Bioactivity and in vitro immunological studies of xenogeneic decellularized extracellular matrix scaffolds for implantable applications

Decellularized scaffolds retain the main bioactive substances of the extracellular matrix, which can better promote cell proliferation and matrix reconstruction at the defect site, and have great potential for morphological and functional restoration in patients with tissue defects. Due to the safety of the material source of allogeneic decellularized scaffolds, there is a great limitation in their clinical application, so the preparation and evaluation of xenodermal acellular scaffolds have attracted much attention. In terms of skin tissue structure and function, porcine skin has a high degree of similarity to human skin and has the advantages of sufficient quantity and no ethical issues. However, there is a risk of immune rejection after xenodermal acellular scaffold transplantation. To address the above problems, this paper focuses on porcine dermal decellularized scaffolds prepared using two common decellularization preparation methods and compares the decellularization efficiency, retention of active components of the extracellular matrix, structural characterization of the decellularized scaffolds, and the effect of porcine dermal decellularized scaffolds on mouse Raw264.7 macrophages, so as to make a functional evaluation of the active components and immune effects of porcine dermal decellularized scaffolds, and to provide a reference for filling trauma-induced defects in humans.

Non-collagenous proteins, rather than the collagens, are key biochemical factors that mediate tenogenic bioactivity of tendon extracellular matrix

Despite the growing clinical use of extracellular matrix (ECM)-based biomaterials for tendon repair, undesired healing outcomes or complications have frequently been reported. A major scientific challenge has been the limited understanding of their functional compositions and mechanisms of action due to the complex nature of tendon ECM. Previously, we have reported a soluble ECM fraction from bovine tendons (tECM) by urea extraction, which exhibited strong, pro-tenogenic bioactivity on human adipose-derived stem cells (hASCs). In this study, to advance our previous findings and gain insights into the biochemical nature of its pro-tenogenesis activity, tECM was fractionated using (i) an enzymatic digestion approach (pepsin, hyaluronidase, and chondroitinase) to yield various enzyme-digested tECM fractions; and (ii) a gelation-based approach to yield collagen matrix-enriched (CM) and non-collagenous matrix-enriched (NCM) fractions. Their tenogenic bioactivity on hASCs was assessed. Our results collectively indicated that non-collagenous tECM proteins, rather than collagens, are likely the important biochemical factors responsible for tECM pro-tenogenesis bioactivity. Mechanistically, RNA-seq analysis revealed that tECM and its non-collagenous portion induced similar transcriptional profiles of hASCs, particularly genes associated with cell proliferation, collagen synthesis, and tenogenic differentiation, which were distinct from transcriptome induced by its collagenous portion. From an application perspective, the enhanced solubility of the non-collagenous tECM, compared to tECM, should facilitate its combination with various water-soluble biomaterials for tissue engineering protocols. Our work provides insight into the molecular characterization of native tendon ECM, which will help to effectively translate their functional components into the design of well-defined, ECM biomaterials for tendon regeneration. STATEMENT OF SIGNIFICANCE: Significant progress has been made in extracellular matrix (ECM)-based biomaterials for tendon repair. However, their effectiveness remains debated, with conflicting research and clinical findings. Understanding the functional composition and mechanisms of action of ECM is crucial for developing safe and effective bioengineered scaffolds. Expanding on our previous work with bovine tendon ECM extracts (tECM) exhibiting strong pro-tenogenesis activity, we fractionated tECM to evaluate its bioactive moieties. Our findings indicate that the non-collagenous matrix within tECM, rather than the collagenous portions, plays a major role in the pro-tenogenesis bioactivity on human adipose-derived stem cells. These insights will drive further optimization of ECM-based biomaterials, including our advanced method for preparing highly soluble, non-collagenous matrix-enriched tendon ECM for effective tendon repair.

In vitro dose-dependent effects of matrix metalloproteinases on ECM hydrogel biodegradation

Matrix metalloproteinases (MMPs) cause proteolysis of extracellular matrix (ECM) in tissues affected by stroke. However, little is known about how MMPs degrade ECM hydrogels implanted into stroke cavities to regenerate lost tissue. To establish a structure-function relationship between different doses of individual MMPs and isolate their effects in a controlled setting, an in vitro degradation assay quantified retained urinary bladder matrix (UBM) hydrogel mass as a measure of degradation across time. A rheological characterization indicated that lower ECM concentrations (<4 mg/mL) did not cure completely at 37 °C and had a high fraction of mobile proteins that were easily washed-out. Hydrolysis by dH2O caused a steady 2 % daily decrease in hydrogel mass over 14 days. An acceleration of degradation to 6 % occurred with phosphate buffered saline and artificial cerebrospinal fluid. MMPs induced a dose-dependent increase and within 14 days almost completely (>95 %) degraded the hydrogel. MMP-9 exerted the most significant biodegradation, compared to MMP-3 and -2. To model the in vivo exposure of hydrogel to MMPs, mixtures of MMP-2, -3, and -9, present in the cavity at 14-, 28-, or 90-days post-stroke, revealed that 14- and 28-days mixtures achieved an equivalent biodegradation, but a 90-days mixture exhibited a slower degradation. These results revealed that hydrolysis, in addition to proteolysis, exerts a major influence on the degradation of hydrogels. Understanding the mechanisms of ECM hydrogel biodegradation is essential to determine the therapeutic window for bioscaffold implantation after a stroke, and they are also key to determine optimal degradation kinetics to support tissue regeneration. STATEMENT OF SIGNIFICANCE: After implantation into a stroke cavity, extracellular matrix (ECM) hydrogel promotes tissue regeneration through the degradation of the bioscaffold. However, the process of degradation of an ECM hydrogel remains poorly understood. We here demonstrated in vitro under highly controlled conditions that hydrogel degradation is very dependent on its protein concentration. Lower protein concentration hydrogels were weaker in rheological measurements and particularly susceptible to hydrolysis. The proteolytic degradation of tissue ECM after a stroke is caused by matrix metalloproteinases (MMPs). A dose-dependent MMP-driven biodegradation of ECM hydrogel exceeded the effects of hydrolysis. These results highlight the importance of in vitro testing of putative causes of degradation to gain a better understanding of how these factors affect in vivo biodegradation.

Creating and Transferring an Innervated, Vascularized Muscle Flap Made from an Elastic, Cellularized Tissue Construct Developed In Situ

Reanimating facial structures following paralysis and muscle loss is a surgical objective that would benefit from improved options for harvesting appropriately sized muscle flaps. The objective of this study is to apply electrohydrodynamic processing to generate a cellularized, elastic, biocomposite scaffold that could develop and mature as muscle in a prepared donor site in vivo, and then be transferred as a thin muscle flap with a vascular and neural pedicle. First, an effective extracellular matrix (ECM) gel type is selected for the biocomposite scaffold from three types of ECM combined with poly(ester urethane)urea microfibers and evaluated in rat abdominal wall defects. Next, two types of precursor cells (muscle-derived and adipose-derived) are compared in constructs placed in rat hind limb defects for muscle regeneration capacity. Finally, with a construct made from dermal ECM and muscle-derived stem cells, protoflaps are implanted in one hindlimb for development and then microsurgically transferred as a free flap to the contralateral limb where stimulated muscle function is confirmed. This construct generation and in vivo incubation procedure may allow the generation of small-scale muscle flaps appropriate for transfer to the face, offering a new strategy for facial reanimation.

