Decellularized kidney matrix for perfused bone engineering

Effect of different decellularization protocols on reendothelialization with human cells for a perfused renal bioscaffold of the rat

BACKGROUND

Scaffolds for tissue engineering can be received by whole organ decellularization while maintaining the site-specific extracellular matrix and the vascular tree. One among other decellularization techniques is the perfusion-based method using specific agents e.g. SDS for the elimination of cellular components. While SDS can disrupt the composition of the extracellular matrix and impair the adherence and growth of site-specific cells there are indications that xenogeneic cell types may benefit from protein denaturation by using higher detergent concentrations. The aim of this work is to investigate the effect of two different SDS-concentrations (i.e. 0.66% and 3%) on the ability of human endothelial cells to adhere and proliferate in an acellular rat kidney scaffold.

MATERIAL AND METHODS

Acellular rat kidney scaffold was obtained by perfusion-based decellularization through the renal artery using a standardized protocol including SDS at concentrations of 0.66% or 3%. Subsequently cell seeding was performed with human immortalized endothelial cells EA.hy 926 via the renal artery. Recellularized kidneys were harvested after five days of pressure-controlled dynamic culture followed sectioning, histochemical and immunohistochemical staining as well as semiquantitative analysis.

RESULTS

Efficacy of decellularization was verified by absence of cellular components as well as preservation of ultrastructure and adhesive proteins of the extracellular matrix. In semiquantitative analysis of recellularization, cell count after five days of dynamic culture more than doubled when using the gentle decellularization protocol with a concentration of SDS at 0.66% compared to 3%. Detectable cells maintained their endothelial phenotype and presented proliferative behavior while only a negligible fraction underwent apoptosis.

CONCLUSION

Recellularization of acellular kidney scaffold with endothelial cells EA.hy 926 seeded through the renal artery benefits from gentle decellularization procedure. Because of that, decellularization with a SDS concentration at 0.66% should be preferred in further studies and coculture experiments.

Effects of chemical and physical methods on decellularization of murine skeletal muscles

Volumetric muscle loss causes functional weakness and is often treated with muscle grafts or implant of biomaterials. Extracellular matrices, obtained through tissue decellularization, have been widely used as biological biomaterials in tissue engineering. Optimal decellularization method varies among tissues and have significant impact on the quality of the matrix. This study aimed at comparing the efficacy of four protocols, that varied according to the temperature of tissue storage and the sequence of chemical reagents, to decellularize murine skeletal muscles. Tibialis anterior muscles were harvested from rats and were frozen at -20°C or stored at room temperature, followed by decellularization in solutions containing EDTA + Tris, SDS and Triton X-100, applied in different sequences. Samples were analyzed for macroscopic aspects, cell removal, decrease of DNA content, preservation of proteins and three-dimensional structure of the matrices. Processing protocols that started with incubation in SDS solution optimized removal of cells and DNA content and preserved the matrix ultrastructure and composition, compared to those that were initiated with EDTA + Tris. Freezing the samples before decellularization favored cell removal, regardless of the sequence of chemical reagents. Thus, to freeze skeletal muscles and to start decellularization with 1% SDS solution showed the best results.

The Renal Extracellular Matrix as a Supportive Scaffold for Kidney Tissue Engineering: Progress and Future Considerations

During the past decades, diverse methods have been used toward renal tissue engineering in order to replace renal function. The goals of all these techniques included the recapitulation of renal filtration, re-absorptive, and secretary functions, and replacement of endocrine/metabolic activities. It is also imperative to develop a reliable, up scalable, and timely manufacturing process. Decellularization of the kidney with intact ECM is crucial for in-vivo compatibility and targeted clinical application. Contemporarily there is an increasing interest and research in the field of regenerative medicine including stem cell therapy and tissue bioengineering in search for new and reproducible sources of kidneys. In this chapter, we sought to determine the most effective method of renal decellularization and recellularization with emphasis on biologic composition and support of stem cell growth. Current barriers and limitations of bioengineered strategies will be also discussed, and strategies to overcome these are suggested.

