Low-molecular-weight peptides derived from extracellular matrix as chemoattractants for primary endothelial cells

Characterization of a biologically derived rabbit tracheal scaffold

There is a clinical need to provide replacement tracheal tissue for the pediatric population affected by congenital defects, as current surgical solutions are not universally applicable. A potential solution is to use tissue engineered scaffold as the framework for regenerating autologous tissue. Rabbit trachea were used and different detergents (Triton x-100 and sodium deoxycholate) and enzymes (DNAse/RNAse) investigated to create a decellularization protocol. Each reagent was initially tested individually and the outcome used to design a combined protocol. At each stage the resultant scaffold was assessed histologically, molecularly for acellularity and matrix preservation. Immunogenicity of the final scaffold was assessed by implantation into a rat model for 4 weeks. Both enzymes and detergents were required to produce a completely acellular (DNA content 42.78 ng/mg) scaffold with preserved collagen and elastin however, GAG content were reduced (8.78 ± 1.35 vs. 5.5 ± 4.8). Following in vivo implantation the scaffold elicited minimal immune response and showed significant cellular infiltration and vasculogenesis. The luminal aspect of the implanted scaffold showed infiltration of host derived cells, which were positive for pan cytokeratin. It is possible to create biologically derived biocompatible scaffolds to address specific pediatric clinical problems. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 2126-2135, 2017.

Modulating In Vivo Degradation Rate of Injectable Extracellular Matrix Hydrogels

Extracellular matrix (ECM) derived hydrogels are increasingly used as scaffolds to stimulate endogenous repair. However, few studies have examined how altering the degradation rates of these materials affect cellular interaction in vivo. This study sought to examine how crosslinking or matrix metalloproteinase (MMP) inhibition by doxycycline could be employed to modulate the degradation rate of an injectable hydrogel derived from decellularized porcine ventricular myocardium. While both approaches were effective in reducing degradation in vitro, only doxycycline significantly prolonged hydrogel degradation in vivo without affecting material biocompatibility. In addition, unlike crosslinking, incorporation of doxycycline into the hydrogel did not affect mechanical properties. Lastly, the results of this study highlighted the need for development of novel crosslinkers for in situ modification of injectable ECM-derived hydrogels, as none of the crosslinking agents investigated in this study were both biocompatible and effective.

Extracellular matrix bioscaffolds in tissue remodeling and morphogenesis

During normal morphogenesis the extracellular matrix (ECM) influences cell motility, proliferation, apoptosis, and differentiation. Tissue engineers have attempted to harness the cell signaling potential of ECM to promote the functional reconstruction, if not regeneration, of injured or missing adult tissues that otherwise heal by the formation of scar tissue. ECM bioscaffolds, derived from decellularized tissues, have been used to promote the formation of site appropriate, functional tissues in many clinical applications including skeletal muscle, fibrocartilage, lower urinary tract, and esophageal reconstruction, among others. These scaffolds function by the release or exposure of growth factors and cryptic peptides, modulation of the immune response, and recruitment of progenitor cells. Herein, we describe this process of ECM induced constructive remodeling and examine similarities to normal tissue morphogenesis.

Topical Collagen-Based Biomaterials for Chronic Wounds: Rationale and Clinical Application

Significance: The extracellular matrix (ECM) is known to be deficient in chronic wounds. Collagen is the major protein in the ECM. Many claims are made while extolling the virtues of collagen-based biomaterials in promoting cell growth and modulating matrix metalloproteinases. This review will explore the rationale for using topical collagen or ECM as an interface for healing. Recent Advances: Rapid improvements in electrospinning and nanotechnology have resulted in the creation of third-generation biomaterials that mimic the native ECM, stimulate cellular and genetic responses in the target tissue, and provide a platform for controlled release of bioactive molecules and live cells. Although the major focus is currently on development of artificial tissues and organ regeneration, better understanding of the mechanisms that stimulate wound healing can be applied to specific deficits in the chronic wound. Critical Issues: When choosing between the various advanced wound-care products and dressings, the clinician is challenged to select the most appropriate material at the right time. Understanding how the ECM components promote tissue regeneration and modulate the wound microenvironment will facilitate those choices. Laboratory discoveries of biomolecular and cellular strategies that promote skin regeneration rather than repair should be demonstrated to translate to deficits in the chronic wound. Future Directions: Cost-effective production of materials that utilize non-mammalian sources of collagen or ECM components combined with synthetic scaffolding will provide an optimal structure for cellular ingrowth and modulation of the chronic wound microenvironment to facilitate healing. These bioengineered materials will be customizable to provide time-released delivery of bioactive molecules or drugs based on the degradation rate of the scaffold or specific signals from the wound.

Naturally Occurring Extracellular Matrix Scaffolds for Dermal Regeneration: Do They Really Need Cells?

The pronounced effect of extracellular matrix (ECM) scaffolds in supporting tissue regeneration is related mainly to their maintained 3D structure and their bioactive components. These decellularized matrix scaffolds could be revitalized before grafting via adding stem cells, fibroblasts, or keratinocytes to promote wound healing. We reviewed the online published literature in the last five years for the studies that performed ECM revitalization and discussed the results of these studies and the related literature. Eighteen articles met the search criteria. Twelve studies included adding cells to acellular dermal matrix (ADM), 3 studies were on small intestinal mucosa (SIS), one study was on urinary bladder matrix (UBM), one study was on amniotic membrane, and one study included both SIS and ADM loaded constructs. We believe that, in chronic and difficult-to-heal wounds, revitalizing the ECM scaffolds would be beneficial to overcome the defective host tissue interaction. This belief still has to be verified by high quality randomised clinical trials, which are still lacking in literature.

Strategies for skeletal muscle tissue engineering: seed vs. soil

The most commonly used tissue engineering approach includes the ex vivo combination of site-appropriate cell(s) and scaffold material(s) to create three-dimensional constructs for tissue replacement or reconstruction. These three-dimensional combinations are typically subjected to a period of culture and conditioning (i.e., self-assembly and maturation) to promote the development of ex vivo constructs which closely mimic native target tissue. This cell-based approach is challenged by the host response to the engineered tissue construct following surgical implantation. As an alternative to the cell-based approach, acellular biologic scaffolds attract endogenous cells and remodel into partially functional mimics of native tissue upon implantation. The present review examines cell-types (i.e., seed), scaffold materials (i.e., soil), and challenges associated with functional tissue engineering. Skeletal muscle is used as the target tissue prototype but the discussed principles will largely apply to most body systems.

