RP system prepares surgeons for action

A rapid prototyping system used by surgeons in their preparations for separating conjoined twins is available in the UK through Unimatic Engineers.

A rapid prototyping system used by surgeons in their preparations for separating conjoined twins is now available in the UK through Unimatic Engineers to the medical, industrial and educational communities.

The twins, Guatemalan girls, were joined at the head, with separate and complete brains.

However, many of the associated veins were interwoven and connected into each others' circulatory system.

Separating conjoined twins is a highly complicated procedure, but surgeons at the University of California's Mattel Children's Hospital determined that an operation was possible.

The hardest part would be sorting out the veins, but using two dimensional X-rays did not help tracking them.

So it was decided to use three-dimensional rapid prototyping to help the surgeons practice separating the girl's skulls, reroute the blood supply and plan skin graft.

Using a software program called Mimic, a set of CT scans was used to build a three dimensional biomodel of the skull and maze of blood vessels.

This was the used to drive a PolyJet rapid prototyping machine to produce perfect resin copies.

Unimatic's Fred Bloggs explains: "The models had to be perfect right down to the finest blood vessels, so only the best prototyping machine was acceptable".

The PolyJet consists of a modelling table over which traverses a jet head that lays down precision positioned dots of resin.

Its resolution is 600 x 300 dot/in, with a dot thickness of 16um.

Mounted on the jet head is a high intensity UV light source which cure the resin dots almost as soon as they are laid down.

Dots are laid on dots in a multi-traverse operation to build up the three dimensional model.

The PolyJet's traversing head consists of multiple dispensing head, partly to speed up the process, partly to improve accuracy and importantly to allow the use of two types of resin.

The first resin is coloured and forms the actual model: the second is transparent and is laid down in order to support the model during production.

As soon as the model is completed, the clear resin can be washed away with a water jet.

With the models dispatched to California, the medical team was able to plan the critical rerouting of the blood vessels and to practise their procedures until they were confident of their abilities.

With such comprehensive preparation, the operation was completed in 22 hours - a marathon for both patients and medics, but a faction of the 97 hours that would have been expected had the 3D modelling not be available.

"At Unimatic we have a policy of offering only best in class production machinery", says Bloggs.

"And we will only provide schools with equipment that has a first class reputation in industry".

"PolyJet's use in this life saving surgery has guaranteed its reputation, even if the kids use it for less dramatic projects".

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