Molecular and Biomechanical Clues From Cardiac Tissue Decellularized Extracellular Matrix Drive Stromal Cell Plasticity

Physical Properties and Biochemical Composition of Extracellular Matrix-Derived Hydrogels Dictate Vascularization Potential in an Organ-Dependent Fashion

The inherent extracellular matrix (ECM) originating from a specific tissue impacts the process of vascularization, specifically vascular network formation (VNF) orchestrated by endothelial cells (ECs). The specific contribution toward these processes of ECM from highly disparate organs such as the skin and lungs remains a relatively unexplored area. In this study, we compared VNF and ECM remodeling mediated by microvascular ECs within gel, lung, and combinations thereof (hybrid) ECM hydrogels. Irrespective of the EC source, the skin-derived ECM hydrogel exhibited a higher propensity to drive and support VNF compared to both lung and hybrid ECM hydrogels. There were distinct disparities in the physical properties of the three types of hydrogels, including viscoelastic properties and complex architectural configurations, including fiber diameter, pore area, and numbers among the fibers. The hybrid ECM hydrogel properties were unique and not the sum of the component ECM parts. Furthermore, cellular ECM remodeling responses varied with skin ECM hydrogels promoting matrix metalloproteinase 1 (MMP1) secretion, while hybrid ECM hydrogels exhibited increased MMP9, fibronectin, and collagen IV deposition. Principal component analysis (PCA) indicated that the influence of a gel's mechanical properties on VNF was stronger than the biochemical composition. These data indicate that the organ-specific properties of an ECM dictate its capacity to support VNF, while intriguingly showing that ECs respond to more than just the biochemical constituents of an ECM. The study suggests potential applications in regenerative medicine by strategically selecting ECM origin or combinations to manipulate vascularization, offering promising prospects for enhancing wound healing through pro-regenerative interventions.

Evaluation of Different Decellularization Protocols for Obtaining and Characterizing Canine Cardiac Extracellular Matrix

Cardiovascular diseases are considered the leading cause of mortality globally; even with low mortality in dogs, such diseases are described in the same way in companion animals and humans. This study aimed to devise an effective decellularization protocol for the canine myocardium through the association of physical, chemical, and enzymatic methods, assessing resultant alterations in the myocardial extracellular matrix to obtain a suitable scaffold. Two canine hearts were collected; the samples were sectioned into ±1 cm2 fragments, washed in distilled water and 1× PBS solution, and followed by treatment under four distinct decellularization protocols. Sodium Dodecyl Sulfate (SDS) 1% 7 days + Triton X-100 1% for 48 h (Protocol I); Sodium Dodecyl Sulfate (SDS) 1% 5 days + Triton X-100 1% for 48 h (Protocol II); Trypsin 0.05% for 1 h at 36 °C + freezing -80 °C overnight + Sodium Dodecyl Sulfate (SDS) 1% for 3 days, Triton-X-100 for 48 h hours (Protocol III); 0.05% trypsin for 1 h at 36 °C + freezing at -80 °C overnight + 1% Sodium Dodecyl Sulfate (SDS) for 2 days + 1% Triton-X-100 for 24 h (Protocol IV). After analysis, Protocols I and II showed the removal of cellular content and preservation of extracellular matrix (ECM) contents, unlike Protocols III and IV, which retracted the ECM and removed essential elements of the matrix. In theory, although Protocols I and II have similar results, Protocol II stands out for the preservation of the architecture and components of the extracellular matrix, along with reduced exposure time to reagents, making it the recommended protocol for the development of a canine myocardial scaffold.

Collagen molecular organization preservation in human fascia lata and periosteum after tissue engineering

Large bone defect regeneration remains a major challenge for orthopedic surgeons. Tissue engineering approaches are therefore emerging in order to overcome this limitation. However, these processes can alter some of essential native tissue properties such as intermolecular crosslinks of collagen triple helices, which are known for their essential role in tissue structure and function. We assessed the persistence of extracellular matrix (ECM) properties in human fascia lata (HFL) and periosteum (HP) after tissue engineering processes such as decellularization and sterilization. Harvested from cadaveric donors (N = 3), samples from each HFL and HP were decellularized following five different chemical protocols with and without detergents (D1-D4 and D5, respectively). D1 to D4 consisted of different combinations of Triton, Sodium dodecyl sulfate and Deoxyribonuclease, while D5 is routinely used in the institutional tissue bank. Decellularized HFL tissues were further gamma-irradiated (minimum 25 kGy) in order to study the impact of sterilization on the ECM. Polarized light microscopy (PLM) was used to estimate the thickness and density of collagen fibers. Tissue hydration and content of hydroxyproline, enzymatic crosslinks, and non-enzymatic crosslinks (pentosidine) were semi-quantified with Raman spectroscopy. ELISA was also used to analyze the maintenance of the decorin (DCN), an important small leucine rich proteoglycan for fibrillogenesis. Among the decellularization protocols, detergent-free treatments tended to further disorganize HFL samples, as more thin fibers (+53.7%) and less thick ones (-32.6%) were recorded, as well as less collagen enzymatic crosslinks (-25.2%, p = 0.19) and a significant decrease of DCN (p = 0.036). GAG content was significantly reduced in both tissue types after all decellularization protocols. On the other hand, HP samples were more sensitive to the D1 detergent-based treatments, with more disrupted collagen organization and greater, though not significant loss of enzymatic crosslinks (-37.4%, p = 0.137). Irradiation of D5 HFL samples, led to a further and significant loss in the content of enzymatic crosslinks (-29.4%, p = 0.037) than what was observed with the decellularization process. Overall, the results suggest that the decellularization processes did not significantly alter the matrix. However, the addition of a gamma-irradiation is deleterious to the collagen structural integrity of the tissue.

