The effect of cell debris within biologic scaffolds upon the macrophage response

Endotoxin, not DNA, determines the host response and tissue regeneration behavior of acellular biologic scaffolds

Established quantitative standards for assessing decellularization of biologic scaffolds based on residual DNA levels have been well-documented and widely acknowledged. However, post-implantation complications, such as fever and seroma, are commonly observed which negatively impact clinical outcomes. The presence of cellular debris following decellularization or using source tissues that are naturally high in endotoxin may contribute to the host response to a biologic scaffold. In the study, several multi-step decellularization methods were used to decellularize small intestinal submucosa (SIS) to obtain materials with three distinct levels of residual DNA, lipid residues, and endogenous endotoxin. The potential influence of these residual components on macrophage and lymphocyte polarization in vitro, as well as on the host inflammatory response in vivo post intra-abdominal implantation or abdominal wall defect repair in rats, was assessed. Urinary bladder matrix (UBM) meeting established decellularization criteria and naturally devoid of endotoxin was utilized as a control. The presence of endogenous endotoxin in SIS-ECM resulted in notable changes in macrophage phenotype. SIS-ECM samples with endotoxin levels below FDA limits still upregulated pro-inflammatory factors in vitro. Conversely, SIS with minimal endotoxin content and UBM controls prompted a shift towards a pro-remodeling M2 phenotype, fostering constructive tissue remodeling in a rodent model of abdominal wall defects, irrespective of DNA content. These findings suggest that endotoxin may be a crucial factor influencing biologic scaffolds that are not fully accounted by current decellularization standards. STATEMENT OF SIGNIFICANCE: Clinically utilized decellularized biologic scaffolds that meet the established quantitative standards still suffer problems in high incidence of inflammatory complications, including fever and seroma. In this study, we confirmed that endotoxin, rather than residual DNA, is the crucial factor influencing host responses and regenerative outcomes. Tissue sources and decellularization processes are critical for reducing endotoxin levels and attenuating immuno-inflammatory complications. These findings enhance the evaluation of ECM scaffold performance for clinical application, thereby facilitating improved preparation and utilization for tissue defect repairs.

HLA Awareness in tissue decellularization: A paradigm shift for enhanced biocompatibility, studied on the model of the human fascia lata graft

Last twenties, tissue engineering has rapidly advanced to address the shortage of organ donors. Decellularization techniques have been developed to mitigate immune rejection and alloresponse in transplantation. However, a clear definition of effective decellularization remains elusive. This study compares various decellularization protocols using the human fascia lata model. Morphological, structural and cytotoxicity/viability analyses indicated that all the five tested protocols were equivalent and met Crapo's criteria for successful decellularization. Interestingly, only the in vivo immunization test on rats revealed differences. Only one protocol exhibited Human Leucocyte Antigen (HLA) content below 1% residual threshold, the only criterion preventing rat immunization with an absence of rat anti-human IgG switch after one month (N=4 donors for each of the 7 groups, added by negative and positive controls, n=28). By respecting a refined set of criteria, i.e. lack of visible nuclear material, <50ng DNA/mg dry weight of extracellular matrix, and <1% residual HLA content, the potential for adverse host reactions can be drastically reduced. In conclusion, this study emphasizes the importance of considering not only nuclear components but also major histocompatibility complex in decellularization protocols and proposes new guidelines to promote safer clinical development and use of bioengineered scaffolds.

Semi-quantitative scoring criteria based on multiple staining methods combined with machine learning to evaluate residual nuclei in decellularized matrix

The detection of residual nuclei in decellularized extracellular matrix (dECM) biomaterials is critical for ensuring their quality and biocompatibility. However, current evaluation methods have limitations in addressing impurity interference and providing intelligent analysis. In this study, we utilized four staining techniques-hematoxylin-eosin staining, acetocarmine staining, the Feulgen reaction and 4',6-diamidino-2-phenylindole staining-to detect residual nuclei in dECM biomaterials. Each staining method was quantitatively evaluated across multiple parameters, including area, perimeter and grayscale values, to establish a semi-quantitative scoring system for residual nuclei. These quantitative data were further employed as learning indicators in machine learning models designed to automatically identify residual nuclei. The experimental results demonstrated that no single staining method alone could accurately differentiate between nuclei and impurities. In this study, a semi-quantitative scoring table was developed. With this table, the accuracy of determining whether a single suspicious point is a cell nucleus has reached over 98%. By combining four staining methods, false positives caused by impurity contamination were eliminated. The automatic recognition model trained based on nuclear parameter features reached the optimal index of the model after several iterations of training in 172 epochs. The trained artificial intelligence model achieved a recognition accuracy of over 90% for detecting residual nuclei. The use of multidimensional parameters, integrated with machine learning, significantly improved the accuracy of identifying nuclear residues in dECM slices. This approach provides a more reliable and objective method for evaluating dECM biomaterials, while also increasing detection efficiency.

From isolation to detection, advancing insights into endothelial matrix-bound vesicles

Matrix-bound vesicles (MBVs), an integral part of the extracellular matrix (ECM), are emerging as pivotal factors in ECM-driven molecular signaling. This study is the first to report the isolation of MBVs from porcine arterial endothelial cell basement membranes (A-MBVs) and thyroid cartilage (C-MBVs), the latter serving as a negative control due to its minimal vascular characteristics. Using Transmission Electron Microscopy (TEM), Nano-Tracking Analysis (NTA), Electrochemical Impedance Spectroscopy (EIS), and Atomic Force Microscopy (AFM), we orthogonally characterized the isolated MBVs. We detected the presence and preservation of vascular endothelial cadherin (CD144) in A-MBVs, its low to non-detetcted in C-MBVs, in which SOX9, a chondrocyte marker, was detected. Moreover, we developed a prototype of an immuno-functionalized screen-printed electrode designed for the immunoadsorption of CD144+ MBVs. This device facilitated the electrochemical detection of the targeted vesicles and allowed for their subsequent topological characterization using AFM, which verified the integrity and morphology of CD144+ MBVs post-immunoadsorption. These advancements enhance our comprehension of MBVs as conveyors of tissue-specific signals and pioneer new avenues for harnessing their cargo in biomedical applications. This research sets a significant precedent for future studies on the application of MBVs in regenerative medicine and ECM signaling.

Matrix-bound nanovesicles alleviate particulate-induced periprosthetic osteolysis

Aseptic loosening of orthopedic implants is an inflammatory disease characterized by immune cell activation, chronic inflammation, and destruction of periprosthetic bone, and is one of the leading reasons for prosthetic failure, affecting 12% of total joint arthroplasty patients. Matrix-bound nanovesicles (MBVs) are a subclass of extracellular vesicle recently shown to mitigate inflammation in preclinical models of rheumatoid arthritis and influenza-mediated "cytokine storm." The molecular mechanism of these anti-inflammatory properties is only partially understood. The objective of the present study was to investigate the effects of MBV on RANKL-induced osteoclast formation in vitro and particulate-induced osteolysis in vivo. Results showed that MBV attenuated osteoclast differentiation and activity by suppressing the NF-κB signaling pathway and downstream NFATc1, DC-STAMP, c-Src, and cathepsin K expression. In vivo, local administration of MBV attenuated ultrahigh molecular weight polyethylene particle-induced osteolysis, bone reconstruction, and periosteal inflammation. The results suggest that MBV may be a therapeutic option for preventing periprosthetic loosening.

