Novel utilization of serum in tissue decellularization

Liver tissue engineering using decellularized scaffolds: Current progress, challenges, and opportunities

Liver transplantation represents the only definitive treatment for patients with end-stage liver disease. However, the shortage of liver donors provokes a dramatic gap between available grafts and patients on the waiting list. Whole liver bioengineering, an emerging field of tissue engineering, holds great potential to overcome this gap. This approach involves two main steps; the first is liver decellularization and the second is recellularization. Liver decellularization aims to remove cellular and nuclear materials from the organ, leaving behind extracellular matrices containing different structural proteins and growth factors while retaining both the vascular and biliary networks. Recellularization involves repopulating the decellularized liver with appropriate cells, theoretically from the recipient patient, to reconstruct the parenchyma, vascular tree, and biliary network. The aim of this review is to identify the major advances in decellularization and recellularization strategies and investigate obstacles for the clinical application of bioengineered liver, including immunogenicity of the designed liver extracellular matrices, the need for standardization of scaffold fabrication techniques, selection of suitable cell sources for parenchymal repopulation, vascular, and biliary tree reconstruction. In vivo transplantation models are also summarized for evaluating the functionality of bioengineered livers. Finally, the regulatory measures and future directions for confirming the safety and efficacy of bioengineered liver are also discussed. Addressing these challenges in whole liver bioengineering may offer new solutions to meet the demand for liver transplantation and improve patient outcomes.

A proposed model of xeno-keratoplasty using 3D printing and decellularization

Corneal opacity is a leading cause of vision impairment and suffering worldwide. Transplantation can effectively restore vision and reduce chronic discomfort. However, there is a considerable shortage of viable corneal graft tissues. Tissue engineering may address this issue by advancing xeno-keratoplasty as a viable alternative to conventional keratoplasty. In particular, livestock decellularization strategies offer the potential to generate bioartificial ocular prosthetics in sufficient supply to match existing and projected needs. To this end, we have examined the best practices and characterizations that have supported the current state-of-the-art driving preclinical and clinical applications. Identifying the challenges that delimit activities to supplement the donor corneal pool derived from acellular scaffolds allowed us to hypothesize a model for keratoprosthesis applications derived from livestock combining 3D printing and decellularization.

The Canine Pancreatic Extracellular Matrix in Diabetes Mellitus and Pancreatitis: Its Essential Role and Therapeutic Perspective

Diabetes mellitus and pancreatitis are common pancreatic diseases in dogs, affecting the endocrine and exocrine portions of the organ. Dogs have a significant role in the history of research related to genetic diseases, being considered potential models for the study of human diseases. This review discusses the importance of using the extracellular matrix of the canine pancreas as a model for the study of diabetes mellitus and pancreatitis, in addition to focusing on the importance of using extracellular matrix in new regenerative techniques, such as decellularization and recellularization. Unlike humans, rabbits, mice, and pigs, there are no reports in the literature characterizing the healthy pancreatic extracellular matrix in dogs, in addition to the absence of studies related to matrix components that are involved in triggering diabetes melittus and pancreatitis. The extracellular matrix plays the role of physical support for the cells and allows the regulation of various cellular processes. In this context, it has already been demonstrated that physiologic and pathologic pancreatic changes lead to ECM remodeling, highlighting the importance of an in-depth study of the changes associated with pancreatic diseases.

Decellularized extracellular matrix mediates tissue construction and regeneration

Contributing to organ formation and tissue regeneration, extracellular matrix (ECM) constituents provide tissue with three-dimensional (3D) structural integrity and cellular-function regulation. Containing the crucial traits of the cellular microenvironment, ECM substitutes mediate cell-matrix interactions to prompt stem-cell proliferation and differentiation for 3D organoid construction in vitro or tissue regeneration in vivo. However, these ECMs are often applied generically and have yet to be extensively developed for specific cell types in 3D cultures. Cultured cells also produce rich ECM, particularly stromal cells. Cellular ECM improves 3D culture development in vitro and tissue remodeling during wound healing after implantation into the host as well. Gaining better insight into ECM derived from either tissue or cells that regulate 3D tissue reconstruction or organ regeneration helps us to select, produce, and implant the most suitable ECM and thus promote 3D organoid culture and tissue remodeling for in vivo regeneration. Overall, the decellularization methodologies and tissue/cell-derived ECM as scaffolds or cellular-growth supplements used in cell propagation and differentiation for 3D tissue culture in vitro are discussed. Moreover, current preclinical applications by which ECM components modulate the wound-healing process are reviewed.

Frequently used strategies to isolate ECM proteins from human placenta and adipose tissue

BACKGROUND

The natural extracellular matrix (ECM) provides the optimal environment for cells. Many enzymatic or non-enzymatic based strategies to extract ECM proteins from tissues were published over the last years. However, every single isolation strategy reported so far is associated with specific bottlenecks. Experiment: In this study, frequently used strategies to isolate extracellular matrix (ECM) from human placenta or adipose tissue using Tris-, serum, or pepsin-based buffers were compared. The resulting ECM proteins were biochemically characterized by analysis of cellular remnants using HOECHST DNA staining, glycosaminoglycan (GAG) content by dimethylemethylene blue (DMMB), visualization of protein bands using SDS PAGE analysis combined with amino acid quantification and assessment of the pro-angiogenic profile using an angiogenesis array.

RESULTS

Tris-NaCl extracted ECM proteins showed a high heterogenic degree of extracted proteins, bioactive growth factors and GAGS, but no collagen-I. Active serum extracted ECM showed significant lower DNA remnants when compared to the Tris-NaCl isolation strategy. Pepsin-extracted ECM was rich in collagen-I and low amounts of remaining bioactive growth factors. This strategy was most effective to reduce DNA amounts when compared to the other isolation strategies. Pepsin-extracted ECM from both tissues easily gelled at 37°C, whereas the other extracted ECM strategies did not gel at 37°C (Tris-NaCl: liquid; serum: sponge).

CONCLUSIONS

All relevant characteristics (DNA residues, ECM diversity and bioactivity, shape) of the extracted ECM proteins highly depend on its isolation strategy and could still be optimized.

Interindividual heterogeneity affects the outcome of human cardiac tissue decellularization

The extracellular matrix (ECM) of engineered human cardiac tissues corresponds to simplistic biomaterials that allow tissue assembly, or animal derived off-the-shelf non-cardiac specific matrices. Decellularized ECM from human cardiac tissue could provide a means to improve the mimicry of engineered human cardiac tissues. Decellularization of cardiac tissue samples using immersion-based methods can produce acceptable cardiac ECM scaffolds; however, these protocols are mostly described for animal tissue preparations. We have tested four methods to decellularize human cardiac tissue and evaluated their efficiency in terms of cell removal and preservation of key ECM components, such as collagens and sulfated glycosaminoglycans. Extended exposure to decellularization agents, namely sodium dodecyl sulfate and Triton-X-100, was needed to significantly remove DNA content by approximately 93% in all human donors. However, the biochemical composition of decellularized tissue is affected, and the preservation of ECM architecture is donor dependent. Our results indicate that standardization of decellularization protocols for human tissue is likely unfeasible, and a compromise between cell removal and ECM preservation must be established in accordance with the scaffold's intended application. Notwithstanding, decellularized human cardiac ECM supported human induced pluripotent-derived cardiomyocyte (hiPSC-CM) attachment and retention for up to 2 weeks of culture, and promoted cell alignment and contraction, providing evidence it could be a valuable tool for cardiac tissue engineering.

