Development of a poly(L-Lactic acid) based drug release system

Dissertação de mestrado em Biofísica e Bionanossistemas

Artificial muscle: the human chimera is the future.

Severe heart failure and cerebral stroke are broadly associated with the impairment of muscular function that conventional treatments struggle to restore. New technologies enable the construction of "smart" materials that could be of great help in treating diseases where the main problem is muscle weakness. These materials "behave" similarly to biological systems, because the material directly converts energy, for example electrical energy into movement. The extension and contraction occur silently like in natural muscles. The real challenge is to transfer this amazing technology into devices that restore or replace the mechanical function of failing muscle. Cardiac assist devices based on artificial muscle technology could envelope a weak heart and temporarily improve its systolic function, or, if placed on top of the atrium, restore the atrial kick in chronic atrial fibrillation. Artificial sphincters could be used to treat urinary incontinence after prostatectomy or faecal incontinence associated with stomas. Artificial muscles can restore the ability of patients with facial paralysis due to stroke or nerve injury to blink. Smart materials could be used to construct an artificial oesophagus including peristaltic movement and lower oesophageal sphincter function to replace the diseased oesophagus thereby avoiding the need for laparotomy to mobilise stomach or intestine. In conclusion, in the near future, smart devices will integrate with the human body to fill functional gaps due to organ failure, and so create a human chimera.

Modelling of iron-filled magneto-active polymers with a dispersed chain-like microstructure

Magneto-active polymers are a class of smart materials commonly manufactured by mixing micron-sized iron particles in a rubber-like matrix. When cured in the presence of an externally applied magnetic field, the iron particles arrange themselves into chain-like structures that lend an overall anisotropy to the material. It has been observed through electron micrographs and X-ray tomographs that these chains are not always perfect in structure, and may have dispersion due to the conditions present during manufacturing or some undesirable material properties. We model the response of these materials to coupled magneto-mechanical loading in this paper using a probability based structure tensor that accounts for this imperfect anisotropy. The response of the matrix material is decoupled from the chain phase, though still being connected through kinematic constraints. The latter is based on the definition of a 'chain deformation gradient' and a 'chain magnetic field'. We conclude with numerical examples that demonstrate the effect of chain dispersion on the response of the material to magnetoelastic loading.

Noise and vibration damping of Fe-Cr-x alloys

The aim of the present work is to study the noise and vibration damping capacity of ferromagnetic Fe-16%Cr base alloys (before and after heat treatment) with different Al and Mo contents. The noise damping was evaluated by the level of sound emission after an impact. The vibration damping was studied using a cantilever device. In addition to these tests, the magnetic structure of the materials was also investigated by Kerr effect. It was verified that the materials can decrease noise level in the frequency range of human earring. The vibration damping is influenced by heat treatment and chemical composition of the alloy. The improvement of vibration damping after heat treatment is ascribed to the decrease of internal stresses in materials and changes in magnetic domain structures.

Photoacoustic studies on thermal parameters of liquid crystal mixtures

Complete thermal characterization of liquid crystal mixtures in the smectic phase consisting of various relative volume fractions of cholesterol and 1-hexadecanol have been carried out using the photoacoustic technique. Thermal diffusivity values of these liquid crystal mixtures are evaluated using the open cell photoacoustic technique whereas the thermal effusivity value is measured using the conventional photoacoustic technique. From the measured values of these transient thermophysical parameters, the thermal conductivity and heat capacity of the sample under investigation are calculated. Analyses of the results show that all the thermophysical parameters depend strongly on the volume fraction of the constituents. Results are interpreted in terms of enhanced hydrogen bonding and the consequent enhancement in cohesive thermal energy transport with increasing volume fraction of 1-hexadecanol

Photoacoustic studies on thermal parameters of liquid crystal mixtures

Complete thermal characterization of liquid crystal mixtures in the smectic phase consisting of various relative volume fractions of cholesterol and 1-hexadecanol have been carried out using the photoacoustic technique. Thermal diffusivity values of these liquid crystal mixtures are evaluated using the open cell photoacoustic technique whereas the thermal effusivity value is measured using the conventional photoacoustic technique. From the measured values of these transient thermophysical parameters, the thermal conductivity and heat capacity of the sample under investigation are calculated. Analyses of the results show that all the thermophysical parameters depend strongly on the volume fraction of the constituents. Results are interpreted in terms of enhanced hydrogen bonding and the consequent enhancement in cohesive thermal energy transport with increasing volume fraction of 1-hexadecanol

