Notes from Dr. Stephen E. Saddow’s presentation, “Silicon Carbide Biomedical Technology for Bone Implants, Stents and Brain-Machine Interfaces”.
Electrical Engineering Department
Department of Molecular Pharmacology and Physiology
University of South Florida
Abstract: Amorphous silicon carbide (SiC) has been used for several years as a non-biofouling coating in biomedical devices such as coronary stents and bone implants. However, up to recently, the biocompatibility of single crystal SiC, which presents appealing bio-sensing potentialities, has been in question. A comprehensive study of the biocompatibility of this wide band-gap semiconductor has been performed with extremely promising results which show the higher performance of SiC in bio-environments with respect to Si, the leading semiconductor, and introduce SiC into a unique class of materials that is both bio- and hemocompatible.
Goal: avoid glial scarring
Carbon electrodes: replace gold/metal electrodes which can become toxic.
- long-term (unlike polymers)
- won’t corrode (unlike metals, eventually)
- …but is it biocompatible/hemocompatible?
Silicon Carbide (SiC):
- biocompatible (“in vivo”)
- hemocompatible (“in vitro”)
- very wide bandgap (low carrier concentration)
- “If we can make a switch using SiC, there will be effectively no leakage current”.
- 3x as hard as Si
- 3x as flexible as Si
SiC is “like bone”. Bone tissue can grow on SiC, but dies on Si.
3C-SiC: “cubic form” of SiC, works better than 4H-SiC (hexagonal).
CNS, PNS: body naturally fails by open-circuit (as opposed to short-circuit).
A high concentration of glial cells on the implant indicates poor biocompatibility (immuno-inflammatory response).
Blood-brain barrier. Brain “eats” Si (“poison”).
SiC shows microglia only found near the surface.
Q: Why do neurons “eat” Si, but not SiC?
A: It appears that the neurons “go on a diet” after C layer is encountered (SiC is “Si wrapping C, wrapping Si, wrapping C, …”).
Q: What is preventing the use of SiC as a replacement in biomedical applications which currently use Si?
A: Mostly, cost of materials (and manufacturing?). The process is not perfected.