Bioactive decellularized extracellular matrix-based hydrogel supports human adipose tissue-derived stem cell maintenance and fibrocartilage phenotype

Articular cartilage is a highly specialized tissue able to tolerate physical stress. However, its capacity for restoration is restricted, and injuries to the cartilage do not recover spontaneously. Interest in mesenchymal stem cells derived from human adipose tissue (hASCs) is growing due to their potential to improve tissue healing and recovery. Decellularized extracellular matrix (dECM)-based hydrogels combined with hASCs could serve as an interface for studying behavior and differentiation properties in a cartilage microenvironment. In the present study, we described the behavior of hASCs cultured in a commercial dECM MatriXpec™. The structural microtopography of MatriXpec™ was analyzed by scanning electron micrography, and its protein composition was accessed by mass spectrometry. The protein composition of MatriXpec™ is mainly represented by collagen proteins, building its fibrous ultrastructure. hASCs were cultured three-dimensionally (3D) on MatriXpec™ to perform cell viability, growth, and cartilage differentiation analysis. We showed that MatriXpec™ could be loaded with hASCs and that it supports cell maintenance for several days. We observed that the three-dimensional ultrastructure of the biomaterial is composed of nanofibers, and its protein composition reflects the tissue from which it was harvested. Finally, we showed that the molecular cues from the hydrogel are biologically active as these influence cell behavior and differentiation phenotype, increasing the expression of fibrocartilage-related genes such as SOX9, COL1, COL10, and MMP13. MatriXpec™ hydrogel can be used as an interface for 3D hASCs culture studies as it maintains cell viability and supports its differentiation process.

Biophysical control of plasticity and patterning in regeneration and cancer

Cells and tissues display a remarkable range of plasticity and tissue-patterning activities that are emergent of complex signaling dynamics within their microenvironments. These properties, which when operating normally guide embryogenesis and regeneration, become highly disordered in diseases such as cancer. While morphogens and other molecular factors help determine the shapes of tissues and their patterned cellular organization, the parallel contributions of biophysical control mechanisms must be considered to accurately predict and model important processes such as growth, maturation, injury, repair, and senescence. We now know that mechanical, optical, electric, and electromagnetic signals are integral to cellular plasticity and tissue patterning. Because biophysical modalities underly interactions between cells and their extracellular matrices, including cell cycle, metabolism, migration, and differentiation, their applications as tuning dials for regenerative and anti-cancer therapies are being rapidly exploited. Despite this, the importance of cellular communication through biophysical signaling remains disproportionately underrepresented in the literature. Here, we provide a review of biophysical signaling modalities and known mechanisms that initiate, modulate, or inhibit plasticity and tissue patterning in models of regeneration and cancer. We also discuss current approaches in biomedical engineering that harness biophysical control mechanisms to model, characterize, diagnose, and treat disease states.

A novel 3D biofabrication strategy to improve cell proliferation and differentiation of human Wharton's jelly mesenchymal stromal cells for cell therapy and tissue engineering

Purpose: Obtaining sufficient numbers of cells in a short time is a major goal of cell culturing in cell therapy and tissue engineering. However, current bidimensional (2D) culture methods are associated to several limitations, including low efficiency and the loss of key cell differentiation markers on cultured cells. Methods: In the present work, we have designed a novel biofabrication method based on a three-dimensional (3D) culture system (FIBRIAGAR-3D). Human Wharton's jelly mesenchymal stromal cells (HWJSC) were cultured in 3D using 100%, 75%, 50%, and 25% concentrations of fibrin-agarose biomaterials (FA100, FA75, FA50 and FA25 group) and compared with control cells cultured using classical 2D systems (CTR-2D). Results: Our results showed a significant increase in the number of cells generated after 7 days of culture, with cells displaying numerous expansions towards the biomaterial, and a significant overexpression of the cell proliferation marker KI67 was found for the FA75 and FA100 groups. TUNEL and qRT-PCR analyses demonstrated that the use of FIBRIAGAR-3D was not associated with an induction of apoptosis by cultured cells. Instead, the 3D system retained the expression of typical phenotypic markers of HWJSC, including CD73, CD90, CD105, NANOG and OCT4, and biosynthesis markers such as types-I and IV collagens, with significant increase of some of these markers, especially in the FA100 group. Finally, our analysis of 8 cell signaling molecules revealed a significant decrease of GM-CSF, IFN-g, IL2, IL4, IL6, IL8, and TNFα, suggesting that the 3D culture system did not induce the expression of pro-inflammatory molecules. Conclusion: These results confirm the usefulness of FIBRIAGAR-3D culture systems to increase cell proliferation without altering cell phenotype of immunogenicity and opens the door to the possibility of using this novel biofabrication method in cell therapy and tissue engineering of the human cornea, oral mucosa, skin, urethra, among other structures.

