The generation of surfaces and interfaces that are able to withstand protein adsorption is a major challenge in the design of blood-contacting materials for both medical implants and bioaffinity sensors. Poly(ethylene glycol)-derived materials are generally considered to be particularly effective candidates for the fabrication of protein-resistant materials. Most metallic biomaterials are covered by a protective, stable oxide film; converting such oxide surfaces, which are known to strongly interact with proteins, into noninteractive surfaces requires a specific design of the surface/interface architecture. A class of copolymers based on poly(L-lysine)g-poly(ethylene glycol) (PLL-g-PEG) was found to spontaneously adsorb from aqueous solutions onto several metal oxide surfaces, such as TiO 2 , Si 0.4 Ti 0.6 O 2 , and Nb 2 O 5 , as measured by the in situ optical waveguide lightmode spectroscopy technique and by ex situ X-ray photoelectron spectroscopy. The resulting adsorbed layers are highly effective in reducing the adsorption both of blood serum and of individual proteins such as fibrinogen, which is known to play a major role in the cascade of events that lead to biomaterial-surfaceinduced blood coagulation and thrombosis. Adsorbed protein levels as low as <5 ng/cm 2 could be achieved for an optimized polymer architecture. The modified surfaces are stable to desorption under flow conditions at 37 °C and pH 7.4 in HEPES [4-(2-hydroxyethyl)piperazine-1-ethanesulfonic acid] and PBS (phosphatebuffered saline) buffers. The adsorbed layer of copolymer is thought to form a comblike structure at the surface, with positively charged primary amine groups of the PLL bound to the negatively charged metal oxide surface, while the hydrophilic and uncharged PEG side chains are exposed to the solution phase.Copolymer architecture is an important factor in the resulting protein resistance; it is discussed on the basis of packing-density considerations and the corresponding radii of gyration of the different PEG chain lengths studied. This surface functionalization technology is believed to be of value for use in both the biomaterial and biosensor areas, as the chosen macromolecules are biocompatible and the application is straightforward and cost-effective. † Part of the special issue "Gabor Somorjai Festschrift".

We report on the design and characterization of a class of biomolecular interfaces based on derivatized poly(L-lysine)-grafted poly-(ethylene glycol) copolymers adsorbed on negatively charged surfaces. As a model system, we synthesized biotin-derivatized poly(L-lysine)-grafted poly(ethylene glycol) copolymers, PLL-g-[(PEGm) (1؊x) (PEG-biotin)x], where x varies from 0 to 1. Monolayers were produced on titanium dioxide substrates and characterized by x-ray photoelectron spectroscopy. The specific biorecognition properties of these biotinylated surfaces were investigated with the use of radiolabeled streptavidin alone and within complex protein mixtures. The PLL-g-PEG-biotin monolayers specifically capture streptavidin, even from a complex protein mixture, while still preventing nonspecific adsorption of other proteins. This streptavidin layer can subsequently capture biotinylated proteins. Finally, with the use of microfluidic networks and protein arraying, we demonstrate the potential of this class of biomolecular interfaces for applications based on protein patterning. C ontrolling immobilization of biomolecules on surfaces, while preventing nonspecific adsorption of unwanted species, has become an important goal for monitoring specific biointeractions and binding of biomolecules or cells. Indeed, in diagnostic assays, biomaterial devices, and surface-related bioanalytical applications, nonspecific protein binding can often be the obstacle to higher sensitivity, reproducibility, or implant integration. Therefore, in past decades, many immobilization strategies have been established. These include physisorption to solid organic or inorganic supports (noncovalent coupling occurs by electrostatic and van der Waals forces), noncovalent chemisorption, and covalent immobilization on organic thin films of different molecular organization.Physisorption of biomolecules directly on the surface of inorganic substrate materials such as glass or organic coatings such as polymeric materials and adhesion layers (polylysine and nitrocellulose) probably constitutes the least technically challenging immobilization procedure. For instance, spotted microarrays of nucleic acids and, more recently, proteins are mostly based on physical adsorption (1). However, these methods suffer from some key limitations, such as their lack of control over the quantity and orientation of adsorbed biomolecules, and, hence, from lower reproducibility, lower interaction efficiencies, and high error rates. Moreover, additional passivation or blocking steps of the remaining sites are often required to limit the extent of nonspecific binding and protein denaturation. These are serious limitations for protein microarray applications.Attempts to control the biomolecular density and orientation of biomolecules at the solid-liquid interface to obtain better reproducibility have been undertaken through various strategies of covalent and site-specific immobilization. These include mostly immobilization via organic thin films such as selfassembled alkanethiol a...

This paper describes the first detailed analytical characterization of the surface properties of a new class of biomolecular interfaces based on derivatized poly(L-lysine)-grafted-poly(ethylene glycol) (PLL-g-PEG) copolymers. Such copolymers spontaneously adsorb to negatively charged surfaces under physiological pH and efficiently repel nonspecific protein adsorption while providing PEG-tethered functional/active sites for specific biomolecular recognition. As a model system, we synthesized biotin-derivatized (PLL-g-PEG) copolymers, PLL-g-[(PEG)1-x(PEG-biotin)x], where x varies from 0 to 1. The copolymers were adsorbed on titanium dioxide substrates. Surface characteristics and biorecognition properties were investigated using X-ray photoelectron spectroscopy and radiometry. We show that the monolayer formed is ∼20-25 Å in thickness. It is organized with its PLL backbone located within the first 10 Å on the substrate and with the PEG side chains located above the PLL. The resulting biotin surface concentration depends linearly on the biotin concentration in the bulk copolymer. This aspect implies that the surface concentration of functional groups can be adjusted by adapting their concentration within the bulk copolymer. The PLLg-PEG(-biotin) monolayers are efficient in repelling nonspecific protein adsorption but can specifically bind streptavidin (SA). Within the biotin range considered, the SA surface concentration increases linearly with the biotin surface concentration of the monolayer.

Thoracoabdominal aortic aneurysm repair, with its requisite intraoperative mesenteric ischemia-reperfusion, often results in the development of systemic inflammatory response syndrome, multiorgan dysfunction syndrome (MODS), and death. In the present study, an adverse clinical outcome following thoracoabdominal aortic aneurysm repair was identified by blood leukocyte genomic and plasma proteomic responses. Time-dependent changes in the expression of 146 genes from blood leukocytes were observed (p &lt; 0.001). Expression of 138 genes (p &lt; 0.001) and the concentration of seven plasma proteins discriminated between patients who developed MODS and those who did not, and many of these differences were evident even before surgery. These findings suggest that changes in blood leukocyte gene expression and plasma protein concentrations can illuminate pathophysiological processes that are subsequently associated with the clinical sequelae of systemic inflammatory response syndrome and MODS. These changes in gene expression and plasma protein concentrations are often observed before surgery, consistent with either a genetic predisposition or pre-existing inflammatory state.