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

PE

O PE

O

PB

PE

O PE

O

PPO

“PBD” “F108”

HYDROPHOBIC

HYDROPHILIC

HYDROPHOBIC

HYDROPHILIC

HYDROPHOBIC

PROT

EI

N

PROT

EI

N

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

HYDROPHOBIC

PROT

EI

N

PROT

EI

N

HYDROPHOBIC

HYDROPHILIC

PE

O PE

O

PBD

HYDROPHOBIC

HYDROPHILIC

PE

O PE

O

PEO

“PBD”

“F108”