Prospect for kidney bioengineering: shortcomings of the status quo

Health economics aspects of kidney transplantation in Sicily: a benchmark analysis on activity and estimated savings

BACKGROUND

International and national registries consistently report substantial differences in kidney transplant (KT) activity despite demonstrable clinical and financial benefits. The study aims to estimate the financial resources gained by KT and produce a benchmark analysis that would inform adequate strategies for the growth of the service.

METHODS

We analyzed the KT activity in our region between 2017 and 2019. The benchmark analysis was conducted with programs identified from national and international registries. The estimate of financial resources was obtained by applying the kidney transplant coefficient of value; subsequently, we compared the different activity levels and savings generated by the three KT programs.

FINDINGS

The KT activity in the region progressively declined in the study years, producing a parallel reduction of the estimated savings. Such savings were substantially inferior when compared to those generated by benchmark programs (range €18-22 million less).

INTERPRETATION

The factors influencing the reduced KT activity in the study period with the related "foregone savings" are multiple, as well as interdependent. Organ donation, access to the transplant waiting list, and KT from living donors appear to be the most prominent determinants of the observed different levels of activities. International experience suggests that a comprehensive strategy in the form of a "task force" may successfully address the critical areas of the service reversing the observed trend. The financial impact of a progressively reduced KT activity may be as critical as its clinical implications, jeopardizing the actual sustainability of services for patients with end-stage kidney disease.

Managing the "Sword of Damocles" of Immunosuppression: Prevention, Early Diagnosis, and Treatment of Infectious Diseases in Kidney Transplantation

The careful tailoring of the most appropriate immunosuppressive strategy for recipients of a kidney transplant (KT) regularly faces a risk of complications that may harm the actual graft and affect patient survival [...].

Out of Box Thinking to Tangible Science: A Benchmark History of 3D Bio-Printing in Regenerative Medicine and Tissues Engineering

Advancements and developments in the 3D bioprinting have been promising and have met the needs of organ transplantation. Current improvements in tissue engineering constructs have enhanced their applications in regenerative medicines and other medical fields. The synergistic effects of 3D bioprinting have brought technologies such as tissue engineering, microfluidics, integrated tissue organ printing, in vivo bioprinted tissue implants, artificial intelligence and machine learning approaches together. These have greatly impacted interventions in medical fields, such as medical implants, multi-organ-on-chip models, prosthetics, drug testing tissue constructs and much more. This technological leap has offered promising personalized solutions for patients with chronic diseases, and neurodegenerative disorders, and who have been in severe accidents. This review discussed the various standing printing methods, such as inkjet, extrusion, laser-assisted, digital light processing, and stereolithographic 3D bioprinter models, adopted for tissue constructs. Additionally, the properties of natural, synthetic, cell-laden, dECM-based, short peptides, nanocomposite and bioactive bioinks are briefly discussed. Sequels of several tissue-laden constructs such as skin, bone and cartilage, liver, kidney, smooth muscles, cardiac and neural tissues are briefly analyzed. Challenges, future perspectives and the impact of microfluidics in resolving the limitations in the field, along with 3D bioprinting, are discussed. Certainly, a technology gap still exists in the scaling up, industrialization and commercialization of this technology for the benefit of stakeholders.

Optimizing Decellularization Strategies for the Efficient Production of Whole Rat Kidney Scaffolds

BACKGROUND

Renal dysfunction remains a global issue, with chronic kidney disease being the 18th most leading cause of death, worldwide. The increased demands in kidney transplants, led the scientific society to seek alternative strategies, utilizing mostly the tissue engineering approaches. Unlike to perfusion decellularization of kidneys, we proposed alternative decellularization strategies to obtain acellular kidney scaffolds. The aim of this study was the evaluation of two different decellularization approaches for producing kidney bioscaffolds.

METHODS

Rat kidneys from Wistar rats, were submitted to decellularization, followed two different strategies. The decellularization solutions used in both approaches were the same and involved the use of 3-[(3-cholamidopropyl) dimethylammonio]-1-propanesulfonate and sodium dodecyl sulfate buffers for 12 h each, followed by incubation in a serum medium. Both approaches involved 3 decellularization cycles. Histological analysis, biochemical and DNA quantification were performed. Cytotoxicity assay and repopulation of acellular kidneys were also applied.

RESULTS

Histological, biochemical and DNA quantification confirmed that the 2nd approach had the best outcome regarding the kidney composition and cell elimination. Acellular kidneys from both approaches were successfully recellularized.

CONCLUSION

Based on the above data, the production of kidney scaffolds with the proposed cost- effective decellularization approaches, was efficient.