Comparative Analysis of Commercially Available Extracellular Matrix Soft Tissue Bioscaffolds

Decellularized extracellular matrix (dECM) products are widely established for soft tissue repair, reconstruction, and reinforcement. These regenerative biomaterials mimic native tissue ECM with respect to structure and biology and are produced from a range of tissue sources and species. Optimal source tissue processing requires a balance between removal of cellular material and the preservation of structural and biological properties of tissue ECM. Despite the widespread clinical use of dECM products there is a lack of comparative information on these products. This study provides a comparative analysis of 12 commercially available dECM products. One group of products consisted of materials intended for dermal repair including ovine forestomach matrix (OFMm), porcine peritoneum (PPN), porcine placenta (PPC), and porcine small intestinal submucosa (SISu). The second group, intended for load-bearing reconstruction, consisted of material derived from ovine forestomach matrix (OFMo), porcine urinary bladder matrix (UBM), porcine small intestinal submucosa (SISb and SISz), human dermis (ADM), porcine dermis (PADM), and fetal/neonatal bovine dermis (BADM). A minimally processed product consisting of human placental tissue was included as a control. Products were compared histologically and by agarose gel electrophoreses to assess structural features and decellularization. Structurally, some dECM products showed a well-preserved collagen architecture with a broad porosity distribution, whereas others showed a significantly altered structure compared with native tissue. Decellularization varied across the products. Some materials surveyed (OFMm, PPN, PPC, OFMo, UBM, SISz, ADM, PADM, and BADM) were essentially devoid of nuclear bodies (mean count of <5 cells per high-powered field [HPF]), whereas others (SISu and SISb) demonstrated an abundance of nuclear bodies (>50 cells per HPF). Pathology assessment of the products demonstrated that OFMm, OFMo, and PADM had the highest qualitative assessment score for collagen fiber orientation and arrangement, matrix porosity, decellularization efficiency, and residual vascular channels scoring 10.5 ± 0.8, 12.8 ± 1.0, and 9.7 ± 0.7 out of a maximum total score of 16, respectively. This analysis of commercially available dECM products in terms of their structure and cellularity includes 12 different commercial materials. The findings highlight the variability of the products in terms of matrix structure and the efficacy of decellularization.

Decellularized extracellular matrix-based bioengineered 3D breast cancer scaffolds for personalized therapy and drug screening

Breast cancer (BC) is the second deadliest cancer after lung cancer. Similar to all cancers, it is also driven by a 3D microenvironment. The extracellular matrix (ECM) is an essential component of the 3D tumor micro-environment, wherein it functions as a scaffold for cells and provides metabolic support. BC is characterized by alterations in the ECM. Various studies have attempted to mimic BC-specific ECMs using artificial materials, such as Matrigel. Nevertheless, research has proven that naturally derived decellularized extracellular matrices (dECMs) are superior in providing the essential in vivo-like cues needed to mimic a cancer-like environment. Developing in vitro 3-D BC models is not straightforward and requires extensive analysis of the data established by researchers. For the benefit of researchers, in this review, we have tried to highlight all developmental studies that have been conducted by various scientists so far. The analysis of the conclusions drawn from these studies is also discussed. The advantages and drawbacks of the decellularization methods employed for generating BC scaffolds will be covered, and the review will shed light on how dECM scaffolds help develop a BC environment. The later stages of the article will also focus on immunogenicity issues arising from decellularization and the origin of the tissue. Finally, this review will also discuss the biofabrication of matrices, which is the core part of the bioengineering process.

Pig-derived ECM-SIS provides a novel matrix gel for tumor modeling

The absence of effective extracellular matrix to mimic the natural tumor microenvironment remains a significant obstacle in cancer research. Matrigel, abundant in various biological matrix components, is limited in its application due to its high cost. This has prompted researchers to explore alternative matrix substitutes. Here, we have investigated the effects of the extracellular matrix derived from pig small intestinal submucosa (ECM-SIS) in xenograft tumor modeling. Our results showed that the pig-derived ECM-SIS effectively promotes the establishment of xenograft tumor models, with a tumor formation rate comparable to that of Matrigel. Furthermore, we showed that the pig-derived ECM-SIS exhibited lower immune rejection and fewer infiltrating macrophages than Matrigel. Gene sequencing analysis demonstrated only a 0.5% difference in genes between pig-derived ECM-SIS and Matrigel during the process of tumor tissue formation. These differentially expressed genes primarily participate in cellular processes, biological regulation, and metabolic processes. These findings emphasize the potential of pig-derived ECM-SIS as a cost-effective option for tumor modeling in cancer research.

Exploring the properties and potential of the neural extracellular matrix for next-generation regenerative therapies

The extracellular matrix (ECM) is a dynamic and complex network of proteins and molecules that surrounds cells and tissues in the nervous system and orchestrates a myriad of biological functions. This review carefully examines the diverse interactions between cells and the ECM, as well as the transformative chemical and physical changes that the ECM undergoes during neural development, aging, and disease. These transformations play a pivotal role in shaping tissue morphogenesis and neural activity, thereby influencing the functionality of the central nervous system (CNS). In our comprehensive review, we describe the diverse behaviors of the CNS ECM in different physiological and pathological scenarios and explore the unique properties that make ECM-based strategies attractive for CNS repair and regeneration. Addressing the challenges of scalability, variability, and integration with host tissues, we review how advanced natural, synthetic, and combinatorial matrix approaches enhance biocompatibility, mechanical properties, and functional recovery. Overall, this review highlights the potential of decellularized ECM as a powerful tool for CNS modeling and regenerative purposes and sets the stage for future research in this exciting field. This article is categorized under: Implantable Materials and Surgical Technologies > Nanotechnology in Tissue Repair and Replacement Therapeutic Approaches and Drug Discovery > Nanomedicine for Neurological Disease Implantable Materials and Surgical Technologies > Nanomaterials and Implants.

Comparative evaluation of two different xenogenic acellular matrices on full-thickness skin wound healing

OBJECTIVE

The purpose of the study was to compare the healing potential of bubaline small intestinal matrix (bSIM) and fish swim bladder matrix (FSBM) on full-thickness skin wounds in rabbits.

METHOD

Four full-thickness skin wounds (each 20×20mm) were created on the dorsum of 18 rabbits that were divided into three groups based on treatment: untreated sham control (I), implanted with double layers of bSIM (II) and implanted with double layers of FSBM (III). Macroscopic, immunologic and histologic observations were made to evaluate wound healing.

RESULTS

Gross healing progression in the bSIM and FSBM groups showed significantly (p<0.05) less wound contraction compared with the sham group. The IgG concentration in rabbit sera was significantly (p<0.05) lower in the FSBM group compared with the bSIM group by enzyme-linked immunosorbent assay. The stimulation index of peripheral blood lymphocytes was significantly (p<0.05) lower in the FSBM group compared with the bSIM group by the MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay. Implantation of FSBM resulted in improved re-epithelialisation, neovascularisation and fibroplasia.

CONCLUSION

The FSBM is a more effective dermal substitute when compared with the bSIM for full-thickness skin wound repair in rabbit.

Soft Biomimetic Approach for the Development of Calcinosis-Resistant Glutaraldehyde-Fixed Biomaterials for Cardiovascular Surgery

Pathological aseptic calcification is the most common form of structural valvular degeneration (SVD), leading to premature failure of heart valve bioprostheses (BHVs). The processing methods used to obtain GA-fixed pericardium-based biomaterials determine the hemodynamic characteristics and durability of BHVs. This article presents a comparative study of the effects of several processing methods on the degree of damage to the ECM of GA-fixed pericardium-based biomaterials as well as on their biostability, biocompatibility, and resistance to calcification. Based on the assumption that preservation of the native ECM structure will enable the creation of calcinosis-resistant materials, this study provides a soft biomimetic approach for the manufacture of GA-fixed biomaterials using gentle decellularization and washing methods. It has been shown that the use of soft methods for preimplantation processing of materials, ensuring maximum preservation of the intactness of the pericardial ECM, radically increases the resistance of biomaterials to calcification. These obtained data are of interest for the development of new calcinosis-resistant biomaterials for the manufacture of BHVs.

