Wnt signaling modulates macrophage polarization and is regulated by biomaterial surface properties

Wnt signalling in oral and maxillofacial diseases

Wnts include more than 19 types of secreted glycoproteins that are involved in a wide range of pathological processes in oral and maxillofacial diseases. The transmission of Wnt signalling from the extracellular matrix into the nucleus includes canonical pathways and noncanonical pathways, which play an important role in tooth development, alveolar bone regeneration, and related diseases. In recent years, with the in-depth study of Wnt signalling in oral and maxillofacial-related diseases, many new conclusions and perspectives have been reached, and there are also some controversies. This article aims to summarise the roles of Wnt signalling in various oral diseases, including periodontitis, dental pulp disease, jaw disease, cleft palate, and abnormal tooth development, to provide researchers with a better and more comprehensive understanding of Wnts in oral and maxillofacial diseases.

Control of innate immune response by biomaterial surface topography, energy, and stiffness

As the focus of implantable biomaterials has shifted from bioinert implants to bioactive designs, recent research has highlighted the complex interactions between cell physiologic systems and material properties, particularly physical cues. From the cells known to interact with implanted biomaterials, the response of the immune system has been a critical target of study recently. Here, we review studies characterizing the response of innate immune cells to various material cues, particularly of those at the surface of implanted materials.The innate immune system consists of cell types with various roles in inflammation. Neutrophils and macrophages serve both phagocytic and signaling roles, especially early in the inflammatory phase of biomaterial implantation. These cell types ultimately dictate the outcome of implants as chronic inflammation, fibrosis, or integration. Other cell types like dendritic cells, mast cells, natural killer cells, and innate lymphoid cells may also serve an immunomodulatory role in the biomaterial context. This review highlights recent advances in our understanding of the role of innate immunity in the response to implantable biomaterials as well as key mechanobiological findings in innate immune cells underpinning these advances. STATEMENT OF SIGNIFICANCE: This review highlights recent advances in the understanding of the role of innate immunity in the response to implantable biomaterials, especially in neutrophils and macrophages, as well as key mechanobiological findings in innate immune cells underpinning these advances. Here we discuss how physicochemical properties of biomaterials control innate immune cell behavior.

Hyaluronic Acid-Dexamethasone Nanoparticles for Local Adjunct Therapy of Lung Inflammation

The delivery of a dexamethasone formulation directly into the lung appears as an appropriate strategy to strengthen the systemic administration, reducing the dosage in the treatment of lung severe inflammations. For this purpose, a hyaluronic acid-dexamethasone formulation was developed, affording an inhalable reconstituted nanosuspension suitable to be aerosolized. The physico-chemical and biopharmaceutical properties of the formulation were tested: size, stability, loading of the spray-dried dry powder, reconstitution capability upon redispersion in aqueous media. Detailed structural insights on nanoparticles after reconstitution were obtained by light and X-ray scattering techniques. (1) The size of the nanoparticles, around 200 nm, is in the proper range for a possible engulfment by macrophages. (2) Their structure is of the core-shell type, hosting dexamethasone nanocrystals inside and carrying hyaluronic acid chains on the surface. This specific structure allows for nanosuspension stability and provides nanoparticles with muco-inert properties. (3) The nanosuspension can be efficiently aerosolized, allowing for a high drug fraction potentially reaching the deep lung. Thus, this formulation represents a promising tool for the lung administration via nebulization directly in the pipe of ventilators, to be used as such or as adjunct therapy for severe lung inflammation.