Decellularized scaffold and its elicited immune response towards the host: the underlying mechanism and means of immunomodulatory modification

The immune response of the host towards a decellularized scaffold is complex. Not only can a number of immune cells influence this process, but also the characteristics, preparation and modification of the decellularized scaffold can significantly impact this reaction. Such factors can, together or alone, trigger immune cells to polarize towards either a pro-healing or pro-inflammatory direction. In this article, we have comprehensively reviewed factors which may influence the immune response of the host towards a decellularized scaffold, including the source of the biomaterial, biophysical properties or modifications of the scaffolds with bioactive peptides, drugs and cytokines. Furthermore, the underlying mechanism has also been recapitulated.

Biofabrication of tissue engineering vascular systems

Cardiovascular disease (CVD) is the leading cause of death among persons aged 65 and older in the United States and many other developed countries. Tissue engineered vascular systems (TEVS) can serve as grafts for CVD treatment and be used as in vitro model systems to examine the role of various genetic factors during the CVD progressions. Current focus in the field is to fabricate TEVS that more closely resembles the mechanical properties and extracellular matrix environment of native vessels, which depends heavily on the advance in biofabrication techniques and discovery of novel biomaterials. In this review, we outline the mechanical and biological design requirements of TEVS and explore the history and recent advances in biofabrication methods and biomaterials for tissue engineered blood vessels and microvascular systems with special focus on in vitro applications. In vitro applications of TEVS for disease modeling are discussed.

Sonication-Assisted Method for Decellularization of Human Umbilical Artery for Small-Caliber Vascular Tissue Engineering

Decellularized vascular grafts are useful for the construction of biological small-diameter tissue-engineered vascular grafts (≤6 mm). Traditional chemical decellularization requires a long treatment time, which may damage the structure and alter the mechanical properties. Decellularization using sonication is expected to solve this problem. The aim of this study was to develop an effective decellularization method using ultrasound followed by washing. Different power values of sonication at 40 kHz were tested for 2, 4, and 8 h followed by a washing procedure. The efficacy of sonication of decellularized human umbilical artery (sDHUA) was evaluated via DNA content, histological staining, mechanical properties, and biocompatibility. The sDHUAs were further implanted into rats for up to 90 days and magnetic resonance angiography (MRA) was performed for the implanted grafts. The results demonstrated that treatment of human umbilical artery (HUA) by sonication at ultrasonic power of 204 W for 4 h followed by washing for 24 h in 2% SDS buffer could eliminate more than 90% of cells and retain similar mechanical properties of the HUA. Recellularization was assessed by scanning electron microscopy (SEM), which indicated that sDHUA provided niches for human umbilical vein endothelial cells (HUVECs) to reside, indicating in vitro cytocompatibility. Further implantation tests also indicated the fitness of the sonication-treated HUA as a scaffold for small-caliber tissue engineering vascular grafts.

Incorporating a structural extracellular matrix gradient into a porcine urinary bladder matrix-based hydrogel dermal scaffold

The increasing prevalence of chronic, nonhealing wounds necessitates the investigation of full-thickness skin substitutes conducive to host integration and wound closure. Extracellular matrix (ECM)-based hydrogel scaffolds mimic the physiological matrix environment of dermal cells, thereby conferring favorable cellular adhesion, infiltration, and proliferation. However, low-concentration ECM hydrogels rapidly lose mechanical strength as they degrade, leaving them susceptible to shrinkage from fibroblast-mediated contraction. Conversely, high-concentration ECM hydrogels are typically too dense to permit nutrient diffusion and cellular migration. This study investigates the design and fabrication of a graded-concentration hydrogel composed of porcine urinary bladder matrix (UBM) as a dermal scaffold for potential use in chronic wound treatment. Our method of UBM isolation and decellularization effectively removed native DNA while preserving matrix proteins. Hydrogels composed of a range of decellularized UBM (dUBM) concentrations were characterized and used to design a three-tiered gradient hydrogel that promoted cellular activity and maintained structural integrity. The gradient dUBM hydrogel showed stability of cross-sectional area during collagenase degradation, despite considerable loss of mass. The gradient dUBM hydrogel also resisted fibroblast-mediated contraction while supporting high surface cell viability, demonstrating the mechanical support provided by denser layers of dUBM. Overall, incorporation of an ECM concentration gradient into a porcine UBM-based hydrogel scaffold capitalizes on the unique advantages of both high and low-concentration ECM hydrogels, and mitigates the structural weaknesses that have limited the efficacy of hydrogel dermal scaffolds for chronic wounds. Our gradient design shows promise for future development of stable, pro-regenerative wound scaffolds with customized architectures using 3D printing.

Re-endothelialization of non-detergent decellularized porcine vessels

Tissue engineering utilizes an interdisciplinary approach to generate constructs for the treatment and repair of diseased organs. Generation of small vessels as vascular grafts or as envisioned central vessel for vascularized constructs is still a challenge. Here, the decellularization of porcine vessels by a non-detergent based protocol was developed and investigated. Perfusion-decellularization with sodium hydroxide solution resulted in removal of cellular material throughout the whole length of the vessel while preserving structural and mechanical integrity. A re-endothelialization of the retrieved matrix with human umbilical vein endothelial cells and cardiac endothelial cells was achieved through rotation-based seeding employing a custom-made bioreactor. A confluent monolayer was detected on the entire luminal surface. Thus, a non-detergent-based decellularization method allowing the re-endothelialization of the luminal surface was developed in this study, thereby paving the way for future implementation of the resulting construct as vascular graft or as central vessel for tissue engineered constructs in need of a perfusion system with readily available anastomosis sites.

