ECM-based materials in cardiovascular applications: Inherent healing potential and augmentation of native regenerative processes

Reduced fibrous capsule elastic fibers from biologic ECM-enveloped CIEDs in minipigs, supported with a novel compression mechanics model

BACKGROUND

Fibrous capsules (Fb) in response to cardiovascular implantable electronic devices (CIEDs), including a pacemaker (P) system, can produce patient discomfort and difficulties in revision surgery due partially to their increased compressive strength, previously linked to elevated tissue fibers.

OBJECTIVE

A preliminary study to quantify structural proteins, determine if biologic extracellular matrix-enveloped CIEDs (PECM) caused differential Fb properties, and to implement a realistic mechanical model.

METHODS

Retrieved Fb (-P and -PECM) from minipigs were subjected to biomechanical (shear oscillation and uniaxial compression) and histological (collagen I and elastin) analyses.

RESULTS

Fb-PECM showed significant decreases compared to Fb-P in: low strain-loss modulus (390 vs. 541 Pa) across angular frequencies, high strain-compressive elastic modulus (1043 vs. 2042 kPa), and elastic fiber content (1.92 vs. 3.15 μg/mg tissue). Decreases in elastin were particularly noted closer to the implant's surface (Fb-PECM = 71% vs. Fb-P = 143% relative to dermal elastin at mid-tangential sections) and verified with a solid mechanics hyperelasticity with direction-dependent fiber viscoelasticity compression simulation (r2 ≥ 98.9%).

CONCLUSIONS

The biologic envelope composed of decellularized porcine small intestine submucosa ECM for CIEDs promoted fibrous tissues with less elastic fibers. Novel compression modeling analyses directly correlated this singular reduction to more desirable subcutaneous tissue mechanics.

Physician antibiotic hydration preferences for biologic antibacterial envelopes during cardiac implantable device procedures

Background

Cardiac implantable electronic device (CIED) infection is a potentially serious complication of CIED procedures. Infection risk mitigation includes using guideline-recommended pre-operative intravenous antibacterial prophylaxis (IV ABX). The use of antibiotic-eluting CIED envelopes has also been shown to reduce infection risk. The relationship between and potential benefits associated with guideline-recommended IV ABX in combination with antibacterial envelopes have not been characterized.

Methods

Biologic envelopes made from non-crosslinked extracellular matrix (ECM) were implanted into 1,102 patients receiving CIEDs. The implanting physician decided patient selection for using a biologic envelope and envelope hydration solution. Observational data was analyzed on IV ABX utilization rates, antibacterial envelope usage, and infection outcomes.

Results

Overall compliance with IV ABX was 96.6%, and most patients received a biologic envelope hydrated in antibiotics (77.1%). After a mean follow-up of 223 days, infection rates were higher for sites using IV ABX <80% of the time vs. sites using ≥80% (5.6% vs. 0.8%, p = 0.008). Physicians demonstrated preference for hydration solutions containing gentamicin in higher-risk patients, which was found by multivariate analysis to be associated with a threefold reduction in infection risk (OR 3.0, 95% CI, 1.0-10.0).

Conclusion

These findings suggest that use of antibiotics, particularly gentamicin, in biologic envelope hydration solution may reduce infection risk, and use of antibacterial envelopes without adjunct IV ABX may not be sufficient to reduce CIED infections.

Clinical trial registration

[https://clinicaltrials.gov/], identifier [NCT02530970].

3D printed biomimetic flexible blood vessels with iPS cell-laden hierarchical multilayers

Successful recovery from vascular diseases has typically relied on the surgical repair of damaged blood vessels (BVs), with the majority of current approaches involving the implantation of autologous BVs, which is plagued by donor site tissue damage. Researchers have attempted to develop artificial vessels as an alternative solution to traditional approaches to BV repair. However, the manufacturing of small-diameter (< 6 mm) BVs is still considered one of the biggest challenges due to its difficulty in the precise fabrication and the replication of biomimetic architectures. In this study, we successfully developed 3D printed flexible small-diameter BVs that consist of smooth muscle cells and a vascularized endothelium. In the developed artificial BV, a rubber-like elastomer was printed as the outermost layer of the vessel, which demonstrated enhanced mechanical properties, while and human induced pluripotent stem cell (iPSC)-derived vascular smooth muscle cells (iSMCs) and endothelial cells (iECs) embedded fibrinogen solutions were coaxially extruded with thrombin solution to form cell-laden fibrin gel inner layers. Our results showed that the 3D BVs possessed proper mechanical properties, and the cells in the fibrin layers substantially proliferated over time to form a stable BV construct. Our study demonstrated that the 3D printed flexible small-diameter BV using iPSCs could be a promising platform for the treatment of vascular diseases.

Inflammation-mediated matrix remodeling of extracellular matrix-mimicking biomaterials in tissue engineering and regenerative medicine

Extracellular matrix (ECM)-mimicking biomaterials are considered effective tissue-engineered scaffolds for regenerative medicine because of their biocompatibility, biodegradability, and bioactivity. ECM-mimicking biomaterials preserve natural microstructures and matrix-related bioactive components and undergo continuous matrix remodeling upon transplantation. The interaction between host immune cells and transplanted ECM-mimicking biomaterials has attracted considerable attention in recent years. Transplantation of biomaterials may initiate injuries and early pro-inflammation reactions characterized by infiltration of neutrophils and M1 macrophages. Pro-inflammation reactions may lead to degradation of the transplanted biomaterial and drive the matrix into a fetal-like state. ECM degradation leads to the release of matrix-related bioactive components that act as signals for cell migration, proliferation, and differentiation. In late stages, pro-inflammatory cells fade away, and anti-inflammatory cells emerge, which involves macrophage polarization to the M2 phenotype and leukocyte activation to T helper 2 (Th2) cells. These anti-inflammatory cells interact with each other to facilitate matrix deposition and tissue reconstruction. Deposited ECM molecules serve as vital components of the mature tissue and influence tissue homeostasis. However, dysregulation of matrix remodeling results in several pathological conditions, such as aggressive inflammation, difficult healing, and non-functional fibrosis. In this review, we summarize the characteristics of inflammatory responses in matrix remodeling after transplantation of ECM-mimicking biomaterials. Additionally, we discuss the intrinsic linkages between matrix remodeling and tissue regeneration. STATEMENT OF SIGNIFICANCE: Extracellular matrix (ECM)-mimicking biomaterials are effectively used as scaffolds in tissue engineering and regenerative medicine. However, dysregulation of matrix remodeling can cause various pathological conditions. Here, the review describes the characteristics of inflammatory responses in matrix remodeling after transplantation of ECM-mimicking biomaterials. Additionally, we discuss the intrinsic linkages between matrix remodeling and tissue regeneration. We believe that understanding host immune responses to matrix remodeling of transplanted biomaterials is important for directing effective tissue regeneration of ECM-mimicking biomaterials. Considering the close relationship between immune response and matrix remodeling results, we highlight the need for studies of the effects of clinical characteristics on matrix remodeling of transplanted biomaterials.