Designing a novel vacuum aspiration system to decellularize large-size enthesis with preservation of physicochemical and biological properties

Background

Functional and rapid enthesis regeneration remains a challenge after arthroscopic rotator cuff (RC) repair. Tissue-engineering a large-size biomimetic scaffold may be an adjuvant strategy to improve this clinical dilemma. Herein, we developed an optimized protocol to decellularize large-size enthesis as scaffolds for augmenting RC tear.

Methods

A novel vacuum aspiration system (VAS) was set up, which can provide a negative pressure to suck out cellular substances from tissue blocks without using chemical detergents. Large-size enthesis tissue specimens were harvested from canine infraspinatus tendon (IT) insertion, and then decellularized with an optimized protocol [freeze-thaw processing followed by nuclease digestion and phosphate buffer saline (PBS) rinsing in the custom-designed VAS], or a conventional protocol (freeze-thaw processing followed by nuclease digestion and PBS rinsing), thus fabricating two kinds of acellular enthesis matrix (AEM), namely C-AEM and O-AEM. After that, the C-AEM and O-AEM were comparatively evaluated from the aspect of their physicochemical and biological properties.

Results

Physiochemically, the O-AEM preserved the morphologies, ingredients, and tensile properties much better than the C-AEM. Biologically, in vitro studies demonstrated that both C-AEM and O-AEM show no cytotoxicity and low immunogenicity, which could promote stem cells attachment and proliferation. Interestingly, O-AEM showed better region-specific inducibility on the interacted stem cell down osteogenic, chondrogenic and tenogenic lineages compared with C-AEM. Additionally, using a canine IT repair model, the injured enthesis patched with O-AEM showed a significant improvement compared with the injured enthesis patched with C-AEM or direct suture histologically.

Conclusions

The proposed VAS may help us fabricate large-size AEM with good physicochemical and biological properties, and this AEM may have potential clinical applications in patching large/massive RC tear.

Bioinspired 3D porous human placental derived extracellular matrix/silk fibroin sponges for accelerated bone regeneration

Critical bone defects arising from traumatic injury and diseases are of major health concern since they are unable to heal spontaneously without clinical intervention. In this context, bone tissue engineering provides an attractive approach to treat bone defects by providing a bioactive template which has the potential to guide osseous tissue regeneration. In this study, porous hybrid placental extracellular matrix sponge (PIMS) was fabricated by a combinatorial method using silk fibroin (SF)/placental derived extracellular matrix and subsequently evaluated its efficacy towards bone tissue regeneration. The presence of intrinsic growth factors was evidenced by immunoblotting of the extracted proteins derived from the placental derived extracellular matrix. This growth factor rich PIMS lends a unique bioactive scaffolding to human amniotic mesenchymal stem cells (HAMSCs) which supported enhanced proliferation as well as superior osteogenic differentiation. Gene expression studies demonstrated significant up-regulation of osteogenic related genes in the PIMS group. PIMS when implanted in the chick chorioallantoic membrane, significantly attracted allantoic vessels revealing its potential to stimulate angiogenesis ex vivo. Furthermore, no severe immune response to the host was observed on subcutaneous implantation of PIMS in vivo. Instead, it supported the formation of blood vessels, revealing its outstanding biocompatibility. Additionally, critical tibial defects treated with PIMS demonstrated higher bone volume after six weeks when analyzed by micro-CT, which was accompanied by high mineral density. Histological and immunofluorescence studies validated the results and revealed enhanced osseous tissue regeneration after six weeks of surgery. All these findings recapitulated that the growth factors incorporated bioactive PIMS could perform as an appropriate matrix for osteogenic differentiation and efficient bone regeneration.