A novel decellularized matrix of Wnt signaling-activated osteocytes accelerates the repair of critical-sized parietal bone defects with osteoclastogenesis, angiogenesis, and neurogenesis

Cell source is the key to decellularized matrix (DM) strategy. This study compared 3 cell types, osteocytes with/without dominant active Wnt/β-catenin signaling (daCO and WTO) and bone marrow stromal cells (BMSCs) for their DMs in bone repair. Decellularization removes all organelles and >95% DNA, and retained >74% collagen and >71% GAG, maintains the integrity of cell basement membrane with dense boundaries showing oval and honeycomb structure in osteocytic DM and smooth but irregular shape in the BMSC-DM. DM produced higher cell survival rate (90%) and higher proliferative activity. In vitro, daCO-DM induces more and longer stress fibers in BMSCs, conducive to cell adhesion, spreading, and osteogenic differentiation. 8-wk after implantation of the critical-sized parietal bone defect model, daCO-DM formed tight structures, composed of a large number of densely-arranged type-I collagen under polarized light microscope, which is similar to and integrated with host bone. BV/TV (>54%) was 1.5, 2.9, and 3.5 times of WTO-DM, BMSC-DM, and none-DM groups, and N.Ob/T.Ar (3.2 × 10²/mm²) was 1.7, 2.9, and 3.3 times. At 4-wk, daCO-DM induced osteoclastogenesis, 2.3 times higher than WTO-DM; but BMSC-DM or none-DM didn't. daCO-DM increased the expression of RANKL and MCSF, Vegfa and Angpt1, and Ngf in BMSCs, which contributes to osteoclastogenesis, angiogenesis, and neurogenesis, respectively. daCO-DM promoted H-type vessel formation and nerve markers β3-tubulin and NeuN expression. Conclusion: daCO-DM produces metabolic and neurovascularized organoid bone to accelerate the repair of bone defects. These features are expected to achieve the effect of autologous bone transplantation, suitable for transformation application.

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Decellularized matrix of osteocytes with dominant-active β-catenin (daCO-DM) promotes osteogenesis for regenerative repair.

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daCO-DM induces BMSCs to form stress fibers, conducive to cell adhesion, spreading, and differentiation towards osteoblasts.

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daCO-DM-induced osteoblasts have strong activity secreting dense and orderly-arranged type I collagen as host bone’s.

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daCO-DM induces BMSCs to express pre-osteoclastogenic cytokine RANKL and MCSF for osteoclastogenesis of marrow monocytes.

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daCO-DM enhances BMSCs to express angiogenic Vegfa and Angpt1, and neurogenic Ngf potentially for neurovascularization.

Bioengineering liver tissue by repopulation of decellularised scaffolds

Liver transplantation is the only curative therapy for end stage liver disease, but is limited by the organ shortage, and is associated with the adverse consequences of immunosuppression. Repopulation of decellularised whole organ scaffolds with appropriate cells of recipient origin offers a theoretically attractive solution, allowing reliable and timely organ sourcing without the need for immunosuppression. Decellularisation methodologies vary widely but seek to address the conflicting objectives of removing the cellular component of tissues whilst keeping the 3D structure of the extra-cellular matrix intact, as well as retaining the instructive cell fate determining biochemicals contained therein. Liver scaffold recellularisation has progressed from small rodent in vitro studies to large animal in vivo perfusion models, using a wide range of cell types including primary cells, cell lines, foetal stem cells, and induced pluripotent stem cells. Within these models, a limited but measurable degree of physiologically significant hepatocyte function has been reported with demonstrable ammonia metabolism in vivo. Biliary repopulation and function have been restricted by challenges relating to the culture and propagations of cholangiocytes, though advances in organoid culture may help address this. Hepatic vasculature repopulation has enabled sustainable blood perfusion in vivo, but with cell types that would limit clinical applications, and which have not been shown to have the specific functions of liver sinusoidal endothelial cells. Minority cell groups such as Kupffer cells and stellate cells have not been repopulated. Bioengineering by repopulation of decellularised scaffolds has significantly progressed, but there remain significant experimental challenges to be addressed before therapeutic applications may be envisaged.

Decellularized extracellular matrix (d-ECM): the key role of the inflammatory process in pre-regeneration after implantation

Clinical medicine is encountering the challenge of repairing soft-tissue defects. Currently, natural and synthetic materials have been developed as natural scaffolds. Among them, the decellularized extracellular matrix (d-ECM) can achieve tissue remodeling following injury and, thus, replace defects due to its advantages of the extensiveness of the source and excellent biological and mechanical properties. However, by analyzing the existing decellularization techniques, we found that different preparation methods directly affect the residual components of the d-ECM, and further have different effects on inflammation and regeneration of soft tissues. Therefore, we analyzed the role of different residual components of the d-ECM after decellularization. Then, we explored the inflammatory process and immune cells in an attempt to understand the mechanisms and causes of tissue degeneration and regeneration after transplantation. In this paper, we summarize the current studies related to updated protocols for the preparation of the d-ECM, biogenic and exogenous residual substances, inflammation, and immune cells influencing the fate of the d-ECM.

Immunogenicity of decellularized extracellular matrix scaffolds: a bottleneck in tissue engineering and regenerative medicine

Tissue-engineered decellularized extracellular matrix (ECM) scaffolds hold great potential to address the donor shortage as well as immunologic rejection attributed to cells in conventional tissue/organ transplantation. Decellularization, as the key process in manufacturing ECM scaffolds, removes immunogen cell materials and significantly alleviates the immunogenicity and biocompatibility of derived scaffolds. However, the application of these bioscaffolds still confronts major immunologic challenges. This review discusses the interplay between damage-associated molecular patterns (DAMPs) and antigens as the main inducers of innate and adaptive immunity to aid in manufacturing biocompatible grafts with desirable immunogenicity. It also appraises the impact of various decellularization methodologies (i.e., apoptosis-assisted techniques) on provoking immune responses that participate in rejecting allogenic and xenogeneic decellularized scaffolds. In addition, the key research findings regarding the contribution of ECM alterations, cytotoxicity issues, graft sourcing, and implantation site to the immunogenicity of decellularized tissues/organs are comprehensively considered. Finally, it discusses practical solutions to overcome immunogenicity, including antigen masking by crosslinking, sterilization optimization, and antigen removal techniques such as selective antigen removal and sequential antigen solubilization.

Engineered neural tissue made using hydrogels derived from decellularised tissues for the regeneration of peripheral nerves

Engineered neural tissue (EngNT) promotes in vivo axonal regeneration. Decellularised materials (dECM) are complex biologic scaffolds that can improve the cellular environment and also encourage positive tissue remodelling in vivo. We hypothesised that we could incorporate a hydrogel derived from a decellularised tissue (dECMh) into EngNT, thereby providing an alternative to the currently used purified collagen I hydrogel for the first time. Decellularisation was carried out on bone (B-ECM), liver (LIV-ECM), and small intestinal (SIS-ECM) tissues and the resultant dECM was biochemically and mechanically characterised. dECMh differed in mechanical and biochemical properties that likely had an effect on Schwann cell behaviour observed in metabolic activity and contraction profiles. Cellular alignment was observed in tethered moulds within the B-ECM and SIS-ECM derived hydrogels only. No difference was observed in dorsal root ganglia (DRG) neurite extension between the dECMh groups and collagen I groups when applied as a coverslip coating, however, when DRG were seeded atop EngNT constructs, only the B-ECM derived EngNT performed similarly to collagen I derived EngNT. B-ECM EngNT further exhibited similar axonal regeneration to collagen I EngNT in a 10 mm gap rat sciatic nerve injury model after 4 weeks. Our results have shown that various dECMh can be utilised to produce EngNT that can promote neurite extension in vitro and axonal regeneration in vivo. STATEMENT OF SIGNIFICANCE: Nerve autografts are undesirable due to the sacrifice of a patient's own nerve tissue to repair injuries. Engineered neural tissue (EngNT) is a type of living artificial tissue that has been developed to overcome this. To date, only a collagen hydrogel has been shown to be effective in the production and utilisation of EngNT in animal models. Hydrogels may be made from decellularised extracellular matrix derived from many tissues. In this study we showed that hydrogels from various tissues may be used to create EngNT and one was shown to comparable to the currently used collagen based EngNT in a rat sciatic nerve injry model.

