Calcium-Modified Silk Patch as a Next-Generation Ultrasound Coupling Medium

Abstract

There is an increasing interest in developing next-generation wearable ultrasound patch systems because of their wide range of applications, such as home healthcare systems and continuous monitoring systems for physiological conditions. A wearable ultrasound patch system requires a stable interface to the skin, an ultrasound coupling medium, a flexible transducer array, and miniaturized operating circuitries. In this study, we proposed a patch composed of calcium (Ca)-modified silk, which serves as both a stable interface and a coupling medium for ultrasound transducer arrays. The Ca-modified silk patch provided not only a stable and conformal interface between the epidermal ultrasound transducer and human skin with high adhesion but also offered acoustic impedance close to that of human skin. The Ca-modified silk patch was flexible and stretchable (∼400% strain) and could be attached to various materials. In addition, because the acoustic impedance of the Ca-modified silk patch was 2.15 MRayl, which was similar to that of human skin (1.99 MRayl), the ultrasound transmission loss of the proposed patch was relatively low (∼0.002 dB). We also verified the use of the Ca-modified silk patch in various ultrasound applications, including ultrasound imaging, ultrasound heating, and transcranial ultrasound stimulation for neuromodulation. The comparable performance of the Ca-modified patch to that of a commercial ultrasound gel and its durability against various environmental conditions confirmed that the Ca-modified silk patch could be a promising candidate as a coupling medium for next-generation ultrasound patch systems.

FPCB as an Acoustic Matching Layer for 1D Linear Ultrasound Transducer Arrays

“…A five-cycle sine wave with 200 mV peak-to-peak voltage was generated by a function generator (33220A, Keysight Technologies, Santa Rosa, CA, USA), amplified by a radio frequency amplifier (5312-004 REV. X1, OPHIR RF Inc., Los Angeles, CA, USA), and transmitted through the matching layer by a commercial ultrasound transducer (HAGISONIC, Daejeon, Republic of Korea) [ 16 ]. Then, the received signal from a 0.5 mm diameter needle-type hydrophone (NH5000, Precision Acoustics, Dorchester, UK) was amplified and displayed on a digital oscilloscope (DSOX2022A, Keysight Technologies, Santa Rosa, CA, USA).…”

“…The speed of sound (c) and acoustic impedance (Z) of the matching layers were calculated with the measured difference in time of flight between transmitted and received signals, the thickness of the matching layer, and reference according to the Formulas (3) and (4) [ 16 ]. where d is the thickness of the matching layer, c o is the speed of sound in oil, ∆t 1 is the time-of-flight difference between the transmitted and received signal when the matching layer is absent, ∆t 2 is the time-of-flight difference between the transmitted and received signal when the matching layer is present, and ρ is the measured density of the matching layer.…”

“…To obtain the ultrasound beam profile of a 1D linear ultrasound transducer array, a single vertical scan was performed in the x-direction to find the point where the beam intensity is maximum. An additional scan was performed across the horizontal plane (26 × 16 mm 2 ) in the yz direction with a step resolution of 300 µm while maintaining the x position [ 16 ]. The maximum output pressure of the 1D linear ultrasound transducer array was calculated by dividing the measured peak-to-peak voltage of the received signal at the point of maximum intensity by the previously calibrated sensitivity of the hydrophone.…”

Recent Advances in Materials and Flexible Sensors for Arrhythmia Detection

“…The design consisted of PZT blocks, serving as the piezoelectric islands, connected with polyimide (PI) serpentine hinges, allowing for stretchability between the otherwise rigid blocks. Lee et al showed that a calcium-modified silk could be used as an interface layer between sensor and skin for ultrasound transducer arrays and that it has a similar acoustic impedance to human skin [64]. Hamelmann et al also introduced an ultrasound array based on PZTs (Figure 4a) [15].…”

“…Hamelmann et al also introduced an ultrasound array based on PZTs (Figure 4a) [15]. Other materials for stretchable ultrasound substrates include polyethylene naphthalate (PEN), PDMS, acrylic, and PET [60,64,65].…”