Reprint of: Extracellular matrix as a biological scaffold material: Structure and function

Biological scaffold materials derived from the extracellular matrix (ECM) of intact mammalian tissues have been successfully used in a variety of tissue engineering/regenerative medicine applications both in preclinical studies and in clinical applications. Although it is recognized that the materials have constructive remodeling properties, the mechanisms by which functional tissue restoration is achieved are not well understood. There is evidence to support essential roles for both the structural and functional characteristics of the biological scaffold materials. This paper provides an overview of the composition and structure of selected ECM scaffold materials, the effects of manufacturing methods upon the structural properties and resulting mechanical behavior of the scaffold materials, and the in vivo degradation and remodeling of ECM scaffolds with an emphasis on tissue function.

A Rodent Model to Evaluate the Tissue Response to a Biological Scaffold When Adjacent to a Synthetic Material

The use of biologic scaffold materials adjacent to synthetic meshes is commonplace. A prevalent clinical example is two-staged breast reconstruction, where biologic scaffolds are used to provide support and coverage for the inferior aspect of the synthetic expander. However, limited data exist regarding either the kinetics of biologic scaffold integration or the host tissue response to the biologic scaffold materials used for this application or other applications in which such scaffold materials are used. The present study evaluated the temporal host response to a biological scaffold when placed adjacent to a synthetic material. Evaluation criteria included quantification of material contracture and characterization of the host cell response and tissue remodeling events. Results show a decreased thickness of the collagenous tissue layer at biologic scaffold/silicone interface compared to the abdominal wall/silicone interface during the 12-week experimental time course. All test materials were readily incorporated into surrounding host tissue.

Naturally derived and synthetic scaffolds for skeletal muscle reconstruction

Skeletal muscle tissue has an inherent capacity for regeneration following injury. However, severe trauma, such as volumetric muscle loss, overwhelms these natural muscle repair mechanisms prompting the search for a tissue engineering/regenerative medicine approach to promote functional skeletal muscle restoration. A desirable approach involves a bioscaffold that simultaneously acts as an inductive microenvironment and as a cell/drug delivery vehicle to encourage muscle ingrowth. Both biologically active, naturally derived materials (such as extracellular matrix) and carefully engineered synthetic polymers have been developed to provide such a muscle regenerative environment. Next generation naturally derived/synthetic "hybrid materials" would combine the advantageous properties of these materials to create an optimal platform for cell/drug delivery and possess inherent bioactive properties. Advances in scaffolds using muscle tissue engineering are reviewed herein.

Decellularization and cell seeding of whole liver biologic scaffolds composed of extracellular matrix

The definitive treatment for patients with end-stage liver disease is orthotropic transplantation. However, this option is limited by the disparity between the number of patients needing transplantation and the number of available livers. This issue is becoming more severe as the population ages and as the number of new cases of end-stage liver failure increases. Patients fortunate enough to receive a transplant are required to receive immunosuppressive therapy and must live with the associated morbidity. Whole organ engineering of the liver may offer a solution to this liver donor shortfall. It has been shown that perfusion decellularization of a whole allogeneic or xenogeneic liver generates a three-dimensional ECM scaffold with intact macro and micro architecture of the native liver. A decellularized liver provides an ideal transplantable scaffold with all the necessary ultrastructure and signaling cues for cell attachment, differentiation, vascularization, and function. In this review, an overview of complementary strategies for creating functional liver grafts suitable for transplantation is provided. Early milestones have been met by combining stem and progenitor cells with increasingly complex scaffold materials and culture conditions.

In Vivo Application of Tissue-Engineered Veins Using Autologous Peripheral Whole Blood: A Proof of Concept Study

Vascular diseases are increasing health problems affecting > 25 million individuals in westernized societies. Such patients could benefit from transplantation of tissue-engineered vascular grafts using autologous cells. One challenge that has limited this development is the need for cell isolation, and risks associated with ex vivo expanded stem cells. Here we demonstrate a novel approach to generate transplantable vascular grafts using decellularized allogeneic vascular scaffolds, repopulated with peripheral whole blood (PWB) in vitro in a bioreactor. Circulating, VEGFR-2 +/CD45 + and a smaller fraction of VEGFR-2 +/CD14 + cells contributed to repopulation of the graft. SEM micrographs showed flat cells on the luminal surface of the grafts consistent with endothelial cells. For clinical validation, two autologous PWB tissue-engineered vein conduits were prepared and successfully used for by-pass procedures in two pediatric patients. These results provide a proof of principle for the generation of transplantable vascular grafts using a simple autologous blood sample, making it clinically feasible globally.

Extracellular matrix as an inductive scaffold for functional tissue reconstruction

The extracellular matrix (ECM) is a meshwork of both structural and functional proteins assembled in unique tissue-specific architectures. The ECM both provides the mechanical framework for each tissue and organ and is a substrate for cell signaling. The ECM is highly dynamic, and cells both receive signals from the ECM and contribute to its content and organization. This process of "dynamic reciprocity" is key to tissue development and for homeostasis. Based upon these important functions, ECM-based materials have been used in a wide variety of tissue engineering and regenerative medicine approaches to tissue reconstruction. It has been demonstrated that ECM-based materials, when appropriately prepared, can act as inductive templates for constructive remodeling. Specifically, such materials act as templates for the induction of de novo functional, site-appropriate, tissue formation. Herein, the diverse structural and functional roles of the ECM are reviewed to provide a rationale for the use of ECM scaffolds in regenerative medicine. Translational examples of ECM scaffolds in regenerative are provided, and the potential mechanisms by which ECM scaffolds elicit constructive remodeling are discussed. A better understanding of the ability of ECM scaffold materials to define the microenvironment of the injury site will lead to improved clinical outcomes associated with their use.

Award winner for outstanding research in the PhD category, 2014 Society for Biomaterials annual meeting and exposition, Denver, Colorado, April 16-19, 2014: Decellularized adipose matrix hydrogels stimulate in vivo neovascularization and adipose formation

Decellularization of tissues offers the ability to produce tissue-specific extracellular matrix (ECM) scaffolds that recreate many of the biochemical aspects of the tissue of interest. In this study, we describe the in vivo function of decellularized adipose ECM hydrogels for treating subcutaneous adipose deficits. Adipose ECM hydrogels were combined with either adipose-derived adult stem cells or a biocompatible cross-linker, injected subcutaneously into nude mice, and evaluated over the course of 1 month. These ECM hydrogels showed improved integration with the surrounding tissue in vivo compared to a clinical standard soft tissue filler, Juvederm, and stimulated neovascularization. More importantly, these adipose ECM hydrogels facilitated new adipose regeneration within the material at 1 month, a feature not seen with current clinical soft tissue fillers. These results contribute to the growing evidence that ECM-based materials are capable of stimulating subcutaneous adipose regeneration, suggesting that future soft tissue filler materials could incorporate ECM elements in order to restore function to adipose deficits instead of simply filling them with static materials.

