“Our idea was that if we minimize the cells’ exposure to the heavy water, we could engineer the system so that we could repeat this measurement over extended time periods without hurting the cell,” Miettinen says.
It takes only one second for a cell to completely exchange its water content, so the researchers could measure the cell’s mass when it was full of heavy water, compare it to the mass in normal water, and then calculate the dry mass. In the system he came up with, cells are exposed to heavy water very briefly as they flow through microfluidic channels. Last year, Miettinen set out to see if he could design a system in which cells could be measured repeatedly with minimal exposure to heavy water. However, heavy water is toxic to cells, so they were only able to obtain a single measurement per cell. These two measurements can be used to calculate the cell’s dry mass. About 10 years ago, they had discovered that they could calculate a cell’s dry mass if they first measured the cell in normal water and then in heavy water (which contains deuterium instead of ordinary hydrogen). This method measures buoyant mass by flowing cells through a channel embedded in a vibrating cantilever, which can be done repeatedly to track changes in a particular cell’s mass over many hours or days.įor their new study, the researchers wanted to adapt the technique so that it could be used to calculate the dry mass of cells, as well as the density of the dry mass. Manalis’ lab has previously developed a technique for measuring the buoyant mass of cells, which is their mass as they float in a fluid such as water. This technique can measure cell growth, but it does not reveal information about the molecular content of the dry mass and it is difficult to use with cells that grow in suspension. Measuring the dry mass of a cell - the weight of its contents not including the water - is commonly done using a microscopy technique called quantitative phase microscopy. MIT biological engineering undergraduates Kevin Ly and Alice Lam are also authors of the paper. Koch Professor of Engineering in the departments of Biological Engineering and Mechanical Engineering, and a member of the Koch Institute for Integrative Cancer Research, is the senior author of the paper, which appears today in eLife. It could allow the newborn cells to be born with more functional contents,” says Teemu Miettinen, an MIT research scientist and the lead author of the new study. “Our hypothesis is that cells might be throwing out things that are building up, toxic components or just things that don’t function properly that you don’t want to have there. The researchers believe that this emptying of trash helps cells to give their offspring a “fresh start,” without the accumulated junk of the parent cell.
Using a new method they developed for measuring the dry mass of cells, the researchers found that cells lose about 4 percent of their mass as they enter cell division. MIT researchers have discovered that before cells start to divide, they do a little cleanup, tossing out molecules that they appear not to need anymore.