New research suggests that hair cells are able to rebuild the hair structure in a 48 hour period. Permanent hearing loss occurs when the damage is severe enough so that the self repair mechanism is not induced. Because of this scientists have been working diligently to give those people who have lost this sense their hearing back. There are a variety of mechanisms that are on the market or that are still in the research phase. Some alleviate the problem while others hold a promise for complete recovery.
External Sound Amplifiers and Cochlear Implants
Current treatments for hearing loss are hearing aids which are external sound amplifiers, and cochlear implants which are electronic devices inserted into the inner ear that send sound-generated electrical pulses directly to the brain. These solutions do not give the same sense of hearing back to the patient and often pick up and amplify background noise creating frustration and embarrassment for the patient.
Drug Therapy
Modern drug therapies are now being researched for hearing loss. During periods of loud noise blood flow is limited to the cochlea. Drugs used to treat peripheral vascular disease maintain blood circulation to the cochlea during exposure to loud noise (www.nidcd.nih.gov)
Stem Cell Technology
Stem cells are undifferentiated cells. Theses cells have not differentiated into more specialized cell type, which have specific functions whether they are there to carry oxygen, maintain skin elasticity or determine pressure differences within the cochlea. These cells differ from the stem cell. The stem cell has the ability to become any one of these specialized cells.
Stem cells are unique because have the ability of self renewal as well as differentiating into specialized cells. Recently it has been observed that these cells are able to populate a tissue after they have been transplanted.
Two types of stem cells can be used for medical applications; embryonic stem cells and adult stem cells. Embryonic stem cells can only be harvested from a developing embryo during the blastula stage. Adult stem cells are found in most tissues of an adult organism. During embryonic development theses cells specialize into different organs of shapes and sizes. Adult stem cells are found in small quantities with in each tissue and are there to serve as a perennial source of differentiated tissue cells.
Growing cells in a laboratory require a special recipe for growing and sustaining the cells. Stem cells are no different. To grow a stem cell in culture is one thing but to cause the cell to differentiate into a desired specialized cell can be a lot more difficult. In certain areas stem cells are already being used to replace cells lost to disease in the body. Scientists have been able to isolate hematopoietic (blood) stem cells (HSC) from a patient. These cells have been transplanted into patients whose bone marrow has been damaged due to radiation or chemotherapy. These cells have shown to repopulate the marrow and initiate the production of various blood cells (Saltzman M, Tran V,).
Stem cells are important to medical applications because they are able to repopulate and regenerate tissues that have been damaged. Current research suggests that stem cell can be differentiated into cochlea hair cells. This line of research began at Harvard Medical School by Stephan Heller, Phd and his team. Initially Heller was able to locate adult stem cells that resided in the inner ear. He extracted these stem cells from a mouse and created cochlea hair cells in a culture dish. With the right nutrients Heller was able to coax the stem cells to grow into mice cochlea hair cells. These cells were transplanted into the embryo of a chicken simply by injecting them into the embryo though a tiny hole in the shell. According to Heller, the mouse stem cells began to grow in the inner ear of the young chicks and showed all the requirements of inner ear hair cells.
His most recent work is on creating inner ear hair cells and auditory neurons from stem cells. He has shown that both embryonic and adult stem cells can be used for this. Currently he is exploring signaling pathways that control hair cell and neuronal regeneration in the lab and in living organisms. In a recent article in Neuroreport his team has shown that certain proteins such as Sonic hedgehog (Shh) accelerates inner ear stem cell proliferation. Initial research will be conducted on mice and if the process seems to work the next step will be on humans. Heller hopes that some day hearing loss can be cured with ear drops containing the proteins, or the stem cells or both. (Heller et. al. 2005)
Activity 8
Students in the lab cannot grow stem cells but a good way to introduce growing cells in culture would be to grow bacterial cells. This activity is a lab in which we grow bacteria in different media to see which nutrients are most suitable for this type of growth.
Noise Canceling Technology
For people who work in environments that are often to loud there is an invention which cancels out unnecessary noise. This is special set of headphones which measures the undesirable noise. A computer then measures the frequency of the noise and figures out how to make the same sound, only 180 degrees out of phase. The new sound is sent back into you ear through the headphones. When the two sounds combine they work against each other and the person is unable to hear the two sounds. The opposing frequencies cancel each other out. (Hsu Tom, 2003)
Activity 9
Students will develop an ad campaign to sell their product which will solve the problem of increased hearing loss among the overall population. Students will have to portray that they understand the properties of sound waves and their damaging affect on the inner hair cells. They will then use their marketing skills to promote the modern biomedical technology their company is involved with.