A peritoneal-based automated wearable artificial kidney

Recent advances in zirconium-based catalysis and its applications in organic synthesis: a review

In recent years, transition metal-catalysed organic synthesis has received great importance. Zirconium, a second-row transition metal, has gained prominence owing to its luster and abundance, but it is more expensive than other transition metals because it is difficult to refine and process. In particular, active zirconia-based catalysts have fascinated researchers owing to their low toxicity, affordability, flexibility and excellent dispersion. This review focuses on the latest zirconium catalysts used in the manufacturing of medicinal compounds, bioactive molecules and pertinent synthesis mechanisms reported since 2020. In this review, the synthesis of various heterocycles such as imidazoles, pyrazole, pyrimidinones, quinolines, quinazolinones, pyridines, pyrroles, benzopyrans, substituted amides and triazolidine-based bioactive molecules is discussed in detail. Future research in this area is based on further understanding the scope of zirconium catalysed sustainable and approachable synthesis of biologically active compounds.

Development of a new miniaturized system for ultrafiltration

Acute decompensated heart failure and fluid overload are the most common causes of hospitalization in heart failure patients, and often, they contribute to disease progression. Initial treatment encompasses intravenous diuretics although there might be a percentual of patients refractory to this pharmacological approach. New technologies have been developed to perform extracorporeal ultrafiltration in fluid overloaded patients. Current equipment allows to perform ultrafiltration in most hospital and acute care settings. Extracorporeal ultrafiltration is then prescribed and conducted by specialized teams, and fluid removal is planned to restore a status of hydration close to normal. Recent clinical trials and European and North American practice guidelines suggest that ultrafiltration is indicated for patients with refractory congestion not responding to medical therapy. Close interaction between nephrologists and cardiologists may be the key to a collaborative therapeutic effort in heart failure patients. Further studies are today suggesting that wearable technologies might become available soon to treat patients in ambulatory and de-hospitalized settings. These new technologies may help to cope with the increasing demand for the care of chronic heart failure patients. Herein, we provide a state-of-the-art review on extracorporeal ultrafiltration and describe the steps in the development of a new miniaturized system for ultrafiltration, called AD1 (Artificial Diuresis).

Artificial kidney: Challenges and opportunities

This review aims to present the developments occurring in the field of artificial organs and particularly focuses on the presentation of developments in artificial kidneys. The challenges for biomedical engineering involved in overcoming the potential difficulties are showcased, as well as the importance of interdisciplinary collaboration in this marriage of medicine and technology. In this review, modern artificial kidneys and the research efforts trying to provide and promise artificial kidneys are presented. But what are the problems faced by each technology and to what extent is the effort enough to date?

Renal Embolization-Induced Uremic Swine Model for Assessment of Next-Generation Implantable Hemodialyzers

Reliable models of renal failure in large animals are critical to the successful translation of the next generation of renal replacement therapies (RRT) into humans. While models exist for the induction of renal failure, none are optimized for the implantation of devices to the retroperitoneal vasculature. We successfully piloted an embolization-to-implantation protocol enabling the first implant of a silicon nanopore membrane hemodialyzer (SNMHD) in a swine renal failure model. Renal arterial embolization is a non-invasive approach to near-total nephrectomy that preserves retroperitoneal anatomy for device implants. Silicon nanopore membranes (SNM) are efficient blood-compatible membranes that enable novel approaches to RRT. Yucatan minipigs underwent staged bilateral renal arterial embolization to induce renal failure, managed by intermittent hemodialysis. A small-scale arteriovenous SNMHD prototype was implanted into the retroperitoneum. Dialysate catheters were tunneled externally for connection to a dialysate recirculation pump. SNMHD clearance was determined by intermittent sampling of recirculating dialysate. Creatinine and urea clearance through the SNMHD were 76-105 mL/min/m2 and 140-165 mL/min/m2, respectively, without albumin leakage. Normalized creatinine and urea clearance measured in the SNMHD may translate to a fully implantable clinical-scale device. This pilot study establishes a path toward therapeutic testing of the clinical-scale SNMHD and other implantable RRT devices.

