Substrate stiffness directs the phenotype and polarization state of cord blood derived macrophages

Collagen-based hydrogels induce hyaline cartilage regeneration by immunomodulation and homeostasis maintenance

Type I collagen (Col I) and hyaluronic acid (HA), derived from the extracellular matrix (ECM), have found widespread application in cartilage tissue engineering. Nevertheless, the potential of cell-free collagen-based scaffolds to induce in situ hyaline cartilage regeneration and the related mechanisms remain undisclosed. Here, we chose Col I and HA to construct Col I hydrogel and Col I-HA composite hydrogel with similar mechanical properties, denoted as Col and ColHA, respectively. Their potential to induce cartilage regeneration was investigated. The results revealed that collagen-based hydrogels could regenerate hyaline cartilage without any additional cells or growth factors. Notably, ColHA hydrogel stood out in this regard. It elicited a moderate activation, recruitment, and reprogramming of macrophages, thus efficiently mitigating local inflammation. Additionally, ColHA hydrogel enhanced stem cell recruitment, facilitated their chondrogenic differentiation, and inhibited chondrocyte fibrosis, hypertrophy, and catabolism, thereby preserving cartilage homeostasis. This study augments our comprehension of cartilage tissue induction theory by enriching immune-related mechanisms, offering innovative prospects for the design of cartilage defect repair scaffolds. STATEMENT OF SIGNIFICANCE: The limited self-regeneration ability and post-injury inflammation pose significant challenges to articular cartilage repair. Type I collagen (Col I) and hyaluronic acid (HA) are extensively used in cartilage tissue engineering. However, their specific roles in cartilage regeneration remain poorly understood. This study aimed to elucidate the functions of Col I and Col I-HA composite hydrogels (ColHA) in orchestrating inflammatory responses and promoting cartilage regeneration. ColHA effectively activated and recruited macrophages, reprogramming them from an M1 to an M2 phenotype, thus alleviating local inflammation. Additionally, ColHA facilitated stem cell homing, induced chondrogenesis, and concurrently inhibited fibrosis, hypertrophy, and catabolism, collectively contributing to the maintenance of cartilage homeostasis. These findings underscore the clinical potential of ColHA for repairing cartilage defects.

Targeting Macrophage Polarization for Reinstating Homeostasis following Tissue Damage

Tissue regeneration and remodeling involve many complex stages. Macrophages are critical in maintaining micro-environmental homeostasis by regulating inflammation and orchestrating wound healing. They display high plasticity in response to various stimuli, showing a spectrum of functional phenotypes that vary from M1 (pro-inflammatory) to M2 (anti-inflammatory) macrophages. While transient inflammation is an essential trigger for tissue healing following an injury, sustained inflammation (e.g., in foreign body response to implants, diabetes or inflammatory diseases) can hinder tissue healing and cause tissue damage. Modulating macrophage polarization has emerged as an effective strategy for enhancing immune-mediated tissue regeneration and promoting better integration of implantable materials in the host. This article provides an overview of macrophages' functional properties followed by discussing different strategies for modulating macrophage polarization. Advances in the use of synthetic and natural biomaterials to fabricate immune-modulatory materials are highlighted. This reveals that the development and clinical application of more effective immunomodulatory systems targeting macrophage polarization under pathological conditions will be driven by a detailed understanding of the factors that regulate macrophage polarization and biological function in order to optimize existing methods and generate novel strategies to control cell phenotype.

Materials Strategies to Overcome the Foreign Body Response

The foreign body response (FBR) is an immune-mediated reaction that can occur with most biomaterials and biomedical devices. The FBR initiates a deterioration in the performance of implantable devices, representing a longstanding challenge that consistently hampers their optimal utilization. Over the last decade, significant strides are achieved based on either hydrogel design or surface modifications to mitigate the FBR. This review delves into recent material strategies aimed at mitigating the FBR. Further, the authors look forward to future novel anti-FBR materials from the perspective of clinical translation needs. Such prospective materials hold the potential to attenuate local immune responses, thereby significantly enhancing the overall performance of implantable devices.

