Fluorescent microscope images of adhered macrophages and foreign body giant cells or FBGCs (with three or more nuclei, indicated by arrows) after staining on compact oxide and nanochannels after four days of culture. The images show a decrease in cellular adhesion and no FBGCs on nanochannels. Scale bar represents 50 µm.
Fluorescent microscope images of adhered macrophages and foreign body giant cells or FBGCs (with three or more nuclei, indicated by arrows) after staining on compact oxide and nanochannels after four days of culture. The images show a decrease in cellular adhesion and no FBGCs on nanochannels. Scale bar represents 50 µm.

Patterning metallic biomedical dental and hip implants with tiny grooves could improve biocompatibility with the body and reduce adverse reactions, according to new research.

The need for biocompatible metallic implants that minimize the body’s natural inflammatory response has driven interest in titanium (Ti) and its alloys. Research is focusing in particular on alloys containing zirconium (Zr) because its mechanical properties are more similar to bone than pure Ti and it is biocompatible. Meanwhile, other investigations have indicated that patterning materials at the nanoscale can also improve biocompatibility.

Now Patrik Schmuki of the University of Erlangen-Nuremberg in Germany and colleagues at the University of Bucharest and the University Politechnica of Bucharest in Romania have combined these two approaches by growing mesoporous oxide layers with nanochannel structures on Ti50Zr alloys [Ion et al., Acta Biomaterialia (2015), http://dx.doi.org/10.1016/j.actbio.2015.06.016].

“There are a lot of studies on TiZr alloys for biomedical applications, evaluating its corrosion resistance, mechanical properties, and biocompatibility… [but] we have studied the influence of nanochannels on TiZr,” explains Schmuki.

The researchers wanted to find out what effect nanochannels have on macrophages – the cells that organize the body’s response to a foreign objects – and how this influences the inflammatory reaction to an implant. The results are promising for TiZr biomedical implants.

First, the researchers devised an anodization process for TiZr in hot glycerol-phosphate electrolyte that produces a uniform partially crystalline oxide layer on the alloy structured with aligned, regular nanoscale channels. Compared to an unstructured oxide layer, the nanochanneled surface appears to limit the number of active macrophages. One of the key indicators of an inflammatory response is that macrophages undergo fusion and proliferate over a surface. But while the macrophages adhere to the nanochanneled surface, they do not undergo fusion and show impaired proliferation.

“This is very important,” says Schmuki, “as macrophages have a key function in the development of the foreign body response, and [it is] macrophage-related inflammation that limits the success of metallic implants.”

Together with a lower concentration of inflammation-related proteins known as cytokines, it appears that nanochanneled oxide-coated TiZr elicits a more favorable biological response than smooth, unstructured surfaces.

“Our next goal is to optimize the geometrical factors of nanochannels for in vitro and in vivo biocompatibility,” Schmuki told Materials Today.

The researchers will be working on incorporating active biomolecules such as anti-inflammatory drugs or growth factors into the nanostructured oxide surface to further reduce the inflammatory response and encourage new tissue growth.