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Nano and Micro Technologies

Nano and Micro Technologies - Poster Session E

Poster K4 - Testing of nanoporous silicon-nitride membrane ultrafiltration for hemodialysis

Saturday, October 26, 2024
10:00 AM – 11:00 AM EST
Location: Exhibit Hall E, F & G

Introduction:  As of June 2024, over 800,000 Americans are living with end-stage renal disease (ESRD), 69% of which require regular dialysis sessions to survive [1]. Dialysis is an imperative treatment option for ESRD, as many patients do not qualify or are waiting for a kidney transplant. The dialysis process takes on average between 12 hr/week and 20 hr/week in clinical sessions [1]. The quality of life for these patients is significantly altered as they must remain attached to machinery for many hours, and often feel unwell for the remainder of the day. Unfortunately, data suggests that longer dialysis sessions can help improve patient health [2]. With the already limiting nature of hospital-based dialysis, new dialysis treatments are needed to improve the overall quality of life for people undergoing hemodialysis. Portable and wearable dialysis devices could fill this need.
We work with nanoporous silicon nitride (NPN) membranes with a pore size of 35nm-0.35 μm to perform hemodialysis in a miniaturized device. Smaller versions of these membranes have shown filtration success in previous testing with buffer solutions and in a small animal model[3]. Larger chips will be able to filter faster, helping the artificial device keep up with the body’s needs. Smaller, lightweight dialysis devices would allow patients to receive constant care, work traditional jobs and generally have their freedom and flexibility back. Here we show filtration of urea from plasma and blood samples is possible using miniature NPN membranes.

Materials and

Methods:  Our lab is testing urea filtration of phosphate-buffered saline (PBS), plasma, and blood through small, customized nanoporous membrane-chips using a large-animal benchtop model. The current chips have increased surface area compared to our previous chips while maintaining the same pore size. We aim to show that greater surface area can increase ultrafiltration rates. The chips are clamped in a 3D-printed housing unit to stabilize and control fluid flow. Using these membranes and housing units, we pump urea-spiked analyte (PBS, bovine plasma, or bovine blood) and PBS buffer as the dialysate, in opposing directions on either side of the membrane. On one side, 180 mL to 500 mL of urea-spiked analyte is pumped over the membrane at a rate of 50 mL/min in a continuous flow manner. On the other side, 5 L of dialysate is pumped in the opposing direction at 120 mL/min into a waste beaker so the solution only passes the membrane once. Dialysis experiments were run for 40 minutes, with 100 µL samples taken from the analyte body at 2.5-minute intervals for the first 20 minutes and 5-minute intervals for the remaining 20 minutes. 100 µL samples were also taken from the dialysate body at the beginning and end of each experiment. Light absorption-based urea assays were used to measure the absorption of the samples and extrapolate the urea in the analyte and dialysate before, after, and during (analyte only) the experiment to determine the extent and rate of filtration using the membranes.

Results, Conclusions, and Discussions: We observed a decrease in urea concentration of the analytes tested with corresponding increases in their respective dialysates in the 40-minute tested timeframe. This rate of clearance suggests that the NPN membranes are effective dialyzers and can be used to filter urea from the blood. This study demonstrates that the NPN membranes are effective at clearing small metabolic waste such as urea from bovine plasma and blood. Additional testing is required due to the change in viscosity. Future directions may include an effort to refilter the spent dialysate allow for a reusable, mobile source.

Acknowledgements (Optional):  1 United States Renal Data System. 2023 USRDS Annual Data Report: Epidemiology of kidney disease in the United States. Retrieved from National Institutes of Health, National Institute of Diabetes and Digestive and Kidney Diseases, Bethesda, MD: https://adr.usrds.org/2023
2 Tentori, F., Zhang, J., Li, Y., Karaboyas, A., Kerr, P., Saran, R., . . . Robinson, B. (2012). Longer dialysis session length is associated with better intermediate outcomes and survival among patients on in-center three times per week hemodialysis: results from the Dialysis Outcomes and Practice Patterns Study (DOPPS). Nephrol Dial Transplant, 27(11), 4180-4188. doi:10.1093/ndt/gfs021
3 Hill, K., Walker, S. N., Salminen, A., Chung, H. L., Li, X., Ezzat, B., . . . Johnson, D. G. (2020). Second Generation Nanoporous Silicon Nitride Membranes for High Toxin Clearance and Small Format Hemodialysis. Adv Healthc Mater, 9(4), e1900750. doi:10.1002/adhm.201900750