This device uses magnetic fields to separate cells by size and shape. Credit: Hur Koser

Researchers at Yale have demonstrated a device that uses a magnetic liquid to separate blood cells based on their size and shape in just minutes.

The device applies a magnetic field to a liquid containing magnetic nanoparticles. The nanoparticles create waves that carry cells along depending on their size, shape and mechanical properties. The researchers, led by electrical engineering professor Hur Koser, hope to develop a cheap alternative to cell-sorting techniques that are time-consuming and sometimes require expensive labeling.

Liquid suspensions of magnetic particles, called ferrofluids, are already used as industrial lubricants and in loudspeakers and computer hard disks. These liquids typically contain other chemicals to keep the particles from clumping together and from coming out of the suspension. Magnetic nanoparticles are also being explored for cancer therapies and as contrast agents for magnetic resonance imaging (MRI)--both applications that require very low concentrations.

But the Yale group is the first to make a high-concentration, biocompatible ferrofluid that doesn't contain any chemicals that are harmful to cells, yet still keeps the particles afloat. "It was very tricky to find the parameters to maintain live cells," says Koser.

In experiments described this week in the Proceedings of the National Academy of Sciences, the Yale researchers made microfluidic channels lined with magnetic-field-generating electrodes. Cells were then added to a ferrofluid in the channel. When magnetic fields were applied along the device, the particles in the fluid pushed the cells along the channel, separating them by size and shape. Something similar can be accomplished using electrical fields, says Koser, but this can damage the cells. His group used the device to separate live blood cells from sickle cells and bacteria.

Koser believes the device could be especially helpful when trying to detect very rare types of blood cell, such as cancerous ones. Rapidly sorting cells using magnetic fields could improve the sensitivity of tests for these rare cells without adding any costly chemical labels. Tumor cells are squishier than healthy ones--possibly because they grow quickly and so don't form a proper internal cell skeleton--and Koser hopes that magnetic fields will also be able to separate cells based on their elasticity and other mechanical properties.

"The next step is to try this in conjunction with existing sensors to improve their sensitivity and cut down on time," says Koser.

In the video below, a magnetic field creates waves in a liquid containing magnetic nanoparticles (the nanoparticles are not visible) to separate two types of microbeads based on their size.

In honor of Veterans Day,Technology Review is again highlighting some recent advances in understanding traumatic brain injury--a central issue for many of the troops returning from Iraq and Afghanistan. We first highlighted this problem in a feature in 2007, Brain Trauma in Iraq.

This year, David Moore, a neurologist highlighted in the feature, showed that diffusion tensor imaging, a brain imaging technology, could distinguish between blast-related injuries and other sources of concussion.

According to a recent story of ours:

The blasts caused by improvised explosive devices in Iraq and Afghanistan appear to inflict a fundamentally different type of brain damage than do more traditional sources of concussions, such as blunt trauma. The findings point toward new approaches to diagnosing and monitoring these injuries, which have been a huge concern to the military in recent years. The research also begins to resolve a controversy in brain-injury research--whether soldiers who are near an explosion but don't get hit in the head can still suffer a unique type of brain damage.

Regular concussions are typically caused by direct impact to the head, such as in a fall, or acceleration injuries, as in car accidents. In contrast, blast-induced brain injuries can include both of these factors as well as one that is unique to explosions--a rapid pressure wave that may wreak its own havoc on the brain. As a growing number of troops return from Iraq and Afghanistan with signs of brain injury--post-deployment surveys suggest that 10 to 20 percent of all deployed troops have experienced concussions--the military has been under increasing pressure to understand how this pressure wave affects the brain, as well as how best to diagnose and treat the resulting injuries.

Typically, damage from concussions does not show up on traditional medical imaging tests, such as CT scans or MRIs. But scientists have recently begun using a variation of MRI known as diffusion tensor imaging (DTI) to detect damage to the brain's white matter--the neural wiring that connects cells--after mild traumatic brain injury.

In the new study, David Moore, a neurologist and deputy director for research at the Defense and Veterans Brain Injury Center in Washington, D.C., and colleagues used DTI to assess troops who had been diagnosed with mild traumatic brain injury following a blast, a direct impact, or an acceleration-induced injury several months prior, as well as healthy people who had never suffered a concussion. They found that those with blast-linked trauma had a more diffuse pattern of damage to the white matter, described as a "pepper-spray pattern," than those whose concussions were caused by direct impact or acceleration. The research was presented at the World Congress for Brain Mapping and Image Guided Therapy conference in Boston last month.

Researchers are also pushing forward a blood test to assess more severe brain injuries. According to the piece,

One blood test already used in Europe to screen head-trauma patients before CT scans detects a protein called S100B, which is released by astrocyte cells in the brain after injury. "The thinking is, if you don't have [this marker] in the blood, then you don't have the kind of brain injury you could see on CAT scan," says Jeffrey Bazarian, an emergency-room physician and scientist at the University of Rochester Medical Center, in New York. The test is not approved for use in the United States, however. In a set of clinical guidelines for evaluating head trauma published recently, Bazarian and others estimated that the S100B test could significantly reduce unnecessary CT scanning. "We predict it could eliminate unnecessary radiation in a lot of people--about 30 percent [of those who come into the ER with brain injury]," he says.