In “Fantastic Voyage”, the campy 1966 science fiction movie, a team of scientists miniaturized a submarine with themselves inside and passed through the body of one of their team members in order to break up a highly dangerous blood clot. A part from micro-humans, one can imagine the inflammation caused by metal sub.
In an ideal situation, implantable or injectable medical devices are expected to be soft just like the body tissues they correlate with besides being electrically functional and small. Researchers from two UChicago labs are investigating the possibility of producing a material comprising all these three characteristics.
The June 27th issue of Nature Materials features a study on the material developed by the researchers. This material forms the foundation of an ingenious light-activated injectable device capable of being used for stimulating nerve cells and controlling the behavior of organs and muscles.
“Most traditional materials for implants are very rigid and bulky, especially if you want to do electrical stimulation,” said Bozhi Tian, an assistant professor in chemistry whose lab collaborated with that of neuroscientist Francisco Bezanilla, the Lillian Eichelberger Cannon Professor of Biochemistry and Molecular Biology.
This new material is extremely small and soft and has a number of particles that are only a few micrometers in diameter that is almost lesser than the width of a human strand of hair. These tiny particles blend effortlessly in a saline solution such that they are ready to be injected. After a couple of months, the particles naturally begin to deteriorate inside the body hence preventing the need to remove them through a surgery.
All the particles are built of two varieties of silicon that combine to develop a structure full of nano-scale pores, resembling an extremely small sponge. The particles are soft like a sponge and are thus a hundred to a thousand times less stiff than the commonly used crystalline silicon in solar cells and transistors.
It is comparable to the rigidity of the collagen fibers in our bodies. So we’re creating a material that matches the rigidity of real tissue.
Yuanwen Jiang, Tian’s graduate student
The materials comprise half of an electrical device that spontaneously develops itself when one of the many silicon particles is injected into a cell culture or ultimately a human body. The particle gets fixed to the cell and develops an interface with the plasma membrane of the cell. The cell membrane and the particle together develop a unit that produces current when light is made to shine on the silicon particle.
“You don’t need to inject the entire device; you just need to inject one component,” said João L. Carvalho-de-Souza, a postdoctoral scholar in Bezanilla’s lab. “This single particle connection with the cell membrane allows sufficient generation of current that could be used to stimulate the cell and change its activity. After you achieve your therapeutic goal, the material degrades naturally. And if you want to do therapy again, you do another injection.”
The nano-casting process was used to create the particles. The team fabricated a silicon dioxide mold made up of extremely small channels also known as nano-wires, which are attached together by majorly small micro-bridges. The silane gas was then injected into the mold. This gas fills the channels and pores and then disintegrates into silicon.
This is the point where things specifically get crafty. The scientists explore the fact that the smaller an object is, the more the atoms present on its surface overpower its reactions based on what surrounds it. Most of the atoms of each micro-bridge exist on the surface as the micro-bridges are very small in size. The micro-bridges work together with oxygen that is present in the silicon dioxide mold, thus forming micro-bridges made of oxidized silicon obtained from the readily available materials. Very few surface atoms are found in the bigger nano-wires, which mostly remain as pure silicon and much less interactive.
This is the beauty of nanoscience. It allows you to engineer chemical compositions just by manipulating the size of things.
The mold is finally dissolved resulting in a web-like structure of silicon nano-wires joined by micro-bridges of oxidized silicon that is capable of absorbing water and increasing the softness of the structure. The pure silicon maintains its potential to absorb light.
The team introduced the particles onto neurons in culture in the lab, glowed light on the particles and witnessed the flow of current into the neurons which in turn activate the cells. The researchers now focus on investigating what happens in living animals. They are specifically keen in stimulating nerves present in the peripheral nervous system that attach to the organs. These nerves are extremely close to the body’s surface thus allowing near-infra-red wavelength light to contact them through the skin.
Tian envisions using the light-activated devices to engineer human tissue and develop artificial organs in order to replace the ones that are damaged. Scientists can currently develop engineered organs with the exact form but without the ideal function.
Manipulation of separate cells in the engineered tissue will help the lab-built organ function properly. A scientist can perform this with the help of the injectable device, and also by altering an individual cell with a firmly focused light beam like a mechanic reaching into an engine and then turning a single bolt. What is fascinating here is the ability to perform this type of synthetic biology without synthetic biology.
No one wants their genetics to be altered. It can be risky. There’s a need for a non-genetic system that can still manipulate cell behavior. This could be that kind of system.
Jiang was in charge of the project’s characterization and material development, and Carvalho-de-Souza was responsible for the biological component of the collaboration in Bezanilla’s lab. Tian stated that these two individuals were the “heroes” of the work.