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At the cutting edge
It is a truism that new technology is often a product looking for a market. In contrast, Oxford University spinout Oxtex’s novel tissue expander is truly an original approach driven purely by clinicians’ demands.
Reconstructive surgery following procedures such as a mastectomy, injuries like burns, or repairs to birth defects such as a cleft palate involves a combination of plastic surgery and tissue regeneration.
But encouraging tissue to grow and expand requires free space between tissue and skin.
Taut skin allows no expansion. Skin placed under tension will grow — a prime example is in a pregnant woman, where abdominal skin grows to accommodate the expansion of the enlarging womb.
The growth under tension lies at the heart of Oxtex’s leading technology.
Company founders David Jackson and Dr Jan Czernuszka demonstrated old and new approaches using the balloon currently in use.
The balloon is a plastic sac with a filler neck rather like a long tail. It is positioned through an incision. Once the incision has healed, saline is pumped into the sac and the pressure expands the skin above it.
Dr Czernuszka said: “The problem is that it is a long process, taking up to a year. And it is painful, so much so that it cannot be used on children.”
Mr Jackson added: “It has a number of problems too, such as wound site infection and the balloon can split and need replacing.”
Making balloons small is pretty impossible and the cleft palate of a young baby is a tiny operation site.
Faced with these restrictions, two surgeons from the John Radcliffe hospital, Marc Swan and Tim Goodacre, approached Dr Czernuszka eight years ago.
They asked him and his team at the university’s Department of Materials Science to develop a solution.
They wanted temporary implants that could be available in a range of sizes which would expand and trigger new skin growth.
Dr Czernuszka added: “Developing a substance that would expand omnidirectionally would not have been too difficult.
“But our surgeons needed something that expanded in only one direction.”
The clinicians’ requirements did not end there. They wanted an implant that expanded gradually, not all at once.
And they needed a period of grace before expansion started to allow the incision for the implant to heal.
The team duly obliged. They came up with a hydrogel, a polymer with groups on its sides that absorb water and cause expansion.
The rate of expansion, called the swelling ratio, is controlled by a coating.
Even so, the ratio is not linear. The initial rate is higher, slowing as the implant reaches full size. A further coating prevents implant expansion for two weeks after insertion.
Expansion complete, the device is removed, any scar excised and the tissue begins to grow.
The advantage of the technique is that the skin is absolutely right for the area of the body.
Skin taken from another part of the body will be a different colour and texture and may lack hair and sweat glands. In a highly visible area like the face, this is not desirable.
Oxtex’s ideas have also caught the eye of a dental surgeon and an oral surgeon.
Dr Kevin Guze, a dentist at Harvard’s Dental School, is working with the company to perfect a technique for replacing extracted molars with artificial teeth.
Once the molars have been removed, the skin tightens over the sockets and the gum recedes.
Any bone implant for the replacement molars will not take or grow under the taut skin.
Employing a dental version of the Oxtex product, the skin can be expanded, allowing the fresh bone to take.
Crossbite, where teeth overlap rather than closing together, can be a serious problem, especially in China.
A Malaysian oral surgeon is working on a procedure to expand the tough and rubbery skin of the palate and permit surgery that brings upper and lower teeth back in line.
Oxtex spun out in July, led by chief executive Mr Jackson, who has many years of experience of high-tech startups.
Funded by high net worth individuals, the company’s initial home will be the Materials Science Department itself.
Manufacturing will be in a clean room assembled from a kit and staff numbers will be low, around four or five. Mr Jackson envisages moving on in 2014, taking his clean room with him.
Clinical trials will begin next year. Trials for drugs demand high patient numbers, long trial periods and a substantial budget.
But trials for a medical device like this can be done in about a year on small numbers of patients and a low budget.
The first applications in the UK, Far East and US are scheduled for late 2012 or early 2013.
Mr Jackson said: “As our product becomes known, we foresee a strong demand for customised versions. Our next move is towards an implant that a surgeon can trim and shape during surgery.”