Zeyu Chen

Multi-frequency intravascular ultrasound (IVUS) imaging

Acute coronary syndrome (ACS) is frequently associated with the sudden rupture of a vulnerable atherosclerotic plaque within the coronary artery. Several unique physiological features, including a thin fibrous cap accompanied by a necrotic lipid core, are the targeted indicators for identifying the vulnerable plaques. Intravascular ultrasound (IVUS), a catheter-based imaging technology, has been routinely performed in clinics for more than 20 years to describe the morphology of the coronary artery and guide percutaneous coronary interventions. However, conventional IVUS cannot facilitate the risk assessment of ACS because of its intrinsic limitations, such as insufficient resolution. Renovation of the IVUS technology is essentially needed to overcome the limitations and enhance the coronary artery characterization. In this paper, a multi-frequency intravascular ultrasound (IVUS) imaging system was developed by incorporating a higher frequency IVUS transducer (80 to 150 MHz) with the conventional IVUS (30-50 MHz) system. The newly developed system maintains the advantage of deeply penetrating imaging with the conventional IVUS, while offering an improved higher resolution image with IVUS at a higher frequency. The prototyped multifrequency catheter has a clinically compatible size of 0.95 mm and a favorable capability of automated image co-registration. In vitro human coronary artery imaging has demonstrated the feasibility and superiority of the multi-frequency IVUS imaging system to deliver a more comprehensive visualization of the coronary artery. This ultrasonic-only intravascular imaging technique, based on a moderate refinement of the conventional IVUS system, is not only cost-effective from the perspective of manufacturing and clinical practice, but also holds the promise of future translation into clinical benefits.

Biomimetic Anisotropic Reinforcement Architectures by Electrically Assisted Nanocomposite 3D Printing

Biomimetic architectures with Bouligand-type carbon nanotubes are fabricated by an electrically assisted 3D-printing method. The enhanced impact resistance is attributed to the energy dissipation by the rotating anisotropic layers. This approach is used to mimic the collagen-fiber alignment in the human meniscus to create a reinforced artificial meniscus with circumferentially and radially aligned carbon nanotubes.

Microanalysis by monochromatic microprobe x-ray fluorescence—physical basis, properties, and future prospects

A monochromatic microprobe for x-ray fluorescence is obtained by a doubly-curved crystal diffractor which focuses characteristic radiation from a small laboratory-based x-ray source. Monochromatic microprobe x-ray fluorescence (MMXRF) provides unique advantages over conventional XRF, i.e., smaller analytical volume, higher sensitivity for the detection of impurities, and more accurate quantitation. Possible photon energies, voltage for the x-ray source, and type of diffractor geometry are discussed. Calculations of geometric aberration, collection solid angle, and beam intensity are given for a Johann-based diffractor. Properties of a mica diffractor used to focus Cu Kα1 x rays are predicted by ray tracing and experimentally verified by x-ray topographs and images of the focal spot. With the mica diffractor and a 20 μm x-ray source at 30 kV and 0.1 mA, ∼1.1×108 photons/s were obtained in a probe of 57 μm×43 μm and probes less than 10 μm appear to be theoretically possible. Energy dispersive spectra for bu...

Microprobe x-ray fluorescence with the use of point-focusing diffractors

A toroidal point-focusing mica crystal diffractor was used to focus monochromatic x rays from a microfocus x-ray source operated at 0.1 mA and 30 kV. The Cu Kα x-ray focal spot of 50 μm×85 μm had 1.6×104 photons/s/μm2. Microprobe x-ray fluorescence (MXRF) spectra were recorded with a Si(Li) energy dispersive detector for bulk specimens of GaAs, Si, and Muscovite. Low background due to monochromatic excitation resulted in predicted detection limits as low as 2 ppm for a measurement time of 500 s. Laboratory MXRF systems based on point-focusing diffractors were shown to provide lower detection limits, larger working distance, and higher theoretical intensity than systems using capillary optics.

Ultrahigh Frequency (100 MHz-300 MHz) Ultrasonic Transducers for Optical Resolution Medical Imagining.

High resolution ultrasonic imaging requires high frequency wide band ultrasonic transducers, which produce short pulses and highly focused beam. However, currently the frequency of ultrasonic transducers is limited to below 100 MHz, mainly because of the challenge in precise control of fabrication parameters. This paper reports the design, fabrication, and characterization of sensitive broadband lithium niobate (LiNbO3) single element ultrasonic transducers in the range of 100–300 MHz, as well as their applications in high resolution imaging. All transducers were built for an f-number close to 1.0, which was achieved by press-focusing the piezoelectric layer into a spherical curvature. Characterization results demonstrated their high sensitivity and a −6 dB bandwidth greater than 40%. Resolutions better than 6.4 μm in the lateral direction and 6.2 μm in the axial direction were achieved by scanning a 4 μm tungsten wire target. Ultrasonic biomicroscopy images of zebrafish eyes were obtained with these transducers which demonstrate the feasibility of high resolution imaging with a performance comparable to optical resolution.

