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
HYDROPHILIC
PEO
PEO

PBD
HYDROPHOBIC
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
HYDROPHILIC
PEO
“PBD”
PEO
PEO
PEO
HYDROPHILIC
“F108”
PPO
PB
HYDROPHOBIC
HYDROPHOBIC
HYDROPHOBIC
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_angle
http://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
Contact Angle of Water on Glass
90
80
Contact Angle (degrees)
70
60
50
40
30
20
10
0
Bare
Bare + BSA
PEO
Treatment
PEO + 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:

› PBD
› F108
PEO
PEO
› PBD + F108
PBD
“PBD”
PEO coated
PEO
› Irradiated
Bare + enzyme
Irradiated + enzyme
PBD + enzyme
F108 + enzyme
PBD + F108 + enzyme
PEO
› Bare
PPO
“F108”
Relative Enzyme Activity on Polycarbonate, 1 mg/mL
Triblock Solutions
100%
Percent Enzyme Activity
80%
60%
40%
20%
0%
Bare
-20%
Bare + e
Irr
PBD
Treatment
F108
PBD + F108
Relative Enzyme Activity on Polycarbonate, 1 mg/mL
Triblock Solutions
Percent Enzyme Activity
100%
80%
60%
40%
20%
0%
Bare
Bare + e
Irr + e
PBD + e
Treatment
F108 + e
PBD + F108 + e
Relative Enzyme Activity on Polycarbonate, 5 mg/mL
triblock solutions
Percent Enzyme Activity
100%
80%
60%
40%
20%
0%
Treatment
Characterization of triblock solution
 Determining the critical micelle
concentration (CMC) of triblocks in
solution

Below CMC

Above CMC, micelle
Unimers adsorb, aggregates do not

Determine the CMC by measuring
surface tension at increasing
concentrations of triblocks in the solution
Surface Tension
CMC
Concentration
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
PEO
PEO
HYDROPHILIC
“PBD”
HYDROPHOBIC
PBD
PEO
PEO
HYDROPHILIC
PEO
“F108”
HYDROPHOBIC
HYDROPHOBIC