis, with the engagement of a complex network of signaling pathways, the activation of mechanosensitive proteins, and changes in immunoregulation and metabolism. Simultaneous with the progression of skin fibrosis, the stiffness of ECM increases, which in turn perturbs mechanical and humoral homeostasis to drive cell fate toward an outcome that maintains and enhances the fibrosis process, thus forming a pro-fibrotic "positive feedback loop". In this review, we highlighted the central role of the ECM and its dynamic changes at both the molecular and cellular levels in skin fibrosis. We paid special attention to signaling pathways regulated by mechanical cues in ECM remodeling. We also systematically summarized antifibrotic interventions targeting the ECM, hopefully enlightening new strategies for fibrotic diseases.

Tuning immunity through tissue mechanotransduction

Immune responses are governed by signals from the tissue microenvironment, and in addition to biochemical signals, mechanical cues and forces arising from the tissue, its extracellular matrix and its constituent cells shape immune cell function. Indeed, changes in biophysical properties of tissue alter the mechanical signals experienced by cells in many disease conditions, in inflammatory states and in the context of ageing. These mechanical cues are converted into biochemical signals through the process of mechanotransduction, and multiple pathways of mechanotransduction have been identified in immune cells. Such pathways impact important cellular functions including cell activation, cytokine production, metabolism, proliferation and trafficking. Changes in tissue mechanics may also represent a new form of 'danger signal' that alerts the innate and adaptive immune systems to the possibility of injury or infection. Tissue mechanics can change temporally during an infection or inflammatory response, offering a novel layer of dynamic immune regulation. Here, we review the emerging field of mechanoimmunology, focusing on how mechanical cues at the scale of the tissue environment regulate immune cell behaviours to initiate, propagate and resolve the immune response.

Continuously released Zn2+ in 3D-printed PLGA/β-TCP/Zn scaffolds for bone defect repair by improving osteoinductive and anti-inflammatory properties

Long-term nonunion of bone defects has always been a major problem in orthopedic treatment. Artificial bone graft materials such as Poly (lactic-co-glycolic acid)/β-tricalcium phosphate (PLGA/β-TCP) scaffolds are expected to solve this problem due to their suitable degradation rate and good osteoconductivity. However, insufficient mechanical properties, lack of osteoinductivity and infections after implanted limit its large-scale clinical application. Hence, we proposed a novel bone repair bioscaffold by adding zinc submicron particles to PLGA/β-TCP using low temperature rapid prototyping 3D printing technology. We first screened the scaffolds with 1 wt% Zn that had good biocompatibility and could stably release a safe dose of zinc ions within 16 weeks to ensure long-term non-toxicity. As designed, the scaffold had a multi-level porous structure of biomimetic cancellous bone, and the Young's modulus (63.41 ± 1.89 MPa) and compressive strength (2.887 ± 0.025 MPa) of the scaffold were close to those of cancellous bone. In addition, after a series of in vitro and in vivo experiments, the scaffolds proved to have no adverse effects on the viability of BMSCs and promoted their adhesion and osteogenic differentiation, as well as exhibiting higher osteogenic and anti-inflammatory properties than PLGA/β-TCP scaffold without zinc particles. We also found that this osteogenic and anti-inflammatory effect might be related to Wnt/β-catenin, P38 MAPK and NFkB pathways. This study lay a foundation for the follow-up study of bone regeneration mechanism of Zn-containing biomaterials. We envision that this scaffold may become a new strategy for clinical treatment of bone defects.

Biophysical heterogeneity of myeloid-derived microenvironment to regulate resistance to cancer immunotherapy

Despite the advances in immunotherapy for cancer treatment, patients still obtain limited benefits, mostly owing to unrestrained tumour self-expansion and immune evasion that exploits immunoregulatory mechanisms. Traditionally, myeloid cells have a dominantly immunosuppressive role. However, the complicated populations of the myeloid cells and their multilateral interactions with tumour/stromal/lymphoid cells and physical abnormalities in the tumour microenvironment (TME) determine their heterogeneous functions in tumour development and immune response. Tumour-associated myeloid cells (TAMCs) include monocytes, tumour-associated macrophages (TAMs), myeloid-derived suppressor cells (MDSCs), dendritic cells (DCs), and granulocytes. Single-cell profiling revealed heterogeneous TAMCs composition, sub-types, and transcriptomic signatures across 15 human cancer types. We systematically reviewed the biophysical heterogeneity of TAMC composition and pro/anti-tumoral and immuno-suppressive/stimulating properties of myeloid-derived microenvironments. We also summarised comprehensive clinical strategies to overcome resistance to immunotherapy from three dimensions: targeting TAMCs, reversing physical abnormalities, utilising nanomedicines, and finally, put forward futuristic perspectives for scientific and clinical research.

