Claudio Domenici

PIEZOELECTRIC GUIDANCE CHANNELS ENHANCE REGENERATION IN THE MOUSE SCIATIC NERVE AFTER AXOTOMY

Piezoelectric nerve guidance channels made of polyvinylidene fluoride (PVDF) were evaluated in a transected mouse sciatic nerve model. Poled PVDF channels were compared to unpoled PVDF channels after 4 and 12 weeks of implantation. In all animals, the proximal and distal nerve stumps were bridged by a continuous nerve cable. Nerves regenerated in poled channels contained a higher number of myelinated axons than those regenerated in unpoled channels at both time periods. We conclude that piezoelectric nerve guidance channels enhance peripheral nerve regeneration and provide a tool to investigate the influence of electrical activity on nerve regeneration.

Shear stress detection in an elastic layer by a piezoelectric polymer tactile sensor

A polyvinylidene fluoride (PVDF) sensor sandwiched between two elastic layers fixed to a rigid foundation is shown to be able to resolve a shear stress component produced by loading the upper layers surface with a rigid indenter. When the measured charge response of the sensor is compared to that predicted by analytical solution of the corresponding axisymmetric elastic contact problem, a significant qualitative agreement between the two responses results. The experimentally determinated sensitivity, on the other hand, is found to be higher than that predicted analytically. Possible causes of this discrepancy are discussed. >

A stress-component-selective tactile sensor array

Abstract A stress-component-selective tactile array, based on piezoelectric polymers, and its associated data acquisition system are described. The seven-taxel sensor array is made up of elements sensitive to one or more components of the stress field acting upon them. The six independent components of the stress tensor can be calculated from a linear combination of the responses of the six miniaturized elements composing each taxel. The array is developed with the aim of obtaining a skin-like tactile sensor able to perform fine-form discrimination of objects in contact with it. It is also thought to be instrumental in revealing phenomena related to incipient slippage during object manipulation and grasping. The multi-component sensor, based on 42 miniaturized piezoelectric polymer discs, is supported by a polyimide sheet with microlithographically defined electrodes. The sensor elements are embedded into a rubber layer with appropriate thickness in order to sample properly the stress field and to obtain good signal-to-noise ratio at the input of the electronic signal processing unit. Preliminary experiments to test the ability of individual sensor elements to resolve normal and shear stress components have shown good agreement with the responses predicted by analytical solutions of elastic contact problems.

In-vitro liver model using microfabricated scaffolds in a modular bioreactor

Hepatocyte function on 3‐D microfabricated polymer scaffolds realised with the pressure‐activated microsyringe was tested under static and dynamic conditions. The dynamic cell culture was obtained using the multicompartment modular bioreactor system. Hepatocyte cell density, glucose consumption, and albumin secretion rate were measured daily over a week. Cells seeded on scaffolds showed an increase in cell density compared with monolayer controls. Moreover, in dynamic culture, cell metabolic function increased three times in comparison with static monolayer cultures. These results suggest that cell density and cell‐cell interactions are mediated by the architecture of the substrate, while the endogenous biochemical functions are regulated by a sustainable supply of nutrients and interstitial‐like flow. Thus, a combination of 3‐D scaffolds and dynamic flow conditions are both important for the development of a hepatic tissue model for applications in drug testing and regenerative medicine.

Multisensor piezoelectric polymer insole for pedobarography

Abstract Analysis of the pressure distribution under the foot in walking and standing patients (pedobarography) can be used to detect orthopaedic as well as neurological defects. Sensorized insoles are increasingly used, at least for research purposes, because of the inherent advantages they offer compared to the force platforms presently available. We have developed and evaluated a piezoelectric polymer insole for pedobarography, using a 200 μm thick polyvinylidene fluoride (PVDF) film which had been uniaxially stretched and poled in selected areas. Sixteen circular aluminium disks, 6 mm diameter each, deposited onto the film by vacuum evaporation, served as the electrodes for the pressure sensors and were located so as to optimize the response of the five metatarsal transducers, which are particularly critical for a correct gait analysis. The 16 sensors were disposed on the ideal loading surface, the response of which identified incorrect foot conformation on loading. Sixteen conductive tracks, one for ...

Hydrostatic pressure and shear stress affect endothelin-1 and nitric oxide release by endothelial cells in bioreactors.

