Integrin-Mediated Interactions Control Macrophage Polarization in 3D Hydrogels

Glucose-regulated protein 94 (Grp94/gp96) in viral pathogenesis: Insights into its role and therapeutic potentials

Glucose-regulated protein 94 (Grp94/gp96) is endoplasmic reticulum (ER) resident form of the 90 kDa heat shock protein 90 (Hsp90) that is responsible for folding, maturation and stabilization of more than 400 client proteins. Grp94 has been implicated for various diseases including metastatic cancer, primary open-angle glaucoma, and infectious diseases. In fact, Grp94 plays critical roles in different stages of viral infection cycle. It chaperones receptor proteins and viral glycoproteins that are necessary for viral entry and replication. Beyond its role in protein homeostasis, Grp94 modulates host cellular processes such as apoptosis and immune responses, which are often exploited by viruses to sustain infection. This work provides an overview of the roles of Grp94 in viral pathogenesis across various viruses and its involvement in immune modulation with the development of Grp94-selective inhibitors and their potential as anti-viral therapeutics.

Mesenchymal stromal/stem cell spheroid-derived extracellular vesicles advance the therapeutic efficacy of 3D-printed vascularized artificial liver lobules in liver failure treatment

Acute liver failure (ALF) is a highly lethal condition characterized by massive tissue necrosis, excessive oxidative stress, and serious inflammatory storms, necessitating prompt medical intervention. Although hepatocyte-like cells (HLCs) derived from mesenchymal stromal/stem cells (MSCs) offer a promising alternative cell source for hepatocyte therapy, their low in-vivo integration and differentiation efficiency may compromise the eventual therapeutic efficacy. To this end, MSCs are bioengineered into multicellular spheroids in the present study. The proteomic analyses and experimental results reveal that extracellular vesicles (EVs) derived from these MSC spheroids (SpEV) contain abundant highly expressed bioactive proteins and can be efficiently endocytosed by recipient cells, resulting in enhanced pro-angiogenic and antioxidative effects. In addition, MSC spheroids exhibit superior hepatic cell differentiation compared to an equivalent number of dissociated single MSCs, particularly when being co-cultured with hexagonally patterned endothelial cells in a liver lobule-like arrangement. Following orthotopic implantation in the mouse model, the enhanced paracrine effects of SpEV, combined with an immunoregulatory decellularized extracellular matrix hydrogel carrier and functional artificial liver lobules (ALL), synergically contribute to the effective amelioration of ALF, highlighting the substantial potential for clinical translation.

Noninvasive and in situ identification of the phenotypes and differentiation stages of individual living cells entrapped within hydrogels

Microscale screening platforms that allow cells to interact in three dimensions (3D) with their microenviroment have been developed as a tool for identifying the extrinsic cues that might stimulate stem cells to replicate without differentiating within artificial cultures. Though these platforms reduce the number of valuable stem cells that must be used for screening, analyzing the fate decisions of cells in these platforms can be challenging. New noninvasive approaches for identifying the lineage-specific differentiation stages of cells while they are entrapped in the hydrogels used for these 3D cultures are especially needed. Here we used Raman spectra acquired from individual, living cells entrapped within a hydrogel matrix and multivariate analysis to identify cell phenotype noninvasively and in situ. We collected a single Raman spectrum from each cell of interest while it was entrapped within a hydrogel matrix and used partial least-squares discriminant analysis (PLS-DA) of the spectra for cell phenotype identification. We first demonstrate that this approach enables identifying the lineages of individual, living cells from different laboratory lines entrapped within two different hydrogels that are used for 3D culture, collagen and gelatin methacrylate (gelMA). Then we use a hematopoietic progenitor cell line that differentiates into different types of macrophages to show that the lineage-specific differentiation stages of individual, living hematopoietic cells entrapped inside of gelMA scaffolds may be identified by PLS-DA of Raman spectra. This ability to noninvasively identify the lineage-specific differentiation stages of cells without removing them from a 3D culture could enable tracking the differentiation of the same cell over time.

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

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

Sequential activation of osteogenic microenvironment via composite peptide-modified microfluidic microspheres for promoting bone regeneration

The osteogenic microenvironment (OME) significantly influences bone repair; however, reproducing its dynamic activation and repair processes remains challenging. In this study, we designed injectable porous microspheres modified with composite peptides to investigate cascade alterations in OME and their underlying mechanisms. Poly l-lactic acid microfluidic microspheres underwent surface modifications through alkaline hydrolysis treatment, involving heterogeneous grafting of bovine serum albumin nanoparticles with stem cell-homing peptides (BNP@SKP) and BMP-2 mimicking peptides (P24), respectively. These modifications well-organized the actions of initial release and subsequent in situ grafting of peptides. Cellular experiments demonstrated varied degrees of chemotactic recruitment and osteogenic differentiation in mesenchymal stem cells. Further biological analysis revealed that BNP@SKP targeted the Ras/Erk axis and upregulated matrix metalloproteinase (MMP)2 and MMP9 expression, thereby enhancing initial chemotaxis and recruitment. In vivo studies validated the establishment of a dynamically regulated OME centered on the microspheres, resulting in increased stem cell recruitment, sequential activation of the differentiation microenvironment, and facilitation of in situ osteogenesis without ectopic ossification. In conclusion, this study successfully fabricated composite peptide-modified microspheres and systematically explored the mechanisms of bone formation through sequential activation of OME via heterogeneous grafting of signaling molecules. This provides theoretical evidence for biomaterials based on microenvironment regulation.

Osteopontin in Chronic Inflammatory Diseases: Mechanisms, Biomarker Potential, and Therapeutic Strategies

Chronic inflammatory diseases, such as rheumatoid arthritis (RA), systemic lupus erythematosus (SLE), multiple sclerosis (MS), atherosclerosis, and inflammatory bowel disease (IBD), pose major global health concerns. These disorders are marked by persistent inflammation, immune system dysfunction, tissue injury, and fibrosis, ultimately leading to severe organ dysfunction and diminished quality of life. Osteopontin (OPN), a multifunctional extracellular matrix protein, plays a crucial role in immune regulation, inflammation, and tissue remodeling. It promotes immune cell recruitment, stimulates pro-inflammatory cytokine production, and contributes to fibrosis through interactions with integrins and CD44 receptors. Additionally, OPN activates key inflammatory pathways, including NF-κB, MAPK, and PI3K/Akt, further aggravating tissue damage in chronic inflammatory conditions. Our review highlights the role of OPN in chronic inflammation, its potential as a biomarker, and its therapeutic implications. We explore promising preclinical approaches, such as monoclonal antibodies, small molecule inhibitors, and natural compounds like curcumin, which have demonstrated potential in mitigating OPN-driven inflammation. However, challenges persist in selectively targeting OPN while maintaining its essential physiological roles, including bone remodeling and wound healing. Our review offers insights into therapeutic strategies and future research directions.

Biofunctionalization of ADA-GEL Hydrogels Based on the Degree of Cross-Linking and Polymer Concentration Improves Angiogenesis

The creation of bioartificial tissues is a promising option for the reconstruction of large-volume defects. The vascularization of tissue engineering constructs, as well as the material properties of the carrier matrix, are important factors for successful clinical application. In this regard, hydrogels are promising biomaterials, providing an extracellular matrix-like milieu that enables the possibility of cell transplantation and de novo tissue formation. Furthermore, biofunctionalization allows for a certain fine-tuning of angiogenic properties. This study aims to investigate vascularization and tissue formation of highly cross-linked alginate dialdehyde (ADA) and gelatin (GEL). This highly cross-linked network is created using a dural cross-linking mechanism combining ionic (Ca2+ ions) and enzymatic (human transglutaminase (hTG)) cross-linking, resulting in reduced swelling and moderate degradation rates. Vascularization of the ADA-GEL-hTG constructs is induced surgically using arteriovenous (AV) loops. Biocompatibility, tissue formation, and vascularization are analyzed by histology and X-ray microscopy. After only 2 weeks, vascularization of the ADA-GEL-hTG constructs is already present. After 4 weeks, both de novo tissue formation and vascularization of the ADA-GEL-hTG matrix increase. In conclusion, ADA-GEL-hTG-based hydrogels are shown to be promising scaffold materials for tissue engineering applications.

