The inflammasome in host response to biomaterials: Bridging inflammation and tissue regeneration

Silk biomaterials for vascular tissue engineering applications

Vascular tissue engineering is a rapidly growing field of regenerative medicine, which strives to find innovative solutions for vascular reconstruction. Considering the limited success of synthetic grafts, research impetus in the field is now shifted towards finding biologically active vascular substitutes bestowing in situ growth potential. In this regard, silk biomaterials have shown remarkable potential owing to their favorable inherent biological and mechanical properties. This review provides a comprehensive overview of the progressive development of silk-based small diameter (<6 mm) tissue-engineered vascular grafts (TEVGs), emphasizing their pre-clinical implications. Herein, we first discuss the molecular structure of various mulberry and non-mulberry silkworm silk and identify their favorable properties at the onset of vascular regeneration. The emergence of various state-of-the-art fabrication methodologies for the advancement of silk TEVGs is rationally appraised in terms of their in vivo performance considering the following parameters: ease of handling, long-term patency, resistance to acute thrombosis, stenosis and aneurysm formation, immune reaction, neo-tissue formation, and overall remodeling. Finally, we provide an update on the pre-clinical status of silk-based TEVGs, followed by current challenges and future prospects. STATEMENT OF SIGNIFICANCE: Limited availability of healthy autologous blood vessels to replace their diseased counterpart is concerning and demands other artificial substitutes. Currently available synthetic grafts are not suitable for small diameter blood vessels owing to frequent blockage. Tissue-engineered biological grafts tend to integrate well with the native tissue via remodeling and have lately witnessed remarkable success. Silk fibroin is a natural biomaterial, which has long been used as medical sutures. This review aims to identify several favorable properties of silk enabling vascular regeneration. Furthermore, various methodologies to fabricate tubular grafts are discussed and highlight their performance in animal models. An overview of our understanding to rationally improve the biological activity fostering the clinical success of silk-based grafts is finally discussed.

Immunomodulatory bioactive glasses for tissue regeneration

The regulatory functions of the immune response in tissue healing, repair, and regeneration have been evidenced in the last decade. Immune cells play central roles in immune responses toward inducing favorable tissue regenerative processes. Modulating and controlling the immune cell responses (particularly macrophages) is an emerging approach to enhance tissue regeneration. Bioactive glasses (BGs) are multifunctional materials exhibiting osteogenic, angiogenic, and antibacterial properties, being increasingly investigated for various tissue regeneration scenarios, including bone regeneration and wound healing. On the other hand, the immunomodulatory effects of BGs in relation to regenerating tissues have started to be understood, and key knowledge is emerging. This is the first review article summarizing the immunomodulatory effects of BGs for tissue repair and regeneration. The immune response to BGs is firstly introduced, discussing potential mechanisms regarding the immunomodulation effects induced by BGs. Moreover, the interactions between the immune cells involved in the immunomodulation process and BGs (dissolution products) are summarized in detail. Particularly, a well-regulated and timely switch of macrophage phenotype from pro-inflammatory to anti-inflammatory is crucial to constructive tissue regeneration through modulating osteogenesis, osteoclastogenesis, and angiogenesis. The influence of BG characteristics on macrophage responses is discussed. We highlight the strategies employed to harness macrophage responses for enhanced tissue regeneration, including the incorporation of active ions, surface functionalization, and controlled release of immunomodulatory molecules. Finally, we conclude with our perspectives on future research challenges and directions in the emerging field of immunomodulatory BGs for tissue regeneration. STATEMENT OF SIGNIFICANCE: Immunomodulatory effects of bioactive glasses (BGs) in relation to bone regeneration and wound healing have started to be understood. We summarize those studies which have focused on immunomodulatory BGs for tissue regeneration. We first introduce the potential mechanisms of the immunomodulation effects induced by BGs. Interactions between the cells involved in immunomodulation processes and BGs (and their dissolution products, biologically active ions) are elaborated. We highlight the strategies employed to modulate macrophage responses for enhancing tissue regeneration, including incorporation of active ions, surface functionalization, and controlled release of immunomodulatory agents. This is the first review article summarizing and outlining the immunomodulatory effects of BGs for tissue regeneration. We anticipate that increasing research efforts will start to emerge in the area of immunomodulatory BGs.