The third dimension of tumor microenvironment-The importance of tumor stroma in 3D cancer models

Recent advances in the three-dimensional (3D) cancer models give rise to a plethora of new possibilities in the development of anti-cancer drug therapies and bring us closer to personalized medicine. Three-dimensional models are undoubtedly more authentic than traditional two-dimensional (2D) cell cultures. Nowadays, they are becoming preferentially used in most cancer research fields due to their more accurate biomimetic characteristics. On the contrary, they still lack the cellular and matrix complexity of the native tumor microenvironment (TME). This review focuses on the description of existing 3D models, the incorporation of TME and fluidics into these models, and their perspective in the future research. It is clear that such an improvement would need not only biological but also technical progress. Therefore, the modern approach to anti-cancer drug discovery should involve various fields.

Decellularized Extracellular Matrix: The Role of This Complex Biomaterial in Regeneration

Organ transplantation is understood as a technique where an organ from a donor patient is transferred to a recipient patient. This practice gained strength in the 20th century and ensured advances in areas of knowledge such as immunology and tissue engineering. The main problems that comprise the practice of transplants involve the demand for viable organs and immunological aspects related to organ rejection. In this review, we address advances in tissue engineering for reversing the current challenges of transplants, focusing on the possible use of decellularized tissues in tissue engineering. We address the interaction of acellular tissues with immune cells, especially macrophages and stem cells, due to their potential use in regenerative medicine. Our goal is to exhibit data that demonstrate the use of decellularized tissues as alternative biomaterials that can be applied clinically as partial or complete organ substitutes.

Evaluation of Structural Viability of Porcine Tracheal Scaffolds after 3 and 6 Months of Storage under Three Different Protocols

Tracheal replacement with a bioengineered tracheal substitute has been developed for long-segment tracheal diseases. The decellularized tracheal scaffold is an alternative for cell seeding. It is not defined if the storage scaffold produces changes in the scaffold's biomechanical properties. We tested three protocols for porcine tracheal scaffold preservation immersed in PBS and alcohol 70%, in the fridge and under cryopreservation. Ninety-six porcine tracheas (12 in natura, 84 decellularized) were divided into three groups (PBS, alcohol, and cryopreservation). Twelve tracheas were analyzed after three and six months. The assessment included residual DNA, cytotoxicity, collagen contents, and mechanical properties. Decellularization increased the maximum load and stress in the longitudinal axis and decreased the maximum load in the transverse axis. The decellularization of the porcine trachea produced structurally viable scaffolds, with a preserved collagen matrix suitable for further bioengineering. Despite the cyclic washings, the scaffolds remained cytotoxic. The comparison of the storage protocols (PBS at 4 °C, alcohol at 4 °C, and slow cooling cryopreservation with cryoprotectants) showed no significant differences in the amount of collagen and in the biomechanical properties of the scaffolds. Storage in PBS solution at 4 °C for six months did not change the scaffold mechanics.

Tumor decellularization reveals proteomic and mechanical characteristics of the extracellular matrix of primary liver cancer

Tumor initiation and progression are critically dependent on interaction of cancer cells with their cellular and extracellular microenvironment. Alterations in the composition, integrity, and mechanical properties of the extracellular matrix (ECM) dictate tumor processes including cell proliferation, migration, and invasion. Also in primary liver cancer, consisting of hepatocellular carcinoma (HCC) and cholangiocarcinoma (CCA), the dysregulation of the extracellular environment by liver fibrosis and tumor desmoplasia is pertinent. Yet, the exact changes occurring in liver cancer ECM remain uncharacterized and underlying tumor-promoting mechanisms remain largely unknown. Herein, an integrative molecular and mechanical approach is used to extensively characterize the ECM of HCC and CCA tumors by utilizing an optimized decellularization technique. We identified a myriad of proteins in both tumor and adjacent liver tissue, uncovering distinct malignancy-related ECM signatures. The resolution of this approach unveiled additional ECM-related proteins compared to large liver cancer transcriptomic datasets. The differences in ECM protein composition resulted in divergent mechanical properties on a macro- and micro-scale that are tumor-type specific. Furthermore, the decellularized tumor ECM was employed to create a tumor-specific hydrogel that supports patient-derived tumor organoids, which provides a new avenue for personalized medicine applications. Taken together, this study contributes to a better understanding of alterations to composition, stiffness, and collagen alignment of the tumor ECM that occur during liver cancer development.