Chirality Regulates Bone Regeneration through Mechanoresponse and Immunoregulation

As an omnipresent occurrence in the natural world, chirality plays a crucial role in numerous biological and physiological processes. Therefore, incorporation of chirality into biointerface materials has been emerging as a research hotspot in the development of regenerative biomaterials. Nevertheless, how chiral biointerface materials interact with biological organisms remains poorly understood. In the current study, a bioinspired chiral self-assembled nanohydroxyapatite material is developed for bone regeneration using a distraction osteogenesis model. We found that the left-handed chirality, rather than the right-handed chirality, possessed the greatest heightened ability for bone regeneration. Molecular mechanism research reveals that the left-handed chirality can activate mechanosensitive pathways to promote Ca2+ influx, subsequently enhancing macrophage type-2 polarization through phosphorylation of signal transducer and activator of transcription (STAT6), which eventually stimulates bone regeneration by harnessing the synergistic effects of angiogenesis and osteogenesis. These findings provide additional insights into the underlying mechanism of chiral recognition between biological systems and biointerface materials, offering alternative pathways for the development of biomaterials.

Cell-scale porosity minimizes foreign body reaction and promotes innervated myofiber formation after volumetric muscle loss

Volumetric muscle loss (VML) from severe traumatic injuries results in irreversible loss of contractile tissue and permanent functional deficits. These injuries resist endogenous healing and clinical treatment due to excessive inflammation, leading to fibrosis, muscle fiber denervation, and impaired regeneration. Using a rodent tibialis anterior VML model, this study demonstrates microporous annealed particle (MAP) hydrogel scaffolds as a biomaterial platform for improved muscle regeneration. Unlike bulk (nanoporous) hydrogel scaffolds, MAP scaffolds enhance integration by preventing a foreign body reaction, slowing implant degradation, and promoting regenerative macrophage polarization. Cell migration and angiogenesis occur throughout the implant before MAP scaffold degradation, with muscle fibers and neuromuscular junctions forming within the scaffolds. These structures continue developing as the implant degrades, suggesting MAP hydrogel scaffolds offer a promising therapeutic approach for VML injuries.

3D bioprinting of engineered exosomes secreted from M2-polarized macrophages through immunomodulatory biomaterial promotes in vivo wound healing and angiogenesis

Biomaterial composition and surface charge play a critical role in macrophage polarization, providing a molecular cue for immunomodulation and tissue regeneration. In this study, we developed bifunctional hydrogel inks for accelerating M2 macrophage polarization and exosome (Exo) cultivation for wound healing applications. For this, we first fabricated polyamine-modified three-dimensional (3D) printable hydrogels consisting of alginate/gelatin/polydopamine nanospheres (AG/NSPs) to boost M2-exosome (M2-Exo) secretion. The cultivated M2-Exo were finally encapsulated into a biocompatible collagen/decellularized extracellular matrix (COL@d-ECM) bioink for studying angiogenesis and in vivo wound healing study. Our findings show that 3D-printed AGP hydrogel promoted M2 macrophage polarization by Janus kinase/signal transducer of activation (JAK/STAT), peroxisome proliferator-activated receptor (PPAR) signaling pathways and facilitated the M2-Exo secretion. Moreover, the COL@d-ECM/M2-Exo was found to be biocompatible with skin cells. Transcriptomic (RNA-Seq) and real-time PCR (qRT-PCR) study revealed that co-culture of fibroblast/keratinocyte/stem cells/endothelial cells in a 3D bioprinted COL@d-ECM/M2-Exo hydrogel upregulated the skin-associated signature biomarkers through various regulatory pathways during epidermis remodeling and downregulated the mitogen-activated protein kinase (MAPK) signaling pathway after 7 days. In a subcutaneous wound model, the 3D bioprinted COL@d-ECM/M2-Exo hydrogel displayed robust wound remodeling and hair follicle (HF) induction while reducing canonical pro-inflammatory activation after 14 days, presenting a viable therapeutic strategy for skin-related disorders.

Investigating the role of gut microbiota in diabetic nephropathy through plasma proteome mediated analysis

Diabetic nephropathy (DN) is the leading cause of end-stage renal disease and poses significant threats to individuals with diabetes. The concept of gut-kidney axis has gained increasing attention in recent years and the in the occurrence and development of DN, alterations in the gut microbiota also plays a crucial and indispensable role. However, the specific causal relationships between various gut microbial communities and DN, as well as the underlying molecular mechanisms, remains unclear. This study utilized data from genome-wide association studies. After screening for qualified instrumental variables, mendelian randomization causal analyses were performed by inverse variance weighting, MR-Egger, weighted median, weighted mode and MR-RAPS methods. Additionally, sensitivity analyses such as heterogeneity, multiplicity, and the direction of the causal effect were carried out to ensure that the results were robust. After identifying significant gut microbiota, protein-proteomics mediation analysis was conducted on potential 3282 plasma proteins to determine those with mediating effects. Finally, Reactome enrichment analysis was performed to ascertain metabolic or signaling pathways with mediating effects. Mendelian randomization analysis indicated associations between 21 gut microbiota and DN. After adjusting significance levels, Catenibacterium and Parasutterella were found to have causal effects on the onset of DN. Subsequently, we identified 22 plasma proteins with mediating effects, along with 27 metabolic or signaling pathways including activated propionic acid metabolism. Increased in the abundance of Catenibacterium and Parasutterella intestinal bacteria are causative factors for DN. More importantly, the underlying mechanism by which the increased abundance of Catenibacterium and Parasutterella intestinal bacteria lead to DN were revealed, providing a blueprint for the involvement of gut-kidney axis in the pathogenesis of DN and paving the way for future studies.

Therapeutic Properties of M2 Macrophages in Chronic Wounds: An Innovative Area of Biomaterial-Assisted M2 Macrophage Targeted Therapy

Wound healing is a dynamic, multi-stage process essential for restoring skin integrity. Dysregulated wound healing is often linked to impaired macrophage function, particularly in individuals with chronic underlying conditions. Macrophages, as key regulators of wound healing, exhibit significant phenotypic diversity, ranging from the pro-healing M2 phenotype to the pro-inflammatory M1 phenotype. Imbalances in the M1/M2 ratio or hyperactivation of the M1 phenotype can delay the normal healing. Consequently, strategies aimed at suppressing the M1 phenotype or promoting the shift of local skin macrophages toward the M2 phenotype can potentially treat chronic non-healing wounds. This manuscript provides an overview of macrophages' role in normal and pathological wound-healing processes. It examines various therapeutic approaches targeting M2 macrophages, such as ex vivo-activated macrophage therapy, immunopharmacological strategies, and biomaterial-directed macrophage polarization. However, it also highlights that M2 macrophage therapies and immunopharmacological interventions may have drawbacks, including rapid phenotypic changes, adverse effects on other skin cells, biotoxicity, and concerns related to biocompatibility, stability, and drug degradation. Therefore, there is a need for more targeted macrophage-based therapies that ensure optimal biosafety, allowing for effective reprogramming of dysregulated macrophages and improved therapeutic outcomes. Recent advances in nano-biomaterials have demonstrated promising regenerative potential compared to traditional treatments. This review discusses the progress of biomaterial-assisted macrophage targeting in chronic wound repair and addresses the challenges faced in its clinical application. Additionally, it explores novel design concepts for combinational therapies, such as incorporating regenerative particles like exosomes into dressing materials or encapsulating them in microneedling systems to enhance wound healing rates.