Human adipose ECM alleviates radiation-induced skin fibrosis via endothelial cell-mediated M2 macrophage polarization

Radiation therapy can lead to late radiation-induced skin fibrosis (RISF), causing movement restriction, pain, and organ dysfunction. This study evaluated adipose-derived extracellular matrix (Ad-ECM) as a mitigator of RISF. Female C57BL/6J mice that were irradiated developed fibrosis, which was mitigated by a single local Ad-ECM injection, improving limb movement and reducing epithelium thickness and collagen deposition. Ad-ECM treatment resulted in decreased expression of pro-inflammatory and fibrotic genes, and upregulation of anti-inflammatory cytokines, promoting M2 macrophage polarization. Co-culture of irradiated human fibroblasts with Ad-ECM down-modulated fibrotic gene expression and enhanced bone marrow cell migration. Ad-ECM treatment also increased interleukin (IL)-4, IL-5, and IL-15 expression in endothelial cells, stimulating M2 macrophage polarization and alleviating RISF. Prophylactic use of Ad-ECM showed effectiveness in mitigation. This study suggests Ad-ECM's potential in treating chronic-stage fibrosis.

Characterizing the inherent activity of urinary bladder matrix for adhesion, migration, and activation of fibroblasts as compared with collagen-based synthetic scaffold

The mechanism of action underlying the intriguing prominent bioactivity of urinary bladder matrix (UBM) for in situ tissue regeneration of soft tissue defects remains to be elucidated. It is speculated that the activity of UBM for cell adhesion, migration, and activation is inherent. The bioactivity of UBM for in situ tissue regeneration and its relation with the structure and intact soluble components of UBM were investigated in comparison to a collagen-based scaffold, PELNAC (PEL). We isolated the soluble component of the two materials with urea buffer, and evaluated the respective effect of these soluble components on the in vitro adhesion and migration of L929 fibroblasts. The spatiotemporal pattern of endogenous-cell ingrowth into the scaffolds and cell activation were investigated using a model of murine subcutaneous implantation. UBM is more capable of promoting the adhesion, migration, and proliferation of fibroblasts than PEL in a serum-independent manner. In vivo, as compared with PEL, UBM exhibits significantly enhanced activity for fast endogenous cell ingrowth and produces a more prominent pro-regenerative and pro-remodeling microenvironment by inducing the expression of TGF-β1, VEGF, MMP-9, and murine type I collagen. Overall, our results suggest the prominent bioactivity of UBM for in situ tissue regeneration is inherent.

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.

Engineered clustered myoblast cell injection augments angiogenesis and muscle regeneration in peripheral artery disease

The low survival rate of administered cells due to ischemic and inflammatory environments limits the efficacy of the current regenerative cell therapy in peripheral artery disease (PAD). This study aimed to develop a new method to enhance the efficacy of cell therapy in PAD using cell sheet technology. Clustered cells (CCs) from myoblast cell sheets obtained from C57/BL6 mice were administered into ischemic mouse muscles 7 days after induction of ischemia (defined as day 0). Control groups were administered with single myoblast cells (SCs) or saline. Cell survival, blood perfusion of the limb, angiogenesis, muscle regeneration, and inflammation status were evaluated. The survival of administered cells was markedly improved in CCs compared with SCs at days 7 and 28. CCs showed significantly improved blood perfusion, augmented angiogenesis with increased density of CD31⁺/α-smooth muscle actin⁺ arterioles, and accelerated muscle regeneration, along with the upregulation of associated genes. Additionally, inflammation status was well regulated by CCs administration. CCs administration increased the number of macrophages and then induced polarization into an anti-inflammatory phenotype (CD11c^-/CD206⁺), along with the increased expression of genes associated with anti-inflammatory cytokines. Our findings suggest clinical potential of rescuing severely damaged limbs in PAD using CCs.

A liquid fraction of extracellular matrix inhibits glioma cell viability in vitro and in vivo

Suppressive effects of extracellular matrix (ECM) upon various cancers have been reported. Glioblastoma multiforme has poor prognosis and new therapies are desired. This work investigated the effects of a saline-soluble fraction of urinary bladder ECM (ECM-SF) upon glioma cells. Viability at 24 hours in 1, 5, or 10 mg/mL ECM-SF-spiked media was evaluated in primary glioma cells (0319, 1015, 1119), glioma cell lines (A172, T98G, U87MG, C6), and brain cell lines (HCN-2, HMC3). Viability universally decreased at 5 and 10 mg/mL with U87MG, HCN-2, and HCM3 being least sensitive. Apoptosis in 0319 and 1119 cells was confirmed via NucView 488. Bi-weekly intravenous injection of ECM-SF (120 mg/kg) for 10 weeks in Sprague-Dawley rats did not affect weight, temperature, complete blood count, or multi-organ histology (N = 5). Intratumoral injection of ECM-SF (10 uL of 30 mg/mL) at weeks 2-4 post C6 inoculation in Wistar rats increased median survival from 24.5 to 51 days (hazard ratio for death 0.22) and decreased average tumor volume at time of death from 349 mm3 to 90 mm3 over 10 weeks (N = 6). Mass spectrometry identified 2,562 protein species in ECM-SF, parent ECM, and originating tissue. These results demonstrate the suppressive effects of ECM on glioma and warrant further study.

Post-Stroke Timing of ECM Hydrogel Implantation Affects Biodegradation and Tissue Restoration

Extracellular matrix (ECM) hydrogel promotes tissue regeneration in lesion cavities after stroke. However, a bioscaffold's regenerative potential needs to be considered in the context of the evolving pathological environment caused by a stroke. To evaluate this key issue in rats, ECM hydrogel was delivered to the lesion core/cavity at 7-, 14-, 28-, and 90-days post-stroke. Due to a lack of tissue cavitation 7-days post-stroke, implantation of ECM hydrogel did not achieve a sufficient volume and distribution to warrant comparison with the other time points. Biodegradation of ECM hydrogel implanted 14- and 28-days post-stroke were efficiently (80%) degraded by 14-days post-bioscaffold implantation, whereas implantation 90-days post-stroke revealed only a 60% decrease. Macrophage invasion was robust at 14- and 28-days post-stroke but reduced in the 90-days post-stroke condition. The pro-inflammation (M1) and pro-repair (M2) phenotype ratios were equivalent at all time points, suggesting that the pathological environment determines macrophage invasion, whereas ECM hydrogel defines their polarization. Neural cells (neural progenitors, neurons, astrocytes, oligodendrocytes) were found at all time points, but a 90-days post-stroke implantation resulted in reduced densities of mature phenotypes. Brain tissue restoration is therefore dependent on an efficient delivery of a bioscaffold to a tissue cavity, with 28-days post-stroke producing the most efficient biodegradation and tissue regeneration, whereas by 90-days post-stroke, these effects are significantly reduced. Improving our understanding of how the pathological environment influences biodegradation and the tissue restoration process is hence essential to devise engineering strategies that could extend the therapeutic window for bioscaffolds to repair the damaged brain.

