Flexible Transient Optical Waveguides and Surface‐Wave Biosensors Constructed from Monocrystalline Silicon

Abstract

Optical technologies offer important capabilities in both biological research and clinical care. Recent interest is in implantable devices that provide intimate optical coupling to biological tissues for a finite time period and then undergo full bioresorption into benign products, thereby serving as temporary implants for diagnosis and/or therapy. The results presented here establish a silicon-based, bioresorbable photonic platform that relies on thin filaments of monocrystalline silicon encapsulated by polymers as flexible, transient optical waveguides for accurate light delivery and sensing at targeted sites in biological systems. Comprehensive studies of the mechanical and optical properties associated with bending and unfurling the waveguides from wafer-scale sources of materials establish general guidelines in fabrication and design. Monitoring biochemical species such as glucose and tracking physiological parameters such as oxygen saturation using near-infrared spectroscopic methods demonstrate modes of utility in biomedicine. These concepts provide versatile capabilities in biomedical diagnosis, therapy, deep-tissue imaging, and surgery, and suggest a broad range of opportunities for silicon photonics in bioresorbable technologies.

Biodegradable Frequency‐Selective Magnesium Radio‐Frequency Microresonators for Transient Biomedical Implants

“…The transfer of Mg microstructures from a non‐biodegradable to a biodegradable substrate has been already demonstrated using a fabrication process based on transfer printing . Additionally, materials such as poly(lactic‐ co ‐glycolic acid) (PLGA), polycaprolactone, or poly(1,8‐octanediol‐ co ‐citrate) have been already used as biodegradable substrates for transient electronics applications. For the electrical characterization in air, the devices can be directly used without any further processing step.…”

Bioresorbable Materials on the Rise: From Electronic Components and Physical Sensors to In Vivo Monitoring Systems

“…Representative examples of optical devices. a) Left: Photograph and sketch of a bioresorbable silicon waveguide . Middle‐Left: Representative photographs of a spiral waveguide dissolution during immersion in PBS at 70 °C.…”

“…Right: Comparison between the measured oxygen saturation and the environmental concentration. Reproduced with permission . Copyright 2018, John Wiley and Sons.…”

“…Bai et al fabricated flexible infrared waveguides using thin filaments of Si NMs to tackle major drawbacks of PLGA and PLLA waveguides, such as, susceptibility to swelling as a result of water uptake, and limited refraction index contrast, resulting in increased propagation losses and poor optical mode confinement in tissues and biofluids (Figure a). Flexible silicon filaments were obtained from SOI wafers by patterning silicon nanomembranes to form planar coiled structures, for instance, zigzag and spiral waveguides, which were then transfer‐printed on and coated with a PLGA layer (10 µm thick).…”

Materials, Mechanics Designs, and Bioresorbable Multisensor Platforms for Pressure Monitoring in the Intracranial Space

“…Here, bioresorbable constituent materials minimize inflammatory responses and eliminate the need for secondary surgical extraction. [ 9–13 ] Recent examples include not only pressure but also temperature sensors for the intracranial space; [ 14–16 ] photonic devices for monitoring physiological status and neural activity; [ 17 ] wireless electronic systems for neuroregenerative therapy; [ 18 ] platforms for spatiotemporal mapping of electrical activity from the cerebral cortex; [ 19 ] drug release vehicles for infection abatement; [ 20 ] and systems for measuring blood flow. [ 21 ] Realizing consistent performance throughout a clinically relevant monitoring period with devices that bioresorb completely over slightly longer timescales represents an important goal.…”