Perforation of the tympanic membrane is a symptom that causes defects such as ruptures and perforations in the tympanic membrane; there are various causes thereof, and in cases of macroscopic dryness in the tympanic cavity without active inflammation, it seems desirable to close the perforation as early as possible. The largest advantage of tympanic membrane closure is an increase in hearing ability. Provided that the inner ear is not disordered, with no special lesions present in the middle ear, an improvement in hearing ability is usually achieved in all cases after tympanic membrane closure, which significantly contributes to an increase in the patient's QOL.
In the presence of a perforation in the tympanic membrane, not only the tympanic membrane is unable to capture adequate sound, but also hearing (listening to words) is further interfered with by the cancelling effect, in which the sound that has directly entered the tympanic cavity goes in the cochlea through the round window and collides with the sound that has entered the cochlea via the normal route. Additionally, the middle ear exposes directly to the ear canal side, which in turn results in weakened resistance to infections and is likely to cause otitis media. A long-persisting infectious state causes sensorineural hearing loss and impaired labyrinthine function due to internal ear hypofunction. For these reasons, it is preferable that the tympanic membrane be closed as much as possible.
For tympanic membrane closure, a variety of therapies are performed according to the size of the perforation, and basically the majority of currently available therapies are surgery-based. Generally, myringoplasty and tympanoplasty are performed. In the former, skin incision in the postauricular part and collection/transplantation of autologous tissue are essential; in the latter, in addition to these procedures, ear canal abrasion is essential. As the perforation of the tympanic membrane increases its size, transplantation of autologous tissue (fascia temporalis) as a substitute for the tympanic membrane becomes more difficult to perform as a surgical technique. Hence, even when surgery is performed, hearing ability is not always be improved. Many sequelae such as postoperative tympanic membrane re-perforation, foreign sensation in the periauricular part, and tinnitus can occur. Furthermore, postoperatively, the tympanic membrane becomes far from the intact tympanic membrane because of latentiation, hypertrophy and the like, and hearing ability decreases. These operations are usually accompanied by hospitalized care for about one day to several weeks, posing drawbacks such as increased mental, physical and economic burdens on the patient.
Likewise, for ear canal soft tissue defects accompanied by bone exposure, surgical treatment has been the only conventional therapy; treatments such as external incision in the postauricular part and collection of autologous tissue have been indispensable.
In recent years, regenerative medicine-oriented methods of tympanic membrane regeneration using a biocompatible scaffold material that carries a growth factor have been proposed (see, for example, Patent Document 1). In particular, some cases of treatment have been reported wherein basic fibroblast growth factor (bFGF) is used as the growth factor, and a sheet-like thin film such as a collagen membrane or a chitin membrane is used as the scaffold material (Non-patent Documents 1 to 3). Also described is a molded product for ear canal reconstruction made of a cylindrical member of bFGF-containing collagen (Patent Document 2).
As another method of regenerating the tympanic membrane that does not rely on surgical operations, a method has been reported in which the perforated portion of the tympanic membrane is covered with the amnion and bonded with fibrin glue (Non-patent Document 2).
However, the efficacy of conventional regenerative medicine-oriented therapies is limited to relatively small tympanic membrane perforations and ear canal defects; these therapies are not applied for tympanic defects larger than a certain size and defects that involve the auditory ossicles because of the inability to repair.
Meanwhile, gelatin sponges are used as a surgical hemostatic, and are also used as a carrier for sustained release of drugs in the treatment of ear diseases (Patent Document 3).