Constructing high-strength nano-micro fibrous woven scaffolds with native-like anisotropic structure and immunoregulatory function for tendon repair and regeneration

Tendon injuries are common debilitating musculoskeletal diseases with high treatment expenditure in sports medicine. The development of tendon-biomimetic scaffolds may be promising for improving the unsatisfactory clinical outcomes of traditional therapies. In this study, we combined an advanced electrospun nanofiber yarn-generating technique with a traditional textile manufacturing strategy to fabricate innovative nano-micro fibrous woven scaffolds with tendon-like anisotropic structure and high-strength mechanical properties for the treatment of large-size tendon injury. Electrospun nanofiber yarns made from pure poly L-lactic acid (PLLA) or silk fibroin (SF)/PLLA blend were fabricated, and their mechanical properties matched and even exceeded those of commercial PLLA microfiber yarns. The PLLA or SF/PLLA nanofiber yarns were then employed as weft yarns interlaced with commercial PLLA microfiber yarns as warp yarns to generate two new types of nanofibrous scaffolds (nmPLLA and nmSF/PLLA) with a plain-weaving structure. Woven scaffolds made from pure PLLA microfiber yarns (both weft and warp directions) (mmPLLA) were used as controls.In vitroexperiments showed that the nmSF/PLLA woven scaffold with aligned fibrous topography significantly promoted cell adhesion, elongation, proliferation, and phenotypic maintenance of tenocytes compared with mmPLLA and nmPLLA woven scaffolds. Moreover, the nmSF/PLLA woven scaffold exhibited the strongest immunoregulatory functions and effectively modulated macrophages towards the M2 phenotype.In vivoexperiments revealed that the nmSF/PLLA woven scaffold notably facilitated Achilles tendon regeneration with improved structure by macroscopic, histological, and ultrastructural observations six months after surgery, compared with the other two groups. More importantly, the regenerated tissue in the nmSF/PLLA group had excellent biomechanical properties comparable to those of the native tendon. Overall, our study provides an innovative biological-free strategy with ready-to-use features, which presents great potential for clinical translation for damaged tendon repair.

Macrophage response mediated by extracellular matrix: recent progress

Biomaterials are one of efficient treatment options for tissue defects in regenerative medicine. Compared to synthetic materials which tend to induce chronic inflammatory response and fibrous capsule, extracellular matrix (ECM) scaffold materials composed of biopolymers are thought to be capable of inducing a pro-regenerative immune microenvironment and facilitate wound healing. Immune cells are the first line of response to implanted biomaterials. In particular, macrophages greatly affect cell behavior and the ultimate treatment outcome based on multiple cell phenotypes with various functions. The macrophage polarization status is considered as a general reflection of the characteristics of the immune microenvironment. Since numerous reports has emphasized the limitation of classical M1/M2 nomenclature, high-resolution techniques such as single-cell sequencing has been applied to recognize distinct macrophage phenotypes involved in host responses to biomaterials. After reviewing latest literatures that explored the immune microenvironment mediated by ECM scaffolds, this paper describe the behaviors of highly heterogeneous and plastic macrophages subpopulations which affect the tissue regeneration. The mechanisms by which ECM scaffolds interact with macrophages are also discussed from the perspectives of the ECM ultrastructure along with the nucleic acid, protein, and proteoglycan compositions, in order to provide targets for potential therapeutic modulation in regenerative medicine.

Biocompatibility and biodistribution of matrix-bound nanovesicles in vitro and in vivo

Matrix-bound nanovesicles (MBV) are a distinct subtype of extracellular vesicles that are firmly embedded within biomaterials composed of extracellular matrix (ECM). MBV both store and transport a diverse, tissue specific portfolio of signaling molecules including proteins, miRNAs, and bioactive lipids. MBV function as a key mediator in ECM-mediated control of the local tissue microenvironment. One of the most important mechanisms by which MBV in ECM bioscaffolds support constructive tissue remodeling following injury is immunomodulation and, specifically, the promotion of an anti-inflammatory, pro-remodeling immune cell activation state. Recent in vivo studies have shown that isolated MBV have therapeutic efficacy in rodent models of both retinal damage and rheumatoid arthritis through the targeted immunomodulation of pro-inflammatory macrophages towards an anti-inflammatory activation state. While these results show the therapeutic potential of MBV administered independent of the rest of the ECM, the in vitro and in vivo safety and biodistribution profile of MBV remain uncharacterized. The purpose of the present study was to thoroughly characterize the pre-clinical safety profile of MBV through a combination of in vitro cytotoxicity and MBV uptake studies and in vivo toxicity, immunotoxicity, and imaging studies. The results showed that MBV isolated from porcine urinary bladder are well-tolerated and are not cytotoxic in cell culture, are non-toxic to the whole organism, and are not immunosuppressive compared to the potent immunosuppressive drug cyclophosphamide. Furthermore, this safety profile was sustained across a wide range of MBV doses. STATEMENT OF SIGNIFICANCE: Matrix-bound nanovesicles (MBV) are a distinct subtype of bioactive extracellular vesicles that are embedded within biomaterials composed of extracellular matrix (ECM). Recent studies have shown therapeutic efficacy of MBV in models of both retinal damage and rheumatoid arthritis through the targeted immunomodulation of pro-inflammatory macrophages towards an anti-inflammatory activation state. While these results show the therapeutic potential of MBV, the in vitro and in vivo biocompatibility and biodistribution profile of MBV remain uncharacterized. The results of the present study showed that MBV are a well-tolerated ECM-derived therapy that are not cytotoxic in cell culture, are non-toxic to the whole organism, and are not immunosuppressive. Collectively, these data highlight the translational feasibility of MBV therapeutics across a wide variety of clinical applications.

Macrophage-extracellular matrix interactions: Perspectives for tissue engineered heart valve remodeling

In situ heart valve tissue engineering approaches have been proposed as promising strategies to overcome the limitations of current heart valve replacements. Tissue engineered heart valves (TEHVs) generated from in vitro grown tissue engineered matrices (TEMs) aim at mimicking the microenvironmental cues from the extracellular matrix (ECM) to favor integration and remodeling of the implant. A key role of the ECM is to provide mechanical support to and attract host cells into the construct. Additionally, each ECM component plays a critical role in regulating cell adhesion, growth, migration, and differentiation potential. Importantly, the immune response to the implanted TEHV is also modulated biophysically via macrophage-ECM protein interactions. Therefore, the aim of this review is to summarize what is currently known about the interactions and signaling networks occurring between ECM proteins and macrophages, and how these interactions may impact the long-term in situ remodeling outcomes of TEMs. First, we provide an overview of in situ tissue engineering approaches and their clinical relevance, followed by a discussion on the fundamentals of the remodeling cascades. We then focus on the role of circulation-derived and resident tissue macrophages, with particular emphasis on the ramifications that ECM proteins and peptides may have in regulating the host immune response. Finally, the relevance of these findings for heart valve tissue engineering applications is discussed.

Can Heart Valve Decellularization Be Standardized? A Review of the Parameters Used for the Quality Control of Decellularization Processes

When a tissue or an organ is considered, the attention inevitably falls on the complex and delicate mechanisms regulating the correct interaction of billions of cells that populate it. However, the most critical component for the functionality of specific tissue or organ is not the cell, but the cell-secreted three-dimensional structure known as the extracellular matrix (ECM). Without the presence of an adequate ECM, there would be no optimal support and stimuli for the cellular component to replicate, communicate and interact properly, thus compromising cell dynamics and behaviour and contributing to the loss of tissue-specific cellular phenotype and functions. The limitations of the current bioprosthetic implantable medical devices have led researchers to explore tissue engineering constructs, predominantly using animal tissues as a potentially unlimited source of materials. The high homology of the protein sequences that compose the mammalian ECM, can be exploited to convert a soft animal tissue into a human autologous functional and long-lasting prosthesis ensuring the viability of the cells and maintaining the proper biomechanical function. Decellularization has been shown to be a highly promising technique to generate tissue-specific ECM-derived products for multiple applications, although it might comprise very complex processes that involve the simultaneous use of chemical, biochemical, physical and enzymatic protocols. Several different approaches have been reported in the literature for the treatment of bone, cartilage, adipose, dermal, neural and cardiovascular tissues, as well as skeletal muscle, tendons and gastrointestinal tract matrices. However, most of these reports refer to experimental data. This paper reviews the most common and latest decellularization approaches that have been adopted in cardiovascular tissue engineering. The efficacy of cells removal was specifically reviewed and discussed, together with the parameters that could be used as quality control markers for the evaluation of the effectiveness of decellularization and tissue biocompatibility. The purpose was to provide a panel of parameters that can be shared and taken into consideration by the scientific community to achieve more efficient, comparable, and reliable experimental research results and a faster technology transfer to the market.