Macrophage-stroma interactions in fibrosis: biochemical, biophysical, and cellular perspectives

Fibrosis results from aberrant wound healing and is characterized by an accumulation of extracellular matrix, impairing the function of an affected organ. Increased deposition of extracellular matrix proteins, disruption of matrix degradation, but also abnormal post-translational modifications alter the biochemical composition and biophysical properties of the tissue microenvironment - the stroma. Macrophages are known to play an important role in wound healing and tissue repair, but the direct influence of fibrotic stroma on macrophage behaviour is still an under-investigated element in the pathogenesis of fibrosis. In this review, the current knowledge on interactions between macrophages and (fibrotic) stroma will be discussed from biochemical, biophysical, and cellular perspectives. Furthermore, we provide future perspectives with regard to how macrophage-stroma interactions can be examined further to ultimately facilitate more specific targeting of these interactions in the treatment of fibrosis. © 2021 The Authors. The Journal of Pathology published by John Wiley & Sons, Ltd. on behalf of The Pathological Society of Great Britain and Ireland.

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

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

SARS-CoV-2 and tissue damage: current insights and biomaterial-based therapeutic strategies

The effect of SARS-CoV-2 infection on humanity has gained worldwide attention and importance due to the rapid transmission, lack of treatment options and high mortality rate of the virus. While scientists across the world are searching for vaccines/drugs that can control the spread of the virus and/or reduce the risks associated with infection, patients infected with SARS-CoV-2 have been reported to have tissue/organ damage. With most tissues/organs having limited regenerative potential, interventions that prevent further damage or facilitate healing would be helpful. In the past few decades, biomaterials have gained prominence in the field of tissue engineering, in view of their major role in the regenerative process. Here we describe the effect of SARS-CoV-2 on multiple tissues/organs, and provide evidence for the positive role of biomaterials in aiding tissue repair. These findings are further extrapolated to explore their prospects as a therapeutic platform to address the tissue/organ damage that is frequently observed during this viral outbreak. This study suggests that the biomaterial-based approach could be an effective strategy for regenerating tissues/organs damaged by SARS-CoV-2.

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.

The effect of normal, metaplastic, and neoplastic esophageal extracellular matrix upon macrophage activation

Introduction

Macrophages are capable of extreme plasticity and their activation state has been strongly associated with solid tumor growth progression and regression. Although the macrophage response to extracellular matrix (ECM) isolated from normal tissue is reasonably well understood, there is a relative dearth of information regarding their response to ECM isolated from chronically inflamed tissues, pre-neoplastic tissues, and neoplastic tissues. Esophageal adenocarcinoma (EAC) is a type of neoplasia driven by chronic inflammation in the distal esophagus, and the length of the esophagus provides the opportunity to investigate macrophage behavior in the presence of ECM isolated from a range of disease states within the same organ.

Methods

Normal, metaplastic, and neoplastic ECM hydrogels were prepared from decellularized EAC tissue. The hydrogels were evaluated for their nanofibrous structure (SEM), biochemical profile (targeted and global proteomics), and direct effect upon macrophage (THP-1 cell) activation state (qPCR, ELISA, immunolabeling) and indirect effect upon epithelial cell (Het-1A) migration (Boyden chamber).

Results

Nanofibrous ECM hydrogels from the three tissue types could be formed, and normal and neoplastic ECM showed distinctive protein profiles by targeted and global mass spectroscopy. ECM proteins functionally related to cancer and tumorigenesis were identified in the neoplastic esophageal ECM including collagen alpha-1(VIII) chain (COL8A1), lumican, and elastin. Metaplastic and neoplastic esophageal ECM induce distinctive effects upon THP-1 macrophage signaling compared to normal esophageal ECM. These effects include activation of pro-inflammatory IFNγ and TNFα gene expression and anti-inflammatory IL1RN gene expression. Most notably, neoplastic ECM robustly increased macrophage TNFα protein expression. The secretome of macrophages pre-treated with metaplastic and neoplastic ECM increases the migration of normal esophageal epithelial cells, similar behavior to that shown by tumor cells. Metaplastic ECM shows similar but less pronounced effects than neoplastic ECM suggesting the abnormal signals also exist within the pre-cancerous state.

Conclusion

A progressively diseased ECM, as exists within the esophagus exposed to chronic gastric reflux, can provide insights into novel biomarkers of early disease and identify potential therapeutic targets.

Extracellular matrix grafts: From preparation to application (Review)

Recently, the increasing emergency of traffic accidents and the unsatisfactory outcome of surgical intervention are driving research to seek a novel technology to repair traumatic soft tissue injury. From this perspective, decellularized matrix grafts (ECM-G) including natural ECM materials, and their prepared hydrogels and bioscaffolds, have emerged as possible alternatives for tissue engineering and regenerative medicine. Over the past decades, several physical and chemical decellularization methods have been used extensively to deal with different tissues/organs in an attempt to carefully remove cellular antigens while maintaining the non-immunogenic ECM components. It is anticipated that when the decellularized biomaterials are seeded with cells in vitro or incorporated into irregularly shaped defects in vivo, they can provide the appropriate biomechanical and biochemical conditions for directing cell behavior and tissue remodeling. The aim of this review is to first summarize the characteristics of ECM-G and describe their major decellularization methods from different sources, followed by analysis of how the bioactive factors and undesired residual cellular compositions influence the biologic function and host tissue response following implantation. Lastly, we also provide an overview of the in vivoapplication of ECM-G in facilitating tissue repair and remodeling.

Extracellular matrix-derived biomaterials in engineering cell function

Extracellular matrix (ECM) derived components are emerging sources for the engineering of biomaterials that are capable of inducing desirable cell-specific responses. This review explores the use of biomaterials derived from naturally occurring ECM proteins and their derivatives in approaches that aim to regulate cell function. Biomaterials addressed are grouped into six categories: purified single ECM proteins, combinations of purified ECM proteins, cell-derived ECM, tissue-derived ECM, diseased and modified ECM, and ECM-polymer coupled biomaterials. Purified ECM proteins serve as a material coating for enhanced cell adhesion and biocompatibility. Cell-derived and tissue-derived ECM, generated by cell isolation and decellularization technologies, can capture the native state of the ECM environment and guide cell migration and alignment patterns as well as stem cell differentiation. We focus primarily on recent advances in the fields of soft tissue, cardiac, and dermal repair, and explore the utilization of ECM proteins as biomaterials to engineer cell responses.

New Insight into Natural Extracellular Matrix: Genipin Cross-Linked Adipose-Derived Stem Cell Extracellular Matrix Gel for Tissue Engineering

The cell-derived extracellular matrix (ECM) is associated with a lower risk of pathogen transfer, and it possesses an ideal niche with growth factors and complex fibrillar proteins for cell attachment and growth. However, the cell-derived ECM is found to have poor biomechanical properties, and processing of cell-derived ECM into gels is scarcely studied. The gel provides platforms for three-dimensional cell culture, as well as injectable biomaterials, which could be delivered via a minimally invasive procedure. Thus, in this study, an adipose-derived stem cell (ADSC)-derived ECM gel was developed and cross-linked by genipin to address the aforementioned issue. The genipin cross-linked ADSC ECM gel was fabricated via several steps, including rabbit ADSC culture, cell sheets, decellularization, freeze-thawing, enzymatic digestion, neutralization of pH, and cross-linking. The physicochemical characteristics and cytocompatibility of the gel were evaluated. The results demonstrated that the genipin cross-linking could significantly enhance the mechanical properties of the ADSC ECM gel. Furthermore, the ADSC ECM was found to contain collagen, fibronectin, biglycan, and transforming growth factor (TGF)-β1, which could substantially maintain ADSC, skin, and ligament fibroblast cell proliferation. This cell-derived natural material could be suitable for future regenerative medicine and tissue engineering application.

