The impact of nanoscale chemical features on micron-scale adhesion: Crossover from heterogeneity-dominated to mean-field behavior

This work explores the impact of nanoscale surface heterogeneity, small relative to the effective contact area between two surfaces, on pairwise colloid-scale interactions. Polycation-based positive patches, of order 10 nm in diameter, arranged randomly and lying flat on otherwise negative substrates, were used to create surfaces whose competing attractive and repulsive features determined the net interactions with opposing surfaces. Lab experiments and simulations of the adhesion of gently flowing dilute negative microparticles varied particle size (0.5–2 μm), ionic strength (κ−1 = 1–12 nm) and the density of heterogeneity on the collectors. Limiting behaviors from heterogeneity-controlled at high ionic strength to mean-field-like interactions at low ionic strength are reported. When heterogeneities are important, pairwise interactions are more attractive than predicted by average surface properties (e.g. per DLVO), and an adhesion threshold, describing the minimum average density of cationic features needed for single particle capture (adhesion), depends strongly on Debye length. In the opposite limit, the threshold becomes insensitive to the Debye length, and the average surface character approximates the interactions. An analytical treatment, reduced to a simple scaling argument predicts a −1/2 power-law dependence of the adhesion threshold on Debye length and particle size. A slightly stronger particle size dependence in experiments and simulations results from hydrodynamic contributions along with slight scaling differences in electrostatic, van der Waals, and hydrodynamic forces. An analogy to biological ligands is made for the heterogeneity-dominated limit: it is discovered, for this particular system, that engagement of as few as 20–100 cationic patches dictates particle adhesion (with details depending on flow, particle size, and ionic strength), similar to reports for selectin-mediated rolling of white blood cells during the inflammatory pathway. Also discovered is a heterogeneity-dependent crossover in the effect of ionic strength on particle capture, where added salt promotes particle adhesion in most cases but stabilizes the particles when the heterogeneity becomes relatively dense

Adsorbed Polyzwitterion Copolymer Layers Designed for Protein Repellency and Interfacial Retention

Poly­(2-meth­acryl­oyl­oxy­ethyl phos­phoryl­choline) (pMPC), when end-tethered to surfaces by the adsorption of copolymeric cationic segments, forms adsorbed layers that substantially reduce protein adsorption. This study examined variations in the molecular architecture of copolymers containing cationic poly­(tri­methyl­am­monium ethyl meth­acrylate (pTMAEMA) anchor blocks that adsorbed strongly to negative surfaces. With appropriate copolymer design, the pTMAEMA blocks were shielded, by pMPC tethers, from solution-phase proteins. The most protein-resistant copolymer layers, eliminating fibrinogen and lysozyme adsorption within detectible limits of 0.01 mg/m², had metrics (the amount of pMPC at the surface and the reduced tether footprint) consistent with the formation of an interfacial polymer brush. The p­(TMAEMA-<i>b</i>-MPC) copolymer layers substantially outperformed the protein resistance of surface-polymerized pMPC layers when compared on a per-polyzwitterion-mass basis or on the basis of the scaled tether area. Additionally, p­(TMAEMA-<i>b</i>-MPC) copolymer layers offered advantages over the much-studied cationically anchored poly­(ethylene glycol) (PEG) graft copolymer system, which forms PEG brushes by the adsorption of a poly l-lysine (PLL) backbone. Although the optimized p­(TMAEMA-<i>b</i>-MPC) and PLL-PEG copolymers were similarly fibrinogen-resistant, the cationic protein lysozyme was repelled by pMPC but adhered to the PEG brush via PEG–lysozyme attractions. Additionally, the adsorbed p­(TMAEMA-<i>b</i>-MPC) copolymers were not displaced by poly l-lysine homopolymers, which completely displaced the PLL-PEG copolymer to expose a protein-adhesive surface. Thus, the p­(TMAEMA-<i>b</i>-MPC) copolymer system comprises a scalable means to produce protein-repellent surfaces, free of the complexities of surface-initiated polymerization and with the advantages of polyzwitterions

Development of proteomic tools to study protein adsorption on a biomaterial, titanium grafted with poly(sodium styrene sulfonate)

1 - ArticleIt is known that protein adsorption is the initial interaction between implanted biomaterials and biological environment. Generally, a complex protein layer will be formed on material surfaces within a few minutes and the composition of this layer at the interface determines the biological response to the implanted material, and therefore the long-term compatibility of the biomaterial. Despite different techniques exist to observe protein adsorption on biomaterials, none of them led to the identification of adsorbed proteins. In this paper, we report a chromatographic technique coupled to proteomics to analyse and identify proteins from complex biological samples adsorbed on biomaterial surfaces. This approach is based on (1) elaboration of the chromatographic support containing the biomaterial (2) a chromatography step involving adsorption of proteins on the biomaterial (3) the high-resolution separation of eluted proteins by 2-DE gel and (4) the identification of proteins by mass spectrometry. Experiments were performed with proteins from platelets rich plasma (PRP) adsorbed on a biomaterial which consist in titanium bioactivated with PolyNaSS. Our results show that chromatographic approach combined to 2-DE gels and mass spectrometry provides a powerful tool for the analysis and identification of proteins adsorbed on various surfaces