Functional hydrogel empowering 3D printing titanium alloys

Titanium alloys are widely used in the manufacture of orthopedic prosthesis given their excellent mechanical properties and biocompatibility. However, the primary drawbacks of traditional titanium alloy prosthesis are their much higher elastic modulus than cancellous bone and poor interfacial adhesion, which lead to poor osseointegration. 3D-printed porous titanium alloys can partly address these issues, but their bio-inertness still requires modifications to adapt to different physiological and pathological microenvironments. Hydrogels composed of three-dimensional networks of hydrophilic polymers can effectively simulate the extracellular matrix of natural bone and are capable of loading bioactive molecules such as proteins, peptides, growths factors, polysaccharides, or nucleotides for localized release within the human body, by directly participating in biological processes. Combining 3D-printed porous titanium alloys with hydrogels to construct a bioactive composite system that regulates cellular adhesion, proliferation, migration, and differentiation in the local microenvironment is of great significance for enhancing the bioactivity of the prosthesis surface. In this review, we focus on three aspects of the bioactive composite system: (Ⅰ) strategies for constructing bioactive interfaces with hydrogels, and (Ⅱ) how bioactive composite systems regulate the microenvironment under different physiological and pathological conditions to enhance the osteointegration and bone regeneration capability of prostheses. Considering the current research status in this field, innovations in orthopedic prosthesis can be achieved through material optimization, personalized customization, and the development of multifunctional composite systems. These advancements provide essential references for the clinical translation of osseointegration and bone regeneration in various physiological and pathological microenvironments.

TPMS-Gyroid Scaffold-Mediated Up-Regulation of ITGB1 for Enhanced Cell Adhesion and Immune-Modulatory Osteogenesis

The porous structure is crucial in bone tissue engineering for promoting osseointegration. Among various structures, triply periodic minimal surfaces (TPMS) -Gyroid has been extensively studied due to its superior mechanical and biological properties. However, previous studies have given limited attention to the impact of unit cell size on the biological performance of scaffolds. In this research, four TPMS-Gyroid titanium scaffolds with different unit cell sizes (TG15, TG20, TG25, and TG30) are fabricated using Selective Laser Melting (SLM) to explore their effects on osseointegration. Mechanical tests revealed that TG15 and TG20 exhibited superior compressive strength. In vitro experiments demonstrated that TG20 facilitated better cell adhesion through robust integrin protein expression initially, which subsequently enhanced cell proliferation and osteogenic differentiation. Furthermore, macrophages on TG20 showed higher Integrin β1 (ITGB1) expression, promoting their polarization to the M2 phenotype, which suppressed inflammation, fostered bone integration, and angiogenesis. In vivo studies confirmed TG20's effectiveness in promoting bone ingrowth by reducing inflammation. This study highlights TG20's structural advantages, making it a promising bone scaffold with exceptional osteogenic and angiogenic properties through osteoimmune microenvironment modulation. Therefore, TG20 holds significant potential for applications in bone tissue engineering.

Enhanced surface hydrophilicity improves osseointegration of titanium implants via integrin-mediated osteoimmunomodulation

Titanium (Ti) implants have become widespread especially in dentistry and orthopedics, where macrophage-driven osteoimmunomodulation is crucial to their success. Hydrophilic modification of Ti represents a promising strategy to enhance its immune and osteogenic responses. Herein, the osteoimmunomodulatory performance and integrin-mediated mechanism of novel non-thermal atmospheric plasma (NTAP) treatment to induce a hydrophilic Ti were investigated for the first time. Compared to a hydrophobic surface, NTAP-modified Ti possessed a 3-fold increase of pro-healing M2 macrophage makers, and the doubled osteogenic differentiation of mesenchymal stem cells was demonstrated in this immune microenvironment, thus improving early osseointegration. Mechanistically, the ameliorative osteoimmunomodulatory properties of NTAP were attributed to its positive and negative modulation in macrophages' integrin β1 or β2, and the subsequent FAK-PI3K/Akt or NF-κB signaling pathway. Collectively, this study highlighted the role of integrins and related signaling pathways in hydrophilic implant-caused macrophage polarization, therefore inventively unveiling the underlying mechanism of NTAP-enhanced osteoimmunomodulation. Furthermore, it established a robust theoretical foundation for the clinical application of this cost-effective, versatile, and transformation-valuable surface engineering strategy for the development of next-generation Ti implants.

Innovative Hydrogel Design: Tailoring Immunomodulation for Optimal Chronic Wound Recovery

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

Development of a biocompatible 3D hydrogel scaffold using continuous liquid interface production for the delivery of cell therapies to treat recurrent glioblastoma

Glioblastoma (GBM) is the most common primary malignant brain tumor diagnosed in adults, carrying with it an extremely poor prognosis and limited options for effective treatment. Various cell therapies have emerged as promising candidates for GBM treatment but fail in the clinic due to poor tumor trafficking, poor transplantation efficiency, and high systemic toxicity. In this study, we design, characterize, and test a 3D-printed cell delivery platform that can enhance the survival of therapeutic cells implanted in the GBM resection cavity. Using continuous liquid interface production (CLIP) to generate a biocompatible 3D hydrogel, we demonstrate that we can effectively seed neural stem cells (NSCs) onto the surface of the hydrogel, and that the cells can proliferate to high densities when cultured for 14 days in vitro. We show that NSCs seeded on CLIP scaffolds persist longer than freely injected cells in vivo, proliferating to 20% higher than their original density in 6 days after implantation. Finally, we demonstrate that therapeutic fibroblasts seeded on CLIP more effectively suppress tumor growth and extend survival in a mouse model of LN229 GBM resection compared to the scaffold or therapeutic cells alone. These promising results demonstrate the potential to leverage CLIP to design hydrogels with various features to control the delivery of different types of cell therapies. Future work will include a more thorough evaluation of the immunological response to the material and improvement of the printing resolution for biocompatible aqueous resins.

A Surface-Mediated Biomimetic Porous Polyether-Ether-Ketone Scaffold for Regulating Immunity and Promoting Osteogenesis

The repair of critical-sized bone defects remains a major challenge for clinical orthopedic surgery. Here, we develop a surface biofunctionalized three-dimensional (3D) porous polyether-ether-ketone (PEEK) scaffold that can simultaneously promote osteogenesis and regulate macrophage polarization. The scaffold is created using polydopamine (PDA)-assisted immobilization of silk fibroin (SF) and the electrostatic self-assembly of nanocrystalline hydroxyapatite (nano-HA) on a 3D-printed porous PEEK scaffold. The SF/nano-HA functionalized surface provides a bone-like microenvironment for osteoblastic cells' adhesion, proliferation, mineralization and osteogenic differentiation. Moreover, the biofunctionalized surface can effectively drive macrophages polarization from the pro-inflammatory M1 phenotype to the anti-inflammatory M2 phenotype. Integrin β1-specific cell-matrix binding and the activation of Ca2+ receptor-mediated signaling pathway play critical roles in the regulation of macrophage polarization. Compared with the as-printed scaffold, the SF/nano-HA functionalized porous PEEK scaffold induces minimal inflammatory response, enhanced angiogenesis, and substantial new bone formation, resulting in improved osseointegration in vivo. This study not only develops a promising candidate for bone repair but also demonstrates a facile surface biofunctionalization strategy for orthopedic implants to improve osseointegration by stimulating osteogenesis and regulating immunity.