Decoding the "Fingerprint" of Implant Materials: Insights into the Foreign Body Reaction

Foreign body reaction (FBR) is a prevalent yet often overlooked pathological phenomenon, particularly within the field of biomedical implantation. The presence of FBR poses a heavy burden on both the medical and socioeconomic systems. This review seeks to elucidate the protein "fingerprint" of implant materials, which is generated by the physiochemical properties of the implant materials themselves. In this review, the activity of macrophages, the formation of foreign body giant cells (FBGCs), and the development of fibrosis capsules in the context of FBR are introduced. Additionally, the relationship between various implant materials and FBR is elucidated in detail, as is an overview of the existing approaches and technologies employed to alleviate FBR. Finally, the significance of implant components (metallic materials and non-metallic materials), surface CHEMISTRY (charge and wettability), and physical characteristics (topography, roughness, and stiffness) in establishing the protein "fingerprint" of implant materials is also well documented. In conclusion, this review aims to emphasize the importance of FBR on implant materials and provides the current perspectives and approaches in developing implant materials with anti-FBR properties.

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.

Modeling mechanical activation of macrophages during pulmonary fibrogenesis for targeted anti-fibrosis therapy

Pulmonary fibrosis is an often fatal lung disease. Immune cells such as macrophages were shown to accumulate in the fibrotic lung, but their contribution to the fibrosis development is unclear. To recapitulate the involvement of macrophages in the development of pulmonary fibrosis, we developed a fibrotic microtissue model with cocultured human macrophages and fibroblasts. We show that profibrotic macrophages seeded on topographically controlled stromal tissues became mechanically activated. The resulting co-alignment of macrophages, collagen fibers, and fibroblasts promoted widespread fibrogenesis in micro-engineered lung tissues. Anti-fibrosis treatment using pirfenidone disrupts the polarization and mechanical activation of profibrotic macrophages, leading to fibrosis inhibition. Pirfenidone inhibits the mechanical activation of macrophages by suppressing integrin αMβ2 and Rho-associated kinase 2. These results demonstrate a potential pulmonary fibrogenesis mechanism at the tissue level contributed by macrophages. The cocultured microtissue model is a powerful tool to study the immune-stromal cell interactions and the anti-fibrosis drug mechanism.

Mechanobiology of myeloid cells

Tissue-resident myeloid cells sense and transduce mechanical signals such as stiffness, stretch and compression. In the past two years, our understanding of the mechanosensitive signalling pathways in myeloid cells has significantly expanded. Moreover, it is increasingly clear which mechanical signals induce myeloid cells towards a pro- or anti-inflammatory phenotype. This is especially relevant in the context of altered matrix mechanics in immune-related pathologies or in the response to implanted biomaterials. A detailed understanding of myeloid cell mechanosensing may eventually lead to more effective cell-based immunotherapies for cancer, the development of mechanically inspired therapies to target fibrosis, and the engineering of safer implants. This review covers these recent advances in the emerging field of mechanoimmunology of myeloid cells.

Fibrous capsule-resistant, controllably degradable and functionalizable zwitterion-albumin hybrid hydrogels

Foreign body response (FBR) represents an immune-mediated cascade reaction capable of inducing the rejection of foreign implants, thereby compromising their in vivo performance. Pure zwitterionic hydrogels have demonstrated the ability to resist long-term FBR, owing to their outstanding antifouling capabilities. However, achieving such a robust anti-FBR effect necessitates stringent requirements concerning the purity of zwitterionic materials, which constrains their broader functional applications. Herein, we present a biocompatible, controllably degradable, and functionalizable zwitterion-albumin hybrid hydrogel. The zwitterionic hydrogel crosslinked with serum albumin exhibits controllable degradation and excels in preventing the adsorption of various proteins and adhesion of cells and bacteria. Moreover, the hydrogel significantly alleviates the host's FBR compared with PEG hydrogels and particularly outperforms PEG-based cross-linker crosslinked zwitterionic hydrogels in reducing collagen encapsulation when subcutaneously implanted into mice. The zwitterion-albumin hybrid hydrogel shows potential as a functionalizable anti-FBR material in the context of implantable materials and biomedical devices.

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.

Umbilical Cord Blood-Derived Monocytes as A Reliable Source of Functional Macrophages for Biomedical Research

OBJECTIVE

Macrophages are multifunctional immune cells widely used in immunological research. While autologous macrophages have been widely used in several biomedical applications, allogeneic macrophages have also demonstrated similar or even superior therapeutic potential. The umbilical cord blood (UCB) is a well-described source of abundant allogenic monocytes and macrophages that is easy to collect and can be processed without invasive methods. Current monocyte isolation procedures frequently result in heterogenous cell products, with limited yields, activated cells, and high cost. This study outlines a simple isolation method that results in high yields and pure monocytes with the potential to differentiate into functional macrophages.