Risk Profiles and Outcomes of Patients Receiving Cardiovascular Implantable Electronic Devices With and Without Antibacterial Envelopes

Background

The increasing use of cardiac implantable electronic devices (CIEDs) in a growing patient population has led to an even greater increase in CIED infection rates. Antibacterial CIED envelopes are often used as part of an infection risk-reduction strategy. However, best practices for when to use an envelope and which envelope to choose remain to be elucidated.

Methods

In this retrospective study, the records of 455 patients undergoing CIED implantation by a single surgeon were reviewed to identify trends in envelope use and outcomes after implantation through 12 months of follow-up. Of these patients, 165 were managed with a biologic antibacterial CIED envelope (CanGaroo®, Aziyo Biologics, Inc., Silver Spring, MD), 219 with a non-biologic envelope (Tyrx®, Medtronic Inc., Monmouth Junction, NJ), and 71 with no envelope.

Results

Most patients had two or more infection risk factors (77.9% with any envelope vs. 52.1% with no envelope; P < 0.001). Factors significantly associated with the use of an envelope included the history of heart failure, systemic anticoagulant use, the use of high-power or more complex devices, and reoperations. The overall rate of adverse events was 9.2% (n = 42). Rates of infection and hematoma were 1.8% and 2.6%, respectively. A decision tree is proposed that may aid clinical decision-making when considering CIED envelope usage.

Conclusions

There were no significant differences between groups in overall or individual adverse event rates. These data provide insight into real-world clinical decisions regarding the use of CIED envelopes and support the use of antibiotic-eluting CIED envelopes to limit infection risk in high-risk patients.

Bioengineering silk into blood vessels

The rising incidence of cardiovascular disease has increased the demand for small diameter (<6 mm) synthetic vascular grafts for use in bypass surgery. Clinically available synthetic grafts (polyethylene terephthalate and expanded polytetrafluorethylene) are incredibly strong, but also highly hydrophobic and inelastic, leading to high rates of failure when used for small diameter bypass. The poor clinical outcomes of commercial synthetic grafts in this setting have driven significant research in search of new materials that retain favourable mechanical properties but offer improved biocompatibility. Over the last several decades, silk fibroin derived from Bombyx mori silkworms has emerged as a promising biomaterial for use in vascular applications. Progress has been driven by advances in silk manufacturing practices which have allowed unprecedented control over silk strength, architecture, and the ensuing biological response. Silk can now be manufactured to mimic the mechanical properties of native arteries, rapidly recover the native endothelial cell layer lining vessels, and direct positive vascular remodelling through the regulation of local inflammatory responses. This review summarises the advances in silk purification, processing and functionalisation which have allowed the production of robust vascular grafts with promise for future clinical application.

Injectable biomaterial shuttles for cell therapy in stroke

Ischemic stroke (IS) is the leading cause of disability and contributes to a significant socio-economic cost in the western world. Brain repair strategies investigated in the pre-clinical models include the delivery of drug or cell-based therapeutics; which is hindered by the complex anatomy and functional organization of the brain. Biomaterials can be instrumental in alleviating some of these challenges by providing a structural support, localization, immunomodulation and/or modulating cellular cross-talk in the brain. This review addresses the significance of and challenges associated with cell therapy in an ischemic brain. This is followed by a detailed insight into the biomaterial-based delivery systems which have been designed to provide sustained trophic factor delivery for endogenous repair and to support transplanted cell survival and integration. A biomaterial intervention uses a multifaceted approach in enhancing the survival and engraftment of cells during transplantation and this has driven them as potential candidates for the treatment of IS. The biological processes that are activated as a response to the biomaterials and how to modulate them is one of the key factors contributing to the success of the biomaterial-based therapeutic approach. Future perspectives highlight the need of a combinative approach of merging the material design with disease biology to fabricate effective biomaterial-based intervention of stroke.

SPIONs and magnetic hybrid materials: Synthesis, toxicology and biomedical applications

In the past decades, a wide variety of different superparamagnetic iron oxide nanoparticles (SPIONs) have been synthesized. Due to their unique properties, such as big surface-to-volume ratio, superparamagnetism and comparatively low toxicity, they are principally well suited for many different technical and biomedical applications. Meanwhile, there are a numerous synthesis methods for SPIONs, but high requirements for biocompatibility have so far delayed a successful translation into the clinic. Moreover, depending on the planned application, such as for imaging, magnetic drug targeting, hyperthermia or for hybrid materials intended for regenerative medicine, specific physicochemical and biological properties are inevitable. Since a summary of all existing SPION systems, their properties and application is far too extensive, this review reports on selected methods for SPION synthesis, their biocompatibility and biomedical applications.

Review: Tissue Engineering of Small-Diameter Vascular Grafts and Their In Vivo Evaluation in Large Animals and Humans

To date, a wide range of materials, from synthetic to natural or a mixture of these, has been explored, modified, and examined as small-diameter tissue-engineered vascular grafts (SD-TEVGs) for tissue regeneration either in vitro or in vivo. However, very limited success has been achieved due to mechanical failure, thrombogenicity or intimal hyperplasia, and improvements of the SD-TEVG design are thus required. Here, in vivo studies investigating novel and relative long (10 times of the inner diameter) SD-TEVGs in large animal models and humans are identified and discussed, with emphasis on graft outcome based on model- and graft-related conditions. Only a few types of synthetic polymer-based SD-TEVGs have been evaluated in large-animal models and reflect limited success. However, some polymers, such as polycaprolactone (PCL), show favorable biocompatibility and potential to be further modified and improved in the form of hybrid grafts. Natural polymer- and cell-secreted extracellular matrix (ECM)-based SD-TEVGs tested in large animals still fail due to a weak strength or thrombogenicity. Similarly, native ECM-based SD-TEVGs and in-vitro-developed hybrid SD-TEVGs that contain xenogeneic molecules or matrix seem related to a harmful graft outcome. In contrast, allogeneic native ECM-based SD-TEVGs, in-vitro-developed hybrid SD-TEVGs with allogeneic banked human cells or isolated autologous stem cells, and in-body tissue architecture (IBTA)-based SD-TEVGs seem to be promising for the future, since they are suitable in dimension, mechanical strength, biocompatibility, and availability.

Extracellular Matrix Patches for Endarterectomy Repair

Patch repair is the preferred method for arteriotomy closure following femoral or carotid endarterectomy. Choosing among available patch options remains a clinical challenge, as current evidence suggests roughly comparable outcomes between autologous grafts and synthetic and biologic materials. Biologic patches have potential advantages over other materials, including reduced risk for infection, mitigation of an excessive foreign body response, and the potential to remodel into healthy, vascularized tissue. Here we review the use of decellularized extracellular matrix (ECM) for cardiovascular applications, particularly endarterectomy repair, and the capacity of these materials to remodel into native, site-appropriate tissues. Also presented are data from two post-market observational studies of patients undergoing iliofemoral and carotid endarterectomy patch repair as well as one histologic case report in a challenging iliofemoral endarterectomy repair, all with the use of small intestine submucosa (SIS)-ECM. In alignment with previously reported studies, high patency was maintained, and adverse event rates were comparable to previously reported rates of patch angioplasty. Histologic analysis from one case identified constructive remodeling of the SIS-ECM, consistent with the histologic characteristics of the endarterectomized vessel. These clinical and histologic results align with the biologic potential described in the academic ECM literature. To our knowledge, this is the first histologic demonstration of SIS-ECM remodeling into site-appropriate vascular tissues following endarterectomy. Together, these findings support the safety and efficacy of SIS-ECM for patch repair of femoral and carotid arteriotomy.

