Tiny Backpacks For Cells

CELLS CAN NOW accessorize with the latest in multilayered polymer patches without fear of cramping their style. The patches attach to immune cell surfaces like backpacks on schoolchildren, and they don't interfere with regular cell functions (Nano Lett., DOI: 10.1021/nl802404h). The nanobackpacks could one day turn cells into drug delivery vehicles.

Several teams have tried to give cells new functions, including drug delivery, by encasing them in polymer shells that can be derivatized. But polymer encasement isn't universally applicable because "many cells need to interact with their surroundings to do their jobs," says MIT materials scientist Michael F. Rubner. Rubner teamed up with MIT engineers Darrell J. Irvine and Robert E. Cohen to figure out how to functionalize immune cells, which need their surfaces to communicate properly.

They settled on three-layer polymer patches that cover only part of cells' surfaces. MIT graduate student Albert J. Swiston built the patches, which contain a customizable cargo layer sandwiched between a hyaluronic acid-based layer for attachment to immune cells and a layer that tethers the patch to a glass surface. After assembly, he delivered cells to the patches with a pipette. A temperature change dissolved the tethering layer, leaving free-floating cells with exposed cargo. The team demonstrated the approach by using patches loaded with magnetic nanoparticles to control the movement of mouse immune cells by applying a magnetic field.

The study is "a step toward exploiting the power and potential of layer-by-layer assembly in biomedical applications," says Mike McShane, an expert in materials patterning at Texas A&M University.

"Living cells don't particularly like to have external, synthetic entities attached to them," says Raz Jelinek, a membrane biophysicist at Ben-Gurion University of the Negev, in Israel. The MIT team's elegant work circumvents that problem, but they still must determine whether the patches elicit immune reactions, he says.

The work is at an early stage and animal testing has yet to take place, Rubner says. But because the cargo-laden polymer patches are made before any cells enter the picture, polymerization and derivatization chemistries do not affect cells directly and therefore can quickly be adapted, he adds.