Hydroxyapatite Polymer Composite Implants Help Surgeons Repair Facial Defects

British and Russian Surgeons are using a revolutionary honeycomb-like polymer implant to help re-build the faces of children injured in accidents or born with serious defects. The material bonds with bone without causing adverse reactions.

It is currently undergoing clinical trials in Moscow where it has been used on around fifty children aged from eighteen months to 18 years.

Among the patients who have undergone surgery are a baby with a jaw tumour and a twelve-year-old girl who had been barely able to open her mouth from birth.

The ‘PolyHap’ implants have been developed by teams led by Professor Steve Howdle in Nottingham and Dr. Vladimir Popov from the Institute of Laser and Information Technology in Troitsk, near Moscow, whose work is described in the current issue of Advanced Materials. Funding has been provided by the Wellcome Trust, Britain’s biggest biomedical research charity.

The made-to-measure implants are light, tough, flexible and cheap, providing an excellent alternative to traditional titanium.

Professor Vitaly Roginsky, one of Russia’s leading children’s cranio-maxillofacial surgeons, said : “ These implants allow us to carry out many more operations than before. They are easier to adjust and re-shape and give us much more flexibility in our work.”

When a child is assessed for an operation at the St. Vladimir Children’s Hospital, Moscow, scientists use X-rays and tomography images to create a three-dimensional plastic cast of the damaged area. These solid biomodels, built by a high-tech process called laser stereolithography allow surgeons to plan operations with great precision before they even lift a scalpel.

Having assessed how much bone needs to be removed the scientists in Troitsk use stereolithography to make the individual PolyHap implants. The technique, which can be completed in a matter of hours, can be used to make the most intricate shapes which are then sent to the hospital.

The outline of the implant is initially “drawn” by a laser beam which leaves a very fine coating of polymer. This process is repeated hundreds of times until the model is complete.

So far the Moscow operations have been carried out to correct jaw or skull deformities. But the implants can be adapted for any part of the skeleton.

Professor Howdle, from the School of Chemistry, University of Nottingham, said : “ Precision is vital in this type of operation since every injury will be unique in some way and the patient is obviously hoping for the best possible visual affect after surgery.

“We are delighted that operations using the polymer implants have gone very well, especially as the surgeons are working with children who have suffered serious injuries.”

The success of PolyHap implants is down to the introduction of a mineral-like substance called hydroxyapatite, which makes the polymer tough and ‘bone-friendly’. The collaborating scientists have also found a way to increase porosity – which is important for new bone growth - and clean out toxins from polymers using high-pressure carbon-dioxide. Without this process the implants could cause damaging reactions in the patients.

Dr Popov said : “ I am convinced polymers will take over from titanium in surgery in the coming years. Now we have found a way to make them stronger they are ideal for implants.

“Our technique allows operations to be performed more quickly and efficiently, which is better for the patient and saves time and money for the hospital.”

Although the PolyHap implants have produced good results there is a possibility they might have to be replaced as the child grows and bones develop.

So Professor Howdle and Dr Popov’s teams have started work on a bio-degradeable version which will slowly dissolve as the repairing bone begins to re-grow.

In order to make these ‘vanishing’ implants they are developing a new Surface Selective Laser Sintering technique. This involves using a laser beam to melt just the polymer surface, leaving the bioactive inner section intact – a crucial factor in creating a bio-degradeable implant.

“If we can push the development on to this stage it will mean children will only have to undergo one operation rather than several,” said Professor Howdle. “The benefits from that are obvious.”

Professor John Lowry, Secretary General of the European Association for Cranio-Maxillofacial Surgery, said : “The technique being developed through this collaboration has some interesting innovations and once perfected or even further developed it should prove a great help to surgeons involved in this complex area of surgery.”

Twelve-year-old Kseniya Gordeeva underwent a PolyHap operation in Moscow recently. She had suffered jaw damage at birth and could barely open her mouth. Kseniya had to eat through a straw, had difficulty talking and found it almost impossible to clean her teeth. Because of the lack of normal nutrition she was also underweight for her age.

During a five-hour operation Professor Roginsky removed the section of damaged bone and inserted a two-inch implant. Nine days later she was able to open her mouth without so much effort and was clearly delighted.

“ If I wanted to get my mouth open before the operation I had to lean my head right back,” she said. “ Now it is much easier. I can talk like my friends and eat normally. I don’t have a favourite food because everything I eat is special.”

Professor Roginsky said : “Kiseniya has made remarkable progress in a short time. We will have to do a little more work on her jaw but the improvement is already very noticeable.

“Now she will be able to eat properly and grow into a fine, pretty girl.”

Anara Djantemiroma, 15, is another of Professor Roginsky’s patients. She suffered under-development of the jaw as a young girl. This was corrected in a series of operations, the final one involving insertion of an implant.

 

Posted January 12th, 2005

 

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