Oct 1 2012
Apart from long-term implantable medical devices, such as metal plates, the majority of short-term implants (for example, devices used for birth control and drug delivery) have to be removed after they’ve served their purpose. The main issue here is the complication in damaging surrounding tissue when removing the medical device.
Scientists have recently advanced the concept of dissolvable electronic devices by developing novel silicon electronics, which marks a tremendous step in the application of integrated circuits like never seen before.
Silk Biopolymer
Researchers have identified silk as an ideal biopolymer for its application in the development of dissolvable electronics. Aesthetically, silk is optically transparent and offers a flexible form making it perfect for the manufacturing of conformable electronics in the field of medicine. What is more prominent about silk is the fact that this material is bioresorbable and water-soluble.
Silk fibroin is the main material used in the fabrication of a dissolvable electronic platform. Polyimide is used to incorporate an electronic structure to the platform. One of the issues with using polyimide films is that they cannot be integrated into a biological system without using a silicon wafer, as on their own these films are too fragile to function. Following electrode fabrication of the polyimide onto a silicon mesh, the whole platform is assembled to a silk film layer, which has been found to serve as a bioresorbable neural recording system.
In an experiment by Kim DH (2010), the ability of a silk integrated electronic system adapted to a biological structure was tested using a human brain model. One of their findings revealed that conformable coverage of this integrated system increased with the decreasing thickness of the electronic film. The research demonstrates an opening for the application of passive electrode systems in living tissue with the potential of delivering a solution for tracking human health by monitoring the system until the electronic film is completely disintegrated.
A surge of interest in conformable electronics has led to the development of silicon electronics by John Rogers (a Professor of engineering at the University of Illinois) that can map human health and serve as biocompatible electronic components. The device is made up of a silicon and magnesium circuit integrated into a water soluble silk film, which as explained is bioresorbable and can dissolve over a set length of time.
Nanomembranes of silicon have been used in this research to create the circuitry for dissolvable medical electronic devices - again, nanotechnology has contributed to the advancement of electronics. The silicon behaves as a porous structure and the magnesium acts as the conductor. Following the encapsulation of both the silicon and magnesium in magnesium oxide, the longevity of this structure becomes apparent using a coating of silk. As all the materials making up the dissolvable electronic system are biocompatible, there should be less chance of its rejection from the human body.
Dissolvable Electronics to Help Fight Infection
In the study by Kim DH (2010), testing the electronic medical device involved the implantation of a heat-radiating electronic platform into mice in an effort to investigate its ability in fighting off infections at a surgical site. The idea here is to use the implant for an estimated two weeks at the surgical site following an operation to help generate enough heat to minimize infection.
The Defense Advanced Research Projects Agency (DARPA) has announced the creation of dissolvable electronics by using ultrathin sheets of silicon and magnesium integrated with silk. As mentioned, research by Kim DH (2010) demonstrated increased conformability with decreasing thickness of the silk platform. However, the thickness of a transient structure will be a determinant of how long a dissolvable electronic medical implant needs to stay in the body to help monitor the surrounding tissue before dissolving in biological fluid. DARPA has identified that the thickness and crystallinity of silk will determine exactly this, which could range from minutes to hours or days.
You may be wondering exactly how a transient electronic device could help fight infection. Well, DARPA has worked on creating such a device that behaves like a programmable bactericide to help limit or block the manifestation of an infection spreading at a surgical site. The following video is a fascinating demonstration of transient electronics dissolving in liquid.
With silicon and magnesium being natural components of the human body in small quantities, the amount of such material used to engineer this bioconformable device is suggested to be physiologically below levels that could compromise the safety of the human body. As this device is absorbed by body fluids, it can be considered eco-friendly, which is important as there is mounting pressure on the electronics industry to manufacture environmentally-friendly consumer devices that will no longer burden landfill sites.
Recent Developments
A study in 2016 used egg proteins, magnesium, and tungsten to create dissolvable switching devices that regulate the flow of electric current. Egg white, or albumen, was coated onto a silicon wafer to form a thin film. The electrodes were made of magnesium and tungsten. The device worked reliably for more than 3 months in a dry atmosphere. However, in water, the albumen and the electrodes dissolved in less than 10 hours, while the chip dissolved in about 3 days, without leaving any residues.
Another group has developed semiconducting polymers that can be used in thin-film transistors and that can dissolve in a mild acid like vinegar. The polymer was thin and flexible enough to be attached to any type of surface, and upon coupling with iron electrodes, can act as a transistor. The team also showed flexible CMOS circuits using the polymer made on a cellulose substrate, making the entire device not only biocompatible but also able to break down easily.
Degradable electronics have also been demonstrated as brain implants. Sensors that can monitor intracranial pressure and temperature in rats were made using a biocompatible polymer on silicon nanomembranes or magnesium. When the implants were tested in rats, the entire sensor dissolved slowly in the cerebrospinal fluid and was reabsorbed by the body. The rats did not show any infection or inflammation of the brain after the implant disintegrated.
Although several technologies have been demonstrated for dissolvable electronics, their use in everyday life requires much more testing and development. However, with the promise of reduced waste and being environmentally friendly, these technologies are poised to grow significantly in the coming years.
Sources and Further Reading
- https://www.darpa.mil/
- Hwang SK, et al. A Physically Transient Form of Silicon Electronics. Science 2012; 337(6102): 1640–1644.
- Kim DH, et al. Dissolvable Films of Fibroin for Ultrathin, Conformable Bio-Integrated Electronics. Nat Mater 2010; 9(6): 511–517.
- He X et al. Transient Resistive Switching Devices Made from Egg Albumen Dielectrics and Dissolvable Electrodes. ACS Applied Materials and Interfaces 2016; 8(17): 10954-10960.
- Lei T et al. Biocompatible and totally disintegrable semiconducting polymer for ultrathin and ultralightweight transient electronics. PNAS 2017; 114(20): 5107-5112.
- Kang S-K et al. Bioresorbable silicon electronic sensors for the brain. Nature 2016; 530:71-76.
This article was updated on 13th February, 2020.