Recreating Physiological Environments In Vitro: Design Rules for Microfluidic-Based Vascularized Tissue Constructs

Vascularization of engineered tissue constructs remains one of the greatest unmet challenges to mimicking the native tissue microenvironment in vitro. The main obstacle is recapitulating the complexity of the physiological environment while providing simplicity in operation and manipulation of the model. Microfluidic technology has emerged as a promising tool that enables perfusion of the tissue constructs through engineered vasculatures and precise control of the vascular microenvironment cues in vitro. The tunable microenvironment includes i) biochemical cues such as coculture, supporting matrix, and growth factors and ii) engineering aspects such as vasculature engineering methods, fluid flow, and shear stress. In this systematic review, the design considerations of the microfluidic-based in vitro model are discussed, with an emphasis on microenvironment control to enhance the development of next-generation vascularized engineered tissues.

Extracellular Matrix-Based Biomaterials and Their Influence Upon Cell Behavior

Biologic scaffold materials composed of allogeneic or xenogeneic extracellular matrix (ECM) are commonly used for the repair and remodeling of injured tissue. The clinical outcomes associated with implantation of ECM-based materials range from unacceptable to excellent. The variable clinical results are largely due to differences in the preparation of the material, including characteristics of the source tissue, the method and efficacy of decellularization, and post-decellularization processing steps. The mechanisms by which ECM scaffolds promote constructive tissue remodeling include mechanical support, degradation and release of bioactive molecules, recruitment and differentiation of endogenous stem/progenitor cells, and modulation of the immune response toward an anti-inflammatory phenotype. The methods of ECM preparation and the impact of these methods on the quality of the final product are described herein. Examples of favorable cellular responses of immune and stem cells associated with constructive tissue remodeling of ECM bioscaffolds are described.

Recent Advances in Scaffold Design and Material for Vascularized Tissue-Engineered Bone Regeneration

Bone tissue is a highly vascularized tissue and concomitant development of the vascular system and mineralized matrix requires a synergistic interaction between osteogenesis and angioblasts. Several strategies have been applied to achieve vascularized tissue-engineered bone, including the addition of cytokines as well as pre-vascularization strategies and co-culture systems. However, the scaffold is another extremely important component to consider, and development of vascularized bone scaffolds remains one of the greatest challenges for engineering clinically relevant bone substitutes. Here, this review highlights the biomaterial selection, preparation of pre-vascularized scaffolds, composition modification of the scaffold, structural design, and the comprehensive use of the above synergistic modifications of scaffold materials for vascular scaffolds in bone tissue engineering. Moreover, a strategy is proposed for the design of future scaffold structures, in which promoting the regeneration of vascularized bone by regulating the microenvironment should be the main focus. This overview can help illuminate progress in this field and identify the most recently developed scaffolds that show the greatest potential for achieving clinically vascularized bone.

Harnessing neurovascular interaction to guide axon growth

Regulating the intrinsic interactions between blood vessels and nerve cells has the potential to enhance repair and regeneration of the central nervous system. Here, we evaluate the efficacy of aligned microvessels to induce and control directional axon growth from neural progenitor cells in vitro and host axons in a rat spinal cord injury model. Interstitial fluid flow aligned microvessels generated from co-cultures of cerebral-derived endothelial cells and pericytes in a three-dimensional scaffold. The endothelial barrier function was evaluated by immunostaining for tight junction proteins and quantifying the permeability coefficient (~10⁻⁷ cm/s). Addition of neural progenitor cells to the co-culture resulted in the extension of Tuj-positive axons in the direction of the microvessels. To validate these findings in vivo, scaffolds were transplanted into an acute spinal cord hemisection injury with microvessels aligned with the rostral-caudal direction. At three weeks post-surgery, sagittal sections indicated close alignment between the host axons and the transplanted microvessels. Overall, this work demonstrates the efficacy of exploiting neurovascular interaction to direct axon growth in the injured spinal cord and the potential to use this strategy to facilitate central nervous system regeneration.