Bioprinting of kidney in vitro models: cells, biomaterials, and manufacturing techniques

The number of patients with end-stage renal disease is continuously increasing worldwide. The only therapies for these patients are dialysis and organ transplantation, but the latter is limited due to the insufficient number of donor kidneys available. Research in kidney disease and alternative therapies are therefore of outmost importance. In vitro models that mimic human kidney functions are essential to provide better insights in disease and ultimately novel therapies. Bioprinting techniques have been increasingly used to create models with some degree of function, but their true potential is yet to be achieved. Bioprinted renal tissues and kidney-like constructs presents challenges, for example, choosing suitable renal cells and biomaterials for the formulation of bioinks. In addition, the fabrication of complex renal biological structures is still a major bottleneck. Advances in pluripotent stem cell-derived renal progenitors has contributed to in vivo-like rudiment structures with multiple renal cells, and these started to make a great impact on the achieved models. Natural- or synthetic-based biomaterial inks, such as kidney-derived extracellular matrix and gelatin-fibrin hydrogels, which show the potential to partially replicate in vivo-like microenvironments, have been largely investigated for bioprinting. As the field progresses, technological, biological and biomaterial developments will be required to yield fully functional in vitro tissues that can contribute to a better understanding of renal disease, to improve predictability in vitro of novel therapeutics, and to facilitate the development of alternative regenerative or replacement treatments. In this review, we resume the main advances on kidney in vitro models reported so far.

Comprehensive characterization of the human pancreatic proteome for bioengineering applications

Interactions between the pancreatic extracellular matrix (ECM) and islet cells are known to regulate multiple aspects of islet physiology, including survival, proliferation, and glucose-stimulated insulin secretion. Recognizing the essential role of ECM in islet survival and function, various engineering approaches have been developed that aim to utilize ECM-based materials to recreate a native-like microenvironment. However, a major impediment to the success of these approaches has been the lack of a robust and comprehensive characterization of the human pancreatic proteome. Herein, by combining mass spectrometry (MS) and multiplex ELISA, we have provided an improved workflow for the in-depth profiling of the proteome, including minor constituents that are generally underrepresented. Moreover, we have further validated the effectiveness of our detergent-free decellularization protocol in the removal of cellular proteins and retention of the matrisome. It has also been established that the decellularized ECM and its derivatives can provide more tissue-specific cues than traditionally used biological scaffolds and are therefore more physiologically relevant for the development of hydrogels, bioinks and medium additives, in order to create a pancreatic niche. The data generated in this study would contribute significantly to the efforts of comprehensively defining the ECM atlas and also serve as a standard for the human pancreatic proteome to provide further guidance for design and engineering strategies for improved tissue engineering scaffolds.

Review of high-content screening applications in toxicology

High-content screening (HCS) technology combining automated microscopy and quantitative image analysis can address biological questions in academia and the pharmaceutical industry. Various HCS experimental applications have been utilized in the research field of in vitro toxicology. In this review, we describe several HCS application approaches used for studying the mechanism of compound toxicity, highlight some challenges faced in the toxicological community, and discuss the future directions of HCS in regards to new models, new reagents, data management, and informatics. Many specialized areas of toxicology including developmental toxicity, genotoxicity, developmental neurotoxicity/neurotoxicity, hepatotoxicity, cardiotoxicity, and nephrotoxicity will be examined. In addition, several newly developed cellular assay models including induced pluripotent stem cells (iPSCs), three-dimensional (3D) cell models, and tissues-on-a-chip will be discussed. New genome-editing technologies (e.g., CRISPR/Cas9), data analyzing tools for imaging, and coupling with high-content assays will be reviewed. Finally, the applications of machine learning to image processing will be explored. These new HCS approaches offer a huge step forward in dissecting biological processes, developing drugs, and making toxicology studies easier.

Instrumented Microphysiological Systems for Real-Time Measurement and Manipulation of Cellular Electrochemical Processes

Recent advancements in electronic materials and subsequent surface modifications have facilitated real-time measurements of cellular processes far beyond traditional passive recordings of neurons and muscle cells. Specifically, the functionalization of conductive materials with ligand-binding aptamers has permitted the utilization of traditional electronic materials for bioelectronic sensing. Further, microfabrication techniques have better allowed microfluidic devices to recapitulate the physiological and pathological conditions of complex tissues and organs in vitro or microphysiological systems (MPS). The convergence of these models with advances in biological/biomedical microelectromechanical systems (BioMEMS) instrumentation has rapidly bolstered a wide array of bioelectronic platforms for real-time cellular analytics. In this review, we provide an overview of the sensing techniques that are relevant to MPS development and highlight the different organ systems to integrate instrumentation for measurement and manipulation of cellular function. Special attention is given to how instrumented MPS can disrupt the drug development and fundamental mechanistic discovery processes.

