How the Surface Nanostructure of Polyethylene Affects Protein Assembly and Orientation

Abstract

Protein adsorption plays a key role in the biological response to implants. We report how nanoscale topography, chemistry, crystallinity, and molecular chain anisotropy of ultrahigh molecular weight polyethylene (UHMWPE) surfaces affect the protein assembly and induce lateral orientational order. We applied ultraflat, melt drawn UHMWPE films to show that highly oriented nanocrystalline lamellae influence the conformation and aggregation into network structures of human plasma fibrinogen by atomic force microscopy with unprecedented clarity and molecular resolution. We observed a transition from random protein orientation at low concentrations to an assembly guided by the UHMWPE surface nanotopography at a close to full surface coverage on hydrophobic melt drawn UHMWPE. This assembly differs from the arrangement at a hydrophobic, on the nanoscale smooth UHMWPE reference. On plasma-modified, hydrophilic melt drawn UHMWPE surfaces that retained their original nanotopography, the influence of the nanoscale surface pattern on the protein adsorption is lost. A model based on protein-surface and protein-protein interactions is proposed. We suggest these nanostructured polymer films to be versatile model surfaces to provide unique information on protein interactions with nanoscale building blocks of implants, such as nanocrystalline UHMWPE lamellae. The current study contributes to the understanding of molecular processes at polymer biointerfaces and may support their future design and molecular scale tailoring.

Biomaterial nanotopography-mediated cell responses: experiment and modeling

“…In fact, a recent study on ultrahigh molecular weight polyethylene surfaces suggests that nanotopography, chemistry, crystallinity, and molecular chain anisotropy could affect protein and assembly at the same time [79]. It is possible, as demonstrated by the study, that nanotopography loses its effectiveness on mediating protein adsorption when surface chemistry and hydrophobicity are changed.…”

Controlling Protein Adsorption through Nanostructured Polymeric Surfaces

“…[91] Diverse grades of PE are widely applied or are in development as biomaterials for ligament replacement, cochlear implants, composites for skull implants, or syringes, tubes, infusion bags, and packing. [72,92] Under standard conditions, melt-drawn UHMWPE forms staggered and stacked lamellar crystals oriented perpendicular to the drawing direction, [93] while iPB-1 forms long extended needle-like crystals [11] ( Figure 3b). The needle crystals align parallel to the drawing direction of the polymer film and their lengths range from a few nanometers to some micrometers, while their diameter is found to be 25-35 nm.…”

“…Keller et al showed that ordered crystalline lamellae of UHWMPE with dimensions similar to the size of the fibrinogen molecules favor preferential alignment of single proteins with their long axis parallel to the lamellae major axis. [93] With nearly a monolayer coverage, fibrinogen molecules assembled into an ordered, densely packed film with Adv. Healthcare Mater.…”

“…Image (right): Adapted with permission. [93] Copyright 2011, American Chemical Society. c) Schematic representation of anisotropic diffusion of protein molecules on a nanostructured HDPE melt-drawn film (left) and the occupancy map (right) of HDPE film at 10 mg L −1 fibrinogen exhibiting segmented and elongated structures in the film drawing direction.…”

Protein Adsorption on Nano-scaled, Rippled TiO2 and Si Surfaces

“…Surface-bonded HPF has a length of 46-49 nm and a height about 0.3-2.5 nm depending on the protein conformation on different substrates and under different environmental conditions [7,[10][11][12][13]. Former studies mostly investigated the adsorption of HPF and a variety of other proteins [14,15] on flat substrates such as commercially pure Ti with a natural TiO 2 layer on top [13], TiO 2 [7], graphite [10,11,16], mica [10,12,13], ultra-high molecular weight polyethylene [17], Si [18] or SiO 2 [19]. In most cases, these investigations concentrated on the adsorption of single proteins in air and/or under aqueous conditions.…”