Porcine Lung-Derived Extracellular Matrix Hydrogel Properties Are Dependent on Pepsin Digestion Time

Hydrogels derived from decellularized lungs are promising materials for tissue engineering in the development of clinical therapies and for modeling the lung extracellular matrix (ECM) in vitro. Characterizing and controlling the resulting physical, biochemical, mechanical, and biologic properties of decellularized ECM (dECM) after enzymatic solubilization and gelation are thus of key interest. As the role of enzymatic pepsin digestion in effecting these properties has been understudied, we investigated the digestion time-dependency on key parameters of the resulting ECM hydrogel. Using resolubilized, homogenized decellularized pig lung dECM as a model system, significant time-dependent changes in protein concentration, turbidity, and gelation potential were found to occur between the 4 and 24 h digestion time points, and plateauing with longer digestion times. These results correlated with qualitative scanning electron microscopy images and quantitative analysis of hydrogel interconnectivity and average fiber diameter. Interestingly, the time-dependent changes in the storage modulus tracked with the hydrogel interconnectivity results, while the Young's modulus values were more closely related to average fiber size at each time point. The structural and biochemical alterations correlated with significant changes in metabolic activity of several representative lung cells seeded onto the hydrogels with progressive decreases in cell viability and alterations in morphology observed in cells cultured on hydrogels produced with dECM digested for >12 and up to 72 h of digestion. These studies demonstrate that 12 h pepsin digest of pig lung dECM provides an optimal balance between desirable physical ECM hydrogel properties and effects on lung cell behaviors.

Decellularized nerve matrix hydrogel and glial-derived neurotrophic factor modifications assisted nerve repair with decellularized nerve matrix scaffolds

Nerve defects are challenging to address clinically without satisfactory treatments. As a reliable alternative to autografts, decellularized nerve matrix scaffolds (DNM-S) have been widely used in clinics for surgical nerve repair. However, DNM-S remain inferior to autografts in their ability to support nerve regeneration for long nerve defects. In this study, we systematically and clearly presented the nano-architecture of nerve-specific structures, including the endoneurium, basement membrane and perineurium/epineurium in DNM-S. Furthermore, we modified the DNM-S by supplementing decellularized nerve matrix hydrogel (DNMG) and glial-derived neurotrophic factor (GDNF) and then bridged a 50-mm sciatic nerve defect in a beagle model. Fifteen beagles were randomly divided into three groups (five per group): an autograft group, DNM-S group and GDNF-DNMG-modified DNM-S (DNM-S/GDNF@DNMG) group. DNM-S/GDNF@DNMG, as optimized nerve grafts, were used to bridge nerve defects in the same manner as in the DNM-S group. The repair outcome was evaluated by behavioural observations, electrophysiological assessments, regenerated nerve tissue histology and reinnervated target muscle examinations. Compared with the DNM-S group, limb function, electrophysiological responses and histological findings were improved in the DNM-S/GDNF@DNMG group 6 months after grafting, reflecting a narrower gap between the effects of DNM-S and autografts. In conclusion, modification of DNM-S with DNMG and GDNF enhanced nerve regeneration and functional recovery, indicating that noncellular modification of DNM-S is a promising method for treating long nerve defects.

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.

[Effect of decellularized adipose tissue combined with vacuum sealing drainage on wound inflammation in pigs]

Objective

To preliminary explore the effect of decellularized adipose tissue (DAT) combined with vacuum sealing drainage (VSD) on wound inflammation in pigs.

Methods

The DAT was prepared through the process of freeze-thaw, enzymatic digestion, organic solvent extraction, and vacuum freeze-drying. The appearance of DAT was observed before and after freeze-drying. HE staining was used to observe its structure and acellular effect. Eighteen male Bama minipigs were recruited, and four dorsal skin soft tissue wounds in diameter of 4 cm were made on each pig and randomly divided into 4 groups for different treatments. The wounds were treated with DAT combined with VSD in DAT/VSD group, DAT in DAT group, VSD in VSD group, and sterile gauze dressing in control group. HE staining was performed at 3, 7, 10, and 14 days after treatment. Moreover, the expressions of inflammatory factors [interleukin 1β (IL-1β), IL-6, and tumor necrosis factor α (TNF-α)], as well as the phenotypes of M1 and M2 macrophage phenotypic markers [inducible nitric oxide synthase (iNOS) and arginase 1 (ARG-1)] were detected by real-time fluorescence quantitative PCR (qRT-PCR). ELISA was used to determine the content of iNOS and ARG-1.

Results

General observation and HE staining showed that DAT obtained in this study had a loose porous structure without cells. The neutrophils of wounds were significantly less in DAT/VSD group than in control group and DAT group ( P<0.05) at 3 days after treatment, and the difference was not significant ( P>0.05) between DAT/VSD group and VSD group. And the neutrophils were significantly less in DAT/VSD group than in other three groups ( P<0.05) at 7, 10, and 14 days. The mRNA expressions of IL-1β, IL-6, TNF-α, and iNOS were significantly lower in DAT/VSD group than in other three groups at 3, 7, 10, and 14 days ( P<0.05), while the mRNA expression of ARG-1 was significantly higher in DAT/VSD group than in other three groups ( P<0.05). ELISA showed that the content of iNOS was significantly lower in DAT/VSD group than in other three groups at 3, 7, 10, and 14 days ( P<0.05), while the content of ARG-1 was significantly higher in DAT/VSD group than in other three groups ( P<0.05).

Conclusion

DAT combined with VSD can significantly reduce inflammatory cell infiltration during wound healing, regulate the expressions of inflammatory factors and macrophage phenotype, and the effect is better than single use of each and conventional dressing change.

Applications of decellularized materials in tissue engineering: advantages, drawbacks and current improvements, and future perspectives

Decellularized materials (DMs) are attracting more and more attention in tissue engineering because of their many unique advantages, and they could be further improved in some aspects through various means.

Inorganic Polyphosphates As Storage for and Generator of Metabolic Energy in the Extracellular Matrix

Inorganic polyphosphates (polyP) consist of linear chains of orthophosphate residues, linked by high-energy phosphoanhydride bonds. They are evolutionarily old biopolymers that are present from bacteria to man. No other molecule concentrates as much (bio)chemically usable energy as polyP. However, the function and metabolism of this long-neglected polymer are scarcely known, especially in higher eukaryotes. In recent years, interest in polyP experienced a renaissance, beginning with the discovery of polyP as phosphate source in bone mineralization. Later, two discoveries placed polyP into the focus of regenerative medicine applications. First, polyP shows morphogenetic activity, i.e., induces cell differentiation via gene induction, and, second, acts as an energy storage and donor in the extracellular space. Studies on acidocalcisomes and mitochondria provided first insights into the enzymatic basis of eukaryotic polyP formation. In addition, a concerted action of alkaline phosphatase and adenylate kinase proved crucial for ADP/ATP generation from polyP. PolyP added extracellularly to mammalian cells resulted in a 3-fold increase of ATP. The importance and mechanism of this phosphotransfer reaction for energy-consuming processes in the extracellular matrix are discussed. This review aims to give a critical overview about the formation and function of this unique polymer that is capable of storing (bio)chemically useful energy.