Bioengineering Organs for Blood Detoxification

For patients with severe kidney or liver failure the best solution is currently organ transplantation. However, not all patients are eligible for transplantation and due to limited organ availability, most patients are currently treated with therapies using artificial kidney and artificial liver devices. These therapies, despite their relative success in preserving the patients' life, have important limitations since they can only replace part of the natural kidney or liver functions. As blood detoxification (and other functions) in these highly perfused organs is achieved by specialized cells, it seems relevant to review the approaches leading to bioengineered organs fulfilling most of the native organ functions. There, the culture of cells of specific phenotypes on adapted scaffolds that can be perfused takes place. In this review paper, first the functions of kidney and liver organs are briefly described. Then artificial kidney/liver devices, bioartificial kidney devices, and bioartificial liver devices are focused on, as well as biohybrid constructs obtained by decellularization and recellularization of animal organs. For all organs, a thorough overview of the literature is given and the perspectives for their application in the clinic are discussed.

Biomarkers for tissue engineering of the tendon-bone interface

The tendon-bone interface (enthesis) is a highly sophisticated biomaterial junction that allows stress transfer between mechanically dissimilar materials. The enthesis encounters very high mechanical demands and the regenerative capacity is very low resulting in high rupture recurrence rates after surgery. Tissue engineering offers the potential to recover the functional integrity of entheses. However, recent enthesis tissue engineering approaches have been limited by the lack of knowledge about the cells present at this interface. Here we investigated the cellular differentiation of enthesis cells and compared the cellular pattern of enthesis cells to tendon and cartilage cells in a next generation sequencing transcriptome study. We integrated the transcriptome data with proteome data of a previous study to identify biomarkers of enthesis cell differentiation. Transcriptomics detected 34468 transcripts in total in enthesis, tendon, and cartilage. Transcriptome comparisons revealed 3980 differentially regulated candidates for enthesis and tendon, 395 for enthesis and cartilage, and 946 for cartilage and tendon. An asymmetric distribution of enriched genes was observed in enthesis and cartilage transcriptome comparison suggesting that enthesis cells are more chondrocyte-like than tenocyte-like. Integrative analysis of transcriptome and proteome data identified ten enthesis biomarkers and six tendon biomarkers. The observed gene expression characteristics and differentiation markers shed light into the nature of the cells present at the enthesis. The presented markers will foster enthesis tissue engineering approaches by setting a bench-mark for differentiation of seeded cells towards a physiologically relevant phenotype.

Engineering a microcirculation for perfusion control of ex vivo-assembled organ systems: Challenges and opportunities

Donor organ shortage remains a clear problem for many end-stage organ patients around the world. The number of available donor organs pales in comparison with the number of patients in need of these organs. The field of tissue engineering proposes a plausible solution. Using stem cells, a patient's autologous cells, or allografted cells to seed-engineered scaffolds, tissue-engineered constructs can effectively supplement the donor pool and bypass other problems that arise when using donor organs, such as who receives the organ first and whether donor organ rejection may occur. However, current research methods and technologies have been unable to successfully engineer and vascularize large volume tissue constructs. This review examines the current perfusion methods for ex vivo organ systems, defines the different types of vascularization in organs, explores various strategies to vascularize ex vivo organ systems, and discusses challenges and opportunities for the field of tissue engineering.

Optimized protocol for whole organ decellularization

BACKGROUND

The idea of tissue decellularization to gain matrices for tissue engineering is promising. The aim of the present study is to establish a safe and reproducible protocol for solid tissue decellularization that prevents the architecture of the matrix with the inherent vascular network.

METHODS

The study was performed in rat kidneys which were decellularized by a SDS-based perfusion protocol. Perfusion time and SDS concentration were systematically changed to obtain the shortest and most gentle protocol that leads to complete decellularization.

RESULTS

We investigated kinetics of protein elution, decellularization success, and remaining cell toxicity. This resulted in a reproducible protocol, leading to safe decellularization with prevention of the inherent vascular network, without remaining detectable cell toxicity. The established protocol leads to solid tissue decellularization in only 7 h, which is by far shorter than the previously published methods.

CONCLUSION

The established technique has the potential to become a relevant platform technology for tissue engineering of solid tissues. It provides a solution for the yet-unsolved problem of vascularization.

