Shell "locked" nanoassemblies ranging in size from 34 to 78 nm have been prepared from interpolyelectrolyte complexation of block copolymer micelles of poly[(N,N-dimethylacrylamide)-b-(N-acryloylalanine)-b-(N-isopropylacrylamide)] with the homopolymer poly(ar-vinylbenzyl)trimethylammonium chloride above the unimer to micelle phase transition temperature of the block copolymer in water. Of technological significance is the reversibility of the shell cross-linking by addition of 0.4 M NaCl, allowing micelle dissociation below the lower critical solution temperature of the copolymer micelles. Poly(N-acryloylalanine) (AAL) and block copolymers were prepared directly in water via controlled reversible addition fragmentation chain transfer (RAFT) polymerization utilizing mono-and difunctional poly(N,N-dimethylacrylamide) macroCTAs.

It is highly desirable to develop a universal nonfouling coating via a simple one-step dip-coating method. Developing such a universal coating method for a hydrophilic polymer onto a variety of surfaces with hydrophobic and hydrophilic properties is very challenging. This work demonstrates a versatile and simple method to attach zwitterionic poly(carboxybetaine methacrylate) (PCB), one of the most hydrophilic polymers, onto both hydrophobic and hydrophilic surfaces to render them nonfouling. This is achieved by the coating of a catechol chain end carboxybetaine methacrylate polymer (DOPA-PCB) assisted by dopamine. The coating process was carried out in water. Water miscible solvents such as methanol and tetrahydrofuran (THF) are added to the coatings if surface wettability is an issue, as for certain hydrophobic surfaces. This versatile coating method was applied to several types of surfaces such as polypropylene (PP), polydimethyl siloxane (PDMS), Teflon, polystyrene (PS), polymethylmethacrylate (PMMA), polyvinyl chloride (PVC) and also on metal oxides such as silicon dioxide.

Here we demonstrate that the film refractive index (RI) can be an even more important parameter than film thickness for identifying nonfouling polymer films to undiluted human blood plasma and serum. The film thickness and RI are two parameters obtained from ellipsometry. Previously, film thickness has been correlated to ultra-low fouling properties. Practically, the film RI can be used to characterize polymer density but is often overlooked. By varying the water content in the surface-initiated atom transfer radical polymerization of zwitterionic carboxybetaine, a minimum of ∼1.5 RI units was necessary to achieve <5 ng/cm(2) of adsorption from undiluted human serum. A model of the film structure versus water content was also developed. These results point to an important parameter and simple approach for identifying surface coatings suitable for real-world applications involving complex media. Therefore, ultra-low fouling using a thin film is possible if it is densely packed.

In this work, we study how film thickness and chain packing density affect the protein-resistant properties of polymer brushes in complex media. Polymer brushes based on dual-functional poly(carboxybetaine acrylamide) (pCB) were prepared via surface-initiated photoiniferter-mediated polymerization. By adjusting UV radiation time and solvent polarity, pCB films with different thicknesses can be achieved and characterized using an ellipsometer. The packing density of pCB polymer chains is directly related to the swelling ratio of swollen to collapsed film thicknesses. Results showed that the dry film thickness alone, used often in the literature, is not sufficient to correlate with nonfouling properties and the chain packing density must be considered for the design of nonfouling surface coatings.

A photo-cross-linkable carboxybetaine (CB)-terminated thiol with only one CB headgroup was introduced to modify gold nanoparticles (GNPs) via self-assembled monolayers (SAMs). This CB-terminated thiol consists of three moieties: (a) an anchoring thiol group, which binds directly to the GNP surface, (b) a CB terminal group, which is highly resistant to protein adsorption, and (c) a diacetylene group in the middle, which is converted to a poly(enyne) structure during UV irradiation via 1,4-topochemical polymerization. Results show that, after cross-linking, CB-modified GNPs are highly resistant to protein adsorption from undiluted human blood serum and cell uptake, and are stable at low pH and high temperature. This cross-linkable CB thiol holds tremendous potentials for biomedical applications where stable and thin coatings are needed.

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