Hydroxyapatite aerogels with piezoelectric particles for bone regeneration

Several materials have been researched to replace the damaged tissues or assist in the regeneration pro-cesses of the bone. New strategies for designing advanced functional biomimetic structures are contin-uously being reviewed and optimized. Advances not only on the chemical composition of the implants but also on their physical surface play an important role in enhancing the functionality of implants. This dissertation focuses on the production of Hydroxyapatite (HAp) aerogels and aerogel composites of HAp with Barium Titanate (BaTiO3) particles for bone tissue regeneration. The aerogels are com-posed of HAp nanowires (NWs) produced through solvothermal synthesis and later freeze dried. All the commercially bought particles, 280nm, 2μm and 3μm, proved to contain BaTiO3 in its tetragonal phase when characterized by an XRD, FTIR and Raman analysis. A thermal analysis (DSC and TGA) of the particles allowed to observe a shift in the phase of BaTiO3, for the 280nm particles, around its Curie temperature, 130.6℃. The product of the solvothermal reaction at a temperature of 180℃ for 18hours was verified to be car-bonated Hydroxyapatite through a XRD and FTIR analysis. The aerogels with and without particles were observed with SEM, proving the existence of Hap wires, heterogeneous sized pores, as well as a good distribution of the BaTiO3 particles. The BaTiO3 particles proved to be non-cytotoxic while the fabricated aerogels with and without particles were considered cytotoxic, however, the higher surface of the aerogels and easy dissolution may have altered the results. In the assays of bioactivity assays, in SEM/EDS, difficulties were found when trying to differentiate between the apatite structures and the surface of the HAp wires. However, a quantitative EDS analysis shows that there is a possibly a cycle of CaP deposition followed by dissolution occurring.Diversos materiais têm sido investigados de modo a substituir tecidos danificados ou auxiliar nos pro-cessos regenerativos do osso. Novas estratégias de modo a produzir estruturas biomiméticas funcionais avançadas são continuamente revisadas e otimizadas. Avanços não apenas na composição química dos implantes, mas também na sua superfície física, desempenham um papel importante em melhorar a funcionalidade dos implantes. Esta dissertação dedica-se à produção de aerogéis de hidroxiapatite (HAp) e compostos de aerogel de HAp com partículas de Titanato de Bário (BaTiO3) para regeneração do tecido ósseo. Os aerogéis são compostos por nanofios (NWs) de HAp produzidos por meio de síntese solvotérmica e posteriormente liofilizados. Todas as partículas comerciais, 280nm, 2μm e 3μm, demonstraram a existência de BaTiO3 em fase tetragonal quando caracterizadas por uma análise de DRX, FTIR e Raman. Uma análise térmica (DSC e TGA) das partículas permitiu observar uma mudança na fase do BaTiO3 em torno de sua temperatura de Curie, 130.6 ℃, para as partículas de 280nm. O produto da reação solvotérmica a uma temperatura de 180℃ por 18 horas demonstrou ser hidroxia-patite carbonatada através de uma análise de DRX e FTIR. Os aerogéis com e sem partículas foram observados no SEM, comprovando a existência de fios de Hap, poros de tamanhos heterogêneos, bem como uma boa distribuição das partículas de BaTiO3. As partículas de BaTiO3 mostraram-se não citotóxicas enquanto os aerogéis fabricados com e sem par-tículas foram considerados citotóxicos, no entanto, a elevada área superficial dos aerogéis e fácil disso-lução podem ter alterado os resultados. Nos ensaios de bioatividade, encontrou-se dificuldade em diferenciar, no SEM/EDS, entre estruturas definidas de apatites e a superfície dos fios de HAp. No entanto, a análise quantitativa de EDS mostra que possivelmente existe um ciclo de deposição de CaP seguido de dissolução

Granting Sensorial Properties to Metal Parts through Friction Stir Processing

The authors would like also to thank to Micronsense-Metrologia Industrial (Leiria, Portugal) for the μCT analysis. The authors would also like to thank Prof. Catarina Santos for granting access to the MicroLab - Electron Microscopy Laboratory (Instituto Superior Técnico) for the SEM analyses.Structural Health Monitoring systems assess the part's current condition. This can be performed with a monitoring system comprising sensors, on the surface or embedded, in the monitored parts. However, surface sensors are subject to damage, and embedding the sensors may result in a weakened part. An innovative Self-Sensing Material and its manufacturing process were developed and are presented herein. As proof of concept, Barium Titanate particles were introduced and dispersed into an AA5083-H111 part by Friction Stir Processing (FSP). The particles’ distribution and concentration was evaluated by a set of characterization techniques, demonstrating that greater concentrations, grant enhanced sensitivity to the material. The use of FSP and the embedded particles improved the part’s mechanical behaviour in the processed zone. The sensorial properties were assessed and the response to a set of dynamic loads was measured, being coherent with the solicitations provided. The developed self-sensing material revealed an electrical sensitivity of 12.0 × 10-4 uV/MPa.publishersversionpublishe

Development of the fabrication process and characterization of piezoelectric BaTiO3/epoxy composite used for coated ultrasonic transducer patterns in structural health monitoring