Feasibility of an implantable bioreactor for renal cell therapy using silicon nanopore membranes

The definitive treatment for end-stage renal disease is kidney transplantation, which remains limited by organ availability and post-transplant complications. Alternatively, an implantable bioartificial kidney could address both problems while enhancing the quality and length of patient life. An implantable bioartificial kidney requires a bioreactor containing renal cells to replicate key native cell functions, such as water and solute reabsorption, and metabolic and endocrinologic functions. Here, we report a proof-of-concept implantable bioreactor containing silicon nanopore membranes to offer a level of immunoprotection to human renal epithelial cells. After implantation into pigs without systemic anticoagulation or immunosuppression therapy for 7 days, we show that cells maintain >90% viability and functionality, with normal or elevated transporter gene expression and vitamin D activation. Despite implantation into a xenograft model, we find that cells exhibit minimal damage, and recipient cytokine levels are not suggestive of hyperacute rejection. These initial data confirm the potential feasibility of an implantable bioreactor for renal cell therapy utilizing silicon nanopore membranes.

Wearable and implantable artificial kidney devices for end-stage kidney disease treatment-Current status and review

BACKGROUND

Chronic kidney disease (CKD) is a major cause of early death worldwide. By 2030, 14.5 million people will have end-stage kidney disease (ESKD, or CKD stage 5), yet only 5.4 million will receive kidney replacement therapy (KRT) due to economic, social, and political factors. Even for those who are offered KRT by various means of dialysis, the life expectancy remains far too low.

OBSERVATION

Researchers from different fields of artificial organs collaborate to overcome the challenges of creating products such as Wearable and/or Implantable Artificial Kidneys capable of providing long-term effective physiologic kidney functions such as removal of uremic toxins, electrolyte homeostasis, and fluid regulation. A focus should be to develop easily accessible, safe, and inexpensive KRT options that enable a good quality of life and will also be available for patients in less-developed regions of the world.

CONCLUSIONS

Hence, it is required to discuss some of the limits and burdens of transplantation and different techniques of dialysis, including those performed at home. Furthermore, hurdles must be considered and overcome to develop wearable and implantable artificial kidney devices that can help to improve the quality of life and life expectancy of patients with CKD.

Novel strategies in nephrology: what to expect from the future?

Chronic kidney disease (CKD) will become the fifth global case of death by 2040. Its largest impact is on premature mortality but the number of persons with kidney failure requiring renal replacement therapy (RRT) is also increasing dramatically. Current RRT is suboptimal due to the shortage of kidney donors and dismal outcomes associated with both hemodialysis and peritoneal dialysis. Kidney care needs a revolution. In this review, we provide an update on emerging knowledge and technologies that will allow an earlier diagnosis of CKD, addressing the current so-called blind spot (e.g. imaging and biomarkers), and improve renal replacement therapies (wearable artificial kidneys, xenotransplantation, stem cell-derived therapies, bioengineered and bio-artificial kidneys).

Artificial Kidney Engineering: The Development of Dialysis Membranes for Blood Purification

The artificial kidney, one of the greatest medical inventions in the 20th century, has saved innumerable lives with end stage renal disease. Designs of artificial kidney evolved dramatically in decades of development. A hollow-fibered membrane with well controlled blood and dialysate flow became the major design of the modern artificial kidney. Although they have been well established to prolong patients’ lives, the modern blood purification system is still imperfect. Patient’s quality of life, complications, and lack of metabolic functions are shortcomings of current blood purification treatment. The direction of future artificial kidneys is toward miniaturization, better biocompatibility, and providing metabolic functions. Studies and trials of silicon nanopore membranes, tissue engineering for renal cell bioreactors, and dialysate regeneration are all under development to overcome the shortcomings of current artificial kidneys. With all these advancements, wearable or implantable artificial kidneys will be achievable.