Pathological Changes of Adult Mitral Valves after Failed CorMatrix ECM Repair

BACKGROUND AND OBJECTIVES

CorMatrix acts as a tissue scaffold and is intended to promote the proliferation of small vessels and tissue remodeling to replicate normal tissue function.

METHODS

At Temple University Hospital, Philadelphia, PA, USA from 2013 to 2016, CorMatrix material was utilized during mitral valve anterior leaflet augmentation repair in 25 adult patients, and four patients required repeat interventions at 4-12 months (8.25 ± 4.35 months) after the initial repair. This study evaluated the pathological changes in four patients.

RESULTS

Histological examination of the CorMatrix showed matrix degradation in all cases. At 4 months after repair, mixed acute and chronic inflammatory cells that included eosinophils were visible within the matrix, which was more severe around the suture material. Later, the extent of inflammation abated and became more chronic with macrophage dominance. Some macrophages and multinucleated cells were visible deep in the matrix. The neovascularization was limited to the tissue-matrix boundary at early time points; the more mature vessels with dilated lumens extended deeper into the matrix as time increased, combined with some elongated fibroblast-like cells. In addition, marked acute and chronic inflammation with neutrophil and eosinophil infiltrate was identified in the surrounding native tissue at 4 months, especially around the suture material. Marked granulomatous inflammation was identified in all cases, with prominent multinucleated giant cells present at later time points (50%). Immunohistochemical staining for CD68 and CD163 showed prominent M2 macrophages in the CorMatrix and surrounding tissue.

CONCLUSIONS

Our results demonstrated time-dependent changes in failed CorMatrix repaired valves after mitral valve repair, with macrophages and neovascularization in the matrix 12 months after the initial repair.

Thoracic aortic surgery: status and upcoming novelties

Several novel technological developments and surgical approaches have characterized the field of aortic surgery in the recent decade. The progressive introduction of endovascular procedures, minimally invasive surgical techniques and hybrid approaches have changed the practice in aortic surgery and generated new trends and questions. Also, the advancements in the manufacturing of tissue engineered vascular grafts as substitutes for aortic replacements are enlightening new avenues in the treatment of aortic disease. This review will provide an overview of the current novel perspectives, debates and trends in major thoracic aortic surgery.

Insight on the endothelialization of small silk-based tissue-engineered vascular grafts

Along with an increased incidence of cardiovascular diseases, there is a strong need for small-diameter vascular grafts. Silk has been investigated as a biomaterial to develop such grafts thanks to different processing options. Endothelialization was shown to be extremely important to ensure graft patency and there is ongoing research on the development and behavior of endothelial cells on vascular tissue-engineered scaffolds. This article reviews the endothelialization of silk-based scaffolds processed throughout the years as silk non-woven nets, films, gel spun, electrospun, or woven scaffolds. Encouraging results were reported with these scaffolds both in vitro and in vivo when implanted in small- to middle-sized animals. The use of coatings and heparin or sulfur to enhance, respectively, cell adhesion and scaffold hemocompatibility is further presented. Bioreactors also showed their interest to improve cell adhesion and thus promoting in vitro pre-endothelialization of grafts even though they are still not systematically used. Finally, the importance of the animal models used to study the right mechanism of endothelialization is discussed.

Using CorMatrix for partial and complete (re)construction of arteriovenous fistulas in haemodialysis patients: (Re)construction of arteriovenous fistulas with CorMatrix

INTRODUCTION

CorMatrix is an acellular extracellular matrix that acts as a biological scaffold and remodels into site-specific tissue. We used it for the (re)construction of arteriovenous fistulas.

METHODS

In this prospective pilot case study, we used CorMatrix in six patients. We included patients who required vascular access reconstruction due to thrombosis of unsalvageable arteriovenous fistulas, patients with high-flow arteriovenous fistulas and patients with microvasculature in which autologous arteriovenous fistulas did not mature, requiring reconstruction with a graft. We sutured the CorMatrix plate into a tubular shape and then constructed arterial and venous anastomoses.

RESULTS

There were no periprocedural complications, CorMatrix-related infections, bleeding or limb swelling after the procedures. CorMatrix was first punctured after 8-10 weeks. In five patients, a percutaneous angioplasty due to CorMatrix stenosis was performed; in one patient, a stent was placed due to refractory stenosis. We observed eight thromboses during the observation period (four in one patient). Perianastomotic stenosis of CorMatrix and interdialytic hypotension were the causes of the thrombosis in five patients, cephalic arch stenosis in two patients and thromboembolism to the brachial artery and arteriovenous fistula in one patient. Thrombendarteriectomy was successful in 87.5% of patients, and one patient required arteriovenous fistula reconstruction. After a median observation period of 12.5 (range 4-23) months, all arteriovenous fistulas were patent, with a median brachial artery flow of 1450 (range 700-1700) mL/min.

CONCLUSION

Arteriovenous fistula (re)construction with CorMatrix seems to be feasible and safe, with a relatively high incidence of neointimal hyperplasia, predominantly at venous anastomoses, but additional clinical studies are needed.

Did aculeate silk evolve as an antifouling material?

Many of the challenges we currently face as an advanced society have been solved in unique ways by biological systems. One such challenge is developing strategies to avoid microbial infection. Social aculeates (wasps, bees and ants) mitigate the risk of infection to their colonies using a wide range of adaptations and mechanisms. These adaptations and mechanisms are reliant on intricate social structures and are energetically costly for the colony. It seems likely that these species must have had alternative and simpler mechanisms in place to ensure the maintenance of hygienic domicile conditions prior to the evolution of these complex behaviours. Features of the aculeate coiled-coil silk proteins are reminiscent of those of naturally occurring α-helical antimicrobial peptides (AMPs). In this study, we demonstrate that peptides derived from the aculeate silk proteins have antimicrobial activity. We reconstruct the predicted ancestral silk sequences of an aculeate ancestor that pre-dates the evolution of sociality and demonstrate that these ancestral sequences also contained peptides with antimicrobial properties. It is possible that the silks evolved as an antifouling material and facilitated the evolution of sociality. These materials serve as model materials for consideration in future biomaterial development.