Fractionation of an ECM hydrogel into structural and soluble components reveals distinctive roles in regulating macrophage behavior

Extracellular matrix (ECM) derived from mammalian tissues has been utilized to repair damaged or missing tissue and improve healing outcomes.

Evaluation of skin regeneration after burns in vivo and rescue of cells after thermal stress in vitro following treatment with a keratin biomaterial

Thermal burns typically display an injury pattern dictated by the transfer of the thermal energy into the skin and underlying tissues and creation of three zones of injury represented by a necrotic zone of disrupted cells and tissue, an intermediate zone of injured and dying cells, and a distant zone of stressed cells that will recover with proper treatment. The wound healing capabilities of a keratin biomaterial hydrogel were studied in two pilot studies, one using a chemical burn model in mice and the other a thermal burn model in swine. In both studies, keratin was shown to prevent enlargement of the initial wound area and promote faster wound closure. Interestingly, treating thermally stressed dermal fibroblast in culture demonstrated that soluble keratin was able to maintain cell viability and promote proliferation. Separation of so-called alpha and gamma fractions of the keratin biomaterial had differential effects, with the gamma fraction producing more pronounced cell survival and recovery. These results suggest that the gamma fraction, composed essentially of degraded alpha keratin proteins, may facilitate cell rescue after thermal injury. Treatment of burns with gamma keratin may therefore represent a potential therapy for wounds with an intermediate zone of damaged tissue that has the potential to contribute to spontaneous healing.

Patch esophagoplasty: esophageal reconstruction using biologic scaffolds

BACKGROUND

Standard techniques for surgical reconstruction of the esophagus remain suboptimal. Primary closure of diseased or injured esophagus has been associated with high morbidity, primarily due to leak and stricture, and synthetic materials are contraindicated due to the high risk of erosion and infection. Degradable bioscaffolds composed of extracellular matrix (ECM) have recently shown promising results in both pre-clinical and clinical settings to prevent stricture after extended endoscopic mucosal resection. We propose a novel surgical technique that utilizes an ECM scaffold as a reconstructive patch to augment the esophageal diameter during primary repair.

METHODS

Four patients requiring esophageal reconstruction underwent a patch esophagoplasty using an ECM scaffold composed of porcine urinary bladder ECM. The full thickness wall of the esophagus was replaced with an ECM patch that was sutured to the edges of the remaining esophagus, similar to the patch angioplasty performed in vascular procedures.

RESULTS

All patients had a favorable clinical outcome with immediate recovery from the procedure and reinstated oral intake after 7 days. One patient had a micro leak at day 5 that closed spontaneously 2 days after drainage. Follow-up studies including barium swallow and esophagogastroduodenoscopy (EGD) showed adequate esophageal emptying through the surgical segment in all patients. The EGD showed complete mucosal remodeling at 2 months, with approximately 20% area contraction at the patch level. The area of the defect was indistinguishable from surrounding healthy tissue. Biopsy of the patch area showed normal squamous epithelium. One of the patients had a separate intrathoracic stricture that required further surgery. Clinical outcomes were otherwise favorable in all cases.

CONCLUSIONS

An alternative for the treatment of esophageal stenosis is presented which uses a biological scaffold and an innovative surgical procedure. Additional work, including prospective studies and long-term follow-up, is required to fully evaluate the potential of this bioscaffold-based regenerative medicine approach for esophageal reconstruction.

Generation of bioartificial heart tissue by combining a three-dimensional gel-based cardiac construct with decellularized small intestinal submucosa

The in vitro generation of a bioartificial cardiac construct (CC) represents a promising tool for the repair of ischemic heart tissue. Several approaches to engineer cardiac tissue in vitro have been conducted. The main drawback of these studies is the insufficient size of the resulting construct for clinical applications. The focus of this study was the generation of an artificial three-dimensional (3D), contractile, and suturable myocardial patch by combining a gel-based CC with decellularized porcine small intestinal submucosa (SIS), thereby engineering an artificial tissue of 11 cm² in size. The alignment and morphology of rat neonatal cardiomyocytes (rCMs) in SIS-CC complexes were investigated as well as the re-organization of primary endothelial cells which were co-isolated in the rCM preparation. The ability of a rat heart endothelial cell line (RHE-A) to re-cellularize pre-existing vessel structures within the SIS or a biological vascularized matrix (BioVaM) was determined. SIS-CC contracted spontaneously, uniformly, and rhythmically with an average rate of 200 beats/min in contrast to undirected contractions observed in CC without SIS support. rCM exhibited an elongated morphology with well-defined sarcomeric structures oriented along the longitudinal axis in the SIS-CC, whereas round-shaped and random-arranged rCM were observed in CC. Electric coupling of rCM was demonstrated by microelectrode array measurements. A dense network of CD31⁺/eNOS⁺ cells was detected as permeating the whole construct. Superficial supplementation of RHE-A cells to SIS-CC led to the migration of these cells through the CC, resulting in the re-population of pre-existing vessel structures within the decelluarized SIS. By infusion of RHE-A cells into the BioVaM venous and arterial pedicles, a re-population of the BioVaM vessel bed as well as distribution of RHE-A cells throughout the CC was achieved. Rat endothelial cells within the CC were in contact with RHE-A cells. Ingrowth and formation of a network by endothelial cells infused through the BioVaM represent a promising step toward engineering a functional perfusion system, enabling the engineering of vascularized and well-nourished 3D CC of dimensions relevant for therapeutic heart repair.

