more than 1.2 million people worldwide suffer from end-stage renal disease (esrd) in their kidneys ...
TRANSCRIPT
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
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
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”
http://en.wikipedia.org/wiki/Contact_anglehttp://www.nature.com/nmat/journal/v1/n1/images/nmat715-f1.jpg
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:› Bare Bare + enzyme› Irradiated Irradiated + enzyme› PBD PBD + enzyme› F108 F108 + enzyme PEO
coated› PBD + F108 PBD + F108 + enzyme
PE
O PE
O
PBDPE
O PE
O
PPO
“PBD” “F108”
Characterization of triblock solution Determining the critical micelle
concentration (CMC) of triblocks in solution
Unimers adsorb, aggregates do not
Below CMC Above CMC, micelle
Determine the CMC by measuring surface tension at increasing concentrations of triblocks in the solution
Surface Tension
Concentration
CMC
http://www.youtube.com/watch?v=mwUBemTAHj0
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