Harnessing the innate and adaptive immune system for tissue repair and regeneration: Considering more than macrophages

Tissue healing and regeneration is a complex, choreographed, spatiotemporal process involving a plethora of cell types, the activity of which is stringently regulated in order for effective tissue repair to ensue post injury. A number of globally prevalent conditions such as heart disease, organ failure, and severe musculoskeletal disorders require new therapeutic strategies to repair damaged or diseased tissue, particularly given an ageing population in which obesity, diabetes, and consequent tissue defects have reached epidemic proportions. This is further compounded by the lack of intrinsic healing and poor regenerative capacity of certain adult tissues. While vast progress has been made in the last decade regarding tissue regenerative strategies to direct self-healing, for example, through implantation of tissue engineered scaffolds, several challenges have hampered the clinical application of these technologies. Control of the immune response is growing as an attractive approach in regenerative medicine and it is becoming increasingly apparent that an in depth understanding of the interplay between cells of the immune system and tissue specific progenitor cells is of paramount importance. Furthermore, the integration of immunology and bioengineering promises to elevate the efficacy of biomaterial-based tissue repair and regeneration. In this review, we highlight the role played by individual immune cell subsets in tissue repair processes and describe new approaches that are being taken to direct appropriate healing outcomes via biomaterial mediated targeting of immune cell activity. STATEMENT OF SIGNIFICANCE: It is becoming increasingly apparent that controlling the immune response is as an attractive approach in regenerative medicine. Here, we propose that an in-depth understanding of immune system and tissue specific progenitor cell interactions may reveal mechanisms by which tissue healing and regeneration takes place, in addition to identifying novel therapeutic targets that could be used to enhance the tissue repair process. To date, most reviews have focused solely on macrophage subsets. This manuscript details the role of other innate and adaptive immune cells such as innate lymphoid cells (ILCs), natural killer (NK) cells and γδT cells (in addition to macrophages) in tissue healing. We also describe new approaches that are being taken to direct appropriate healing outcomes via biomaterial mediated cytokine and drug delivery.

Immunomodulatory Biomaterials for Tissue Repair

All implanted biomaterials are targets of the host's immune system. While the host inflammatory response was once considered a detrimental force to be blunted or avoided, in recent years, it has become a powerful force to be leveraged to augment biomaterial-tissue integration and tissue repair. In this review, we will discuss the major immune cells that mediate the inflammatory response to biomaterials, with a focus on how biomaterials can be designed to modulate immune cell behavior to promote biomaterial-tissue integration. In particular, the intentional activation of monocytes and macrophages with controlled timing, and modulation of their interactions with other cell types involved in wound healing, have emerged as key strategies to improve biomaterial efficacy. To this end, careful design of biomaterial structure and controlled release of immunomodulators can be employed to manipulate macrophage phenotype for the maximization of the wound healing response with enhanced tissue integration and repair, as opposed to a typical foreign body response characterized by fibrous encapsulation and implant isolation. We discuss current challenges in the clinical translation of immunomodulatory biomaterials, such as limitations in the use of in vitro studies and animal models to model the human immune response. Finally, we describe future directions and opportunities for understanding and controlling the biomaterial-immune system interface, including the application of new imaging tools, new animal models, the discovery of new cellular targets, and novel techniques for in situ immune cell reprogramming.

The potential regulatory role of BMP9 in inflammatory responses

Inflammation is a protective response of the body to pathogens and injury. Hence, it is particularly important to explore the pathogenesis and key regulatory factors of inflammation. BMP9 is a unique member of the BMP family, which is widely known for its strong osteogenic potential and insensitivity to the inhibition of BMP3. Recently, several studies have reported an underlying pivotal link between BMP9 and inflammation. What is clear, though not well understood, is that BMP9 plays a role in inflammation in a carefully choreographed manner in different contexts. In this review, we have summarized current studies focusing on BMP9 and inflammation in various tissues and the latest advances in BMP9 expression, signal transduction, and crystal structure to better understand the relationship between BMP9 and inflammation. In addition, we also briefly summarized the inflammatory characteristics of some TGF-β superfamily members to provide better insights and ideas for the study of BMP9 and inflammation.

Effect of Oxidative Stress on Bone Remodeling in Periprosthetic Osteolysis

The success of implant performance and arthroplasty is based on several factors, including oxidative stress-induced osteolysis. Oxidative stress is a key factor of the inflammatory response. Implant biomaterials can release wear particles which may elicit adverse reactions in patients, such as local inflammatory response leading to tissue damage, which eventually results in loosening of the implant. Wear debris undergo phagocytosis by macrophages, inducing a low-grade chronic inflammation and reactive oxygen species (ROS) production. In addition, ROS can also be directly produced by prosthetic biomaterial oxidation. Overall, ROS amplify the inflammatory response and stimulate both RANKL-induced osteoclastogenesis and osteoblast apoptosis, resulting in bone resorption, leading to periprosthetic osteolysis. Therefore, a growing understanding of the mechanism of oxidative stress-induced periprosthetic osteolysis and anti-oxidant strategies of implant design as well as the addition of anti-oxidant agents will help to improve implants’ performances and therapeutic approaches.

