PVDF Ultrasonic Sensors for In-Air Applications: A Review.

Polyvinylidene fluoride (PVDF), a material with ferroelectric characteristics, is still extremely topical for the manufacturing of transducers, and different examples, some of which have been actively commercialized since the 1980s, are reported in the literature. In this work, we present a review focused on the PVDF technology for the manufacturing of in-air ultrasonic transducers, which found application in medical robotics, sonar systems, and automation industry (e.g., proximity sensors and obstacle detection). The aim is to provide a comprehensive view on the development of such ultrasonic transducers, highlighting the constructive choices and the advantages/disadvantages in a thorough and concise way.

Ultrasonic Transducers Shaped in Archimedean and Fibonacci Spiral: A Comparison.

We developed and investigated a particular geometry of transducers, emulating the shape of bats' cochlea, to transmit and receive ultrasounds in the air. Their design involved the use of polyvinylidene fluoride (PVDF) as a piezoelectric material, thanks to its excellent conformability and flexibility. This material offers the primary requirements for sensing devices in applications such as sonar system or energy harvesting technology. The piezo film was folded according to both the Archimedean and Fibonacci spirals, and their performances were investigated in the frequency range from 20 kHz up to more than 80 kHz. The finite element analysis (FEA) of the proposed transducers highlighted the presence of multiple resonance vibrations, proved by the experimental measurements of the equivalent electric impedance and frequency response. Far-field radiation patterns demonstrated, horizontally and vertically, omnidirectional properties both as transmitters and receivers. All was enough to establish the best validity of the spiral shaped transducers for applications based on the bio sonar principle.

Influence of the Fabrication Accuracy of Hot-Embossed PCL Scaffolds on Cell Growths.

Polycaprolactone (PCL) is a biocompatible and biodegradable polymer widely used for the realization of 3D scaffold for tissue engineering applications. The hot embossing technique (HE) allows the obtainment of PCL scaffolds with a regular array of micro pillars on their surface. The main drawback affecting this kind of micro fabrication process is that such structural superficial details can be damaged when detaching the replica from the mold. Therefore, the present study has focused on the optimization of the HE processes through the development of an analytical model for the prediction of the demolding force as a function of temperature. This model allowed calculating the minimum demolding force to obtain regular micropillars without defects. We demonstrated that the results obtained by the analytical model agree with the experimental data. To address the importance of controlling accurately the fabricated microstructures, we seeded on the PCL scaffolds human stromal cell line (HS-5) and monocytic leukemia cell line (THP-1) to evaluate how the presence of regular or deformed pillars affect cells viability. In vitro viability results, scanning electron and fluorescence microscope imaging analysis show that the HS-5 preferentially grows on regular microstructured surfaces, while the THP-1 on irregular microstructured ones.

Spiral-Shaped Biologically-Inspired Ultrasonic Sensor.

Up to now, low-frequency ultrasonic transducers have been manufactured using different materials and technologies and have been inspired by the biological world, mainly by the biosonar of dolphins and bats. Our research moves in this context, which is dedicated to investigating the feasibility of developing a piezopolymer sensor capable of covering the wide frequency range of a bat's biosonar. We propose an ultrasonic sensor manufactured using a sheet of polyvinylidene fluoride curved according to a logarithmic spiral geometry as it is present in biological models of the cochlea. Experiments were carried out both in transmission and reception, and demonstrated that a spiral-shaped transducer can transmit and receive ultrasonic signals similar to the specific vocalizations of most of the bats in the range between 20 and 80 kHz. The resonant frequencies of the transducer were evaluated through a finite element analysis, in agreement with experimental data covering the entire broadband. During transmission, the sound pressure level showed a maximum value of 90 dB, while during reception, the sensitivity spanned from t103.8 up to t89.1 dB. Directivity measurements demonstrated omnidirectional properties both on horizontal and vertical planes, representing a breakthrough in the field of broadband ultrasonic sensors.

Effects of sulodexide on stability of sclerosing foams.

BACKGROUND AND OBJECTIVES: Foam sclerotherapy is a clinical procedure for the treatment of unhealthy veins. The aim of this study was to investigate the effect of sulodexide (SUL) on stability of foams prepared using polidocanol (POL) and sodium tetradecyl sulfate (STS) detergents, more specifically with 0.25% aethoxysclerol and 0.2% Fibro-Vein sclerosing solutions. METHODS: Foams were produced by the Tessari method using three different weight ratios of POL-SUL and STS-SUL (1:0, 1:1, and 1:3). RESULTS: The half-life of STS foams resulted as follows: 82 ± 1.6 s, 101.8 ± 2.6 s, and 109.7 ± 2.1 s for 1:0, 1:1, and 1:3 STS-SUL weight ratios, respectively. The same ratios were used for POL foams with the following results: 90.6 ± 3 s, 106.8 ± 2.6 s, and 107.6 ± 2.7 s for 1:0, 1:1, and 1:3 POL-SUL weight ratios, respectively. CONCLUSION: The addition of SUL in sclerosing solutions can prolong the half-life of foams, and it could be potentially used as a foam stabilizer.

