Prosthetic Biomaterials used in the ear Mustafa and Hamel Shelina (Sam) Megan Amrita Howard

Autografted ear Disadvantages Advantages Lack of availability in chronically diseased ears Prolonged operative time to obtain and shape the material Resorption and/or loss of rigidity (especially with cartilage) Possible fixation to the walls of the middle ear. Very surgically intensive process Advantages Would not be rejected from the body or initiate a host response due to being formed from tissue from the body Ear is able to distinguish sounds better

Artificial Tympanic Membrane Tympanic membrane is a thin membrane that separates the external ear from the middle ear Function to transmit sound from the air to the ossicles inside the middle ear Rupture or perforations of the tympanic membrane leads to conductive hearing loss A tympanic membrane prosthesis is: Flat Planar membrane sized to cover the perforation Each mechanical fixation device has: A sharp, piercing distal end, An enlarged proximal end A shaft. http://www.freepatentsonline.com/6309419.html Perforations can be due to infection or injuries to the ear. Childhood perforations are usually self healing. Symptoms of perforations are drainage from the ear canal, bloody discharge and loss of hearing. The first order of treatment include ear drops, antibiotics and ear powders. It usually heals after a few weeks. http://www.freepatentsonline.com/6309419.html

TYMPANOPLASTY Tissue is taken either from the back of the ear or from the small cartilaginous lobe of skin in front the ear called the tragus. The tissues are thinned and dried. An absorbable gelatin sponge is placed under the drum to allow for support of the graft. The graft is then inserted underneath the remaining drum remnant and the drum remnant is folded back onto the perforation to provide closure. Thin silastic sheeting is placed against the top of the graft to prevent it from sliding out of the ear A small amount of Gelfoam is placed on the outside of the silastic to hold it into position in a sandwich type layer If the perforation is very large an incision behind the ear is performed. This elevates the entire outer ear forward, gaining access to the perforation. Once the hole is exposed fully, the perforated remnant is rotated forward, and the bones of hearing are inspected. There may be scar tissue and bands surrounding the bones of hearing. Having identified the bones of hearing, the ossicular chain is pressed to determine if the chain is mobile and functioning. If the chain is mobile, then the remaining surgery concentrates on repairing the drum defect. Tissue is taken either from the back of the ear or from the small cartilaginous lobe of skin in front the ear called the tragus. The tissues are thinned and dried. An absorbable gelatin sponge is placed under the drum to allow for support of the graft. The graft is then inserted underneath the remaining drum remnant and the drum remnant is folded back onto the perforation to provide closure. http://www.earsurgery.org/tympan.html

Bone grafts for bone replacement in the ear: Long standing perforations are more severe due to infection and degredation of the middle ear bones Ossicular reconstruction at time of tympanoplasty Decide if bone is replaced at time of operation Bone degredation occurs at tip of incus Connects to stapes Prior infections prevent circulation to tip of bone Wears away – no contact Ossicular reconstruction can be performed in two ways……. http://www.tonmeister.ca/main/textbook/node319.html

Bone grafts for bone replacement in the ear: Small gap = bone or cartilage from tragus or behind ear Large gap = incus bone removed modelled into a tooth-like prosthesis Re-inserted between stapes and malleus Other options include: T.O.R.P and P.O.R.P - titanium Artificial strut – hydroxyapatitie Porous so allows ingrowth of blood vessels and osseointegration Less chance of rejection Porous plastics Rejection occured http://upload.wikimedia.org/wikipedia/commons/b/b8/Ear.jpg http://www.earsurgery.org/tympan.html

Ossicular replacements... Come into use in 3 cases: Erosion or absence of the incus Erosion or absence of the incus and malleus Erosion or absence of the incus and stapes Ear infections (Waddington disease). Two types of replacement: PORPs: Partial Ossicular Replacement Prosthesis (between oval window and eardrum) TORPs: Total Ossicular Replacement Prosthesis (between ossicle chain and eardrum or oval window). Erosion of these bones can occur due to ear infections, such as, Waddington disease: degradation of the bones leads to development of scar tissue, binding the bones together, fixing them in place. TORPs span between the oval window and the ear drum, and PORPs between the end of an intact portion of the ossicle chain and either the eardrum or oval window http://illumin.usc.edu/article.php?articleID=19&page=3

Requirements: Possible materials: Rigid Durable High density polymers Hydroxyapatite Stainless steel Ceramic Gelfoam – absorbable gelatin. Rigid: to transmit sound but relatively low density to stiffness ratio. Durable: Maintain properties and integrity for a long time. Gelfoam: sterile compressed sponge All these materials are brittle and rigid. Rigidity is desirable for acoustical purposes. Attempts were made to overcome the brittle nature by combining it with surgical grade rubber – very limited success. http://www.ghorayeb.com/OSSICULARRECONSTRUCTION.html http://illumin.usc.edu/article.php?articleID=19&page=2

Artificial Ear (Cochleal implant) Disadvantages The implantation process inevitably results in damage to nerve cells within the cochlea Incapable of replicating the quality of sound processed by a natural cochlea May be at higher risk for meningitis. Advantages Allows you to Hear Permenant- (Dependant on Part Reliability) Not just a Sound Amplifier (i.e. Hearing Aid) Advantages Not just A Sound Amplifier (i.e. Hearing Aid) Disadvantages The implantation process inevitably results in damage to nerve cells within the cochlea, which often results in a permanent loss of most residual natural hearing The device can help the recipient better hear and understand sounds in their environment, it is simply incapable of replicating the quality of sound processed by a natural cochlea. As a result, some recipients can only distinguish the difference between simple sounds, such as a ringing phone vs a doorbell, while others can clearly understand speech in quiet environments. The success rate depends on a variety of factors, including technology used and condition of the recipient's cochlea.

Artificial Cochlea The cochlea is the portion of the inner ear that senses sound vibrations and converts them into electrical signals that the auditory system can interpret. An artificeal choclea replaces the function of damaged or removed cochlea. They consist of a microelectromechanical-system (MEMS) which employs a frequency sensitive membrane immersed in fluid. Different parts of the membrane vibrate depending of the frequency of the sound input this is then translated into a nervous signal that is passed into the auditory nerve. The cochlea is the portion of the inner ear that senses sound vibrations and converts them into electrical signals that the auditory system can interpret The cochlea is an example of active cellular mechanical forcing and structural processing in which the shape and physical composition of the sensory organ work in combination to accomplish a complex transform The cochlea is a curled structure, which is filled with fluid that moves in response to the vibrations coming through the oval window from the middle ear. Along the length of the cochlea are thousands of hairs that are set in motion in the liquid at the resonance points of the incoming sound wave http://www.edn.com/article/CA6598375.html

Artificial Cochlea Artificial cochlea: an example of structural processing Prying Eyes: A MEMS-based artificial cochlea mimics the real thing in form and function. By Robert Cravotta, Technical Editor -- EDN, 10/2/2008 http://a330.g.akamai.net/7/330/2540/20080924145228/www.edn.com/contents/images/20eyes1LG.jpg

References http://www.earsurgery.org/tympan.html