Basic Studies of Electrically Controlled Elasticity of Lead Zirconate Titanate (PZT) Ceramic and its Application to Intercepting Elastic Waves
We studied a novel technique for controlling the elastic coefficient of a piezoelectric lead zirconate titanate (PZT) ceramic by connecting a negative-capacitance circuit that behaves as a "negative capacitor". Thus, we can realize control through a mechanism in which PZT is softened and hardened. On the basis of this technology, we developed a simple experimental system for intercepting elastic waves in the frequency range from 8 kHz to 110 kHz. We determined the attenuation factor in transmission loss of the experimental system, which was more than 10 dB in this frequency range. The maximum attenuation factor in transmission loss was about 60 dB at a frequency of 91 kHz.
Sound isolation by piezoelectric polymer films connected with negative capacitance circuits
Sound pressure produces strain and polarization in piezoelectric polymer films. The electric charge induced by the polarization in the electrode of the films is introduced to a negative capacitance circuit and the resulting voltage is fed back to the electrode. The field-induced strain cancels the stress-induced strain, leading to the increase of the elastic coefficient of the films. If the capacitance of the circuit is controlled to be equal to that of the film, the elastic coefficient approaches infinity. Using this principle, the sound isolation by piezoelectric polymer films connected with a negative capacitance circuit was undertaken. A PVDF film with a curved plane was located in the middle of an acoustic tube and the transmission loss through the film was determined in the audio frequency range. At any single frequency, the complete isolation of sound was achieved by adjusting the feedback. The precise matching of complex capacitance of the circuit with that of the film was required to obtain the increase of the transmission loss over a broad frequency range.
Cross talk between redox signalling and metabolic activity of osteoblasts and fibroblasts in the presence of hydroxyapatite-based biomaterials influences bone regeneration
Regeneration of bone tissue defects that result from metabolic disorders, including periodontal diseases, can be supported by biomaterials based on hydroxyapatite. Despite of good biocompatibility of biomaterials they can cause oxidative stress and inflammatory processes as a result of mechanical interaction with surrounding tissues. Because osteoblasts are responsible for bone regeneration process in which gingival fibroblasts may also participate, the aim of the work was to investigate the influence of hydroxyapatite-based biomaterials (allogeneic and xenogeneic) and biomaterials combined with enamel matrix derivative (Emdogain) on osteoblast and fibroblast redox balance in the context of osteoblast proliferation and differentiation.
The results showed that examined substitutes were not cytotoxic in vitro, but affected redox balance of osteoblasts and fibroblasts (ROS level increase and GSH level decrease) which led to oxidative stress (MDA and protein carbonyl groups level increase) resulting in an increase of the Nrf2 and NFκB expression. The consequence of these changes was partial inhibition of proliferation and osteoblast differentiation. Emdogain alone and combined with biomaterials decreased ROS generation and increased GSH level in both osteoblasts and fibroblasts leading to reduction of transcription factors expression especially proinflammatory NFκB, which promoted osteoblast differentiation and mineralization process.