 More than 1.2 million people worldwide suffer from end-stage renal disease (ESRD) in their kidneys  Increasing at 6-7% annually  Require hemodialysis therapy: › 3 treatments per week › 4-5 hours per treatment › Removes toxins from blood

 Miniaturization of hemodialysis  Higher efficiency  Potentially wearable, implantable  Longer duration, 8-hour daily treatment › Less physically intensive › Also better mimics natural kidney function

 Downscaling the device increases the surface-to-volume blood contact ratio inside blood flow channels  Increased risk of blood clotting

 Coat the surfaces of interest with polyethylene oxide (PEO) brush layers  PEO in a brush configuration (coating) has been shown to prevent proteins from adsorbing to surfaces HYDROPHOBIC HYDROPHILIC PEO PBD HYDROPHOBIC SURFACE

 Coating the microchannel surfaces of the hemodialyzer with a PEO layer can be accomplished with the use of triblock copolymers of the form “A-B-A” where: › the “A” block is PEO › the “B” block is a polymer chain that will bind permanently to the underlying material  This must be accomplished without the use of harsh chemicals and without compromising the integrity of the underlying material  Portable hemodialysis device will be constructed out of polycarbonate, material of primary interest

PEO PB PEO PPO “PBD”“F108” HYDROPHOBIC HYDROPHILIC HYDROPHOBIC HYDROPHILIC

HYDROPHOBIC PROTEIN

 Coat polycarbonate samples with PEO  Evaluate PEO brush layer quality: › Challenging with protein › To find and develop a consistent method of exposing test surfaces to protein and then be able to quantify any protein adsorption on polycarbonate samples  Characterize the “PBD” triblock

 Previous work: › Protein staining techniques  Protein detection: › Contact angle › Enzyme adsorption assay  Triblock characterization: › Tensiometry

 Contact angle to detect presence of protein on a surface  Place a drop of water on test surface  Hydrophobicity of surface affects how the water drop “sits”

 Used glass microscope slides as model surface to determine if contact angle is sufficient in determining surface changes  Ran 4 sample types: › Bare › Bare + bovine serum albumin (BSA) › PEO coated › PEO coated + BSA

 Coated test surfaces with PEO as appropriate › Prepared solution of PEO containing triblocks in water › Placed polycarbonate in solution › Irradiated and rinsed  Exposed test surfaces to the enzyme β-galactosidase as appropriate, to gauge potential for non-specific protein adsorption › o-nitrophenyl-β-galactoside (oNPG) when in the presence of β-galactosidase reacts to form oNP and glucose › oNP turns yellow when the pH is raised above 7, allows for indirect detection of enzyme, if present at the test surface

 Exposed all test surfaces to oNPG solution to check for enzyme presence  Resulting oNPG/oNP solutions from each sample surface were extracted and the pH of the sample solutions were raised

 Used rectangular polycarbonate strips as testing surface  Ran 10 sample types: › BareBare + enzyme › IrradiatedIrradiated + enzyme › PBDPBD + enzyme › F108F108 + enzyme PEO coated › PBD + F108PBD + F108 + enzyme PEO PBD PEO PPO “PBD”“F108”

 Characterization of triblock solution  Determining the critical micelle concentration (CMC) of triblocks in solution  Unimers adsorb, aggregates do not Below CMCAbove CMC, micelle

 Determine the CMC by measuring surface tension at increasing concentrations of triblocks in the solution Surface Tension Concentration CMC

 Contact angle was not sensitive enough to detect protein adsorption  Enzyme detection assay was sensitive enough  Work so far shows that treated surfaces can prevent protein adsorption: › implies presence of PEO on the polycarbonate › This confirms the hypothesis and indicates that PEO can indeed be placed on polycarbonate surfaces using polymer triblocks

 Optimize triblock adsorption conditions: › Solution concentrations › Exposure times › Radiation dosages  Test in microchannel dialyzer

Special thanks to:  Dr. Joseph McGuire  Dr. Karl “Rat” Schilke  Dr. Woo Kul Lee  Joshua Snider  Keely Heintz  Rose Felber  Julie Auxier  Dr. Kevin Ahern  Howard Hughes Medical Institute  URISC  NIH R01EB011567

 Osmotic pressure: › Crushed the layer down when protein comes › Creates higher concentration of PEO › Creates an osmotic pressure/imbalance › Water wants to rush in and re-establish the regular brush layer configuration(?) and then pushes the protein away

HYDROPHOBIC PROTEIN HYDROPHOBIC HYDROPHILIC PEO PBD HYDROPHOBIC HYDROPHILIC PEO “PBD” “F108”