Immunomodulatory matrix-bound nanovesicles mitigate acute and chronic pristane-induced rheumatoid arthritis

Rheumatoid arthritis (RA) is an autoimmune disease characterized by chronic inflammation and destruction of synovial joints affecting ~7.5 million people worldwide. Disease pathology is driven by an imbalance in the ratio of pro-inflammatory vs. anti-inflammatory immune cells, especially macrophages. Modulation of macrophage phenotype, specifically an M1 to M2, pro- to anti-inflammatory transition, can be induced by biologic scaffold materials composed of extracellular matrix (ECM). The ECM-based immunomodulatory effect is thought to be mediated in part through recently identified matrix-bound nanovesicles (MBV) embedded within ECM. Isolated MBV was delivered via intravenous (i.v.) or peri-articular (p.a.) injection to rats with pristane-induced arthritis (PIA). The results of MBV administration were compared to intraperitoneal (i.p.) administration of methotrexate (MTX), the clinical standard of care. Relative to the diseased animals, i.p. MTX, i.v. MBV, and p.a. MBV reduced arthritis scores in both acute and chronic pristane-induced arthritis, decreased synovial inflammation, decreased adverse joint remodeling, and reduced the ratio of synovial and splenic M1 to M2 macrophages (p < 0.05). Both p.a. and i.v. MBV reduced the serum concentration of RA and PIA biomarkers CXCL10 and MCP-3 in the acute and chronic phases of disease (p < 0.05). Flow-cytometry revealed the presence of a systemic CD43hi/His48lo/CD206+, immunoregulatory monocyte population unique to p.a. and i.v. MBV treatment associated with disease resolution. The results show that the therapeutic efficacy of MBV is equal to that of MTX for the management of acute and chronic pristane-induced arthritis and, further, this effect is associated with modulation of local synovial macrophages and systemic myeloid populations.

Acceleration of Bone Regeneration Induced by a Soft-Callus Mimetic Material

Clinical implementation of endochondral bone regeneration (EBR) would benefit from the engineering of devitalized cartilaginous constructs of allogeneic origins. Nevertheless, development of effective devitalization strategies that preserves extracellular matrix (ECM) is still challenging. The aim of this study is to investigate EBR induced by devitalized, soft callus-mimetic spheroids. To challenge the translatability of this approach, the constructs are generated using an allogeneic cell source. Neo-bone formation is evaluated in an immunocompetent rat model, subcutaneously and in a critical size femur defect. Living spheroids are used as controls. Also, the effect of spheroid maturation towards hypertrophy is evaluated. The devitalization procedure successfully induces cell death without affecting ECM composition or bioactivity. In vivo, a larger amount of neo-bone formation is observed for the devitalized chondrogenic group both ectopically and orthotopically. In the femur defect, accelerated bone regeneration is observed in the devitalized chondrogenic group, where defect bridging is observed 4 weeks post-implantation. The authors' results show, for the first time, a dramatic increase in the rate of bone formation induced by devitalized soft callus-mimetics. These findings pave the way for the development of a new generation of allogeneic, "off-the-shelf" products for EBR, which are suitable for the treatment of every patient.

Comparative study of decellularization techniques to obtain natural extracellular matrix scaffolds of human peripheral-nerve allografts

BACKGROUND

We hypothesize that adding sonication cycles to the process of decellularization of cadaveric human peripheral nerves will increase the removal of cell debris and myelin sheath, increasing their utility as allografts.

METHODS

Our aim of this study was to develop a decellularization protocol that allows the removal of cells and myelin sheath without detrimental effects on nerve architecture. Segments of ulnar and median nerves from human donors, isolated both before and after cardiac arrest, were subjected to two methods of decellularization: two-detergent-based (M1) and the same method with sonication added (M2). We evaluated the histology of unprocessed and decellularized nerves (n = 24 per group) for general morphology, presence of cell nuclei, nuclear remnants, collagen fibers, and myelin. We performed immunohistochemistry to verify the removal of Schwann cells associated with histomorphometry. We used scanning electron microscopy (EM) to evaluate the ultrastructure of both native and decellularized nerves. The efficacy of decellularization was assessed by analysis of genomic DNA.

RESULTS

Histology confirmed that both decellularization protocols were adequate and maintained natural nerve architecture. Scanning EM showed that 3D ultrastructural architecture also was maintained. Histomorphometric parameters showed a more complete removal of the myelin with the M2 protocol than with M1 (p = 0.009). Fiber diameter and density were not modified by decellularization methods.

CONCLUSIONS

Sonication can be a complementary method to decellularization of peripheral nerve allografts with sonication increasing the effectiveness of detergent-based protocols for the removal of unwanted cellular components from peripheral nerve allografts.

Development and characterization of matrix-derived microcarriers from decellularized tissues using electrospraying techniques

Stirred bioreactor systems integrating microcarriers represent a promising approach for therapeutic cell manufacturing. While a variety of microcarriers are commercially available, current options do not integrate the tissue-specific composition of the extracellular matrix (ECM), which can play critical roles in directing cell function. The current study sought to generate microcarriers comprised exclusively of ECM from multiple tissue sources. More specifically, porcine decellularized dermis, porcine decellularized myocardium, and human decellularized adipose tissue were digested with α-amylase to obtain ECM suspensions that could be electrosprayed into liquid nitrogen to generate 3D microcarriers that were stable over a range of ECM concentrations without the need for chemical crosslinking or other additives. Characterization studies confirmed that all three microcarrier types had similar soft and compliant mechanical properties and were of a similar size range, but that their composition varied depending on the native tissue source. In vivo testing in immunocompetent mice revealed that the microcarriers integrated into the host tissues, supporting the infiltration of host cells including macrophages and endothelial cells at 2 weeks post-implantation. In vitro cell culture studies validated that the novel microcarriers supported the attachment of tissue-specific stromal cell populations under dynamic culture conditions within spinner flasks, with a significant increase in live cell numbers observed over 1 week on the dermal- and adipose-derived microcarriers. Overall, the findings demonstrate the versatility of the electrospraying methods and support the further development of the microcarriers as cell culture and delivery platforms.

Three-Dimensional Cell Printed Lock-Key Structure for Oral Soft and Hard Tissue Regeneration

Alveolar ridge absorbs rapidly following tooth extraction. To promote implant rehabilitation, an adequate bone and soft tissue volume are required. Three-dimensional (3D) cell printing technique provides the advantages of precise spatial distribution and personalization. In this study, 3D cell printing was used to establish a soft-hard construct that is composed of alginate/gelatin (AG)/gingival fibroblast cells (GFs) and alginate/gelatin/nano-hydroxyapatite (AGH)/bone marrow-derived mesenchymal stem cells (BMSCs). Physicochemical results showed that nano-hydroxyapatite (nHA) added in the bioink maintained its crystalline phase. In addition, an increase of viscosity, the improvement of compressive modulus (p < 0.01), and slow degradation rate (p < 0.01) were found after adding nHA. SEM showed cell stretched and attached well on the surface of the 3D printed construct. At day 7 after printing, the viability of GFs in AG was 94.80% ± 1.14%, while BMSC viability in AGH was 86.59% ± 0.75%. Polymerase chain reaction results indicated that the expression levels of ALP, RUNX-2, and OCN in BMSCs were higher in AGH than AG bioink (p < 0.01). After 8-week implantation into the dorsum of 6- to 8-week-old male athymic and inbred (BALB/c) nude mice, the cellular printed construct displayed a more integrated structure and better healing of subcutaneous tissue compared with the acellular printed construct. In conclusion, this 3D cell printed soft-hard construct exhibits favorable biocompatibility and has potential for alveolar ridge preservation. Impact statement Alveolar ridge resorption after tooth extraction has posed great difficulty in the subsequent restorative procedure. Clinically, to preserve the dimension of alveolar ridge, covering soft tissue healing and underlying bone formation is necessary after tooth extraction. Three-dimensional (3D) cell printing, which can distribute different biomaterials and cells with spatial control, provides a novel approach to develop a customized plug to put in the fresh socket to minimize bone resorption and improve gingiva growth. In this study, an integrated and heterogeneous soft-hard construct with lock-key structure was successfully developed using 3D cell printing. The physicochemical and biological properties were tested in vitro and in vivo. This 3D cell printed soft-hard construct will be a customized plug in alveolar ridge preservation in the future.

