Russian scientists from the Lebedev Physical Institute (LPI) have proposed a new method for titanium surface modification, giving it the unique optical and mechanical properties, as well as improving the biocompatibility of the sample. Implants made ​​of the nanocrystalline titanium with the new biocompatible coating are currently in preclinical testing. The proposed modifications of the titanium coating production consist of irradiating the surface of the nanocrystalline titanium using femtosecond laser, causing the formation of periodic structures with dimension scale ranging from submicron to micron. The accomplished studies showed that it is possible to control the sizes of occurring structures, and hence the properties of the material, by varying the laser emission parameters, while maintaining the unique mechanical properties of nanocrystalline material.

“We decided to explore this area together with our colleagues from the Center for Nanostructured Materials and Nanotechnology of the Belgorod State University, led by professor Yuri Kolobov. His staff has successfully studied the creation and practical applications of nanocrystalline titanium, which is attractive for its unique mechanical properties – high strength and super-plasticity. However, nano- and microtexture surfaces, which create an “incubator” for osteoblast cells and thus improve the biocompatibility, are required for biomedical applications – particularly for the surface modification of titanium implants”, said Dr. Andrey Ionin, head of the Gas Lasers Laboratory at the LPI. Initially, it was very difficult to create the surface-based nano- and microtexture while maintaining the inherent structure of nanocrystalline material using the conventional treatment. For example, plasma etching or annealing techniques heat up a pretty thick surface layer – the sintering or fusion of the nanocrystals occurs and consequently microcrystals are formed, which greatly affect the mechanical properties of titanium. But when the sample is exposed to ultra-short laser pulses, only a thin surface layer is heated to high temperatures due to the effect of high beam power amplitude. After that, the energy begins to spread deeper into material and the temperature drops, therefore there are no undesirable sintering of nanocrystals. The resulting nanostructured surface is a well-defined one-dimensional lattice with a characteristic step of 70-600 nm. Thus, when the energy density of the laser radiation is 17 mJ/cm2, the pulse series of 500 pulses form a sequence of narrow grooves (thickness about 100 nm) spaced apart by 400 nm in average on the surface of a titanium target. The scientists explain the emergence of such quasi-periodic structures by the impact of interference between electric field of the incident radiation and the field of surface electromagnetic waves that are generated by the femtosecond laser pulses.