Poly(l-lysine)-graft-poly(ethylene glycol) Assembled Monolayers on Niobium Oxide Surfaces:  A Quantitative Study of the Influence of Polymer Interfacial Architecture on Resistance to Protein Adsorption by ToF-SIMS and in Situ OWLS

Abstract

Poly(l-lysine) grafted with poly(ethylene glycol) (PLL-g-PEG), a polycationic copolymer that is positively charged at neutral pH, spontaneously adsorbs from aqueous solution onto negatively charged surfaces, resulting in the formation of stable polymeric monolayers and rendering the surfaces protein-resistant to a degree related to the PEG surface density. A set of PLL-g-PEG polymers with different architectures was synthesized. The grafting ratio, g, of the polymer, defined as the ratio of the number of lysine monomers to the number of PEG side chains, was systematically varied between 2 and 23, and PEG molecular weights of 1, 2, and 5 kDa were used. The polymers were adsorbed onto niobium oxide-coated substrates, leading to highly different but well-controlled PEG surface densities with maximal values of 0.9, 0.5, and 0.3 chains/nm2 for the three PEG molecular weights, respectively. Time-of-flight secondary-ion mass spectrometry (ToF-SIMS) was used in conjunction with the in situ optical waveguide lightmode spectroscopy (OWLS) technique to investigate the interface architecture. While ToF-SIMS provided surface-analytical data on the polymeric adlayer, OWLS allowed the quantitative determination of the adsorbed polymer mass. Extremely good correlations were established between the ToF-SIMS data (obtained in UHV) and the in situ OWLS results. The amount of serum adsorbed, determined quantitatively by OWLS, was found to depend systematically on the surface coverage in terms of the ethylene glycol (EG) density, controlled by both PEG molecular weight and grafting ratio, g. Serum adsorption dropped gradually from 590 ng/cm2 on bare Nb2O5 to <2 ng/cm2 (=detection limit of the OWLS technique) for EG densities ≥ 20 nm-2. The PLL-g-PEG technology shows itself to be an efficient, cost-effective, and robust tool for the immobilization of PEG chains onto metal oxide surfaces. The precise control over PEG surface density across a wide range allows for the production of tailored surfaces with controlled degrees of bio-interactiveness. Such surfaces are expected to have a substantial potential for applications in biomedical and bioanalytical devices.

Influence of the molecular architecture on the adsorption onto solid surfaces: comb-like polymers

“…The adsorbed mass increases with the size of the grafted chains, it is expected that the PEG chains are expanded into the solution as water is a good solvent. 39 The latter conclusion is in agreement with the results for PLL-g-PEG by Perry et al 18 and Mu¨ller et al 26 Our results show that the adsorption is not governed solely by the length of the grafted chains, but also by the chemical nature of the main chain as shown in Fig. 4d and e. The latter figures show that the adsorption of G2 is higher than that of G3, while the length of the grafted chains is identical in both cases.…”

Surface-immobilised antimicrobial peptoids

“…After adequate equilibration of the sensors in HEPES buffer, human serum solution was injected and allowed to adsorb for 20 minutes at 37°C before rinsing with HEPES buffer. A refractive index value of 1.33127 was used for the HEPES buffer, and a standard value of 0.182 cm 3 /g was used for dn/dc in the protein-adsorption calculations (Pasche et al, 2003). Averages and standard deviations from 3 replicates are reported.…”

Improved Performances of Intraocular Lenses by Poly(ethylene glycol) Chemical Coatings

“…[22][23][24][25][26][27] The covalent grafting of PEG onto a variety of substrates, including silicon, 24,28 polyurethane-urea, 29 glass, 30,31 fluorinated ethylene-propylene copolymers, 32 and polysulfone membranes, 33 has been reported along with a quite satisfactory protein-repellent effect. It may be anticipated that the proteinrepellent properties of PEG would prevent an extracellular matrix from being formed and, thus, cells from adhering.…”