Immunopolarization-regulated 3D printed-electrospun fibrous scaffolds for bone regeneration

Three-dimension (3D)-printed bioscaffolds are precise and personalized for bone regeneration. However, customized 3D scaffolds may activate the immune response in vivo and consequently impede bone formation. In this study, with layer-by-layer deposition and electrospinning technology to control the physical structure, 3D-printed PCL scaffolds with PLLA electrospun microfibrous (3D-M-EF) and nanofibrous (3D-N-EF) composites were constructed, and their immunomodulatory effect and the subsequent osteogenic effects were explored. Compared to 3D-N-EF scaffolds, 3D-M-EF scaffolds polarized more RAW264.7 cells toward alternatively activated macrophages (M2), as demonstrated by increased M2 and deceased classically activated macrophage (M1) phenotypic marker expression in the cells. In addition, the 3D-M-EF scaffolds shifted RAW264.7 cells to the M2 phenotype through PI3K/AKT signaling and enhanced VEGF and BMP-2 expression. Conditional medium from the RAW264.7 cells seeded in 3D-M-EF scaffolds promoted osteogenesis of MC3T3-E1 cells. Furthermore, in vivo study of repairing rat calvarial defects, the 3D-M-EF scaffolds increased the polarization of M2 macrophages, enhanced angiogenesis, and accelerated new bone formation. Collectively, our data suggested that well-designed 3D-M-EF scaffolds are favorable for osteogenesis through regulation of M2 polarization. Therefore, it is potential to utilize the physical structure of 3D-printed scaffolds to manipulate the osteoimmune environment to promote bone regeneration.

Macrophages activated by akermanite/alginate composite hydrogel stimulate migration of bone marrow-derived mesenchymal stem cells

Akermanite (Aker) has been widely used for bone regeneration through regulating osteogenesis of bone marrow-derived mesenchymal stem cells (BMSCs). Previously, we developed an injectable Aker/sodium alginate (Aker/SA) hydrogel to facilitate bone regeneration. However, the effect of this injectable hydrogel on the in vivo response, particularly the inflammatory response, has not been fully understood. Here, to elucidate the response following the implantable of Aker/SA hydrogel, we investigated the interaction among Aker/SA hydrogel, inflammatory cells and cells involved in bone regeneration (BMSCs). Specifically, we cultured macrophages (RAW 264.7 cell line) with the extract liquid of Aker/SA and assessed their phenotypic changes. Subsequently, BMSCs (2*10^5 cells per 24 well) were cultured with different conditioned media including that of Aker/SA hydrogel-activated macrophages to investigate their effect on cell migration. Finally, Aker/SA hydrogel was injected subcutaneously (1*10^6 cells per ml) in rat to verify its effect in vivo. The in vitro results indicated that Aker/SA hydrogel activated macrophages towards M2 phenotype and stimulated macrophages to express anti-inflammatory factors. In addition, the conditioned medium collected from Aker-activated macrophages could accelerate the migration of BMSCs in 24h. Consistent with the in vitro results, when the Aker/SA hydrogel was injected subcutaneously, more M2 macrophages could be observed than when the SA solution was injected after 7 days. Besides, when BMSCs were delivered via subcutaneous injection, more BMSCs were recruited by the Aker/SA hydrogel than the SA solution. All these results suggest that the Aker/SA hydrogel can modulate the immune environment at the implantation site and subsequently recruit BMSCs, which can be one of the mechanisms through which the Aker/SA hydrogel accelerates new bone formation.

Zebrafish as a potential biomaterial testing platform for bone tissue engineering application: A special note on chitosan based bioactive materials

Biomaterials function as an essential aspect of tissue engineering and have a profound impact on cell growth and subsequent tissue regeneration. The development of new biomaterials requires a potential platform to understand the host-biomaterial interaction, which is crucial for successful biomaterial implantation. Biomaterials analyzed in rodent models for in vivo research are cost-effective but tedious, and the practice has many technical difficulties. As an alternative, zebrafish provide an excellent biomaterial testing platform over the current rodent models. During growth and recovery, zebrafish bone morphogenesis shows a variety of inductive signals involved in the cycle that are close to those influencing differentiation of bone and cartilage in mammals, including humans. This platform is cheap, optically transparent, quick to change genes, and provides reliable reproducibility on short life cycles. Chitosan is a well-known biomaterial in the field of tissue engineering. In view of its documented use in bone regeneration, the biological characterization of chitosan-based bioactive materials in the zebrafish model has been featured in an outstanding note. We, therefore, outlined this review of the zebrafish as a potential in vivo research model for the rapid characterization of the biological properties of new biomaterials for bone tissue engineering applications.

