A salt pinch can steer colloids to improve purification and drug delivery

The ability to better manipulate particles suspended in liquids can lead to better water purification processes, new drug delivery systems, and other applications. According to Yale researchers, a key ingredient is the pinch of salt.

The research team led by Professor Amir Pahlavan published the results in a physical review letter.

The diffusion-like phenomenon moves suspended particles known as colloids due to the different concentrations (gradients) of the dissolved substance in the solution. Haoyu Liu, a graduate student at Pahlavan’s lab, points out that the phenomenon was discovered over 50 years ago, but its application to microfluids and its impact on environmental flow has recently been realized.

“Chemical gradients are actually everywhere in our natural systems and everywhere in our industrial processes,” says Liu, the lead author of the study. “So this phenomenon has attracted a lot of attention from scientists and engineers.”

Scientists have traditionally used electric or magnetic fields to manipulate colloids. However, Pahlavan and Liu report that various concentrations of salt can lead to spontaneous movement of colloids. These effects can even create swirling vortices that lead to unexpected results and reverse the normal path of the particle.

Using gradients of salts, polymers, or other molecular solutes, they say there are several advantages over other processes.

“The first is the simplicity of using salt gradients,” says Pahlavan, an assistant professor of mechanical engineering and materials science. “All you need is saltier or less water to operate the colloid, as opposed to a more refined setup.”

This process can be most useful in natural systems

“You don’t always have an electric or magnetic field, but you always have a salt or chemical gradient due to human activity and many other processes that take place in nature.”

As far as applications go, Pahlavan and Liu said that it could benefit the cleansing of the environment.

“Contaminants repair allows the polymer particles to be injected and reacted somewhere with the chemical plume to prevent further spreading, using the solute gradient to ensure that the particles being injected are in the right place,” says Pahlavan.

Drug Delivery is another potential application.

“Here we want to supply particles to certain tumor cells or perhaps biofilms,” he said. “Maybe we can use solute gradients to guide particles to get where we want. These are hidden targets, where we don’t know a priori. But solute gradients can steer the colloid towards the right destination.”