Scanning-SAXS of microfluidic flows: nanostructural mapping of soft matter

Abstract

The determination of in situ structural information of soft matter under flow is challenging, as it depends on many factors, such as temperature, concentration, confinement, channel geometry, and type of imposed flow. Here, we combine microfluidics and scanning small-angle X-ray scattering (scanning-SAXS) to create a two-dimensional spatially resolved map, which represents quantitatively the variation of molecular properties under flow. As application examples, mappings of confined amyloid fibrils and wormlike micelles under flow into various channel geometries are compared. A simple process to fabricate X-rays resistant chips, based on polyimide and UV-curing resin, is discussed. During experiments, these chips remained in high-energy synchrotron radiation for more than 24 hours, causing constant low background scattering. Thus, sufficient statistics were obtained from sample scattering at exposure times as low as 0.1 s, even with the small scattering volumes in microfluidic channels. Scanning-SAXS of microfluidic flows has many potential applications from biology to fundamental soft matter physics. In general, any fluid which has enough contrast for X-ray scattering can be measured to obtain the dependence of molecular shape, conformation, alignment and size on the flow field. Besides, dynamic processes of soft matter caused by flow, temperature, concentration gradient, and confinement, for example self-assembling, aggregation, mixing, diffusion, and disintegration of macromolecules, can be quantified and visualized on a single image by this mapping technique.

Flow-assisted assembly of nanostructured protein microfibers

“…However, forced extension toward alignment of fibrils is a common component of wet spinning techniques, which have emerged as promising procedures for controlled fiber formation (12-18). We here make use of recent insights into the behavior of nanofibrils under elongational flow and the developments in X-ray transparent small-scale flow devices and high-brilliance microfocused X-ray beams (13,17,19) to carry out in situ investigations of the assembly of PNFs during the flow orientation. …”

Advances in Biological Liquid Crystals

“…In general, biological LCs are immediately reoriented along the flow direction with an increased degree of ordering as soon as a very weak flow field is applied . But in the contraction downstream of microchannel, alignment perpendicular to the microflow direction is detected in the case of amyloid fibrils . Thomas et al also detected an unexpected perpendicular orientation at the maximum strain rate during the process of DNA compaction in the presence of cationic dendrimers .…”

Multiscale X-Ray Analysis of Biological Cells and Tissues by Scanning Diffraction and Coherent Imaging

“…Continued progress in X-ray optics has enabled diffraction experiments with spot sizes in the micron and even nanometer range [113], well-suited to record the smallangle X-ray scattering (SAXS) of complex soft-matter structures [146], biomaterials [28,139], or biological cells with spot sizes smaller than a single organelle [41-44, 62, 147]. Recently, we have aimed at resolving the cytoskeletal structure of single cardiomyocyte cells at different preparation states.…”