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Graphic element Research > Growth > Research projects > Previous projects > Medicine and Health > Cement makes an impact on medical implants
Graphic element Cement makes an impact on medical implants
Advanced biomedical devices, including internal prostheses, have improved the quality of life for countless patients around the world. Cochlear implants for the deaf are just one example of such aids, transmitting electrical signals directly into the human nervous system through the inner ear. While the enormity of these technological leaps are mind-boggling, certain practical aspects such as how to fix the implants in place can still be problematic. A Brite-Euram project set out to overcome one problem by developing an improved biomedical cement, combining advanced testing and production methodologies in a worthy challenge to American domination in this sector.

Current glass-based dental cements formed by reacting powdered fluoro-alumino-silicate glasses with weak polyacrylic acid have attractive properties for use with implants, but they lack toughness and wear resistance and tend to break down over time. In cochlear implants, this can lead to loosening and ultimately to hearing-aid failure. In addition, volatile silicon tetrafluoride and hydroflouric acid are often formed during the glass-melting process.

Diagnosing the problem

Launched in 1993, the objective of the project consortium was to develop an improved glass polyalkenoate cement for biomedical applications. The new cement was based on novel glass compositions and was designed specifically for use in cochlea implants and other prosthetic devices.
First, the mechanism of failure of existing cements was determined through ion release studies. Results demonstrated that breakdown is due to ion exchange whereby a fluoride ion in the cement is exchanged for a hydroxyl ion in the aqueous medium. This discovery contradicted the previously accepted model which had alkali cations and flouride ions being released simultaneously from the set cement. These and other findings pointed to the use of ion leachable fluoro-alumino-silicate glass as a possible solution. The term 'ion leachable' refers to the ability to remove cations from the material before it sets.

Cementing properties

By combining ion leachable fluoro-alumino-silicate glass with polyacrylic acid a more stable, hydrophilic cement was produced which was ideally suited for use in the aqueous environment of the human body. The aluminium to silicon ratio of the glass was found to be less significant than previously thought, and toxic silicon tetraflouride production was shown to be preventable in the presence of sufficient oxygen in relation to silicon and sufficient aluminium in relation to fluorine.
Thus, a strong correlation was established between glass composition and the setting properties, the mechanical properties and life span, allowing the production of an extremely hard, ceramic-like, water-based adhesive displaying a very low risk of failure.

Biocompatibility and Exploitation

In-vivo biocompatibility studies proved positive, both in animals and humans, and the new cement has now received medical certification and carries the 'CE' mark of European approval.
A licensing agreement with the project consortium allows Corinthian Medical Limited to produce and market glass polyalkenoate cements under the trade name Biocem for the ear, nose and throat market and especially for use with cochlea implants. The consortium has been earning royalties since 1997 and is expecting increased gains as further non-medical applications are developed and exploited. The global market for cochlear implant cement alone has been estimated at around 8 million euro. This is a new and exciting development for European producers in a market traditionally dominated by US companies.
From a medical perspective, the new cement allows for simpler and safer cochlear implant procedures. Improved fixation means reduced risk of hearing-aid failure and consequent improved quality of life for the patient. The new material can also be used in dental applications as an ultra-hard filling material that can bond to dentine and enamel. Finally, biomedical applications are envisaged, such as joint replacement prostheses or mouldable bone substitutes.
Credit for the project's success goes to excellent technical expertise and Cupertino between partners and industrial sponsors, as well as commercial contacts in the medical device industry.

Cordis RCN: 6652
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