How can medical services change by biomedical devices that can be integrated on or in the body? Here we highlight wearable/implantable bioelectronic devices that are soft, flexible and elastic so that they can be interfaced to tissue. This type of device let us perform biomedical diagnosis and treatment in a personal, mobile and real-time manner. Hybrids of inorganic electronic and soft organic substrates can provide high-performance electronics with flexible/conformal interfaces. We design various types of sensors such as body temperature, intra-cavity pressure, humidity, thermodiffusion, flow rate sensors to pH, glucose, and other biochemical sensors. This work also includes research on mechanical understanding on the deformation and human movement, and on fabrication methodologies for biomedical electronics.

The following describes some recent examples of soft and conformal biomedical devices

Stretchable pH and ECG sensors

pH is a critical biomarker that can signal an abnormal body status of body, for example in the diagnosis of brain injury such as cerebral hemorrhage, stroke, traumatic injury, etc. We introduce an extremely thin Si nanomembrane (~<100 nm) as pH-sensitive electrode, so can measure the pH variation in the biofluid. The extremely thin and flexible substrate allows sensor to have conformal contact on the curvature of organ and tissue and to have mechanical stability.
After it monitors brain pressure for around a week, the device starts to dissolve away, so it need not be extracted, leading to vastly improved patient experience and reduced costs.

 

 

 

 

Near-field communication (NFC) system integrated with temperature/pressure sensors

Advances in wireless operation are an essential feature of mobile/implantable biomedical devices. Here we introduce a near-field communication system of micro-scale thickness and look at a sample application in biomedical sensors. The fabrication of 50-μm-thick magnesium foil yields an inductor coil for electromagnetic transfer, and the integration of diode, capacitor and IC chip on flexible polymer substrates around 30 μm thick offers a flexible and miniaturized wireless system. This technique lets sensors communicate with an outside receiver over ~10 cm distance.

 

 

 

 

Injectable sensor for the deep brain

This unusual form of sensor is necessary to reach information in the deep body. In particular, the deep brain is commonly described as a sea of treasure with large unexplored areas. The most accurate way to measure deep-brain activity is to inject a sensor into deep site, but this approach always leads to brain tissue damage. The sensor must be thin and flexible in order to minimize this damage but also must have rigid edges to penetrate the tissue smoothly. We thus proposed the usual sacrificial injection carrier of magnesium thin films (~80 μm thick) but made their edges needle-sharp. Using this platform, we could precisely measure the temperature and pressure in the deep-brain zone.

 

 

 

 

References

• S.-K. Kang et al. "Bioresorbable Silicon Electronic Sensors for the Intracranial Space and the Deep Brain", Nature 530, 71-76 (2016).
• S.I. Park et al. "Stretchable Multi-channel Antennas in Soft Wireless Optoelectronic Implants for Optogenetics",
  Proceedings of the National Academy of Sciences 113(50), E8169-E8177 (2016).
• A. Koh et al. "Ultrathin Injectable Sensors of Temperature, Thermal Conductivity, and Heat Capacity for Cardiac Ablation Monitoring",
  Advanced Healthcare Materials 5, 373 (2016)
• C.H. Lee et al. "Biological Lipid Membranes for On-Demand, Wireless Drug Delivery from Thin, Bioresorbable Electronic Implants,"
  NPG Asia Materials 7, e227 (2015).
• S.-W. Hwang et al. "Biodegradable Elastomers and Silicon Nanomembranes/Nanoribbons for Stretchable,
  Transient Electronics and Biosensors", Nano Letter 15, 2801 (2015).
• S.-W. Hwang et al. "Materials for programmed, functional transformation in transient electronic systems",
  Advanced Materials 27, 47 (2015).
• X. Huang et al. "Biodegradable Materials for Multilayer Transient Printed Circuit Boards", Advanced Materials 26, 7376 (2014).
• H.L. Hernandez et al. "Triggered Transience of Metastable Poly(Phthalaldehyde) for Transient Electronics",
  Advanced Materials 26, 7637 (2014).
• S.-W. Hwang et al. "High-Performance Biodegradable/Transient Electronics on Biodegradable Polymers",
  Advanced Materials, 26, 3905 (2014)