Tissue implant could transform reconstructive procedures

A new hydrogel surgical implant that can be grown in a controlled, directional way could transform a number of reconstructive procedures.

The new technology builds on an existing technique called tissue expansion, which is basically a way of stretching out new skin to then be used in cosmetic procedures.

‘Whether it’s a burn or you’ve had cancer or a road accident, the common problem is the lack of skin,’ said Marc Swan, a plastic surgeon at John Radcliffe Hospital in Oxford who helped develop the new technology. ‘Skin grafts are fine but they don’t look great, particularly for the face.’

Current methods for tissue expansion use implanted balloons that are gradually inflated — usually on a weekly basis — by injecting saline solution through an external filling port.

The problem with these devices is that they are rather crude and bulky, and are not well tolerated by children. Moreover, they can only expand isotropically — that is equally in all directions — which makes them unsuitable for small, delicate procedures where control is key. 

Swan, along with colleague Tim Goodacre, also at John Radcliffe, approached materials scientists Jan Czernuszka of Oxford University and David Bucknall at the Georgia Institute of Technology in the US for a solution.

The team came up with a novel hydrogel-based material with an underlying polymer structure of vinyl pyrrolidone cross-linked with methyl methacrylate.

‘What we do is compress it under pressure at its glass-transition temperature to realign the previously random vinyl-pyrrolidone molecules and therefore they will swell in a direction perpendicular to the alignment of the molecules — that was a pretty major improvement for small, delicate areas,’ Swan said.

‘You can manufacture any shape you wish, so for the scalp you want a hemisphere shape but in the finger you want a little rod, while in the eyelid or ear you might want a more rectangular shape.’

Unlike the previous balloon devices, the hydrogel implant is entirely sealed, so the team also needed a way of controlling the rate, as well as the direction of the expansion.

For this, the team uses a semi-permeable membrane around the hydrogel that allows bodily tissue fluid to enter osmotically to expand the device, but in a way that can also be controlled through modifications in the structure of the membrane.

The technology has now formed the basis of a spin-out company, Oxtexs, with the help of Isis Innovation, the technology-transfer office of Oxford University, and the company has secured £365,000 of seed funding.