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David Bradley ISSUE #43
January - February 2005

Polymer Technology Saves Face

The lives of a baby with a jaw tumor, a twelve-year-old girl barely able to open her mouth from birth, and more than fifty other children, have been transformed by a new mineral-polymer composite - PolyHap.
   Steve Howdle
 Steve Howdle

The material is currently undergoing clinical trials in Moscow, with surgeons testing it in rebuilding the faces of children involved in serious accidents or with facial birth defects. PolyHap implants were developed by teams led by Steve Howdle of Nottingham University and Vladimir Popov of the Institute of Laser and Information Technology in Troitsk, near Moscow, and allow made-to-measure implants to be produced from a light weight, tough, flexible, and inexpensive material. PolyHap, they explain, readily bonds with bone with no adverse side effects. The material might ultimately replace titanium in prosthetics and bone repair surgery.

Prior to surgery this Russian girl could barely open her mouth  
Prior to surgery this Russian girl could barely open her mouth
 




 
Successful surgery with PolyHap has transformed the girl's life  
Successful surgery with PolyHap has transformed the girl's life


 
"These implants allow us to carry out many more operations than before," explains leading pediatric crania-maxillofacial surgeon Vitaly Roginsky of the St. Vladimir Children's Hospital, Moscow. He added, "They are easier to adjust and re-shape and give us much more flexibility in our work." The patient is assessed for an operation, and X-rays or NMR tomography images create a three-dimensional plastic biomodel of the damaged area using Laser Stereolithography. This biomodel is then used to fabricate a mould of a precise PolyHap implant needed for that patient. The process takes just a few hours and almost any can be produced in form suitable for the surgical implant procedure. A final flush through with supercritical carbon dioxide removes chemical residues and toxins, making it safe for implantation. "Such precision is vital in this type of operation," explains Howdle, "since every injury will be unique in some way and the patient is obviously hoping for the best possible result after surgery."

PolyHap implants have several properties which make them more desirable than titanium and related materials. For instance, they are infused with the mineral hydroxyapatite, which not only makes the polymer tough - but because this mineral is related to natural bone, it makes the polymer biocompatible. The porosity of the implants can also be increased using different preparative conditions so that the implant is more amenable to new bone growth. "I am convinced polymers will take over from titanium in surgery in the coming years," adds Popov, "Now we have found a way to make them stronger, they are ideal for implants."

   PolyHap implants are being trialed in Moscow


 
PolyHap implants are being trialed in Moscow

Twelve-year-old Kseniya Gordeeva is doing well after her recent PolyHap operation in Moscow. Having suffered jaw damage during birth she could barely open her mouth and had to eat and drink through a straw. During a five-hour operation 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 favorite food because everything I eat is special."

A polymer cast of a patient's skull can be used to create bone repair implants  
A polymer cast of a patient's skull can be used to create bone repair implants



 

One disadvantage of the current PolyHap formulation is that it is biostable and for some younger patients it will have to be replaced as the child grows and bones develop. To circumvent this problem, Howdle and Popov are working on a biodegradable version that will be slowly dissolved by the body and replaced by growing bone. In order to make these "vanishing" implants, the researchers are developing a new Surface Selective Laser Sintering technique to create biodegradable custom-designed implants.

  SEM micrograph showing the intricate honeycombing of the PolyHap materials



 
SEM micrograph showing the intricate honeycombing of the PolyHap materials

This technique allows them to treat a biodegradable poly-lactic acid polymer powder using a near infra-red (NIR) laser to sinter it and produce a porous implantable structure with demanded shape and architecture.

Adv Mater, 2005, in press; http://dx.doi.org/10.1002/adma.200400838

http://www.laser.ru (English version is at http://www.laser.ru/indexe.html)

http://www.nottingham.ac.uk/chemistry/staff/howdle.html