Regulation of decellularized matrix mediated immune response

The substantially growing gap between suitable donors and patients waiting for new organ transplantation has compelled tissue engineers to look for suitable patient-specific alternatives. Lately, a decellularized extracellular matrix (dECM), obtained primarily from either discarded human tissues/organs or other species, has shown great promise in the constrained availability of high-quality donor tissues. In this review, we have addressed critical gaps and often-ignored aspects of understanding the innate and adaptive immune response to the dECM. Firstly, although most of the studies claim preservation of the ECM ultrastructure, almost all methods employed for decellularization would inevitably cause a certain degree of disruption to the ECM ultrastructure and modulation in secondary conformations, which may elicit a distinct immunogenic response. Secondly, it is still a major challenge to find ways to conserve the native biochemical, structural and biomechanical cues by making a judicious decision regarding the choice of decellularization agents/techniques. We have critically analyzed various decellularization protocols and tried to find answers on various aspects such as whether the secondary structural conformation of dECM proteins would be preserved after decellularization. Thirdly, to keep the dECM ultrastructure as close to the native ECM we have raised the question "How good is good enough?" Even residual cellular antigens or nucleic acid fragments may elicit antigenicity leading to a low-grade immune response. A combinative knowledge of macrophage plasticity in the decellularized tissue and limits of decellularization will help achieve the native ultrastructure. Lastly, we have shifted our focus on the scientific basis of the presently accepted criteria for decellularization, and the effect on immune response concerning the interaction between the decellularized extracellular matrix and macrophages with the subsequent influence of T-cell activation. Amalgamating suitable decellularization approaches, sufficient knowledge of macrophage plasticity and elucidation of molecular pathways together will help fabricate functional immune informed decellularized tissues in vitro that will have substantial implications for efficient clinical translation and prediction for in vivo reprogramming and tissue regeneration.

Decellularized Extracellular Matrix-based Bioinks for Engineering Tissue- and Organ-specific Microenvironments

Biomaterials-based biofabrication methods have gained much attention in recent years. Among them, 3D cell printing is a pioneering technology to facilitate the recapitulation of unique features of complex human tissues and organs with high process flexibility and versatility. Bioinks, combinations of printable hydrogel and cells, can be utilized to create 3D cell-printed constructs. The bioactive cues of bioinks directly trigger cells to induce tissue morphogenesis. Among the various printable hydrogels, the tissue- and organ-specific decellularized extracellular matrix (dECM) can exert synergistic effects in supporting various cells at any component by facilitating specific physiological properties. In this review, we aim to discuss a new paradigm of dECM-based bioinks able to recapitulate the inherent microenvironmental niche in 3D cell-printed constructs. This review can serve as a toolbox for biomedical engineers who want to understand the beneficial characteristics of the dECM-based bioinks and a basic set of fundamental criteria for printing functional human tissues and organs.

Assessment of decellularized pericardial extracellular matrix and poly(propylene fumarate) biohybrid for small-diameter vascular graft applications

Autologous grafts are the current gold standard of care for coronary artery bypass graft surgeries, but are limited by availability and plagued by high failure rates. Similarly, tissue engineering approaches to small diameter vascular grafts using naturally derived and synthetic materials fall short, largely due to inappropriate mechanical properties. Alternatively, decellularized extracellular matrix from tissue is biocompatible and has comparable strength to vessels, while poly(propylene fumarate) (PPF) has shown promising results for vascular grafts. This study investigates the integration of decellularized pericardial extracellular matrix (dECM) and PPF to create a biohybrid scaffold (dECM+PPF) suitable for use as a small diameter vascular graft. Our method to decellularize the ECM was efficient at removing DNA content and donor variability, while preserving protein composition. PPF was characterized and added to dECM, where it acted to preserve dECM against degradative effects of collagenase without disturbing the material's overall mechanics. A transport study showed that diffusion occurs across dECM+PPF without any effect from collagenase. The modulus of dECM+PPF matched that of human coronary arteries and saphenous veins. dECM+PPF demonstrated ample circumferential stress, burst pressure, and suture retention strength to survive in vivo. An in vivo study showed re-endothelialization and tissue growth. Overall, the dECM+PPF biohybrid presents a robust solution to overcome the limitations of the current methods of treatment for small diameter vascular grafts. STATEMENT OF SIGNIFICANCE: In creating a dECM+PPF biohybrid graft, we have observed phenomena that will have a lasting impact within the scientific community. First, we found that we can reduce donor variability through decellularization, a unique use of the decellularization process. Additionally, we coupled a natural material with a synthetic polymer to capitalize on the benefits of each: the cues provided to cells and the ability to easily tune material properties, respectively. This principle can be applied to other materials in a variety of applications. Finally, we created an off-the-shelf alternative to autologous grafts with a newly developed material that has yet to be utilized in any scaffolds. Furthermore, bovine pericardium has not been investigated as a small diameter vascular graft.

Removal of an abluminal lining improves decellularization of human umbilical arteries

The decellularization of long segments of tubular tissues such as blood vessels may be improved by perfusing decellularization solution into their lumen. Particularly, transmural flow that may be introduced by the perfusion, if any, is beneficial to removing immunogenic cellular components in the vessel wall. When human umbilical arteries (HUAs) were perfused at a transmural pressure, however, very little transmural flow was observed. We hypothesized that a watertight lining at the abluminal surface of HUAs hampered the transmural flow and tested the hypothesis by subjecting the abluminal surface to enzyme digestion. Specifically, a highly viscous collagenase solution was applied onto the surface, thereby restricting the digestion to the surface. The localized digestion resulted in a water-permeable vessel without damaging the vessel wall. The presence of the abluminal lining and its successful removal were also supported by evidence from SEM, TEM, and mechanical testing. The collagenase-treated HUAs were decellularized with 1% sodium dodecyl sulfate (SDS) solution under either rotary agitation, simple perfusion, or pressurized perfusion. Regardless of decellularization conditions, the decellularization of HUAs was significantly enhanced after the abluminal lining removal. Particularly, complete removal of DNA was accomplished in 24 h by pressurized perfusion of the SDS solution. We conclude that the removal of the abluminal lining can improve the perfusion-assisted decellularization.

Development of Acellular Respiratory Mucosal Matrix Using Porcine Tracheal Mucosa

BACKGROUND

Respiratory mucosa defects result in airway obstruction and infection, requiring subsequent functional recovery of the respiratory epithelium. Because site-specific extracellular matrix (ECM) facilitates restoration of organ function by promoting cellular migration and engraftment, previous studies considered decellularized trachea an ideal ECM; however, incomplete cell removal from cartilage and mucosal-architecture destruction are frequently reported. Here, we developed a decellularization protocol and applied it to the respiratory mucosa of separated porcine tracheas.

METHODS

The trachea was divided into groups according to decellularization protocol: native mucosa, freezing-thawing (FT), FT followed by the use of Perasafe-based chemical agents before mucosal separation (wFTP), after mucosal separation (mFTP), and followed by DNase decellularization (mFTD). Decellularization efficacy was evaluated by DNA quantification and hematoxylin and eosin staining, and ECM content of the scaffold was evaluated by histologic analysis and glycosaminoglycan and collagen assays. Biocompatibility was assessed by cell-viability assay and in vivo transplantation.

RESULTS

The mFTP mucosa showed low antigenicity and maintained the ECM to form a proper microstructure. Additionally, tonsil-derived stem cells remained viable when cultured with or seeded onto mFTP mucosa, and the in vivo host response showed a constructive pattern following implantation of the mFTP scaffolds.

CONCLUSION

These results demonstrated that xenogenic acellular respiratory mucosa matrix displayed suitable biocompatibility as a scaffold material for respiratory mucosa engineering.