Decellularized bone extracellular matrix in skeletal tissue engineering

Bone possesses an intrinsic regenerative capacity, which can be compromised by aging, disease, trauma, and iatrogenesis (e.g. tumor resection, pharmacological). At present, autografts and allografts are the principal biological treatments available to replace large bone segments, but both entail several limitations that reduce wider use and consistent success. The use of decellularized extracellular matrices (ECM), often derived from xenogeneic sources, has been shown to favorably influence the immune response to injury and promote site-appropriate tissue regeneration. Decellularized bone ECM (dbECM), utilized in several forms - whole organ, particles, hydrogels - has shown promise in both in vitro and in vivo animal studies to promote osteogenic differentiation of stem/progenitor cells and enhance bone regeneration. However, dbECM has yet to be investigated in clinical studies, which are needed to determine the relative efficacy of this emerging biomaterial as compared with established treatments. This mini-review highlights the recent exploration of dbECM as a biomaterial for skeletal tissue engineering and considers modifications on its future use to more consistently promote bone regeneration.

Characterization of Inflammatory and Fibrotic Aspects of Tissue Remodeling of Acellular Dermal Matrix in a Nonhuman Primate Model

Human acellular dermal matrices (hADMs) are applied in various soft tissue reconstructive surgeries as scaffolds to support tissue remodeling and regeneration. To evaluate the clinical efficacy of hADM implants, it is integral that the hADM does not induce a host chronic inflammatory response leading to fibrotic encapsulation of the implant. In this study, we characterized the inflammatory and fibrosis-related tissue remodeling response of 2 commercial hADM products (SimpliDerm and AlloDerm RTU) in a nonhuman primate model using histology and gene expression profiling.

METHODS

Eighteen African green monkeys with abdominal wall defects were applied to evaluate the performance of SimpliDerm and AlloDerm RTU implants (N = 3) at 2, 4, and 12-weeks post-implantation. Using histology and gene expression profiling, tissue responses such as implant integration, degradation, cell infiltration, immune response, neovascularization, and pro-fibrotic responses over time were evaluated.

RESULTS

SimpliDerm showed a lower initial inflammatory response and slower implant degradation rate than AlloDerm RTU evidenced by histomorphological analysis. These factors led to a more anti-inflammatory and pro-remodeling microenvironment within SimpliDerm, demonstrated by lower TNFα levels and lower expression levels of pro-fibrotic markers, and promoted tissue repair and regeneration by 3-months post-implantation.

CONCLUSIONS

Overall, histology and gene expression profiling analyses shown in this study demonstrated an effective model for analyzing hADM performance in terms of host inflammatory and fibrotic response. Further studies are warranted to fully evaluate the utility of this novel hADM in the clinical setting and verify the prognosis of our pre-clinical analysis model.

An Exploratory Study into the Implantation of Arytenoid Cartilage Scaffold in the Horse

Respiratory function in the horse can be severely compromised by arytenoid chondritis, or arytenoid chondropathy, a pathologic condition leading to deformity and dysfunction of the affected cartilage. Current treatment in cases unresponsive to medical management is removal of the cartilage, which can improve the airway obstruction, but predisposes the patient to other complications like tracheal penetration of oropharyngeal content and dynamic collapse of the now unsupported soft tissue lateral to the cartilage. A tissue engineering approach to reconstructing the arytenoid cartilage would represent a significant advantage in the management of arytenoid chondritis. In this study, we explored if decellularized matrix could potentially be incorporated into the high motion environment of the arytenoid cartilages of horses. Equine arytenoid cartilages were decellularized and a portion of the resultant acellular scaffolds was implanted in a full-thickness defect created in the arytenoids of eight horses. The implantation was performed bilaterally in each horse, with one side randomly selected to receive an implant seeded with autologous bone marrow-derived nucleated cells (BMNCs). Arytenoids structure and function were monitored up to 4 months. In vivo assessments included laryngeal ultrasound, and laryngeal endoscopy at rest and during exercise on a high-speed treadmill. Histologic evaluation of the arytenoids was performed postmortem. Implantation of the cartilaginous graft had no adverse effect on laryngeal respiratory function or swallowing, despite induction of a transient granuloma on the medial aspect of the arytenoids. Ultrasonographic monitoring detected a postoperative increase in the thickness and cross-sectional area of the arytenoid body that receded faster in the arytenoids not seeded with BMNCs. The explanted tissue showed epithelialization of the mucosal surface, integration of the implant into the native arytenoid, with minimal adverse cellular reaction. Remodeling of the scaffold material was evident by 2 months after implantation. Preseeding the scaffold with BMNCs increased the rate of scaffold degradation and incorporation. Replacement of arytenoid portion with a tissue-engineered cartilaginous graft preseeded with BMNCs is surgically feasible in the horse, is well tolerated, and results in appropriate integration within the native tissue, also preventing laryngeal tissue collapse during exercise.

Bioreactivity of decellularized animal, plant, and fungal scaffolds: perspectives for medical applications

Numerous biomedical applications imply supportive materials to improve protective, antibacterial, and regenerative abilities upon surgical interventions, oncotherapy, regenerative medicine, and others. With the increasing variability of the possible sources, the materials of natural origin are among the safest and most accessible biomedical tools. Animal, plant, and fungal tissues can further undergo decellularization to improve their biocompatibility. Decellularized scaffolds lack the most reactive cellular material, nuclear and cytoplasmic components, that predominantly trigger immune responses. At the same time, the outstanding initial three-dimensional microarchitecture, biomechanical properties, and general composition of the scaffolds are preserved. These unique features make the scaffolds perfect ready-to-use platforms for various biomedical applications, implying cell growth and functionalization. Decellularized materials can be repopulated with various cells upon request, including epithelial, endothelial, muscle and neuronal cells, and applied for structural and functional biorepair within diverse biological sites, including the skin and musculoskeletal, cardiovascular, and central nervous systems. However, the molecular and cellular mechanisms behind scaffold and host tissue interactions remain not fully understood, which significantly restricts their integration into clinical practice. In this review, we address the essential aspects of decellularization, scaffold preparation techniques, and its biochemical composition and properties, which determine the biocompatibility and immunogenicity of the materials. With the integrated evaluation of the scaffold profile in living systems, decellularized animal, plant, and fungal scaffolds have the potential to become essential instruments for safe and controllable biomedical applications.

Potential anti-neuroinflammatory compounds from Australian plants - A review

Neuroinflammation is a complex response to brain injury involving the activation of glia, release of inflammatory mediators, such as cytokines and chemokines, and generation of reactive oxygen and nitrogen species. Even though it is considered an event secondary to neuronal death or dysfunction, neuro-inflammation comprises a majority of the non-neuronal contributors to the cause and progression of neurodegenerative diseases like Alzheimer's Disease (AD), Parkinson's Disease (PD), Multiple Sclerosis (MS), Chronic Traumatic Encephalopathy (CTE) and others. As a result of the lack of effectiveness of current treatments for neurodegenerative diseases, neuroinflammation has become a legitimate therapeutic target for drug discovery, leading to the study of various in vivo and in vitro models of neuroinflammation. Several molecules sourced from plants have displayed anti-inflammatory properties in the study of neurodegenerative diseases. A group of these anti-inflammatory compounds has been classified as cytokine-suppressive anti-inflammatory drugs (CSAIDs), which target the pro-inflammatory AP1 and nuclear factor-κB signaling pathways and inhibit the expression of many pro-inflammatory cytokines, such as interleukin IL-1, IL-6, TNF-α, or nitric oxide. Australian plants, thriving amid the driest inhabited continent of the world, are an untapped source of chemical diversity in the form of secondary metabolites. These compounds are produced in response to biotic and abiotic stresses that the plants are exposed to in the highly biodiverse environment. This review is an attempt to highlight anti-inflammatory compounds isolated from Australian plants.

