Toward a closed loop dialysis with urea adsorption by PhenylGlyoxAldehyde (PGA): Experiments and modeling

This study investigated the use of PhenylGlyoxAldehyde (PGA)-functionalized polymer beads as urea sorbents for closed-loop hemodialysis. The impact of initial urea concentration and volumetric flow rate was assessed through dynamic in vitro experiments using packed columns (8 g PGA beads; 12–40 mL/min; 15–30 mM urea). The adsorption kinetics were modeled using a pseudo-second-order equation combined with a Langmuir isotherm (binding capacity up to 1.85 mmol/g at 37 °C). Within the low-Reynolds-number regime explored, the pseudo-kinetic constant increased linearly with average section velocity (3.86–5.51 × 10−6 L mol⁻¹·s⁻¹ for 2.4–8 cm/min), in line with the expected increased mass transport. The model accurately predicted urea adsorption in single and dual-column (series and parallel) configurations, and it was extended to simulate in vivo closed-loop dialysis. To remove ∼330 mmol of urea — equivalent to daily production — in a 2.5 h session, a total of 1 kg of dry PGA (3.5 kg of wet PGA) would be required, making the system suitable for portable hemodialysis. When dialysis is extended to 8 h (e.g., nocturnal home therapy), the sorbent requirement reduces to 0.6 kg of dry PGA (2.1 kg of wet PGA). While not wearable, this configuration may enable the development of compact bedside dialysis systems. The validated model offers a predictive framework for optimizing system design and scaling to other sorbates and clinical scenarios.