Towards a Bioengineered Kidney: Recellularization Strategies for Decellularized Native Kidney Scaffolds

Patients with end-stage renal disease often undergo dialysis as a partial substitute for kidney function while waiting for their only treatment option: a kidney transplant. Several research directions emerged for alternatives in support of the ever-growing numbers of patients. Recent years brought big steps forward in the field, with researchers questioning and improving the current dialysis devices as well as moving towards the design of a bioengineered kidney. Whole-organ engineering is also being explored as a possibility, making use of animal or human kidney scaffolds for engineering a transplantable organ. While this is not a new strategy, having been applied so far for thin tissues, it is a novel approach for complex organs such as the kidneys. Kidneys can be decellularized and the remaining scaffold consisting of an extracellular matrix can be repopulated with (autologous) cells, aiming at growing ex vivo a fully transplantable organ. In a broader view, such organs might also be used for a better understanding of fundamental biological concepts and disease mechanisms, drug screening and toxicological investigations, opening new pathways in the treatment of kidney disease.

Decellularization of whole organs has been widely explored and described; therefore, this manuscript only briefly reviews some important considerations with an emphasis on scaffold decontamination, but focuses further on recellularization strategies. Critical aspects, including cell types and sources that can be used for recellularization, seeding strategies and possible applications beyond renal replacement are discussed.

Advances in the Knowledge about Kidney Decellularization and Repopulation

End-stage renal disease (ESRD) is characterized by the progressive deterioration of renal function that may compromise different tissues and organs. The major treatment indicated for patients with ESRD is kidney transplantation. However, the shortage of available organs, as well as the high rate of organ rejection, supports the need for new therapies. Thus, the implementation of tissue bioengineering to organ regeneration has emerged as an alternative to traditional organ transplantation. Decellularization of organs with chemical, physical, and/or biological agents generates natural scaffolds, which can serve as basis for tissue reconstruction. The recellularization of these scaffolds with different cell sources, such as stem cells or adult differentiated cells, can provide an organ with functionality and no immune response after in vivo transplantation on the host. Several studies have focused on improving these techniques, but until now, there is no optimal decellularization method for the kidney available yet. Herein, an overview of the current literature for kidney decellularization and whole-organ recellularization is presented, addressing the pros and cons of the actual techniques already developed, the methods adopted to evaluate the efficacy of the procedures, and the challenges to be overcome in order to achieve an optimal protocol.

Decellularized scaffold of cryopreserved rat kidney retains its recellularization potential

The multi-cellular nature of renal tissue makes it the most challenging organ for regeneration. Therefore, till date whole organ transplantations remain the definitive treatment for the end stage renal disease (ESRD). The shortage of available organs for the transplantation has, thus, remained a major concern as well as an unsolved problem. In this regard generation of whole organ scaffold through decellularization followed by regeneration of the whole organ by recellularization is being viewed as a potential alternative for generating functional tissues. Despite its growing interest, the optimal processing to achieve functional organ still remains unsolved. The biggest challenge remains is the time line for obtaining kidney. Keeping these facts in mind, we have assessed the effects of cryostorage (3 months) on renal tissue architecture and its potential for decellularization and recellularization in comparison to the freshly isolated kidneys. The light microscopy exploiting different microscopic stains as well as immuno-histochemistry and Scanning electron microscopy (SEM) demonstrated that ECM framework is well retained following kidney cryopreservation. The strength of these structures was reinforced by calculating mechanical stress which confirmed the similarity between the freshly isolated and cryopreserved tissue. The recellularization of these bio-scaffolds, with mesenchymal stem cells quickly repopulated the decellularized structures irrespective of the kidneys status, i.e. freshly isolated or the cryopreserved. The growth pattern employing mesenchymal stem cells demonstrated their equivalent recellularization potential. Based on these observations, it may be concluded that cryopreserved kidneys can be exploited as scaffolds for future development of functional organ.