Activation of Bone Remodeling Compartments in BMP-2-Injected Knees Supports a Local Vascular Mechanism for Arthritis-Related Bone Changes

BACKGROUND

Synovial membrane-derived factors are implicated in arthritis-related bone changes. The route that synovial factors use to access subchondral bone and the mechanisms responsible for these bone changes remain unclear. A safety study involving intra-articular injection of bone morphogenetic protein-2 (BMP-2)/calcium phosphate matrix (CPM) or CPM addresses these issues.

METHODS

Knee joints in 21 monkeys were injected with CPM or 1.5 or 4.5 mg/mL BMP-2/CPM and were evaluated at 1 and 8 weeks. Contralateral joints were injected with saline solution. Knee joints in 4 animals each were injected with 1.5 or 4.5 mg/mL BMP-2/CPM. Contralateral joints were injected with corresponding treatments at 8 weeks. Both joints were evaluated at 16 weeks. Harvested joints were evaluated grossly and with histomorphometry. Knee joints in 3 animals were injected with 125I-labeled BMP-2/CPM and evaluated with scintigraphy and autoradiography at 2 weeks to determine BMP-2 distribution.

RESULTS

All treatments induced transient synovitis and increased capsular vascularization, observed to anastomose with metaphyseal venous sinusoids, but did not damage articular cartilage. Both treatments induced unanticipated activation of vascular-associated trabecular bone remodeling compartments (BRCs) restricted to injected knees. Bone volume increased in BMP-2/CPM-injected knees at 8 and 16 weeks. Scintigraphy demonstrated metaphyseal 125I-labeled BMP-2 localization restricted to injected knees, confirming local rather than systemic BMP-2 release. Autoradiography demonstrated that BMP-2 diffusion through articular cartilage into the metaphysis was blocked by the tidemark. The lack of marrow activation or de novo bone formation, previously reported following metaphyseal BMP-2/CPM administration, confirmed BMP-2 and synovial-derived factors were not free in the marrow. The 125I-labeled BMP-2/CPM, observed within venous sinusoids of injected knees, confirmed the potential for capsular and metaphyseal venous portal communication.

CONCLUSIONS

This study identifies a synovitis-induced venous portal circulation between the joint capsule and the metaphysis as an alternative to systemic circulation and local diffusion for synovial membrane-derived factors to reach subchondral bone. This study also identifies vascular-associated BRCs as a mechanism for arthritis-associated subchondral bone changes and provides additional support for their role in physiological trabecular bone remodeling and/or modeling.

CLINICAL RELEVANCE

Inhibition of synovitis and accompanying abnormal vascularization may limit bone changes associated with arthritis.

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.

Regulation of decellularized matrix mediated immune response

The substantially growing gap between suitable donors and patients waiting for new organ transplantation has compelled tissue engineers to look for suitable patient-specific alternatives. Lately, a decellularized extracellular matrix (dECM), obtained primarily from either discarded human tissues/organs or other species, has shown great promise in the constrained availability of high-quality donor tissues. In this review, we have addressed critical gaps and often-ignored aspects of understanding the innate and adaptive immune response to the dECM. Firstly, although most of the studies claim preservation of the ECM ultrastructure, almost all methods employed for decellularization would inevitably cause a certain degree of disruption to the ECM ultrastructure and modulation in secondary conformations, which may elicit a distinct immunogenic response. Secondly, it is still a major challenge to find ways to conserve the native biochemical, structural and biomechanical cues by making a judicious decision regarding the choice of decellularization agents/techniques. We have critically analyzed various decellularization protocols and tried to find answers on various aspects such as whether the secondary structural conformation of dECM proteins would be preserved after decellularization. Thirdly, to keep the dECM ultrastructure as close to the native ECM we have raised the question "How good is good enough?" Even residual cellular antigens or nucleic acid fragments may elicit antigenicity leading to a low-grade immune response. A combinative knowledge of macrophage plasticity in the decellularized tissue and limits of decellularization will help achieve the native ultrastructure. Lastly, we have shifted our focus on the scientific basis of the presently accepted criteria for decellularization, and the effect on immune response concerning the interaction between the decellularized extracellular matrix and macrophages with the subsequent influence of T-cell activation. Amalgamating suitable decellularization approaches, sufficient knowledge of macrophage plasticity and elucidation of molecular pathways together will help fabricate functional immune informed decellularized tissues in vitro that will have substantial implications for efficient clinical translation and prediction for in vivo reprogramming and tissue regeneration.

