Ultra-small-angle x-ray scattering (USAXS) imaging of human and artificial tissues.

USAXS imaging is a high-contrast imaging technique being developed by NIST researchers. It provides direct images of the shapes and three-dimensional arrangement of the scattering objects within a sample that is unobtainable using conventional x-ray imaging methods. USAXS imaging, combined with USAXS analysis, provides information on the size distributions, shapes, and three-dimensional arrangements of scattering objects. When applied to human and artificial tissues, these techniques improve the understanding of these materials and assist in the development of new man-made biomaterials. The goal of this research is nondestructive observation of the critical structures responsible for the properties of natural and man-made tissues.

The following paragraphs describe our most recent results from USAXS imaging and USAXS analysis on human ankle cartilage and man-made tissue scaffolds.

USAXS images and USAXS scans were made of human ankle cartilage mounted in a wet cell to forestall dehydration. Images were recorded at locations near the bone/cartilage interface, in the center, and near the cartilage surface. Images taken with the scattering vector parallel to the cartilage surface showed few structures. Images taken with the scattering vector perpendicular to the surface showed copious structures both near the surface, where the collagen fibers are parallel to the surface, and on the opposite side near the bone where the collagen fibers are perpendicular to the bone. The middle of the sample showed few distinct structures supporting the model of "disorder" in this region.

Polymer-based tissue scaffolds for growing tissues are under development, but the degree of crystallinity on the pore surfaces can strongly affect cell growth. To explore this effect, a polymer scaffold (porous Poly-Capraloactone, PCL) was produced with an additional annealing/cooling step to alter the degree of crystallinity. USAXS scans from the tissue scaffolds contained a pronounced peak produced by the lamellar structure of the polymer. The density difference between the amorphous and crystalline phases of the scaffold leads to enhanced scattering at the boundaries. Comparison and superposition of the images made in radiographic mode and USAXS imaging mode allowed researchers to determine the locations of the crystallites relative to the pore surfaces, and an analysis of the scattering curve enabled them to extract the crystallite size distribution.

CONTACT: Gabrielle Long, [phone]; [e-mail] or Lyle Levine, [phone]; [e-mail].