Decellularized Extracellular Matrix Powder Accelerates Metabolic Maturation at Early Stages of Cardiac Differentiation in Human Induced Pluripotent Stem Cell-Derived Cardiomyocytes

During fetal development, cardiomyocytes switch from glycolysis to oxidative metabolism to sustain the energy requirements of functional cells. State-of-the-art cardiac differentiation protocols yield phenotypically immature cardiomyocytes, and common methods to improve metabolic maturation require multistep protocols to induce maturation only after cardiac specification is completed. Here, we describe a maturation method using ventricle-derived decellularized extracellular matrix (dECM) that promoted early-stage metabolic maturation of cardiomyocytes differentiated from human induced pluripotent stem cells (hiPSCs). Chemically and architecturally preserved particles (45-500 μm) of pig ventricular dECM were added to hiPSCs at the start of differentiation. At the end of our maturation protocol (day 15 of cardiac differentiation), we observed an intimate interaction between cardiomyocytes and dECM particles without impairment of cardiac differentiation efficiency (approx. 70% of cTNT+). Compared with control cells (those cultured without pig dECM), 15-day-old dECM-treated cardiomyocytes demonstrated increased expression of markers related to cardiac metabolic maturation, MAPK1, FOXO1, and FOXO3, and a switch from ITGA6 (the immature integrin isoform) to ITGA3 and ITGA7 (those present in adult cardiomyocytes). Electrical parameters and responsiveness to dobutamine also improved in pig ventricular dECM-treated cells. Extending the culture time to 30 days, we observed a switch from glucose to fatty acid metabolism, indicated by decreased glucose uptake and increased fatty acid consumption in cells cultured with dECM. Together, these data suggest that dECM contains endogenous cues that enable metabolic maturation of hiPSC-CMs at early stages of cardiac differentiation.

A modified hydrogel production protocol to decrease cellular content

PURPOSE

To analyze the cytotoxicity and cell in porcine-derived decellularized skin matrix.

METHODS

We analyzed the effect of multiple decellularization processes by histological analysis, DNA quantification, and flow cytometry. Subsequently, we analyzed the most appropriate hydrogel concentration to minimize cytotoxicity on fibroblast culture and to maximize cell proliferation.

RESULTS

After the fourth decellularization, the DNA quantification showed the lowest DNA concentration (< 50 ng/mg). Histological analysis showed no cell components in the hydrogel. Moreover, hematoxylin and eosin showed a heterogeneous structure of collagen fibers. The best hydrogel concentration ranged from 3 to 25%, and there was no significant difference between the 24 hours and seven days.

CONCLUSIONS

The process of hydrogel production was effective for removing cells and DNA elements. The best hydrogel concentration ranged from 3 to 25%.

From Macro to Micro: Comparison of Imaging Techniques to Detect Vascular Network Formation in Left Ventricle Decellularized Extracellular Matrix Hydrogels

Background: Angiogenesis is a crucial process in physiological maintenance and tissue regeneration. To understand the contribution of angiogenesis, it is essential to replicate this process in an environment that reproduces the biochemical and physical properties which are largely governed by the extracellular matrix (ECM). We investigated vascularization in cardiac left ventricular ECM hydrogels to mimic post-myocardial repair. We set out to assess and compare different destructive and non-destructive methods, optical as well as non-optical, to visualize angiogenesis and associated matrix remodeling in myocardial ECM hydrogels. Methods: A total of 100,000, 300,000, and 600,000 Human Pulmonary Microvascular Endothelial Cells (HPMEC) were seeded in left ventricular cardiac ECM hydrogel in 48-well plates. After 1, 7, and 14 days of culture, the HPMEC were imaged by inverted fluorescence microscopy and 3D confocal laser scanning microscopy (Zeiss Cell Discoverer 7). In addition, cell-seeded ECM hydrogels were scanned by optical coherence tomography (OCT). Fixed and paraffin-embedded gels were thin-sectioned and assessed for ECM components via H&E, picrosirius red histochemical staining, and immunostaining for collagen type I. ImageJ-based densitometry was used to quantify vascular-like networks and GraphPad was used for statistical analyses. Results: Qualitative analyses were realized through fluoromicrographs obtained by the confocal laser scanning microscope which allowed us to visualize the extensive vascular-like networks that readily appeared at all seeding densities. Quantification of networks was only possible using fluoromicrographs from inverted microscopy. These showed that, after three days, the number of master junctions was seeding density-dependent. The resolution of optical coherence tomography was too low to distinguish between signals caused by the ECM and cells or networks, yet it did show that gels, irrespective of cells, were heterogeneous. Interestingly, (immuno)histochemistry could clearly distinguish between the cast cardiac-derived matrix and newly deposited ECM in the hydrogels. The H&E staining corroborated the presence of vascular-like network structures, albeit that sectioning inevitably led to the loss of 3D structure. Conclusions: Except for OCT, all methods had complementary merit and generated qualitative and quantitative data that allowed us to understand vascular network formation in organ-derived ECM hydrogels.

Decellularized Extracellular Matrix Scaffolds for Cardiovascular Tissue Engineering: Current Techniques and Challenges

Cardiovascular diseases are the leading cause of global mortality. Over the past two decades, researchers have tried to provide novel solutions for end-stage heart failure to address cardiac transplantation hurdles such as donor organ shortage, chronic rejection, and life-long immunosuppression. Cardiac decellularized extracellular matrix (dECM) has been widely explored as a promising approach in tissue-regenerative medicine because of its remarkable similarity to the original tissue. Optimized decellularization protocols combining physical, chemical, and enzymatic agents have been developed to obtain the perfect balance between cell removal, ECM composition, and function maintenance. However, proper assessment of decellularized tissue composition is still needed before clinical translation. Recellularizing the acellular scaffold with organ-specific cells and evaluating the extent of cardiomyocyte repopulation is also challenging. This review aims to discuss the existing literature on decellularized cardiac scaffolds, especially on the advantages and methods of preparation, pointing out areas for improvement. Finally, an overview of the state of research regarding the application of cardiac dECM and future challenges in bioengineering a human heart suitable for transplantation is provided.

