Tympanic membrane retraction commercially available devices (e.g. Otovent and Ear Popper). A ventilation tube, also known as a tympanostomy tube or a grommet, may be placed through the eardrum to equalize middle ear pressure. Although this intervention may be effective, research has not yet shown whether it provides better results than simple observation. Further weakness or perforation of the eardrum may occur. These are intended to improve Eustachian tube function. Adenoidectomy can improve middle ear function and nasal steroid sprays can reduce adenoid size but it is not known whether these treatments alter tympanic membrane retraction. Enlargement of the Eustachian tube opening in
Semipermeable membrane the rate and the permeability. Many natural and synthetic materials thicker than a membrane are also semipermeable. One example of this is the thin film on the inside of the egg. Note that a semipermeable membrane is not the same as a selectively permeable membrane. Semipermeable membrane describes a membrane that allows some particles to pass through (by size), whereas the selectively permeable membrane "chooses" what passes through (size is not a factor). An example of a biological semi-permeable membrane is the lipid bilayer, on which is based on the plasma membrane that surrounds all biological cells. A group of