Polydocanol foam stabilized by liposomes: Supramolecular nanoconstructs for sclerotherapy.

Vascular pathology of the lower limbs is a widespread disease affecting the quality of life for more than 30% of the adult world population. Polydocanol foam is presently the main therapeutic option for treating varicosities, inflammation, and chronic disease which affect the vascular endothelium and blood vessels. Unfortunately, the commercial product contains detergents and surfactants which can provoke several side effects and decrease the efficacy of therapy. In an attempt to overcome these drawbacks, polydocanol foam was mixed with different liposomes before use. The resulting mixture was stable and generated supramolecular nanoconstructs, which may prevent the interaction of the components of the commercial polydocanol foam with the vascular endothelium. This effect depends on the presence of liposomes, which can induce polydocanol foam to change its structure from micelles to complex nanostructures, thus improving its stability. In this attempt, the physicochemical features of the resulting nanoconstructs were tested through dynamic- and multiple light scattering analyses, rheological studies and gel permeation chromatography, while the stability was tested in biological fluids. Our preliminary results showed that the nanoconstructs have some potential as therapeutic agents in sclerotherapy.

EGFET-Based Sensors for Bioanalytical Applications: A Review.

Since the 1970s, a great deal of attention has been paid to the development of semiconductor-based biosensors because of the numerous advantages they offer, including high sensitivity, faster response time, miniaturization, and low-cost manufacturing for quick biospecific analysis with reusable features. Commercial biosensors have become highly desirable in the fields of medicine, food, and environmental monitoring as well as military applications, whereas increasing concerns about food safety and health issues have resulted in the introduction of novel legislative standards for these sensors. Numerous devices have been developed for monitoring biological processes such as nucleic acid hybridization, protein⁻protein interaction, antigen⁻antibody bonds, and substrate⁻enzyme reactions, just to name a few. Since the 1980s, scientific interest moved to the development of semiconductor-based devices, which also include integrated front-end electronics, such as the extended-gate field-effect transistor (EGFET) biosensor, one of the first miniaturized chemical sensors. This work is intended to be a review of the state of the art focused on the development of biosensors and chemosensors based on extended-gate field-effect transistor within the field of bioanalytical applications, which will highlight the most recent research reported in the literature. Moreover, a comparison among the diverse EGFET devices will be presented, giving particular attention to the materials and technologies.

Size of Sclerosing Foams Prepared by Ultrasound, Mechanical Agitation, and the Handmade Tessari Method for Treatment of Varicose Veins.

OBJECTIVES: Sclerotherapy is a therapeutic method used in the treatment of varicose veins and works by occluding damaged blood vessels with a chemical solution. Foam sclerotherapy is an attractive treatment because the results are more effective than those obtained by using liquid sclerosants. However, serious neurologic complications, which are likely related to air embolism, have been reported after treatment with foams generated by the handmade method (Tessari technique) most often used clinically. We present an alternative ultrasonic technique for preparation of sclerosing foams to treat varicose veins. METHODS: Three methods of foam generation were compared: ultrasound, mechanical agitation, and Tessari techniques. RESULTS: Optical microscopic analyses showed that low-frequency ultrasound can generate foams with smaller bubble distributions compared to those produced by handmade and mechanical agitation methods: 98% of the bubble population was less than 55 ± 10 µm for sonicated foams (mean ± SD, 19 ± 1.8 µm; maximum bubble size, <138.3 ± 32.5 µm), 196.7 ± 38.2 µm for mechanically agitated foams (mean, 37.1 ± 10.6 µm; maximum bubble size, <350 ± 70.9 µm), and 211.7 ± 20.8 µm for handmade foams (mean, 30.8 ± 3.8 µm; maximum bubble size, <445 ± 32.8 µm). CONCLUSIONS: Low-frequency ultrasonic foam generation yields smaller bubbles and more uniform size distributions than other investigated methods. These properties may reduce serious adverse events reported for sclerotherapy of varicose veins, increasing the safety of foam treatment.