Assessment of Patient Experience of Care in Home Dialysis Around the World: Enhancing the Patient’s Voice in Home Dialysis Care and Research

With the global growth in the use of home dialysis modalities, there is a need to better understand patients’ experiences with their home dialysis care.  Patient-reported experience measures or PREMs, are standardized survey questionnaires that allow patients to provide input on processes and experiences of care in a confidential and validated manner.  Until recently, no validated PREM has been available for assessment of patient-reported experience of care for home dialysis modalities, including peritoneal dialysis or home hemodialysis.  The Home Dialysis Care Experience instrument (Home-DCE) is a newly developed and content-valid PREM for use among patients treated with home dialysis modalities.  The survey instrument includes 26 core survey questions and 20 demographic questions, and is now available in English, Spanish, and French.  Domains of care assessed in the Home-DCE include staff education and patient-centered communication, care coordination, patient safety, concern and helpfulness of the care team, and staff care proficiency.  Worldwide use of the Home-DCE will allow incorporation of patients’ experiences and preferences in initiatives to enhance quality of care for home dialysis patients globally.  Translation and deployment of a PREM in additional languages should be done using established cultural adaptation methods, the gold standard for which is termed linguistic validation.  Translation and linguistic validation are hurdles to global use of the Home-DCE, but challenges that should be met to enhance home dialysis patients’ voice in clinical kidney care.

From Cells to Organs: The Present and Future of Regenerative Medicine

Regenerative medicine promises a bright future where damaged body parts can be restored, rejuvenated, and replaced. The application of regenerative medicine is interdisciplinary and covers nearly all fields of medical sciences and molecular engineering. This review provides a road map on how regenerative medicine is applied on the levels of cell, tissue, and organ and summarizes the advantages and limitation of human pluripotent stem cells in disease modeling and regenerative application.

Description and In-Vitro Test Results of a New Wearable/Portable Device for Extracorporeal Blood Ultrafiltration

This paper presents the design of Rene Artificiale Portatile (RAP), a novel wearable and portable device for extracorporeal blood ultrafiltration, capable of providing remote treatment of fluid overload in patients with kidney diseases and/or congestive heart failure. The development of the device is based on a new design paradigm, since the layout of the device is box-shaped, as to fit a backpack or a trolley case, differentiating it from other existing devices. The efficient layout and component placement guarantee minimalization and ergonomics, as well as an efficient and cost-effective use. The redundant control architecture of the device has been implemented to ensure a high level of safety and an effective implementation of the clinical treatment. The consistency of the design and its effective implementation are assessed by the results of the preliminary in-vitro tests presented and discussed in this work.

Recirculating peritoneal dialysis system using urease-fixed silk fibroin membrane filter with spherical carbonaceous adsorbent

The chronic kidney disease (CKD) patients are undergoing continuous ambulatory peritoneal dialysis (CAPD). However, there are some constraints, the frequent exchange of the dialysate and limitation of outside activity, associated with CAPD remain to be solved. In this study, we designed the wearable artificial kidney (WAK) system for peritoneal dialysis (PD) using urease-immobilized silk fibroin (SF) membrane and polymer-based spherical carbonaceous adsorbent (PSCA). We evaluated this kit's removal abilities of uremic toxins such as urea, creatinine, uric acid, phosphorus, and β2-microglobulin from the dialysate of end-stage renal disease (ESRD) patients in vitro. The uremic toxins including urea, creatinine, uric acid, and phosphorus were removed about 99% by immobilized SF membrane and PSCA filter after 24 h treatment. However, only 50% of β2-microglobulin was removed by this filtering system after 24 h treatment. In vivo study result shows that our filtering system has more uremic toxins removal efficiency than exchanged dialysate at every 6 h. We suggest that recirculating PD system using urease-immobilized SF membrane with PSCA could be more efficient than traditional dialysate exchange system for a WAK for PD.