MATERIALS AND METHODS

In the experimental study, we describe a simple and efficient protocol to isolate highpurity monocytes. After collection of human UCB samples, we used a gradient-based procedure composed of three consecutive gradient steps: i. Hydroxyethyl starch-based erythrocytes sedimentation, followed by ii. Mononuclear cells (MNCs) isolation by Ficoll-Hypaque gradient, and iii. Separation of monocytes from lymphocytes by a slight hyperosmolar Percoll gradient (0.573 g/ml). Then the differentiation potential of isolated monocytes to pro- and antiinflammatory macrophages were evaluated in the presence of granulocyte colony-stimulating factor (GM-CSF) and macrophage CSF (M-CSF), respectively. The macrophages were functionally characterized as well.

RESULTS

A high yield of monocytes after isolation (25 to 50 million) with a high purity (>95%) could be obtained from every 100-150 ml UCB. Isolated monocytes were defined based on their phenotype and surface markers expression pattern. Moreover, they possess the ability to differentiate into pro- or anti-inflammatory macrophages with specific phenotypes, gene/surface protein markers, cytokine secretion patterns, T-cell interactions, and phagocytosis activity.

CONCLUSION

Here we describe a simple and reproducible procedure for isolation of pure monocytes from UCB, which could be utilized to provide functional macrophages as a reliable and feasible source of allogenic macrophages for biomedical research.

Modeling Mechanical Activation of Macrophages During Pulmonary Fibrogenesis for Targeted Anti-Fibrosis Therapy

Pulmonary fibrosis, as seen in idiopathic pulmonary fibrosis (IPF) and COVID-induced pulmonary fibrosis, is an often-fatal lung disease. Increased numbers of immune cells such as macrophages were shown to accumulate in the fibrotic lung, but it is unclear how they contribute to the development of fibrosis. To recapitulate the macrophage mechanical activation in the fibrotic lung tissue microenvironment, we developed a fibrotic microtissue model with cocultured human macrophages and fibroblasts. We show that profibrotic macrophages seeded on topographically controlled stromal tissue constructs become mechanically activated. The resulting co-alignment of macrophages, collagen fibers and fibroblasts promote widespread fibrogenesis in micro-engineered lung tissues. Anti-fibrosis treatment using pirfenidone disrupts the polarization and mechanical activation of profibrotic macrophages, leading to fibrosis inhibition. Pirfenidone inhibits the mechanical activation of macrophages by suppressing integrin αMβ2 (CD11b/CD18) and Rho-associated kinase 2, which is a previously unknown mechanism of action of the drug. Together, these results demonstrate a potential pulmonary fibrogenesis mechanism at the tissue level contributed by mechanically activated macrophages. We propose the coculture, force-sensing microtissue model as a powerful tool to study the complex immune-stromal cell interactions and the mechanism of action of anti-fibrosis drugs.

Destructive fibrotic teamwork: how both microenvironment stiffness and profibrotic interleukin 13 impair alveolar macrophage phenotype and function

The pulmonary fibrotic microenvironment is characterized by increased stiffness of lung tissue and enhanced secretion of profibrotic soluble cues contributing to a feedback loop that leads to dysregulated wound healing and lung failure. Pinpointing the individual and tandem effects of profibrotic stimuli in impairing immune cell response remains difficult and is needed for improved therapeutic strategies. We utilized a statistical design of experiment (DOE) to investigate how microenvironment stiffness and interleukin 13 (IL13), a profibrotic soluble factor linked with disease severity, contribute to the impaired macrophage response commonly observed in pulmonary fibrosis. We used engineered bioinspired hydrogels of different stiffness, ranging from healthy to fibrotic lung tissue, and cultured murine alveolar macrophages (MH-S cells) with or without IL13 to quantify cell response and analyze independent and synergistic effects. We found that, while both stiffness and IL13 independently influence macrophage morphology, phenotype, phagocytosis and efferocytosis, these factors work synergistically to exacerbate impaired macrophage phenotype and efferocytosis. These unique findings provide insights into how macrophages in fibrotic conditions are not as effective in clearing debris, contributing to fibrosis initiation/progression, and more broadly inform how underlying drivers of fibrosis modulate immune cell response to facilitate therapeutic strategies.

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.