Transcription Factor-7-Like-2 (TCF7L2) in Atherosclerosis: A Potential Biomarker and Therapeutic Target

Transcription factor-7-like-2 (TCF7L2), a vital member of the T-cell factor/lymphoid enhancer factor (TCF/LEF) family, plays an important role in normal human physiological and pathological processes. TCF7L2 exhibits multiple anti-atherosclerotic effects through the activation of specific molecular mechanisms, including regulation of metabolic homeostasis, macrophage polarization, and neointimal hyperplasia. A single-nucleotide substitution of TCF7L2, rs7903146, is a genetic high-risk factor for type 2 diabetes and indicates susceptibility to cardiovascular disease as a link between metabolic disorders and atherosclerosis. In this review, we summarize the anti-atherosclerosis effect and novel mechanisms underlying the function of TCF7L2 to elucidate its potential as an anti-atherosclerosis biomarker and provide a novel therapeutic target for cardiovascular diseases.

Mesenchymal stem cell exosomal tsRNA-21109 alleviate systemic lupus erythematosus by inhibiting macrophage M1 polarization

Systemic lupus erythematosus (SLE) is a chronic autoimmune disease with M1-type macrophage activation. Mesenchymal stem cells (MSCs) therapies have shown promise in models of pathologies relevant to SLE, while the function and mechanism of MSC-derived exosomes (MSC-exo) were still unclear. We aimed to interrogate the effect of MSC-exo on M1-type polarization of macrophage and investigate mechanisms underlying MSC-exo. Exosomes were isolated from MSC and the effect of MSC-exo on macrophage polarization was evaluated. The key tRNA-derived fragments (tRFs) carried by exosomes were identified by small RNA sequencing and verified in clinical samples. The effect of exosomal-tRFs on macrophage polarization was examined. In this study, MSC-exo dramatically suppressed expression of M1 markers, and reduced the levels of TNF-α and IL-1β, while increased M2 markers in macrophages. A total of 243 differently expressed tRFs (DEtRFs) were identified between MSC-exo treated and untreated macrophage, among which 103 DEtRFs were up-regulated in response to MSC-exo treatment, including tsRNA-21109. The target genes of tsRNA-21109 were mainly enriched in DNA transcription-related GO function, and mainly involved in inflammatory-related pathways, including Rap1, Ras, Hippo, Wnt, MAPK, TGF-beta signaling pathway. The tsRNA-21109 was lowly expressed in clinical samples and was associated with the patient data in SLE. Compared to the normal MSC-exo, the tsRNA-21109-privative MSC-exo up-regulated M1 marker (CD80, NOS2, MCP1) and down-regulated M2 marker (CD206, ARG1, MRC2), also increased the levels of TNF-α and IL-1β in macrophages. Western blot and immunofluorescence confirmed that the proportion of CD80/ARG-1 was increased in macrophages treated with tsRNA-21109-privatived MSC-exo compared to that with control MSC-exo. In conclusion, MSC-exo inhibited the M1-type polarization of macrophages, possibly through transferring tsRNA-21109, which may develop as a novel therapeutic target for SLE.

Modulating immune microenvironment during bone repair using biomaterials: Focusing on the role of macrophages

Bone is a self-regenerative tissue that can repair small defects and fractures. In large defects, bone tissue is unable to provide nutrients and oxygen for repair, and autologous grafting is used as the gold standard. As an alternative method, the bone tissue regeneration approach uses osteoconductive biomaterials to overcome bone graft disadvantages. However, biomaterials are considered as foreign components that can stimulate host immune responses. Although traditional principles have been aimed to minimize immune reactions, the design of biomaterials has steadily shifted toward creating an immunomodulatory microenvironment to harness immune cells and responses to repair damaged tissue. Among immune cells, macrophages secrete various immunomodulatory mediators and crosstalk with bone-forming cells and play key roles in bone tissue engineering. Macrophage polarization toward M1 and M2 subtypes mediate pro-inflammatory and anti-inflammatory responses, respectively, which are crucial for bone repairing at different stages. This review provides an overview of the crosstalk between various immune cells and biomaterials, macrophage polarization, and the effect of physicochemical properties of biomaterials on the immune responses, especially macrophages, in bone tissue engineering.

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.