YIGSR, A Laminin-Derived Peptide, Dictates a Concentration-Dependent Impact on Macrophage Phenotype Response

Purpose

Macrophage immune cells play crucial roles in the inflammatory (M1) and regenerative (M2) processes. The extracellular matrix (ECM) composition, including presentation of embedded ligands, governs macrophage function. Laminin concentration is abundant in the basement membrane and is dependent on pathological state: reduced in inflammation and increased during regeneration. Distinct laminin ligands, such as IKVAV and YIGSR, have disparate roles in dictating cell function. For example, IKVAV, derived from the alpha chain of laminin, promotes angiogenesis and metastasis of cancer cells whereas YIGSR, beta chain derived, impedes angiogenesis and tumor progression. Previous work has demonstrated IKVAV's inflammation inhibiting properties in macrophages. Given the divergent role of IKVAV and YIGSR in interacting with cells through varied integrin receptors, we ask: what role does laminin derived peptide YIGSR play in governing macrophage function?

Methods

We quantified the influence of YIGSR on macrophage phenotype in 2D and 3D via immunostaining assessments for M1 marker inducible nitric oxide synthase (iNOS) and M2 marker Arginase-1 (Arg-1). We also analysed the secretome of human and murine macrophage response to YIGSR via a Luminex bead assay.

Results

YIGSR impact on macrophage phenotype occurs in a concentration-dependent manner. At lower concentrations of YIGSR, macrophage inflammation was increased whereas, at higher concentrations of YIGSR the opposite effect was seen within the same time frame. Secretomic assessments also demonstrate that pro-inflammatory chemokines and cytokines were increased at low YIGSR concentrations in M0, M1, M2 macrophages while pro-inflammatory secretion was reduced at higher concentrations.

Conclusions

YIGSR can be used as a tool to modulate macrophage inflammatory state within M1 and M2 phenotypes depending on the concentration of peptide. YIGSR's impact on macrophage function can be leveraged for the development of immunoengineering strategies in regenerative medicine and cancer therapy.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12195-024-00810-5.

Conjugation of IL-33 to Microporous Annealed Particle Scaffolds Enhances Type 2-Like Immune Responses In Vitro and In Vivo

The inflammatory foreign body response (FBR) is the main driver of biomaterial implant failure. Current strategies to mitigate the onset of a FBR include modification of the implant surface, release of anti-inflammatory drugs, and cell-scale implant porosity. The microporous annealed particle (MAP) scaffold platform is an injectable, porous biomaterial composed of individual microgels, which are annealed in situ to provide a structurally stable scaffold with cell-scale microporosity. MAP scaffold does not induce a discernible foreign body response in vivo and, therefore, can be used a "blank canvas" for biomaterial-mediated immunomodulation. Damage associated molecular patterns (DAMPs), such as IL-33, are potent regulators of type 2 immunity that play an important role in tissue repair. In this manuscript, IL-33 is conjugated to the microgel building-blocks of MAP scaffold to generate a bioactive material (IL33-MAP) capable of stimulating macrophages in vitro via a ST-2 receptor dependent pathway and modulating immune cell recruitment to the implant site in vivo, which indicates an upregulation of a type 2-like immune response and downregulation of a type 1-like immune response.

Ablation of the Integrin CD11b Mac-1 Limits Deleterious Responses to Traumatic Spinal Cord Injury and Improves Functional Recovery in Mice

Spinal cord injury (SCI) triggers microglial/monocytes activation with distinct pro-inflammatory or inflammation-resolving phenotypes, which potentiate tissue damage or facilitate functional repair, respectively. The major integrin Mac-1 (CD11b/CD18), a heterodimer consisting of CD11b and CD18 chains, is expressed in multiple immune cells of the myeloid lineage. Here, we examined the effects of CD11b gene ablation in neuroinflammation and functional outcomes after SCI. qPCR analysis of C57BL/6 female mice showed upregulation of CD11b mRNA starting from 1 d after injury, which persisted up to 28 d. CD11b knockout (KO) mice and their wildtype littermates were subjected to moderate SCI. At 1 d post-injury, qPCR showed increased expression of genes involved with inflammation-resolving processes in CD11b KO mice. Flow cytometry analysis of CD45intLy6C-CX3CR1+ microglia, CD45hiLy6C+Ly6G- monocytes, and CD45hiLy6C+Ly6G+ neutrophils revealed significantly reduced cell counts as well as reactive oxygen species (ROS) production in CD11b KO mice at d3 post-injury. Further examination with NanoString and RNA-seq showed upregulation of pro-inflammatory genes, but downregulation of the ROS pathway. Importantly, CD11b KO mice exhibited significantly improved locomotor function, reduced cutaneous mechanical/thermal hypersensitivity, and limited tissue damage at 8 weeks post-injury. Collectively, our data suggest an important role for CD11b in regulating tissue inflammation and functional outcome following SCI.

Shaping the immune landscape: Multidimensional environmental stimuli refine macrophage polarization and foster revolutionary approaches in tissue regeneration

In immunology, the role of macrophages extends far beyond their traditional classification as mere phagocytes; they emerge as pivotal architects of the immune response, with their function being significantly influenced by multidimensional environmental stimuli. This review investigates the nuanced mechanisms by which diverse external signals ranging from chemical cues to physical stress orchestrate macrophage polarization, a process that is crucial for the modulation of immune responses. By transitioning between pro-inflammatory (M1) and anti-inflammatory (M2) states, macrophages exhibit remarkable plasticity, enabling them to adapt to and influence their surroundings effectively. The exploration of macrophage polarization provides a compelling narrative on how these cells can be manipulated to foster an immune environment conducive to tissue repair and regeneration. Highlighting cutting-edge research, this review presents innovative strategies that leverage the dynamic interplay between macrophages and their environment, proposing novel therapeutic avenues that harness the potential of macrophages in regenerative medicine. Moreover, this review critically evaluates the current challenges and future prospects of translating macrophage-centered strategies from the laboratory to clinical applications.

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.

Structure driven bio-responsive ability of injectable nanocomposite hydrogels for efficient bone regeneration

Injectable hydrogels are promising for treatment of bone defects in clinic owing to their minimally invasive procedure. Currently, there is limited emphasis on how to utilize injectable hydrogels to mobilize body's regenerative potential for enhancing bone regeneration. Herein, an injectable bone-mimicking hydrogel (BMH) scaffold assembled from nanocomposite microgel building blocks was developed, in which a highly interconnected microporous structure and an inorganic/organic (methacrylated hydroxyapatite and methacrylated gelatin) interweaved nano structure were well-designed. Compared with hydrogels lacking micro-nano structures or only showing microporous structure, the BMH scaffold enhanced the ingrowth of vessels and promoted the formation of dense cellular networks (including stem cells and M2 macrophages), across the entire scaffold at early stage after subcutaneous implantation. Moreover, the BMH scaffold could not only directly trigger osteogenic differentiation of the infiltrated stem cells, but also provided an instructive osteo-immune microenvironment by inducing macrophages into M2 phenotype. Mechanistically, our results reveal that the nano-rough structure of the BMH plays an essential role in inducing macrophage M2 polarization through activating mechanotransduction related RhoA/ROCK2 pathway. Overall, this work offers an injectable hydrogel with micro-nano structure driven bio-responsive abilities, highlighting harnessing body's inherent regenerative potential to realize bone regeneration.

