Acoustodynamic Covalent Materials Engineering for the Remote Control of Physical Properties Inside Materials.

Advances in vat photopolymerization (VP) 3D printing (3DP) technology enable the production of highly precise 3D objects. However, it is a major challenge to create dynamic functionalities and to manipulate the physical properties of the inherently insoluble and infusible cross-linked material generated from VP-3DP without reproduction. The fabrication of light- and high-intensity focused ultrasound (HIFU)-responsive cross-linked polymeric materials linked with hexaarylbiimidazole (HABI) in polymer chains based on VP-3DP is reported here. Although the photochemistry of HABI produces triphenylimidazolyl radicals (TPIRs) during the process of VP-3DP, the orthogonality of the photochemistry of HABI and photopolymerization enables the introduction of reversible cross-links derived from HABIs in the resulting 3D-printed objects. While photostimulation cleaves a covalent bond between two imidazoles in HABI to generate TPIRs only near the surface of the 3D-printed objects, HIFU triggers cleavage in the interior of materials. In addition, HIFU travels beyond an obstacle to induce a response of HABI-embedded cross-linked polymers, which cannot be attainable with photostimulation. The present system would be beneficial for tuning the physical properties and recycling of various polymeric materials, but it will also open the door for pinpoint modification, healing, and reshaping of materials when coupled to various dynamic covalent materials.

Patterned Interference Radiation Force for Transcranial Neuromodulation.

Compared with the conventional method of transcranial focused ultrasound stimulation using a single transducer or a focused beam, the compression and tensile forces are generated from the high-pressure gradient of a standing wave that can generate increased stimulation. We experimentally verified a neuromodulation system using patterned interference radiation force (PIRF) and propose a method for obtaining the magnitude of the radiation force, which is considered the main factor influencing ultrasound neuromodulation. The radiation forces generated using a single focused transducer and a standing wave created via two focused transducers were compared using simulations. Radiation force was calculated based on the relationship between the acoustic pressure, radiation force and time-averaged second-order pressure obtained using an acoustic streaming simulation. The presence of the radiation force was verified by measuring the time-averaged second-order pressure generated due to the radiation force, by using a glass tube.

Fault-tolerant strategies for an implantable centrifugal blood pump using a radially controlled magnetic bearing.

In our laboratory, an implantable centrifugal blood pump (CBP) with a two degrees-of-freedom radially controlled magnetic bearing (MB) to support the impeller without contact has been developed to assist the pumping function of the weakened heart ventricle. In order to maintain the function of the CBP after damage to the electromagnets (EMs) of the MB, fault-tolerant strategies for the CBP are proposed in this study. Using a redundant MB design, magnetic levitation of the impeller was maintained with damage to up to two out of a total of four EMs of the MB; with damage to three EMs, contact-free support of the impeller was achieved using hydrodynamic and electromagnetic forces; and with damage to all four EMs, the pump operating point, of 5 l/min against 100 mmHg, was achieved using the motor for rotation of the impeller, with contact between the impeller and the stator.