Candida albicans/Macrophage Biointerface on Human and Porcine Decellularized Adipose Matrices

Macrophages, cells effective in sensing, internalizing and killing Candida albicans, are intertwined with the extracellular matrix (ECM) through different signals, which include the release of specific cytokines. Due to the importance of these interactions, the employment of in vitro models mimicking a fungal infection scenario is essential to evaluate the ECM effects on the macrophage response. In this work, we have analyzed the effects of human and porcine decellularized adipose matrices (DAMs), obtained by either enzymatic or organic solvent treatment, on the macrophage/Candida albicans interface. The present study has allowed us to detect differences on the activation of macrophages cultured on either human- or porcine-derived DAMs, evidencing changes in the macrophage actin cytoskeleton, such as distinct F-actin-rich membrane structures to surround the pathogen. The macrophage morphological changes observed on these four DAMs are key to understand the defense capability of these cells against this fungal pathogen. This work has contributed to the knowledge of the influence that the extracellular matrix and its components can exert on macrophage metabolism, immunocompetence and capacity to respond to the microenvironment in a possible infection scenario.

Host Response to Biomaterials for Cartilage Tissue Engineering: Key to Remodeling

Biomaterials play a core role in cartilage repair and regeneration. The success or failure of an implanted biomaterial is largely dependent on host response following implantation. Host response has been considered to be influenced by numerous factors, such as immune components of materials, cytokines and inflammatory agents induced by implants. Both synthetic and native materials involve immune components, which are also termed as immunogenicity. Generally, the innate and adaptive immune system will be activated and various cytokines and inflammatory agents will be consequently released after biomaterials implantation, and further triggers host response to biomaterials. This will guide the constructive remolding process of damaged tissue. Therefore, biomaterial immunogenicity should be given more attention. Further understanding the specific biological mechanisms of host response to biomaterials and the effects of the host-biomaterial interaction may be beneficial to promote cartilage repair and regeneration. In this review, we summarized the characteristics of the host response to implants and the immunomodulatory properties of varied biomaterial. We hope this review will provide scientists with inspiration in cartilage regeneration by controlling immune components of biomaterials and modulating the immune system.

Bioactive Ibuprofen-Loaded PLGA Coatings for Multifunctional Surface Modification of Medical Devices

To modulate the biofunctionality of implantable medical devices commonly used in clinical practice, their surface modification with bioactive polymeric coatings is an attractive and successful emerging strategy. Biodegradable coatings based on poly(lactic acid-co-glycolic acid), PLGA, represent versatile and safe candidates for surface modification of implantable biomaterials and devices, providing additional tunable ability for topical delivery of desired therapeutic agents. In the present study, Ibuprofen-loaded PLGA coatings (PLGA/IBUP) were obtained by using the dip-coating and drop-casting combined protocol. The composite materials demonstrated long-term drug release under biologically simulated dynamic conditions. Reversible swelling phenomena of polymeric coatings occurred in the first two weeks of testing, accompanied by the gradual matrix degradation and slow release of the therapeutic agent. Irreversible degradation of PLGA coatings occurred after one month, due to copolymer's hydrolysis (evidenced by chemical and structural modifications). After 30 days of dynamic testing, the cumulative release of IBUP was ~250 µg/mL. Excellent cytocompatibility was revealed on human-derived macrophages, fibroblasts and keratinocytes. The results herein evidence the promising potential of PLGA/IBUP coatings to be used for surface modification of medical devices, such as metallic implants and wound dressings.

Tailoring Materials for Modulation of Macrophage Fate

Human immune system acts as a pivotal role in the tissue homeostasis and disease progression. Immunomodulatory biomaterials that can manipulate innate immunity and adaptive immunity hold great promise for a broad range of prophylactic and therapeutic purposes. This review is focused on the design strategies and principles of immunomodulatory biomaterials from the standpoint of materials science to regulate macrophage fate, such as activation, polarization, adhesion, migration, proliferation, and secretion. It offers a comprehensive survey and discussion on the tunability of material designs regarding physical, chemical, biological, and dynamic cues for modulating macrophage immune response. The range of such tailorable cues encompasses surface properties, surface topography, materials mechanics, materials composition, and materials dynamics. The representative immunoengineering applications selected herein demonstrate how macrophage-immunomodulating biomaterials are being exploited for cancer immunotherapy, infection immunotherapy, tissue regeneration, inflammation resolution, and vaccination. A perspective on the future research directions of immunoregulatory biomaterials is also provided.