Endothelialization mechanisms in vascular grafts

Despite the wide variety of tissue-engineered vascular grafts that are currently being developed, autologous vessels, such as the saphenous vein, are still the gold standard grafts for surgical treatment of vascular disease. Recently developed technologies have shown promising results in preclinical studies, but they still do not overcome the issues that native vessels present, and only a few have made the transition into clinical use. The endothelial lining is a key aspect for the success or failure of the grafts, especially on smaller diameter grafts (<5 mm). However, during the design and evaluation of the grafts, the mechanisms for the formation of this layer are not commonly examined. Therefore, a significant amount of established research might not be relevant to the clinical context, due to important differences that exist between the vascular regeneration mechanisms found in animal models and humans. This article reviews current knowledge about endothelialization mechanisms that have been so far identified: in vitro seeding, transanastomotic growth, transmural infiltration, and fallout endothelialization. Emphasis is placed on the models used for study of theses mechanisms and their effects on the development of tissue-engineering vascular conduits.

Bioengineered tissue solutions for repair, correction and reconstruction in cardiovascular surgery

The treatment of cardiac alterations is still nowadays a dramatic issue in the cardiosurgical practice. Synthetic materials applied in this surgery have failed in their long-term therapeutic efficacy due to low biocompatibility and compliance, especially when used in contractile sites. In order to overcome these treatment pitfalls, novel solutions have been developed based on biological tissues. Patches in pericardium, small intestinal submucosa, as well as engineered tissues of myocardium, heart valves and blood vessels have undergone a large preclinical investigation in regenerative medicine studies. Clinical translation has been started or reached by several of these new bioengineered treatment alternatives. This review will describe the preclinical and clinical experiences realized so far with the application of biological tissues in cardiovascular surgery. It will depict the progressive steps realized in the evolution of this research, as well as it will point out the challenges yet to face in order to generate the ideal biomaterial for cardiovascular repair, corrective and reconstructive surgery.

Effect of Multilaminate Small Intestinal Submucosa as a Barrier Membrane on Bone Formation in a Rabbit Mandible Defect Model

A barrier membrane (BM) is essential for guided bone regeneration (GBR) procedures. Absorbable BMs based on collagen have been widely applied clinically due to their excellent biocompatibility. The extracellular matrix (ECM) provides certain advantages that can compensate for the rapid degradation and insufficient mechanical strength of pure collagen membrane due to the porous scaffold structure. Recently, small intestinal submucosa (SIS), one of the most widely used ECM materials, has drawn much attention in bone tissue engineering. In this study, we adopted multilaminate SIS (mSIS) as a BM and evaluated its in vivo and in vitro properties. mSIS exhibited a multilaminate structure with a smooth upper surface and a significantly coarser bottom layer according to microscopic observation. Tensile strength was 13.10 ± 2.56 MPa. In in vivo experiments, we selected a rabbit mandibular defect model and subcutaneous implantation to compare osteogenesis and biodegradation properties with one of the most commonly used commercial collagen membranes. mSIS was retained for up to 3 months and demonstrated longer biodegradation time than commercial collagen membrane. Quantification of bone regeneration revealed significant differences in each group. Micro-computed tomography (micro-CT) revealed that the quantity and maturity of bones in the mSIS group were significantly higher than those in the blank control group (P < 0.05) and were similar to those in a commercial collagen membrane group (P > 0.05) at 4 and 12 weeks after surgery. Hematoxylin and eosin staining revealed large amounts of mature lamellar bone at 12 weeks in mSIS and commercial collagen membrane groups. Therefore, we conclude that mSIS has potential as a future biocompatible BM in GBR procedures.

Animal models of cardiovascular disease as test beds of bioengineered vascular grafts

The last two decades have seen many advances in regenerative medicine, including the development of tissue engineered vessels (TEVs) for replacement of damaged or diseased arteries or veins. Biomaterials from natural sources as well as synthetic polymeric materials have been employed in engineering vascular grafts. Recently, cell-free grafts have become available opening new possibilities for the next generation, off-the-shelf products. These TEVs are first tested in small or large animal models, which are usually young and healthy. However, the majority of patients in need of vascular grafts are elderly and suffer from comorbidities that may complicate their response to the implants. Therefore, it is important to evaluate TEVs in animal models of vascular disease in order to increase their predictive value and learn how the disease microenvironment may affect the patency and remodeling of vascular grafts. Small animals with various disease phenotypes are readily available due to the availability of transgenic or gene knockout technologies and can be used to address mechanistic questions related to vascular grafting. On the other hand, large animal models with similar anatomy, hematology and thrombotic responses to humans have been utilized in a preclinical setting. We propose that large animal models with certain pathologies or age range may provide more clinically relevant platforms for testing TEVs and facilitate the clinical translation of tissue engineering technologies by increasing the likelihood of success in clinical trials.

The use of decellularised animal tissue to study disseminating cancer cells

Since the establishment of cell culture, common practice has been to grow adherent cells in 2D monolayers. Although cells behave completely differently when grown in these artificial conditions, the ease of 2D culturing has meant that this practice still prevails today, and adopting conditions that more closely reflect the natural microenvironment has been met with substantial inertia. The alternative, animal models that mimic natural human physiology, are less accessible, strictly regulated and require licences and expensive facilities. Although transition from 2D to 3D cell culturing is gathering momentum, there is a clear need for alternative culturing methods that more closely resemble in vivo conditions. Here we show that decellularised organs gleaned from discarded animal carcasses are ideal biomimetic scaffolds to support secondary tumour initiation in vitro. This article describes how to decellularise tissue, perform basic histochemistry and immunofluorescence procedures for cell and matrix detection; and follows cancer cell behaviour on this matrix by way of an example. As integration into the traditional work flow is easy and inexpensive we hope this article will encourage other researchers to adopt this approach.

Enhanced Antimicrobial Effects of Decellularized Extracellular Matrix (CorMatrix) with Added Vancomycin and Gentamicin for Device Implant Protection

BACKGROUND

The incidence of cardiac implantable electronic device (CIED) infections has risen significantly over the past years. Although several devices are currently available to decrease the incidence of infection, most are made from nonviable synthetic material and are more prone to infection than vascularized tissue.

OBJECTIVE

This study was undertaken to assess the resistance to infection of the CorMatrix CanGaroo (CorMatrix Cardiovascular, Roswell, GA, USA), a CIED envelope made of decellularized extracellular matrix (ECM) hydrated in different antibiotic solutions.

METHODS

This study was comprised of two in vitro tests and one animal trial. For all the tests, the ECM was hydrated in a mixture of vancomycin (25 mg/mL) and gentamicin (20 mg/mL) or gentamicin alone (40 mg/mL). The drug elution characteristics were assessed followed by the effectiveness of CanGaroo to prevent the bacterial growth of Staphylococcus aureus and Staphylococcus epidermidis in culture. Then, the direct inoculation of pacemaker implant pockets with both Staphylococcus species was performed in rabbits implanted with either a pacemaker alone or a pacemaker with antibiotic-soaked CorMatrix ECM pouches.