Abundant experimental evidence demonstrates that endothelial cells are sensitive to flow; however, the effect of fluid pressure or pressure gradients that are used to drive viscous flow is not well understood. There are two principal physical forces exerted on the blood vessel wall by the passage of intra‐luminal blood: pressure and shear. To analyze the effects of pressure and shear independently, these two stresses were applied to cultured cells in two different types of bioreactors: a pressure‐controlled bioreactor and a laminar flow bioreactor, in which controlled levels of pressure or shear stress, respectively, can be generated. Using these bioreactor systems, endothelin‐1 (ET‐1) and nitric oxide (NO) release from human umbilical vein endothelial cells were measured under various shear stress and pressure conditions. Compared to the controls, a decrease of ET‐1 production by the cells cultured in both bioreactors was observed, whereas NO synthesis was up‐regulated in cells under shear stress, but was not modulated by hydrostatic pressure. These results show that the two hemodynamic forces acting on blood vessels affect endothelial cell function in different ways, and that both should be considered when planning in vitro experiments in the presence of flow. Understanding the individual and synergic effects of the two forces could provide important insights into physiological and pathological processes involved in vascular remodeling and adaptation.

Artificial sensing skin mimicking mechanoelectrical conversion properties of human dermis

Intrinsic mechanoelectrical conversion properties of skin tissues are investigated, and their origin is suggested to originate primarily from electrokinetic phenomena (streaming potentials) operating in the dermis. Human dermis is considered in analogy to other connective tissue as a biphasic, composite material in which the extracellular fluid permeates a negatively charged gel-like matrix of glycoproteins. A synthetic analog implementing a mechanoelectrical transduction mechanism thought to operate in dermis is realized. A biomorphic tactile sensor is devised and its dynamic transduction response is theoretically and experimentally analyzed. The streaming potential artificial skin appears to be particularly suited for applications in which ideal mechanical matching with body tissues or soft touch grasp are required.<<ETX>>

Piezoelectric properties and dielectric losses in PVDF-PMMA blends

Abstract Piezoelectric properties and dielectric losses have been measured in polyvinylidene fluoride (PVDF)/polymethyl methacrylate (PMMA) blends to assess the value of this class of polymers as ultrasonic transducer materials. The electromechanical coupling factor kt has been found to become vanishingly small in blends having a PMMA content of about 20% by weight. For the same blend composition, the peak of dielectric losses, which at room temperature is located in the low megahertz range, decreases only by 20%. For low PMMA content blends at room temperature, the slow decrease of dielectric losses and the slight frequency shift of the loss peak in the megahertz region are ascribed to the presence of two conjugate amorphous phases. This structure prevents much stronger effects on dielectric losses which could be expected from blending PVDF with a polymer having a high glass transition temperature, such as PMMA. PVDF–PMMA blends, therefore do not represent an attractive class of ultrasonic transducer mat...

Analogs of biological tissues for mechanoelectrical transduction: tactile sensors and muscle-like actuators

In this article the authors report their current attempts toward the development of new “skin-like” tactile sensors and “muscle-like” linear actuators potentially useful in the design of dexterous end effectors. The underlying design philosophy resides on mimicking electromechanical conversion properties of biological tissue making use of synthetic piezoelectric polymers or polyelectrolyte gels. A brief introduction is also given to the physical mechanisms which govern mechanical to electrical transduction in polymeric systems. It is a belief of the authors that substantial progress in the development of sophisticated tactile sensors and artificial muscles can be obtained by resorting to a “molecular bionics” approach.

A comparative study of chemical derivatisation methods for spatially differentiated cell adhesion on 2-dimensional microfabricated polymeric matrices.

This paper describes a study of surface derivatisation methods applied to two-dimensional polymer matrices microfabricated using the Pressure-Assisted Microsyringe (PAM) technique. A blend of polylactide and polycaprolactone was used as the matrix material, and surface chemistry techniques based on silanes and polyethyleneglycol (PEG) derivatives were employed to render the surface underlying the scaffold anti-adhesive whilst polylysine was covalently coupled to the surface of the polymer matrix to enhance cell adhesion. Prior to cell-adhesion tests, the surfaces and matrices were analysed using physico-chemical techniques, such as surface tension, surface potential and fluorescence. Adhesion of primary endothelial cells was evaluated using cell counting techniques. The results demonstrate that both PEGs and silanes are about 66% efficient at demarcating endothelial cell adhesion in short term experiments and that covalently-bound polylysine to the polymer matrix increases cell adhesion twofold with respect to the adsorbed polypeptide.