Polydimethylsiloxane (PDMS) is widely used in biomedical science and can form composites that have broad applicability. One promising application where PDMS composites offer several advantages is optical ultrasound generation via the photoacoustic effect. Here, methods to create these PDMS composites are reviewed and classified. It is highlighted how the composites can be applied to a range of substrates, from micrometer‐scale, temperature‐sensitive optical fibers to centimeter‐scale curved and planar surfaces. The resulting composites have enabled all‐optical ultrasound imaging of biological tissues both ex vivo and in vivo, with high spatial resolution and with clinically relevant contrast. In addition, the first 3D all‐optical pulse‐echo ultrasound imaging of ex vivo human tissue, using a PDMS‐multiwalled carbon nanotube composite and a fiber‐optic ultrasound receiver, is presented. Gold nanoparticle‐PDMS and crystal violet‐PDMS composites with prominent absorption at one wavelength range for pulse‐echo ultrasound imaging and transmission at a second wavelength range for photoacoustic imaging are also presented. Using these devices, images of diseased human vascular tissue with both structural and molecular contrast are obtained. With a broader perspective, literature on recent advances in PDMS microfabrication from different fields is highlighted, and methods for incorporating them into new generations of optical ultrasound generators are suggested.
All-optical ultrasound transducers are promising for imaging applications in minimally invasive surgery. In these devices, ultrasound is transmitted and received through laser modulation, and they can be readily miniaturized using optical fibers for light delivery. Here, we report optical ultrasound transmitters fabricated by electrospinning an absorbing polymer composite directly onto the end-face of optical fibers. The composite coating consisting of an aqueous dispersion of multi-walled carbon nanotubes (MWCNTs) in polyvinyl alcohol was directly electrospun onto the cleaved surface of a multimode optical fiber and subsequently dip-coated with polydimethylsiloxane (PDMS). This formed a uniform nanofibrous absorbing mesh over the optical fiber end-face wherein the constituent MWCNTs were aligned preferentially along individual nanofibers. Infiltration of the PDMS through this nanofibrous mesh onto the underlying substrate was observed and the resulting composites exhibited high optical absorption (>97%). Thickness control from 2.3 μm to 41.4 μm was obtained by varying the electrospinning time. Under laser excitation with 11 μJ pulse energy, ultrasound pressures of 1.59 MPa were achieved at 1.5 mm from the coatings. On comparing the electrospun ultrasound transmitters with a dip-coated reference fabricated using the same constituent materials and possessing identical optical absorption, a five-fold increase in the generated pressure and wider bandwidth was observed. The electrospun transmitters exhibited high optical absorption, good elastomer infiltration, and ultrasound generation capability in the range of pressures used for clinical pulse-echo imaging. All-optical ultrasound probes with such transmitters fabricated by electrospinning could be well-suited for incorporation into catheters and needles for diagnostics and therapeutic applications.
We show an active artificial iris based on solely thin-film components, wherein several LCD elements are controlled a metal-oxide TFT and by powered by thin-film photovoltaics (TFPV). Key aspects for the driver are size and low power consumption. We demonstrate power consumption down to 25µW for the full iris.
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