Researchers at Florida International University, Miami, US, have been using the method to quantify the adhesion strength of biological cells and 1D nanostructures on different underlying substrates. The same team is also developing plasma-sprayed carbon nanotube reinforced HA coatings for orthopaedic applications. Measurement of the adhesion of osteoblasts on HA-CNT coatings is an indicator of the osseointegration on the implant surface.

Test rig

The nano-scratch technique is performed using a Hysitron TI 900 nanoindenter, and exploits the principle of shear force measurement to quantify the adhesion of a single cell (see above image). Unlike some other methods, the technique measures the force directly and does not rely on calibration and indirect computation of the force. A scratch is also made under similar conditions without a cell, but with the culture medium to subtract the contribution of the medium and underlying substrate in the lateral force measured. As a result, this technique overcomes the limitations of existing methods to give an accurate measurement of the adhesion force for a single cell.

The adhesion force was measured for osteoblasts cultured for 1, 3 and 5 days on plastic slides, HA and HA-CNT coated surfaces to determine the effect of carbon nanotubes on cell attachment. It can be clearly seen (image right) that the adhesion energy of a single cell increases as the culture time increases from 1 to 5 days and is the highest for a HA-CNT coated surface.

Staining of an osteoblast cytoskeleton revealed a more intense and well oriented actin filament network on the HA-CNT surface compared with the HA-coated sample. Better attachment and spreading of osteoblasts in the presence of CNTs is due to nanotubes' affinity towards integrins and other cell adhesive proteins. This research has two major outcomes: (i) the presence of CNTs promote osseointegration and (ii) nano-scratch technique using nanoindenter is an effective and reliable method to quantify the adhesion of a single cell.

Also works on graphene

The research team is currently using a similar technique for quantifying the adhesion strength of cells on graphene modified surfaces. The team is also investigating the use of nanoindentation as a potential diagnostic tool for cancerous cells by studying their nanoscale mechanics.

The researchers presented their work in the journal Nanotechnology.