Nanowire Coating Strengthens Implants

R&D DIGEST

A bioceramic nanowire coating that helps tissue adhere more effectively to an implant is paving the way for longer-lasting devices. The material is applied to the surface of biocompatible titanium implants and could be used on devices from hip replacements to vascular stents.

Researchers at the University of Arkansas (Fayetteville) selected metal titanium for the implant, because its mechanical strength and density are close to those of natural bone. Because the surface of many bone implants is too smooth, they chemically corroded the metal's surface to generate a tough outside layer. “The new science here is that the scaffolding nanowires root deeply inside the substrate through the corrosion process and grow on the top, eventually forming the scaffold through the self-assembly process,” says Z. Ryan Tian, PhD, assistant professor of chemistry and biochemistry at the University of Arkansas.

“We needed a porous structure with large pores for a scaffold—at least 20 µm—so that the tissue cell could grow on the surface and integrate into the bone structure,” says Tian. “If the surface is too smooth, the tissue can't adhere [to it] in the first place and will slowly fall off over time.” If the tissue falls off, the implant becomes weak and patients may need additional surgery.

Tian's team can also control the kinetic parameters of the nanowire scaffold, including temperature, concentration and time, and pore size. Having control over the pore size could allow doctors to use the technology to minimize complications by slowly releasing drugs without worrying about polymer biodegradation. A variety of drugs, from antibiotics to immunoreaction medications, could be loaded inside the scaffold before implantation. The pore size needed to promote bone tissue growth would be around 20 µm, whereas the size needed to control a drug release pattern would be about 0.1–0.2 µm.

The researchers are working to optimize the coating's thickness, which currently ranges from 5 to 40 µm. If the coating is too thick, the structure of the implant won't be robust, according to Tian.

A provisional patent has been filed for the nanowire scaffold on biocompatible titanium. The researchers hope to publish more testing results about surface function and how to best induce fast tissue growth. They're also looking for parties interested in pushing the commercialization of the technology.

Work on the implant coating was reported in the September 4 issue of the journal Chemistry of Materials.

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