RESULTS

The hydration of CanGaroo envelopes in both antibiotic mixtures resulted in antimicrobial activity against both Staphylococcus species, with an early bolus release of antibiotics followed by a slow release lasting for up to 6 days. In vivo, there was a substantial decrease in the occurrence of infection.

CONCLUSIONS

The hydration of the CanGaroo ECM with an antibiotic solution prevented Staphylococcus species growth in vitro and substantially reduced the incidence of CIED pocket infections in an in vivo rabbit model.

The pathology of the foreign body reaction against biomaterials

The healing process after implantation of biomaterials involves the interaction of many contributing factors. Besides their in vivo functionality, biomaterials also require characteristics that allow their integration into the designated tissue without eliciting an overshooting foreign body reaction (FBR). The targeted design of biomaterials with these features, thus, needs understanding of the molecular mechanisms of the FBR. Much effort has been put into research on the interaction of engineered materials and the host tissue. This elucidated many aspects of the five FBR phases, that is protein adsorption, acute inflammation, chronic inflammation, foreign body giant cell formation, and fibrous capsule formation. However, in practice, it is still difficult to predict the response against a newly designed biomaterial purely based on the knowledge of its physical-chemical surface features. This insufficient knowledge leads to a high number of factors potentially influencing the FBR, which have to be analyzed in complex animal experiments including appropriate data-based sample sizes. This review is focused on the current knowledge on the general mechanisms of the FBR against biomaterials and the influence of biomaterial surface topography and chemical and physical features on the quality and quantity of the reaction. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 927-940, 2017.

Use of a small intestine submucosa extracellular matrix patch in repeated carotid endarterectomy

Various patches have been described in the literature for patients undergoing carotid endarterectomy. In the present report, the authors present the case of a 71-year-old woman who had bilateral carotid endarterectomies 17 years earlier and greater than 80% restenosis of the right internal carotid artery. The patient underwent a repeated right carotid endarterectomy using a small intestine submucosa extracellular matrix patch for closure of the arteriotomy. Given the unique biologic properties of the small intestine submucosa patch and the technical advantages associated with its use for patch angioplasty, further studies to define its efficacy are warranted.

Mechanocompatible Polymer-Extracellular-Matrix Composites for Vascular Tissue Engineering

Small-diameter vascular grafts developed from vascular extracellular matrix (ECM) can potentially be used for bypass surgeries and other vascular reconstruction and repair procedures. The addition of heparin to the ECM improves graft hemocompatibility but often involves chemical cross-linking, which increases ECM mechanical stiffness compared to native arteries. Herein, the importance of maintaining ECM mechanocompatibility is demonstrated, and a mechanocompatible strategy to immobilize heparin onto the ECM via a biodegradable elastomer is described. Specifically, poly(1,8-octamethylene citrate)-co-cysteine is hybridized to the ECM, forming a polymer-ECM composite that allows for heparin immobilization via maleimide-thiol "click" chemistry. Heparinized composites reduce platelet adhesion by >60% in vitro, without altering the elastic modulus of the ECM. In a rat abdominal aortic interposition model, intimal hyperplasia in heparinized mechanocompatible grafts is 65% lower when compared to ECM-only control grafts at four weeks. In contrast, grafts that are heparinized with carbodiimide chemistry exhibit increased intimal hyperplasia (4.2-fold) and increased macrophage infiltration (3.5-fold) compared to ECM-only control grafts. All grafts show similar, partial endothelial cell coverage and little to no ECM remodeling. Overall, a mechanocompatible strategy to improve ECM thromboresistance is described and the importance of ECM mechanical properties for proper in vivo graft performance is highlighted.

Porcine Intestinal Submucosa (CorMatrix) for Semilunar Valve Repair in Children: A Word of Caution After Midterm Results

Surgery for congenital valve anomalies in children is a challenging topic. We aim to assess early and late functional outcomes of CorMatrix scaffold after repair of aortic and pulmonary valves (PV) in congenital heart disease in a prospective nonrandomized clinical study on children with congenital aortic (Group 1) or PV (Group 2) disease. Primary endpoints were reoperation or reintervention on semilunar valves and echocardiographic evidence of regurgitation or stenosis greater than mild. Results of PV repair in tetralogy of Fallot were compared with a control group of patients who underwent PV repair with polytetrafluoroethylene. A total of 22 consecutive selected patients with complex congenital heart disease were included: PV repair in 18 and aortic valve repair in 4. At discharge bidimensional echocardiography, semilunar valve regurgitation was mild in 50% of all patients. At a median follow-up of 23 months (4.3-51.3), reoperation for aortic valve replacement was necessary in 2; right ventricular outflow tract obstruction occurred in 3, requiring interventional treatment in 2. Pulmonary regurgitation degree worsened in most patients of Group 2 at follow up. When comparing patients with tetralogy of Fallot in Group 2 with patients who underwent PV repair with polytetrafluoroethylene, there were no significant differences in PV function at follow up. We conclude that CorMatrix scaffold for semilunar valve reconstruction does not present with significant advantages to traditional materials at mid term follow up. In addition, when used for pulmonary valve reconstruction, CorMatrix seems to show gradual functional deterioration in the mid term.

Position Paper of the European Society of Cardiology Working Group Cellular Biology of the Heart: cell-based therapies for myocardial repair and regeneration in ischemic heart disease and heart failure

Despite improvements in modern cardiovascular therapy, the morbidity and mortality of ischaemic heart disease (IHD) and heart failure (HF) remain significant in Europe and worldwide. Patients with IHD may benefit from therapies that would accelerate natural processes of postnatal collateral vessel formation and/or muscle regeneration. Here, we discuss the use of cells in the context of heart repair, and the most relevant results and current limitations from clinical trials using cell-based therapies to treat IHD and HF. We identify and discuss promising potential new therapeutic strategies that include ex vivo cell-mediated gene therapy, the use of biomaterials and cell-free therapies aimed at increasing the success rates of therapy for IHD and HF. The overall aim of this Position Paper of the ESC Working Group Cellular Biology of the Heart is to provide recommendations on how to improve the therapeutic application of cell-based therapies for cardiac regeneration and repair.

ECM hydrogel for the treatment of stroke: Characterization of the host cell infiltrate

Brain tissue loss following stroke is irreversible with current treatment modalities. The use of an acellular extracellular matrix (ECM), formulated to produce a hydrogel in situ within the cavity formed by a stroke, was investigated as a method to replace necrotic debris and promote the infiltration of host brain cells. Based on magnetic resonance imaging measurements of lesion location and volume, different concentrations of ECM (0, 1, 2, 3, 4, 8 mg/mL) were injected at a volume equal to that of the cavity (14 days post-stroke). Retention of ECM within the cavity occurred at concentrations >3 mg/mL. A significant cell infiltration into the ECM material in the lesion cavity occurred with an average of ∼36,000 cells in the 8 mg/mL concentration within 24 h. An infiltration of cells with distances of >1500 μm into the ECM hydrogel was observed, but the majority of cells were at the tissue/hydrogel boundary. Cells were typically of a microglia, macrophage, or neural and oligodendrocyte progenitor phenotype. At the 8 mg/mL concentration, ∼60% of infiltrating cells were brain-derived phenotypes and 30% being infiltrating peripheral macrophages, polarizing toward an M2-like anti-inflammatory phenotype. These results suggest that an 8 mg/mL ECM concentration promotes a significant acute endogenous repair response that could potentially be exploited to treat stroke.