Fabrication of Kidney Proximal Tubule Grafts Using Biofunctionalized Electrospun Polymer Scaffolds

The increasing prevalence of end-stage renal disease and persistent shortage of donor organs call for alternative therapies for kidney patients. Dialysis remains an inferior treatment as clearance of large and protein-bound waste products depends on active tubular secretion. Biofabricated tissues could make a valuable contribution, but kidneys are highly intricate and multifunctional organs. Depending on the therapeutic objective, suitable cell sources and scaffolds must be selected. This study provides a proof-of-concept for stand-alone kidney tubule grafts with suitable mechanical properties for future implantation purposes. Porous tubular nanofiber scaffolds are fabricated by electrospinning 12%, 16%, and 20% poly-ε-caprolactone (PCL) v/w (chloroform and dimethylformamide, 1:3) around 0.7 mm needle templates. The resulting scaffolds consist of 92%, 69%, and 54% nanofibers compared to microfibers, respectively. After biofunctionalization with L-3,4-dihydroxyphenylalanine and collagen IV, 10 × 106 proximal tubule cells per mL are injected and cultured until experimental readout. A human-derived cell model can bridge all fiber-to-fiber distances to form a monolayer, whereas small-sized murine cells form monolayers on dense nanofiber meshes only. Fabricated constructs remain viable for at least 3 weeks and maintain functionality as shown by inhibitor-sensitive transport activity, which suggests clearance capacity for both negatively and positively charged solutes.

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.

Tomorrow today: organ-on-a-chip advances towards clinically relevant pharmaceutical and medical in vitro models

Organ-on-a-chip technology offers the potential to recapitulate human physiology by keeping human cells in a precisely controlled and artificial tissue-like microenvironment. The current and potential advantages of organs-on-chips over conventional cell cultures systems and animal models have captured the attention of scientists, clinicians and policymakers as well as advocacy groups in the past few years. Recent advances in tissue engineering and stem cell research are also aiding the development of clinically relevant chip-based organ and diseases models with organ level physiology for drug screening, biomedical research and personalized medicine. Here, the latest advances in organ-on-a-chip technology are reviewed and future clinical applications discussed.

3D bioprinting of tissues and organs for regenerative medicine

3D bioprinting is a pioneering technology that enables fabrication of biomimetic, multiscale, multi-cellular tissues with highly complex tissue microenvironment, intricate cytoarchitecture, structure-function hierarchy, and tissue-specific compositional and mechanical heterogeneity. Given the huge demand for organ transplantation, coupled with limited organ donors, bioprinting is a potential technology that could solve this crisis of organ shortage by fabrication of fully-functional whole organs. Though organ bioprinting is a far-fetched goal, there has been a considerable and commendable progress in the field of bioprinting that could be used as transplantable tissues in regenerative medicine. This paper presents a first-time review of 3D bioprinting in regenerative medicine, where the current status and contemporary issues of 3D bioprinting pertaining to the eleven organ systems of the human body including skeletal, muscular, nervous, lymphatic, endocrine, reproductive, integumentary, respiratory, digestive, urinary, and circulatory systems were critically reviewed. The implications of 3D bioprinting in drug discovery, development, and delivery systems are also briefly discussed, in terms of in vitro drug testing models, and personalized medicine. While there is a substantial progress in the field of bioprinting in the recent past, there is still a long way to go to fully realize the translational potential of this technology. Computational studies for study of tissue growth or tissue fusion post-printing, improving the scalability of this technology to fabricate human-scale tissues, development of hybrid systems with integration of different bioprinting modalities, formulation of new bioinks with tuneable mechanical and rheological properties, mechanobiological studies on cell-bioink interaction, 4D bioprinting with smart (stimuli-responsive) hydrogels, and addressing the ethical, social, and regulatory issues concerning bioprinting are potential futuristic focus areas that would aid in successful clinical translation of this technology.