Bioscaffold-Induced Brain Tissue Regeneration

Brain tissue lost after a stroke is not regenerated, although a repair response associated with neurogenesis does occur. A failure to regenerate functional brain tissue is not caused by the lack of available neural cells, but rather the absence of structural support to permit a repopulation of the lesion cavity. Inductive bioscaffolds can provide this support and promote the invasion of host cells into the tissue void. The putative mechanisms of bioscaffold degradation and its pivotal role to permit invasion of neural cells are reviewed and discussed in comparison to peripheral wound healing. Key differences between regenerating and non-regenerating tissues are contrasted in an evolutionary context, with a special focus on the neurogenic response as a conditio sine qua non for brain regeneration. The pivotal role of the immune system in biodegradation and the formation of a neovasculature are contextualized with regeneration of peripheral soft tissues. The application of rehabilitation to integrate newly forming brain tissue is suggested as necessary to develop functional tissue that can alleviate behavioral impairments. Pertinent aspects of brain tissue development are considered to provide guidance to produce a metabolically and functionally integrated de novo tissue. Although little is currently known about mechanisms involved in brain tissue regeneration, this review outlines the various components and their interplay to provide a framework for ongoing and future studies. It is envisaged that a better understanding of the mechanisms involved in brain tissue regeneration will improve the design of biomaterials and the methods used for implantation, as well as rehabilitation strategies that support the restoration of behavioral functions.

Stem cells from the dental apical papilla in extracellular matrix hydrogels mitigate inflammation of microglial cells

After spinal cord injury (SCI) chronic inflammation hampers regeneration. Influencing the local microenvironment after SCI may provide a strategy to modulate inflammation and the immune response. The objectives of this work were to determine whether bone or spinal cord derived ECM hydrogels can deliver human mesenchymal stem cells from the apical papilla (SCAP) to reduce local inflammation and provide a regenerative microenvironment. Bone hydrogels (8 and 10 mg/ml, B8 and B10) and spinal cord hydrogels (8 mg/ml, S8) supplemented with fibrin possessed a gelation rate and a storage modulus compatible with spinal cord implantation. S8 and B8 impact on the expression of anti and pro-inflammatory cytokines (Arg1, Nos2, Tnf) in LPS treated microglial cells were assessed using solubilised and solid hydrogel forms. S8 significantly reduced the Nos2/Arg1 ratio and solubilised B8 significantly reduced Tnf and increased Arg1 whereas solid S8 and B8 did not impact inflammation in microglial cells. SCAP incorporation within ECM hydrogels did not impact upon SCAP immunoregulatory properties, with significant downregulation of Nos2/Arg1 ratio observed for all SCAP embedded hydrogels. Tnf expression was reduced with SCAP embedded in B8, reflecting the gene expression observed with the innate hydrogel. Thus, ECM hydrogels are suitable vehicles to deliver SCAP due to their physical properties, preservation of SCAP viability and immunomodulatory capacity.

Extracellular Matrices to Modulate the Innate Immune Response and Enhance Bone Healing

Extracellular matrices (ECMs) have emerged as promising off-the-shelf products to induce bone regeneration, with the capacity not only to activate osteoprogenitors, but also to influence the immune response. ECMs generated starting from living cells such as mesenchymal stromal cells (MSCs) have the potential to combine advantages of native tissue-derived ECMs (e.g., physiological presentation of multiple regulatory factors) with those of synthetic ECMs (e.g., customization and reproducibility of composition). MSC-derived ECMs could be tailored by enrichment not only in osteogenic cytokines, but also in immunomodulatory factors, to skew the innate immune response toward regenerative processes. After reviewing the different immunoregulatory properties of ECM components, here we propose different approaches to engineer ECMs enriched in factors capable to regulate macrophage polarization, recruit host immune and mesenchymal cells, and stimulate the synthesis of other immunoinstructive cytokines. Finally, we offer a perspective on the possible evolution of the paradigm based on biological and chemico-physical design considerations, and the use of gene editing approaches.

Extracellular Matrix Degradation Products Downregulate Neoplastic Esophageal Cell Phenotype

IMPACT STATEMENT

Extracellular matrix (ECM) biomaterials were used to treat esophageal cancer patients after cancer resection and promoted regrowth of normal mucosa without recurrence of cancer. The present study investigates the mechanisms by which these materials were successful to prevent the cancerous phenotype. ECM downregulated neoplastic esophageal cell function (proliferation, metabolism), but normal esophageal epithelial cells were unaffected in vitro, and suggests a molecular basis (downregulation of PI3K-Akt, cell cycle) for the promising clinical results. The therapeutic effect appeared to be enhanced using homologous esophageal ECM. This study suggests that ECM can be further investigated to treat cancer patients after resection or in combination with targeted therapy.

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.

Modulation of inflammation in wounds of diabetic patients treated with porcine urinary bladder matrix

Aim: To determine if porcine urinary bladder matrix (UBM) treatment is associated with modulation of wound inflammation in diabetic patients. Patients & methods: mRNA associated with M1 and M2 macrophages were measured in wounds of diabetic and nondiabetic patients pre- and post-treatment with UBM and an M1:M2 score was calculated. Results: Wound tissue from diabetic subjects exhibited elevated M1:M2 scores compared with nondiabetic patients, suggesting a greater pro-inflammatory state prior to treatment. Post-treatment, there was significantly greater reduction in the magnitude of the individual M1:M2 scores in the diabetic patients resulting in similar levels in both groups of patients. Conclusions: UBM may assist in diabetic wound healing by restoring an inflammatory state similar to that of nondiabetic patients.

Modulating macrophage responses to promote tissue regeneration by changing the formulation of bone extracellular matrix from filler particles to gel bioscaffolds

Extracellular matrices (ECMs) derived from native tissues/organs have been used as biomaterials for tissue engineering and regenerative medicine in a wide range of preclinical and clinical settings. The success or failure of these applications is largely contingent on the host responses to the matrices in vivo. Despite retaining their native structural and functional proteins, bone ECM-based transplants have been reported to evoke adverse immune responses in many cases; thus, optimizing the immunomodulatory properties of bone ECMs is critical for ensuring downstream regenerative outcomes. Using a simple digestion-neutralization protocol, we transformed the commonly used bone-derived filler particles into gel bioscaffolds. Instead of inducing macrophages toward proinflammatory (M1) polarization, as reported in the literature and confirmed in the present study for ECM particles, the ECM gels were found to be more likely to polarize macrophages toward regulatory/anti-inflammatory (M2) phenotypes, leading to enhanced tissue regeneration in a rat periodontal defect model. The present work demonstrates a simple, practical and economical strategy to modify the immunomodulatory properties of bone ECMs before their in vivo transplantation and hence has important implications that may facilitate the use of ECM-based bioscaffolds derived from diverse sources of tissues for regenerative purposes.

