Poly(l-lysine)-g-poly(ethylene glycol) Layers on Metal Oxide Surfaces:  Surface-Analytical Characterization and Resistance to Serum and Fibrinogen Adsorption

Abstract

Poly(L-lysine)-g-poly(ethylene glycol) (PLL-g-PEG) is a member of a family of polycationic PEG-grafted copolymers that have been shown to chemisorb on anionic surfaces, including various metal oxide surfaces, providing a high degree of resistance to protein adsorption. PLL-g-PEG-modified surfaces are attractive for a variety of applications including sensor chips for bioaffinity assays and blood-contacting biomedical devices. The analytical and structural properties of PLL-g-PEG adlayers on niobium oxide (Nb2O5), tantalum oxide (Ta2O5), and titanium oxide (TiO2) surfaces were investigated using reflection-absorption infrared spectroscopy (RAIRS), angle-dependent X-ray photoelectron spectroscopy (XPS), and time-of-flight secondary ion mass spectrometry (ToF-SIMS). The combined analytical information provides clear evidence for an architecture with the cationic poly(L-lysine) attached electrostatically to the oxide surfaces (charged negatively at physiological pH) and the poly(ethylene oxide) side chains extending out from the surface. The relative intensities of the vibrational modes in the RAIRS spectra and the angle-dependent XPS data point to the PLL backbone being located directly at and parallel to the oxide/polymer interface, whereas the PEG chains are preferentially oriented in the direction perpendicular to the surface. Both positive and negative ToF-SIMS spectra are dominated by PEG-related secondary ion fragments with strongly reduced metal (oxide) intensities pointing to an (almost) complete coverage by the densely packed PEG comblike grafts. The three different transition metal oxide surfaces with isoelectric points well below 7 were found to behave very similarly, both in respect to the kinetics of the polymer adlayer adsorption and properties as well as in terms of protein resistance of the PLL-g-PEG-modified surface. Adsorption of serum and fibrinogen was evaluated using the OWLS optical planar waveguide technique. The amount of human serum adsorbed on the modified surfaces was consistently below the detection limit of the optical sensor technique used (<1-2 ng cm -2 ), and fibrinogen adsorption was reduced by 96-98% in comparison to the nonmodified (bare) oxide surfaces.

Aqueous Lubrication of SiC and Si3N4 Ceramics Aided by a Brush-like Copolymer Additive, Poly(l-lysine)-graft-poly(ethylene glycol)

“…The N1s spectrum contained a NSi 3 contribution at 397.5 eV, but a shoulder corresponding to the NH 2 contribution at 399.3 eV, as reported by Bertoti, was not found. After PLL-g-PEG adsorption there is good agreement with the values of Huang et al [33] (referred to C1s at 284.6 eV). The O1s-Si peak overlaps with the NHC=O, [39].…”

“…The C-Si component of the C1s peak shows a slight shift to 283.2 ± 0.03 eV. The C-C/C-H component is found at 285.6 ± 0.05 eV, which is 0.6 eV higher than the bare SiC value reported by Contarini et al [39] or the theoretical PLL-g-PEG value reported by Huang et al [33], and is shifted by about 1.6 eV from the value measured on bare SiC. Additionally, a C-O/C-N component at 287.2 ± 0.05 eV is shifted 1.4 eV from the measurement on bare SiC, and is around 0.7 eV higher than the theoretical value of the C-O component for PLL-g-PEG.…”

Microtubule nucleation remote from centrosomes may explain how asters span large cells

“…PLL-PEG was synthesized as in ref. 32 and adsorbed to glass coverslips (cleaned by sequential sonication in 3M KOH solution and ethanol) during a 15-min incubation as a 0.01-mg/mL solution in 10 mM K-Hepes (pH 7.8) buffer. Tetrahymena pellicles were a gift from Jan Brugues, MPI-CBG, Dresden, Germany.…”

Force-controlled spatial manipulation of viable mammalian cells and micro-organisms by means of FluidFM technology

“…Bacterial motility on the substrate was hindered by a poly͑L-lysine͒ coating of the glass slide, whereas the cantilever was functionalized with a layer of poly͑L-lysine͒-g-poly͑ethylene glycol͒ ͑PLL-g-PEG͒, a polymer known for its simplicity and effectiveness in resisting the absorption of biomolecules. 33 Figure 3͑b͒ shows five E. coli cells spatially displaced one after the other in order to be arranged along a virtual line.…”