The developers of the Vincenza wearable artificial kidney (ViWAK) conceived a wearable system consisting of a double-lumen peritoneal catheter with a miniature rotary pump [4]. The system would employ a circuit for dialysate regeneration using parallel waterproof cartridges containing a mixture of activated carbon and polystyrene resins, a filter for deaeration and a dialysate inflow line. The device is controlled remotely by a handheld computer. ViWAK is designed to weigh approximately 2 kg and a standard glucose-based dialysate would be used. The dialysate is allowed to dwell for 2 h and then recycled through the double-lumen peritoneal dialysis catheter allowing continuous flow peritoneal dialysis powered by a lightweight battery-powered pump. After an initial 2 h period, peritoneal dialysate is then continuously recycled by the passage of spent dialysate through a series of sorbents. Sorbents have difficulty clearing urea and most sorbent designs have incorporated urease to clear urea to ammonium and carbon dioxide. Consequently, the dialysate effluent would be pumped first through degassing chamber before returning to the patient. In the evening the patient would drain out the dialysate and instill a fresh bag of 7.5 % icodextrin to aid solute clearance and volume control. The device provides good creatinine and β2-microglobulin clearance of 12–14 l/day. ViWAK would require the patient to perform two standard peritoneal dialysis exchanges per day.

Potential limitations of ViWAK revolve around the stability of dialysate composition as it is recycled. Spent peritoneal dialysate effluent contains proteins in low concentration, including fibrin, but with reuse cumulative protein buildup in the circuit would occur. Additional filters would be required to prevent protein coating of the sorbents, which degrades their efficiency. With these obstacles added to the costs of replacing the sorbents each day, the ViWAK has not progressed from the bench to clinical trials.

The automated wearable artificial kidney (AWAK) is another wearable peritoneal dialysis device with technology focused on dialysate fluid regeneration. AWAK uses a standard single-lumen peritoneal dialysis catheter and unlike the ViWAK is a discontinuous flow system of peritoneal dialysate [2]. The primary difference between current peritoneal dialysis and AWAK is that patients do not have to reestablish the dialysate regularly as it is continuously regenerated. There are two modules, one designed to be changed on a daily basis and the other to be changed monthly. The outflow circuit with spent dialysate in the AWAK pumps the effluent through fibrin filters to produce a protein-free ultrafiltrate. The ultrafiltrate is then passed through sorbents containing urease and then through a degassing chamber before being retained in a storage chamber. The refreshed dialysate is then pumped back into the patient.

Sorbent capacity is a key factor in designing a wearable and portable peritoneal dialysis system. Smaller sorbent quantities will mean earlier saturation and sorbent exhaustion leading to increased frequency of sorbent exchanges. Additional sorbent will reduce the frequency of sorbent exchanges at the cost of adding weight to the system. The AWAK design has two proposed versions, one weighing around 1 kg and the other 3 kg determined by the size of the sorbent cartridges. Replacing sorbent cartridges currently requires the patient to drain out peritoneal dialysate and then re-instill fresh dialysate. Therefore, it is imperative that sorbents have the capacity for at least 24 h to prevent the patient having to perform additional peritoneal dialysis exchanges. Clinical trials aimed at testing sorbent capacity for the AWAK are expected in 2015.

Given that it is based on peritoneal dialysis therapy, the AWAK shows the same limitations as the ViWAK with regard to dialysate stability and the use of glucose-based exchange solutes.

Early developers of a wearable hemodialysis system were confronted with technical challenges including vascular access, circuit anticoagulation, device size, and mechanical reliability. Some conceived devices used an arterial blood supply, and those that worked with venous flow required a fail-safe pump and a continuous electrical power source. Ideally, the device must be able to deliver proposed creatinine clearance targets of 30 ml/min and an ultrafiltration target of 30 ml/min. Importantly, connecting to the patient’s circulation requires additional safety features to prevent air emboli and blood loss and a mechanism to halt the ultrafiltration pump if such events should occur. Hence, pumping systems are the most critical components of the entire device. Advancements in nanotechnology have led to miniaturization of pump mechanisms and circuits that led to the current devices being developed and on clinical trial.