Blocking TRPV4 Ameliorates Osteoarthritis by Inhibiting M1 Macrophage Polarization via the ROS/NLRP3 Signaling Pathway

Osteoarthritis (OA) is a low-level inflammatory disease in which synovial macrophage M1 polarization exacerbates the progression of synovitis and OA. Notedly, the ROS (reactive oxygen species) level in macrophages is intimately implicated in macrophage M1 polarization. TRPV4 (transient receptor potential channel subfamily V member 4), as an ion channel, plays a pivotal role in oxidative stress and inflammation. In this study, we investigated the role of TRPV4 in OA progression and M1 macrophage polarization. Male adult Sprague-Dawley (SD) rats underwent a medial meniscus radial transection operation to create an OA model in vivo and RAW 264.7 cells were intervened with 100 ng/mL LPS (lipopolysaccharide) to induce M1-polarized macrophages in vitro. We demonstrated that the infiltration of M1 synovial macrophages and the expression of TRPV4 were increased significantly in OA synovium. In addition, intra-articular injection of HC067074 (a specific inhibitor of TRPV4) alleviated the progression of rat OA and significantly decreased synovial macrophage M1 polarization. Further mechanisms suggested that ROS production by M1 macrophages was decreased after TRPV4 inhibition. In addition, NLRP3 (pyrin domain containing protein 3) as a downstream effector of ROS in M1-polarized macrophage, was significantly suppressed following TRPV4 inhibition. In conclusion, this study discovered that inhibition of TRPV4 delays OA progression by inhibiting M1 synovial macrophage polarization through the ROS/NLRP3 pathway.

Mechanosensing in macrophages and dendritic cells in steady-state and disease

Macrophages and dendritic cells are myeloid cells that play critical roles in immune responses. Macrophages help to maintain homeostasis through tissue regeneration and the clearance of dead cells, but also mediate inflammatory processes against invading pathogens. As the most potent antigen-presenting cells, dendritic cells are important in connecting innate to adaptive immune responses via activation of T cells, and inducing tolerance under physiological conditions. While it is known that macrophages and dendritic cells respond to biochemical cues in the microenvironment, the role of extracellular mechanical stimuli is becoming increasingly apparent. Immune cell mechanotransduction is an emerging field, where accumulating evidence suggests a role for extracellular physical cues coming from tissue stiffness in promoting immune cell recruitment, activation, metabolism and inflammatory function. Additionally, many diseases such as pulmonary fibrosis, cardiovascular disease, cancer, and cirrhosis are associated with changes to the tissue biophysical environment. This review will discuss current knowledge about the effects of biophysical cues including matrix stiffness, topography, and mechanical forces on macrophage and dendritic cell behavior under steady-state and pathophysiological conditions. In addition, we will also provide insight on molecular mediators and signaling pathways important in macrophage and dendritic cell mechanotransduction.

Fabrication Strategies Towards Hydrogels for Biomedical Application: Chemical and Mechanical Insights

This review aims at giving selected chemical and mechanical insights on design criteria that should be taken into account in hydrogel production for biomedical applications. Particular emphasis will be given to the chemical aspects involved in hydrogel design: macromer chemical composition, cross-linking strategies and chemistry towards "conventional" and smart/stimuli responsive hydrogels. Mechanical properties of hydrogels in view of regenerative medicine applications will also be considered.

Recent advances in nanomedicines for regulation of macrophages in wound healing

Macrophages are essential immune cells and play a major role in the immune response as pro-inflammatory or anti-inflammatory agents depending on their plasticity and functions. Infiltration and activation of macrophages are usually involved in wound healing. Herein, we first described macrophage polarization and their critical functions in wound healing process. It is addressed how macrophages collaborate with other immune cells in the wound microenvironment. Targeting macrophages by manipulating or re-educating macrophages in inflammation using nanomedicines is a novel and feasible strategy for wound management. We discussed the design and physicochemical properties of nanomaterials and their functions for macrophages activation and anti-inflammatory signaling during wound therapy. The mechanism of action of the strategies and appropriate examples are also summarized to highlight the pros and cons of those approaches. Finally, the potential of nanomedicines to modulate macrophage polarization for skin regeneration is discussed.

