July 30, 1998 A University of Colorado at Boulder chemical engineering team has developed new techniques and materials that show promise for faster healing of severe bone fractures and the regeneration of cartilage in ailing joints.
The process involves the use of ultraviolet light to create repeating chains of complex molecules called polymers into putty-like, three-dimensional "scaffolds" that can be implanted into areas of bone or cartilage injury, said Assistant Professor Kristi Anseth of chemical engineering. Although the process has been used in fields like fiber optics, this is the first application of photopolymerization for medical bone and joint problems.
In the case of bone, a new class of polymer developed by Anseth and her team of graduate students acts as scaffolding as it is placed inside a severe fracture or in the cavity where a bone tumor was removed. As the bone heals, the customized substance -- which degrades over time like a bar of soap -- can be engineered to time-release medications and human-growth factors to aid in the healing process, said Anseth, the project director.
The new bone-healing process, patented by Anseth several years ago through CU and licensed by a major Midwest biotechnology company, has shown promise in animal studies, she said. The advantages to making polymers with UV light are that they can be created at any temperature, the reactions occur quickly, the process can be easily turned on and off, and the polymer material can be applied in small, targeted areas using laser beams.
"A common procedure to treat severe fractures is the use of screws and plates," said Anseth. "But our degradable polymers form a bone-like material that maintains its strength as it degrades, eliminating the problem of weaker and more porous bones and the necessity for second surgeries."
Research results "have been encouraging," she said. "But we will have to wait at least a year to see how effective this method is."
The creation of new polymers to treat cartilage damage in joints is a more difficult problem because cartilage does not have the capacity to heal itself like bone, said Anseth. As a result, she and her team have developed a liquid solution to make polymer scaffolds by using light to form gels that are more elastic than bone polymer material.
They first suspend cartilage-forming cells, called chondrocytes, in a liquid solution, then use a UV light laser beam to convert the liquid to a gel. The resulting polymer, based on polyethylene glycol, has been modified by the CU team to make it degradable over time as the chondrocytes multiply.
"Cartilage is a tissue easier to engineer than organs and other tissues," she said. "Our method makes an elastic "hydrogel" that allows cartilage to form, then subsequently degrades. But the problem still remains that tissue-engineered cartilage is not as strong as natural cartilage in the human body."
Plastic surgeons at Massachusetts General Hospital in Boston have used Anseth's technique on animal models, but have not yet been able to create strong enough cartilage polymers to withstand joint stresses.
While the bone-polymer scaffolding resembles a small, tight mesh of repeating chemical sequences, the cartilage polymer scaffolding made of the same repeating sequences has larger pores to let in more water and sustain the cartilage's pliability, she said.
"The days of using off-the-shelf polymers for processes like these are gone," said Anseth. "We now have the ability to design material so that it behaves exactly as we intend it to."
Anseth's recent research has been promising enough to earn her a prestigious David and Lucille Packard Fellowship for $500,000 over five years, a National Institutes of Health FIRST Award for $500,000 over five years and a $210,000 Career Award from the National Science Foundation.
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