ECM roles and biomechanics in cardiac tissue decellularization

Natural biomaterials hold enormous potential for tissue regeneration. The rapid advance of several tissue-engineered biomaterials, such as natural and synthetic polymer-based scaffolds, has led to widespread application of these materials in the clinic and in research. However, biomaterials can have limited repair capacity; obstacles result from immunogenicity, difficulties in mimicking native microenvironments, and maintaining the mechanical and biochemical (i.e., biomechanical) properties of native organs/tissues. The emergence of decellularized extracellular matrix (ECM)-derived biomaterials provides an attractive solution to overcome these hurdles since decellularized ECM provides a nonimmune environment with native three-dimensional structures and bioactive components. More importantly, decellularized ECM can be generated from the tissue of interest, such as the heart, and keep its native macro- and microstructure and tissue-specific composition. These decellularized cardiac matrices/scaffolds can then be reseeded using cardiac cells, and the resulting recellularized construct is considered an ideal choice for regenerating functional organs/tissues. Nonetheless, the decellularization process must be optimized and depends on tissue type, age, and functional goal. Although most decellularization protocols significantly reduce immunogenicity and deliver a matrix that maintains the tissue macrostructure, suboptimal decellularization can change ECM composition and microstructure, which affects the biomechanical properties of the tissue and consequently changes cell-matrix interactions and organ function. Herein, we review methods of decellularization, with particular emphasis on cardiac tissue, and how they can affect the biomechanics of the tissue, which in turn determines success of reseeding and in vivo viability. Moreover, we review recent developments in decellularized ECM-derived cardiac biomaterials and discuss future perspectives.

A Beginner’s Guide to the Characterization of Hydrogel Microarchitecture for Cellular Applications

The extracellular matrix (ECM) is a three-dimensional, acellular scaffold of living tissues. Incorporating the ECM into cell culture models is a goal of cell biology studies and requires biocompatible materials that can mimic the ECM. Among such materials are hydrogels: polymeric networks that derive most of their mass from water. With the tuning of their properties, these polymer networks can resemble living tissues. The microarchitectural properties of hydrogels, such as porosity, pore size, fiber length, and surface topology can determine cell plasticity. The adequate characterization of these parameters requires reliable and reproducible methods. However, most methods were historically standardized using other biological specimens, such as 2D cell cultures, biopsies, or even animal models. Therefore, their translation comes with technical limitations when applied to hydrogel-based cell culture systems. In our current work, we have reviewed the most common techniques employed in the characterization of hydrogel microarchitectures. Our review provides a concise description of the underlying principles of each method and summarizes the collective data obtained from cell-free and cell-loaded hydrogels. The advantages and limitations of each technique are discussed, and comparisons are made. The information presented in our current work will be of interest to researchers who employ hydrogels as platforms for cell culture, 3D bioprinting, and other fields within hydrogel-based research.

Gelatin/sodium alginate hydrogel-coated decellularized porcine coronary artery to construct bilayer tissue engineered blood vessels

Cardiovascular diseases and vascular trauma can be commonly found in the population. Scholars worldwide hope to develop small-diameter vascular grafts that can replace autologous vessels for clinical use. Decellularized blood vessels can retain the original morphology, structure, and physical properties of blood vessels, which is conducive to cell growth, proliferation, and differentiation. In this study, porcine coronary arteries (PCAs) were decellularized to prepare decellularized porcine coronary artery (DPCA), and bilayer hybrid scaffolds were prepared by coating gelatin and sodium alginate mixed hydrogel of seven different proportions and combined with mouse fibroblasts (L929 cells) to study the construction of tissue engineering vessels in vitro. The obtained bilayer hybrid scaffolds were 3-7 cm in length, 5 mm in external diameter, and 1 mm in average wall thickness. All seven bilayer hybrid scaffolds showed good biocompatibility after cell inoculation. Compared with 2D culture, cells on 3D scaffolds grew relatively slowly in the first 4 days, and the number of cells proliferated rapidly at 7 days. In the same culture days, different concentrations of hydrogel also had an impact on cell proliferation. With the increase of hydrogel content, cells on the 3D scaffold formed cell colonies faster. The results showed that the scaffold had good biocompatibility and could meet the needs of artificial blood vessel construction.