From hurdle to springboard: The macrophage as target in biomaterial-based bone regeneration strategies

The past decade has seen a growing appreciation for the role of the innate immune response in mediating repair and biomaterial directed tissue regeneration. The long-held view of the host immune/inflammatory response as an obstacle limiting stem cell regenerative activity, has given way to a fresh appreciation of the pivotal role the macrophage plays in orchestrating the resolution of inflammation and launching the process of remodelling and repair. In the context of bone, work over the past decade has established an essential coordinating role for macrophages in supporting bone repair and sustaining biomaterial driven osteogenesis. In this review evidence for the role of the macrophage in bone regeneration and repair is surveyed before discussing recent biomaterial and drug-delivery based approaches that target macrophage modulation with the goal of accelerating and enhancing bone tissue regeneration.

Suppression of the fibrotic encapsulation of silicone implants by inhibiting the mechanical activation of pro-fibrotic TGF-β

The fibrotic encapsulation of implants involves the mechanical activation of myofibroblasts and of pro-fibrotic transforming growth factor beta 1 (TGF-β1). Here, we show that both softening of the implant surfaces and inhibition of the activation of TGF-β1 reduce the fibrotic encapsulation of subcutaneous silicone implants in mice. Conventionally stiff silicones (elastic modulus, ~2 MPa) coated with a soft silicone layer (elastic modulus, ~2 kPa) reduced collagen deposition as well as myofibroblast activation without affecting the numbers of macrophages and their polarization states. Instead, fibroblasts around stiff implants exhibited enhanced intracellular stress, increased the recruitment of α_v and β₁ integrins, and activated TGF-β1 signalling. In vitro, the recruitment of α_v integrin to focal adhesions and the activation of β₁ integrin and of TGF-β were higher in myofibroblasts grown on latency-associated peptide (LAP)-coated stiff silicones than on soft silicones. Antagonizing α_v integrin binding to LAP through the small-molecule inhibitor CWHM-12 suppressed active TGF-β signalling, myofibroblast activation and the fibrotic encapsulation of stiff subcutaneous implants in mice.

Inflammation Drives Stiffness Mediated Uptake of Lipoproteins in Primary Human Macrophages and Foam Cell Proliferation

Macrophage to foam cell transition and their accumulation in the arterial intima are the key events that trigger atherosclerosis, a multifactorial inflammatory disease. Previous studies have linked arterial stiffness and cardiovascular disease and have highlighted the use of arterial stiffness as a potential early-stage marker. Yet the relationship between arterial stiffness and atherosclerosis in terms of macrophage function is poorly understood. Thus, it is pertinent to understand the mechanobiology of macrophages to clarify their role in plaque advancement. We explore how substrate stiffness affects proliferation of macrophages and foam cells, traction forces exerted by macrophages and uptake of native and oxidized low-density lipoproteins. We demonstrate that stiffness influences foam cell proliferation under both naïve and inflammatory conditions. Naïve foam cells proliferated faster on the 4 kPa polyacrylamide gel and glass whereas under inflammatory conditions, maximum proliferation was recorded on glass. Macrophage and foam cell traction forces were positively correlated to the substrate stiffness. Furthermore, the influence of stiffness was demonstrated on the uptake of lipoproteins on macrophages treated with lipopolysaccharide + interferon gamma. Cells on softer 1 kPa substrates had a significantly higher uptake of low-density lipoproteins and oxidized low-density lipoproteins compared to stiffer substrates. The results herein indicate that macrophage function is modulated by stiffness and help better understand ways in which macrophages and foam cells could contribute to the development and progression of atherosclerotic plaque.

Aged Breast Extracellular Matrix Drives Mammary Epithelial Cells to an Invasive and Cancer-Like Phenotype

Age is a major risk factor for cancer. While the importance of age related genetic alterations in cells on cancer progression is well documented, the effect of aging extracellular matrix (ECM) has been overlooked. This study shows that the aging breast ECM alone is sufficient to drive normal human mammary epithelial cells (KTB21) to a more invasive and cancer-like phenotype, while promoting motility and invasiveness in MDA-MB-231 cells. Decellularized breast matrix from aged mice leads to loss of E-cadherin membrane localization in KTB21 cells, increased cell motility and invasion, and increased production of inflammatory cytokines and cancer-related proteins. The aged matrix upregulates cancer-related genes in KTB21 cells and enriches a cell subpopulation highly expressing epithelial-mesenchymal transition-related genes. Lysyl oxidase knockdown reverts the aged matrix-induced changes to the young levels; it relocalizes E-cadherin to cell membrane, and reduces cell motility, invasion, and cytokine production. These results show for the first time that the aging ECM harbors key biochemical, physical, and mechanical cues contributing to invasive and cancer-like behavior in healthy and cancer mammary cells. Differential response of cells to young and aged ECMs can lead to identification of new targets for cancer treatment and prevention.