Understanding roles of porcine small intestinal submucosa in urinary bladder regeneration: identification of variable regenerative characteristics of small intestinal submucosa

Neuropathic bladders are the result from damages to the central or peripheral nervous system, and ultimately may require surgical reconstruction to increase bladder volumes and to reduce the risk of damages to the kidneys. Surgical reconstruction through bladder augmentation has traditionally been practiced using a segment of the ileum, colon, or stomach from the patient through enterocystoplasty. However, the use of gastrointestinal segments can lead to serious adverse consequences. Porcine small intestinal submucosa (SIS), a xenogeneic, acellular, biocompatable, biodegradable, and collagen-based bioscaffold is best known to encourage bladder regeneration without ex vivo cell seeding before implantation in various experimental and preclinical animal models. Although it has been demonstrated that SIS supports bladder cell growth in vitro, and SIS-regenerated bladders are histologically and functionally indistinguishable from normal functional tissues, clinical utilization of SIS for bladder augmentation has been hampered by inconsistent preclinical results. Several variables in SIS, such as the age of pigs, the region of the small intestine, and method of sterilization, can have different physical properties, biochemical characteristics, inflammatory cell infiltration, and regenerative capacity due to cellular responses in vitro and in vivo. These parameters are particularly important for bladder regeneration due to its specific biological function in urine storage. Clinical application of SIS for surgical bladder reconstruction may require graft materials to be prepared from a specific region of the small intestine, or to be further formulated or processed to provide uniform physical and biochemical properties for consistent, complete, and functional bladder regeneration.

Cardiogenic differentiation of mesenchymal stem cells on elastomeric poly (glycerol sebacate)/collagen core/shell fibers

AIM: To facilitate engineering of suitable biomaterials to meet the challenges associated with myocardial infarction.

METHODS: Poly (glycerol sebacate)/collagen (PGS/collagen) core/shell fibers were fabricated by core/shell electrospinning technique, with core as PGS and shell as collagen polymer; and the scaffolds were characterized by scanning electron microscope (SEM), fourier transform infrared spectroscopy (FTIR), contact angle and tensile testing for cardiac tissue engineering. Collagen nanofibers were also fabricated by electrospinning for comparison with core/shell fibers. Studies on cell-scaffold interaction were carried out using cardiac cells and mesenchymal stem cells (MSCs) co-culture system with cardiac cells and MSCs separately serving as positive and negative controls respectively. The co-culture system was characterized for cell proliferation and differentiation of MSCs into cardiomyogenic lineage in the co-culture environment using dual immunocytochemistry. The co-culture cells were stained with cardiac specific marker proteins like actinin and troponin and MSC specific marker protein CD 105 for proving the cardiogenic differentiation of MSCs. Further the morphology of cells was analyzed using SEM.

RESULTS: PGS/collagen core/shell fibers, core is PGS polymer having an elastic modulus related to that of cardiac fibers and shell as collagen, providing natural environment for cellular activities like cell adhesion, proliferation and differentiation. SEM micrographs of electrospun fibrous scaffolds revealed porous, beadless, uniform fibers with a fiber diameter in the range of 380 ± 77 nm and 1192 ± 277 nm for collagen fibers and PGS/collagen core/shell fibers respectively. The obtained PGS/collagen core/shell fibrous scaffolds were hydrophilic having a water contact angle of 17.9 ± 4.6° compared to collagen nanofibers which had a contact angle value of 30 ± 3.2°. The PGS/collagen core/shell fibers had mechanical properties comparable to that of native heart muscle with a young’s modulus of 4.24 ± 0.7 MPa, while that of collagen nanofibers was comparatively higher around 30.11 ± 1.68 MPa. FTIR spectrum was performed to confirm the functional groups present in the electrospun scaffolds. Amide I and amide II of collagen were detected at 1638.95 cm^-1 and 1551.64 cm^-1 in the electrospun collagen fibers and at 1646.22 cm^-1 and 1540.73 cm^-1 for PGS/collagen core/shell fibers respectively. Cell culture studies performed using MSCs and cardiac cells co-culture environment, indicated that the cell proliferation significantly increased on PGS/collagen core/shell scaffolds compared to collagen fibers and the cardiac marker proteins actinin and troponin were expressed more on PGS/collagen core/shell scaffolds compared to collagen fibers alone. Dual immunofluorescent staining was performed to further confirm the cardiogenic differentiation of MSCs by employing MSC specific marker protein, CD 105 and cardiac specific marker protein, actinin. SEM observations of cardiac cells showed normal morphology on PGS/collagen fibers and providing adequate tensile strength for the regeneration of myocardial infarction.

CONCLUSION: Combination of PGS/collagen fibers and cardiac cells/MSCs co-culture system providing natural microenvironments to improve cell survival and differentiation, could bring cardiac tissue engineering to clinical application.

Small intestinal submucosa segments as matrix for tissue engineering: review

Tissue engineering (TE) is an emerging interdisciplinary field aiming at the restoration or improvement of impaired tissue function. A combination of cells, scaffold materials, engineering methods, and biochemical and physiological factors is employed to generate the desired tissue substitute. Scaffolds often play a pivotal role in the engineering process supporting a three-dimensional tissue formation. The ideal scaffold should mimic the native extracellular environment providing mechanical and biological properties to allow cell attachment, migration, and differentiation, as well as remodeling by the host organism. The scaffold should be nonimmunogenic and should ideally be resorbed by the host over time, leaving behind only the regenerated tissue. More than 40 years ago, a preparation of the small intestine was introduced for the replacement of vascular structures. Since then the small intestinal submucosa (SIS) has gained a lot of interest in TE and subsequent clinical applications, as this material exhibits key features of a highly supportive scaffold. This review will focus on the general properties of the SIS and its applications in therapeutical approaches as well as in generating tissue substitutes in vitro. Furthermore, the main problem of TE, which is the insufficient nourishment of cells within three-dimensional, artificial tissues exceeding certain dimensions is addressed. To solve this issue the implementation of another small intestine-derived preparation, the biological vascularized matrix (BioVaM), could be a feasible option. The BioVaM comprises in addition to SIS the arterial and venous mesenteric pedicles and exhibits thereby a perfusable vessel bed that is preserved after decellularization.

An in vivo model system for evaluation of the host response to biomaterials

We describe an in vivo model system designed to evaluate the host response to implanted biomaterials: The partial thickness rat abdominal wall defect model. The model allows for determination of the temporal and spatial distribution of the cellular and vascular response, the remodeling of the implanted material and surrounding host soft tissue, and the function of the remodeled tissue over time.

Comparison of methods for whole-organ decellularization in tissue engineering of bioartificial organs

Organ transplantation is now a well-established procedure for the treatment of end-stage organ failure due to various causes, but is a victim of its own success in that there is a growing disparity in numbers between the donor organ pool available for transplantation and the patients eligible for such a procedure; hence, an alternative solution to the limited donor organ pool is both desirable and necessary. Tissue engineering is an interdisciplinary field that applies the principles of engineering and life sciences toward the development of functional replacement tissues for clinical use. A recent innovation in tissue and organ engineering is the technique of whole-organ decellularization, which allows the production of complex three-dimensional extracellular matrix (ECM) bioscaffolds of the entire organ with preservation of the intrinsic vascular network. These bioscaffolds can then be recellularized to create potentially functional organ constructs as a regenerative medicine strategy for organ replacement. We review the current applications and methods in using xenogeneic whole-organ ECM scaffolds to create potentially functional bioartificial organ constructs for surgical implantation, and present a comparison of specific trends within this new and developing technique.

