Nanoscale Intermolecular Interactions between Human Serum Albumin and Low Grafting Density Surfaces of Poly(ethylene oxide)

Abstract

The net nanoscale interaction between a probe tip covalently bound with the blood plasma protein human serum albumin (HSA) and a surface of end-grafted poly(ethylene oxide) (PEO) mushrooms (Mn ∼ 50K, Flory radius RF ∼ 9 nm, contour length Lcontour ∼ 393 nm) was measured directly on approach (loading) and retract (unloading) in aqueous buffer solution using the technique of high-resolution force spectroscopy (HRFS). On approach of the HSA probe tip to the PEO surface, a monotonic nonlinear repulsive net force was observed for tip−sample separation distances of <30 nm, the magnitude of which is much larger than that predicted by either electrostatic double layer or steric theories based on configurational entropy. Attractive contacts between the PEO and HSA are formed during experimentation, enabling the tethering and extension of individual PEO chains on retraction. The mean binding force of the HSA probe tip to individual PEO chains was determined to be 〈Fadh〉 = 0.06 ± 0.10 nN or 〈Fadh/Radius〉 = 0.9 ± 1.6 mN/m (where Radius is the end radius of the probe tip as measured by scanning electron microscopy). By combining the results of HRFS experiments with theoretical approaches, we have shown that this technique is a valuable tool for understanding biocompatibility at the nanoscale and can provide valuable information that may be used as a guideline for the design of improved synthetic macromolecular systems for future biomedical applications.

Synthesis and Single Molecule Force Spectroscopy of Graft Copolymers of Poly(2-hydroxyethyl methacrylate-g-ethylene glycol)

“…Previously, we approximated the net approach surface interaction of polymer mushrooms end-grafted on Au as a linear addition of the polymer and Au interactions taken separately. 44 The bare polycrystalline Au used in this study has been found previously 43 to have a net negative charge under these solution conditions due to adsorbed anions with a surface charge per unit area of σ(Au) ) 0.0144 C/m 2 , and the Si 3 N 4 probe tip is known [45][46][47] to also have a net negative charge due to ionized silanol (SiO -) and silylamine (SiN -) groups of σ (Si 3 N 4 ) ) -0.032 C/m 2 , yielding an electrostatic double-layer (EDL) repulsion with an electrical interaction Debye length (calculated from the solution IS ) 0.15 M), κ -1 of ∼1 nm in PBS and ∼39 nm in DI H 2 O. 48 The EDL repulsion solely due to the Si 3 N 4 vs Au interaction in PBS (i.e., for 90% and 86% of total surface area for the poly(HEMA-g-EG) 16K and poly(HEMA-g-EG) 120K samples, respectively) was modeled using a constant surface charge approximation based on the numerical solution to the nonlinear Poisson-Boltzmann (PB) equation including divalent ions, [49][50][51] and these simulated curves are shown in Figure 8 as solid lines.…”

Determination of the molar mass of surface-grafted weak polyelectrolyte brushes using force spectroscopy

“…Experiments were conducted in deionized water (15 MΩ resistivity, Elga PURELab option water purifier) at room temperature with a z-piezo velocity of 400 nm/s. Details of the MFP and the force-distance curve analysis can be found elsewhere [34,39]. The spring constant of each cantilever was characterized using the built-in thermal calibration method [40].…”

End-grafted Sugar Chains as Aqueous Lubricant Additives: Synthesis and Macrotribological Tests of Poly(l-lysine)-graft-Dextran (PLL-g-dex) Copolymers

“…PEG (5) is composed of 113.6 monomer units (ethylene glycol (EG)), whose fully extended chain length is estimated to be 40.5 nm (based on the molecular length of EG, 0.358 nm [46]), whereas dex(5.2) is composed of 31.8 monomer units (sugar rings), whose fully extended chain length is estimated to be only 22.3 nm (based on the molecular length of dextran: 0.7 nm [47]). While the lubricating film thickness generated by the adsorption of comb-like copolymer will be determined by many parameters, the fully extended length of side chains will set the upper bound of the film thickness.…”