A team of U.S. researchers has found a new and inexpensive way to create a nanowire coating for titanium surfaces used in bone implants. Their nanowire scaffolds can be used 'to create more effective surfaces for hip replacement, dental reconstruction and vascular stenting.' As said the lead researcher, '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,' who added that the process was also extremely sustainable, requiring only that the device be rinsed in reusable water after the heating process. These nanowire scaffolds might also be used in hospitals or in meat-processing plants to kill bacteria.
The images above "show the titanium scaffolding with different pore sizes, plus bone tissue growth on the titanium scaffolding" (Credit: Z. Ryan Tian). Here is a link to a larger version of these pictures.
This research effort has been led by Z. Ryan Tian, assistant professor of chemistry and biochemistry at the University of Arkansas. But why did these scientists try to build better bone implants? Simply because they don't last forever. "Reconstructive bone surgeries, such as hip replacements, use titanium implants. However, muscle tissue may not adhere well to titanium's smooth surface, causing the implant to fail after a decade or so and requiring the patient to undergo a second surgery. Tian and his colleagues created a nanowire-coated joint and placed it in mice. After four weeks, the researchers found that tissue had adhered to the joint. 'We saw beautiful tissue growth -- lots of muscle fibers,' Tian said. 'We've added one more function to the currently-in-use titanium implant.'"
This is only one potential use for these nanowire bioscaffolds. "Because the researchers can control the size and shape of the pores in the nanowire scaffold, the material also could be coated onto stents used in patients with coronary artery disease and in potential stroke victims. Conventional stents sometimes become reclogged with fat after implantation. The most recent stent used to address this problem, called the drug-eluting stent, consists of a polymer coating mixed with the drugs, but the coating may be vulnerable to biodegradation, and may not function for long. The nanowire coating without the degradation problem could be used to carry drugs that would help keep the arteries clear over a long period of time."
For more information, this research work has been published in the journal Chemistry of Materials under the name "Multifunctional Nanowire Bioscaffolds on Titanium" (Volume 19, Number 18, Pages 4454-4459, September 4, 2007). Here is the abstract. "This paper reports a new fabrication of multifunctional nanowire bioscaffolds directly on titanium (Ti) through a simple and scale-up easy hydrothermal reaction of alkali with the Ti metal without using any seeds, templates, TiO2 powder, or stabilizers. The nanowires root firmly inside the Ti substrate and grow on top to eventually self-assemble into macroporous scaffolds. The effects of the alkali concentration, reaction time, and temperature on the bioscaffold morphologies were investigated. The novel solid-state chemistry for the nanowires' downward/upward co-growth and the accompanied self-assembly were tackled. Thus-formed coating of scaffolds on the metal implant surface, mimicking the natural extracellular matrix in structure, can promote cell adhesion and proliferation on Ti implant and perform controlled on-site drug release and photocatalytic sterilization."
Sources: American Chemical Society news release, via EurekAlert!, August 27, 2007; and various websites
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