New materials developments will help boost the already booming market for medical implants.
Researchers at the University of Arkansas hope to commercialize a process in which biocompatible titanium is coated with a ceramic nanowire material, creating surfaces that can last longer for hip replacements, dental reconstruction and vascular stents. Muscle tissue may not adhere well to the smooth surface on uncoated titanium, potentially reducing the useful life of the implant to just 10 years.
An alkali and heat are used to create the titanium-oxide-based ceramic nanowires. “The cost of the process would add $1 or less to each titanium implant,” says Z. Ryan Tian, assistant professor of chemistry and biochemistry in the J. William Fulbright College of Arts and Sciences in Fayetteville, AR. The University of Arkansas plans to license the technology.
A month after Tian and a group of researchers placed a nanowire-coated joint in mice, muscle tissue was growing on the surface. “We saw beautiful tissue growth — lots of muscle fibers,” Tian said. “We've added one more function to the currently in-use titanium implant.”
The nanowire material is engineered to encourage growth.
“We can control the length, the height, the pore openings and the pore volumes within the nanowire scaffolds” by varying the time, temperature and alkali concentration in the reaction, says Tian. “This process is also extremely sustainable,” requiring only that the device be rinsed in reusable water after the heating process, he says.
The sizes and shapes of the pores can be changed so the coating can be applied to vascular stents used in patients to support diseased arteries. Tian says the nanowire coating could potentially replace a complex polymer structure that releases drugs through a mechanical process over time. According to Tian, the ceramic coating could deliver drugs over a longer period of time.
There are indications that use of drug-eluting stents may be waning due to reports of patient problems. One Swiss study reported at the World Congress of Cardiology last year that patient death rates were higher if they had drug-eluting stents. It wasn’t known if the carrier material had any culpability in the problem.
The material may find more immediate use as a coating for medical instruments generally. Items coated with the materials are easily sterilized when rinsed in water and exposed to ultraviolet light. Tian says photons cause a charge separation on the material, splitting water molecules into free radicals that destroy bacteria. “You could just use water to rinse and UV light to sterilize surfaces,” Tian says.
In the meantime, Tian said his research team is studying application of the ceramic coating to plastics and other materials.
Other researchers are studying different ways to improve the performance of implants. One route to improve hardness is to coat titanium with a diamond-like carbon material. The National Natural Science Foundation of China has studied application of boactive ceramic coatings to improve the effectiveness of titanium implants. In Switzerland, Nobel Biocare has developed a full ceramic dental implant that replaces titanium. The implant has been in clinical trials for more than two years and is still under evaluation. The company has been working with industrial ceramics for more than 20 years. The effort is part of a drive to develop metal-free components for dental restoration.
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