3D printing3D printing custom hearing aids

Hearing aids are one of the paramount examples of how personalised medical devices have benefitted from the development of 3D printing. In fact, according to Belgian software and 3D printing service provider Materialise some 99% of the world’s hearing aids are now custom-manufactured through 3D printing. In addition to Materialise, global manufacturers such as EnvisionTEC, Formlabs, and Sonova have also been 3D printing hearing aids and custom earpieces for years. In 2017, EnvisionTEC announced a new partnership with 3D scanning and software company 3Shape to continue offering 3D printed in-ear devices, while at CES 2018 Formlabs also partnered with 3Shape to showcase the combined power of its Form 2 3D printer and 3Shape’s Phoenix in-ear scanner to make customized earbuds.

Having started using 3D printers to manufacture hearing aids in the early 2000s, Sonova and its subsidiary brand Phonak produce hundreds of thousands of custom-made hearing aids each year. In 2017, the firm produced its first titanium 3D printed hearing aid, Virto B-Titanium, using powder bed fusion (PBF) metal additive manufacturing.

Elsewhere, Australian hearing company Blamey Saunders Hears introduced a “world first” 3D printed modular, self-fittable hearing aid with smartphone control. The main aim of the project, which also saw the involvement of Extel Technologies, Melbourne-based RMIT University, and Swinburne University, was to eliminate the social stigma associated with hearing loss.

Virto BA Virto B-Titanium hearing aid. Image via Phonak

Fabricating hearing aids via DLP 

The prolonged use of hearing aids can alter the ear canal microbiota and increase the risk of fungal and bacterial infections. According to the UCL researchers, treating ear infections with topical antibiotics is far more effective than ear cleaning alone, however hearing aids with anti-biofilm properties are yet to be developed in any real capacity. Therefore, the scientists set out on a mission to employ DLP 3D printing to manufacture drug-loaded hearing aids for patients with ear infections. If successful, the novel drug-device combination could help to avoid the discontinuation of hearing aids due to infections. Ciprofloxacin and fluocinolone acetonide were chosen for the drug combination, as they are commonly used in ear drops used to treat ear infections.

To prepare the photopolymer solutions, Flexible resin and ENG hard resin were mixed with 12% ciprofloxacin and 0.5% fluocinolone acetonide. The resulting photopolymer solution was then loaded into a Kudo3D Titan 2 HR 3D printer, equipped with a digital light projector optimised for printing the hearing aids. Templates were then used to print the hearing aids, having been obtained from the molds of the right ears of two volunteers and exported as a stereolithography file into Kudo3D’s 3D printing software. Once printed, the hearing aids were washed in isopropyl alcohol and cured for an hour at 60°C with UV-visible light.

During testing, the drug-loaded hearing devices exhibited efficient anti-biofilm activity and completely inhibited the growth of bacteria on the surface of the devices. When examining the drug release properties of the hearing aids, it was observed that the DLP 3D printed drug-loaded discs sustained the release of both ciprofloxacin and fluocinolone acetonide for more than seven days, continuing thereafter at much slower rates. Otitis, or inflammation of the ear, generally requires between one and two weeks of pharmacological treatment, indicating the researchers’ drug-loaded devices would provide effective treatment across the required time period.

dlp(A) 3D scan model of the hearing aid; DLP 3D printed hearing aids using (B) ENG hard resin and (C) Flexible resin

Significance of drug-loaded hearing aids

Through this study, the UCL researchers have successfully demonstrated the ability to incorporate a combination of drugs, typically used as ear drops to treat ear infections, into DLP 3D printed hearing aids to prevent and treat biofilm-related infections. The flexibility of the DLP process enabled personalisation of the hearing aid to fit it to the ear anatomy of the patient. Compared with other manufacturing methods such as moulding, DLP 3D printing was found to be cost-effective when the production volume is low and avoids the need of making moulds, which requires extra costs on machinery, material, and labor. The scientists are now seeking to extend the applicability of their work through investigating the feasibility of combining DLP 3D printing and cochlear implants. The proof-of-concept research could also be transitioned and extended for the treatment of other diseases with various different devices, enabling a greater level of personalised treatment.

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