Limited efficacy of adipose stromal cell secretome-loaded skin-derived hydrogels to augment skin flap regeneration in rats

Insufficient vascularization is a recurring cause of impaired pedicled skin flap healing. The administration of adipose tissue-derived stromal cells' (ASC) secretome is a novel approach to augment vascularization. Yet, the secretome comprised soluble factors that require a sustained release vehicle to increase residence time. We hypothesized that administration of a hydrogel derived from decellularized extracellular matrix (ECM) of porcine skin with bound trophic factors from ASCs, enhances skin flap viability and wound repair in a rat model. Porcine skin was decellularized and pepsin-digested to form a hydrogel at 37°C. Conditioned medium (CMe) of human ASC was collected, concentrated twentyfold and mixed with the hydrogel. Sixty Wistar rats were included. A dorsal skin flap (caudal based) of 3 x 10 cm was elevated for topical application of: DMEM medium (group I), a pre-hydrogel with or without ASC CMe (group II and III) or ASC CMe (group IV). After 7, 14 and 28 days, perfusion was measured and skin flaps were harvested for wound healing assessment and immunohistochemical analysis. Decellularized skin ECM hydrogel contained negligible amounts of DNA (11.6 ± 0.6 ng/mg), was noncytotoxic and well-tolerated by rats. Irrespective of ASC secretome, ECM hydrogel application resulted macroscopically and microscopically in similar dermal wound healing in terms of proliferation, immune response and matrix remodeling as the control group. However, ASC CMe alone increased vessel density after seven days. Concluding, porcine skin derived ECM hydrogels loaded with ASC secretome are non-cytotoxic but demand optimization to significantly augment wound healing of skin flaps.

Exploring the multifaceted role of TGF-β signaling in diabetic complications

Diabetes is one of the most comprehensive metabolic disorders and is spread across the globe. The data from IDF Diabetes Atlas and National Diabetes Statistics mentions that the number of patients with diabetes is increasing at an exponential rate which is challenging the current therapeutics used for the management of diabetes. However, current therapies used for the treatment may provide symptomatic relief but lack in preventing the progression of the disease and thereby limiting the treatment of diabetes-associated complications. A thorough review and analysis were conducted using various databases including EMBASE, MEDLINE, and Google Scholar to extract the available information on challenges faced by current therapies which have triggered the development of novel molecules or drugs. From the analysis, it was analyzed that transforming growth factor βs (TGF-βs) have been shown to exhibit pleiotropic activity and are responsible for maintaining homeostasis and its overexpression is convoluted in the pathogenesis of various disorders. Therefore, developing drugs that block TGF-β signaling may provide therapeutic benefits. This extensive review concluded that drugs targeting TGF-β signaling pathway and its subsequent blockade have shown promising results and hold the potential to become drugs of choice in the management of diabetes and associated complications.

Impact of microstructure on cell behavior and tissue mechanics in collagen and dermal decellularized extra-cellular matrices

Skin models are used for many applications such as research and development or grafting. Unfortunately, most lack a proper microenvironment producing poor mechanical properties and inaccurate extra-cellular matrix composition and organization. In this report we focused on mechanical properties, extra-cellular matrix organization and cell interactions in human skin samples reconstructed with pure collagen or dermal decellularized extra-cellular matrices (S-dECM) and compared them to native human skin. We found that Full-thickness S-dECM samples presented stiffness two times higher than collagen gel and similar to ex vivo human skin, and proved for the first time that keratinocytes also impact dermal mechanical properties. This was correlated with larger fibers in S-dECM matrices compared to collagen samples and with a differential expression of F-actin, vinculin and tenascin C between S-dECM and collagen samples. This is clear proof of the microenvironment's impact on cell behaviors and mechanical properties. STATEMENT OF SIGNIFICANCE: In vitro skin models have been used for a long time for clinical applications or in vitro knowledge and evaluation studies. However, most lack a proper microenvironment producing a poor combination of mechanical properties and appropriate biological outcomes, partly due to inaccurate extra-cellular matrix (ECM) composition and organization. This can lead to limited predictivity and weakness of skin substitutes after grafting. This study shows, for the first time, the importance of a complex and rich microenvironment on cell behaviors, matrix macro- and micro-organization and mechanical properties. The increased composition and organization complexity of dermal skin decellularized extra-cellular matrix populated with differentiated cells produces in vitro skin models closer to native human skin physiology.

Organ-Specific Endothelial Cell Differentiation and Impact of Microenvironmental Cues on Endothelial Heterogeneity

Endothelial cells throughout the body are heterogeneous, and this is tightly linked to the specific functions of organs and tissues. Heterogeneity is already determined from development onwards and ranges from arterial/venous specification to microvascular fate determination in organ-specific differentiation. Acknowledging the different phenotypes of endothelial cells and the implications of this diversity is key for the development of more specialized tissue engineering and vascular repair approaches. However, although novel technologies in transcriptomics and proteomics are facilitating the unraveling of vascular bed-specific endothelial cell signatures, still much research is based on the use of insufficiently specialized endothelial cells. Endothelial cells are not only heterogeneous, but their specialized phenotypes are also dynamic and adapt to changes in their microenvironment. During the last decades, strong collaborations between molecular biology, mechanobiology, and computational disciplines have led to a better understanding of how endothelial cells are modulated by their mechanical and biochemical contexts. Yet, because of the use of insufficiently specialized endothelial cells, there is still a huge lack of knowledge in how tissue-specific biomechanical factors determine organ-specific phenotypes. With this review, we want to put the focus on how organ-specific endothelial cell signatures are determined from development onwards and conditioned by their microenvironments during adulthood. We discuss the latest research performed on endothelial cells, pointing out the important implications of mimicking tissue-specific biomechanical cues in culture.