Decellularized Human Chorion Membrane as a Novel Biomaterial for Tissue Regeneration

Although some placenta-derived products are already used for tissue regeneration, the human chorion membrane (HCM) alone has been poorly explored. In fact, just one study uses decellularized HCM (dHCM) with native tissue architecture (i.e., without extracellular matrix (ECM) suspension creation) as a substrate for cell differentiation. The aim of this work is to fully characterize the dHCM for the presence and distribution of cell nuclei, DNA and ECM components. Moreover, mechanical properties, in vitro biological performance and in vivo biocompatibility were also studied. Our results demonstrated that the HCM was successfully decellularized and the main ECM proteins were preserved. The dHCM has two different surfaces, the reticular layer side and the trophoblast side; and is biocompatible both in vitro and in vivo. Importantly, the in vivo experiments demonstrated that on day 28 the dHCM starts to be integrated by the host tissue. Altogether, these results support the hypothesis that dHCM may be used as a biomaterial for different tissue regeneration strategies, particularly when a membrane is needed to separate tissues, organs or other biologic compartments.

Biological responses to physicochemical properties of biomaterial surface

Biomedical scientists use chemistry-driven processes found in nature as an inspiration to design biomaterials as promising diagnostic tools, therapeutic solutions, or tissue substitutes. While substantial consideration is devoted to the design and validation of biomaterials, the nature of their interactions with the surrounding biological microenvironment is commonly neglected. This gap of knowledge could be owing to our poor understanding of biochemical signaling pathways, lack of reliable techniques for designing biomaterials with optimal physicochemical properties, and/or poor stability of biomaterial properties after implantation. The success of host responses to biomaterials, known as biocompatibility, depends on chemical principles as the root of both cell signaling pathways in the body and how the biomaterial surface is designed. Most of the current review papers have discussed chemical engineering and biological principles of designing biomaterials as separate topics, which has resulted in neglecting the main role of chemistry in this field. In this review, we discuss biocompatibility in the context of chemistry, what it is and how to assess it, while describing contributions from both biochemical cues and biomaterials as well as the means of harmonizing them. We address both biochemical signal-transduction pathways and engineering principles of designing a biomaterial with an emphasis on its surface physicochemistry. As we aim to show the role of chemistry in the crosstalk between the surface physicochemical properties and body responses, we concisely highlight the main biochemical signal-transduction pathways involved in the biocompatibility complex. Finally, we discuss the progress and challenges associated with the current strategies used for improving the chemical and physical interactions between cells and biomaterial surface.

Immunomodulation of surface biofunctionalized 3D printed porous titanium implants

Additive manufacturing (AM) techniques have provided many opportunities for the rational design of porous metallic biomaterials with complex and precisely controlled topologies that give rise to unprecedented combinations of mechanical, physical, and biological properties. These favorable properties can be enhanced by surface biofunctionalization to enable full tissue regeneration and minimize the risk of implant-associated infections (IAIs). There is, however, an increasing need to investigate the immune responses triggered by surface biofunctionalized AM porous metals. Here, we studied the immunomodulatory effects of AM porous titanium (Ti-6Al-4V) printed using selective laser melting, and of two additional groups consisting of AM implants surface biofunctionalized using plasma electrolytic oxidation (PEO) with/without silver nanoparticles. The responses of human primary macrophages and human mesenchymal stromal cells (hMSCs) were studied in terms of cell viability, cell morphology and biomarkers of macrophage polarization. Non-treated AM porous titanium triggered a strong pro-inflammatory response in macrophages, albeit combined with signs of anti-inflammatory effects. The PEO treatment of AM porous titanium implants showed a higher potential to induce polarization towards a pro-repair macrophage phenotype. We detected no cytotoxicity against hMSCs in any of the groups. However, the incorporation of silver nanoparticles resulted in strong cytotoxicity against attached macrophages. The results of this study indicate the potential immunomodulatory effects of the AM porous titanium enhanced with PEO treatment, and point towards caution and further research when using silver nanoparticles for preventing IAIs.