Perspectives on whole-organ assembly: moving toward transplantation on demand

There is an ever-growing demand for transplantable organs to replace acute and chronically damaged tissues. This demand cannot be met by the currently available donor organs. Efforts to provide an alternative source have led to the development of organ engineering, a discipline that combines cell biology, tissue engineering, and cell/organ transplantation. Over the last several years, engineered organs have been implanted into rodent recipients and have shown modest function. In this article, we summarize the most recent advances in this field and provide a perspective on the challenges of translating this promising new technology into a proven regenerative therapy.

Bone marrow-derived cells participate in the long-term remodeling in a mouse model of esophageal reconstruction

BACKGROUND

The default response of the esophagus to injury includes inflammation and scar tissue formation often leading to stricture. Biologic scaffolds composed of extracellular matrix (ECM) have been associated with the reconstitution of functional esophageal tissue in preclinical studies and clinical case reports of esophageal mucosal resection, anastomotic reinforcement, and full circumferential replacement. However, the mechanisms responsible for this change in the default response to esophageal injury are not fully understood.

METHODS

The objective of the present study was to determine whether bone marrow-derived cells (BMCs) participate in the long-term remodeling of ECM scaffolds in the esophageal location in a mouse model.

RESULTS

BMCs were present in low numbers in remodeling ECM scaffolds. Compared with the untreated control mice, the ECM-implanted animals showed better remodeling of the epithelial layer.

CONCLUSIONS

BMCs are involved in ECM remodeling process during tissue repair after esophageal injury, but the low numbers argue against any significant involvement in the constructive remodeling process.

Monitoring tissue development in acellular matrix-based regeneration for bladder tissue engineering: multiexponential diffusion and T2* for improved specificity

Cell-seeded acellular matrices (ACMs) are a promising approach for the tissue engineering of soft tissues and organs, such as the urinary bladder. ACM contains site-preferred structural and functional molecules, and degradation products derived from ACM play important roles in tissue remodeling. Regeneration proceeds along concurrent trajectories of cell growth and matrix degradation, characterized by evolving biophysical and biochemical properties. The assessment of tissue development through a noninvasive imaging technique, such as MRI, must therefore be capable of distinguishing these concurrent biophysical and biochemical changes. However, although MRI provides exquisite sensitivity to tissue microstructure, composition and function, specificity remains limited. In this study, multiexponential diffusion and the effective transverse relaxation time T(2)* were investigated for their ability to assess cell growth and tissue composition, respectively. Bladder ACMs prepared with and without hyaluronic acid, and ACMs seeded with smooth muscle cells, were assessed on MRI. The slow diffusion fraction from multiexponential diffusion analysis demonstrated the best correlation with cellularity, with minimal influence from underlying matrix degradation. T(2)* measurements were sensitive to macromolecular content, specifically the presence of hyaluronic acid, without confounding influence from tissue hydration. T(2)* also appeared to be sensitive to cell filling of the matrix pore space. Compared with these metrics, commonly used MRI parameters, such as T(1), T(2) and single diffusion coefficients, were more limited in specificity. The use of T(2) to measure tissue structure and composition is limited by its large dependence on water content, and single diffusion can only reflect the overall characteristics of the extra- and intracellular environment. These findings are important for further development of more specific MRI methods for the monitoring of regeneration in tissue-engineered systems.

Macrophage phenotype as a predictor of constructive remodeling following the implantation of biologically derived surgical mesh materials

Macrophages have been classified as having plastic phenotypes which exist along a spectrum between M1 (classically activated; pro-inflammatory) and M2 (alternatively activated; regulatory, homeostatic). To date, the effects of polarization towards an M1 or M2 phenotype have been studied largely in the context of response to pathogen or cancer. Recently, M1 and M2 macrophages have been shown to play distinct roles in tissue remodeling following injury. In the present study, the M1/M2 paradigm was utilized to examine the role of macrophages in the remodeling process following implantation of 14 biologically derived surgical mesh materials in the rat abdominal wall. In situ polarization of macrophages responding to the materials was examined and correlated to a quantitative measure of the observed tissue remodeling response to determine whether macrophage polarization is an accurate predictor of the ability of a biologic scaffold to promote constructive tissue remodeling. Additionally the ability of M1 and M2 macrophages to differentially recruit progenitor-like cells in vitro, which are commonly observed to participate in the remodeling of those ECM scaffolds which have a positive clinical outcome, was examined as a possible mechanism underlying the differences in the observed remodeling responses. The results of the present study show that there is a strong correlation between the early macrophage response to implanted materials and the outcome of tissue remodeling. Increased numbers of M2 macrophages and higher ratios of M2:M1 macrophages within the site of remodeling at 14 days were associated with more positive remodeling outcomes (r(2)=0.525-0.686, p<0.05). Further, the results of the present study suggest that the constructive remodeling outcome may be due to the recruitment and survival of different cell populations to the sites of remodeling associated with materials that elicit an M1 vs. M2 response. Both M2 and M0 macrophage conditioned media were shown to have higher chemotactic activities than media conditioned by M1 macrophages (p<0.05). A more thorough understanding of these issues will logically influence the design of next generation biomaterials and the development of regenerative medicine strategies for the formation of functional host tissues.

Inductive, scaffold-based, regenerative medicine approach to reconstruction of the temporomandibular joint disk

PURPOSE

A device composed of extracellular matrix (ECM) was investigated as an inductive template in vivo for reconstruction of the temporomandibular joint (TMJ) disk after discectomy.

MATERIALS AND METHODS

A scaffold material composed of porcine-derived ECM was configured to mimic the shape and size of the TMJ. This device was implanted in a canine model of bilateral TMJ discectomy. After discectomy, 1 side was repaired with an ECM scaffold material and the contralateral side was left empty as a control. At 6 months after implantation, the joint space was opened, the joints were evaluated for signs of gross pathologic degenerative changes, and newly formed tissue was excised for histologic, biochemical, and biomechanical analysis.

RESULTS

The results showed that implantation of an initially acellular material supported the formation of site-appropriate, functional host tissue that resembled that of the native TMJ disk. Furthermore, this prevented gross degenerative changes in the temporal fossa and mandibular condyle. No tissue formation and mild to severe gross pathologic changes were observed in the contralateral controls.