Removal of urea by electro-oxidation in a miniature dialysis device: a study in awake goats

The key to success in developing a wearable dialysis device is a technique to safely and efficiently regenerate and reuse a small volume of dialysate in a closed-loop system. In a hemodialysis model in goats, we explored whether urea removal by electro-oxidation (EO) could be effectively and safely applied in vivo. A miniature dialysis device was built, containing 1 or 2 "EO units," each with 10 graphite electrodes, with a cumulative electrode surface of 585 cm2 per unit. The units also contained poly(styrene-divinylbenzene) sulfonate beads, FeOOH beads, and activated carbon for respective potassium, phosphate, and chlorine removal. Urea, potassium, and phosphate were infused to create "uremic" conditions. Urea removal was dependent on total electrode surface area [removal of 8 mmol/h (SD 1) and 16 mmol/h (SD 2) and clearance of 12 ml/min (SD 1) and 20 ml/min (SD 3) with 1 and 2 EO units, respectively] and plasma urea concentration but not on flow rate. Extrapolating urea removal with 2 EO units to 24 h would suffice to remove daily urea production, but for intermittent dialysis, additional units would be required. EO had practically no effects on potassium and phosphate removal or electrolyte balance. However, slight ammonium releasewas observed, and some chlorine release at higher dialysate flow rates. Minor effects on acid-base balance were observed, possibly partly due to infusion of chloride. Mild hemolysis occurred, which seemed related to urea infusion. In conclusion, clinically relevant urea removal was achieved in vivo by electro-oxidation. Efficacy and safety testing in a large-animal model with uremia is now indicated.

Innovations in Wearable and Implantable Artificial Kidneys

More than 2 million people worldwide receive treatment for end-stage renal disease (ESRD). Current modalities of renal replacement therapy include in-center hemodialysis, peritoneal dialysis, home hemodialysis, and kidney transplantation. Patient survival has gradually increased during the past 2 decades and efforts continue to improve mortality and quality of life for patients with ESRD. Developments in sorbent technology, nanotechnology, and cell culture techniques provide promise for new innovations in ESRD management. New modalities currently in testing include wearable (WAKs) and implantable artificial kidneys (IAKs). The automated WAK (AWAK) and WAK are devices that have undergone small trials in humans. Additional study is needed before regulatory approval, coverage decisions, and widespread clinical implementation. The IAK is a biohybrid combining artificial filters and living cells currently in preclinical testing. These portable devices reduce the need for large quantities of water and continuous electrical supply. This could lower some barriers to home dialysis, making self-care renal replacement therapy more accessible and desirable. If widely successful, these devices could reduce the need to build and staff dialysis facilities, thus lowering health care costs associated with dialysis. The potential advantages and shortcomings of the AWAK, WAK, and IAK are described here.

A regenerable potassium and phosphate sorbent system to enhance dialysis efficacy and device portability: a study in awake goats

Background

Patients on standard intermittent haemodialysis suffer from strong fluctuations in plasma potassium and phosphate. Prolonged dialysis with a wearable device, based on continuous regeneration of a small volume of dialysate using ion exchangers, could moderate these fluctuations and offer increased clearance of these electrolytes. We report in vivo results on the efficacy of potassium and phosphate adsorption from a wearable dialysis device. We explore whether equilibration of ion exchangers at physiological Ca 2+ , Mg 2+ and hypotonic NaCl can prevent calcium/magnesium adsorption and net sodium release, respectively. Effects on pH and HCO3- were studied.

Methods

Healthy goats were instrumented with a central venous catheter and dialysed. Potassium and phosphate were infused to achieve plasma concentrations commonly observed in dialysis patients. An adsorption cartridge containing 80 g sodium poly(styrene-divinylbenzene) sulphonate and 40 g iron oxide hydroxide beads for potassium and phosphate removal, respectively, was incorporated in a dialysate circuit. Sorbents were equilibrated and regenerated with a solution containing NaCl, CaCl 2 and MgCl 2 . Blood was pumped over a dialyser and dialysate was recirculated over the adsorption cartridge in a countercurrent direction.