Photoacoustic studies on thermal parameters of liquid crystal mixtures

Complete thermal characterization of liquid crystal mixtures in the smectic phase consisting of various relative volume fractions of cholesterol and 1-hexadecanol have been carried out using the photoacoustic technique. Thermal diffusivity values of these liquid crystal mixtures are evaluated using the open cell photoacoustic technique whereas the thermal effusivity value is measured using the conventional photoacoustic technique. From the measured values of these transient thermophysical parameters, the thermal conductivity and heat capacity of the sample under investigation are calculated. Analyses of the results show that all the thermophysical parameters depend strongly on the volume fraction of the constituents. Results are interpreted in terms of enhanced hydrogen bonding and the consequent enhancement in cohesive thermal energy transport with increasing volume fraction of 1-hexadecanol

Synthesis, characterization and properties of Conductive elastomeric composites based on Polypyrrole and short Nylon-6 fiber

The search for new materials especially those possessing special properties continues at a great pace because of ever growing demands of the modern life. The focus on the use of intrinsically conductive polymers in organic electronic devices has led to the development of a totally new class of smart materials. Polypyrrole (PPy) is one of the most stable known conducting polymers and also one of the easiest to synthesize. In addition, its high conductivity, good redox reversibility and excellent microwave absorbing characteristics have led to the existence of wide and diversified applications for PPy. However, as any conjugated conducting polymer, PPy lacks processability, flexibility and strength which are essential for industrial requirements. Among various approaches to making tractable materials based on PPy, incorporating PPy within an electrically insulating polymer appears to be a promising method, and this has triggered the development of blends or composites. Conductive elastomeric composites of polypyrrole are important in that they are composite materials suitable for devices where flexibility is an important parameter. Moreover these composites can be moulded into complex shapes. In this work an attempt has been made to prepare conducting elastomeric composites by the incorporation of PPy and PPy coated short Nylon-6 fiber with insulating elastomer matrices- natural rubber and acrylonitrile butadiene rubber. It is well established that mechanical properties of rubber composites can be greatly improved by adding short fibers. Generally short fiber reinforced rubber composites are popular in industrial fields because of their processing advantages, low cost, and their greatly improved technical properties such as strength, stiffness, modulus and damping. In the present work, PPy coated fiber is expected to improve the mechanical properties of the elastomer-PPy composites, at the same time increasing the conductivity. In addition to determination of DC conductivity and evaluation of mechanical properties, the work aims to study the thermal stability, dielectric properties and electromagnetic interference shielding effectiveness of the composites. The thesis consists of ten chapters.

Defining Structure in Electrospun Polymer Fibres

We use a combination of microscopy, x-ray scattering and neutron scattering to show how structure develops in micro and nano-size polymer fibres prepared by electrospinning. The technique has been applied to a range of different polymers, an amorphous system (polystyrene), a crystallisable polymer (poly-epsilon-caprolactone), a composite systems (polyethylene oxide or poly vinyl alcohol containing polypyrrole) and consider the possibility of self assembly (gelatin).

Structural FRF acquisition via electric impedance measurement applied to damage location

Continuing development of new materials makes systems lighter and stronger permitting more complex systems to provide more functionality and flexibility that demands a more effective evaluation of their structural health. Smart material technology has become an area of increasing interest in this field. The combination of smart materials and artificial neural networks can be used as an excellent tool for pattern recognition, turning their application adequate for monitoring and fault classification of equipment and structures. In order to identify the fault, the neural network must be trained using a set of solutions to its corresponding forward Variational problem. After the training process, the net can successfully solve the inverse variational problem in the context of monitoring and fault detection because of their pattern recognition and interpolation capabilities. The use of structural frequency response function is a fundamental portion of structural dynamic analysis, and it can be extracted from measured electric impedance through the electromechanical interaction of a piezoceramic and a structure. In this paper we use the FRF obtained by a mathematical model (FEM) in order to generate the training data for the neural networks, and the identification of damage can be done by measuring electric impedance, since suitable data normalization correlates FRF and electrical impedance.

