Removal of Urea in a Wearable Dialysis Device: A Reappraisal of Electro‐Oxidation

Abstract

A major challenge for a wearable dialysis device is removal of urea, as urea is difficult to adsorb while daily production is very high. Electro-oxidation (EO) seems attractive because electrodes are durable, small, and inexpensive. We studied the efficacy of urea oxidation, generation of chlorine by-products, and their removal by activated carbon (AC). EO units were designed. Three electrode materials (platinum, ruthenium oxide, and graphite) were compared in single pass experiments using urea in saline solution. Chlorine removal by AC in series with EO by graphite electrodes was tested. Finally, urea-spiked bovine blood was dialyzed and dialysate was recirculated in a dialysate circuit with AC in series with an EO unit containing graphite electrodes. Platinum electrodes degraded more urea (21 ± 2 mmol/h) than ruthenium oxide (13 ± 2 mmol/h) or graphite electrodes (13 ± 1 mmol/h). Chlorine generation was much lower with graphite (13 ± 4 mg/h) than with platinum (231 ± 22 mg/h) or ruthenium oxide electrodes (129 ± 12 mg/h). Platinum and ruthenium oxide electrodes released platinum (4.1 [3.9-8.1] umol/h) and ruthenium (83 [77-107] nmol/h), respectively. AC potently reduced dialysate chlorine levels to < 0.10 mg/L. Urea was removed from blood by EO at constant rate (9.5 ± 1.0 mmol/h). EO by graphite electrodes combined with AC shows promising urea removal and chlorine release complying with Association for the Advancement of Medical Instrumentation standards, and may be worth further exploring for dialysate regeneration in a wearable system.

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

“…A miniature dialysis device of~1.5 kg (plus battery pack of 250 g for 3 h of dialysis) was built and provided by Nanodialysis BV (Oirschot, the Netherlands). One or two "EO unit(s)" (weight: 250 g per unit) were incorporated in the dialysate circuit, each containing 10 graphite electrodes with a cumulative electrode surface of 585 cm 2 per EO unit (39). Each unit contained 80 g (when using 1 unit) or 90 g (when using 2 units) poly(styrene-divinylbenzene) (PS-DVB) sulfonate beads and 40 g (when using 1 unit) or 30 g (when using 2 units) FeOOH beads for respective potassium and phosphate removal (the amounts were adjusted after the experiments with 1 unit to achieve the target potassium/phosphate removal ratio of~2-3:1).…”

“…Previously, we explored electro-oxidation (EO) in vitro using graphite electrodes incorporated in a sorbent cartridge containing sorbent particles for potassium and phosphate removal (39). In this technology, a current is applied to the dialysate by which urea is converted into nitrogen, carbondioxide, and water, either directly at the anode or indirectly in the bulk solution via the intermediate EO-product hypochlorite.…”

“…However, these can be neutralized by activated carbon (AC). We achieved clinically relevant urea degradation in blood [9.5 mmol/h (SD 1.0)] with an EO unit in series with AC (39). Chlorine release was below maximum acceptable levels as defined by the Association for the Advancement of Medical Instrumentation (AAMI) standards (1).…”

Urea removal from aqueous solutions—a review

“…Ginval'd et al described specific concepts for the design of artificial kidneys coupled with an electrochemical dialysate regenerator system [8,[100][101][102]. According to a review of electrochemical methods for urea removal in portable dialysis devices written by Wester et al [103], chloride-based electrolytes were still taken into consideration. In this work, different electrode materials (Pt, Ru, and graphite) were studied.…”

Creating a wearable artificial kidney: where are we now?

“…This approach was found to be effective in an in vitro setting. A drawback of electro-oxidation is the oxidation of chloride leading to the formation of reactive chlorine species, such as chloramines, which have to be removed by activated carbon downstream from the electrodes [8]. The prototype (Nephron+) which is based on this approach currently has a weight of around 3 kg.…”