Results

Potassium and phosphate adsorption was 7.7 ± 2.7 and 4.9 ± 1.3 mmol in 3 h, respectively. Adsorption capacity remained constant during consecutive dialysis sessions and increased with increasing K + and PO43-. Equilibration at physiological Ca 2+ and Mg 2+ prevented net adsorption, eliminating the need for post-cartridge calcium and magnesium infusion. Equilibration at hypotonic NaCl prevented net sodium release Fe 2+ and arterial pH did not change. Bicarbonate was adsorbed, which could be prevented by equilibrating at HCO3- 15 mM.

Conclusion

We demonstrate clinically relevant, concentration-dependent, pH-neutral potassium and phosphate removal in vivo with small volumes of regenerable ion exchangers in our prototype wearable dialysis device. Application of the selected ion exchangers for potassium and phosphate removal in a wearable dialysis device appears to be effective with a low-risk profile.

In vitro trials of a wearable artificial kidney (WAK)

BACKGROUND

This paper presents results of in vitro trials of a wearable artificial kidney (WAK).

MATERIALS AND METHODS

To carry out the trials, a test bench was developed. It consisted of a patient imitator, a tubing set and measuring equipment.

RESULTS

Our WAK can eliminate urea, uric acid and creatinine from spent dialysate with mean mass rates of 0.85 ± 0.1 g/h, 0.10 ± 0.04 g/h and 0.05 ± 0.01 g/h, respectively. Concentrations of Na+, Cl- and Ca2+ ions were kept in the 10% range from initial values. We demonstrated that our WAK can operate for 38 hours without having to replace expendable materials.

CONCLUSIONS

The WAK that we developed can eliminate metabolites from spent dialysis fluid with mass rates that are sufficient to maintain stable, physiologically normal metabolite concentrations in patients' blood.

Diffusive Silicon Nanopore Membranes for Hemodialysis Applications

Hemodialysis using hollow-fiber membranes provides life-sustaining treatment for nearly 2 million patients worldwide with end stage renal disease (ESRD). However, patients on hemodialysis have worse long-term outcomes compared to kidney transplant or other chronic illnesses. Additionally, the underlying membrane technology of polymer hollow-fiber membranes has not fundamentally changed in over four decades. Therefore, we have proposed a fundamentally different approach using microelectromechanical systems (MEMS) fabrication techniques to create thin-flat sheets of silicon-based membranes for implantable or portable hemodialysis applications. The silicon nanopore membranes (SNM) have biomimetic slit-pore geometry and uniform pores size distribution that allow for exceptional permeability and selectivity. A quantitative diffusion model identified structural limits to diffusive solute transport and motivated a new microfabrication technique to create SNM with enhanced diffusive transport. We performed in vitro testing and extracorporeal testing in pigs on prototype membranes with an effective surface area of 2.52 cm² and 2.02 cm², respectively. The diffusive clearance was a two-fold improvement in with the new microfabrication technique and was consistent with our mathematical model. These results establish the feasibility of using SNM for hemodialysis applications with additional scale-up.

A wearable artificial kidney for patients with end-stage renal disease

BACKGROUND

Stationary hemodialysis machines hinder mobility and limit activities of daily life during dialysis treatments. New hemodialysis technologies are needed to improve patient autonomy and enhance quality of life.

METHODS

We conducted a FDA-approved human trial of a wearable artificial kidney, a miniaturized, wearable hemodialysis machine, based on dialysate-regenerating sorbent technology. We aimed to determine the efficacy of the wearable artificial kidney in achieving solute, electrolyte, and volume homeostasis in up to 10 subjects over 24 hours.

RESULTS

During the study, all subjects remained hemodynamically stable, and there were no serious adverse events. Serum electrolytes and hemoglobin remained stable over the treatment period for all subjects. Fluid removal was consistent with prescribed ultrafiltration rates. Mean blood flow was 42 ± 24 ml/min, and mean dialysate flow was 43 ± 20 ml/min. Mean urea, creatinine, and phosphorus clearances over 24 hours were 17 ± 10, 16 ± 8, and 15 ± 9 ml/min, respectively. Mean β₂-microglobulin clearance was 5 ± 4 ml/min. Of 7 enrolled subjects, 5 completed the planned 24 hours of study treatment. The trial was stopped after the seventh subject due to device-related technical problems, including excessive carbon dioxide bubbles in the dialysate circuit and variable blood and dialysate flows.

