Biotech Byte: Kirigami, Body Tubes, and Drug Delivery
The human body is filled with tubes - lots and lots and lots of tubes. In fact, the digestive tract is made up of nearly 10 meters of tubes, but that’s still really tiny compared to the length of tubing that makes up the circulation system. Blood vessels are made up of nearly 100 000 km of tubes - that’s enough to wrap around planet Earth TWICE! All that tubing is stuffed into our bodies, along with other tubing for the reproductive system, lymphatic system, and respiratory system.
Unfortunately, as useful as the tubes inside us are, it has been a challenge for the medicine to target specific sections of tubing in the body. If there is an infection along the wall of a blood vessel that needs to be treated, medication is required to travel through the body (through its many tubes), and treat the infection while passing through. Imagine going down a long, dark, twisty water slide with many junctions holding a ball, and at some point you must throw the ball and hit a target on the side of the water slide, except you don’t know when the target is going to appear or if you have even taken the correct path through the water slide! In medicine, in order to ensure that medication hits its “target”, not only does there have to be enough of it to survive traveling through the entire body, but it also has to be at a high enough concentration to actually treat the vessel’s wall while passing by. This is called systemic drug administration and it's similar to having a bunch of people going down the slide at the same time with many balls to increase the chances that the target in this twisty multi-channeled water slide gets hit. Luckily, researchers at the Massachusetts Institute of Technology (MIT) and Harvard Medical School have come up with a creative way to target medication delivery in tubes. They were inspired by kirigami.
Kirigami is similar to the more familiar Japanese paper-folding art form, origami, except that it involves cutting a single piece of folded paper. The term was originally coined in 1962 by Florence Temko in America and is likely most commonly recognized as the technique used to make paper snowflakes. Dr. Giovanni Traverso’s group modified stents to be able to safely cling to the side of tubular structures and release medication in a localized area, as pictured below. Stents are most often used in blood vessels to keep them open, especially after a procedure called an angioplasty which is used to widen narrow or obstructed blood vessels.
What makes the kirigami-inspired stent unique is that the cylinder is made up of silicon-based rubber and Kevlar, which is wrapped by a polyester sheet with laser-cut, tiny tooth-like structures that mimic snakeskin with barb-shaped needles, but think of it more like velcro than needles. When pressure is applied, the tooth-like structures stick out, resembling a kirigami-like shell that sticks to the inside walls of the tube. Pressure can then be removed, which causes the tooth-like structures to flatten, and then the stent can be removed from the tissue. This kirigami device doesn’t even have to stay in the tube for very long to even deliver the medicine to a specific location. The tiny needles are filled with medication that is then administered when pressure is applied to the device and the needles hook onto the side of the blood vessel, airway, digestive tract, or other tubular structure. In fact, Traverso and colleagues were able to measure the presence of an anti-inflammatory medicine, budesonide, for up to 7 days in esophagus tissue after only activating the kirigami stent device in the esophagus for two minutes before removing it. Another exciting part about the development of this technology is that this kind of device can be made to fit a wide variety of tubes while still applying the same kirigami-inspired principles. That means that medicine can be locally administered to all different types and sizes of tubes in the body! Check out the exciting primary article here, and if you scroll to the bottom of the article under Supplementary Information, you can check out some really near videos demonstrating this kirigami-inspired medication administration technique.