Interleukin-4-Loaded Gelatin Methacryloyl Hydrogel Promotes Subcutaneous Chondrogenesis of Engineered Auricular Cartilage in a Rabbit Model

Tissue engineering technology offers a promising solution for ear reconstruction; however, it faces the challenge of foreign body reaction and neocartilage malformation. This study investigates the impact of interleukin-4 (IL-4), an anti-inflammatory factor, on cartilage regeneration of hydrogel encapsulating autologous auricular chondrocytes in a rabbit subcutaneous environment. Initially, we assessed the influence of IL-4 on chondrocyte proliferation and determined the appropriate concentration using the CCK-8 test in vitro. Subsequently, we loaded IL-4 into gelatin methacryloyl (GelMA) hydrogel containing chondrocytes and measured its release profile through ELISA. The constructs were then implanted autologously into rabbits' subcutis, and after 3, 7, 14, and 28 days, cartilage matrix formation was evaluated by histological examinations, and gene expression levels were detected by qRT-PCR. Results demonstrated that IL-4 promotes chondrocyte proliferation in vitro, and maximum release from constructs occurred during the first week. In the rabbit subcutaneous implantation model, IL-4-loaded constructs (20 ng/mL) maintained a superior chondrocytic phenotype compared to controls with increased expression of anti-inflammatory factors. These findings highlight IL-4 as a potential strategy for promoting chondrogenesis in a subcutaneous environment and improving ear reconstruction.

Biomimetic Dual-Network Collagen Fibers with Porous and Mechanical Cues Reconstruct Neural Stem Cell Niche via AKT/YAP Mechanotransduction after Spinal Cord Injury

Tissue engineering scaffolds can mediate the maneuverability of neural stem cell (NSC) niche to influence NSC behavior, such as cell self-renewal, proliferation, and differentiation direction, showing the promising application in spinal cord injury (SCI) repair. Here, dual-network porous collagen fibers (PCFS) are developed as neurogenesis scaffolds by employing biomimetic plasma ammonia oxidase catalysis and conventional amidation cross-linking. Following optimizing the mechanical parameters of PCFS, the well-matched Young's modulus and physiological dynamic adaptability of PCFS (4.0 wt%) have been identified as a neurogenetic exciter after SCI. Remarkably, porous topographies and curving wall-like protrusions are generated on the surface of PCFS by simple and non-toxic CO2 bubble-water replacement. As expected, PCFS with porous and matched mechanical properties can considerably activate the cadherin receptor of NSCs and induce a series of serine-threonine kinase/yes-associated protein mechanotransduction signal pathways, encouraging cellular orientation, neuron differentiation, and adhesion. In SCI rats, implanted PCFS with matched mechanical properties further integrated into the injured spinal cords, inhibited the inflammatory progression and decreased glial and fibrous scar formation. Wall-like protrusions of PCFS drive multiple neuron subtypes formation and even functional neural circuits, suggesting a viable therapeutic strategy for nerve regeneration and functional recovery after SCI.

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.

Modulating the immune system towards a functional chronic wound healing: A biomaterials and Nanomedicine perspective

Chronic non-healing wounds persist as a substantial burden for healthcare systems, influenced by factors such as aging, diabetes, and obesity. In contrast to the traditionally pro-regenerative emphasis of therapies, the recognition of the immune system integral role in wound healing has significantly grown, instigating an approach shift towards immunological processes. Thus, this review explores the wound healing process, highlighting the engagement of the immune system, and delving into the behaviors of innate and adaptive immune cells in chronic wound scenarios. Moreover, the article investigates biomaterial-based strategies for the modulation of the immune system, elucidating how the adjustment of their physicochemical properties or their synergistic combination with other agents such as drugs, proteins or mesenchymal stromal cells can effectively modulate the behaviors of different immune cells. Finally this review explores various strategies based on synthetic and biological nanostructures, including extracellular vesicles, to finely tune the immune system as natural immunomodulators or therapeutic nanocarriers with promising biophysical properties.

Surface Deformation of Biocompatible Materials: Recent Advances in Biological Applications

The surface topography of substrates is a crucial factor that determines the interaction with biological materials in bioengineering research. Therefore, it is important to appropriately modify the surface topography according to the research purpose. Surface topography can be fabricated in various forms, such as wrinkles, creases, and ridges using surface deformation techniques, which can contribute to the performance enhancement of cell chips, organ chips, and biosensors. This review provides a comprehensive overview of the characteristics of soft, hard, and hybrid substrates used in the bioengineering field and the surface deformation techniques applied to the substrates. Furthermore, this review summarizes the cases of cell-based research and other applications, such as biosensor research, that utilize surface deformation techniques. In cell-based research, various studies have reported optimized cell behavior and differentiation through surface deformation, while, in the biosensor and biofilm fields, performance improvement cases due to surface deformation have been reported. Through these studies, we confirm the contribution of surface deformation techniques to the advancement of the bioengineering field. In the future, it is expected that the application of surface deformation techniques to the real-time interaction analysis between biological materials and dynamically deformable substrates will increase the utilization and importance of these techniques in various fields, including cell research and biosensors.

A new direction in periodontitis treatment: biomaterial-mediated macrophage immunotherapy

Periodontitis is a chronic inflammation caused by a bacterial infection and is intimately associated with an overactive immune response. Biomaterials are being utilized more frequently in periodontal therapy due to their designability and unique drug delivery system. However, local and systemic immune response reactions driven by the implantation of biomaterials could result in inflammation, tissue damage, and fibrosis, which could end up with the failure of the implantation. Therefore, immunological adjustment of biomaterials through precise design can reduce the host reaction while eliminating the periodontal tissue's long-term chronic inflammation response. It is important to note that macrophages are an active immune system component that can participate in the progression of periodontal disease through intricate polarization mechanisms. And modulating macrophage polarization by designing biomaterials has emerged as a new periodontal therapy technique. In this review, we discuss the role of macrophages in periodontitis and typical strategies for polarizing macrophages with biomaterials. Subsequently, we discuss the challenges and potential opportunities of using biomaterials to manipulate periodontal macrophages to facilitate periodontal regeneration.

Recent advancements in cartilage tissue engineering innovation and translation

Articular cartilage was expected to be one of the first successfully engineered tissues, but today, cartilage repair products are few and they exhibit considerable limitations. For example, of the cell-based products that are available globally, only one is marketed for non-knee indications, none are indicated for severe osteoarthritis or rheumatoid arthritis, and only one is approved for marketing in the USA. However, advances in cartilage tissue engineering might now finally lead to the development of new cartilage repair products. To understand the potential in this field, it helps to consider the current landscape of tissue-engineered products for articular cartilage repair and particularly cell-based therapies. Advances relating to cell sources, bioactive stimuli and scaffold or scaffold-free approaches should now contribute to progress in therapeutic development. Engineering for an inflammatory environment is required because of the need for implants to withstand immune challenge within joints affected by osteoarthritis or rheumatoid arthritis. Bringing additional cartilage repair products to the market will require an understanding of the translational vector for their commercialization. Advances thus far can facilitate the future translation of engineered cartilage products to benefit the millions of patients who suffer from cartilage injuries and arthritides.