Engineering immunomodulatory hydrogels and cell-laden systems towards bone regeneration

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

Functionalized 3D scaffolds for engineering the hematopoietic niche

Hematopoietic stem cells (HSCs) reside in a subzone of the bone marrow (BM) defined as the hematopoietic niche where, via the interplay of differentiation and self-renewal, they can give rise to immune and blood cells. Artificial hematopoietic niches were firstly developed in 2D in vitro cultures but the limited expansion potential and stemness maintenance induced the optimization of these systems to avoid the total loss of the natural tissue complexity. The next steps were adopted by engineering different materials such as hydrogels, fibrous structures with natural or synthetic polymers, ceramics, etc. to produce a 3D substrate better resembling that of BM. Cytokines, soluble factors, adhesion molecules, extracellular matrix (ECM) components, and the secretome of other niche-resident cells play a fundamental role in controlling and regulating HSC commitment. To provide biochemical cues, co-cultures, and feeder-layers, as well as natural or synthetic molecules were utilized. This review gathers key elements employed for the functionalization of a 3D scaffold that demonstrated to promote HSC growth and differentiation ranging from 1) biophysical cues, i.e., material, topography, stiffness, oxygen tension, and fluid shear stress to 2) biochemical hints favored by the presence of ECM elements, feeder cell layers, and redox scavengers. Particular focus is given to the 3D systems to recreate megakaryocyte products, to be applied for blood cell production, whereas HSC clinical application in such 3D constructs was limited so far to BM diseases testing.

The Culture Dish Surface Influences the Phenotype and Dissociation Strategy in Distinct Mouse Macrophage Populations

The nature of the culture dish surface and the technique used to detach adherent cells could very likely influence the cell viability and cell membrane protein integrity of harvested macrophages. Several previous studies assessed the detachment efficacies of enzymatic and non-enzymatic methods for harvesting the single cell suspensions of macrophages, but a comprehensive study assessing different dissociation methods and culture conditions for detaching functionally different macrophage populations has not yet been reported. In this study, via the well-established GM-CSF and M-CSF differentiated bone marrow derived macrophage models (GM-BMDMs and M-BMDMs), we compared four commonly used enzymatic (trypsin and accutase) and non-enzymatic (PBS and EDTA) dissociation methods along with necessary mechanical detaching steps (scraping and pipetting) to evaluate the viable cell recovery and cell surface marker integrality of GM-BMDMs and M-BMDMs cultured on standard cell culture dish (TC dish), or on culture dish (noTC dish) that was not conditioned to enhance adherence. The data showed that accutase yielded a better recovery of viable cells comparing with PBS and EDTA, especially for tightly adherent GM-BMDMs on TC dishes, with a relatively higher level of detected cell membrane marker F4/80 than trypsin. An additional gradient centrifugation-based dead cell removal approach could increase the proportion of viable cells for TC cultured GM-BMDMs after accutase dissociation. Furthermore, transcriptome analysis was performed to evaluate the putative influence of culture dishes. At steady state, BMDMs cultured on noTC dishes exhibited more proinflammatory gene expression signatures (e.g. IL6, CXCL2 and ILlβ) and functions (e.g. TNF and IL17 signaling pathways). Similar inflammatory responses were observed upon LPS challenge regardless of culture conditions and differentiation factors. However, in LPS treated samples, the difference of gene expression patterns, signaling pathways and molecular functions between TC and noTC cultured BMDMs were largely dependent on the types of growth factors (M-CSF and GM-CSF). This observation might provide valuable information for in vitro macrophage studies.

Two-Photon Polymerization of 2.5D and 3D Microstructures Fostering a Ramified Resting Phenotype in Primary Microglia

Microglia are the resident macrophages of the central nervous system and contribute to maintaining brain’s homeostasis. Current 2D “petri-dish” in vitro cell culturing platforms employed for microglia, are unrepresentative of the softness or topography of native brain tissue. This often contributes to changes in microglial morphology, exhibiting an amoeboid phenotype that considerably differs from the homeostatic ramified phenotype in healthy brain tissue. To overcome this problem, multi-scale engineered polymeric microenvironments are developed and tested for the first time with primary microglia derived from adult rhesus macaques. In particular, biomimetic 2.5D micro- and nano-pillar arrays (diameters = 0.29–1.06 µm), featuring low effective shear moduli (0.25–14.63 MPa), and 3D micro-cages (volume = 24 × 24 × 24 to 49 × 49 × 49 μm³) with and without micro- and nano-pillar decorations (pillar diameters = 0.24–1 µm) were fabricated using two-photon polymerization (2PP). Compared to microglia cultured on flat substrates, cells growing on the pillar arrays exhibit an increased expression of the ramified phenotype and a higher number of primary branches per ramified cell. The interaction between the cells and the micro-pillar-decorated cages enables a more homogenous 3D cell colonization compared to the undecorated ones. The results pave the way for the development of improved primary microglia in vitro models to study these cells in both healthy and diseased conditions.