US engineers "print" functioning artificial ear

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Scientists at Princeton University in the US used off-the-shelf printing tools to create a functional ear that can ‘hear’ radio frequencies beyond the range of normal human capability.

The researchers’ primary purpose was to explore an efficient and versatile means to merge electronics with tissue. The scientists used 3D printing of cells and nanoparticles followed by cell culture to combine a small coil antenna with cartilage, creating what they term a bionic ear.

‘In general, there are mechanical and thermal challenges with interfacing electronic materials with biological materials,’ said Michael McAlpine, an assistant professor of mechanical and aerospace engineering at Princeton and the lead researcher. ‘Previously, researchers have suggested some strategies to tailor the electronics so that this merger is less awkward. That typically happens between a 2D sheet of electronics and a surface of the tissue. However, our work suggests a new approach - to build and grow the biology up with the electronics synergistically and in a 3D interwoven format.’

Last year, a research effort led by McAlpine and Naveen Verma, an assistant professor of electrical engineering, and Fio Omenetto of Tufts University, resulted in the development of a ‘tattoo’ made up of a biological sensor and antenna that can be fixed to the surface of a tooth.

This project, which appears in the Nano Letters,is the team’s first effort to create a fully functional organ that not replicates human ability and extends it using embedded electronics.

According to the University, standard tissue engineering involves seeding types of cells, such as those that form ear cartilage, onto a scaffold of a polymer material called a hydrogel. However, the researchers said that this technique has problems replicating complicated three dimensional biological structures and ear reconstruction is said to remain one of the most difficult problems in the field of plastic and reconstructive surgery.

To solve the problem, the team turned to 3D printing, a technique that allowed the researchers to combine the antenna electronics with tissue within the highly complex topology of a human ear. The researchers used an ordinary 3D printer to combine a matrix of hydrogel and calf cells with silver nanoparticles that form an antenna. The calf cells later develop into cartilage.

David Gracias, an associate professor at Johns Hopkins and co-author on the publication, said that bridging the divide between biology and electronics represents a formidable challenge that needs to be overcome to enable the creation of smart prostheses and implants.

‘Biological structures are soft and squishy, composed mostly of water and organic molecules, while conventional electronic devices are hard and dry, composed mainly of metals, semiconductors and inorganic dielectrics,’ he said in a statement. ‘The differences in physical and chemical properties between these two material classes could not be any more pronounced.’

The finished ear consists of a coiled antenna inside a cartilage structure. Two wires lead from the base of the ear and wind around a helical ‘cochlea’ – the part of the ear that senses sound – which can connect to electrodes.

Although McAlpine cautions that further work and extensive testing would need to be done before the technology could be used on a patient, he said the ear in principle could be used to restore or enhance human hearing.

He said electrical signals produced by the ear could be connected to a patient’s nerve endings, similar to a hearing aid. The current system receives radio waves, but he said the research team plans to incorporate other materials, such as pressure-sensitive electronic sensors, to enable the ear to register acoustic sounds.

Look out for our feature on artificial organs in the May issue of The Engineer - available here on Wednesday 8th May.