Small intestinal submucosa extracellular matrix (CorMatrix®) in cardiovascular surgery: a systematic review

Extracellular matrix (ECM) derived from small intestinal submucosa (SIS) is widely used in clinical applications as a scaffold for tissue repair. Recently, CorMatrix® porcine SIS-ECM (CorMatrix Cardiovascular, Inc., Roswell, GA, USA) has gained popularity for 'next-generation' cardiovascular tissue engineering due to its ease of use, remodelling properties, lack of immunogenicity, absorbability and potential to promote native tissue growth. Here, we provide an overview of the biology of porcine SIS-ECM and systematically review the preclinical and clinical literature on its use in cardiovascular surgery. CorMatrix® has been used in a variety of cardiovascular surgical applications, and since it is the most widely used SIS-ECM, this material is the focus of this review. Since CorMatrix® is a relatively new product for cardiovascular surgery, some clinical and preclinical studies published lack systematic reporting of functional and pathological findings in sufficient numbers of subjects. There are also emerging reports to suggest that, contrary to expectations, an undesirable inflammatory response may occur in CorMatrix® implants in humans and longer-term outcomes at particular sites, such as the heart valves, may be suboptimal. Large-scale clinical studies are needed driven by robust protocols that aim to quantify the pathological process of tissue repair.

Advancing biomaterials of human origin for tissue engineering

Biomaterials have played an increasingly prominent role in the success of biomedical devices and in the development of tissue engineering, which seeks to unlock the regenerative potential innate to human tissues/organs in a state of deterioration and to restore or reestablish normal bodily function. Advances in our understanding of regenerative biomaterials and their roles in new tissue formation can potentially open a new frontier in the fast-growing field of regenerative medicine. Taking inspiration from the role and multi-component construction of native extracellular matrices (ECMs) for cell accommodation, the synthetic biomaterials produced today routinely incorporate biologically active components to define an artificial in vivo milieu with complex and dynamic interactions that foster and regulate stem cells, similar to the events occurring in a natural cellular microenvironment. The range and degree of biomaterial sophistication have also dramatically increased as more knowledge has accumulated through materials science, matrix biology and tissue engineering. However, achieving clinical translation and commercial success requires regenerative biomaterials to be not only efficacious and safe but also cost-effective and convenient for use and production. Utilizing biomaterials of human origin as building blocks for therapeutic purposes has provided a facilitated approach that closely mimics the critical aspects of natural tissue with regard to its physical and chemical properties for the orchestration of wound healing and tissue regeneration. In addition to directly using tissue transfers and transplants for repair, new applications of human-derived biomaterials are now focusing on the use of naturally occurring biomacromolecules, decellularized ECM scaffolds and autologous preparations rich in growth factors/non-expanded stem cells to either target acceleration/magnification of the body's own repair capacity or use nature's paradigms to create new tissues for restoration. In particular, there is increasing interest in separating ECMs into simplified functional domains and/or biopolymeric assemblies so that these components/constituents can be discretely exploited and manipulated for the production of bioscaffolds and new biomimetic biomaterials. Here, following an overview of tissue auto-/allo-transplantation, we discuss the recent trends and advances as well as the challenges and future directions in the evolution and application of human-derived biomaterials for reconstructive surgery and tissue engineering. In particular, we focus on an exploration of the structural, mechanical, biochemical and biological information present in native human tissue for bioengineering applications and to provide inspiration for the design of future biomaterials.

Physiological Growth, Remodeling Potential, and Preserved Function of a Novel Bioprosthetic Tricuspid Valve: Tubular Bioprosthesis Made of Small Intestinal Submucosa-Derived Extracellular Matrix

BACKGROUND

Prosthetic valves currently used in children lack the ability to grow with the patient and often require multiple reoperations. Small intestinal submucosa-derived extracellular matrix (SIS-ECM) has been used successfully as a patch for repair in various tissues, including vessels, valves, and myocardium.

OBJECTIVES

This study sought to assess the remodeling potential of a tubular tricuspid valve (TV) bioprosthesis made of SIS-ECM by evaluating its growth, structure, and function in a growing ovine model.

METHODS

A total of 12 3-month-old lambs were studied for a period of 3 or 8 months. SIS-ECM TVs were placed in 8 lambs; conventional bioprosthetic valves and native valves (NV) were studied as controls. All lambs underwent serial echocardiography, measuring annulus diameter and valve and right ventricular function.

RESULTS

The SIS-ECM valves demonstrated an incremental increase in annular diameter similar to NV. SIS-ECM valve function was normal in 7 of 8; 1 valve had severe regurgitation due to a flail leaflet. Explanted SIS-ECM valves approximated native tissue in gross appearance. Histopathology demonstrated migration of resident mesenchymal cells into the scaffold and trilaminar ECM organization similar to an NV, without inflammation or calcification at 8 months. Ex vivo mechanical testing of SIS-ECM valve tissue showed normalization of the elastic modulus by 8 months.

CONCLUSIONS

In an ovine model, tubular SIS-ECM TV bioprostheses demonstrate "growth" and a cell-matrix structure similar to mature NVs while maintaining normal valve function. The SIS-ECM valve may provide a novel solution for TV replacement in children and adults.

The Tissue-Engineered Vascular Graft-Past, Present, and Future

Cardiovascular disease is the leading cause of death worldwide, with this trend predicted to continue for the foreseeable future. Common disorders are associated with the stenosis or occlusion of blood vessels. The preferred treatment for the long-term revascularization of occluded vessels is surgery utilizing vascular grafts, such as coronary artery bypass grafting and peripheral artery bypass grafting. Currently, autologous vessels such as the saphenous vein and internal thoracic artery represent the gold standard grafts for small-diameter vessels (<6 mm), outperforming synthetic alternatives. However, these vessels are of limited availability, require invasive harvest, and are often unsuitable for use. To address this, the development of a tissue-engineered vascular graft (TEVG) has been rigorously pursued. This article reviews the current state of the art of TEVGs. The various approaches being explored to generate TEVGs are described, including scaffold-based methods (using synthetic and natural polymers), the use of decellularized natural matrices, and tissue self-assembly processes, with the results of various in vivo studies, including clinical trials, highlighted. A discussion of the key areas for further investigation, including graft cell source, mechanical properties, hemodynamics, integration, and assessment in animal models, is then presented.

