Three types of cell lines, from humans and cattle, were used for the study

Nanomotors and their applications in biomedicine have gained huge interest in recent times and now researchers from Indian Institute of Science (IISc), Bengaluru, have successfully shown how to move them around inside living cells.

In a paper published recently in Advanced Materials, the team demonstrated the manoeuvrability of magnetic-material-coated silica nanomotors inside different cell lines. Less than 3 microns in length, they can be used for targeted drug delivery, nanosensing and in therapeutics.

The group fabricated two helical nanomotors with different dimensions for their experiments. They found that nanomotors could move inside the cells when a rotating magnetic field of less than eighty Gauss (much below the safe level for human beings) is given.

The smaller ones (250 nm thick and 2.4 micron long) could move at a speed of around 500 nanometer per second, throughout the cell much easier than the big ones (400 nm thick and 2.8 microns long) due to the natural porosity of intracellular environment.

Three types of cell lines — human cervical cancer cells, human embryonic kidney and endothelial cells from cattle — were used for the study.

Incubated nanomotors

Around 100,000 cells were spread on a petri dish and a million nanomotors were incubated along with the cells for 24 hours. During incubation, the nanomotors come close to the cells and get internalised by the cell through an engulfing process (phagocytosis).

Using optical microscopy studies, the researchers found that the motors can be manoeuvred with high precision, direction and speed when rotating magnetic field was applied.

“We found that some of the motors were unable to move or moved very slowly inside the cells,” says Prof. Ambarish Ghosh at the Centre for Nano Science and Engineering and corresponding author of the paper. “We ruptured the cells with a solution to find out if the reduced speed was due to loss of magnetic property or some other reason. After the cells were broken, the motors were able to move, showing that they were getting entangled in the components of the cell, just like getting stuck in a traffic jam.”

The group developed a strategy to get the nanomotors out of the jam and move in the desired path. When the nanomotors faced an obstacle, a change in rotation was effected to take it back slightly and change its direction (10-15 degrees) to allow them to move towards its destination.

“The nanomotors can be used as a new imaging tool to study the organelles of the cell up-close. The way the motor moves inside the cell and the hindered motion patterns can help us get a better understanding of the make-up of cells in the body,” explains Malay Pal, PhD student at the Centre and first author of the paper. “Since normal and cancerous cells have variations in the intracellular environment (pH, temperature, energy), we have planned to study the differences in the fluidity of the intracellular matrix using nanomotors.”