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Protein redox is responsible for many crucial biological processes; thus, the ability to modulate the redox proteins through external stimuli presents a unique opportunity to tune the system. In this work, we present an acousto-nanodevice that is capable of oxidizing redox protein under ultrasonic irradiation via surface-engineered barium titanate (BTO) nanoparticles with a gold half-coating. Using cytochrome c as the model protein, we demonstrate nanodevice-mediated protein oxidation. BINased on our experimental observations, we reveal that the electron transfer occurs in one direction due to the alternating electrical polarization of BTO under ultrasound. Such unique unidirectional electron transfer is enabled by modulating the work function of the gold surface with respect to the redox center. The new class of ultrasonically powered nano-sized protein redox agents could be a modulator for biological processes with high selectivity and deeper treatment sites. 

Ultrasonic powering is an emerging power source for implantable microdevices due to its superior efficiency in energy transfer at millimeter-scale, long operation distance, and near omnidirectionality. In this paper, we investigate a novel polyhedral ultrasound transducer with emphasis on angular alignment between piezoelectric poling vector and incident waves. Three different polyhedrons (i.e., sphere, octahedron, and dodecahedron) are fabricated via 3D printing lead-free barium titanate ceramic. The maximum output voltage for a unit area occurred at 0° when the poling and waves direction aligned, which were measured to be 0.677±0.071,1.058±0.049 , and 0.709±0.092 V , respectively. At the extreme angular misalignment at 90° (poling and waves perpendicular to each other), only the dodecahedron could sustain the voltage output with 21% reduction, whereas sphere and octahedron dropped by 46%. The results imply that the geometry factor may overcome the poling vector, enabling omnidirectional ultrasonic powering for implantable microdevices. 

In this paper, we introduce an oral motion-powered Smart Tooth system that can monitor oral health. Lower pH is an indicator of bacterial accumulation in the oral cavity, which can cause tooth decay, periodontal or peri-implant diseases. Thus, in situ monitoring pH inside of the mouth is critical to prevent oral diseases. Using a piezoelectric dental crown, Smart Tooth system converts oral motions, such as chewing, to electrical power which can impinge a surface integrated LC transponder. The LC transponder also incorporates iron oxide nanoparticles-embedded pH-sensitive hydrogel that modulates the resonant frequency via shrinking or swelling. As a proof of concept, the fabricated prototype measures pH levels ranging from pH 4 to 12 and sends data wirelessly to the receiver placed up to 5 cm away (wireless transmission path loss at 3 cm was 50.79 dB). The results indicate that the Smart Tooth system can monitor oral health while replacing missing teeth. 

This paper reports on a novel transducer for wireless biochemical sensing. The bilayer transducer consists of a fractal piezoelectric membrane and pH-sensitive chemo-mechanical hydrogel, which overcomes many shortcomings in the chemical and biochemical sensing. The fractal design on the piezoelectric membrane enhances frequency response and linearity by employing periodically repeated pore architecture. As a basis of the pore, a Hilbert space-filling curve with modifications is used. On the surface of the fractal piezoelectric membrane, the hydrogel is laminated. When the bilayer transducer is introduced to a pH environment (e.g., pH = 4, 8, and 12), the hydrogel swells (or shrinks) and induces the curling of the bilayer transducer (10.47°/pH). The curvature then exhibits various ultrasound responses when the bilayer transducer was excited. The measured voltage outputs using an ultrasonic receiver were 0.393, 0.341, 0.250 mV/cm 2 when curvature angles were 30°, 60°, and 120°, respectively. Overall pH sensitivity was 0.017 mV/cm 2 /pH. Ultimately, the biochemical sensing principle using a novel bilayer ultrasound transducer suggests a simple, low-cost, battery-less, and long-range wireless readout system as compared to traditional biochemical sensing. 

Wireless monitoring of the physio-biochemical information is becoming increasingly important for healthcare. In this work, we present a proof-of-concept hydrogel-based wireless biochemical sensing scheme utilizing ultrasound. The sensing system utilizes silica-nanoparticle embedded hydrogel deposited on a thin glass substrate, which presents two prominent interfaces for ultrasonic backscattering (tissue/glass and hydrogel/glass). To overcome the effect of the varying acoustic properties of the intervening biological tissues between the sensor and the external transducer, we implemented a differential mode of ultrasonic back-scattering. Here, we demonstrate a wireless pH measurement with a resolution of 0.2 pH level change and a wireless sensing range around 10 cm in a water tank.