Study on the potential mechanism of anti-inflammatory activity of covalently immobilized hyaluronan and heparin

Inflammation and subsequent fibrotic encapsulation that occur after implantation of biomaterials are issues that fostered efforts in designing novel biocompatible materials to modulate the immune response. In this study, glycosaminoglycans (GAG) like hyaluronic acid (HA) and heparin (Hep) that possess anti-inflammatory activity were covalently bound to NH₂ -modified surfaces using EDC/NHS cross-linking chemistry. Immobilization and physical surface properties were characterized by atomic forces microscopy, water contact angle studies and streaming potential measurements demonstrating the presence of GAG on the surfaces that became more hydrophilic and negatively charged compared to NH₂ -modified. THP-1 derived macrophages were used here to study the mechanism of action of GAG to affect the inflammatory responses illuminated by studying macrophage adhesion, the formation of multinucleated giant cells (MNGCs) and IL-1β release that were reduced on GAG-modified surfaces. Detailed investigation of the signal transduction processes related to macrophage activation was performed by immunofluorescence staining of NF-κB (p65 subunit) together with immunoblotting. We studied also association and translocation of FITC-labeled GAG. The results show a significant decrease in NF-κB level as well as the ability of macrophages to associate with and take up HA and Hep. These results illustrate that the anti-inflammatory activity of GAG is not only related to making surfaces more hydrophilic, but also their active involvement in signal transduction processes related to inflammatory reactions, which may pave the way to design new anti-inflammatory surface coatings for implantable biomedical devices.

Targeting NLRP3 Inflammasome in Inflammatory Bowel Disease: Putting out the Fire of Inflammation

Inflammatory bowel disease (IBD) is a group of inflammatory conditions of the colon and small intestine, comprised of ulcerative colitis and Crohn's disease. Among the complicated pathogenic factors of IBD, the overaction of inflammatory and immune reaction serves as an important factor. Inflammasome is a form of innate immunity as well as inflammation. Among all kinds of inflammasomes, the NOD-like receptor family, pyrin domain-containing 3 (NLRP3) inflammasome is the most studied one, and has been revealed to be involved in the pathogenesis and progression of IBD. Here, in this review, the association between the NLRP3 inflammasome and IBD will be discussed. Furthermore, several NLRP3 inflammasome inhibitors which have been demonstrated to be effective in the alleviation of IBD will be described in this review.

Role of rheological properties on physical chitosan aerogels obtained by supercritical drying

Chitosan aerogels were obtained after using supercritical carbon dioxide to dry physical hydrogels, studying the effect of the rheological behavior of hydrogels and solutions on the final aerogels properties. An increase on the solutions pseudoplasticity increased the subsequent hydrogels physical entanglement, without showing a significant effect on aerogels morphology (nanoporous) and textural properties (pores of about 10 nm). However, an increase of hydrogel physical entanglement promoted the formation of aerogels with a higher compressive strength (from 0.2 to 0.80 MPa) and higher thermal decomposition range, while decreasing the porosity (from 90 % to 94 %). Aerogels stress-strain responses were also successfully fitted using a hyperelastic equation with three adjustable parameters (Yeoh), showing that this type of models must be taken into account when large stresses are studied.

A mussel-inspired catecholic ABA triblock copolymer exhibits better antifouling properties compared to a diblock copolymer

The scheme of the chemical architecture, aggregation, assembly and antifouling properties of two copolymers.

In Vivo Evaluation of the Biocompatibility of Biomaterial Device

Biomaterials are widely used to produce devices for regenerative medicine. After its implantation, an interaction between the host immune system and the implanted biomaterial occurs, leading to biomaterial-specific cellular and tissue responses. These responses may include inflammatory, wound healing responses, immunological and foreign-body reactions, and even fibrous encapsulation of the implanted biomaterial device. In fact, the cellular and molecular events that regulate the success of the implant and tissue regeneration are played at the interface between the foreign body and the host inflammation, determined by innate and adaptive immune responses. This chapter focuses on host responses that must be taken into consideration in determining the biocompatibility of biomaterial devices when implanted in vivo of animal models.

Hybridization of a phospholipid polymer hydrogel with a natural extracellular matrix using active cell immobilization

Three-dimensional tissue organization is still an obstacle in the field of tissue engineering, which generally involves cell immobilization, proliferation, and organization. As an artificial extracellular matrix (ECM) for providing a suitable environment of cells to construct tissues, combination of cytocompatible polymer hydrogels and natural ECM produced by the immobilized cells was considered. In this research, we designed a spontaneously forming hydrogel system between two water-soluble polymers for the immobilization of cells. These polymers were poly(2-methacryloyloxyethyl phosphorylcholine-co-n-butyl methacrylate-co-p-vinylphenylboronic acid-co-N-succinimidyloxycarbonyl tetra(ethylene glycol)methacrylate) (PMBVS) and poly(vinyl alcohol) (PVA) to form a PMBVS/PVA hydrogel in a cell culture medium under mild conditions. Basic fibroblast growth factor (bFGF) was conjugated with PMBVS (PMBV-bFGF). To enhance the growth of the immobilized cells, mouse fibroblast L929 cells were immobilized in the PMBVS/PVA hydrogel and the PMBV-bFGF/PVA hydrogel, and their proliferation and secretion of the ECM under stimulation with bFGF was observed. The ECM infiltrated and replaced the hydrogel, resulting in the formation of a hybrid hydrogel with the ECM and laden cells.