Predicting the In Vivo Performance of Cardiovascular Biomaterials: Current Approaches In Vitro Evaluation of Blood-Biomaterial Interactions

The therapeutic efficacy of a cardiovascular device after implantation is highly dependent on the host-initiated complement and coagulation cascade. Both can eventually trigger thrombosis and inflammation. Therefore, understanding these initial responses of the body is of great importance for newly developed biomaterials. Subtle modulation of the associated biological processes could optimize clinical outcomes. However, our failure to produce truly blood compatible materials may reflect our inability to properly understand the mechanisms of thrombosis and inflammation associated with biomaterials. In vitro models mimicking these processes provide valuable insights into the mechanisms of biomaterial-induced complement activation and coagulation. Here, we review (i) the influence of biomaterials on complement and coagulation cascades, (ii) the significance of complement-coagulation interactions for the clinical success of cardiovascular implants, (iii) the modulation of complement activation by surface modifications, and (iv) in vitro testing strategies.

Glycosaminoglycan content of a mineralized collagen scaffold promotes mesenchymal stem cell secretion of factors to modulate angiogenesis and monocyte differentiation

Effective design of biomaterials to aid regenerative repair of craniomaxillofacial (CMF) bone defects requires approaches that modulate the complex interplay between exogenously added progenitor cells and cells in the wound microenvironment, such as osteoblasts, osteoclasts, endothelial cells, and immune cells. We are exploring the role of the glycosaminoglycan (GAG) content in a class of mineralized collagen scaffolds recently shown to promote osteogenesis and healing of craniofacial bone defects. We previously showed that incorporating chondroitin-6-sulfate or heparin improved mineral deposition by seeded human mesenchymal stem cells (hMSCs). Here, we examine the effect of varying scaffold GAG content on hMSC behavior, and their ability to modulate osteoclastogenesis, vasculogenesis, and the immune response. We report the role of hMSC-conditioned media produced in scaffolds containing chondroitin-6-sulfate (CS6), chondroitin-4-sulfate (CS4), or heparin (Heparin) GAGs on endothelial tube formation and monocyte differentiation. Notably, endogenous production by hMSCs within Heparin scaffolds most significantly inhibits osteoclastogenesis via secreted osteoprotegerin (OPG), while the secretome generated by CS6 scaffolds reduced pro-inflammatory immune response and increased endothelial tube formation. All conditioned media down-regulated many pro- and anti-inflammatory cytokines, such as IL6, IL-1β, and CCL18 and CCL17 respectively. Together, these findings demonstrate that modifying mineralized collagen scaffold GAG content can both directly (hMSC activity) and indirectly (production of secreted factors) influence overall osteogenic potential and mineral biosynthesis as well as angiogenic potential and monocyte differentiation towards osteoclastic and macrophage lineages. Scaffold GAG content is therefore a powerful stimulus to modulate reciprocal signaling between multiple cell populations within the bone healing microenvironment.

Implant Fibrosis and the Underappreciated Role of Myofibroblasts in the Foreign Body Reaction

Body implants and implantable medical devices have dramatically improved and prolonged the life of countless patients. However, our body repair mechanisms have evolved to isolate, reject, or destroy any object that is recognized as foreign to the organism and inevitably mounts a foreign body reaction (FBR). Depending on its severity and chronicity, the FBR can impair implant performance or create severe clinical complications that will require surgical removal and/or replacement of the faulty device. The number of review articles discussing the FBR seems to be proportional to the number of different implant materials and clinical applications and one wonders, what else is there to tell? We will here take the position of a fibrosis researcher (which, coincidentally, we are) to elaborate similarities and differences between the FBR, normal wound healing, and chronic healing conditions that result in the development of peri-implant fibrosis. After giving credit to macrophages in the inflammatory phase of the FBR, we will mainly focus on the activation of fibroblastic cells into matrix-producing and highly contractile myofibroblasts. While fibrosis has been discussed to be a consequence of the disturbed and chronic inflammatory milieu in the FBR, direct activation of myofibroblasts at the implant surface is less commonly considered. Thus, we will provide a perspective how physical properties of the implant surface control myofibroblast actions and accumulation of stiff scar tissue. Because formation of scar tissue at the surface and around implant materials is a major reason for device failure and extraction surgeries, providing implant surfaces with myofibroblast-suppressing features is a first step to enhance implant acceptance and functional lifetime. Alternative therapeutic targets are elements of the myofibroblast mechanotransduction and contractile machinery and we will end with a brief overview on such targets that are considered for the treatment of other organ fibroses.