Mechanotransduction in small intestinal submucosa scaffolds: fabrication parameters potentially modulate the shear-induced expression of PECAM-1 and eNOS

In small intestinal submucosa (SIS) scaffolds for functional tissue engineering, the impact of scaffold fabrication parameters on cellular response and tissue regeneration may relate to the mechanotransductory properties of the final arrangement of collagen fibres. We previously proved that two fabrication parameters, (a) preservation (P) or removal (R) of a dense collagen layer present in SIS, and (b) SIS in a final dehydrated (D) or hydrated (H) state, have an effect on the micromechanical environment of SIS. In a continuation of our studies, we herein hypothesized that these fabrication parameters also modulate early mechanotransduction in cells populating the scaffold. Mechanotransduction was investigated by seeding human umbilical vein endothelial cells (HUVECs) on scaffolds, exposing them to pulsatile shear stress (12 ± 4 dyne/cm² ) for 1 h (n = 5) in a cone-and-plate shear system, and evaluating the expression of the mechanosensitive genes Pecam1 and Enos by immunofluorescence and qPCR. Expression of mechanosensitive genes was highest in PD grafts, followed by PH and RH grafts. The RD group had similar expression to that of unsheared control cells, suggesting that the RD combination potentially reduced mechanotransduction of shear to cells. We concluded that the two fabrication parameters studied, which modify SIS micromechanics, also potentially modulated the early shear-induced expression of mechanosensitive genes in seeded HUVECs. Our findings suggest that fabrication parameters influence the outcome of SIS as a therapeutic scaffold. Copyright © 2015 John Wiley & Sons, Ltd.

Modular Small Diameter Vascular Grafts with Bioactive Functionalities

We report the fabrication of a novel type of artificial small diameter blood vessels, termed biomimetic tissue-engineered blood vessels (bTEBV), with a modular composition. They are composed of a hydrogel scaffold consisting of two negatively charged natural polymers, alginate and a modified chitosan, N,O-carboxymethyl chitosan (N,O-CMC). Into this biologically inert scaffold two biofunctionally active biopolymers are embedded, inorganic polyphosphate (polyP) and silica, as well as gelatin which exposes the cell recognition signal, Arg-Gly-Asp (RGD). These materials can be hardened by exposure to Ca(2+) through formation of Ca(2+) bridges between the polyanions, alginate, N,O-CMC, and polyP (alginate-Ca(2+)-N,O-CMC-polyP). The bTEBV are formed by pressing the hydrogel through an extruder into a hardening solution, containing Ca(2+). In this universal scaffold of the bTEBV biomaterial, polycations such as poly(L-Lys), poly(D-Lys) or a His/Gly-tagged RGD peptide (three RGD units) were incorporated, which promote the adhesion of endothelial cells to the vessel surface. The mechanical properties of the biopolymer material (alginate-Ca(2+)-N,O-CMC-polyP-silica) revealed a hardness (elastic modulus) of 475 kPa even after a short incubation period in CaCl2 solution. The material of the artificial vascular grafts (bTEBVs with an outer size 6 mm and 1.8 mm, and an inner diameter 4 mm and 0.8 mm, respectively) turned out to be durable in 4-week pulsatile flow experiments at an alternating pressure between 25 and 100 mbar (18.7 and 75.0 mm Hg). The burst pressure of the larger (smaller) vessels was 850 mbar (145 mbar). Incorporation of polycationic poly(L-Lys), poly(D-Lys), and especially the His/Gly-tagged RGD peptide, markedly increased the adhesion of human, umbilical vein/vascular endothelial cells, EA.HY926 cells, to the surface of the hydrogel. No significant effect of the polyP samples on the clotting of human plasma is measured. We propose that the metabolically degradable polymeric scaffold bTEBV is a promising biomaterial for future prosthetic vascular grafts.

Vascular replacement using a layered elastin-collagen vascular graft in a porcine model: one week patency versus one month occlusion

A persistent clinical demand exists for a suitable arterial prosthesis. In this study, a vascular conduit mimicking the native 3-layered artery, and constructed from the extracellular matrix proteins type I collagen and elastin, was evaluated for its performance as a blood vessel equivalent. A tubular 3-layered graft (elastin-collagen-collagen) was prepared using highly purified type I collagen fibrils and elastin fibers, resembling the 3-layered native blood vessel architecture. The vascular graft was crosslinked and heparinised (37 ± 4 μg heparin/mg graft), and evaluated as a vascular graft using a porcine bilateral iliac artery model. An intra-animal comparison with clinically-used heparinised ePTFE (Propaten®) was made. Analyses included biochemical characterization, duplex scanning, (immuno)histochemistry and scanning electron microscopy. The tubular graft was easy to handle with adequate suturability. Implantation resulted in pulsating grafts without leakage. One week after implantation, both ePTFE and the natural acellular graft had 100% patencies on duplex scanning. Grafts were partially endothelialised (Von Willebrand-positive endothelium with a laminin-positive basal membrane layer). After one month, layered thrombi were found in the natural (4/4) and ePTFE graft (1/4), resulting in occlusion which in case of the natural graft is likely due to the porosity of the inner elastin layer. In vivo application of a molecularly-defined tubular graft, based on nature's matrix proteins, for vascular surgery is feasible.

Crosslinking decreases the hemocompatibility of decellularized, porcine small intestinal submucosa

Decellularized tissues have been widely used as scaffolds for biomedical applications due to their presentation of adhesion peptide sequences and growth factors, which facilitate integration with surrounding tissue. One of the most commonly used decellularized tissues is derived from porcine small intestinal submucosa (SIS). In some applications, SIS is crosslinked to modulate the mechanical properties or degradation rate of the scaffold. Despite the widespread use of SIS, there has been no mechanistic characterization of blood reactions with SIS, or how crosslinking affects these reactions. Therefore, we characterized the effect of SIS and carbodiimide-crosslinked SIS (cSIS) on plasma coagulation, including targeted assessments of the intrinsic and extrinsic coagulation pathways, and thrombus formation using flowing whole blood. SIS inhibited plasma coagulation initiated by recalcification, as well as low concentrations of thrombin or tissue factor. SIS prolonged the activated partial thromboplastin time by 14.3 ± 1.54s, indicating inhibition of the intrinsic coagulation pathway. Carbodiimide crosslinking abrogated all anticoagulant effects of SIS, as did heparinase I and III treatment, suggesting that heparin and heparan sulfate are predominantly responsible for SIS anticoagulant effects. Inhibiting contact activation of the intrinsic pathway prevented cSIS-mediated coagulation. When tubular SIS devices were connected to a nonhuman primate arteriovenous shunt loop, which enables whole blood to flow across devices without the use of anticoagulants, SIS demonstrated remarkably limited platelet accumulation and fibrinogen incorporation, while cSIS initiated significantly higher platelet and fibrinogen accumulation. These results demonstrate that SIS is a thromboresistant material and crosslinking markedly reduces the hemocompatibility of SIS.