Pulp ECM-derived macroporous scaffolds for stimulation of dental-pulp regeneration process

OBJECTIVE

Recent studies suggest xenogeneic extracellular matrices as potential regenerative tools in dental pulp regeneration. This study aimed to fabricate and characterize a novel three-dimensional macroporous pulp-derived scaffold that enables the attachment, penetration, proliferation and differentiation of mesenchymal stem cells.

METHOD

Bovine pulp was decellularized and characterized with histological and DNA content methods. This scaffold was prepared using finely milled lyophilized decellularized pulp extracellular matrix (ECM) digested with pepsin. Three different concentrations of ECM (1.50, 2.25 and 3.00mg/ml) were freeze-dried and were tested with/without chemical crosslinking. The specimens were subjected to physicochemical characterization, cell viability and quantitative real time polymerase chain reaction assessments with human bone marrow mesenchymal stem cells (hBMMSCs). All scaffolds were subcutaneously implanted in rats for two weeks and histological and immunostaining analyses were performed.

RESULTS

Histological and DNA analysis confirmed complete decellularization. All samples demonstrated more than 97% porosity and 1.50mg/ml scaffold demonstrated highest water absorption. The highest cell viability and proliferation of hBMMSCs was observed on the 3.00mg/ml crosslinked scaffolds. The gene expression analysis showed a significant increase of dmp-1 and collagen-I on 3.00mg/ml crosslinked scaffolds compared to the other scaffolds. Histological examination of subcutaneous implanted scaffolds revealed low immunological response, and enhanced angiogenesis in cross-linked samples compared to non-crosslinked samples.

SIGNIFICANCE

The three-dimensional macroporous pulp-derived injectable scaffold developed and characterized in this study displayed potential for regenerative therapy. While the scaffold biodegradability was decreased by crosslinking, the biocompatibility of post-crosslinked scaffold was significantly improved.

In vivo engineered extracellular matrix scaffolds with instructive niches for oriented tissue regeneration

Implanted scaffolds with inductive niches can facilitate the recruitment and differentiation of host cells, thereby enhancing endogenous tissue regeneration. Extracellular matrix (ECM) scaffolds derived from cultured cells or natural tissues exhibit superior biocompatibility and trigger favourable immune responses. However, the lack of hierarchical porous structure fails to provide cells with guidance cues for directional migration and spatial organization, and consequently limit the morpho-functional integration for oriented tissues. Here, we engineer ECM scaffolds with parallel microchannels (ECM-C) by subcutaneous implantation of sacrificial templates, followed by template removal and decellularization. The advantages of such ECM-C scaffolds are evidenced by close regulation of in vitro cell activities, and enhanced cell infiltration and vascularization upon in vivo implantation. We demonstrate the versatility and flexibility of these scaffolds by regenerating vascularized and innervated neo-muscle, vascularized neo-nerve and pulsatile neo-artery with functional integration. This strategy has potential to yield inducible biomaterials with applications across tissue engineering and regenerative medicine.

Self-mineralizing Ca-enriched methacrylated gellan gum beads for bone tissue engineering

In this study, methacrylated gellan-gum (GG-MA) heteropolysaccharide is proposed as a hydrogel for drug delivery and bone tissue engineering applications. Calcium-enriched beads obtained from the crosslinking of 1% (w/v) GG-MA solutions with 0.1 MCaCl₂ were investigated, considering their intrinsic capacity to promote self-mineralization by ion binding and deposition. Indeed, when immersed in a physiological environment, the Ca-enriched beads promoted the development of a bone-like apatite layer, as confirmed by EDS and XRD chemical analysis. Additionally, the mild production process is compatible with drugs incorporation and release. After encapsulation, Dextran with different molecular weights as well as Dexamethasone 21-phosphate were efficiently released to the surrounding environment. The engineered system was also evaluated considering its biocompatibility, by means of qualitative determination of total complement activation, macrophage proliferation, cytokine release and in vitro cell culture. These experiments showed that the developed hydrogels may not stimulate a disproportionate pro-inflammatory reaction once transplanted. At last, when implanted subcutaneously in CD1 male mice up to 8 weeks, the beads were completely calcified, and no inflammatory reaction was observed. Summing up, these results show that calcium-enriched GG-MA hydrogel beads hold great potential as news tools for bone tissue regeneration and local drug delivery applications. STATEMENT OF SIGNIFICANCE: This work describes a low-cost and straightforward strategy to prepare bioactive methacrylated gellan gum (GG-MA) hydrogels, which can be used as drug delivery systems. GG-MA is a highly anionic polymer, that can be crosslinked with divalent ions, as calcium. Taking advantage of this feature, it was possible to prepare Ca-enriched GG-MA hydrogel beads. These beads display a bioactive behavior, since they promote apatite deposition when placed in physiological conditions. Studies on the immune response suggest that the developed beads do not trigger severe immune responses. Importantly, the mild processing method render these beads compliant with drug delivery strategies, paving the way for the application of dual-functional materials on bone tissue engineering.

