Microchips, soluble without sediment
Scientists at Stanford University (Palo Alto, California), working under the guidance of Professor of chemical Technology Zhenan Bao, have developed electronic devices made of organic materials that completely decompose in the body. Such soluble microcircuits can be used in the production of temporary medical implants and for targeted prolonged drug delivery.
According to Robert Langer, a professor at the Massachusetts Institute of Technology who was not involved in the work, this opens up new opportunities in the manufacture of implants. They may contain organic electronic devices with biodegradable polymers that release drugs.
Earlier this month, researchers at Taft University and the University of Illinois published the results of work on the creation of silicon electronic devices on a biodegradable silk base. The performance of silicon electronics is higher compared to the performance of analogues made of organic semiconductors, but silicon does not decompose in the body. For the first time, Stanford scientists managed to create microchips that work stably in a humid environment, but completely decompose in the conditions of the body: after 70 days, only metal contacts with a thickness of several tens of nanometers remain from them.
Silicon devices are more suitable for the production of implants designed for long-term functioning, for example, acting as interfaces with the brain, and in cases where high performance is a critical parameter. At the same time, electronics that disappear after completing their task can play a good service for such areas as, for example, tissue engineering and regulated drug delivery. Doctors can implant such devices during surgery and, if necessary, release antibiotics during recovery, activate them from the outside using radio signals. Such devices can also be used to monitor the process of postoperative recovery of patients.
To date, the developers have demonstrated the ability of their organic electronics to function in humid conditions and slowly decompose in a slightly alkaline saline solution – in blood plasma or intercellular fluid. To ensure the integrity and functioning of such a device for some time, it must be covered with a shell more resistant to destruction, which will first decompose itself and only after that will provide its "stuffing" to the destructive action of the organism.
The prototype of a biodegradable electronic device described in the article "Organic Thin-Film Transistors Fabricated on Resorbable Biomaterial Substrates", published in the preliminary on-line version of the journal Advanced Materials, is made of biodegradable plastic, already approved by the FDA, biodegradable semiconductor material and gold and silver contacts. The use of these metals for implantation into the body has also received official approval.
Disappearing microchip: A complex of electronic components made of biodegradable materials is destroyed over time.
The photo in the upper left corner shows the chip before it is immersed in a saline solution (the gray stripes are electrical contacts).
Subsequent images were taken on the 10th, 30th, 40th, 50th and 70th days after the dive.
The red line in the photo in the lower right corner corresponds to 5 millimeters.
In the near future, the developers plan to reduce the operating voltage of the devices, which is currently too high for safe functioning in the body – it is enough to ionize water molecules. The reason for this problem is the layer of an insulating layer or dielectric, which in the prototype is represented by a film of polyvinyl alcohol with a thickness of 800 nanometers. The disadvantage of polyvinyl alcohol chosen because of its biodegradability is that its layer is a dense interweaving of polymer chains, which electrons can cross only at a sufficiently high voltage. Researchers are already testing thinner layers of dielectrics, including lipid membranes several dozen atoms thick.
Another task currently being solved is the selection of the substrate material to which flexible organic transistors are attached and which in the prototype is made of brittle plastic. The developers plan to test various substrates based on rubber and stretchable polymers, which will ensure a tight fit of the devices to the tissues. They also test various variants of shells capable of maintaining the integrity of the entire device in the body environment for a given time. The shell covering the prototype described in the publication, when immersed in an environment whose acidity level corresponds to the acidity level of the body, immediately begins to decompose.
Evgeniya Ryabtseva
Portal "Eternal youth" http://vechnayamolodost.ru based on the materials of Technology Review: Biodegradable Transistors. http://www.technologyreview.com/biomedicine/23940/16.11.2009