Understanding protein adsorption behavior on rough and wrinkled surfaces is vital to applications including biosensors and flexible biomedical devices. Despite this, there is a dearth of study on protein interaction with regularly undulating surface topographies, particularly in regions of negative curvature. Here we report nanoscale adsorption behavior of immunoglobulin M (IgM) and immunoglobulin G (IgG) on wrinkled and crumpled surfaces via atomic force microscopy (AFM). Hydrophilic plasma treated poly(dimethylsiloxane) (PDMS) wrinkles with varying dimensions exhibit higher surface coverage of IgM on wrinkle peaks over valleys. Negative curvature in the valleys is determined to reduce protein surface coverage based both on an increase in geometric hindrance on concave surfaces, and reduced binding energy as calculated in coarse-grained molecular dynamics simulations. The smaller IgG molecule in contrast shows no observable effects on coverage from this degree of curvature. The same wrinkles with an overlayer of monolayer graphene show hydrophobic spreading and network formation, and inhomogeneous coverage across wrinkle peaks and valleys attributed to filament wetting and drying effects in the valleys. Additionally, adsorption onto uniaxial buckle delaminated graphene shows that when wrinkle features are on the length scale of the protein diameter, hydrophobic deformation and spreading do not occur and both IgM and IgG molecules retain their dimensions. These results demonstrate that undulating wrinkled surfaces characteristic of flexible substrates can have significant effects on protein surface distribution with potential implications for design of materials for biological applications.
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Morphology and kinetics of asphalt binder microstructure at gas, liquid and solid interfaces
We combined optical and atomic force microscopy to observe morphology and kinetics of microstructures (typically referred to as bees) that formed at free surfaces of unmodified Performance Graded (PG) 64‐22 asphalt binders upon cooling from 150°C to room temperature (RT) at 5°C min–1, and changes in these microstructures when the surface was terminated with a transparent solid (glass) or liquid (glycerol) overlayer. The main findings are: (1) at free binder surfaces, wrinkled microstructures started to form near the crystallization temperature (∼45°C) of saturates such as wax observed by differential scanning calorimetry, then grew to ∼5 µm diameter, ∼25 nm wrinkle amplitude and 10–30% surface area coverage upon cooling to RT, where they persisted indefinitely without observable change in shape or density. (2) Glycerol coverage of the binder surface during cooling reduced wrinkled area and wrinkle amplitude three‐fold compared to free binder surfaces upon initial cooling to RT; continued glycerol coverage at RT eliminated most surface microstructures within ∼4 h. (3) No surface microstructures were observed to form at binder surfaces covered with glass. (4) Submicron bulk microstructures were observed by near‐infrared microscopy beneath the surfaces of all binder samples, with size, shape and density independent of surface coverage. No tendency of such structures to float to the top or sink to the bottom of mm‐thick samples was observed. (5) We attribute the dependence of surface wrinkling on surface coverage to variation in interface tension, based on a thin‐film continuum mechanics model.
Asphalt binder, or bitumen, is the glue that holds aggregate particles together to form a road surface. It is derived from the heavy residue that remains after distilling gasoline, diesel and other lighter products out of crude oil. Nevertheless, bitumen varies widely in composition and mechanical properties. To avoid expensive road failures, bitumen must be processed after distillation so that its mechanical properties satisfy diverse climate and load requirements. International standards now guide these mechanical properties, but yield varying long‐term performance as local source composition and preparation methods vary.
- NSF-PAR ID:
- 10459572
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- Journal of Microscopy
- Volume:
- 276
- Issue:
- 3
- ISSN:
- 0022-2720
- Page Range / eLocation ID:
- p. 109-117
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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