Optical fiber laser-generated-focused-ultrasound transducers for intravascular therapies

In this paper, we report the development of optical fiber laser-generated-focused-ultrasound (LGFU) transducers for intravascular therapies. By combining advantages of fiber optics and photoacoustics, high frequency (>10 MHz), high pressure (> 10 MPa), short pulse (<10 ns) shock waves can be generated from a small aperture (<1 mm in diameter), which is immune to electromagnetic noise. In this work, candle soot nanoparticle (CSNP)-polydimethylsiloxane (PDMS) composite film was used as a photoacoustic layer owing to its high photoacoustic energy conversion efficiency (∼0.004) and simple fabrication procedure. A 2 mm-diameter transparent concave lens was developed by using optical adhesive and capillary-rise technique, and the CSNP-PDMS composite film was coated on it by dip-coating method. The fabricated transducer was integrated with an optical fiber (diameter of 0.6 mm), followed by acoustic characterizations to evaluate the wave form, center frequency, and pressure output. We confirmed that the optical fiber CSNP-PDMS LGFU transducer can generate 12 MHz, high pressure shock wave (peak pressure of 16 MPa) at approximately 1.3 mm away from the transducer surface by low laser energy excitation (1.5 mJ/cm²). The corresponding mechanical index of the achieved pressure output is 1.7, which is sufficient to induce inertial cavitation in microbubble-mediated therapies.