Collagen Fibril Orientation in Tissue Specimens From Atherosclerotic Plaque Explored Using Small Angle X-Ray Scattering

Abstract

Atherosclerotic plaques can gradually develop in certain arteries. Disruption of fibrous tissue in plaques can result in plaque rupture and thromboembolism, leading to heart attacks and strokes. Collagen fibrils are important tissue building blocks and tissue strength depends on how fibrils are oriented. Fibril orientation in plaque tissue may potentially influence vulnerability to disruption. While X-ray scattering has previously been used to characterize fibril orientations in soft tissues and bones, it has never been used for characterization of human atherosclerotic plaque tissue. This study served to explore fibril orientation in specimens from human plaques using small angle X-ray scattering. Plaque tissue was extracted from human femoral and carotid arteries, and each tissue specimen contained a region of calcified material. 3D collagen fibril orientation was determined along scan lines that started away from and then extended towards a given calcification. At locations several millimeters or more from a calcification, fibrils were found to be oriented predominantly in the circumferential direction of the plaque tissue. However, in a number of cases, the dominant fibril direction changed markedly near a calcification, from circumferential to longitudinal. Further study is needed to elucidate how these fibril patterns may change plaque tissue behavior.

Sample Preparation of Atherosclerotic Plaque for SAXS/WAXS Experimentation

“…The use of SAXS and WAXS with atherosclerosis is a relatively new technique. Currently, it has been used to model the structure of LDLs and investigate the orientation of collagen fibrils. , …”

“…Currently, it has been used to model the structure of LDLs and investigate the orientation of collagen fibrils. 16 For SAXS and WAXS analyses, the intensities of X-rays scattered by a material are measured as a function of the scattering angle. This is applicable to both crystalline and amorphous materials.…”

“…Currently, it has been used to model the structure of LDLs and investigate the orientation of collagen fibrils. 16 , 17 …”

Hierarchical Structure and Properties of the Bone at Nano Level

“…There are several techniques that are used to characterize the orientation of the collagen fibrils. Some of these techniques are polarized Raman spectroscopy [ 14 , 15 ], polarized Fourier transform infrared spectroscopy [ 16 ], polarized second harmonic generation [ 17 , 18 ], small-angle light scattering spectroscopy [ 19 , 20 , 21 , 22 ], elastic scattering spectroscopy [ 23 , 24 ], electron transmission diffraction [ 25 , 26 ], electron backscatter diffraction [ 27 ], magnetic resonance imaging [ 28 ], and microwave method [ 29 ]. The main limitations with these techniques are the limited resolution, they are time consuming, costly, and lack the ability to visualize the three-dimensional orientation.…”

Biomedical Applications of Collagen

“…An additional area of application is the small angle X-ray scattering (SAXS) as a cancer diagnostic tool sensing the local collagen organization [36][37][38][39]. The direct correlation between 3D collagen fibril orientation and its SAXS was recently demonstrated [40]. The areas lacking in fundamental knowledge are also described, including the mechanistic insight into how and why collagen undergoes spatial patterning within tumors.…”