A roadmap for promoting endogenous in situ tissue restoration using inductive bioscaffolds after acute brain injury

The regeneration of brain tissue remains one of the greatest unsolved challenges in medicine and by many is considered unfeasible. Indeed, the adult mammalian brain does not regenerate tissue, but there is ongoing endogenous neurogenesis, which is upregulated after injury and contributes to tissue repair. This endogenous repair response is a conditio sine que non for tissue regeneration. However, scarring around the lesion core and cavitation provide unfavorable conditions for tissue regeneration in the brain. Based on the success of using extracellular matrix (ECM)-based bioscaffolds in peripheral soft tissue regeneration, it is plausible that the provision of an inductive ECM-based hydrogel inside the volumetric tissue loss can attract neural cells and create a de novo viable tissue. Following perturbation theory of these successes in peripheral tissues, we here propose 9 perturbation parts (i.e. requirements) that can be solved independently to create an integrated series to build a functional and integrated de novo neural tissue. Necessities for tissue formation, anatomical and functional connectivity are further discussed to provide a new substrate to support the improvement of behavioral impairments after acute brain injury. We also consider potential parallel developments of this tissue engineering effort that can support therapeutic benefits in the absence of de novo tissue formation (e.g. structural support to veterate brain tissue). It is envisaged that eventually top-down inductive "natural" bioscaffolds composed of decellularized tissues (i.e. ECM) will be replaced by bottom-up synthetic designer hydrogels that will provide very defined structural and signaling properties, potentially even opening up opportunities we currently do not envisage using natural materials.

3D type I collagen environment leads up to a reassessment of the classification of human macrophage polarizations

Macrophages have multiple roles in development, tissue homeostasis and repair and present a high degree of phenotypic plasticity embodied in the concept of polarization. One goal of macrophage biology field is to characterize these polarizations at the molecular level. To achieve this task, it is necessary to integrate how physical environment signals are interpreted by macrophages under immune stimulation. In this work, we study how a 3D scaffold obtained from polymerized fibrillar rat type I collagen modulates the polarizations of human macrophages and reveal that some traditionally used markers should be reassessed. We demonstrate that integrin β₂ is a regulator of STAT1 phosphorylation in response to IFNγ/LPS as well as responsible for the inhibition of ALOX15 expression in response to IL-4/IL-13 in 3D. Meanwhile, we also find that the CCL19/CCL20 ratio is reverted in 3D under IFNγ/LPS stimulation. 3D also induces the priming of the NLRP3 inflammasome resulting in an increased IL-1β and IL-6 secretion. These results give the molecular basis for assessing collagen induced immunomodulation of human macrophages in various physiological and pathological contexts such as cancer.

Macrophage and Fibroblast Interactions in Biomaterial-Mediated Fibrosis

Biomaterial-mediated inflammation and fibrosis remain a prominent challenge in designing materials to support tissue repair and regeneration. Despite the many biomaterial technologies that have been designed to evade or suppress inflammation (i.e., delivery of anti-inflammatory drugs, hydrophobic coatings, etc.), many materials are still subject to a foreign body response, resulting in encapsulation of dense, scar-like extracellular matrix. The primary cells involved in biomaterial-mediated fibrosis are macrophages, which modulate inflammation, and fibroblasts, which primarily lay down new extracellular matrix. While macrophages and fibroblasts are implicated in driving biomaterial-mediated fibrosis, the signaling pathways and spatiotemporal crosstalk between these cell types remain loosely defined. In this review, the role of M1 and M2 macrophages (and soluble cues) involved in the fibrous encapsulation of biomaterials in vivo is investigated, with additional focus on fibroblast and macrophage crosstalk in vitro along with in vitro models to study the foreign body response. Lastly, several strategies that have been used to specifically modulate macrophage and fibroblast behavior in vitro and in vivo to control biomaterial-mediated fibrosis are highlighted.