Hybrid Hydrogel Composed of Hyaluronic Acid, Gelatin, and Extracellular Cartilage Matrix for Perforated TM Repair

A novel series of composite hydrogels, built from the three components 1), hyaluronic acid methacryloyl (HAMA); 2), gelatin methacryloyl (GelMA), and 3), extracellular cartilage matrix (ECM), was prepared and studied regarding the possible utility in the surgical repair of damaged (perforated) tympanic membrane (TM). Noteworthy is component 3), which was harvested from the ribs of α-1,3-galactosidyltransferase-knockout (α-1,3 GalT-KO) pigs. The absence of α-1,3-galactosyl glycoprotein is hypothesized to prevent rejection due to foreign-body immunogenicity. The composite hydrogels were characterized by various aspects, using a variety of physicochemical techniques: aqueous swelling, structural degradation, behavior under compression, and morphology, e.g., in vitro biocompatibility was assessed by the CCK-8 and live–dead assays and through cytoskeleton staining/microscopy. Alcian blue staining and real-time PCR (RT-PCR) were performed to examine the chondrogenic induction potential of the hydrogels. Moreover, a rat TM defect model was used to evaluate the in vivo performance of the hydrogels in this particular application. Taken together, the results from this study are surprising and promising. Much further development work will be required to make the material ready for surgical use.

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.

Adipose Tissue-Derived Stromal Cells Alter the Mechanical Stability and Viscoelastic Properties of Gelatine Methacryloyl Hydrogels

The extracellular matrix provides mechanical cues to cells within it, not just in terms of stiffness (elasticity) but also time-dependent responses to deformation (viscoelasticity). In this work, we determined the viscoelastic transformation of gelatine methacryloyl (GelMA) hydrogels caused by adipose tissue-derived stromal cells (ASCs) through mathematical modelling. GelMA-ASCs combination is of interest to model stem cell-driven repair and to understand cell-biomaterial interactions in 3D environments. Immortalised human ASCs were embedded in 5%, 10%, and 15% (w/v) GelMA hydrogels and evaluated for 14 d. GelMA had a concentration-dependent increase in stiffness, but cells decreased this stiffness over time, across concentrations. Viscoelastic changes in terms of stress relaxation increased progressively in 5% GelMA, while mathematical Maxwell analysis showed that the relative importance (R_i) of the fastest Maxwell elements increased proportionally. The 10% GelMA only showed differences at 7 d. In contrast, ASCs in 15% GelMA caused slower stress relaxation, increasing the R_i of the slowest Maxwell element. We conclude that GelMA concentration influenced the stiffness and number of Maxwell elements. ASCs changed the percentage stress relaxation and R_i of Maxwell elements transforming hydrogel viscoelasticity into a more fluid environment over time. Overall, 5% GelMA induced the most favourable ASC response.

Architecture and Composition Dictate Viscoelastic Properties of Organ-Derived Extracellular Matrix Hydrogels

The proteins and polysaccharides of the extracellular matrix (ECM) provide architectural support as well as biochemical and biophysical instruction to cells. Decellularized, ECM hydrogels replicate in vivo functions. The ECM’s elasticity and water retention renders it viscoelastic. In this study, we compared the viscoelastic properties of ECM hydrogels derived from the skin, lung and (cardiac) left ventricle and mathematically modelled these data with a generalized Maxwell model. ECM hydrogels from the skin, lung and cardiac left ventricle (LV) were subjected to a stress relaxation test under uniaxial low-load compression at a 20%/s strain rate and the viscoelasticity determined. Stress relaxation data were modelled according to Maxwell. Physical data were compared with protein and sulfated GAGs composition and ultrastructure SEM. We show that the skin-ECM relaxed faster and had a lower elastic modulus than the lung-ECM and the LV-ECM. The skin-ECM had two Maxwell elements, the lung-ECM and the LV-ECM had three. The skin-ECM had a higher number of sulfated GAGs, and a highly porous surface, while both the LV-ECM and the lung-ECM had homogenous surfaces with localized porous regions. Our results show that the elasticity of ECM hydrogels, but also their viscoelastic relaxation and gelling behavior, was organ dependent. Part of these physical features correlated with their biochemical composition and ultrastructure.

Bidirectional relationship between cardiac extracellular matrix and cardiac cells in ischemic heart disease

Ischemic heart diseases (IHDs), including myocardial infarction and cardiomyopathies, are a leading cause of mortality and morbidity worldwide. Cardiac-derived stem and progenitor cells have shown promise as a therapeutic for IHD but are limited by poor cell survival, limited retention, and rapid washout. One mechanism to address this is to encapsulate the cells in a matrix or three-dimensional construct, so as to provide structural support and better mimic the cells' physiological microenvironment during administration. More specifically, the extracellular matrix (ECM), the native cellular support network, has been a strong candidate for this purpose. Moreover, there is a strong consensus that the ECM and its residing cells, including cardiac stem cells, have a constant interplay in response to tissue development, aging, disease progression, and repair. When externally stimulated, the cells and ECM work together to mutually maintain the local homeostasis by initially altering the ECM composition and stiffness, which in turn alters the cellular response and behavior. Given this constant interplay, understanding the mechanism of bidirectional cell-ECM interaction is essential to develop better cell implantation matrices to enhance cell engraftment and cardiac tissue repair. This review summarizes current understanding in the field, elucidating the signaling mechanisms between cardiac ECM and residing cells in response to IHD onset. Furthermore, this review highlights recent advances in native ECM-mimicking cardiac matrices as a platform for modulating cardiac cell behavior and inducing cardiac repair.