Matrix-bound nanovesicles prevent ischemia-induced retinal ganglion cell axon degeneration and death and preserve visual function

Injury to retinal ganglion cells (RGC), central nervous system neurons that relay visual information to the brain, often leads to RGC axon degeneration and permanently lost visual function. Herein this study shows matrix-bound nanovesicles (MBV), a distinct class of extracellular nanovesicle localized specifically to the extracellular matrix (ECM) of healthy tissues, can neuroprotect RGCs and preserve visual function after severe, intraocular pressure (IOP) induced ischemia in rat. Intravitreal MBV injections attenuated IOP-induced RGC axon degeneration and death, protected RGC axon connectivity to visual nuclei in the brain, and prevented loss in retinal function as shown by histology, anterograde axon tracing, manganese-enhanced magnetic resonance imaging, and electroretinography. In the optic nerve, MBV also prevented IOP-induced decreases in growth associated protein-43 and IOP-induced increases in glial fibrillary acidic protein. In vitro studies showed MBV suppressed pro-inflammatory signaling by activated microglia and astrocytes, stimulated RGC neurite growth, and neuroprotected RGCs from neurotoxic media conditioned by pro-inflammatory astrocytes. Thus, MBV can positively modulate distinct signaling pathways (e.g., inflammation, cell death, and axon growth) in diverse cell types. Since MBV are naturally derived, bioactive factors present in numerous FDA approved devices, MBV may be readily useful, not only experimentally, but also clinically as immunomodulatory, neuroprotective factors for treating trauma or disease in the retina as well as other CNS tissues.

Tissue/organ-derived bioink formulation for 3D bioprinting

Tissue/organ-derived bioink formulations open up new avenues in 3D bioprinting research with the potential to create functional tissue or organs. Printing of tissue construct largely depends on material properties, as it needs to be fabricated in an aqueous environment while encapsulating living cells. The decellularized extracellular matrix bioinks proved to be a potential option for functional tissue development in vivo and as an alternative to chemically cross-linked bioinks. However, certain limitations such as printability and limited mechanical strength need to be addressed for enhancing their widespread applications. By drawing knowledge from the existing literature, emphasis has been given in this review to the development of decellularized extracellular matrix bioinks and their applications in printing functional tissue constructs.

Tunable Hydrogels Derived from Genetically Engineered Extracellular Matrix Accelerate Diabetic Wound Healing

Hydrogels composed of solubilized decellularized extracellular matrix (ECM) are attractive materials because they combine the complexity of native ECM with injectability and ease of use. Nevertheless, these materials are typically only tunable by altering the concentration, which alters the ligand landscape, or by incorporating synthetic components, which can result in an unfavorable host response. Herein, we demonstrate the fabrication of genetically tunable ECM-derived materials, by utilizing wild type (WT) and (thrombospondin-2 knockout) TSP-2 KO decellularized skins to prepare hydrogels. The resulting materials exhibited distinct mechanical properties characterized by rheology and different concentrations of collagens when characterized by quantitative proteomics. Mixtures of the gels achieved intermediate effects between the WT and the KO, permitting tunability of the gel properties. In vivo, the hydrogels exhibited tunable cell invasion with a correlation between the content of TSP-2 KO hydrogel and the extent of cell invasion. Additionally, TSP-2 KO hydrogels significantly improved diabetic wound healing at 10 and 21 days. Furthermore, hydrogels derived from genetically engineered in vitro cell-derived matrix mimicked the trends observed for tissue-derived matrix, providing a platform for faster screening of novel manipulations and easier clinical translation. Overall, we demonstrate that genetic engineering approaches impart tunability to ECM-based hydrogels and can result in materials capable of enhanced regeneration.

Heart valve tissue-derived hydrogels: Preparation and characterization of mitral valve chordae, aortic valve, and mitral valve gels

Heart valve (HV) diseases are among the leading causes of death and continue to threaten public health worldwide. The current clinical options for HV replacement include mechanical and biological prostheses. However, an ongoing problem with current HV prostheses is their failure to integrate with the host tissue and their inability grow and remodel within the body. Tissue engineered heart valves (TEHVs) are a promising solution to these problems, as they are able to grow and remodel somatically with the rest of the body. Recently, decellularized HVs have demonstrated great potential as valve replacements because they are tissue specific, but recellularization is still a challenge due to the dense HV extracellular matrix (ECM) network. In this proof-of-concept work, we decellularized porcine mitral valve chordae, aortic valve leaflets, and mitral valve leaflets and processed them into injectable hydrogels that could accommodate any geometry. While the three valvular ECMs contained various amounts of collagen, they displayed similar glycosaminoglycan contents. The hydrogels had similar nanofibrous structures and gelation kinetics with various compressive strengths. When encapsulated with NIH 3 T3 fibroblasts, all the hydrogels supported cell survivals up to 7 days. Decellularized HV ECM hydrogels may show promising potential HV tissue engineering applications. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B: 1732-1740, 2019.

Regulation of decellularized tissue remodeling via scaffold-mediated lentiviral delivery in anatomically-shaped osteochondral constructs

Cartilage-derived matrix (CDM) has emerged as a promising scaffold material for tissue engineering of cartilage and bone due to its native chondroinductive capacity and its ability to support endochondral ossification. Because it consists of native tissue, CDM can undergo cellular remodeling, which can promote integration with host tissue and enables it to be degraded and replaced by neotissue over time. However, enzymatic degradation of decellularized tissues can occur unpredictably and may not allow sufficient time for mechanically competent tissue to form, especially in the harsh inflammatory environment of a diseased joint. The goal of the current study was to engineer cartilage and bone constructs with the ability to inhibit aberrant inflammatory processes caused by the cytokine interleukin-1 (IL-1), through scaffold-mediated delivery of lentiviral particles containing a doxycycline-inducible IL-1 receptor antagonist (IL-1Ra) transgene on anatomically-shaped CDM constructs. Additionally, scaffold-mediated lentiviral gene delivery was used to facilitate spatial organization of simultaneous chondrogenic and osteogenic differentiation via site-specific transduction of a single mesenchymal stem cell (MSC) population to overexpress either chondrogenic, transforming growth factor-beta 3 (TGF-β3), or osteogenic, bone morphogenetic protein-2 (BMP-2), transgenes. Controlled induction of IL-1Ra expression protected CDM hemispheres from inflammation-mediated degradation, and supported robust bone and cartilage tissue formation even in the presence of IL-1. In the absence of inflammatory stimuli, controlled cellular remodeling was exploited as a mechanism for fusing concentric CDM hemispheres overexpressing BMP-2 and TGF-β3 into a single bi-layered osteochondral construct. Our findings demonstrate that site-specific delivery of inducible and tunable transgenes confers spatial and temporal control over both CDM scaffold remodeling and neotissue composition. Furthermore, these constructs provide a microphysiological in vitro joint organoid model with site-specific, tunable, and inducible protein delivery systems for examining the spatiotemporal response to pro-anabolic and/or inflammatory signaling across the osteochondral interface.