Substrate stiffness induces neutrophil extracellular trap (NET) formation through focal adhesion kinase activation

Neutrophils predominate the early inflammatory response to tissue injury and implantation of biomaterials. Recent studies have shown that neutrophil activation can be regulated by mechanical cues such as stiffness or surface wettability; however, it is not known how neutrophils sense and respond to physical cues, particularly how they form neutrophil extracellular traps (NET formation). To examine this, we used polydimethylsiloxane (PDMS) substrates of varying physiologically relevant stiffness (0.2-32 kPa) and examined the response of murine neutrophils to untreated surfaces or to surfaces coated with various extracellular matrix proteins recognized by integrin heterodimers (collagen, fibronectin, laminin, vitronectin, synthetic RGD). Neutrophils on higher stiffness PDMS substrates had increased NET formation and higher secretion of pro-inflammatory cytokines and chemokines. Extracellular matrix protein coatings showed that fibronectin induced the most NET formation and this effect was stiffness dependent. Synthetic RGD peptides induced similar levels of NET formation and pro-inflammatory cytokine release than the full-length fibronectin protein. To determine if the observed NET formation in response to substrate stiffness required focal adhesion kinase (FAK) activity, which is down stream of integrin activation, FAK inhibitor PF-573228 was used. Inhibition of FAK using PF-573228 ablated the stiffness-dependent increase in NET formation and pro-inflammatory molecule secretion. These findings demonstrate that neutrophils regulate NET formation in response to physical and mechanical biomaterial cues and this process is regulated through integrin/FAK signaling.

Surface characteristics on commercial dental implants differentially activate macrophages in vitro and in vivo

OBJECTIVES

Biomaterial implantation provokes an inflammatory response that controls integrative fate. M2 macrophages regulate the response to implants by resolving the inflammatory phase and recruiting progenitor cells to aid healing. We have previously shown that modified titanium (Ti) disks directly induce M2 macrophage polarization. The aim of this study was to examine macrophage response to commercially available Ti or Ti alloy implants with comparable roughness and varying hydrophilicity.

MATERIAL AND METHODS

Eleven commercially available Ti (A-F) or Ti alloy (G-K) dental implants were examined in this study. Surface topography, chemistry, and hydrophilicity were characterized for each implant. To compare the immune response in vitro, human monocyte-derived macrophages were seeded on implants and secreted pro- and anti-inflammatory proteins measured. To evaluate the inflammatory response in vivo, mice were subcutaneously instrumented with clinical implants, and implant adherent macrophage populations were characterized by flow cytometry.

RESULTS

Macrophages on hydrophobic Implant C produced the highest level of pro-inflammatory proteins in vitro. In contrast, hydrophilic Implant E produced the second-highest pro-inflammatory response. Implants F and K, both hydrophilics, produced the highest anti-inflammatory protein secretions. Likewise, pro-inflammatory CD80hi macrophages predominated in vivo on implants C and E, and M2 CD206 + macrophages predominated on implants F and K.

CONCLUSIONS

These findings show that hydrophilicity alone is insufficient to predict the anti-inflammatory effect on macrophage polarization and that other properties-surface composition or topography-determine immune modulation. This in vivo model may be a useful screening method to compare the immunomodulatory response to clinical implants of disparate geometry or size.