Efficient decellularization for tissue engineering of the tendon-bone interface with preservation of biomechanics

Interfaces between tendon/ligament and bone (“entheses”) are highly specialized tissues that allow for stress transfer between mechanically dissimilar materials. Entheses show very low regenerative capacity resulting in high incidences of failure after surgical repair. Tissue engineering is a promising approach to recover functionality of entheses. Here, we established a protocol to decellularize porcine entheses as scaffolds for enthesis tissue engineering. Chemical detergents as well as physical treatments were investigated with regard to their efficiency to decellularize 2 mm thick porcine Achilles tendon entheses. A two-phase approach was employed: study 1 investigated the effect of various concentrations of sodium dodecyl sulfate (SDS) and t-octylphenoxypolyethoxy-ethanol (Triton X-100) as decellularization agents. The most efficient combination of SDS and Triton was then carried forward into study 2, where different physical methods, including freeze-thaw cycles, ultrasound, perfusion, and hydrostatic washing were used to enhance the decellularization effect. Cell counts, DNA quantification, and histology showed that washing with 0.5% SDS + 1% Triton X-100 for 72 h at room temperature could remove ~ 98% cells from the interface. Further investigation of physical methods proved that washing under 200 mmHg hydrostatic pressure shortened the detergent exposing time from 72 h to 48 h. Biomechanical tensile testing showed that the biomechanical features of treated samples were preserved. Washing under 200 mmHg hydrostatic pressure with 0.5% SDS + 1% Triton X-100 for 48 h efficiently decellularized entheses with preservation of matrix structure and biomechanical features. This protocol can be used to efficiently decellularize entheses as scaffolds for tissue engineering.

Re-epithelialization of whole porcine kidneys with renal epithelial cells

Decellularized porcine kidneys were recellularized with renal epithelial cells by three methods: perfusion through the vasculature under high pressure, perfusion through the ureter under high pressure, or perfusion through the ureter under moderate vacuum. Histology, scanning electron microscopy, confocal microscopy, and magnetic resonance imaging were used to assess vasculature preservation and the distribution of cells throughout the kidneys. Cells were detected in the magnetic resonance imaging by labeling them with iron oxide. Perfusion of cells through the ureter under moderate vacuum (40 mmHg) produced the most uniform distribution of cells throughout the kidneys.

Controlling stem cell behavior with decellularized extracellular matrix scaffolds

Decellularized tissues have become a common regenerative medicine platform with multiple materials being researched in academic laboratories, tested in animal studies, and used clinically. Ideally, when a tissue is decellularized the native cell niche is maintained with many of the structural and biochemical cues that naturally interact with the cells of that particular tissue. This makes decellularized tissue materials an excellent platform for providing cells with the signals needed to initiate and maintain differentiation into tissue-specific lineages. The extracellular matrix (ECM) that remains after the decellularization process contains the components of a tissue specific microenvironment that is not possible to create synthetically. The ECM of each tissue has a different composition and structure and therefore has unique properties and potential for affecting cell behavior. This review describes the common methods for preparing decellularized tissue materials and the effects that decellularized materials from different tissues have on cell phenotype.

The Effect of Sterilization Methods on the Structural and Chemical Properties of Fibrin Microthread Scaffolds

A challenge for the design of scaffolds in tissue engineering is to determine a terminal sterilization method that will retain the structural and biochemical properties of the materials. Since commonly used heat and ionizing energy-based sterilization methods have been shown to alter the material properties of protein-based scaffolds, the effects of ethanol and ethylene oxide (EtO) sterilization on the cellular compatibility and the structural, chemical, and mechanical properties of uncrosslinked, UV crosslinked, or 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC) crosslinked fibrin microthreads in neutral (EDCn) or acidic (EDCa) buffers are evaluated. EtO sterilization significantly reduces the tensile strength of uncrosslinked microthreads. Surface chemistry analyses show that EtO sterilization induces alkylation of EDCa microthreads leading to a significant reduction in myoblast attachment. The material properties of EDCn microthreads do not appear to be affected by the sterilization method. These results significantly enhance the understanding of how sterilization or crosslinking techniques affect the material properties of protein scaffolds.

