Copper combats otitis in hearing aid patients


Copper was the first metal certified as antimicrobial, a property which led otorhinolaryngologist Gustavo Bravo to investigate whether its use could prevent external otitis in hearing aid users. The first moulds with Cu+ in their interior will be tried out in the coming days in Chile.

In March 2008, the US Environmental Protection Agency (EPA) certified copper as the first metal with an antimicrobial capacity. This acknowledgement followed numerous lab tests showing that microorganisms as aggressive and prevalent as methicillin-resistant Staphylococcus aureus, E. coli, or Pseudomonas aeruginosa are destroyed in a couple of hours after entering into contact with the surfaces of copper o their alloys. In March 2008, Dr. Gustavo Bravo was finishing his specialisation in otorhinolaryngology at the University of Chile Clinic Hospital. His attention was attracted by information about the properties of copper. As he was working in an ENT service, he was aware that due to its nutrient, humidity, and darkness conditions, the auditory canal proves an ideal environment for the proliferation of microorganisms, especially in the case of people using BTE, intra, or CIC (completely in canal) hearing aids. “So, I wondered if by putting copper in earmoulds, its antimicrobial properties could eliminate pathogenic microorganisms to prevent external otitis in hearing aid users.”

Turning into an extensive research project over the last four years, it has won awards from several medical institutions, been the object of a patent, been presented at international conferences, and attracted the attention of several firms.


Meanwhile, Gustavo Bravo, now otorhinolaryngologist at the University of Chile’s Clinic Hospital (HCUCh) sees himself as “buzzing, accelerated, and hooked on doing all that is within my reach,” in carrying out microbiological research to analyse the effectiveness of copper in hearing aid earmoulds. He made contact with Dr. Valeria Prado, an academic on the Programme of Microbiology and Micology of the Institute of Biomedical Science at the University of Chile, and researcher in Chile in the testing of clinical applications of copper as a microbicide. “We designed a project for in vitro testing of the effect copper would have on the main materials hearing aids are made of and its action on the most common microorganisms causing external otitis.” The materials analysed were silicone, which is used in soft moulds; acrylic, used in hard moulds; and ultraviolet sensitive polymer (Biopor), a semi-soft material.

All three were exposed with and without copper to cultures of the Pseudomona aeruginosa and Staphylococcus aureau bacterias, and Aspergillus nigers and Candida albicans fungus. More than 80 tests with different combinations of materials and pathogens were carried out. “We concluded that copper has an antimicrobial effect on three materials and on the four microorganisms, but with a greater effect in the case of ultraviolet sensitive polymer. This probably occurs because the material is more porous, so the copper ions can be better spread. Furthermore, it is a material to which fewer germs adhere, so with copper there is a synergy,” explains Bravo. The results of this study are currently undergoing a process of revision before being published in the journal of the American Academy of Otorhinolaryngology-Head and Neck Surgery (AAO-HNS).

Testing in humans

In 2011, the study won awards at Chilean otorhinolaryngology and infectology conferences before, in September, the results were presented in a speech by Dr. Bravo at the annual conference of AAO-HNS in Washington D.C., where the study’s conclusion attracted great interest from delegates. “What they most asked was when we would be doing studies in humans, a stage we have just begun,” said Bravo.

At this moment, he added, the clinical study design is going being submitted for approval by the HCUCh ethics committee, and a decision is expected in the coming weeks. “We planned to recruit at least 50 hearing aid users, those with no degree of immunosuppression or diabetes, and who suffer from bilateral hypoacusis so we can compare the use of an earmould with copper and another without this metal.” The design takes in follow-up over six months, at the start of which a culture will be taken from the mould, another to be taken at the end, thus allowing for determination of whether the metal has continued to have a microbicidal action over this period. “We will be measuring the incidence or number of cases of external otitis to appear, the degree of colonisation by organisms found in the auditory canal but without exercising a pathogenic action and, besides this, we want to analyse other associated effects. For example, we want to know whether the use of earmoulds with copper reduces itching or production of cerumen,” the specialist explained.

Following several tests to determine the most effective and safest way to incorporate copper in moulds, the team directed by Bravo concluded that a small red metal cylinder of roughly one centimetre in length and 0.6 cm in diameter should be placed inside them. “The optimum distance between the cylinder and the mould surface varies between 0.3 and 0.6 mm, and it is important to stress that since it is contained within the material, the metal never enters into direct contact with the skin, thus reducing the risk of allergies.” Bravo points out that this application has resulted in a patent through the Patent Co-operation Treaty (PCT), and this gave rise to AudiCopper, a company created to advance the research and development of microbicide applications of copper in hearing.

The expert explained how, on entering into contact with oxygen, the metallic plate oxidises and liberates copper ions (Cu+) capable of passing through the covering. These ions are what has the microbicidal power, and this is due to two mechanisms. Firstly, copper disintegrates the bacteria and fungus cell membrane lipids, and this produces nutrients and the consequential death of the cells. A second theory involves the Cu+ joining to proteins required by the microorganisms to function and, on doing this, it inhibits or changes their production. This results in the death of the pathogen.

Bravo points out that the powerful action of the pathogen does not merely help prevent otitis in hearing aid users. The use of this metal could also benefit millions of people who introduce objects into their ears, from stethoscopes to earphones for music or phone listening, or even waterproof plugs, on a daily basis. This health potential will help turn copper into a real gold mine.

Seeking out the cause

On beginning his research into the use of copper to combat otitis, Gustavo Bravo noticed that in Chile there was no recent investigation into the etiology and microbiology of external otitis. This year, he presented a research plan in this respect, winning ‘Internal basic clinical and scientific research Award 2012’ from the HCUCh.

The prize will allow for the purchase of the reagents and supplies needed to explore the causes of this complaint and take cultures from one hundred patients presenting with external otitis at the hospital. The complaint is characterised by inflammation of the pinna, the external ear, or the tympanic membrane. Symptoms include itching, pussing, pain, swelling or reddening of the area and, in some cases, hearing loss and tinnitus. In immunodepressed persons or diabetics, the complaint can worsen into malignant external otitis, a potentially lethal condition which commonly involves Pseudomona aeruginosa.

Multiple applications

Since being certified as a metal with microbicidal properties, the applications of copper have extended to several spheres. A multicentric study in seven hospitals in England, the USA, Germany, Japan, and Chile, showed that the use of copper in bed rails and hand grips, patient tables, drip stands, the arms of visitor chairs, and pencils used by nurses to monitor vital signs reduced by 91 percent the count of bacteria which cause septicemia and lung, urogenital, and skin infections. In Chile, the metal is now used in socks for diabetics, stethoscopes, tanks for fish cultivation and, as an experiment, in rails and handrails in underground train stations and the surfaces of school desks. In spite of its multiple applications in hearing, Dr. Gustavo Bueno emphasises that “trying out copper in a medical hearing device is the best way to obtain the evidence and support to show that copper works since, strictly speaking, a hearing aid user is more at risk of suffering from otitis externa.”

Paula Leighton N.