CONCLUSIONS

These results suggest that an ECM-based bioscaffold could represent an off-the-shelf solution for TMJ disk replacement.

Extracellular matrix as an inductive template for temporomandibular joint meniscus reconstruction: a pilot study

PURPOSE

A device consisting of powdered porcine urinary bladder extracellular matrix (UBM-ECM) encapsulated within sheets of the same material was investigated as a scaffold for temporomandibular joint (TMJ) meniscus reconstruction.

MATERIALS AND METHODS

Five dogs underwent unilateral resection of the native meniscus and replacement with a UBM-ECM device. Necropsies were performed at 3, 4, 8, 12, and 24 weeks. Two additional dogs underwent bilateral resection of the meniscus with replacement with a UBM-ECM device on 1 side, leaving the contralateral side empty as a control. Necropsies were performed at 24 weeks for bilaterally treated animals.

RESULTS

Macroscopically, the UBM-ECM implants were remodeled rapidly and were indistinguishable from newly deposited host tissue at all time points. Microscopically, remodeling was characterized by a dense infiltration of predominantly CD68(+) mononuclear cells and smooth muscle actin-positive fibroblast-like cells at early time points changing with time to a sparse population of smooth muscle actin-negative spindle-shaped cells resembling those of the native fibrocartilaginous TMJ meniscus. Furthermore, the remodeling process showed deposition of predominantly type I collagen, the density and organization of which resembled those of the native meniscus by the 24-week time point. Ingrowth of calsequestrin-positive skeletal muscle tissue was also observed at the periphery of the remodeled UBM-ECM device and was similar to that found at the attachment site of the native meniscus to the surrounding soft tissues. Histologic results were identical for samples excised from both unilaterally and bilaterally treated animals. No adverse changes in the articulating surfaces of the condyle or fossa were observed in UBM-ECM-implanted joints. In the bilaterally treated animals, the unimplanted control side was characterized by degeneration and pitting of the articulating surfaces of both the condyle and the fossa, with disorganized bands of fibrous connective tissue observed within the joint space.

CONCLUSION

Results of this study suggest that the UBM-ECM device provides an effective interpositional material while serving as an inductive template for reconstruction of the TMJ meniscus.

Right ventricular outflow tract repair with a cardiac biologic scaffold

BACKGROUND

Surgical reconstruction of congenital heart defects is often limited by the nonresorbable material used to approximate normal anatomy. In contrast, biologic scaffold materials composed of resorbable non-cross-linked extracellular matrix (ECM) have been used for tissue reconstruction of multiple organs and are replaced by host tissue. Preparation of whole organ ECM by decellularization through vascular perfusion can maintain much of the native three-dimensional (3D) structure, strength, and tissue-specific composition. A 3D cardiac ECM (C-ECM) biologic scaffold material would logically have structural and functional advantages over materials such as Dacron™ for myocardial repair, but the in vivo remodeling characteristics of C-ECM have not been investigated to date.

METHODS AND RESULTS

A porcine C-ECM patch or Dacron patch was used to reconstruct a full-thickness right ventricular outflow tract (RVOT) defect in a rat model with end points of structural remodeling function at 16 weeks. The Dacron patch was encapsulated by dense fibrous tissue and showed little cellular infiltration. Echocardiographic analysis showed that the right ventricle of the hearts patched with Dacron were dilated at 16 weeks compared to presurgery baseline values. The C-ECM patch remodeled into dense, cellular connective tissue with scattered small islands of cardiomyocytes. The hearts patched with C-ECM showed no difference in the size or function of the ventricles as compared to baseline values at both 4 and 16 weeks.

CONCLUSIONS

The C-ECM patch was associated with better functional and histomorphological outcomes compared to the Dacron patch in this rat model of RVOT reconstruction.

An isolated cryptic peptide influences osteogenesis and bone remodeling in an adult mammalian model of digit amputation

Biologic scaffolds composed of extracellular matrix (ECM) have been used successfully in preclinical models and humans for constructive remodeling of functional, site-appropriate tissue after injury. The mechanisms underlying ECM-mediated constructive remodeling are not completely understood, but scaffold degradation and site-directed recruitment of progenitor cells are thought to play critical roles. Previous studies have identified a cryptic peptide derived from the C-terminal telopeptide of collagen IIIα that has chemotactic activity for progenitor cells. The present study characterized the osteogenic activity of the same peptide in vitro and in vivo in an adult murine model of digit amputation. The present study showed that the cryptic peptide increased calcium deposition, alkaline phosphatase activity, and osteogenic gene expression in human perivascular stem cells in vitro. Treatment with the cryptic peptide in a murine model of mid-second phalanx digit amputation led to the formation of a bone nodule at the site of amputation. In addition to potential therapeutic implications for the treatment of bone injuries and facilitation of reconstructive surgical procedures, cryptic peptides with the ability to alter stem cell recruitment and differentiation at a site of injury may serve as powerful new tools for influencing stem cell fate in the local injury microenvironment.

The pro-myogenic environment provided by whole organ scale acellular scaffolds from skeletal muscle

In the pursuit of a transplantable construct for the replacement of large skeletal muscle defects arising from traumatic or pathological conditions, several attempts have been made to obtain a highly oriented, vascularized and functional skeletal muscle. Acellular scaffolds derived from organ decellularization are promising, widely used biomaterials for tissue engineering. However, the acellular skeletal muscle extra cellular matrix (ECM) has been poorly characterized in terms of production, storage and host-donor interactions. We have produced acellular scaffolds at the whole organ scale from various skeletal muscles explanted from mice. The acellular scaffolds conserve chemical and architectural features of the tissue of origin, including the vascular bed. Scaffolds can be sterilely stored for weeks at +4°C or +37°C in tissue culture grade conditions. When transplanted in wt mice, the grafts are stable for several weeks, whilst being colonized by inflammatory and stem cells. We demonstrate that the acellular scaffold per se represents a pro-myogenic environment supporting de novo formation of muscle fibers, likely derived from host cells with myogenic potential. Myogenesis within the implant is enhanced by immunosuppressive treatment. Our work highlights the fundamental role of this niche in tissue engineering application and unveils the clinical potential of allografts based on decellularized tissue for regenerative medicine.