CONCLUSION

Treatment with the wearable artificial kidney was well tolerated and resulted in effective uremic solute clearance and maintenance of electrolyte and fluid homeostasis. These results serve as proof of concept that, after redesign to overcome observed technical problems, a wearable artificial kidney can be developed as a viable novel alternative dialysis technology.

TRIAL REGISTRATION

ClinicalTrials.gov NCT02280005.

FUNDING

The Wearable Artificial Kidney Foundation and Blood Purification Technologies Inc.

Nanoporous biomaterials for uremic toxin adsorption in artificial kidney systems: A review

Hemodialysis, one of the earliest artificial kidney systems, removes uremic toxins via diffusion through a semipermeable porous membrane into the dialysate fluid. Miniaturization of the present hemodialysis system into a portable and wearable device to maintain continuous removal of uremic toxins would require that the amount of dialysate used within a closed-system is greatly reduced. Diffused uremic toxins within a closed-system dialysate need to be removed to maintain the optimum concentration gradient for continuous uremic toxin removal by the dialyzer. In this dialysate regenerative system, adsorption of uremic toxins by nanoporous biomaterials is essential. Throughout the years of artificial kidney development, activated carbon has been identified as a potential adsorbent for uremic toxins. Adsorption of uremic toxins necessitates nanoporous biomaterials, especially activated carbon. Nanoporous biomaterials are also utilized in hemoperfusion for uremic toxin removal. Further miniaturization of artificial kidney system and improvements on uremic toxin adsorption capacity would require high performance nanoporous biomaterials which possess not only higher surface area, controlled pore size, but also designed architecture or structure and surface functional groups. This article reviews on various nanoporous biomaterials used in current artificial kidney systems and several emerging nanoporous biomaterials. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 1232-1240, 2017.

Nanofibrous polymeric beads from aramid fibers for efficient bilirubin removal

Polymer based hemoperfusion has been developed as an effective therapy to remove the extra bilirubin from patients.

Wearable devices for blood purification: principles, miniaturization, and technical challenges

The prevalences of end-stage renal disease (ESRD) and renal replacement therapy (RRT) continue to increase across the world imposing staggering costs on providers. Therefore, strategies to optimize the treatment and improve survival are of fundamental importance. Despite the benefits of daily dialysis, its implementation is difficult and wearable hemodialysis might represent an alternative by which frequent treatments can be delivered to ESRD patients with much less interference in their routines promoting better quality of life. The development of the wearable artificial kidney (WAK) requires incorporation of basic components of a dialysis system into a wearable device that allows mobility, miniaturization, and above all, patient-oriented management. The technical requirements necessary for WAK can be divided into the following broad categories: dialysis membranes, dialysis regeneration, vascular access, patient monitoring systems, and power sources. Pumping systems for blood and other fluids are the most critical components of the entire device.

Wak engineering evolution

The wearable artificial kidney (WAK) is a device that allows prolonged and frequent dialysis treatments for patients with end stage renal disease. It potentially provides a practical and feasible solution to satisfy the need for an optimal delivered dialysis. Until now, the WAK has already been presented in several models, proposing different therapeutic modalities and engineering approaches. The ideal solution of a WAK may come from a combination of all the prototypes developed and/or those currently in development. Consequently, it is important to have a complete overview and a deep knowledge of the possible engineering solutions in order to achieve the incremental steps necessary to solve the remaining issues of wearable extracorporeal blood purification devices. Since technical advances are continuously evolving and it is important to focus on clinical requirements and needs, a multidisciplinary collaboration has to be coordinated to achieve the final objective of the practical realization of a wearable artificial kidney. In such a context, the main aim of this article was to analyze more in detail the WAK Engineeristic Development.

Portable and wearable dialysis devices for the treatment of patients with end-stage kidney failure: Wishful thinking or just over the horizon?

