Prof Jonathan Corney, principle researcher on the project, believes that the current solution restricts artificial limb performance. The difficulty, he claims, is in the uniform pore size of the polyurethane, causing the flexibility in the material to remain constant throughout.
‘Your typical NHS cover is really just a tube of foam that’s slapped on the top,’ said Corney. ‘You can imagine something that looks a bit like a sausage. Not only does it not look very convincing, but these things often last only a few months as a result of excess wear.’
The two-year project aims to use a combination of computational modelling, rapid prototyping and ultrasonic irradiation to customise the manipulation of the pore structure to replicate the flexibility and appearance of a human limb.
Corney said that ultrasonic waves cause particles of the irradiated medium to be set into vibrational motion, which causes the bubbles to pulsate creating a phenomenon known as ’stable cavitation’.
The result is that when a foam is subject to certain frequencies of acoustic pressure, the size of the bubbles in the material change, reflecting the peaks and troughs of the ultrasound field.
‘If the kinetic energy of bubbles in the foam is less, they grow bigger, leading to more flexible material,’ he added. ‘By doing this, you can make it stronger in one area and softer in another… This could lead to a cheaper method of manufacturing foam covers that are both visually realistic and have improved functionality.’
The project has been awarded £245,000 of funding from the Engineering and Physical Sciences Research Council (EPSRC) and is due to begin next month. If successful, Corney hopes that the technique could lead to the widespread replacement of standard polyurethane foam in the NHS.