Author: Doshi Ojus
Date: September 2007
Last month, scientists at the University of Arkansas and University of New Mexico announced the finding of a new, economical method to generate nanowire scaffolding on titanium metal. The research, published in the August issue of Chemistry of Materials, gives scientists and doctors the opportunity to make more durable, longer-lasting, and multi-functional bone implants and stents. The find comes at a time when the number of people needing bone replacements is increasing, and cardiovascular disease continues to be the number one killer in the United States.
Dr. Ryan Tian, the main director in the research effort, believes his group's work will solve several problems associated with titanium implants and stent technology in an economical way.
"This is a very simple, low cost, sustainable idea for the formation of a nanowire scaffold," he commented. "We take advantage of corrosion. We use chemical corrosion with a metal surface to create a metal oxide scaffold."
The process involves a hydrothermal reaction of an alkali (basic solution with a high pH) and titanium. The result is a coating of titanium oxide nanowires which spontaneously grow both upwards and downwards, making the coating more robust than its predecessors.
"If you think about a nanostructure coating on a metal, a single smear will remove all the structure on the coating. In this coating we created, you cannot remove anything. This is because the nanowire has a very specific mechanism such that the nanowires root deeply and the top part spontaneously grows and self-assembles. This is why they are robust," Tian explained.
The nanowires will prove especially useful for titanium bone and dental implants, whose surfaces are often too smooth for surrounding bone tissue to permanently attach,even with currently existing microscaffolding. The controllable pore-size of these new nanowires solves this problem by allowing better connective tissue growth, making it less likely that the implant will need to be replaced in short amount of time.
Tian's group collaborated with the University of Arkansas Medical School's Dr. Joshua Epstein, Professor of Medicine in the Myeloma Institute for Research and Therapy, who carried out biological experiments related to the new scaffolding on the implants.
"We implanted certain structures coated with the microwires into mice sub-cutaneously and tested the survival of mesenchymal stem cells on these implants," Epstein said. "We were testing the quality of implant integration into the tissues of the mice."
"We saw beautiful tissue growth - lots of muscle fibers," Tian said.
An additional application of the new nanowire technology enhances the function of stents, or metal devices intended to open clogged arteries. Doctors currently use drug-eluting stents (DES), which release a drug that prevents an accumulation of fat deposits which would re-clog the stent. These drugs, which are stored in pores on the stent coating, are used up after a short period of time, requiring new stent implantation.
"It is not that easy to optimize scaffolding structure to maximally load the drug to have ultra long time release, so current DES can only function for 1-3 years," Tian mentioned.
But the controllable pore size of the research group's scaffolding again provides an advantage.
"Our scaffold can be precisely tailored into form with larger pore volume and a small pore opening," Tian said. This enables the stents to function for a much longer time period.
"We are seeking collaborations with medical schools to further finalize this. We want to quickly move to a truly clinical viable form," Tian stated. "Because we have a few million people suffering from bone fractures, this is a tremendous market for new bone implants. Not to mention so many people are in need of stents, so we are targeting two different markets."
Author: Ojus Doshi
Reviewed by: Emma Wear
Published by: Konrad Sawicki