Extracellular matrix powder protects against bleomycin-induced pulmonary fibrosis

Pulmonary fibrosis refers to a group of lung diseases characterized by inflammation, fibroblast proliferation, and excessive collagen deposition. Although the mechanisms underlying pulmonary fibrosis are poorly understood, current evidence suggests that epithelial injury contributes to the development of fibrosis. Regenerative medicine approaches using extracellular matrix (ECM) scaffolds have been shown to promote site-specific tissue remodeling. This led to the hypothesis that particulate ECM would promote normal tissue repair and attenuate bleomycin-induced pulmonary fibrosis. C57BL/6 mice were treated intratracheally with bleomycin or saline with or without a particulate form of ECM scaffold from porcine urinary bladder matrix (UBM-ECM) or enzymatically digested UBM-ECM. Mice were sacrificed 5 and 14 days after exposure. Compared to control mice, bleomycin-exposed mice had similar increases in inflammation in the bronchoalveolar lavage fluid regardless of UBM-ECM treatment. However, 14 days after exposure, lung histology and collagen levels revealed that mice treated with bleomycin and the particulate or digested UBM-ECM had negligible fibrosis, whereas mice given only bleomycin had marked fibrosis. Administration of the particulate UBM-ECM 24 h after bleomycin exposure also significantly protected against pulmonary injury. In vitro epithelial cell migration and wound healing assays revealed that particulate UBM-ECM promoted epithelial cell chemotaxis and migration. This suggests that promotion of epithelial wound repair may be one mechanism in which UBM-ECM limits pulmonary fibrosis.

Patient-to-patient variability in autologous pericardial matrix scaffolds for cardiac repair

The pursuit of alternate therapies for end-stage heart failure post-myocardial infarction has led to the development of a variety of in situ gelling materials to be used as cellular or acellular scaffolds for cardiac repair. Previously, a protocol was established to decellularize human and porcine pericardia and process the extracellular matrix (ECM) into an injectable form. The resulting gels were found to retain components of the native extracellular matrix; cell infiltration was facilitated in vivo, and neovascularization was observed by 2 weeks. However, the assertion that an injectable form of human pericardial tissue could be a potentially autologous scaffold for myocardial tissue engineering requires assessment of the patient-to-patient variability. With this work, seven human pericardia from a relevant patient demographic are processed into injectable matrix materials that gel when brought to physiologic conditions. The resulting materials are compared with respect to their protein composition, glycosaminoglycan content, in vitro degradation, in vivo gelation, and microstructure. It is observed that a diminished collagen content in a subset of samples prevents in vitro gelation but not in vivo gelation at lower ECM concentrations. The structure is similarly fibrous and porous across all samples, implying the cell infiltration may be similarly facilitated. The biochemical composition as characterized by tandem mass spectrometry is comparable; basic ECM components are conserved across all samples, and the presence of a wide variety of ECM proteins and glycoproteins demonstrate the retention of biochemical complexity post-processing. It is concluded that the variability within human pericardial tissue specimens does not prevent them from being processed into injectable scaffolds; therefore, pericardial tissue offers a promising source as an autologous, injectable biomaterial scaffold.

Recruitment of progenitor cells by an extracellular matrix cryptic peptide in a mouse model of digit amputation

Biologic scaffolds composed of extracellular matrix (ECM) have been used successfully in preclinical models and humans for constructive remodeling of functional, site-appropriate tissue after injury. The mechanisms underlying ECM-mediated constructive remodeling are not completely understood, but scaffold degradation and site-directed recruitment of both differentiated and progenitor cells are thought to play critical roles. Previous studies have shown that degradation products of ECM scaffolds can recruit a population of progenitor cells both in vitro and in vivo. The present study identified a single cryptic peptide derived from the α subunit of the collagen III molecule that is chemotactic for a well-characterized perivascular stem cell in vitro and causes the site-directed accumulation of progenitor cells in vivo. The oligopeptide was additionally chemotactic for human cortical neural stem cells, rat adipocyte stem cells, C2C12 myoblast cells, and rat Schwann cells in vitro. In an adult murine model of digit amputation, treatment with this peptide after mid-second phalanx amputation resulted in a greater number of Sox2+ and Sca1+,Lin- cells at the site of injury compared to controls. Since progenitor cell activation and recruitment are key prerequisites for epimorphic regeneration in adult mammalian tissues, endogenous site-directed recruitment of such cells has the potential to alter the default wound healing response from scar tissue toward regeneration.

Injectable hydrogel scaffold from decellularized human lipoaspirate

Soft tissue fillers are rapidly gaining popularity for aesthetic improvements or repair of adipose tissue deficits. Several injectable biopolymers have been investigated for this purpose, but often show rapid resorption or limited adipogenesis and do not mimic the native adipose extracellular matrix (ECM). We have generated an injectable adipose matrix scaffold by efficiently removing both the cellular and lipid contents of human lipoaspirate. The decellularized material retained the complex composition of peptides and glycosaminoglycans found in native adipose ECM. This matrix can be further processed by solubilizing the extracted ECM to generate a thermally responsive hydrogel that self-assembles upon subcutaneous injection. This hydrogel also supports the growth and survival of patient matched adipose-derived stem cells in vitro. The development of an injectable hydrogel from human lipoaspirate represents a minimally invasive option for adipose tissue engineering in terms of both the collection of source material and delivery of the scaffold.

Comparison of three methods for the derivation of a biologic scaffold composed of adipose tissue extracellular matrix

Extracellular matrix (ECM)-based scaffold materials have been used successfully in both preclinical and clinical tissue engineering and regenerative medicine approaches to tissue reconstruction. Results of numerous studies have shown that ECM scaffolds are capable of supporting the growth and differentiation of multiple cell types in vitro and of acting as inductive templates for constructive tissue remodeling after implantation in vivo. Adipose tissue represents a potentially abundant source of ECM and may represent an ideal substrate for the growth and adipogenic differentiation of stem cells harvested from this tissue. Numerous studies have shown that the methods by which ECM scaffold materials are prepared have a dramatic effect upon both the biochemical and structural properties of the resultant ECM scaffold material as well as the ability of the material to support a positive tissue remodeling outcome after implantation. The objective of the present study was to characterize the adipose ECM material resulting from three methods of decellularization to determine the most effective method for the derivation of an adipose tissue ECM scaffold that was largely free of potentially immunogenic cellular content while retaining tissue-specific structural and functional components as well as the ability to support the growth and adipogenic differentiation of adipose-derived stem cells. The results show that each of the decellularization methods produced an adipose ECM scaffold that was distinct from both a structural and biochemical perspective, emphasizing the importance of the decellularization protocol used to produce adipose ECM scaffolds. Further, the results suggest that the adipose ECM scaffolds produced using the methods described herein are capable of supporting the maintenance and adipogenic differentiation of adipose-derived stem cells and may represent effective substrates for use in tissue engineering and regenerative medicine approaches to soft tissue reconstruction.