Laminin-derived peptide, IKVAV, modulates macrophage phenotype through integrin mediation

Macrophages are highly plastic immune cells known to exist on a spectrum of phenotypes including pro-inflammatory (M1) or pro-healing (M2). Macrophages interact with extracellular matrix (ECM) ligands, such as fragments of collagen and laminin. Interaction of macrophages with ECM ligands is mediated through integrin receptors. However, the role of ECM ligands in directing macrophage function through integrins is not yet fully understood. Particularly, α2β1 has been implicated in modulating macrophage function, but complexity in mechanisms employed for integrin-ligation especially with laminin-derived peptides makes it challenging to understand macrophage-ECM interactions. We hypothesize that targeting α2β1 through laminin-derived peptide, IKVAV, will modulate macrophage phenotype. In this work we: i) investigated macrophage response to IKVAV in 2D and in a 3D platform, and ii) identified α2β1's role as it pertains to macrophage modulation via IKVAV. Soluble IKVAV treatment significantly reduced M1 markers and increased M2 markers via immunocytochemistry and gene expression. While the 3D ECM-mimicking PEG-IKVAV hydrogels did not have significant effects in modulating macrophage phenotype, we found that macrophage modulation via IKVAV is dependent on the concentration of peptide used and duration of exposure. To investigate integrin-ligand interactions for macrophages, α2β1 signaling was modulated by antagonists and agonists. We observed that blocking α2β1 reduces M1 activation. To understand integrin-ligand interactions and leveraging the therapeutic ability of macrophages in designing immunomodulatory solutions, it is critical to elucidate IKVAV's role in mediating macrophage phenotype.

Multifunctional hydrogel dressing based on fish gelatin/oxidized hyaluronate for promoting diabetic wound healing

Non-healing chronic diabetic wound treatment remains an unsolved healthcare challenge and still threatens patients' lives. Recently, hydrogel dressings based on natural biomaterials have been widely investigated to accelerate the healing of diabetic wounds. In this study, we introduce a bioactive hydrogel based on fish gelatin (FG) as a candidate for diabetic wound treatments, which is a recently emerged substitute for mammalian derived gelatin. The composite hydrogel simply fabricated with FG and oxidized hyaluronate (OHy) through Schiff base reaction could successfully accelerate wound healing due to their adequate mechanical stability and self-healing ability. In vitro studies showed that the fabricated hydrogels exhibited cytocompatibility and could reduce pro-inflammatory cytokine expression such as NO, IL-1β, TNF-α, and PGE2 in lipopolysaccharide (LPS)-stimulated RAW 264.7 macrophages. In addition, the production of reactive oxygen species (ROS), a key marker of free radicals producing oxidative stress, was also reduced by fabricated hydrogels. Furthermore, in vivo experiments demonstrated that the hydrogel could promote wound closure, re-epithelialization, collagen deposition, and protein expression of CD31, CD206, and Arg1 in diabetic mice models. Our study highlights the advanced potential of FG as a promising alternative material and indicates that FOHI can be successfully used for diabetic wound healing applications.

Decellularized kidney extracellular matrix-based hydrogels for renal tissue engineering

Kidney regeneration is hindered by the limited pool of intrinsic reparative cells. Advanced therapies targeting renal regeneration have the potential to alleviate the clinical and financial burdens associated with kidney disease. Delivery systems for cells, extracellular vesicles, or growth factors aimed at enhancing regeneration can benefit from vehicles enabling targeted delivery and controlled release. Hydrogels, optimized to carry biological cargo while promoting regeneration, have emerged as promising candidates for this purpose. This study aims to develop a hydrogel from decellularized kidney extracellular matrix (DKECM) and explore its biocompatibility as a biomaterial for renal regeneration. The resulting hydrogel crosslinks with temperature and exhibits a high concentration of extracellular matrix. The decellularization process efficiently removes detergent residues, yielding a pathogen-free biomaterial that is non-hemolytic and devoid of α-gal epitope. Upon interaction with macrophages, the hydrogel induces differentiation into both pro-inflammatory and anti-inflammatory phenotypes, suggesting an adequate balance to promote biomaterial functionality in vivo. Renal progenitor cells encapsulated in the DKECM hydrogel demonstrate higher viability and proliferation than in commercial collagen-I hydrogels, while also expressing tubular cells and podocyte markers in long-term culture. Overall, the injectable biomaterial derived from porcine DKECM is anticipated to elicit minimal host reaction while fostering progenitor cell bioactivity, offering a potential avenue for enhancing renal regeneration in clinical settings. STATEMENT OF SIGNIFICANCE: The quest to improve treatments for kidney disease is crucial, given the challenges faced by patients on dialysis or waiting for transplants. Exciting new therapies combining biomaterials with cells can revolutionize kidney repair. In this study, researchers created a hydrogel from pig kidney. This gel could be used to deliver cells and other substances that help in kidney regeneration. Despite coming from pigs, it's safe for use in humans, with no harmful substances and reduced risk of immune reactions. Importantly, it promotes a balanced healing response in the body. This research not only advances our knowledge of kidney repair but also offers hope for more effective treatments for kidney diseases.

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.

Hydrogel-based immunoregulation of macrophages for tissue repair and regeneration

The rational design of hydrogel materials to modulate the immune microenvironment has emerged as a pivotal approach in expediting tissue repair and regeneration. Within the immune microenvironment, an array of immune cells exists, with macrophages gaining prominence in the field of tissue repair and regeneration due to their roles in cytokine regulation to promote regeneration, maintain tissue homeostasis, and facilitate repair. Macrophages can be categorized into two types: classically activated M1 (pro-inflammatory) and alternatively activated M2 (anti-inflammatory and pro-repair). By regulating the physical and chemical properties of hydrogels, the phenotypic transformation and cell behavior of macrophages can be effectively controlled, thereby promoting tissue regeneration and repair. A full understanding of the interaction between hydrogels and macrophages can provide new ideas and methods for future tissue engineering and clinical treatment. Therefore, this paper reviews the effects of hydrogel components, hardness, pore size, and surface morphology on cell behaviors such as macrophage proliferation, migration, and phenotypic polarization, and explores the application of hydrogels based on macrophage immune regulation in skin, bone, cartilage, and nerve tissue repair. Finally, the challenges and future prospects of macrophage-based immunomodulatory hydrogels are discussed.

Macrophage Polarization Dynamics in Biomaterials: Implications for in Vitro Wound Healing

The interaction between biomaterials and the immune system plays a pivotal role in determining the success or failure of implantable devices. Macrophages, as key orchestrators of immune responses, exhibit diverse reactions that influence tissue integration or lead to implant failure. This study focuses on unraveling the intricate relationship between macrophage phenotypes and biomaterials, specifically hydrogels, by employing THP-1 cells as a model. Through a comprehensive investigation using polysaccharide, polymer, and protein-based hydrogels, our research sheds light on how the properties of hydrogels influence macrophage polarization. Phenotypic observations, biochemical assays, surface marker expression, and gene expression profiles collectively demonstrate the differential macrophage polarization abilities of polysaccharide-, polymer-, and protein-based hydrogels. Moreover, our indirect coculture studies reveal that hydrogels fostering M2 polarization exhibit exceptional wound-healing capabilities. These findings highlight the crucial role of the hydrogel microenvironment in adjusting macrophage polarization, offering a fresh avenue for refining biomaterials to bolster advantageous immune responses and improve tissue integration. This research contributes valuable insights for designing biomaterials with tailored properties that can guide macrophage behavior, ultimately improving the overall success of implantable devices.

Immunomodulatory hydrogels for skin wound healing: cellular targets and design strategy

Skin wounds significantly impact the global health care system and represent a significant burden on the economy and society due to their complicated dynamic healing processes, wherein a series of immune events are required to coordinate normal and sequential healing phases, involving multiple immunoregulatory cells such as neutrophils, macrophages, keratinocytes, and fibroblasts, since dysfunction of these cells may impede skin wound healing presenting persisting inflammation, impaired vascularization, and excessive collagen deposition. Therefore, cellular target-based immunomodulation is promising to promote wound healing as cells are the smallest unit of life in immune response. Recently, immunomodulatory hydrogels have become an attractive avenue to promote skin wound healing. However, a detailed and comprehensive review of cellular targets and related hydrogel design strategies remains lacking. In this review, the roles of the main immunoregulatory cells participating in skin wound healing are first discussed, and then we highlight the cellular targets and state-of-the-art design strategies for immunomodulatory hydrogels based on immunoregulatory cells that cover defect, infected, diabetic, burn and tumor wounds and related scar healing. Finally, we discuss the barriers that need to be addressed and future prospects to boost the development and prosperity of immunomodulatory hydrogels.