Host macrophage response to injectable hydrogels derived from ECM and α-helical peptides

Tissue engineering materials play a key role in how closely the complex architectural and functional characteristics of native healthy tissue can be replicated. Traditional natural and synthetic materials are superseded by bespoke materials that cross the boundary between these two categories. Here we present hydrogels that are derived from decellularised extracellular matrix and those that are synthesised from de novo α-helical peptides. We assess in vitro activation of murine macrophages to our hydrogels and whether these gels induce an M1-like or M2-like phenotype. This was followed by the in vivo immune macrophage response to hydrogels injected into rat partial-thickness abdominal wall defects. Over 28 days we observe an increase in mononuclear cell infiltration at the hydrogel-tissue interface without promoting a foreign body reaction and see no evidence of hydrogel encapsulation or formation of multinucleate giant cells. We also note an upregulation of myogenic differentiation markers and the expression of anti-inflammatory markers Arginase1, IL-10, and CD206, indicating pro-remodelling for all injected hydrogels. Furthermore, all hydrogels promote an anti-inflammatory environment after an initial spike in the pro-inflammatory phenotype. No difference between the injected site and the healthy tissue is observed after 28 days, indicating full integration. These materials offer great potential for future applications in regenerative medicine and towards unmet clinical needs. STATEMENT OF SIGNIFICANCE: Materials play a key role in how closely the complex architectural and functional characteristics of native healthy tissue can be replicated in tissue engineering. Here we present injectable hydrogels derived from decellularised extracellular matrix and de novo designed α-helical peptides. Over 28 days in the rat abdominal wall we observe an increase in mononuclear cell infiltration at the hydrogel-tissue interface with no foreign body reaction, no evidence of hydrogel encapsulation and no multinucleate giant cells. Our data indicate pro-remodelling and the promotion of an anti-inflammatory environment for all injected hydrogels with evidence of full integration with healthy tissue after 28 days. These unique materials offer great potential for future applications in regenerative medicine and towards designing materials for unmet clinical needs.

Extracellular Matrix-Based Biomaterials and Their Influence Upon Cell Behavior

Biologic scaffold materials composed of allogeneic or xenogeneic extracellular matrix (ECM) are commonly used for the repair and remodeling of injured tissue. The clinical outcomes associated with implantation of ECM-based materials range from unacceptable to excellent. The variable clinical results are largely due to differences in the preparation of the material, including characteristics of the source tissue, the method and efficacy of decellularization, and post-decellularization processing steps. The mechanisms by which ECM scaffolds promote constructive tissue remodeling include mechanical support, degradation and release of bioactive molecules, recruitment and differentiation of endogenous stem/progenitor cells, and modulation of the immune response toward an anti-inflammatory phenotype. The methods of ECM preparation and the impact of these methods on the quality of the final product are described herein. Examples of favorable cellular responses of immune and stem cells associated with constructive tissue remodeling of ECM bioscaffolds are described.

Unsaturated polyurethane films grafted with enantiomeric polylysine promotes macrophage polarization to a M2 phenotype through PI3K/Akt1/mTOR axis

The immune system responds immediately to tissue trauma and to biomaterial implants under the participation of M1/M2 macrophages polarization. The surface properties of biomaterials can significantly influence the tissue repair progress through modulating the macrophage functions. In this study, the surface of poly(propylene fumarate) polyurethane films (PPFU) is grafted with a same density of enantiomeric poly-l-lysine (PPFU-g-PLL) and poly-d-lysine (PPFU-g-PDL), leading to a similar level of enhanced surface wettability for the PPFU-g-PLL and PPFU-g-PDL. The polylysine-grafted PPFU can restrict the M1 polarization, whereas promote M2 polarization of macrophages in vitro, judging from the secretion of cytokines and expression of key M1 and M2 related genes. Comparatively, the PPFU-g-PDL has a stronger effect in inducing M2 polarization in vivo, resulting in a thinner fibrous capsule surrounding the implant biomaterials. The CD44 and integrins of macrophages participate in the polarization process probably by activating focal adhesion kinase (FAK) and Rho-associated protein kinase (ROCK), and downstream PI3K/Akt1/mTOR signal axis to up regulate M2 related gene expression. This study confirms for the first time that polylysine coating is an effective method to regulate the immune response of biomaterials, and the polylysine-modified thermoplastic PPFU with the advantage to promote M2 polarization may be applied widely in regenerative medicine.

Molecular regulation of TLR signaling in health and disease: mechano-regulation of macrophages and TLR signaling

Immune cells encounter tissues with vastly different biochemical and physical characteristics. Much of the research emphasis has focused on the role of cytokines and chemokines in regulating immune cell function, but the role of the physical microenvironment has received considerably less attention. The tissue mechanics, or stiffness, of healthy tissues varies dramatically from soft adipose tissue and brain to stiff cartilage and bone. Tissue mechanics also change due to fibrosis and with diseases such as atherosclerosis or cancer. The process by which cells sense and respond to their physical microenvironment is called mechanotransduction. Here we review mechanotransduction in immunologically important diseases and how physical characteristics of tissues regulate immune cell function, with a specific emphasis on mechanoregulation of macrophages and TLR signaling.

Meniscus-Derived Matrix Bioscaffolds: Effects of Concentration and Cross-Linking on Meniscus Cellular Responses and Tissue Repair

Meniscal injuries, particularly in the avascular zone, have a low propensity for healing and are associated with the development of osteoarthritis. Current meniscal repair techniques are limited to specific tear types and have significant risk for failure. In previous work, we demonstrated the ability of meniscus-derived matrix (MDM) scaffolds to augment the integration and repair of an in vitro meniscus defect. The objective of this study was to determine the effects of percent composition and dehydrothermal (DHT) or genipin cross-linking of MDM bioscaffolds on primary meniscus cellular responses and integrative meniscus repair. In all scaffolds, the porous microenvironment allowed for exogenous cell infiltration and proliferation, as well as endogenous meniscus cell migration. The genipin cross-linked scaffolds promoted extracellular matrix (ECM) deposition and/or retention. The shear strength of integrative meniscus repair was improved with increasing percentages of MDM and genipin cross-linking. Overall, the 16% genipin cross-linked scaffolds were most effective at enhancing integrative meniscus repair. The ability of the genipin cross-linked scaffolds to attract endogenous meniscus cells, promote glycosaminoglycan and collagen deposition, and enhance integrative meniscus repair reveals that these MDM scaffolds are promising tools to augment meniscus healing.

Preparation, characterization, and xenotransplantation of the caprine acellular dermal matrix

BACKGROUND

Caprine skin is a promising biomaterial for tissue-engineering applications. However, tissue processing is required before its xenogenic use.

AIMS

Therefore, the purpose of this study was to evaluate the structural integrity and biocompatibility of the caprine skin after de-epithelialization, using sodium chloride (NaCl) and trypsin solutions, followed by de-cellularization using sodium dodecyl sulfate (SDS) solution.

MATERIALS & METHODS

The caprine skin was de-epithelialized using NaCl (2-4 mol/L) and trypsin (0.25%-0.5%) followed by the treatment of SDS (1%-4%) solution over a period of time. Acellularity of the prepared matrix was confirmed histologically and characterized by appropriate staining, scanning electron microscopy (SEM), DNA quantification, and Fourier-transform infrared (FTIR) spectroscopy. The caprine acellular dermal matrix (CADM) was used for the repair of spontaneously occurring abdominal hernia in ten buffaloes. The biocompatibility of the CADM was evaluated using clinical, hematological, biochemical, and anti-oxidant parameters.

RESULTS

Histologically, the skin treated with 0.25% trypsin in 4 mol/L NaCl for 8 hours resulted in complete de-epithelialization. Further treatment with 2% SDS for 48 hours demonstrated complete acellularity and orderly arranged collagen fibers. The SEM confirmed a preservation of collagen arrangement within CADM. The DNA content was significantly (P < .05) lower in CADM (46.20 ± 7.94 ng/mg) as compared to fresh skin (662.56 ± 156.11 ng/mg) indicating effective acellularity. The FTIR spectra showed characteristic collagen peaks of amide A, amide B, amide I, amide II, and amide III in CADM. All the 10 animals recovered uneventfully and remained sound. Hematological, biochemical, and anti-oxidants findings were unremarkable.

CONCLUSION

Results indicated the acceptance and biocompatibility of the xenogenic caprine acellular dermal matrix for abdominal hernia repair in buffaloes without complications.

