Collagen Fiber (Collagen Fiber) is the most widely distributed in the connective tissue with the highest content of a fiber, widely distributed in a variety of organs, of which the skin, sclera, tendons are the most abundant. Type I collagen fibers are mainly bone, skin and tendon fibers; type II collagen fibers are mainly cartilage collagen; type III collagen fibers are mainly in embryonic tissues, adult blood vessels, gastrointestinal tract; type IV collagen fibers are mainly in basement membrane.

VG staining solution consists of compound red and lining dye, which is an important part of Van Gieson collagen fiber staining solution, and its staining principle is that each component is related to the size of the anionic dye molecule and the penetration of the tissue, the size of the molecule is reflected by the molecular weight, small molecular weight is easy to penetrate the tissue of dense structure and low permeability, while the large molecular weight can only get into the structure of the lax tissue and high permeability; PA molecular weight is small, Lichun red and compound red are the next largest, light green molecular weight is the largest; VG staining of muscle fibers is yellow, collagen fibers are red.