Towards a Novel Patch Material for Cardiac Applications: Tissue-Specific Extracellular Matrix Introduces Essential Key Features to Decellularized Amniotic Membrane

There is a growing need for scaffold material with tissue-specific bioactivity for use in regenerative medicine, tissue engineering, and for surgical repair of structural defects. We developed a novel composite biomaterial by processing human cardiac extracellular matrix (ECM) into a hydrogel and combining it with cell-free amniotic membrane via a dry-coating procedure. Cardiac biocompatibility and immunogenicity were tested in vitro using human cardiac fibroblasts, epicardial progenitor cells, murine HL-1 cells, and human immune cells derived from buffy coat. Processing of the ECM preserved important matrix proteins as demonstrated by mass spectrometry. ECM coating did not alter the mechanical characteristics of decellularized amniotic membrane but did cause a clear increase in adhesion capacity, cell proliferation and viability. Activated monocytes secreted less pro-inflammatory cytokines, and both macrophage polarization towards the pro-inflammatory M1 type and T cell proliferation were prevented. We conclude that the incorporation of human cardiac ECM hydrogel shifts and enhances the bioactivity of decellularized amniotic membrane, facilitating its use in future cardiac applications.

Fetal extracellular matrix nerve wraps locally improve peripheral nerve remodeling after complete transection and direct repair in rat

In peripheral nerve (PN) injuries requiring surgical repair, as in PN transection, cellular and ECM remodeling at PN epineurial repair sites is hypothesized to reduce PN functional outcomes by slowing, misdirecting, or preventing axons from regrowing appropriately across the repair site. Herein this study reports on deriving and analyzing fetal porcine urinary bladder extracellular matrix (fUB-ECM) by vacuum assisted decellularization, fabricating fUBM-ECM nerve wraps, and testing fUB-ECM nerve wrap biocompatibility and bioactivity in a trigeminal, infraorbital nerve (ION) branch transection and direct end-to-end repair model in rat. FUB-ECM nerve wraps significantly improved epi- and endoneurial organization and increased both neovascularization and growth associated protein-43 (GAP-43) expression at PN repair sites, 28-days post surgery. However, the number of neurofilament positive axons, remyelination, and whisker-evoked response properties of ION axons were unaltered, indicating improved tissue remodeling per se does not predict axon regrowth, remyelination, and the return of mechanoreceptor cortical signaling. This study shows fUB-ECM nerve wraps are biocompatible, bioactive, and good experimental and potentially clinical devices for treating epineurial repairs. Moreover, this study highlights the value provided by precise, analytic models, like the ION repair model, in understanding how PN tissue remodeling relates to axonal regrowth, remyelination, and axonal response properties.

Blood prefabricated hydroxyapatite/tricalcium phosphate induces ectopic vascularized bone formation via modulating the osteoimmune environment

Blood prefabricated hydroxyapatite/tricalcium phosphate induces ectopic vascularized bone formation via modulating the osteoimmune environment.

Targeted delivery of tungsten oxide nanoparticles for multifunctional anti-tumor therapy via macrophages

Tumor-associated macrophages are highly versatile effector cells that have been used to kill tumor cells.

Immunomodulation and Mobilization of Progenitor Cells by Extracellular Matrix Bioscaffolds for Volumetric Muscle Loss Treatment

Acellular bioscaffolds composed of extracellular matrix (ECM) have been effectively used to promote functional tissue remodeling in both preclinical and clinical studies of volumetric muscle loss, but the mechanisms that contribute to such outcomes are not fully understood. Thirty-two C57bl/6 mice were divided into eight groups of four animals each. A critical-sized defect was created in the quadriceps muscle and was repaired with a small intestinal submucosa ECM bioscaffold or left untreated. Animals were sacrificed at 3, 7, 14, or 56 days after surgery. The spatiotemporal cellular response in both treated and untreated groups was characterized by immunolabeling methods. Early time points showed a robust M2-like macrophage phenotype following ECM treatment in contrast to the predominant M1-like macrophage phenotype present in the untreated group. ECM implantation promoted perivascular stem cell mobilization, increased presence of neurogenic progenitor cells, and was associated with myotube formation. These cell types were present not only at the periphery of the defect near uninjured muscle, but also in the center of the ECM-filled defect. ECM bioscaffolds modify the default response to skeletal muscle injury, and provide a microenvironment conducive to a constructive healing response.

Long-term retention of ECM hydrogel after implantation into a sub-acute stroke cavity reduces lesion volume

Salvaging or functional replacement of damaged tissue caused by stroke in the brain remains a major therapeutic challenge. In situ gelation and retention of a hydrogel bioscaffold composed of 8mg/mL extracellular matrix (ECM) can induce a robust invasion of cells within 24h and potentially promote a structural remodeling to replace lost tissue. Herein, we demonstrate a long-term retention of ECM hydrogel within the lesion cavity. A decrease of approximately 32% of ECM volume is observed over 12weeks. Lesion volume, as measured by magnetic resonance imaging and histology, was reduced by 28%, but a battery of behavioral tests (bilateral asymmetry test; footfault; rotameter) did not reveal a therapeutic or detrimental effect of the hydrogel. Glial scarring and peri-infarct astrocytosis were equivalent between untreated and treated animals, potentially indicating that permeation into host tissue is required to exert therapeutic effects. These results reveal a marked difference of biodegradation of ECM hydrogel in the stroke-damaged brain compared to peripheral soft tissue repair. Further exploration of these structure-function relationships is required to achieve a structural remodeling of the implanted hydrogel, as seen in peripheral tissues, to replace lost tissue and promote behavioral recovery.

STATEMENT OF SIGNIFICANCE

In situ gelation of ECM is essential for its retention within a tissue cavity. The brain is a unique environment with restricted access that necessitates image-guided delivery through a thin needle to access tissue cavities caused by stroke, as well as other conditions, such as traumatic brain injury or glioma resection. Knowledge about a brain tissue response to implanted hydrogels remains limited, especially in terms of long-term effects and potential impact on behavioral function. We here address the long-term retention of hydrogel within the brain environment, its impact on behavioral function, as well as its ability to reduce further tissue deformation caused by stroke. This study highlights considerable differences in the brain's long-term response to an ECM hydrogel compared to peripheral soft tissue. It underlines the importance of understanding the effect of the structural presence of a hydrogel within a cavity upon host brain tissue and behavioral function. As demonstrated herein, ECM hydrogel can fill a cavity long-term to reduce further progression of the cavity, while potentially serving as a reservoir for local drug or cell delivery.

Extracellular Matrix Bioscaffolds as Immunomodulatory Biomaterials<sup/>

Suppression of the recipient immune response is a common component of tissue and organ transplantation strategies and has also been used as a method of mitigating the inflammatory and scar tissue response to many biomaterials. It is now recognized, however, that long-term functional tissue replacement not only benefits from an intact host immune response but also depends upon such a response. The present article reviews the limitations associated with the traditionally held view of avoiding the immune response, the ability of acellular biologic scaffold materials to modulate the host immune response and promote a functional tissue replacement outcome, and current strategies within the fields of tissue engineering and biomaterials to develop immune-responsive and immunoregulatory biomaterials.

Macrophage phenotype in response to ECM bioscaffolds

Macrophage presence and phenotype are critical determinants of the healing response following injury. Downregulation of the pro-inflammatory macrophage phenotype has been associated with the therapeutic use of bioscaffolds composed of extracellular matrix (ECM), but phenotypic characterization of macrophages has typically been limited to small number of non-specific cell surface markers or expressed proteins. The present study determined the response of both primary murine bone marrow derived macrophages (BMDM) and a transformed human mononuclear cell line (THP-1 cells) to degradation products of two different, commonly used ECM bioscaffolds; urinary bladder matrix (UBM-ECM) and small intestinal submucosa (SIS-ECM). Quantified cell responses included gene expression, protein expression, commonly used cell surface markers, and functional assays. Results showed that the phenotype elicited by ECM exposure (M_ECM) is distinct from both the classically activated IFNγ+LPS phenotype and the alternatively activated IL-4 phenotype. Furthermore, the BMDM and THP-1 macrophages responded differently to identical stimuli, and UBM-ECM and SIS-ECM bioscaffolds induced similar, yet distinct phenotypic profiles. The results of this study not only characterized an M_ECM phenotype that has anti-inflammatory traits but also showed the risks and challenges of making conclusions about the role of macrophage mediated events without consideration of the source of macrophages and the limitations of individual cell markers.

