A Study of Mass Transport Towards the Design and Characterization of an Artificial Kidney
This dissertation focuses on the design, fabrication, and study necessary for a renal cell device that mimics the bioreactor component of a bioartificial kidney. The motivation behind the project is to further the development toward an implantable bioartificial human kidney that will improve the quality of life for end stage renal disease (ESRD) patients. The bioartificial kidney system contains two units: i) a hemofilter based upon nanoporous silicon membranes, and ii) a bioreactor composed of kidney proximal tubule (PT) cells. The Roy group has pioneered work in membranes that have been engineered with the use of silicon-based microfabrication techniques to attain pore slits with a width of 8-11 nm. The fabricated nanopore membranes allow for a device with tight pore size distribution, complete immunoisolation, and modifiable surface chemistry. These are critical membrane specifications that make them well suited for this application. These silicon nanopore membranes (SNMs) serve the basis of a hemofilter for a bioartificial kidney. The function of the hemofilter is to selectively pass molecules in the blood that are smaller than proteins and cells found in the blood to produce filtrate. The filtrate, essentially plasma, then can be passed to the bioreactor for sufficient reabsorption of water and vital molecules back into the blood, thereby concentrating the remaining filtrate and passing it on to the bladder as waste. In order to prevent an immune response by the host one needs to design the bioreactor with a sufficient immunoisolation barrier between the cells and the blood. The aforementioned membranes are a likely candidate.
In order to evaluate the performance of the overall bioreactor module the mass transport through each layer of this system has been characterized. First, a process flow system has been designed to measure the membrane permeability to specific solutes of therapeutic interest NaCl (MW 58 Da), urea (MW 60 Da), creatinine (MW 113 Da), beta 2-microglobulin (B2M) (MW 11,800 Da) dissolved in a phosphate buffered saline (PBS) solution with bovine serum albumin (BSA) (66,000 Da). Second, a device compatible with commercially available Corning SnapwellTM inserts was designed to characterize proximal tubule cell function in planar flow. Lewis Lung Cancer Porcine Kidney Cells (LLC-PK1) were statically cultured on the porous membranes of the Snapwells before assembly into the devices and exposing cells to physiological shear stress levels. Finally, using rapid fabrication techniques a SNM cell culture scaffold has been developed in order to fix a SNM membrane adjacent to a commercial polycarbonate tissue culture membrane for viability and characterization of solute reabsorption.
It has been shown that the diffusive permeability through the SNM is on the same order as commercial hemodialyzer membranes. Moreover, membrane resistance is sufficiently low to allow the bioreactor system to be cellular-transport limited. Additionally, the Snapwell system maintains LLC-PK1 barrier function with 3.5 fold increase in reabsorption performance with increasing shear stress rates. Finally, the SNM tissue culture system shows viability on SNM for up to 1 week with sustained creatinine and urea barrier performance.