Stability of Polyethylene Glycol and Zwitterionic Surface Modifications in PDMS Microfluidic Flow Chambers

Blood-material interactions are crucial to the lifetime, safety, and overall success of blood contacting devices. Hydrophilic polymer coatings have been employed to improve device lifetime by shielding blood contacting materials from the natural foreign body response, primarily the intrinsic pathway of the coagulation cascade. These coatings have the ability to repel proteins, cells, bacteria, and other micro-organisms. Coatings are desired to have long-term stability, so that the nonthrombogenic and nonfouling effects gained are long lasting. Unfortunately, there exist limited studies which investigate their stability under dynamic flow conditions as encountered in a physiological setting. In addition, direct comparisons between multiple coatings are lacking in the literature. In this study, we investigate the stability of polyethylene glycol (PEG), zwitterionic sulfobetaine silane (SBSi), and zwitterionic polyethylene glycol sulfobetaine silane (PEG-SBSi) grafted by a room temperature, sequential flow chemistry process on polydimethylsiloxane (PDMS) over time under ambient, static fluid (no flow), and physiologically relevant flow conditions and compare the results to uncoated PDMS controls. PEG, SBSi, and PEG-SBSi coatings maintained contact angles below 20° for up to 35 days under ambient conditions. SBSi and PEG-SBSi showed increased stability and hydrophilicity after 7 days under static conditions. They also retained contact angles ≤40° for all shear rates after 7 days under flow, demonstrating their potential for long-term stability. The effectiveness of the coatings to resist platelet adhesion was also studied under physiological flow conditions. PEG showed a 69% reduction in adhered platelets, PEG-SBSi a significant 80% reduction, and SBSi a significant 96% reduction compared to uncoated control samples, demonstrating their potential applicability for blood contacting applications. In addition, the presented coatings and their stability under shear may be of interest in other applications including marine coatings, lab on a chip devices, and contact lenses, where it is desirable to reduce surface fouling due to proteins, cells, and other organisms.

Development of a chitosan-based tissue-engineered renal proximal tubule conduit

Renal proximal tubule cells (RPTCs) are responsible for glomerular filtration and maintenance of water/electrolyte balance. To regenerate a proximal tubule, sufficient cell numbers and normal cell function are requisite. Collagen has been routinely used as a substrate for culturing human RPTCs (HRPTCs); however, the role of biomaterials has not been thoroughly explored. In this study, RPTCs retrieved from human nephrectomy/nephroureterectomy specimens were cultivated on chitosan as a substrate in serum-free condition for up to 150 days. HRPTCs could maintain a typical epithelial morphology and the specific differentiation feature of transporting epithelia after such long-term culture. As compared with HRPTCs cultivated on collagen, those cultivated on chitosan showed more dome formation, higher Na⁺ -K⁺ ATPase expression, lower vimentin expression, and lower transepithelial electrical resistance, indicating that HRPTCs cultivated on chitosan presented better differentiation status and would be more functional with better active transportation. Thus, the current study indicates greater scope for the use of chitosan as a biomaterial for preparing a HRPTC-coated chitosan conduit, which might be useful for the scaffold design of tissue-engineered proximal tubules. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 9-20, 2018.

[Renal transplantation in 2046: Future and perspectives]

OBJECTIVES

To report major findings that may build the future of kidney transplantation.

MATERIAL AND METHODS

Relevant publications were identified through Medline (http://www.ncbi.nlm.nih.gov) and Embase (http://www.embase.com) database from 1960 to 2016 using the following keywords, in association, "bio-engineering; heterotransplantation; immunomodulation; kidney; regenerative medicine; xenotransplantation". Articles were selected according to methods, language of publication and relevance. A total of 5621 articles were identified including 2264 for xenotransplantation, 1058 for regenerative medicine and 2299 for immunomodulation; after careful selection, 86 publications were eligible for our review.

RESULTS

Despite genetic constructs, xenotransplantation faces the inevitable obstacle of species barrier. Uncertainty regarding xenograft acceptance by recipients as well as ethical considerations due to the debatable utilization of animal lives, are major limits for its future. Regenerative medicine and tridimensional bioprinting allow successful implantation of organs. Bioengineering, using decellularized tissue matrices or synthetic scaffold, seeded with pluripotent cells and assembled using bioreactors, provide exciting results but remain far for reconstituting renal complexity and vascular patency. Immune tolerance may be achieved through a tough initial T-cell depletion or a combined haplo-identical bone marrow transplant leading to lymphohematopoietic chimerism.

CONCLUSION

Current researches aim to increase the pool of organs available for transplantation (xenotransplants and bio-artificial kidneys) and to increase allograft survival through the induction of immune tolerance. Reported results suggest the onset of a thrilling new era for renal transplantation providing end-stage renal disease-patients with an improved survival and quality of life.