Dialysis is a life-sustaining treatment for patients with end-stage kidney disease. In a different context, for many patients this treatment is the focal point around which their life revolves, not only due to the time spent travelling to and from treatment sessions and the time dedicated to the dialysis treatment itself, but also due to the accompanying dietary and fluid restrictions and medication burden. Wearable and portable dialysis devices could potentially improve patient quality of life by allowing patients to continue with their daily activities of life while undergoing dialysis, as well as by loosening-or removing entirely-dietary and fluid restrictions and reducing pill burden. Advances in nanotechnology manufacturing coupled with advances in electronics and miniaturisation have allowed a new generation of wearable and portable dialysis devices to be developed which are now undergoing large animal and patient clinical trials. We are therefore potentially at a new dawn in the treatment of dialysis patients with the first generation of wearable and portable dialysis devices, which may well revolutionise the treatment and quality of life for patients with end-stage kidney disease.

Microelectromechanical systems and nephrology: the next frontier in renal replacement technology

Microelectromechanical systems (MEMS) are playing a prominent role in the development of many new and innovative biomedical devices, but they remain a relatively underused technology in nephrology. The future landscape of clinical medicine and research will only see further expansion of MEMS-based technologies in device designs and applications. This enthusiasm stems from the ability to create small-scale device features with high precision in a cost-effective manner. MEMS also offers the possibility to integrate multiple components into a single device. The adoption of MEMS has the potential to revolutionize how nephrologists manage kidney disease by improving the delivery of renal replacement therapies and enhancing the monitoring of physiologic parameters. To introduce nephrologists to MEMS, this review will first define relevant terms and describe the basic processes used to fabricate devices. Next, a survey of MEMS devices being developed for various biomedical applications will be illustrated with current examples. Finally, MEMS technology specific to nephrology will be highlighted and future applications will be examined. The adoption of MEMS offers novel avenues to improve the care of kidney disease patients and assist nephrologists in clinical practice. This review will serve as an introduction for nephrologists to the exciting world of MEMS.

Review: understanding sorbent dialysis systems

Although maintenance haemodialysis once had the benefit of two distinctly different dialysate preparation and delivery systems - (1) a pre-filtration and reverse osmosis water preparation plant linked to a single pass proportioning system and (2) a sorbent column dependent dialysate regeneration and recirculation system known as the REDY system - the first came to dominate the market and the second waned. By the early 1990s, the REDY had disappeared from clinical use. The REDY system had strengths. It was a small, mobile, portable and water-efficient, only 6 L of untreated water being required for each dialysis. In comparison, single pass systems are bulky, immobile and water (and power) voracious, typically needing 400-600 L/treatment of expensively pretreated water. A resurgence of interest in home haemodialysis - short and long, intermittent and daily - has provided impetus to redirect technological research into cost-competitive systems. Miniaturization, portability, flexibility, water-use efficiency and 'wearability' are ultimate goals. Sorbent systems are proving an integral component of this effort. In sorbent dialysate regeneration, rather than draining solute-rich dialyser effluent to waste - as do current systems - the effluent repetitively recirculates across a sorbent column capable of adsorption, ion exchange or catalytic conversion of all solute such that, at exit from the column, an ultra-pure water solution emerges. This then remixes with a known electrolyte concentrate for representation to the dialyser. As the same small water volume can recirculate, at least until column exhaustion, water source independence is assured. Many current technological developments in dialysis equipment are now focusing on sorbent-based dialysate circuitry. Although possibly déjà vu for some, it is timely for a brief review of sorbent chemistry and its application to dialysis systems.

The renaissance of home hemodialysis: where we are, why we got here, what is happening in the United States and elsewhere

Home hemodialysis has been around since 1964, but its use has declined over the years in most countries, this despite its advantages, particularly improved patient survival and quality of life and significant cost savings. Experience has shown that home hemodialysis can be performed successfully by many more patients than at present. Recently, with the demonstration of even better results with more frequent hemodialysis that is obviously best performed at home and with the development of new, more patient-friendly machines, the use of home hemodialysis is beginning to increase again.