Scaffolds in vascular regeneration: current status

An ideal vascular substitute, especially in <6 mm diameter applications, is a major clinical essentiality in blood vessel replacement surgery. Blood vessels are structurally complex and functionally dynamic tissue, with minimal regeneration potential. These have composite extracellular matrix (ECM) and arrangement. The interplay between ECM components and tissue specific cells gives blood vessels their specialized functional attributes. The core of vascular tissue engineering and regeneration relies on the challenges in creating vascular conduits that match native vessels and adequately regenerate in vivo. Out of numerous vascular regeneration concerns, the relevance of ECM emphasizes much attention toward appropriate choice of scaffold material and further scaffold development strategies. The review is intended to be focused on the various approaches of scaffold materials currently in use in vascular regeneration and current state of the art. Scaffold of choice in vascular tissue engineering ranges from natural to synthetic, decellularized, and even scaffold free approach. The applicability of tubular scaffold for in vivo vascular regeneration is under active investigation. A patent conduit with an ample endothelial luminal layer that can regenerate in vivo remains an unanswered query in the field of small diameter vascular tissue engineering. Besides, scaffolds developed for vascular regeneration, should aim at providing functional substitutes for use in a regenerative approach from the laboratory bench to patient bedside.

Vascular Tissue Engineering: Recent Advances in Small Diameter Blood Vessel Regeneration

Cardiovascular diseases are the leading cause of mortality around the globe. The development of a functional and appropriate substitute for small diameter blood vessel replacement is still a challenge to overcome the main drawbacks of autografts and the inadequate performances of synthetic prostheses made of polyethylene terephthalate (PET, Dacron) and expanded polytetrafluoroethylene (ePTFE, Goretex). Therefore, vascular tissue engineering has become a promising approach for small diameter blood vessel regeneration as demonstrated by the increasing interest dedicated to this field. This review is focused on the most relevant and recent studies concerning vascular tissue engineering for small diameter blood vessel applications. Specifically, the present work reviews research on the development of tissue-engineered vascular grafts made of decellularized matrices and natural and/or biodegradable synthetic polymers and their realization without scaffold.

Tissue engineering in the vasculature

Tissue engineering holds great promise to address complications and limitations encountered with the use of traditional prosthetic materials, such as thrombogenicity, infection, and future degeneration which represent the major morbidity and mortality after device implant surgery. The general concept of tissue engineering consists of three main components: a scaffold material, a cell type for seeding the scaffold, and biochemical, physio-chemical signaling and remodeling process. This remodeling process is guided by cell signals derived from both seeded cells and host inflammatory cells that infiltrate the scaffold and deposit extracellular matrix, forming the neotissue. Vascular tissue engineering is at the forefront in the translation of this technology to clinical practice, as tissue engineered vascular grafts (TEVGs) have now been successfully implanted in children with congenital heart disease. In this report, we review the history, advances, and state of the art in TEVGs.

Preliminary experience with cardiac reconstruction using decellularized porcine extracellular matrix scaffold: human applications in congenital heart disease

An ideal material for repair of congenitally malformed hearts would encourage tissue regeneration with growth potential. Decellularized porcine small intestinal submucosa extracellular matrix (SIS-ECM) promotes tissue regeneration in animal models and noncardiac human applications. This retrospective review evaluates SIS-ECM for reconstruction of congenital heart defects. From June 2007 to May 2009, SIS-ECM patches were used in 43 operations on 40 patients aged 2 days to 13 years. In 16 cases, the SIS-ECM was used for pericardial closure. The SIS-ECM was used for cardiac or great vessel repair in 37 cases: atrial septal defect repair in 11, pulmonary arterioplasty in 10, right ventricular outflow tract patch in 6, pulmonary monocusp valve creation in 5, superior vena cava patch in 2 and aortoplasty in 2, valve leaflet augmentation in 2, and repair of unroofed coronary sinus in 1. Follow-up was complete. There were 5 deaths, all unrelated to the SIS-ECM. Mean follow-up was 7.85 months (0.5-24 months). No pericardial effusions or intracardiac or intravascular thromboses occurred related to the SIS-ECM. The patches did not shrink or calcify. Four of 5 monocusp valves were competent and none were stenotic. One patient who underwent tricuspid valve anterior leaflet augmentation with SIS-ECM required tricuspid valve replacement 4 months later for severe regurgitation following a catheter-based procedure. Explanted tissue showed resorption of the SIS-ECM, replacement with organized collagen, and re-endothelialization. Repair of congenital heart defects using SIS-ECM is feasible and safe. In valve reconstruction, this procedure shows potential for replacement by autologous tissue. Longer-term follow-up is required to assess the potential for growth.

Absence of immune responses with xenogeneic collagen and elastin

Novel tissue-engineering approaches for cardiovascular matrices based on xenogeneic extracellular matrix protein (ECMp) constituents require a detailed evaluation of their interaction with essential immune cell subsets playing a role in innate or adaptive immunity. Therefore, in this study, the effects of xenogeneic (porcine, bovine) collagen type I and elastin as the two main components of the heart valve ECM were analyzed in comparison to their human equivalents. First, their potential to induce maturation and cytokine secretion of human dendritic cells (DC) was tested by flow cytometry. Second, the influence on proliferation and cytokine release of purified human B and T cells was measured. We could demonstrate that xenogeneic collagen type I and elastin are not able to trigger the maturation of DC as verified by the lack of CD83 induction accompanied by a low tumor necrosis factor-α release. Moreover, both ECMp showed no effect on the proliferation and the interleukin-6 release of either unstimulated or prestimulated B cells. Additionally, anti-CD3-induced purified T cell proliferation and secretion of cytokines was not affected. All in vitro data verify the low immunogenicity of porcine and bovine collagen type I and elastin and favor their suitability for tissue-engineered scaffolds.

Leveraging "raw materials" as building blocks and bioactive signals in regenerative medicine

Components found within the extracellular matrix (ECM) have emerged as an essential subset of biomaterials for tissue engineering scaffolds. Collagen, glycosaminoglycans, bioceramics, and ECM-based matrices are the main categories of "raw materials" used in a wide variety of tissue engineering strategies. The advantages of raw materials include their inherent ability to create a microenvironment that contains physical, chemical, and mechanical cues similar to native tissue, which prove unmatched by synthetic biomaterials alone. Moreover, these raw materials provide a head start in the regeneration of tissues by providing building blocks to be bioresorbed and incorporated into the tissue as opposed to being biodegraded into waste products and removed. This article reviews the strategies and applications of employing raw materials as components of tissue engineering constructs. Utilizing raw materials holds the potential to provide both a scaffold and a signal, perhaps even without the addition of exogenous growth factors or cytokines. Raw materials contain endogenous proteins that may also help to improve the translational success of tissue engineering solutions to progress from laboratory bench to clinical therapies. Traditionally, the tissue engineering triad has included cells, signals, and materials. Whether raw materials represent their own new paradigm or are categorized as a bridge between signals and materials, it is clear that they have emerged as a leading strategy in regenerative medicine. The common use of raw materials in commercial products as well as their growing presence in the research community speak to their potential. However, there has heretofore not been a coordinated or organized effort to classify these approaches, and as such we recommend that the use of raw materials be introduced into the collective consciousness of our field as a recognized classification of regenerative medicine strategies.