Blood protein adsorption and blood platelet adhesion onto surface-attached poly(alkylacrylamide) networks that exhibit small and systematic variations in chemical composition are investigated. The polymer coatings are generated by depositing a thin layer of benzophenone-group-containing copolymer onto a solid substrate, followed by photo crosslinking and simultaneous surface-attachment. The correlation of the swelling of the obtained surface-attached networks with the adsorption of blood proteins and cellular adhesion is studied. The swollen surface-attached layers are inert to blood proteins and platelet cells. These results suggest that the hydrogel-coated materials are promising candidates for the generation of hemocompatible surfaces.

We describe a simple approach to generate surface-attached biocompatible hydrogels with tunable cross-link density and employ them to study the effect of gel structure on protein adsorption. Using free-radical polymerization, we synthesize a series of random copolymers comprising N-isopropylacrylamide (NIPAm) and the photoactive curing agent 4-methacryloyl-oxy-benzophenone (MABP) of mole fractions ranging from 2.5 to 10%. We deposit a thin film of the precursor copolymer (∼150 nm) on a silicon or glass substrate, which is precoated with monolayers of benzophenone-silane, then cross-link it through UV irradiation at 365 nm (dose ≈ 6-10 J/cm) to generate surface-attached networks. A systematic investigation of the network properties such as gel fraction, cross-link density, and swelling ratio reveals that gels with higher MABP content (≥5%) produce densely cross-linked hydrophobic networks with low or no swelling in an aqueous medium. We study the adsorption of fibrinogen (Fg) on such hydrogel substrates and establish that the amount of adsorbed Fg depends on the degree of cross-linking and the swelling capacity of the networks. Specifically, although Fg adsorbs heavily on denser networks, loosely bound gels that swell in aqueous medium repel proteins. We attribute the latter behavior to entropic shielding and size-exclusion factors.

We present a versatile synthetic route leading toward generating surface-attached polyacrylamide gels, in which the cross-link density varies continuously and gradually across the substrate in two orthogonal directions. We employ free radical polymerization to synthesize random copolymers comprising ~5% of photoactive methacrylyloxybenzophenone (MABP), ~5% of thermally active styrene sulfonyl azide (SSAz), and ~90% of N-isopropylacrylamide (NIPAAm) units. The presence of MABP and SSAz in the copolymer facilitates control over the cross-link density of the gel in an orthogonal manner using photoactivated and thermally activated cross-linking chemistries, respectively. Spectroscopic ellipsometry is employed to determine the degree of swelling of the gel in water and methanol as a function of position on the substrate. Network swelling varies continuously and gradually across the substrate and is high in regions of low gel fractions and low in regions of high gel fractions.

We synthesized a series of novel degradable alternating copolyesters composed of diglycolic anhydride (DGA) and two epoxides, epoxymethoxytriethylene glycol (ETEG) and a photoactive crosslinking agent epoxy benzophenone (EBP). After UV crosslinking, soaking the films in a good solvent (tetrahydrofuran) removed uncrosslinked material, and the resulting film gel fractions were calculated. These network films were then degraded in buffer solutions of varying pH values. The degradation of networks with lower gel fraction (fewer crosslinks) was faster and followed first-order kinetics. In contrast, the denser network degraded slower and followed zeroth-order kinetics. The lower gel fraction networks possess a higher swelling ratio and resist bovine serum albumin (BSA) adsorption better by entropic shielding and faster degradation. In comparison, higher gel fraction networks with higher EBP mole fractions adsorb more BSA due to hydrophobic interactions and slower degradation.

The compressive and tribological behavior of chemically crosslinked, surface-attached hydrogel layers has been investigated by indentation and friction tests using an atomic force microscope provided with a colloidal probe, where the probe is covered with a chemically identical hydrogel layer. The hydrogel layers are composed of a polydimethyl acrylamide copoly mer containing methacryloyl benzophenone units which is photochemically crosslinked and bound to substrates carrying self-assembled monolayers of a benzophenone group containing silane. The compression and friction behavior of the thus generated surface-attached hydrogel samples, which due to the surface attachment can only swell in one dimension, are studied as a function of fi lm thickness and crosslink density. It is found that the pressure-induced deswelling in the contact region dominates the friction between two surfaces coated with surface-attached hydrogels and that the rate of loading and the fi lm thickness determine the tribological properties, especially when the layer thicknesses are lower than 1 μm. properties of materials has evolved from more empiric, macroscopic investigations in the direction of molecularly oriented studies at the micro-or even nanoscale. [ 1,2 ] A very attractive research topic in bio-tribology is to elucidate how natural joints obtain their unique friction an wear properties. Joints like human hips or knees are designed to last (hopefully) for a life time and provide low friction values and good wear properties despite that under certain circumstances the forces, both normal and shear forces, acting on the joints are very high. This is especially the case during sports activities such as long-distance running, weight lifting, or skiing or upon impact such as landing with a parachute to name just a few examples. In all these cases, strong forces act upon the joints and occasional peak loads occur, putting strong demands on the stability of the assembly and onto a reduction of the friction. The coeffi cient of friction (COF) between cartilage surfaces can be as low as μ = 0.001, which, despite strong advances in the development of lubricants, can be hardly duplicated even by the most sophisticated technological means on such a macroscopic level. Breakdown of the lubrication process can lead to wear of the cartilage, and more than 50% of the population may eventually suffer osteoarthritic pains