Modulating macrophage activities to promote endogenous bone regeneration: Biological mechanisms and engineering approaches

A coordinated interaction between osteogenesis and osteoimmune microenvironment is essential for successful bone healing. In particular, macrophages play a central regulatory role in all stages of bone repair. Depending on the signals they sense, these highly plastic cells can mediate the host immune response against the exterior signals of molecular stimuli and implanted scaffolds, to exert regenerative potency to a varying extent. In this article, we first encapsulate the immunomodulatory functions of macrophages during bone regeneration into three aspects, as sweeper, mediator and instructor. We introduce the phagocytic role of macrophages in different bone healing periods ('sweeper') and overview a variety of paracrine cytokines released by macrophages either mediating cell mobilisation, vascularisation and matrix remodelling ('mediator'), or directly driving the osteogenic differentiation of bone progenitors and bone repair ('instructor'). Then, we systematically classify and discuss the emerging engineering strategies to recruit, activate and modulate the phenotype transition of macrophages, to exploit the power of endogenous macrophages to enhance the performance of engineered bone tissue.

Modulation of immune-inflammatory responses through surface modifications of biomaterials to promote bone healing and regeneration

Control of inflammation is indispensable for optimal oral wound healing and tissue regeneration. Several biomaterials have been used to enhance the regenerative outcomes; however, the biomaterial implantation can ensure an immune-inflammatory response. The interface between the cells and the biomaterial surface plays a critical role in determining the success of soft and hard tissue regeneration. The initial inflammatory response upon biomaterial implantation helps in tissue repair and regeneration, however, persistant inflammation impairs the wound healing response. The cells interact with the biomaterials through extracellular matrix proteins leading to protein adsorption followed by recruitment, attachment, migration, and proliferation of several immune-inflammatory cells. Physical nanotopography of biomaterials, such as surface proteins, roughness, and porosity, is crucial for driving cellular attachment and migration. Similarly, modification of scaffold surface chemistry by adapting hydrophilicity, surface charge, surface coatings, can down-regulate the initiation of pro-inflammatory cascades. Besides, functionalization of scaffold surfaces with active biological molecules can down-regulate pro-inflammatory and pro-resorptive mediators' release as well as actively up-regulate anti-inflammatory markers. This review encompasses various strategies for the optimization of physical, chemical, and biological properties of biomaterial and the underlying mechanisms to modulate the immune-inflammatory response, thereby, promoting the tissue integration and subsequent soft and hard tissue regeneration potential of the administered biomaterial.

Recent Advances in Antiinflammatory Material Design

Implants and prostheses are widely used to replace damaged tissues or to treat various diseases. However, besides the risk of bacterial or fungal infection, an inflammatory response usually occurs. Here, recent progress in the field of anti-inflammatory biomaterials is described. Different materials and approaches are used to decrease the inflammatory response, including hydrogels, nanoparticles, implant surface coating by polymers, and a variety of systems for anti-inflammatory drug delivery. Complex multifunctional systems dealing with inflammation, microbial infection, bone regeneration, or angiogenesis are also described. New promising stimuli-responsive systems, such as pH- and temperature-responsive materials, are also being developed that would enable an "intelligent" antiinflammatory response when the inflammation occurs. Together, different approaches hold promise for creation of novel multifunctional smart materials allowing better implant integration and tissue regeneration.

Biomimetic Design for Bio-Matrix Interfaces and Regenerative Organs

The urgent demand for transplanted organs has motivated the development of regenerative medicine to biomimetically reconstruct the structure and function of natural tissues or organs. The prerequisites for constructing multicellular organs include specific cell sources, suitable scaffolding material, and interconnective biofunctional interfaces. As some of the most complex systems in nature, human organs, tissues, and cellular units have unique "bio-matrix" physicochemical interfaces. Human tissues support a large number of cells with distinct biofunctional interfaces for compartmentalization related to metabolism, material exchange, and physical barriers. These naturally shaped biofunctional interfaces support critical metabolic functions that drive adaptive human behavior. In contrast, mutations and disorders during organogenesis can disrupt these interfaces as a consequence of disease and trauma. To replicate the appropriate structure and physiological function of tissues and organs, the biomaterials used in these approaches should have properties that mimic those of natural biofunctional interfaces. In this review, the focus is on the biomimetic design of functional interfaces and hierarchical structures for four regenerative organs, liver, kidney, lung, heart, and the immune system. Research on these organs provides understanding of cell-matrix interactions for hierarchically bioinspired material engineering, and guidance for the design of bioartificial organs. Finally, we provide perspectives on future challenges in biofunctional interface designs and discuss the obstacles that remain toward the generation of functional bioartificial organs.