Allogenic Bone Graft Enriched by Periosteal Stem Cell and Growth Factors for Osteogenesis in Critical Size Bone Defect in Rabbit Model: Histopathological and Radiological Evaluation

Background & Objective:

This study aimed to investigate the effect of decellularized allogeneic bone graft enriched by periosteal stem cells (PSCs) and growth factors on the bone repair process in a rabbit model, which could be used in many orthopedic procedures.

Methods:

In this experimental study, a critical size defect (CSD) (10 mm) was created in the radial diaphysis of 40 rabbits. In group A, the defect was left intact with no medical intervention. In group B, the defect was filled by a decellularized bone graft. In group C, the defect was implanted by a decellularized bone graft enriched with platelet growth factors. In group D, the defect was treated by a decellularized bone graft seeded by periosteal mesenchymal stem cells (MSCs). Also, in group E, the defect was filled by a decellularized bone graft enriched with platelet growth factors and periosteal MSCs. Radiological evaluation was done on the first day and then in the second, fourth, and eighth weeks after the operation. The specimens were harvested on the 28th and 56th postoperative days and evaluated for histopathological criteria.

Results:

The radiologic and microscopic analysis of the healing process in bone defects of the treated groups (C, D, and E) revealed more advanced repair criteria than those of groups A and B significantly (P<0.05).

Conclusion:

Based on this study, it appears that implantation of concentrated PSCs in combination with growth factors and allogeneic cortical bone graft is an effective therapy for the repair of large bone defects.

Modular design of a tissue engineered pulsatile conduit using human induced pluripotent stem cell-derived cardiomyocytes

Single ventricle heart defects (SVDs) are congenital disorders that result in a variety of complications, including increased ventricular mechanical strain and mixing of oxygenated and deoxygenated blood, leading to heart failure without surgical intervention. Corrective surgery for SVDs are traditionally handled by the Fontan procedure, requiring a vascular conduit for completion. Although effective, current conduits are limited by their inability to aid in pumping blood into the pulmonary circulation. In this report, we propose an innovative and versatile design strategy for a tissue engineered pulsatile conduit (TEPC) to aid circulation through the pulmonary system by producing contractile force. Several design strategies were tested for production of a functional TEPC. Ultimately, we found that porcine extracellular matrix (ECM)-based engineered heart tissue (EHT) composed of human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) and primary cardiac fibroblasts (HCF) wrapped around decellularized human umbilical artery (HUA) made an efficacious basal TEPC. Importantly, the TEPCs showed effective electrical and mechanical function. Initial pressure readings from our TEPC in vitro (0.68 mmHg) displayed efficient electrical conductivity enabling them to follow electrical pacing up to a 2 Hz frequency. This work represents a proof of principle study for our current TEPC design strategy. Refinement and optimization of this promising TEPC design will lay the groundwork for testing the construct's therapeutic potential in the future. Together this work represents a progressive step toward developing an improved treatment for SVD patients. STATEMENT OF SIGNIFICANCE: Single Ventricle Cardiac defects (SVD) are a form of congenital disorder with a morbid prognosis without surgical intervention. These patients are treated through the Fontan procedure which requires vascular conduits to complete. Fontan conduits have been traditionally made from stable or biodegradable materials with no pumping activity. Here, we propose a tissue engineered pulsatile conduit (TEPC) for use in Fontan circulation to alleviate excess strain in SVD patients. In contrast to previous strategies for making a pulsatile Fontan conduit, we employ a modular design strategy that allows for the optimization of each component individually to make a standalone tissue. This work sets the foundation for an in vitro, trainable human induced pluripotent stem cell based TEPC.

The Antithrombotic Function of Sphingosine-1-Phosphate on Human Adipose-Stem-Cell-Recellularized Tissue Engineered Vascular Graft In Vitro

Adipose stem cells (ASCs) show potential in the recellularization of tissue engineerined vascular grafts (TEVGs). However, whether sphingosine-1-phosphate (S1P) could further enhance the adhesion, proliferation, and antithrombosis of ASCs on decellularized vascular scaffolds is unknown. This study investigated the effect of S1P on the recellularization of TEVGs with ASCs. Human ASCs were derived from lipoaspirate. Scaffolds were derived from human umbilical arteries (HUAs) with treatment of 0.1% sodium dodecyl sulfate (SDS) for 48 h (decellularized HUAs; DHUAs). The adhesion, proliferation, and antithrombotic functions (kinetic clotting time and platelet adhesion) of ASCs on DHUAs with S1P or without S1P were evaluated. The histology and DNA examination revealed a preserved structure and the elimination of the nuclear component more than 95% in HUAs after decellularizaiton. Human ASCs (hASCs) showed CD29(+), CD73(+), CD90(+), CD105(+), CD31(-), CD34(-), CD44(-), HLA-DR(-), and CD146(-) while S1P-treated ASCs showed marker shifting to CD31(+). In contrast to human umbilical vein endothelial cells (HUVECs), S1P didn't significantly increase proliferation of ASCs on DHUAs. However, the kinetic clotting test revealed prolonged blood clotting in S1P-treated ASC-recellularized DHUAs. S1P also decreased platelet adhesion on ASC-recellularized DHUAs. In addition, S1P treatment increased the syndecan-1 expression of ASCs. TEVG reconstituted with S1P and ASC-recellularized DHUAs showed an antithrombotic effect in vitro. The preliminary results showed that ASCs could adhere to DHUAs and S1P could increase the antithrombotic effect on ASC-recellularized DHUAs. The antithrombotic effect is related to ASCs exhibiting an endothelial-cell-like function and preventing of syndecan-1 shedding. A future animal study is warranted to prove this novel method.

Decellularization and recellularization of cornea: Progress towards a donor alternative

The global shortage of donor corneas for transplantation has led to corneal bioengineering being investigated as a method to generate transplantable tissues. Decellularized corneas are among the most promising materials for engineering corneal tissue since they replicate the complex structure and composition of real corneas. Decellularization is a process that aims to remove cells from organs or tissues resulting in a cell-free scaffold consisting of the tissues extracellular matrix. Here different decellularization techniques are described, including physical, chemical and biological methods. Analytical techniques to confirm decellularization efficiency are also discussed. Different cell sources for the recellularization of the three layers of the cornea, recellularization methods used in the literature and techniques used to assess the outcome of the implantation of such scaffolds are examined. Studies involving the application of decellularized corneas in animal models and human clinical studies are discussed. Finally, challenges for this technology are explored involving scalability, automatization and regulatory affairs.

Biocompatibility and Immunogenicity of Decellularized Allogeneic Aorta in the Orthotopic Rat Model

The generation of a small-caliber arterial graft, utilizing a large vessel of a small animal, such as the aorta of the rat or rabbit, for clinical use in the peripheral arterial tree, can widen the options for arterial prostheses. This in vivo study demonstrated the ability of the decellularization protocol that was used to produce a noncytotoxic acellular small-caliber arterial graft, with sufficient biomechanical and biological integrity to withstand the demanding flow and pressure environment of the rat aorta. This work also demonstrated the superiority of the decellularized homograft over its intact counterpart, in terms of lower immunogenicity.