Meniscus-Derived Matrix Scaffolds Promote the Integrative Repair of Meniscal Defects

Meniscal tears have a poor healing capacity, and damage to the meniscus is associated with significant pain, disability, and progressive degenerative changes in the knee joint that lead to osteoarthritis. Therefore, strategies to promote meniscus repair and improve meniscus function are needed. The objective of this study was to generate porcine meniscus-derived matrix (MDM) scaffolds and test their effectiveness in promoting meniscus repair via migration of endogenous meniscus cells from the surrounding meniscus or exogenously seeded human bone marrow-derived mesenchymal stem cells (MSCs). Both endogenous meniscal cells and MSCs infiltrated the MDM scaffolds. In the absence of exogenous cells, the 8% MDM scaffolds promoted the integrative repair of an in vitro meniscal defect. Dehydrothermal crosslinking and concentration of the MDM influenced the biochemical content and shear strength of repair, demonstrating that the MDM can be tailored to promote tissue repair. These findings indicate that native meniscus cells can enhance meniscus healing if a scaffold is provided that promotes cellular infiltration and tissue growth. The high affinity of cells for the MDM and the ability to remodel the scaffold reveals the potential of MDM to integrate with native meniscal tissue to promote long-term repair without necessarily requiring exogenous cells.

Alarmins of the extracellular space

The ability of the immune system to discriminate between healthy-self, abnormal-self, and non-self has been attributed mainly to alarmins signaling as "danger signals". It is now evident, however, that alarmins are much more complex and can perform specialized functions that can regulate a wide spectrum of processes ranging from propagation of disease to tissue homeostasis. As such, alarmins and their signaling mechanisms are now actively pursued as therapeutic targets. The clinical utility of alarmins requires an understanding of their specific localization. Specifically, many alarmins can function paradoxically depending upon their localization, intra or extracellular. The present review focuses upon alarmin presence and differential expression in the extracellular space versus within the cell and how variation of the localization of alarmins can reveal important mechanistic insights into alarmin functions and their efficacy as biomarkers of disease and therapeutic targets.

How to build a lung: latest advances and emerging themes in lung bioengineering

Chronic respiratory diseases remain a major cause of morbidity and mortality worldwide. The only option at end-stage disease is lung transplantation, but there are not enough donor lungs to meet clinical demand. Alternative options to increase tissue availability for lung transplantation are urgently required to close the gap on this unmet clinical need. A growing number of tissue engineering approaches are exploring the potential to generate lung tissue ex vivo for transplantation. Both biologically derived and manufactured scaffolds seeded with cells and grown ex vivo have been explored in pre-clinical studies, with the eventual goal of generating functional pulmonary tissue for transplantation. Recently, there have been significant efforts to scale-up cell culture methods to generate adequate cell numbers for human-scale bioengineering approaches. Concomitantly, there have been exciting efforts in designing bioreactors that allow for appropriate cell seeding and development of functional lung tissue over time. This review aims to present the current state-of-the-art progress for each of these areas and to discuss promising new ideas within the field of lung bioengineering.

Current Concepts in Meniscus Tissue Engineering and Repair

The meniscus is the most commonly injured structure in the human knee. Meniscus deficiency has been shown to lead to advanced osteoarthritis (OA) due to abnormal mechanical forces, and replacement strategies for this structure have lagged behind other tissue engineering endeavors. The challenges include the complex 3D structure with individualized size parameters, the significant compressive, tensile and shear loads encountered, and the poor blood supply. In this progress report, a review of the current clinical treatments for different types of meniscal injury is provided. The state-of-the-art research in cellular therapies and novel cell sources for these therapies is discussed. The clinically available cell-free biomaterial implants and the current progress on cell-free biomaterial implants are reviewed. Cell-based tissue engineering strategies for the repair and replacement of meniscus are presented, and the current challenges are identified. Tissue-engineered meniscal biocomposite implants may provide an alternative solution for the treatment of meniscal injury to prevent OA in the long run, because of the limitations of the existing therapies.

Acellular vascular matrix grafts from human placenta chorion: Impact of ECM preservation on graft characteristics, protein composition and in vivo performance

Small diameter vascular grafts from human placenta, decellularized with either Triton X-100 (Triton) or SDS and crosslinked with heparin were constructed and characterized. Graft biochemical properties, residual DNA, and protein composition were evaluated to compare the effect of the two detergents on graft matrix composition and structural alterations. Biocompatibility was tested in vitro by culturing the grafts with primary human macrophages and in vivo by subcutaneous implantation of graft conduits (n = 7 per group) into the flanks of nude rats. Subsequently, graft performance was evaluated using an aortic implantation model in Sprague Dawley rats (one month, n = 14). In situ graft imaging was performed using MRI angiography. Retrieved specimens were analyzed by electromyography, scanning electron microscopy, histology and immunohistochemistry to evaluate cell migration and the degree of functional tissue remodeling. Both decellularization methods resulted in grafts of excellent biocompatibility in vitro and in vivo, with low immunogenic potential. Proteomic data revealed removal of cytoplasmic proteins with relative enrichment of ECM proteins in decelluarized specimens of both groups. Noteworthy, LC-Mass Spectrometry analysis revealed that 16 proteins were exclusively preserved in Triton decellularized specimens in comparison to SDS-treated specimens. Aortic grafts showed high patency rates, no signs of thrombus formation, aneurysms or rupture. Conduits of both groups revealed tissue-specific cell migration indicative of functional remodeling. This study strongly suggests that decellularized allogenic grafts from the human placenta have the potential to be used as vascular replacement materials. Both detergents produced grafts with low residual immunogenicity and appropriate mechanical properties. Observed differences in graft characteristics due to preservation method had no impact on successful in vivo performance in the rodent model.

Cell-material interactions in tendon tissue engineering

The interplay between cells and materials is a fundamental topic in biomaterial-based tissue regeneration. One of the principles for biomaterial development in tendon regeneration is to stimulate tenogenic differentiation of stem cells. To this end, efforts have been made to optimize the physicochemical and bio-mechanical properties of biomaterials for tendon tissue engineering. However, recent progress indicated that innate immune cells, especially macrophages, can also respond to the material cues and undergo phenotypical changes, which will either facilitate or hinder tissue regeneration. This process has been, to some extent, neglected by traditional strategies and may partially explain the unsatisfactory outcomes of previous studies; thus, more researchers have turned their focus on developing and designing immunoregenerative biomaterials to enhance tendon regeneration. In this review, we will first summarize the effects of material cues on tenogenic differentiation and paracrine secretion of stem cells. A brief introduction will also be made on how material cues can be manipulated for the regeneration of tendon-to-bone interface. Then, we will discuss the characteristics and influences of macrophages on the repair process of tendon healing and how they respond to different materials cues. These principles may benefit the development of novel biomaterials provided with combinative bioactive cues to activate tenogenic differentiation of stem cells and pro-resolving macrophage phenotype.

STATEMENT OF SIGNIFICANCE

The progress achieved with the rapid development of biomaterial-based strategies for tendon regeneration has not yielded broad benefits to clinical patients. In addition to the interplay between stem cells and biomaterials, the innate immune response to biomaterials also plays a determinant role in tissue regeneration. Here, we propose that fine-tuning of stem cell behaviors and alternative activation of macrophages through material cues may lead to effective tendon/ligament regeneration. We first review the characteristics of key material cues that have been manipulated to promote tenogenic differentiation and paracrine secretion of stem cells in tendon regeneration. Then, we discuss the potentiality of corresponding material cues in activating macrophages toward a pro-resolving phenotype to promote tissue repair.

Immunomodulation of Biomaterials by Controlling Macrophage Polarization

Macrophages are key players in innate immune responses to foreign substances. They participate in the phagocytosis of biomaterial-derived particles, angiogenesis, recruitment of fibroblasts, and formation of granulation tissues. Most macrophage functions are achieved through the release of various cytokines and chemokines; the release profile of cytokines is dependent on the phenotype of macrophages, namely proinflammatory M1 or antiinflammatory M2. M1 and M2 macrophages coexist during an inflammatory phase, and the M1/M2 ratio is considered to be an important factor for wound-healing or tissue regeneration. This ratio depends on the chemical and physical properties of biomaterials. To obtain a favorable foreign body reaction to biomaterials, the phenotypes of the macrophages can be modulated by cytokines, antibodies, small chemicals, and microRNAs. Geometrical surface fabrication of biomaterials can also be used for modulating the phenotype of macrophages.