Surface sulfonates lock serum albumin into a "hard" corona.

The composition of the layer of proteins adsorbed to macro- or microscopic surfaces of synthetic origin influences the response of living systems to these materials. This adsorbed layer of proteins usually comprises a "soft" coating or corona of labile or exchangeable adsorbed proteins on top of a more tenaciously held "hard" corona in contact with the surface. Here, we link the dependence of cell adhesion on a 20 nm film of polyelectrolyte complex to the "hardness" of the initial corona using albumin, the most prevalent protein in serum. The ease with which albumin can be lost depends on the surface functional group - carboxylate or sulfonate, in particular aromatic sulfonate. Carboxylate permits easier loss of albumin, which presumably allows the subsequent adsorption of proteins such as fibronectin, required for cell adhesion. Sulfonate holds on to albumin more strongly, producing a persistent hard corona likely to remain biocompatible. The mechanism is thought to be related to the higher energy of interaction between sulfonate and amine than between carboxylate and amine, and provides insight on possible reasons why so-called "tissue culture plastic" works so well for in vitro cell culture.

Engineering Thiolated Surfaces with Polyelectrolyte Multilayers.

Interfaces bearing firmly attached thiol groups are useful for many applications requiring the versatile and facile chemistry of the -SH functionality. In this work, rugged ultrathin films were prepared on substrates using layer-by-layer assembly. The surface of these smooth films was capped with a co-polymer containing benzyl mercaptan units. The utility of this coating was illustrated by three applications. First, thiol-ene "click" chemistry was used to introduce the Arg-Gly-Asp (RGD) adhesive peptide sequence on a surface that otherwise resisted good adhesion of fibroblasts. This treatment promoted cell adhesion and spreading. Similar Michael addition chemistry was employed to attach poly(ethylene glycol) to the surface, which reduced fouling by (adhesion of) serum albumin. Finally, the affinity of gold for -SH was exploited by depositing a layer of gold nanoparticles on the thiolated surface or by evaporating a tenacious film of gold without using the classical chromium "primer" layer.

Antifouling Ion-Exchange Resins.

Large quantities of organic ion-exchange resins are used worldwide for water decontamination and polishing. Fouling by microorganisms and decomposition products of natural organic matter severely limits the lifetime of these resins. Much research has thus been invested in polymer-based antifouling coatings. In the present study, poly(4-styrenesulfonate) (PSS) and a co-polymer of PSS and a zwitterionic group were used to spontaneously coat commercial Dowex 1X8 anion-exchange resin. UV-visible spectroscopy provided a precise measure of the kinetics and amount of PSS sorbed onto or into resin beads. When challenged with Chlamydomonas reinhardtii algae, uncoated resin was rapidly fouled by algae. Coating the resin with either the homopolymer of PSS or the co-polymer with zwitterion eliminated fouling. Using narrow- and wide-molecular-weight distribution PSS, a cutoff molecular weight of about 240 repeat units was found, above which PSS was unable to diffuse into the resin. Thus, only one monolayer of added PSS was sufficient to confer a highly desirable antifouling property on this resin while consuming less than 0.1% of the exchanger capacity. Radioactive sulfate ions were used to probe the kinetics of (self)exchange, which were virtually unaffected by the PSS coating. This resin treatment is a fast, ultra-low-cost step for potentially enhancing the lifetime of ion exchangers.

Precision Polyelectrolytes with Phenylsulfonic Acid Branches at Every Five Carbons.

A precision polyethylene containing phenyl branches at every fifth carbon (p5Ph) is nearly quantitatively functionalized (≈95%) with sulfonic acid groups on the para-position of each phenyl branch (p5PhS-H). Unlike polystyrene sulfonate (PSS), p5PhS-H has a glass transition temperature (Tg = 109 °C) well below its thermal decomposition temperature (Td ≈ 200 °C), making this new material capable of thermal processing into molds and films at temperatures between these thermal limits. Neutralization of the sulfonic acid groups with varying counter cations (Li+ , Na+ , Cs+ ) produces a new class of precision polyelectrolytes. Neutralization and increasing size of the counter cation improves the thermal decomposition temperature (Td ) to over 400 °C for the Cs+ form. Neutralization causes Tg to increase above Td for the Li+ and Na+ form. The Cs+ form is found to have an accessible Tg = 294 °C. Further investigations of water absorption and the polyelectrolyte effect of these systems are discussed.

Cell resistant zwitterionic polyelectrolyte coating promotes bacterial attachment: an adhesion contradiction.

Polymers of various architectures with zwitterionic functionality have recently been shown to effectively suppress nonspecific fouling of surfaces by proteins and prokaryotic (bacteria) or eukaryotic (mammalian) cells as well as other microorganisms and environmental contaminants. In this work, zwitterionic copolymers were used to make thin coatings on substrates with the layer-by-layer method. Polyelectrolyte multilayers, PEMUs, were built with [poly(allylamine hydrochloride)], PAH, and copolymers of acrylic acid and either the AEDAPS zwitterionic group 3-[2-(acrylamido)-ethyldimethyl ammonio] propane sulfonate (PAA-co-AEDAPS), or benzophenone (PAABp). Benzophenone allowed the PEMU to be toughened by photocrosslinking post-deposition. The attachment of two mammalian cell lines, rat aortic smooth muscle (A7r5) and mouse fibroblasts (3T3), and the biofilm-forming Gram-negative bacteria Escherichia coli was studied on PEMUs terminated with PAA-co-AEDAPS. Consistent with earlier studies, it is shown that PAH/PAA-co-AEDAPS PEMUs resist the adhesion of mammalian cells, but, contrary to our initial hypothesis, are bacterial adhesive and significantly so after maximizing the surface presentation of PAA-co-AEDAPS. This unexpected contrast in the adhesive behavior of prokaryotic and eukaryotic cells is explained by differences in adhesion mechanisms as well as different responses to the topology and morphology of the multilayer surface.