Structural health monitoring (SHM) is based on integrating and/or adapting a sensor system into a structure such that a tolerable damage to occur can be monitored. This requires a network of transducers specifically when this SHM approach is considered as a monitoring system such as based on guided waves. A desirable solution would be to get a transducer network simply ‘printed’ on the structure considered once the network has been designed such as through a simulation approach. In the paper proposed the fabrication process and characterization of a piezoelectric composite to be used as an ultrasonic transducer for damage sensing of structures based on SHM using guided waves is first considered. The composite consists of piezoelectric BaTiO3 particles homogenously distributed in an epoxy resin matrix. A paste with a solid volume fraction of up to 50 vol% was prepared by the direct mechanical mixing of the piezoelectric particles in the epoxy matrix. Due to the ferroelectric properties of BaTiO3 the polarization of the composite is required with a high electric field prior to use. Two electrodes placed on both sides of the samples are required to measure the dielectric and electromechanical properties of the composite in the form of a thick film. The influence of the volume fraction of BaTiO3 on the dialectic properties and piezoelectric transversal constant (d33) of the piezoelectric composite will be shown. Beyond this more materials processing related work performance of those transducers will be demonstrated. This will be done in terms of getting those coated as a transducer pattern/network on a hosting structure after having had the transducer network determined through simulation. Validation of the approach will be done by looking at the transducer network’s performance in terms of detecting guided acoustic waves

New hybrid polymer nanocomposites for passive vibration damping by incorporation of carbon nanotubes and lead zirconate titanate particles

A new hybrid nanocomposite for vibration damping has been elaborated. Ferroelectric lead zirconate titanate particles and carbon nanotubes are dispersed simultaneously in an engineering semi-crystalline thermoplastic matrix by an extrusion processing. Ferroelectric particles have been made piezoelectric once incorporated into the polymer matrix through a poling step. The dynamic response of nanocomposites has been characterized by dynamic mechanical analysis and vibration test. The shear mechanical modulus exhibits an increase of the conservative and dissipative components after the poling step of nanocomposites. By vibration test, the first bending mode of the frequency response function has been followed and a significant damping inherent to poling is also recorded. These evolutions are heightened by the use of two constrained elastic layers. For the first time, a synergy between poled piezoelectric particles responsible for the transduction phenomena and conductive particles allowing a local dissipation of electric charges has been revealed by two complementary techniques for the improvement of the polymer damping

Piezoelectric and mechanical properties of a high performance thermoplastic composite

To protect aircraft and satellite structures from mechanical solicitations such as vibrations, a piezoelectric-based passive damping concept is studied. Most of the time, the piezoelectric elements are surface bonded or embedded in the host structure that needs to be damped. There are integrated with an external shunted circuit. When the piezoelectric material is de-formed, it generates an electrical potential that is dissipated by Joule effect in a resistive ele-ment. More precisely, the purpose of this work is to integrate this passive macroscopic damping con-cept to the composite scale. For this, a hybrid piezoelectric composite based on high perfor-mance thermoplastic polymer as structural matrix is developed. This structural matrix belongs to the PAEK (Poly Aryl Ether Ketone) family. The high glass transition temperature of these thermostable polymers is a critical parameter in the choice of the piezoelectric ceramic. Its Cu-rie temperature has to be higher than the Tg of the composite. In addition, one of the main challenges is to ensure homogeneous particle dispersion with a sufficiently low content to maintain the matrix ductility. We propose to present the piezoelectric and mechanical proper-ties of a thermoplastic polymer / micronic piezoelectric particle composites as a function of their chemical composition

Acoustic Phonon Tunneling and Heat Transport due to Evanescent Electric Fields

The authors describe how acoustic phonons can directly tunnel through vacuum and, therefore, transmit energy and conduct heat between bodies that are separated by a vacuum gap. This effect is enabled by introducing a coupling mechanism, such as piezoelectricity, that strongly couples electric field and lattice deformation. The electric field leaks into the vacuum as an evanescent field, which leads to finite solid-vacuum-solid transmission probability. Due to strong resonances in the system some phonons can go through the vacuum gap with (or close to) unity transmission, which leads to significant thermal conductance and heat flux.Comment: main text, 3 figures, supplementary materia

Fabrication of Piezoelectric Composites Using High-Temperature Dielectrophoresis

In this paper, we present a method to create a highly sensitive piezoelectric quasi 1–3 composite using a thermoplastic material filled with a piezoelectric powder. An up-scalable high-temperature dielectrophoresis (DEP) process is used to manufacture the quasi 1–3 piezoelectric polymer-ceramic composites. For this work, thermoplastic cyclic butylene terephthalate (CBT) is used as a polymer matrix and PZT (lead zirconium titanate) ceramic powder is chosen as the piezoelectric active filler material. At high temperatures, the polymer is melted to provide a liquid medium to align the piezoelectric particles using the DEP process inside the molten matrix. The resulting distribution of aligned particles is frozen upon cooling the composite down to room temperature in as little as 10 min. A maximum piezoelectric voltage sensitivity (g33) value of 54 ± 4 mV·m/N is reported for the composite with 10 vol% PZT, which is twice the value calculated for PZT based ceramics

Flexible piezoelectric nano-composite films for kinetic energy harvesting from textiles

This paper details the enhancements in the dielectric and piezoelectric properties of a low-temperature screen-printable piezoelectric nano-composite film on flexible plastic and textile substrates. These enhancements involved adding silver nano particles to the nano-composite material and using an additional cold isostatic pressing (CIP) post-processing procedure. These developments have resulted in a 18% increase in the free-standing piezoelectric charge coefficient d33 to a value of 98 pC/N. The increase in the dielectric constant of the piezoelectric film has, however, resulted in a decrease in the peak output voltage of the composite film. The potential for this material to be used to harvest mechanical energy from a variety of textiles under compressive and bending forces has been evaluated theoretically and experimentally. The maximum energy density of the enhanced piezoelectric material under 800 N compressive force was found to be 34 J/m3 on a Kermel textile. The maximum energy density of the enhanced piezoelectric material under bending was found to be 14.3 J/m3 on a cotton textile. These results agree very favourably with the theoretical predictions. For a 10x10 cm piezoelectric element 100 µm thick this equates to 38 μJ and 14.3 μJ of energy generated per mechanical action respectively which is a potentially useful amount of energy