Re-establishment of macrophage homeostasis by titanium surface modification in type II diabetes promotes osseous healing

Titanium surface mediated immunomodulation may address compromised post-implantation bone healing in diabetes mellitus. To assess in vitro phenotypic changes, M1 and M2 polarised Type 2 diabetic rat (Goto Kakizaki, GK) macrophages were cultured on micro-rough (SLA) or hydrophilic nanostructured SLA (modSLA) titanium. The in vivo effects of the SLA and modSLA surfaces on macrophage phenotype, wound-associated protein expression and bone formation were investigated using a critical-sized calvarial defect model. Compared to healthy macrophages, GK M2 macrophage function was compromised, secreting significantly lower levels of the anti-inflammatory cytokine IL-10. The modSLA surface attenuated the pro-inflammatory cellular environment, reducing pro-inflammatory cytokine production and promoting M2 macrophage phenotype differentiation. ModSLA also suppressed gene expression associated with macrophage multinucleation and giant cell formation and stimulated pro-osteogenic genes in co-cultured osteoblasts. In vivo, modSLA enhanced osteogenesis compared to SLA in GK rats. During early healing, proteomic analysis of both surface adherent and wound exudate material showed that modSLA promoted an immunomodulatory pro-reparative environment. The modSLA surface therefore successfully compensated for the compromised M2 macrophage function in Type 2 diabetes by attenuating the pro-inflammatory response and promoting M2 macrophage activity, thus restoring macrophage homeostasis and resulting in a cellular environment favourable for enhanced osseous healing.

Antibacterial and Osteogenic Functionalization of Titanium With Silicon/Copper-Doped High-Energy Shot Peening-Assisted Micro-Arc Oxidation Technique

Antibacterial and osteogenic functionalization of titanium (Ti) implants will greatly expand their clinical indications in immediate implant therapy, accelerate osteointegration, and enhance long-term prognosis. We had recently shown that the high-energy shot peening (HESP)-assisted micro-arc oxidation (MAO) significantly improved the bioactivity and coating stability of Ti-based substrates. In this study, we further functionalized Ti with antibacterial and osteogenic properties by doping silicon (Si) and/or copper (Cu) ions into HESP/MAO-treated coatings. Physicochemical characterization displayed that the doping of Si and Cu in HESP/MAO-treated coatings (Si/Cu-MAO) did not significantly change their surface topography, roughness, crystal structure, coating thickness, bonding strength, and wettability. The results of X-ray photoelectron spectroscopy (XPS) showed that Si and Cu in the Si/Cu-MAO coating was in the form of silicate radical (SiO₃ ^2-) and bivalent copper (Cu²⁺), respectively. The total amounts of Si and Cu were about 13.5 and 5.8 μg/cm², which released about 33.2 and 31.3% within 14 day, respectively. Compared with the control group (MAO), Si doping samples (MAO-Si) significantly increased the cell viability, alkaline phosphatase (ALP) activity, mineralization and osteogenic genes (ALP, collagen I and osteocalcin) expression of MC3T3-E1 cells. Furthermore, the addition of Cu presented good bactericidal property against both Staphylococcus aureus and Streptococcus mutans (even under the co-culture condition of bacteria and MC3T3-E1 cells): the bacteriostatic rate of both bacteria was over 95%. In conclusion, the novel bioactive Si/Cu-MAO coating with antibacterial and osteogenic properties is a promising functionalization method for orthopedic and dental implants, especially in the immediate implant treatment with an infected socket.