Mac-1 deficiency ameliorates pressure overloaded heart failure through inhibiting macrophage polarization and activation

Persistent pressure overload commonly leads to pathological cardiac hypertrophy and remodeling, ultimately leading to heart failure (HF). Cardiac remodeling is associated with the involvement of immune cells and the inflammatory response in pathogenesis. The macrophage-1 antigen (Mac-1) is specifically expressed on leukocytes and regulates their migration and polarization. Nonetheless, the involvement of Mac-1 in cardiac remodeling and HF caused by pressure overload has not been determined. The Mac-1-knockout (KO) and wild-type (WT) mice were subjected to transverse aortic constriction (TAC) for 6 weeks. Echocardiography and pressure-volume loop assessments were used to evaluate cardiac function, and cardiac remodeling and macrophage infiltration and polarization were estimated by histopathology and molecular techniques. The findings of our study demonstrated that Mac-1 expression was markedly increased in hearts subjected to TAC treatment. Moreover, compared with WT mice, Mac-1-KO mice exhibited dramatically ameliorated TAC-induced cardiac dysfunction, hypertrophy, fibrosis, oxidative stress and apoptosis. The potential positive impacts may be linked to the inhibition of macrophage infiltration and M1 polarization via reductions in NF-kB and STAT1 expression and upregulation of STAT6. In conclusion, this research reveals a new function of Mac-1 deficiency in reducing pathological cardiac remodeling and HF caused by pressure overload. Additionally, inhibiting Mac-1 could be a potential treatment option for patients with HF in a clinical setting.

Calcium phosphate coating enhances osteointegration of melt electrowritten scaffold by regulating macrophage polarization

The osteoimmune microenvironment induced by implants plays a significant role in bone regeneration. It is essential to efficiently and timely switch the macrophage phenotype from M1 to M2 for optimal bone healing. This study examined the impact of a calcium phosphate (CaP) coating on the physiochemical properties of highly ordered polycaprolactone (PCL) scaffolds fabricated using melt electrowritten (MEW). Additionally, it investigated the influence of these scaffolds on macrophage polarization and their immunomodulation on osteogenesis. The results revealed that the CaP coated PCL scaffold exhibited a rougher surface topography and higher hydrophilicity in comparison to the PCL scaffold without coating. Besides, the surface morphology of the coating and the release of Ca2+ from the CaP coating were crucial in regulating the transition of macrophages from M1 to M2 phenotypes. They might activate the PI3K/AKT and cAMP-PKA pathways, respectively, to facilitate M2 polarization. In addition, the osteoimmune microenvironment induced by CaP coated PCL could not only enhance the osteogenic differentiation of bone marrow-derived mesenchymal stem cells (BMSCs) in vitro but also promote the bone regeneration in vivo. Taken together, the CaP coating can be employed to control the phenotypic switching of macrophages, thereby creating a beneficial immunomodulatory microenvironment that promotes bone regeneration.

dECM restores macrophage immune homeostasis and alleviates iron overload to promote DTPI healing

Due to its highly insidious and rapid progression, deep tissue pressure injury (DTPI) is a clinical challenge. Our previous study found that DTPI may be a skeletal muscle injury dominated by macrophage immune dysfunction due to excessive iron accumulation. Decellularized extracellular matrix (dECM) hydrogel promotes skeletal muscle injury repair. However, its role in polarizing macrophages and regulating iron metabolism in DTPI remains unclear. Here, porcine dECM hydrogel was prepared, and its therapeutic function and mechanism in repairing DTPI were investigated. The stimulus of dECM hydrogel toward RAW264.7 cells resulted in a significantly higher percentage of CD206+ macrophages and notably decreased intracellular divalent iron levels. In mice DTPI model, dECM hydrogel treatment promoted M1 to M2 macrophage conversion, improved iron metabolism and reduced oxidative stress in the early stage of DTPI. In the remodeling phase, the dECM hydrogel remarkably enhanced revascularization and accelerated skeletal muscle repair. Furthermore, the immunomodulation of dECM hydrogels in vivo was mainly involved in the P13k/Akt signaling pathway, as revealed by GO and KEGG pathway analysis, which may ameliorate the iron deposition and promote the healing of DTPI. Our findings indicate that dECM hydrogel is promising in skeletal muscle repair, inflammation resolution and tissue injury healing by effectively restoring macrophage immune homeostasis and normalizing iron metabolism.

Polarization of M2 Tumor-Associated Macrophages (TAMs) in Cancer Immunotherapy

We have witnessed in the last decade new milestones in the treatment of various resistant cancers with new immunotherapeutic modalities. These advances have resulted in significant objective durable clinical responses in a subset of cancer patients. These findings strongly suggested that immunotherapy should be considered for the treatment of all subsets of cancer patients. Accordingly, the mechanisms underlying resistance to immunotherapy must be explored and develop new means to target these resistant factors. One of the pivotal resistance mechanisms in the tumor microenvironment (TME) is the high infiltration of tumor-associated macrophages (TAMs) that are highly immunosuppressive and responsible, in large part, of cancer immune evasion. Thus, various approaches have been investigated to target the TAMs to restore the anti-tumor immune response. One approach is to polarize the M2 TAMS to the M1 phenotype that participates in the activation of the anti-tumor response. In this review, we discuss the various and differential properties of the M1 and M2 phenotypes, the molecular signaling pathways that participate in the polarization, and various approaches used to target the polarization of the M2 TAMs into the M1 anti-tumor phenotype. These approaches include inhibitors of histone deacetylases, PI3K inhibitors, STAT3 inhibitors, TLR agonists, and metabolic reprogramming. Clearly, due to the distinct features of various cancers and their heterogeneities, a single approach outlined above might only be effective against some cancers and not others. In addition, targeting by itself may not be efficacious unless used in combination with other therapeutic modalities.

CD11b mediates hypertensive cardiac remodeling by regulating macrophage infiltration and polarization

INTRODUCTION

Leukocyte infiltration is an early event during cardiac remodeling frequently leading to heart failure (HF). Integrins mediate leukocyte infiltration during inflammation. However, the importance of specific integrins in hypertensive cardiac remodeling is still unclear.

OBJECTIVES

To elucidate the significance of CD11b in hypertensive cardiac remodeling.

METHODS

Angiotensin (Ang II) or deoxycorticosterone acetate (DOCA)-salt was used to induce cardiac remodeling in mice of gene knockout (KO), bone marrow (BM) chimera, and the CD11b neutralizing antibody or agonist leukadherin-1 (LA1) treatment.

RESULTS

Our microarray data showed that integrin subunits Itgam (CD11b) and Itgb2 (CD18) were the most highly upregulated in Ang II-infused hearts. CD11b expression and CD11b/CD18+ myelomonocytes were also time-dependently increased. KO or pharmacological blockade of CD11b greatly attenuated cardiac remodeling and macrophage infiltration and M1 polarization induced by Ang II or DOCA-salt. This protection was verified in wild-type mice transplanted with CD11b-deficient BM cells. Conversely, administration of CD11b agonist LA1 showed the opposite effects. Further, CD11b KO reduced Ang II-induced macrophage adhesion and M1 polarization, leading to reduction of cardiomyocyte enlargement and fibroblast differentiation in vitro. The numbers of CD14+CD11b+CD18+ monocytes and CD15+CD11b+CD18+ granulocytes were obviously higher in HF patients than in normal controls.