3D‐Printed Biomimetic Super‐Hydrophobic Structure for Microdroplet Manipulation and Oil/Water Separation

Biomimetic functional surfaces are attracting increasing attention for various technological applications, especially the superhydrophobic surfaces inspired by plant leaves. However, the replication of the complex hierarchical microstructures is limited by the traditional fabrication techniques. In this paper, superhydrophobic micro-scale artificial hairs with eggbeater heads inspired by Salvinia molesta leaf was fabricated by the Immersed surface accumulation three dimensional (3D) printing process. Multi-walled carbon nanotubes were added to the photocurable resins to enhance the surface roughness and mechanical strength of the microstructures. The 3D printed eggbeater surface reveals interesting properties in terms of superhydrophobilicity and petal effect. The results show that a hydrophilic material can macroscopically behave as hydrophobic if a surface has proper microstructured features. The controllable adhesive force (from 23 μN to 55 μN) can be easily tuned with different number of eggbeater arms for potential applications such as micro hand for droplet manipulation. Furthermore, a new energy-efficient oil/water separation solution based on our biomimetic structures was demonstrated. The results show that the 3D-printed eggbeater structure could have numerous applications, including water droplet manipulation, 3D cell culture, micro reactor, oil spill clean-up, and oil/water separation.

Piezoelectric component fabrication using projection-based stereolithography of barium titanate ceramic suspensions

Purpose Conventional machining methods for fabricating piezoelectric components such as ultrasound transducer arrays are time-consuming and limited to relatively simple geometries. The purpose of this paper is to develop an additive manufacturing process based on the projection-based stereolithography process for the fabrication of functional piezoelectric devices including ultrasound transducers. Design/methodology/approach To overcome the challenges in fabricating viscous and low-photosensitive piezocomposite slurry, the authors developed a projection-based stereolithography process by integrating slurry tape-casting and a sliding motion design. Both green-part fabrication and post-processing processes were studied. A prototype system based on the new manufacturing process was developed for the fabrication of green-parts with complex shapes and small features. The challenges in the sintering process to achieve desired functionality were also discussed. Findings The presented additive manufacturing process can achieve relatively dense piezoelectric components (approximately 95 per cent). The related property testing results, including X-ray diffraction, scanning electron microscope, dielectric and ferroelectric properties as well as pulse-echo testing, show that the fabricated piezo-components have good potentials to be used in ultrasound transducers and other sensors/actuators. Originality/value A novel bottom-up projection system integrated with tape casting is presented to address the challenges in the piezo-composite fabrication, including small curing depth and viscous ceramic slurry recoating. Compared with other additive manufacturing processes, this method can achieve a thin recoating layer (as small as 10 μm) of piezo-composite slurry and can fabricate green parts using slurries with significantly higher solid loadings. After post processing, the fabricated piezoelectric components become dense and functional.

Simulation and fabrication of 0–3 composite PZT films for ultrahigh frequency (100–300 MHz) ultrasonic transducers

This paper presents simulation, fabrication, and characterization of single-element ultrahigh frequency (100–300-MHz) needle ultrasonic transducers based on 0–3 composite Pb(Zr0.52Ti0.48)O3 (PZT) films prepared by using composite ceramic sol-gel film and sol-infiltration technique. The center frequency of the developed transducer at 300-MHz was the highest frequency of PbTiO3 ceramic-based ultrasonic transducers ever reported. Furthermore, a brief description of the composite model was followed by the development of a new expression for predicting the longitudinal velocity, the clamped dielectric constant, and the complex electromechanical coupling coefficient kt of these films, which is very important in ultrasonic transducer design. Moreover, these parameters are difficult to obtain by measuring the frequency dependence of impedance and phase angle because of the weak signal of the previous 0–3 composite films transducer (>100 MHz). The modeling results show that the Cubes model with a geometric factor ...

High-Frequency Ultrasonic Imaging with Lead-free (Na,K)(Nb,Ta)O3 Single Crystal:

Lead-free (Na,K)(Nb,Ta)O3 (KNNT) piezoelectric single crystal has been successfully grown using the top-seeded solution growth technique. The electromechanical coupling factors are very high (k33 = 0.827, kt = 0.646), and the dielectric loss tangent is as low as 0.004. Acoustic impedance was calculated to be 26.5 MRayl. From the single crystal, a single element transducer was fabricated. The transducer achieved a 57.6% −6 dB bandwidth and 32.3 µm axial resolution at the center frequency of 45.4 MHz, which can identify the cornea of porcine eyeball with high resolution. Comparison between KNNT single crystal and lead-based single crystal was discussed. The results suggest that this single crystal transducer is an excellent candidate to replace lead-containing transducer for high-frequency ultrasonic imaging applications.

Stretchable ultrasonic transducer arrays for three-dimensional imaging on complex surfaces

Ultrasound adds the third dimension to wearable sensors. Ultrasonic imaging has been implemented as a powerful tool for noninvasive subsurface inspections of both structural and biological media. Current ultrasound probes are rigid and bulky and cannot readily image through nonplanar three-dimensional (3D) surfaces. However, imaging through these complicated surfaces is vital because stress concentrations at geometrical discontinuities render these surfaces highly prone to defects. This study reports a stretchable ultrasound probe that can conform to and detect nonplanar complex surfaces. The probe consists of a 10 × 10 array of piezoelectric transducers that exploit an “island-bridge” layout with multilayer electrodes, encapsulated by thin and compliant silicone elastomers. The stretchable probe shows excellent electromechanical coupling, minimal cross-talk, and more than 50% stretchability. Its performance is demonstrated by reconstructing defects in 3D space with high spatial resolution through flat, concave, and convex surfaces. The results hold great implications for applications of ultrasound that require imaging through complex surfaces.