The marked increase in surface-to-volume ratio associated with microscale devices for hemodialysis leads to problems with hemocompatibility and blood flow distribution that are more challenging to manage than those encountered at the conventional scale. In this work stable surface modifications with pendant polyethylene oxide (PEO) chains were produced on polydimethylsiloxane (PDMS), polycarbonate microchannel, and polyacrylonitrile membrane materials used in construction of microchannel hemodialyzer test articles. PEO layers were prepared by radiolytic grafting of PEO-polybutadiene-PEO (PEO-PB-PEO) triblock polymers to the material surfaces. Protein repulsion was evaluated by measurement of surface-bound enzyme activity following contact of uncoated and PEO-coated surfaces with β-galactosidase. Protein adsorption was decreased on PEO-coated polycarbonate and PDMS materials to about 20% of the level recorded on the uncoated materials. Neither the triblocks nor the irradiation process was observed to have any effect on protein interaction with the polyacrylonitrile membrane, or its permeability to urea. This approach holds promise as a means for in situ application of safe, efficacious coatings to microfluidic devices for blood processing that will ensure good hemocompatibility and blood flow distribution, with no adverse effects on mass transfer.

Cleavable amphiphilic triblock surfactants with methoxypolyethylene oxide (PEO) side-chains attached to polybutadiene (PBD) center blocks by ester linkages were synthesized. The PEO-PBD-PEO triblocks were adsorbed on hydrophobic silicon wafers and covalently stabilized by g-irradiation. The PEO side-chains were then cleaved from the PBD backbones by acid hydrolysis. Decoration of the immobilized centerblocks with b-cyclodextrin allowed direct imaging by standard atomic force microscopy techniques. Widely varied surface coverage, layer morphology and distributions of the PBD centerblocks were observed on surfaces coated with different triblock concentrations and PEO:PBD ratios. Surfaces coated from 1 mg/mL solutions of triblocks (near the critical aggregation concentration (CAC), 0.28-0.53 mg/mL) were sparsely coated, and triblocks containing 75-85% PEO exhibited negligible surface coverage, possibly due to poor adsorption or facile desorption during rinsing. Dense surface packings, albeit some with evident defects sufficiently large to allow for protein adsorption, were produced from 10 mg/mL triblock solutions (an order of magnitude above the CAC). This proof-of-concept report describes a method that may be useful in optimizing surface coatings on model substrates, and thus lend insight into optimization of coating conditions for economical production of non-fouling triblock-based PEO coatings on clinically relevant biomedical materials.

Earlier work provided direction for development of responsive drug delivery systems based on modulation of the structure, amphiphilicity, and surface density of bioactive peptides entrapped within pendant polyethylene oxide (PEO) brush layers. In this work, we describe the sequential and competitive adsorption behavior of such peptides at pendant PEO layers. Three cationic peptides were used for this purpose: the arginine-rich, amphiphilic peptide WLBU2, a peptide chemically identical to WLBU2 but of scrambled sequence (S-WLBU2), and the nonamphiphilic peptide poly-L-arginine (PLR). Optical waveguide lightmode spectroscopy (OWLS) was used to quantify the rate and extent of peptide adsorption and elution at surfaces coated with PEO. UV spectroscopy and time-of-flight secondary ion mass spectrometry (TOF-SIMS) were used to quantify the extent of peptide exchange during the course of sequential and competitive adsorption. Circular dichroism (CD) was used to evaluate conformational changes after adsorption of peptide mixtures at PEO-coated silica nanoparticles. Results indicated that amphiphilic peptides are able to displace adsorbed, non-amphiphilic peptides in PEO layers, while non-amphiphilic peptides were not able to displace more amphiphilic peptides. In addition, peptides of greater amphiphilicity dominated the adsorption at the PEO layer from mixtures with less amphiphilic or non-amphiphilic peptides.