Electron microscopic observations on the repair of perforated tympanic membranes in the guinea-pig

Experimental perforations of the tympanic membrane in the guinea-pig have been examined electron microscopically. The perforation site became filled with maturing granulation tissue, covered on its external (meatal) and internal (middle ear) surfaces by cells derived from the epithelia of the respective surfaces of the normal membrane. The fibrils and interfibrillar matrix of the normal tympanic membrane in this species have a unique ultrastructure. The fibrils are quadrangular, apparently composed of four subunits, and the surrounding matrix is more electron-dense than in most connective tissues. During repair this type of fibril and matrix was not reconstituted within the 6 month period examined. In its place were formed fibrils of varying diameter, probably collagenous, and differing from those of normal membrane both in size and in the lack of characteristic interfibrillar matrix. The fibroblasts of the wound site, even if of local origin, thus do not appear to be capable of synthesizing the local type of connective tissue.