Current Cell-Based Strategies for Whole Kidney Regeneration

Chronic kidney diseases affect thousands of people worldwide. Although hemodialysis alleviates the situation by filtering the patient's blood, it does not replace other kidney functions such as hormone release or homeostasis regulation. Consequently, orthotopic transplantation of donor organs is the ultimate treatment for patients suffering from end-stage renal failure. Unfortunately, the number of patients on the waiting list far exceeds the number of donors. In addition, recipients must remain on immunosuppressive medications for the remainder of their lives, which increases the risk of morbidity due to their weakened immune system. Despite recent advancements in whole organ transplantation, 40% of recipients will face rejection of implanted organs with a life expectancy of only 10 years. Bioengineered patient-specific kidneys could be an inexhaustible source of healthy kidneys without the risk of immune rejection. The purpose of this article is to review the pros and cons of several bioengineering strategies used in recent years and their unresolved issues. These strategies include repopulation of natural scaffolds with a patient's cells, de-novo generation of kidneys using patient-induced pluripotent stem cells combined with stepwise differentiation, and the creation of a patient's kidney in the embryos of other mammalian species.

Decellularized Renal Matrix and Regenerative Medicine of the Kidney: A Different Point of View

Over the past years, extracellular matrix (ECM) obtained from whole organ decellularization has been investigated as a platform for organ engineering. The ECM is composed of fibrous and nonfibrous molecules providing structural and biochemical support to the surrounding cells. Multiple decellularization techniques, including ours, have been optimized to maintain the composition, microstructure, and biomechanical properties of the native renal ECM that are difficult to obtain during the generation of synthetic substrates. There are evidences suggesting that in vivo implanted renal ECM has the capacity to induce formation of vasculature-like structures, but long-term in vivo transplantation and filtration activity by these tissue-engineered constructs have not been investigated or reported. Therefore, even if the process of renal decellularization is possible, the repopulation of the renal matrix with functional renal cell types is still very challenging. This review aims to summarize the current reports on kidney tissue engineering with the use of decellularized matrices and addresses the challenges in creating functional kidney units. Finally, this review discusses how future studies investigating cell-matrix interaction may aid the generation of a functional renal unit that would be transplantable into patients one day.

Investigating the potential of human placenta-derived extracellular matrix sponges coupled with amniotic membrane-derived stem cells for osteochondral tissue engineering

Placental extracellular matrix for osteochondral defects.

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.

Epithelial Cell Repopulation and Preparation of Rodent Extracellular Matrix Scaffolds for Renal Tissue Development

This protocol details the generation of acellular, yet biofunctional, renal extracellular matrix (ECM) scaffolds that are useful as small-scale model substrates for organ-scale tissue development. Sprague Dawley rat kidneys are cannulated by inserting a catheter into the renal artery and perfused with a series of low-concentration detergents (Triton X-100 and sodium dodecyl sulfate (SDS)) over 26 hr to derive intact, whole-kidney scaffolds with intact perfusable vasculature, glomeruli, and renal tubules. Following decellularization, the renal scaffold is placed inside a custom-designed perfusion bioreactor vessel, and the catheterized renal artery is connected to a perfusion circuit consisting of: a peristaltic pump; tubing; and optional probes for pH, dissolved oxygen, and pressure. After sterilizing the scaffold with peracetic acid and ethanol, and balancing the pH (7.4), the kidney scaffold is prepared for seeding via perfusion of culture medium within a large-capacity incubator maintained at 37 °C and 5% CO2. Forty million renal cortical tubular epithelial (RCTE) cells are injected through the renal artery, and rapidly perfused through the scaffold under high flow (25 ml/min) and pressure (~230 mmHg) for 15 min before reducing the flow to a physiological rate (4 ml/min). RCTE cells primarily populate the tubular ECM niche within the renal cortex, proliferate, and form tubular epithelial structures over seven days of perfusion culture. A 44 µM resazurin solution in culture medium is perfused through the kidney for 1 hr during medium exchanges to provide a fluorometric, redox-based metabolic assessment of cell viability and proliferation during tubulogenesis. The kidney perfusion bioreactor permits non-invasive sampling of medium for biochemical assessment, and multiple inlet ports allow alternative retrograde seeding through the renal vein or ureter. These protocols can be used to recellularize kidney scaffolds with a variety of cell types, including vascular endothelial, tubular epithelial, and stromal fibroblasts, for rapid evaluation within this system.