3D bioprinting of cardiac tissue: current challenges and perspectives

Demand for donor hearts has increased globally due to cardiovascular diseases. Recently, three-dimensional (3D) bioprinting technology has been aimed at creating clinically viable cardiac constructs for the management of myocardial infarction (MI) and associated complications. Advances in 3D bioprinting show promise in aiding cardiac tissue repair following injury/infarction and offer an alternative to organ transplantation. This article summarizes the basic principles of 3D bioprinting and recent attempts at reconstructing functional adult native cardiac tissue with a focus on current challenges and prospective strategies.

Engineering new microvascular networks on-chip: ingredients, assembly, and best practices

Tissue engineered grafts show great potential as regenerative implants for diseased or injured tissues within the human body. However, these grafts suffer from poor nutrient perfusion and waste transport, thus decreasing their viability post-transplantation. Graft vascularization is therefore a major area of focus within tissue engineering because biologically relevant conduits for nutrient and oxygen perfusion can improve viability post-implantation. Many researchers utilize microphysiological systems as testing platforms for potential grafts due to an ability to integrate vascular networks as well as biological characteristics such as fluid perfusion, 3D architecture, compartmentalization of tissue-specific materials, and biophysical and biochemical cues. While many methods of vascularizing these systems exist, microvascular self-assembly has great potential for bench-to-clinic translation as it relies on naturally occurring physiological events. In this review, we highlight the past decade of literature and critically discuss the most important and tunable components yielding a self-assembled vascular network on chip: endothelial cell source, tissue-specific supporting cells, biomaterial scaffolds, biochemical cues, and biophysical forces. This article discusses the bioengineered systems of angiogenesis, vasculogenesis, and lymphangiogenesis, and includes a brief overview of multicellular systems. We conclude with future avenues of research to guide the next generation of vascularized microfluidic models and future tissue engineered grafts.

Bioactive decellularized cardiac extracellular matrix-based hydrogel as a sustained-release platform for human adipose tissue-derived stromal cell-secreted factors

The administration of trophic factors (TFs) released by mesenchymal stromal cells (MSCs) as therapy for cardiovascular diseases requires a delivery vehicle capable of binding and releasing the TF in a sustained manner. We hypothesized that hydrogels derived from cardiac decellularized extracellular matrix (cardiac dECM) bind MSC secretome-derived TF and release these in a sustained fashion. Pig-derived ventricular tissue was decellularized, milled to powder, digested, and assembled as a hydrogel upon warming at 37 °C. The conditioned medium (CMed) of adipose tissue-derived stromal cells (ASC) was collected, concentrated, and incorporated into the hydrogel at 1×, 10×, and 100× the original concentration. The release of 11 ASC-secreted factors (angiopoietin-1, angiopoietin-2, fibroblast growth factor-1, hepatocyte growth factor, platelet-derived growth factor-AA, vascular endothelial growth factor, interleukin-1β, interleukin-6, interleukin-8, CCL2, and matrix metalloproteinase-1) from hydrogels was immune assessed. Bioactivity was determined by endothelial cell proliferation, function, and assessment of endothelial mesenchymal transition. We showed that dECM hydrogels could be loaded with human ASC-secreted TFs, which are released in a sustained manner for several days subsequently. Different trophic factors had different release kinetics, which correlates with the initial concentration of CMed in the hydrogel. We observed that the more concentrated was the hydrogel, the more inflammation-related cytokines, and the less pro-regenerative TFs were released. Finally, we showed that the factors secreted by the hydrogel are biologically active as these influence cell behavior. The use of dECM hydrogels as a platform to bind and release paracrine factors secreted by (mesenchymal) cells is a potential alternative in the context of cardiovascular regeneration.

Decellularized Extracellular Matrices and Cardiac Differentiation: Study on Human Amniotic Fluid-Stem Cells

Cell therapy with a variety of stem populations is increasingly being investigated as a promising regenerative strategy for cardiovascular (CV) diseases. Their combination with adequate scaffolds represents an improved therapeutic approach. Recently, several biomaterials were investigated as scaffolds for CV tissue repair, with decellularized extracellular matrices (dECMs) arousing increasing interest for cardiac tissue engineering applications. The aim of this study was to analyze whether dECMs support the cardiac differentiation of CardiopoieticAF stem cells. These perinatal stem cells, which can be easily isolated without ethical or safety limitations, display a high cardiac differentiative potential. Differentiation was previously achieved by culturing them on Matrigel, but this 3D scaffold is not transplantable. The identification of a new transplantable scaffold able to support CardiopoieticAF stem cell cardiac differentiation is pivotal prior to encouraging translation of in vitro studies in animal model preclinical investigations. Our data demonstrated that decellularized extracellular matrices already used in cardiac surgery (the porcine CorTMPATCH and the equine MatrixPatchTM) can efficiently support the proliferation and cardiac differentiation of CardiopoieticAF stem cells and represent a useful cellular scaffold to be transplanted with stem cells in animal hosts.