High resolution electron microscopic investigation of atomic structural images in human atherosclerotic plaque.

Atomic structural images in the calcified matrix of human atherosclerotic plaques were characterized by high-resolution electron microscopy (HREM). The mineral elements distributed in the calcified matrix were analysed by energy dispersive X-ray microanalysis. Careful HREM observations revealed that a large number of microcrystallites and crystal particles with a broad spectrum of crystal size and perfection were embedded in the amorphous matrix of the calcified plaques. The amorphous phase in the calcified matrix was made up of a dense network of granulo-fibrillar substructures. The lattice-fringes with regular arrangement of atom columns along the lattice arrays were clearly demonstrated in the crystalline particles of the calcified plaques. A number of characteristic granulo-fibrillar substructures in the amorphous phase could be seen to be tightly connected to the lattice-fringes in the crystalline phase along the interfaces between the amorphous and crystalline phases. The crystal lattices at the boundary between two crystals were very well matched with the periodicity of visible atoms continuous through the two crystals. The mineral elements such as calcium and phosphorus were detected to be diffusely distributed in the calcified matrix of the atherosclerotic plaques. Based on these findings, it is concluded that: (1) an interlacing network of granulo-fibrillar substructures in the amorphous matrix may play a structural and/or regulatory role for the organic matrix by providing sites for nucleation; and (2) the deposition of the mineral elements may be effective for the transformation of the amorphous nucleation phase to well-crystallized nucleation phase.