Optimization of Decellularization Procedure in Rat Esophagus for Possible Development of a Tissue Engineered Construct

Background: Current esophageal treatment is associated with significant morbidity. The gold standard therapeutic strategies are stomach interposition or autografts derived from the jejunum and colon. However, severe adverse reactions, such as esophageal leakage, stenosis and infection, accompany the above treatments, which, most times, are life threating. The aim of this study was the optimization of a decellularization protocol in order to develop a proper esophageal tissue engineered construct. Methods: Rat esophagi were obtained from animals and were decellularized. The decellularization process involved the use of 3-[(3-cholamidopropyl) dimethylammonio]-1-propanesulfonate (CHAPS) and sodium dodecyl sulfate (SDS) buffers for 6 h each, followed by incubation in a serum medium. The whole process involved two decellularization cycles. Then, a histological analysis was performed. In addition, the amounts of collagen, sulphated glycosaminoglycans and DNA content were quantified. Results: The histological analysis revealed that only the first decellularization cycle was enough to produce a cellular and nuclei free esophageal scaffold with a proper extracellular matrix orientation. These results were further confirmed by biochemical quantification. Conclusions: Based on the above results, the current decellularization protocol can be applied successfully in order to produce an esophageal tissue engineered construct.

Tenogenesis of Decellularized Porcine Achilles Tendon Matrix Reseeded with Human Tenocytes in the Nude Mice Xenograft Model

Cultivation of autologous human tenocytes in a cell-free xenogenic extracellular tendon matrix (xECM) could present an approach for tendon reconstruction. The aim of this study was to achieve tendon-like tissue formation by implanting decellularized porcine Achilles tendons recellularized with human hamstring tendon-derived tenocytes into nude mice. The structure of decellularized xECM was histologically monitored before being dynamically reseeded with human tenocytes. After 6⁻12 weeks in vivo, construct quality was monitored using macroscopical and histological scoring systems, vitality assay and quantitative DNA and glycosaminoglycan (GAG) assays. For comparison to tendon xECM, a synthetic polyglycolic acid (PGA) polymer was implanted in a similar manner. Despite decellularized xECM lost some GAGs and structure, it could be recellularized in vitro with human tenocytes, but the cell distribution remained inhomogeneous, with accumulations at the margins of the constructs. In vivo, the xECM constructs revealed in contrast to the PGA no altered size, no inflammation and encapsulation and a more homogeneous cell distribution. xECM reseeded with tenocytes showed superior histological quality than cell-free implanted constructs and contained surviving human cells. Their DNA content after six and 12 weeks in vivo resembled that of native tendon and xECM recellularized in vitro. Results suggest that reseeded decellularized xECM formed a tendon-like tissue in vivo.

Effects of antigen removal on a porcine osteochondral xenograft for articular cartilage repair

Given the limited availability of fresh osteochondral allografts and uncertainty regarding performance of decellularized allografts, this study was undertaken as part of an effort to develop an osteochondral xenograft for articular cartilage repair. The purpose was to evaluate a simple antigen removal procedure based mainly on treatment with SDS and nucleases. Histology demonstrated a preservation of collagenous structure and removal of most nuclei. Immunohistochemistry revealed the apparent retention of α-Gal within osteocyte lacunae unless the tissue underwent an additional α-galactosidase processing step. Cytoplasmic protein was completely removed as shown by Western blot. Quantitatively, the antigen removal protocol was found to extract approximately 90% of DNA from cartilage and bone, and it extracted over 80% of glycosaminoglycan from cartilage. Collagen content was not affected. Mechanical testing of cartilage and bone were performed separately, in addition to testing the cartilage-bone interface, and the main effect of antigen removal was an increase in cartilage hydraulic permeability. In vivo immunogenicity was assessed by subcutaneous implantation into DBA/1 J mice, and the response was typical of a foreign body rather than immune reaction. Thus, an osteochondral xenograft produced as described has the potential for further development into a treatment for osteochondral lesions in the human knee. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 2251-2260, 2018.

* Tissue-Specific Extracellular Matrix Enhances Skeletal Muscle Precursor Cell Expansion and Differentiation for Potential Application in Cell Therapy

Skeletal muscle precursor cells (MPCs) are considered a key candidate for cell therapy in the treatment of skeletal muscle dysfunction due to injury, disease, or age. However, expansion of a sufficient number of functional skeletal muscle cells in vitro from a small tissue biopsy has been challenging due to changes in phenotypic expression of these cells under traditional culture conditions. Thus, the aim of the study was to develop a better culture system for the expansion and myo-differentiation of MPCs that could further be used for therapy. For this purpose, we developed an ideal method of tissue decellularization and compared the ability of different matrices to support MPC growth and differentiation. Porcine-derived skeletal muscle and liver and kidney extracellular matrix (ECM) were generated by decellularization methods consisting of distilled water, 0.2 mg/mL DNase, or 5% fetal bovine serum. Acellular matrices were further homogenized, dissolved, and combined with a hyaluronic acid-based hydrogel decorated with heparin (ECM-HA-HP). The cell proliferation and myogenic differentiation capacity of human MPCs were assessed when grown on gel alone, ECM, or each ECM-HA-HP substrate. Human MPC proliferation was significantly enhanced when cultured on the ECM-HA-HP substrates compared to the other substrates tested, with the greatest proliferation on the muscle ECM-HA-HP (mECM-HA-HP) substrate. The number of differentiated myotubes was significantly increased on the mECM-HA-HP substrate compared to the other gel-ECM substrates, as well as the numbers of MPCs expressing specific myogenic cell markers (i.e., myosin, desmin, myoD, and myf5). In conclusion, skeletal mECM-HA-HP as a culture substrate provided an optimal culture microenvironment potentially due to its similarity to the in vivo environment. These data suggest a potential use of skeletal muscle-derived ECM gel for the expansion and differentiation of human MPCs for cell-based therapy for skeletal muscle dysfunction.

Generation and characterisation of decellularised human corneal limbus

PURPOSE

Limbal epithelial stem cells (LESC) reside in a niche in the corneo-scleral transition zone. Deficiency leads to pain, corneal opacity, and eventually blindness. LESC transplantation of ex-vivo expanded human LESC on a carrier such as human amniotic membrane is a current treatment option. We evaluated decellularised human limbus (DHL) as a potential carrier matrix for the transplantation of LESC.

METHODS

Human corneas were obtained from the local eye bank. The limbal tissue was decellularised by sodium desoxychelate and DNase solution and sterilised by γ-irradiation. Native limbus- and DHL-surface structures were assessed by scanning electron microscopy and collagen ultrastructure using transmission electron microscopy. Presence and preservation of limbal basement membrane proteins in native limbus and DHL were analysed immunohistochemically. Absence of DNA after decellularisation was assessed by Feulgen staining and DNA quantification. Presence of immune cells was explored by CD45 staining, and potential cytotoxicity was tested using a cell viability assay.

