Protrusion-tip antibody placement on a DNA origami nanoparticle enhances endothelial ICAM-1 targeting through glycocalyx: a single-donor microphysiological pilot study

Inside the human body, the lining of every blood vessel is not a smooth, bare wall. It is coated with a thick, gel-like layer made of sugar-protein chains, known as the glycocalyx. Think of this layer as a dense, protective forest that grows right on the surface of the cells. This forest is vital for health; it helps regulate blood flow and keeps the vessel walls from reacting to every passing particle. However, for scientists trying to deliver medicine or diagnostic tools to the vessel wall, this forest is a formidable obstacle. Conventional tiny particles, no matter how small or chemically tuned, often get stuck in the outer branches of this sugar forest. They cannot reach the specific receptors on the cell surface underneath, which are the intended targets for treating inflammation or detecting disease early.

To solve this problem, researchers have turned to a unique type of microscopic structure called DNA origami. Just as paper can be folded into complex shapes, long strands of DNA can be programmed to fold into precise, rigid structures. By designing these structures with specific shapes, scientists can position molecules exactly where they need to be. In a recent pilot study, researchers asked a simple but profound question: if a nanoparticle has a long, stiff arm sticking out of it, will placing a targeting molecule at the very tip of that arm allow it to reach through the sugar forest better than if that same molecule were stuck directly onto the main body of the particle?

The team, working with a single donor's cells, built a microscopic platform shaped like an L. The base of the L was a flat platform, and extending from it was a single, rigid arm made of bundled DNA strands. They created two versions of this device. In the first version, they attached an antibody—a protein that seeks out a specific marker called ICAM-1—at the very tip of the long arm. In the second version, which served as a control, they attached the exact same antibody to the flat base of the L. Both devices were coated in a protective layer to prevent them from sticking to the wrong things, and both were loaded with a glowing dye so the researchers could track them.

These devices were then introduced into a laboratory model of a tiny human blood vessel, which was lined with living cells. The researchers tested the devices under different conditions. In some cases, they left the cells in a calm, healthy state. In others, they treated the cells with a chemical signal that mimics early-stage inflammation, which causes the sugar forest to thin slightly and makes the target markers more abundant. The blood vessel model was kept in motion to simulate the natural flow of blood, and the researchers watched how well the two different versions of the device could grab onto the target markers on the cell surface.

The results showed a clear advantage for the design with the extended arm. When the cells were in a healthy, baseline state with a full sugar forest, the device with the antibody at the tip of the arm found the target markers about five times more often than the device with the antibody on the flat base. Even when the cells were in an early state of inflammation, where the sugar forest was slightly thinner, the tip-placed antibody still performed about twice as well as the base-placed one. The difference was not just a matter of how much stuck to the cells; it was also a matter of speed. The tip-placed device reached its target quickly, while the base-placed device took much longer to achieve a similar level of binding, suggesting it was struggling to push through the barrier.

The researchers noted that this effect happened even though the total size of the two devices was the same and they carried the same amount of antibody. The only difference was where the antibody was located. This suggests that the rigid arm acts like a bridge, allowing the antibody to extend past the outer layers of the sugar forest and touch the cell surface directly, whereas the antibody on the flat base remains trapped in the outer branches. The study was a pilot experiment using cells from a single donor, so the findings are a strong initial proof of concept rather than a final conclusion for all humans. However, the data clearly indicates that the shape of a nanoparticle and the precise placement of its targeting tools are critical factors. By moving the targeting molecule from the body of the particle to the end of a rigid protrusion, scientists may have found a way to bypass the natural defenses of blood vessels, opening a new path for delivering drugs and diagnostics to places that were previously out of reach.