Autologous Cells for Kidney Bioengineering

Worldwide, increasing numbers of patients are developing end-stage renal disease, and at present, the only treatment options are dialysis or kidney transplantation. Dialysis is associated with increased morbidity and mortality, poor life quality and high economic costs. Transplantation is by far the better option, but there are insufficient numbers of donor kidneys available. Therefore, there is an urgent need to explore alternative approaches. In this review, we discuss how this problem could potentially be addressed by using autologous cells and appropriate scaffolds to develop 'bioengineered' kidneys for transplantation. In particular, we will highlight recent breakthroughs in pluripotent stem cell biology that have led to the development of autologous renal progenitor cells capable of differentiating to all renal cell types and will discuss how these cells could be combined with appropriate scaffolds to develop a bioengineered kidney.

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.

Kidney-on-a-Chip Technology for Drug-Induced Nephrotoxicity Screening

Improved model systems to predict drug efficacy, interactions, and drug-induced kidney injury (DIKI) are crucially needed in drug development. Organ-on-a-chip technology is a suitable in vitro system because it reproduces the 3D microenvironment. A kidney-on-a-chip can mimic the structural, mechanical, transport, absorptive, and physiological properties of the human kidney. In this review we address the application of state-of-the-art microfluidic culturing techniques, with a focus on culturing kidney proximal tubules, that are promising for the detection of biomarkers that predict drug interactions and DIKI. We also discuss high-throughput screening and the challenges for in vitro to in vivo extrapolation (IVIVE) that will need to be overcome for successful implementation.

Chronic Hemodialysis Therapy in the West

BACKGROUND

Chronic hemodialysis (HD) in the 1960s encompassed a wide variety of prescriptions from twice weekly to five times per week HD. Over time, HD prescriptions in the West became standardized at three times per week, 2.5-4 h per session, with occasional additional treatments for volume overload.

SUMMARY

When clinical trials of dialysis dose failed to show significant benefit of extending time compared with the traditional dialysis prescription, interest in more frequent HD was renewed. Consequently, there has been growth in home HD therapies as well as alternative dialysis prescriptions. Data from recent randomized clinical trials have demonstrated the benefits and risks of these more frequent therapies, with surprising differences in outcomes between short daily HD and long nocturnal HD. More frequent therapies improve control of both hypertension and hyperphosphatemia, but at the expense of increased vascular access complications and, at least for nocturnal HD, a faster loss of residual renal function.

KEY MESSAGES

In the West, the standard HD prescription is three treatments per week with a minimal time of 3.0 h and dialysis is performed in an outpatient dialysis center. A minority of patients will have a fourth treatment per week for volume issues. Alternative HD prescriptions, although rare, are more available compared to the recent past.

FACTS FROM EAST AND WEST

(1) While developed Western and Asian countries provide end-stage renal disease patients full access to HD, healthcare systems from South and South-East Asia can offer access to HD only to a limited fraction of the patients in need. Even though the annual costs of HD are much lower in less developed countries (for instance 30 times lower in India compared to the US), patients often cannot afford costs not covered by health insurance. (2) The recommended dialysis pattern in the West is at least three sessions weekly with high-flux dialyzers. Studies from Shanghai and Taiwan might however indicate a benefit of twice versus thrice weekly sessions. In less developed Asian countries, a twice weekly pattern is common, sometimes with dialyzer reuse and inadequate water treatment. A majority of patients decrease session frequency or discontinue the program due to financial constraint. (3) As convective therapies are gaining popularity in Europe, penetration in Asia is low and limited by costs. (4) In Asian countries, in particular in the South and South-East, hepatitis and tuberculosis infections in HD patients are higher than in the West and substantially increase mortality. (5) Progress has recently been made in countries like Thailand and Brunei to provide universal HD access to all patients in need. Nevertheless, well-trained personnel, reliable registries and better patient follow-up would improve outcomes in low-income Asian countries.

Tissue-Engineering Approaches to Restore Kidney Function

Kidney transplantation for the treatment of chronic kidney disease has established outcome and quality of life. However, its implementation is severely limited by a chronic shortage of donor organs; consequently, most candidates remain on dialysis and on the waiting list while accruing further morbidity and mortality. Furthermore, those patients that do receive kidney transplants are committed to a life-long regimen of immunosuppressive drugs that also carry significant adverse risk profiles. The disciplines of tissue engineering and regenerative medicine have the potential to produce alternative therapies which circumvent the obstacles posed by organ shortage and immunorejection. This review paper describes some of the most promising tissue-engineering solutions currently under investigation for the treatment of acute and chronic kidney diseases. The various stem cell therapies, whole embryo transplantation, and bioengineering with ECM scaffolds are outlined and summarized.

Courage and character, leaders and legends: an interview with Giuseppe Orlando, MD, PhD

Through our unwavering commitment to patients and through the love of family and friends, nature and people, we relentlessly continue to push the boundaries of medicine with the aim of bettering people's lives. 1