RESULTS

In the DHL, the DNA content was reduced from 1.5 ± 0.3 μg/mg to 0.15 ± 0.01 μg/mg; the three-dimensional structure and the arrangement of the collagen fibrils were preserved. Main basement membrane proteins such as collagen IV, laminin, and fibronectin were still present after decellularisation and γ-irradiation. CD45-expressing cells were evident neither in the native limbus nor in the DHL. DHL did not convey cytotoxicity.

CONCLUSIONS

The extracellular matrix (ECM) of the limbus provides a tissue specific morphology and three-dimensionality consisting of particular ECM proteins. It therefore represents a substantial component of the stem cell niche. The DHL provides a specific limbal niche surrounding, and might serve as an easily producible carrier matrix for LESC transplantation.

Human Umbilical Vessels: Choosing the Optimal Decellularization Method

There is an increasing demand of small-diameter vascular grafts for treatment of circulatory pathologies. Decellularization offers the possibility of using human blood vessels as scaffolds to create vascular grafts. Umbilical vessels have great potential because of their availability and morphological characteristics. Various decellularization techniques have been used in umbilical vessels, but consensus on which is the most appropriate has not yet been reached. The objective of this review is to analyze the morphological and biomechanical characteristics of decellularized human umbilical arteries and veins with different techniques. Evidence indicates that the umbilical vessels are a viable option to develop small-diameter vascular grafts. Detergents are the agents most often used and with most evidence. However, further studies are needed to accurately analyze the components of the extracellular matrix and biomechanical characteristics, as well as the capacity for recellularization and in vivo functionality.

Functional liver tissue engineering by an adult mouse liver-derived neuro-glia antigen 2-expressing stem/progenitor population

Deaths due to end-stage liver diseases are increasingly registered annually in the world. Liver transplantation is the ultimate treatment for end-stage liver diseases to date, which has been hampered by a critical shortage of organs. The potential of decellularized liver scaffolds (DLS) derived from solid organs as a three-dimensional platform has been evolved as a promising approach in liver tissue engineering for translating functional liver organ replacements, but questions still exist regarding the optimal cell population for seeding in DLS and the preparation of the DLS themselves. The aim of our study was to utilize a sodium dodecyl sulfate decellularization procedure in combination with a low concentration of trypsin (0.005%)-ethylenediaminetetraacetic acid (0.002%) process to manufacture DLS from whole mouse livers and recellularized with hepatic stem/progenitors for use in liver tissue engineering and injured liver treatment. Results showed that the DLS generated with all the necessary microstructure and the extracellular components to support seeded hepatic stem/progenitor cell attachment, functional hepatic cell differentiation. Hepatic differentiation from stem/progenitor cells loaded by DLS was more efficient than that of the stem/progenitor cells in the two-dimensional cell culture model. In summary, the method of DLS loaded by hepatic stem/progenitor cells provided by this study was effective in maintaining DLS extracellular matrix to introduce seeded stem/progenitor cell differentiation, hepatic-like tissue formation and functional hepatic protein production in vitro that promoted functional recovery and survival in a mouse model of dimethylnitrosamine-induced liver cirrhosis after auxiliary heterotopic liver transplantation. Copyright © 2016 John Wiley & Sons, Ltd.

Sphingosine-1-phosphate improves endothelialization with reduction of thrombosis in recellularized human umbilical vein graft by inhibiting syndecan-1 shedding in vitro

Sphingosine-1-phosphate (S1P) has been known to promote endothelial cell (EC) proliferation and protect Syndecan-1 (SDC1) from shedding, thereby maintaining this antithrombotic signal. In the present study, we investigated the effect of S1P in the construction of a functional tissue-engineered blood vessel by using human endothelial cells and decellularized human umbilical vein (DHUV) scaffolds. Both human umbilical vein endothelial cells (HUVEC) and human cord blood derived endothelial progenitor cells (EPC) were seeded onto the scaffold with or without the S1P treatment. The efficacy of re-cellularization was determined by using the fluorescent marker CellTracker CMFDA and anti-CD31 immunostaining. The antithrombotic effect of S1P was examined by the anti-aggregation tests measuring platelet adherence and clotting time. Finally, we altered the expression of SDC1, a major glycocalyx protein on the endothelial cell surface, using MMP-7 digestion to explore its role using platelet adhesion tests in vitro. The result showed that S1P enhanced the attachment of HUVEC and EPC. Based on the anti-aggregation tests, S1P-treated HUVEC recellularized vessels when grafted showed reduced thrombus formation compared to controls. Our results also identified reduced SDC1 shedding from HUVEC responsible for inhibition of platelet adherence. However, no significant antithrombogenic effect of S1P was observed on EPC. In conclusion, S1P is an effective agent capable of decreasing thrombotic risk in engineered blood vessel grafts.

STATEMENT OF SIGNIFICANCE

Sphingosine-1phosphate (S1P) is a low molecular-weight phospholipid mediator that regulates diverse biological activities of endothelial cell, including survival, proliferation, cell barrier integrity, and also influences the development of the vascular system. Based on these characters, we the first time to use it as an additive during the process of a small caliber blood vessel construction by decellularized human umbilical vein and endothelial cell/endothelial progenitor. We further explored the function and mechanism of S1P in promoting revascularization and protection against thrombosis in this tissue engineered vascular grafts. The results showed that S1P could not only accelerate the generation but also reduce thrombus formation of small caliber blood vessel.

Cell-free vascular grafts: Recent developments and clinical potential

Recent advances in vascular tissue engineering have led to the development of cell-free grafts that are available off-the-shelf for on demand surgery. Challenges associated with cell-based technologies including cell sourcing, cell expansion and long-term bioreactor culture motivated the development of completely cell-free vascular grafts. These are based on decellularized arteries, decellularized cultured cell-based tissue engineered grafts or biomaterials functionalized with biological signals that promote in situ tissue regeneration. Clinical trials undertaken to demonstrate the applicability of these grafts are also discussed. This comprehensive review summarizes recent developments in vascular graft technologies, with potential applications in coronary artery bypass procedures, lower extremity bypass, vascular injury and trauma, congenital heart diseases and dialysis access shunts, to name a few.

Decellularization Methods for Scaffold Fabrication

Decellularization is the process of removal of native cells from tissue, leaving behind a three-dimensional (3D) ultrastructure of extracellular matrix (ECM) proteins while preserving the bioactivity and mechanics of the tissue. It offers a unique top-down approach for fabricating ECM based natural scaffold for tissue engineering application. Herein, this chapter presents the fabrication of decellularized scaffold employing different methods: whole organ perfusion, immersion and agitation, pressure gradient, and supercritical fluid. The decellularized scaffold aims to exploit the nature-designed 3D architecture, a successful platform technology, for creating scaffolding materials for tissue engineering and regenerative medicine.