Scaffolds from surgically removed kidneys as a potential source of organ transplantation

End stage renal disease (ESRD) is a common disease, which relates to nearly 600 million people in the total population. What is more, it seems to be a crucial problem from the epidemiological point of view. These facts lead to a further necessity of renal replacement therapy development connected with rising expenditures for the health care system. The aim of kidney tissue engineering is to develop and innovate methods of obtaining renal extracellular matrix (ECM) scaffolds derived from kidney decellularization. Recently, progress has been made towards developing a functional kidney graft in vitro on demand. In fact, decellularized tissues constitute ideal natural scaffolds, due to the preservation of native ECM architecture, as well as of cell-ECM binding domains critical in promoting cell attachment, migration, and proliferation. One of the potential sources of the natural scaffolds is the kidney, which cannot be transplanted immediately after excision.

Optimization and critical evaluation of decellularization strategies to develop renal extracellular matrix scaffolds as biological templates for organ engineering and transplantation

The ability to generate patient-specific cells through induced pluripotent stem cell (iPSC) technology has encouraged development of three-dimensional extracellular matrix (ECM) scaffolds as bioactive substrates for cell differentiation with the long-range goal of bioengineering organs for transplantation. Perfusion decellularization uses the vasculature to remove resident cells, leaving an intact ECM template wherein new cells grow; however, a rigorous evaluative framework assessing ECM structural and biochemical quality is lacking. To address this, we developed histologic scoring systems to quantify fundamental characteristics of decellularized rodent kidneys: ECM structure (tubules, vessels, glomeruli) and cell removal. We also assessed growth factor retention--indicating matrix biofunctionality. These scoring systems evaluated three strategies developed to decellularize kidneys (1% Triton X-100, 1% Triton X-100/0.1% sodium dodecyl sulfate (SDS) and 0.02% Trypsin-0.05% EGTA/1% Triton X-100). Triton and Triton/SDS preserved renal microarchitecture and retained matrix-bound basic fibroblast growth factor and vascular endothelial growth factor. Trypsin caused structural deterioration and growth factor loss. Triton/SDS-decellularized scaffolds maintained 3 h of leak-free blood flow in a rodent transplantation model and supported repopulation with human iPSC-derived endothelial cells and tubular epithelial cells ex vivo. Taken together, we identify an optimal Triton/SDS-based decellularization strategy that produces a biomatrix that may ultimately serve as a rodent model for kidney bioengineering.

Biotechnological challenges of bioartificial kidney engineering

With the world-wide increase of patients with renal failure, the development of functional renal replacement therapies have gained significant interest and novel technologies are rapidly evolving. Currently used renal replacement therapies insufficiently remove accumulating waste products, resulting in the uremic syndrome. A more preferred treatment option is kidney transplantation, but the shortage of donor organs and the increasing number of patients waiting for a transplant warrant the development of novel technologies. The bioartificial kidney (BAK) is such promising biotechnological approach to replace essential renal functions together with the active secretion of waste products. The development of the BAK requires a multidisciplinary approach and evolves at the intersection of regenerative medicine and renal replacement therapy. Here we provide a concise review embracing a compact historical overview of bioartificial kidney development and highlighting the current state-of-the-art, including implementation of living-membranes and the relevance of extracellular matrices. We focus further on the choice of relevant renal epithelial cell lines versus the use of stem cells and co-cultures that need to be implemented in a suitable device. Moreover, the future of the BAK in regenerative nephrology is discussed.