Extracellular matrix degradation products and low-oxygen conditions enhance the regenerative potential of perivascular stem cells

Tissue and organ injury results in alterations of the local microenvironment, including the reduction in oxygen concentration and degradation of the extracellular matrix (ECM). The response of perivascular stem cells to these microenvironment changes are of particular interest because of their wide distribution throughout the body and their potential involvement in tissue and organ response to injury. The chemotactic, mitogenic, and phenotypic responses of this stem cell population were evaluated in response to a combination of decreased oxygen concentration and the presence of ECM degradation products. Culture in low-oxygen conditions resulted in increased proliferation and migration of the cells and increased activation of the ERK signaling pathway and associated integrins without a change in cell surface marker phenotype. The addition of ECM degradation products were additive to these processes. Reactive oxygen species within the cells were increased in association with the mitogenic and chemotactic responses. The increased proliferation and chemotactic properties of this stem cell population without any changes in phenotype and differentiation potential has important implications for both in vitro cell expansion and for in vivo behavior of these cells at the site of injury.

The emerging relationship between regenerative medicine and physical therapeutics

Dramatic changes in the health care landscape over the next few decades undoubtedly will affect rehabilitation specialists' practice. In the multidisciplinary field of regenerative medicine, cell, tissue, or organ substitutes are used to enhance the healing potential of the body. Given that the restoration of normal functioning of injured or diseased tissues is expected to be the ultimate goal of these therapies, the future of regenerative medicine is, undeniably, tightly intertwined with that of rehabilitation. Rehabilitation specialists not only must be aware of cutting-edge medical advances as they relate to regenerative medicine but also must work closely with basic scientists to guide the development of clinically relevant protocols. The purposes of this article are to provide a current perspective on biological approaches to the management of musculoskeletal disorders and to highlight the needed integration of physical therapeutics with regenerative medicine.

Vascular differentiation of bone marrow stem cells is directed by a tunable three-dimensional matrix

Microenvironmental cues are critical in regulating cell behavior and fate. The roles that matrix mechanical signals play in regulating cell behavior have recently been elucidated. An artificial matrix that can maintain the appropriate characteristics for transplanted stem cells is therefore needed to achieve a desired cell phenotype. The objective of this study was to develop a three-dimensional (3-D) matrix with tunable physical and mechanical properties and investigate their effects on mesenchymal stem cell (MSC) differentiation towards vascular cell types. In this study we developed an extracellular microenvironment by modifying fibrinogen with various polyethylene glycol (PEG) derivatives. We hypothesized that adjusting the type of PEG derivative to modify the resultant physical and mechanical characteristics of fibrin would allow us to create a tunable system for use in culture or in vivo in conjunction with a regenerative medicine strategy. Human MSC (hMSC) were entrapped into PEGylated fibrin matrices at a density of 50,000 cells ml(-1). Cell phenotypes were confirmed by immunofluorescent staining as well as the use of oligonucleotide arrays. Vascular phenotypes were correlated with measured mechanical properties and fiber diameters of the PEGylated fibrin matrices. Blocking studies were performed to identify mechanistic factors controlling MSC differentiation through selected blocking of matrix degradation or cell contraction. Cell-matrix interactions were also examined in vivo. Our results demonstrate that transdifferentiation of MSC towards an endothelial cell phenotype is profoundly affected by the 3-D matrix microenvironment. Our work provides a predictive road map for the creation of fibrin-based matrices that support robust endothelial cell gene expression and tubulogenesis.

Design and characterization of an injectable pericardial matrix gel: a potentially autologous scaffold for cardiac tissue engineering

Following ischemic injury in the heart, little to no repair occurs, causing a progressive degeneration of cardiac function that leads to congestive heart failure. Cardiac tissue engineering strategies have focused on designing a variety of injectable scaffolds that range in composition from single-component materials to complex extracellular matrix (ECM)-derived materials. In this study, the pericardial ECM, a commonly used biomaterial, was investigated for use as an injectable scaffold for cardiac repair. It was determined that a solubilized form of decellularized porcine pericardium could be injected and induced to gel in vivo, prompting investigation with human pericardium, which has the decided advantage of offering an autologous therapy. Characterization showed that the matrix gels retained components of the native pericardial ECM, with extant protein and glycosaminoglycan content identified. The results of an in vitro migration assay indicate that the porcine pericardial matrix is a stronger chemoattractant for relevant cell types, but in vivo results showed that the two materials caused statistically similar amounts of neovascularization, demonstrating feasibility as injectable treatments. Potential stem cell mobilization was supported by the presence of c-Kit+ cells within the matrix injection regions. With this work, the pericardium is identified as a novel source for an autologous scaffold for treating myocardial infarction.

Extracellular matrix-derived products modulate endothelial and progenitor cell migration and proliferation in vitro and stimulate regenerative healing in vivo

Most adult mammals heal without restorative replacement of lost tissue and instead form scar tissue at an injury site. One exception is the adult MRL/MpJ mouse that can regenerate ear and cardiac tissue after wounding with little evidence of scar tissue formation. Following production of a MRL mouse ear hole, 2mm in diameter, a structure rapidly forms at the injury site that resembles the amphibian blastema at a limb amputation site during limb regeneration. We have isolated MRL blastemal cells (MRL-B) from this structure and adapted them to culture. We demonstrate by RT-PCR that even after continuous culturing of these cells they maintain expression of several progenitor cell markers, including DLK (Pref-1), and Msx-1. We have isolated the underlying extracellular matrix (ECM) produced by these MRL-B cells using a new non-proteolytic method and studied the biological activities of this cell-free ECM. Multiplex microELISA analysis of MRL-B cell-free ECM vs. cells revealed selective enrichment of growth factors such as bFGF, HGF and KGF in the matrix compartment. The cell-free ECM, degraded by mild enzyme treatment, was active in promoting migration and proliferation of progenitor cells in vitro and accelerating wound closure in a mouse full thickness cutaneous wound assay in vivo. In vivo, a single application of MRL-B cell matrix-derived products to full thickness cutaneous wounds in non-regenerative mice, B6, induced re-growth of pigmented hair, dermis and epidermis at the wound site whereas scar tissue replaced these tissues at wound sites in mice treated with vehicle alone. These studies suggest that matrix-derived products can stimulate regenerative healing and avert scar tissue formation in adult mammals.