Heart Valve Replacements with Regenerative Capacity

The incidence of severe valvular dysfunctions (e.g., stenosis and insufficiency) is increasing, leading to over 300,000 valves implanted worldwide yearly. Clinically used heart valve replacements lack the capacity to grow, inherently requiring repetitive and high-risk surgical interventions during childhood. The aim of this review is to present how different tissue engineering strategies can overcome these limitations, providing innovative valve replacements that proved to be able to integrate and remodel in pre-clinical experiments and to have promising results in clinical studies. Upon description of the different types of heart valve tissue engineering (e.g., in vitro, in situ, in vivo, and the pre-seeding approach) we focus on the clinical translation of this technology. In particular, we will deepen the many technical, clinical, and regulatory aspects that need to be solved to endure the clinical adaptation and the commercialization of these promising regenerative valves.

The cytoprotective capacity of processed human cardiac extracellular matrix

Freshly isolated human cardiac extracellular matrix sheets (cECM) have been shown to support stem cell proliferation and tissue-specific lineage commitment. We now developed a protocol for standardized production of durable, bio-functional hcECM microparticles and corresponding hydrogel, and tested its cytoprotective effects on contractile cells subjected to ischemia-like conditions. Human ventricular myocardium was decellularized by a 3-step protocol, including Tris/EDTA, SDS and serum incubation (cECM). Following snap-freezing and lyophilization, microparticles were created and characterized by laser diffraction, dynamic image analysis (DIA), and mass spectrometry. Moreover, cECM hydrogel was produced by pepsin digestion. Baseline cell-support characteristics were determined using murine HL-1 cardiomyocytes, and the cytoprotective effects of ECM products were tested under hypoxia and glucose/serum deprivation. In cECM, glycoproteins (thrombospondin 1, fibronectin, collagens and nidogen-1) and proteoglycans (dermatopontin, lumican and mimecan) were preserved, but residual intracellular and blood-borne proteins were also detected. The median particle feret diameter was 66 μm (15-157 μm) by laser diffraction, and 57 μm (20-182 μm) by DIA with crystal violet staining. HL-1 cells displayed enhanced metabolic activity (39 ± 12 %, P < 0.05) and proliferation (16 ± 3 %, P < 0.05) when grown on cECM microparticles in normoxia. During simulated ischemia, cECM microparticles exerted distinct cytoprotective effects (MTS conversion, 240 ± 32 %; BrdU uptake, 45 ± 14 %; LDH release, -72 ± 7 %; P < 0.01, each). When cECM microparticles were solubilized to form a hydrogel, the cytoprotective effect was initially abolished. However, modifying the preparation process (pepsin digestion at pH 2 and 25 °C, 1 mg/ml final cECM concentration) restored the cytoprotective cECM activity. Extracellular matrix from human myocardium can be processed to yield standardized durable microparticles that exert specific cytoprotective effects on cardiomyocyte-like cells. The use of processed cECM may help to optimize future clinical-grade myocardial tissue engineering approaches.

Biocompatibility evaluation of tissue-engineered decellularized scaffolds for biomedical application

Biomaterials based on seeding of cells on decellularized scaffolds have gained increasing interest in the last few years and suggested to serve as an alternative approach to bioengineer artificial organs and tissues for transplantation. The reaction of the host toward the decellularized scaffold and transplanted cells depends on the biocompatibility of the construct. Before proceeding to the clinical application step of decellularized scaffolds, it is greatly important to apply a number of biocompatibility tests in vitro and in vivo. This review describes the different methodology involved in cytotoxicity, pathogenicity, immunogenicity and biodegradability testing for evaluating the biocompatibility of various decellularized matrices obtained from human or animals.

Kidney bioengineering in regenerative medicine: An emerging therapy for kidney disease

The prevalence of end-stage renal disease is emerging as a serious worldwide public health problem because of the shortage of donor organs and the need to take lifelong immunosuppressive medication in patients who receive a transplanted kidney. Recently, tissue bioengineering of decellularization and recellularization scaffolds has emerged as a novel strategy for organ regeneration, and we review the critical technologies supporting these methods. We present a summary of factors associated with experimental protocols that may shed light on the future development of kidney bioengineering and we discuss the cell sources and bioreactor techniques applied to the recellularization process. Finally, we review some artificial renal engineering technologies and their future prospects, such as kidney on a chip and the application of three-dimensional and four-dimensional printing in kidney tissue engineering.

Decellularized biological matrices: an interesting approach for cardiovascular tissue repair and regeneration

The repair and replacement of blood vessels is one of the most challenging topics for biomedical research. Autologous vessels are preferred as graft materials, but they still have many issues to overcome: for instance, they need multiple surgical procedures and often patients may not have healthy and surgically valuable arteries useful as an autograft. A tissue-engineering approach is widely desirable to generate biological vascular prostheses. Recently, decellularization of native tissue has gained significant attention in the biomedical research field. This method is used to obtain biological scaffolds that are expected to maintain the complex three-dimensional structure of the extracellular matrix, preserving the biomechanical properties of the native tissues. The decellularizing methods and the biomechanical characteristics of these products are presented in this review. Decellularization of biological matrices induces the loss of major histocompatibility complex (MHC), which is expected to promote an immunological response by the host. All the studies showed that decellularized biomaterials possess adequate properties for xenografting. Concerning their mechanical properties, several studies have demonstrated that, although chemical decellularization methods do not affect the scaffolds' mechanical properties, these materials can be modified through different treatments in order to provide the desired mechanical characteristics, depending on the specific application. A short overview of legislative issues concerning the use of decellularized substitutes and future perspectives in surgical applications is also presented. Copyright © 2015 John Wiley & Sons, Ltd.

Production of decellularized porcine lung scaffolds for use in tissue engineering

There is a growing body of work dedicated to producing acellular lung scaffolds for use in regenerative medicine by decellularizing donor lungs of various species. These scaffolds typically undergo substantial matrix damage due to the harsh conditions required to remove cellular material (e.g., high pH, strong detergents), lengthy processing times, or pre-existing tissue contamination from microbial colonization. In this work, a new decellularization technique is described that maintains the global tissue architecture, key matrix components, mechanical composition and cell-seeding potential of lung tissue while effectively removing resident cellular material. Acellular lung scaffolds were produced from native porcine lungs using a combination of Triton X-100 and sodium deoxycholate (SDC) at low concentrations in 24 hours. We assessed the effect of matrix decellularization by measuring residual DNA, biochemical composition, mechanical characteristics, tissue architecture, and recellularization capacity.

