Ultrasonic Transducers Made From Freeze-Cast Porous Piezoceramics.

Porous and composite piezoelectric ceramics are of interest for underwater ultrasonic transducers due to their improved voltage sensitivity and acoustic matching with water, compared with their dense counterparts. Commonly, these materials are fabricated by dice-and-fill of sintered blocks of polycrystalline piezoceramic, which results in a high volume of waste. The freeze-casting technique offers a low waste and scalable alternative to the dice-and-fill method to produce porous piezoceramics with highly orientated, anisometric pores. In this article, we have fabricated underwater ultrasonic transducers from freeze-cast lead zirconate titanate (PZT) with a range of porosities. The porous PZT samples were characterized in terms of their piezoelectric and dielectric properties before being encapsulated for acoustic performance testing in water. Off resonance, the on- axis receive sensitivity of the manufactured devices was approximately [Formula: see text]; the transmit voltage response (TVR) was in the range of approximately [Formula: see text] at 60 kHz to [Formula: see text] at 180 kHz. The most porous transducer devices (0.51, 0.43, and 0.33 pore fraction) exhibited primarily a thickness mode resonance, whereas the least porous transducers (0.29 pore fraction and dense benchmark) exhibited an undesired radial mode, which was observed as an additional resonant peak in the electrical impedance measurements and lateral off-axis lobes in the acoustic beampatterns. Our results show that the acoustic sensitivities and TVRs of the porous freeze-cast transducers are comparable to those of a dense pressed transducer. However, the freeze-cast transducers with porosity exceeding 0.30 pore fraction were shown to achieve an effective structure with aligned porosity that suppressed undesired radial mode resonances.

Effect of TiO2 Nanotube Pore Diameter on Human Mesenchymal Stem Cells and Human Osteoblasts.

The pore diameter of uniformly structured nanotubes can significantly change the behaviour of cells. Recent studies demonstrated that the activation of integrins is affected not by only the surface chemistry between the cell-material interfaces, but also by the features of surface nanotopography, including nanotube diameter. While research has been carried out in this area, there has yet to be a single systemic study to date that succinctly compares the response of both human stem cells and osteoblasts to a range of TiO2 nanotube pore diameters using controlled experiments in a single laboratory. In this paper, we investigate the influence of surface nanotopography on cellular behaviour and osseointegrative properties through a systemic study involving human mesenchymal stem cells (hMSCs) and human osteoblasts (HOBs) on TiO2 nanotubes of 20 nm, 50 nm and 100 nm pore diameters using in-vitro assessments. This detailed study demonstrates the interrelationship between cellular behaviour and nanotopography, revealing that a 20 nm nanotube pore diameter is preferred by hMSCs for the induction of osteogenic differentiation, while 50 nm nanotubular structures are favourable by HOBs for osteoblastic maturation.

Anisotropy Factors and Electromechanical Coupling in Lead-Free 1-3-Type Composites.

The effective electromechanical properties and anisotropy factors of novel lead-free 1-3-type composites are studied to demonstrate their large piezoelectric anisotropy and considerable level of electromechanical coupling. The composites studied contain two single-crystal (SC) components and a polymer component. The first piezoactive component is a domain-engineered [001]-poled SC based on ferroelectric alkali niobates-tantalates, and this component is in the form of a system of long rods that are parallel to the poling axis . The second SC component is a system of spheroidal piezoelectric Li2B4O7 inclusions aligned in a continuous and relatively large polymer matrix. The SC rods are surrounded by an SC/polymer matrix, and the connectivity of the composite is 1-0-3. It is shown that the conditions , which indicates a large degree of anisotropy of the piezoelectric coefficients, and and , which indicate a large anisotropy of the electromechanical coupling factors (ECFs), can be achieved simultaneously in specific ranges of the component volume fractions and inclusion aspect ratios. Moreover, in the same volume-fraction and aspect-ratio ranges, large ECFs ( -0.9) are also achieved. In this context, the important role of the elastic properties of the continuous anisotropic matrix is discussed. The properties and anisotropy factors of the lead-free 1-3-type composites are compared to the similar parameters of conventional lead-containing piezoelectric materials, and the advantages of the composite system studied are described.

Piezoelectric Performance and Hydrostatic Parameters of Novel 2-2-Type Composites.