Optimal and robust modal control of a flexible structure using an active dynamic vibration absorber

This paper is concerned with feedback vibration control of a lightly damped flexible structure that has a large number of well-separated modes. A single active electrical dynamic absorber is used to reduce a particular single vibration mode selectively or multiple modes simultaneously. The absorber is realized electrically by feeding back the structural acceleration at one position to a collocated piezoceramic patch actuator via a controller consisting of one or several second order lowpass filters. A simple analytical method is presented to design a modal control filter that is optimal in that it maximally flattens the mobility frequency response of the target mode, as well as robust in that it works within a prescribed maximum control spillover of 2 dB at all frequencies. Experiments are conducted with a free-free beam to demonstrate its ability to control any single mode optimally and robustly. It is also shown that an active absorber with multiple such filters can effectively control multiple modes simultaneously.

Robust broadband vibration control of a flexible structure using an electrical dynamic absorber

This paper presents a simple but practical feedback control method to suppress the vibration of a flexible structure in the frequency range between 10 Hz and 1 kHz. A dynamic vibration absorber is designed for this, which has a natural frequency of 100 Hz and a normalized bandwidth (twice the damping ratio) of 9.9. The absorber is realized electrically by feeding back the structural acceleration at one position on the host structure to a collocated piezoceramic patch actuator via an analog controller consisting of a second-order lowpass filter. This absorber is equivalent to a single degree-of-freedom mechanical oscillator consisting of a serially connected mass-spring-damper system. A first-order lowpass filter is additionally used to improve stability at very high frequencies. Experiments were conducted on a free-free beam embedded with a piezoceramic patch actuator and an accelerometer at its center. It is demonstrated that the single absorber can simultaneously suppress multiple vibration modes within the control bandwidth. It is further shown that the control system is robust to slight changes in the plant. The method described can be applied to many other practical structures, after retuning the absorber parameters for the structure under control.

Fabrication and testing of a poly(vinylidene fluoride) (PVDF) microvalve for gas flow control

A microactuator made from poly(vinylidene fluoride) (PVDF), a piezoelectric polymer, was fabricated to control the gas flow rate through a glass micronozzle. The actuator was formed by gluing together two PVDF sheets with opposite polarization directions. The sheets were covered with thin conducting films on one side, that were then used as electrodes to apply an electric field to move the valve. The actuator has a rectangular shape, 3 mm x 6 mm. The device was incorporated with a micronozzle fabricated by a powder blasting technique. Upon applying a DC voltage across the actuator electrodes, one sheet expands while the other contracts, generating an opening motion. A voltage of +300 V DC was used to open the device by moving the actuator 30 mu m, and a voltage of -200 V DC was used to close the device by moving the actuator 20 mu m lower than the relaxed position. Flow measurements were performed in a low-pressure vacuum system, maintaining the microvalve inlet pressure constant at 266 Pa. Tests carried out with the actuator in the open position and with a pressure ratio (inlet pressure divided by outlet pressure) of 0.5, indicated a flow rate of 0.36 sccm. In the closed position, and with a pressure ratio of 0.2, a flow rate of 0.32 sccm was measured.

Experimental analysis of the effect of the structure area on the PZT-based SHM systems

The structural health monitoring (SHM) systems based on electromechanical (E/M) impedance technique have been widely investigated. Although many studies indicate the reliability of this technique, some practical considerations still have to be considered in real applications. This paper presents an experimental analysis of the effect of the structure area on the system's performance. The results indicate that the sensitivity of the system to detect damage decreases significantly when the host structure has large cross-section area. Copyright © 2009 by ASME.

An investigations on local and global behavior of a (SMA) oscillator of 3 - DOF driven by a limited power supply

SMART material systems offer great possibilities in terms of providing novel and economical solutions to engineering problems. The technological advantages of these materials over traditional ones are due to their unique microstructure and molecular properties. Smart materials such as shape memory alloys (SMA), has been used in such diverse areas of engineering science, nowadays. In this paper, we present a numerical investigation of the dynamics interaction of a nonideal structure (NIS). We analyze the phenomenon of the passage through resonance region in the steady state processes. We remarked that this kind of problem can lead to the so-called Sommerfeld effect: steady state frequencies of the DC motor will usually increase as more power (voltage) is given to it in a step-by-step fashion. When a resonance condition with the structure it is reached, the better part of this energy it is consumed to generate large amplitude vibrations of the foundation without sensible change of the motor frequency as before. The results obtained by using numerical simulations are discussed in details. Copyright © 2009 by ASME.