A novel technique for simultaneous whole-body and multi-organ decellularization: umbilical artery catheterization as a perfusion-based method in a sheep foetus model

The aim of this study was to develop a method to generate multi-organ acellular matrices. Using a foetal sheep model have developed a method of systemic pulsatile perfusion via the umbilical artery which allows for simultaneous multi-organ decellularization. Twenty sheep foetuses were systemically perfused with Triton X-100 and sodium dodecyl sulphate. Following completion of the whole-body decellularization, multiple biopsy samples were taken from different parts of 21 organs to ascertain complete cell component removal in the preserved extracellular matrices. Both the natural and decellularized organs were subjected to several examinations. The samples were obtained from the skin, eye, ear, nose, throat, cardiovascular, respiratory, gastrointestinal, urinary, musculoskeletal, central nervous and peripheral nervous systems. The histological results depicted well-preserved extracellular matrix (ECM) integrity and intact vascular structures, without any evidence of residual cellular materials, in all decellularized bioscaffolds. Scanning electron microscope (SEM) and biochemical properties remained intact, similar to their age-matched native counterparts. Preservation of the collagen structure was evaluated by a hydroxyproline assay. Dense organs such as bone and muscle were also completely decellularized, with a preserved ECM structure. Thus, as shown in this study, several organs and different tissues were decellularized using a perfusion-based method, which has not been previously accomplished. Given the technical challenges that exist for the efficient generation of biological scaffolds, the current results may pave the way for obtaining a variety of decellularized scaffolds from a single donor. In this study, there have been unique responses to the single acellularization protocol in foetuses, which may reflect the homogeneity of tissues and organs in the developing foetal body.

Development of decellularized scaffolds for stem cell-driven tissue engineering

Organ transplantation is an effective treatment for chronic organ dysfunctioning conditions. However, a dearth of available donor organs for transplantation leads to the death of numerous patients waiting for a suitable organ donor. The potential of decellularized scaffolds, derived from native tissues or organs in the form of scaffolds has been evolved as a promising approach in tissue-regenerative medicine for translating functional organ replacements. In recent years, donor organs, such as heart, liver, lung and kidneys, have been reported to provide acellular extracellular matrix (ECM)-based scaffolds through the process called 'decellularization' and proved to show the potential of recellularization with selected cell populations, particularly with stem cells. In fact, decellularized stem cell matrix (DSCM) has also emerged as a potent biological scaffold for controlling stem cell fate and function during tissue organization. Despite the proven potential of decellularized scaffolds in tissue engineering, the molecular mechanism responsible for stem cell interactions with decellularized scaffolds is still unclear. Stem cells interact with, and respond to, various signals/cues emanating from their ECM. The ability to harness the regenerative potential of stem cells via decellularized ECM-based scaffolds has promising implications for tissue-regenerative medicine. Keeping these points in view, this article reviews the current status of decellularized scaffolds for stem cells, with particular focus on: (a) concept and various methods of decellularization; (b) interaction of stem cells with decellularized scaffolds; (c) current recellularization strategies, with associated challenges; and (iv) applications of the decellularized scaffolds in stem cell-driven tissue engineering and regenerative medicine. Copyright © 2015 John Wiley & Sons, Ltd.

Mechanical properties of endothelialized fibroblast-derived vascular scaffolds stimulated in a bioreactor

There is an ongoing clinical need for tissue-engineered small-diameter (<6mm) vascular grafts since clinical applications are restricted by the limited availability of autologous living grafts or the lack of suitability of synthetic grafts. The present study uses our self-assembly approach to produce a fibroblast-derived decellularized vascular scaffold that can then be available off-the-shelf. Briefly, scaffolds were produced using human dermal fibroblasts sheets rolled around a mandrel, maintained in culture to allow for the formation of cohesive and three-dimensional tubular constructs, and then decellularized by immersion in deionized water. Constructs were then endothelialized and perfused for 1week in an appropriate bioreactor. Mechanical testing results showed that the decellularization process did not influence the resistance of the tissue and an increase in ultimate tensile strength was observed following the perfusion of the construct in the bioreactor. These fibroblast-derived vascular scaffolds could be stored and later used to deliver readily implantable grafts within 4weeks including an autologous endothelial cell isolation and seeding process. This technology could greatly accelerate the clinical availability of tissue-engineered blood vessels.

Stem cells with decellularized liver scaffolds in liver regeneration and their potential clinical applications

End-stage hepatic failure is a potentially life-threatening condition for which orthotopic liver transplantation (OLT) is the only effective treatment. However, a shortage of available donor organs for transplantation each year results in the death of many patients waiting for liver transplantation. Cell-based therapies and hepatic tissue engineering have been considered as alternatives to liver transplantation. However, primary hepatocyte transplantation has rarely produced therapeutic effects because mature hepatocytes cannot be effectively expanded in vitro, and the availability of hepatocytes is often limited by shortages of donor organs. Decellularization is an attractive technique for scaffold preparation in stem cell-based liver engineering, as the resulting material can potentially retain the liver architecture, native vessel network and specific extracellular matrix (ECM). Thus, the reconstruction of functional and practical liver tissue using decellularized scaffolds becomes possible. This review focuses on the current understanding of liver tissue engineering, whole-organ liver decellularization techniques, cell sources for recellularization and potential clinical applications and challenges.

Evaluation of decellularization in umbilical cord artery

Major achievements in creating decellularized whole tissue scaffolds have drawn considerable attention to decellularization as a promising approach for tissue engineering. Developing a tissue-engineered small-diameter (≤2 mm) vascular graft, using decellularized human umbilical arteries (hUAs), for reconstructive surgery is a challenging task. Polymers used in the past, proved unsuitable due to serious adverse effects and autologous vessels are available only in 40% of patients. In this study, histological and proteomic analysis was performed to evaluate the efficiency of two decellularization protocols. In decellularization protocol A, hUAs were incubated in 3-[(3-cholamidopropyl) dimethylammonio]-1-propanesulfonate (CHAPS) and sodium dodecyl sulfate (SDS) followed by incubation in alpha minimal essential medium (α-MEM) with foetal bovine serum (FBS) while in decellularization protocol B the hUAs were incubated in Hypotonic Tris and SDS followed by incubation in nuclease solution. Histological analysis of decelullarised hUA with both protocols revealed good preservation of extracellular cell matrix (ECM) proteins and immunofluorescent staining detected collagen I and fibronectin. The DNA content within the hUAs after decellularization with protocol A was 6.2% and with protocol B 17.3%. Proteomic analysis identified cytoplasmic enzymes such as, dehydrogenase X, α-enolase and peptidyl-prolyl cis-trans isomerase A only in native samples, while, cytoskeletal proteins such as a-actin, filamin and ECM proteins like collagens were found both in native and decellularised hUA. In conclusion, both decellularization protocols effectively removed the cellular material while the ECM remained intact. Future studies are warranted to elucidate the specific effects of altered structure-function relationships on the overall fate of decellularized hUAs.

Strategies and processes to decellularize and recellularize hearts to generate functional organs and reduce the risk of thrombosis

Heart failure is one of the leading causes of death in the United States. Current therapies, such as heart transplants and bioartificial hearts, are helpful, but not optimal. Decellularization of porcine whole hearts followed by recellularization with patient-specific human cells may provide the ultimate solution for patients with heart failure. Great progress has been made in the development of efficient processes for decellularization, and the design of automated bioreactors. Challenges remain in selecting and culturing cells, growing the cells on the decellularized scaffolds without contamination, characterizing the regenerated organs, and preventing thrombosis. Various strategies have been proposed to prevent thrombosis of blood-contacting devices, including reendothelization and the creation of nonfouling surfaces using surface modification technologies. This review discusses the progress and remaining challenges involved with recellularizing whole hearts, focusing on the prevention of thrombosis.