This paper provides a detailed study of the structure-piezoelectric property relationships and the hydrostatic response of 2-2-Type composites based on relaxor-ferroelectric 0.72 Pb (Mg1/3Nb2/3)O3-0.28PbTiO3 single crystal (SC) material. Type I layers in the composite system are represented by a single-domain [111]-poled SC. Changes in the orientation of the crystallographic axes in the Type I layer are undertaken to determine the maximum values of the hydrostatic piezoelectric coefficients dh∗ , gh∗ , and eh∗ , and squared figure of merit dh∗ gh∗ of the composite. The Type II layers are a 0-3 composite whereby inclusions of modified PbTiO3 ceramic are distributed in a polymer matrix. A new effect is described for the first time due to the impact of anisotropic elastic properties of the Type II layers on the hydrostatic piezoelectric response that is coupled with the polarization orientation effect in the Type I layers. Large hydrostatic parameters gh∗ ≈ 300 -400 mV · m/N, eh∗ ≈ 40 -45 C/ [Formula: see text], and dh∗ gh∗  âˆ¼ 10-11 Pa -1 are achieved in the composite based on the 0.72 Pb(Mg1/3Nb2/3)O3-0.28PbTiO3 SC. Examples of the large piezoelectric anisotropy ( |d33∗ /d3f∗ | ≥ 5 or | g33∗ /g3f∗ | ≥ 5 ) are discussed. The hydrostatic parameters of this novel compositesystem are compared to those of conventional 2-2 piezocomposites.

Understanding the peculiarities of the piezoelectric effect in macro-porous BaTiO3.

This work demonstrates the potential of porous BaTiO3 for piezoelectric sensor and energy-harvesting applications by manufacture of materials, detailed characterisation and application of new models. Ferroelectric macro-porous BaTiO3 ceramics for piezoelectric applications are manufactured for a range of relative densities, α = 0.30-0.95, using the burned out polymer spheres method. The piezoelectric activity and relevant parameters for specific applications are interpreted by developing two models: a model of a 3-0 composite and a 'composite in composite' model. The appropriate ranges of relative density for the application of these models to accurately predict piezoelectric properties are examined. The two models are extended to take into account the effect of 90° domain-wall mobility within ceramic grains on the piezoelectric coefficients [Formula: see text]. It is shown that porous ferroelectrics provide a novel route to form materials with large piezoelectric anisotropy [Formula: see text] at 0.20 ≤ α ≤ 0.45 and achieve a high squared figure of merit [Formula: see text] [Formula: see text]. The modelling approach allows a detailed analysis of the relationships between the properties of the monolithic and porous materials for the design of porous structures with optimum properties.

Effects of iontophoresis, hydration, and permeation enhancers on human nail plate: infrared and impedance spectroscopy assessment.

PURPOSE: To investigate whether permeation enhancement techniques affect the nail plate. METHODS: Infrared and impedance spectroscopies examined the effects of hydration, iontophoresis and N-acetyl-L-cysteine on the human nail. RESULTS: While significant shifts to higher wavenumbers were observed for the symmetric and asymmetric -CH2 stretching vibrations these changes were essentially the same for the three treatments suggesting they were principally due to hydration alone. Spectral changes associated with amide bonds from nail protein were particularly evident post-treatment with N-acetyl-L-cysteine. The alternating current conductivity and permittivity of the nail, particularly at low frequencies, increased with hydration. Iontophoresis increased the low frequency ac conductivity of the nail but had less effect on the nail capacitance/permittivity. Further, the effects seemed to return gradually to baseline after termination of current passage. Treatment with N-acetyl-L-cysteine produced a greater perturbation, leading to increased low-frequency conductivity and a shift of the frequency-dependent conductivity region to a higher frequency. CONCLUSIONS: Overall, the effects of iontophoresis on infrared and impedance spectroscopic profiles of the nail were attributable simply to increased hydration and similar to those observed after skin iontophoresis. In contrast, both spectroscopy techniques indicated that N-acetyl-L-cysteine disrupted nail structure in line with the enhancer's known effect on keratin.

The fabrication of mono-domain highly ordered nanoporous alumina on a wafer scale by a guided electric field.

This paper describes the formation of mono-domain highly ordered nanoporous alumina on the scale of a 2 inch diameter silicon wafer by anodization of aluminium evaporated on a patterned SiO(2) mask on a silicon substrate. The position of the ordered pores correlates with holes in the SiO(2) mask, which guide the electric field during anodization and initiates pore nucleation. The technique is suitable for the production of ordered nanoporous alumina on a wafer scale and overcomes the time, cost and scale limitations of existing processes.

An in vitro study of electrically active hydroxyapatite-barium titanate ceramics using Saos-2 cells.

Electrically active ceramics are of interest as bone graft substitute materials. This study investigated the ferroelectric properties of hydroxyapatite-barium titanate (HABT) composites and the behaviour of osteoblast-like cells seeded on their surfaces. A piezoelectric coefficient (d(33)) of 57.8 pCN(-1) was observed in HABT discs prepared for cell culture. The attachment, proliferation, viability, morphology and metabolic activity of cells cultured on unpoled HABT were comparable to those observed on commercially available hydroxyapatite at all time points. No indication of the cytotoxicity of HABT was detected. At one day after seeding, cell attachment was modified on both the positive and negative surfaces of poled HABT. After longer incubations, all parameters observed were comparable on poled and unpoled ceramics. The results indicate that HABT ceramics are biocompatible in the short term in vitro and that further investigation of cell responses to these materials under mechanical load and at longer incubation times is warranted.