Tissue-specific bioactivity of soluble tendon-derived and cartilage-derived extracellular matrices on adult mesenchymal stem cells

BACKGROUND

Biological scaffolds composed of tissue-derived extracellular matrix (ECM) can promote homologous (i.e., tissue-specific) cell differentiation through preservation of biophysical and biochemical motifs found in native tissues. Solubilized ECMs derived from decellularized tendon and cartilage have recently been promoted as tissue-specific biomaterials, but whether tissue-specific bioactivity is preserved following solubilization is unknown. This study explored the tissue-specific bioactivity of soluble decellularized tendon and cartilage ECMs on human bone marrow-derived mesenchymal stem cells (MSCs) presented across different culture microenvironments, including two-dimensional (2D) tissue culture plastic, aligned electrospun nanofibers, cell pellets, and cell-seeded photocrosslinkable hydrogels.

METHODS

Tendon and cartilage ECMs were decellularized using established methods and solubilized either via pepsin digestion or urea extraction. The effect of soluble ECMs on cell proliferation and differentiation was initially explored by supplementing basal medium of human MSCs cultured on 2D tissue culture plastic. In subsequent experiments, MSCs were cultured on aligned electrospun nanofibers, ascell pellets, or encapsulated within photocrosslinkable methacrylated gelatin (GelMA) hydrogels. Urea-extracted tendon and cartilage ECMs were added as supplements.

RESULTS

Pepsin-digested ECMs did not promote homologous differentiation in human MSCs, whether provided as a medium supplement or three-dimensional (3D) hydrogels. In contrast, urea-extracted ECMs tended to promote tissue-specific differentiation of MSCs cultured in 2D and 3D microenvironments. The application of the small molecule TGF-β signaling inhibitor SB-431542 largely negated the tissue-specific gene expression patterns mediated by tendon and cartilage ECMs. This suggests that the action of endogenous TGF-β was required, but was not sufficient, to impart tissue-specific bioactivity of urea-extracted ECMs. When urea-extracted cartilage ECM was incorporated within a photocurable GelMA hydrogel it independently enhanced chondrogenesis in encapsulated MSCs, and showed additive prochondrogenesis upon TGF-β supplementation in the medium.

CONCLUSIONS

Urea-extracted ECM fractions of decellularized tendon and cartilage are soluble supplements capable of enhancing tissue-specific differentiation of adult stem cells.

The Effect of Mechanical Loading Upon Extracellular Matrix Bioscaffold-Mediated Skeletal Muscle Remodeling

Mounting evidence suggests that site-appropriate loading of implanted extracellular matrix (ECM) bioscaffolds and the surrounding microenvironment is an important tissue remodeling determinant, although the role at the cellular level in ECM-mediated skeletal muscle remodeling remains unknown. This study evaluates crosstalk between progenitor cells and macrophages during mechanical loading in ECM-mediated skeletal muscle repair. Myoblasts were exposed to solubilized ECM bioscaffolds and were mechanically loaded at 10% strain, 1 Hz for 5 h. Conditioned media was collected and applied to bone marrow-derived macrophages followed by immunolabeling for proinflammatory M1-like markers and proremodeling M2-like markers. Macrophages were subjected to the same loading protocol and their secreted products were collected for myoblast migration, proliferation, and differentiation analysis. A mouse hind limb unloading volumetric muscle loss model was used to evaluate the effect of loading upon the skeletal muscle microenvironment after ECM implantation. Animals were sacrificed at 14 or 180 days. Isometric torque production was tested and tissue sections were immunolabeled for macrophage phenotype and muscle fiber content. Results show that loading augments the ability of myoblasts to promote an M2-like macrophage phenotype following exposure to ECM bioscaffolds. Mechanically loaded macrophages promote myoblast chemotaxis and differentiation. Lack of weight bearing impaired muscle remodeling as indicated by Masson's Trichrome stain. Isometric torque was significantly increased following ECM implantation when compared to controls, a response not present in the hind limb-unloaded group. This work provides an important mechanistic insight of the effects of rehabilitation upon ECM-mediated remodeling and could have broader implications in clinical practice, advocating multidisciplinary approaches to regenerative medicine, emphasizing rehabilitation.

Urinary bladder extracellular matrix hydrogels and matrix-bound vesicles differentially regulate central nervous system neuron viability and axon growth and branching

Central nervous system neurons often degenerate after trauma due to the inflammatory innate immune response to injury, which can lead to neuronal cell death, scarring, and permanently lost neurologic function. Extracellular matrix bioscaffolds, derived by decellularizing healthy tissues, have been widely used in both preclinical and clinical studies to promote positive tissue remodeling, including neurogenesis, in numerous tissues, with extracellular matrix from homologous tissues often inducing more positive responses. Extracellular matrix hydrogels are liquid at room temperature and enable minimally invasive extracellular matrix injections into central nervous system tissues, before gelation at 37℃. However, few studies have analyzed how extracellular matrix hydrogels influence primary central nervous system neuron survival and growth, and whether central nervous system and non-central nervous system extracellular matrix specificity is critical to neuronal responses. Urinary bladder extracellular matrix hydrogels increase both primary hippocampal neuron survival and neurite growth to similar or even greater extents, suggesting extracellular matrix from non-homologous tissue sources, such as urinary bladder matrix-extracellular matrix, may be a more economical and safer alternative to developing central nervous system extracellular matrices for central nervous system applications. Additionally, we show matrix-bound vesicles derived from urinary bladder extracellular matrix are endocytosed by hippocampal neurons and positively regulate primary hippocampal neuron neurite growth. Matrix-bound vesicles carry protein and RNA cargos, including noncoding RNAs and miRNAs that map to the human genome and are known to regulate cellular processes. Thus, urinary bladder matrix-bound vesicles provide natural and transfectable cargoes which offer new experimental tools and therapeutic applications to study and treat central nervous system neuron injury.

The host response to naturally-derived extracellular matrix biomaterials

Biomaterials based on natural materials including decellularized tissues and tissue-derived hydrogels are becoming more widely used for clinical applications. Because of their native composition and structure, these biomaterials induce a distinct form of the foreign body response that differs from that of non-native biomaterials. Differences include direct interactions with cells via preserved moieties as well as the ability to undergo remodeling. Moreover, these biomaterials could elicit adaptive immune responses due to the presence of modified native molecules. Therefore, these biomaterials present unique challenges in terms of understanding the progression of the foreign body response. This review covers this response to natural materials including natural polymers, decellularized tissues, cell-derived matrix, tissue derived hydrogels, and biohybrid materials. With the expansion of the fields of regenerative medicine and tissue engineering, the current repertoire of biomaterials has also expanded and requires continuous investigation of the responses they elicit.