CONCLUSION

Our data demonstrate an important role of CD11b+ myeloid cells in hypertensive cardiac remodeling, and suggest that HF may benefit from targeting CD11b.

Investigating Immunomodulatory Biomaterials for Preventing the Foreign Body Response

Implantable biomaterials represent the forefront of regenerative medicine, providing platforms and vessels for delivering a creative range of therapeutic benefits in diverse disease contexts. However, the chronic damage resulting from implant rejection tends to outweigh the intended healing benefits, presenting a considerable challenge when implementing treatment-based biomaterials. In response to implant rejection, proinflammatory macrophages and activated fibroblasts contribute to a synergistically destructive process of uncontrolled inflammation and excessive fibrosis. Understanding the complex biomaterial-host cell interactions that occur within the tissue microenvironment is crucial for the development of therapeutic biomaterials that promote tissue integration and minimize the foreign body response. Recent modifications of specific material properties enhance the immunomodulatory capabilities of the biomaterial and actively aid in taming the immune response by tuning interactions with the surrounding microenvironment either directly or indirectly. By incorporating modifications that amplify anti-inflammatory and pro-regenerative mechanisms, biomaterials can be optimized to maximize their healing benefits in harmony with the host immune system.

An ECM-mimicking assembled gelatin/hyaluronic acid hydrogel with antibacterial and radical scavenging functions for accelerating open wound healing

A multifunctional hydrogel dressing with hemostatic, antibacterial, and reactive oxygen species (ROS)-removing properties is highly desirable for the clinical treatment of open wounds. Although many wound dressings have been prepared, the modification of polymers is often involved in the preparation process, and the uncertainty of biological safety and stability of modified polymers hinders the clinical application of products. In this study, inspired by the composition and crosslinking pattern of extracellular matrix (ECM), a deeply ECM-mimicking multifunctional hydrogel dressing is created. Tannic acid (TA) and poly-ϵ-lysine (EPL) are added into a gelatin/hyaluronic acid (Gel/HA) matrix, and a stable hydrogel is formed due to the formation of the triple helix bundles of gelatin and hydrogen bonds between polymers. The introduction of TA and EPL endows the ECM-mimicking hydrogel with stable rheological properties, as well as antibacterial and hemostatic functions. The as-produced hydrogels have suitable swelling ratio, enzyme degradability, and good biocompatibility. In addition, it also shows a significant ability to eliminate ROS, which is confirmed by the elimination of 2,2-diphenyl-1-picrylhydrazyl free radical. Full-thickness skin wound repair experiment and histological analysis of the healing site in mice demonstrate that the developed ECM-mimicking Gel/HA hydrogels have a prominent effect on ECM formation and promotion of wound closure. Taken together, these findings suggest that the multifunctional hydrogels deeply mimicking the ECM are promising candidates for the clinical treatment of open wounds.

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.

ECM-engineered electrospun fibers with an immune cascade effect for inhibiting tissue fibrosis

Tissue regeneration/fibrosis after injury is intricately regulated by the immune cascade reaction and extracellular matrix (ECM). Dysregulated cascade signal could jeopardize tissue homeostasis leading to fibrosis. Bioactive scaffolds mimicking natural ECM microstructure and chemistry could regulate the cascade reaction to achieve tissue regeneration. The current study constructed an ECM-engineered micro/nanofibrous scaffold using self-assembled nanofibrous collagen and decorin (DCN)-loaded microfibers to regulate the immune cascade reaction. The ECM-engineered scaffold promoted anti-inflammatory and pro-regenerative effects, M2 polarization of macrophages, by nanofibrous collagen. The ECM-engineered scaffold could release DCN to inhibit inflammation-associated fibrous angiogenesis. Yet, to prevent excessive M2 activity leading to tissue fibrosis, controlled release of DCN was expected to elicit M1 activity and achieve M1/M2 balance in the repair process. Regulated cascade reaction guided favorable crosstalk between macrophages, endothelial cells and fibroblasts by proximity. Additionally, decorin could also antagonize TGF-β1 via TGF-β/Smad3 pathway to suppress fibrotic activity of fibroblasts. Hence, ECM-engineered scaffolds could exert effective regulation of the immune cascade reaction by microstructure and DCN release and achieve the balance between tissue fibrosis and regeneration. STATEMENT OF SIGNIFICANCE: With the incidence of up to 74.6%, failed back surgery syndrome (FBSS) has been a lingering issue in spine surgery, which poses a heavy socio-economic burden to society. Epidural fibrosis is believed to be responsible for the onset of FBSS. Current biomaterial-based strategies treating epidural fibrosis mainly rely on physical barriers and unidirectional suppression of inflammation. Regulation of the immune cascade reaction for inhibiting fibrosis has not been widely studied. Based on the simultaneous regulation of M1/M2 polarization and intercellular crosstalk, the ECM-engineered micro/nanofibrous scaffolds constructed in the current study could exert an immune cascade effect to coordinate tissue regeneration and inhibit fibrosis. This finding makes a significant contribution in the development of a treatment for epidural fibrosis and FBSS.

Components and physical properties of hydrogels modulate inflammatory response and cartilage repair

Collagen and hyaluronic acid are commonly applied in cartilage tissue engineering, yet there has been limited investigation into their inflammatory response, a crucial factor in articular cartilage repair. This study aimed to evaluate the impact of components and physical properties of hydrogels on inflammatory response and cartilage repair. Three kinds of hydrogels with comparable storage moduli at low frequencies were designed and fabricated, namely, methacrylic anhydride-modified hyaluronic acid hydrogel (HAMA), methacrylic anhydride-modified type I collagen hydrogel (CMA) and unmodified type I collagen hydrogel (Col). HAMA hydrogel was unfavorable for adhesion and spreading of BMSCs. Furthermore, HAMA hydrogel stimulated rapid migration and pro-inflammatory M1 polarization of macrophages, leading to persistent and intense inflammation, which was unfavorable for cartilage repair. CMA and Col hydrogels possessed the same component and facilitated the adhesion, spreading and proliferation of BMSCs. Compared with CMA hydrogel, Col hydrogel induced rapid migration and moderate M1 polarization of macrophages at the early stage of injury, which was mainly influenced by its fast dissolution rate, small pore size fiber network structure and rapid stress relaxation. In addition, the phenotype of macrophages timely transformed into anti-inflammatory M2 due to the properties of the collagen component, which shortened the duration of inflammation and enhanced cartilage repair. The results indicated that moderate macrophage activation adjusted by hydrogel components and physical properties was critical in modulating inflammation and cartilage regeneration.

Potential effects of biomaterials on macrophage function and their signalling pathways

The use of biomaterials in biomedicine and healthcare has increased in recent years. Macrophages are the primary immune cells that induce inflammation and tissue repair after implantation of biomaterials. Given that macrophages exhibit high heterogeneity and plasticity, the influence of biomaterials on macrophage phenotype should be considered a crucial evaluation criterion during the development of novel biomaterials. This review provides a comprehensive summary of the physicochemical, biological, and dynamic characteristics of biomaterials that drive the regulation of immune responses in macrophages. The mechanisms involved in the interaction between macrophages and biomaterials, including endocytosis, receptors, signalling pathways, integrins, inflammasomes and long non-coding RNAs, are summarised in this review. In addition, research prospects of the interaction between macrophages and biomaterials are discussed. An in-depth understanding of mechanisms underlying the spatiotemporal changes in macrophage phenotype induced by biomaterials and their impact on macrophage polarization can facilitate the identification and development of novel biomaterials with superior performance. These biomaterials may be used for tissue repair and regeneration, vaccine or drug delivery and immunotherapy.