Photoacoustic Emission Efficiency of Polymer Matrix Nanocomposites for Use in Epiretinal Prosthetics*

When used as photoacoustic transmitters, the design of polymer matrix nanocomposites can significantly impact the efficiency of the photon-to-acoustic conversion process. This efficiency is critical in applications using these transmitters as epiretinal prosthetic devices where delicate tissues can be damaged by excess energy if it is not effectively dissipated by naturally occurring biological processes. In these prosthetic devices, pulsed laser excitation of the nanocomposite produces acoustic wave emission that neuromodulates cells contained in the retina. For the nanocomposite materials studied in this work, the matrix is highly transparent at the excitation wavelengths of interest while the nanoparticles distributed in the bulk of the material serve as optical absorbers that photothermally heat the matrix when excited by laser pulses. Matrix thermal expansion launches ultrasonic waves that ultimately reach the retina and produce the desired neuromodulation. In this work, the efficiency of the photoacoustic process in these nanocomposites is analyzed with the aim of identifying critical laser and material parameters that affect the performance of these materials as epiretinal prosthetics.