Francesca Passaretti

Intraoral laser welding: ultrastructural and mechanical analysis to compare laboratory laser and dental laser

The Nd:YAG laser has been used since 1970 in dental laboratories to weld metals on dental prostheses. Recently in several clinical cases, we have suggested that the Nd:YAG laser device commonly utilized in the dental office could be used to repair broken fixed, removable and orthodontic prostheses and to weld metals directly in the mouth. The aim of this work was to evaluate, using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and dynamic mechanical analysis (DMA), the quality of the weld and its mechanical strength, comparing a device normally used in dental laboratory and a device normally used in the dental office for oral surgery, the same as that described for intraoral welding. Metal plates of a Co-Cr-Mo dental alloy and steel orthodontic wires were subjected to four welding procedures: welding without filler metal using the laboratory laser, welding with filler metal using the laboratory laser, welding without filler metal using the office laser, and welding with filler metal using the office laser. The welded materials were then analysed by SEM, EDS and DMA. SEM analysis did not show significant differences between the samples although the plates welded using the office laser without filler metal showed a greater number of fissures than the other samples. EDS microanalysis of the welding zone showed a homogeneous composition of the metals. Mechanical tests showed similar elastic behaviours of the samples, with minimal differences between the samples welded with the two devices. No wire broke even under the maximum force applied by the analyser. This study seems to demonstrate that the welds produced using the office Nd:YAG laser device and the laboratory Nd:YAG laser device, as analysed by SEM, EDS and DMA, showed minimal and nonsignificant differences, although these findings need to be confirmed using a greater number of samples.

Design and thermo-mechanical analysis of a new NiTi shape memory alloy fixing clip

In this work, a new NiTi shape memory alloy (SMA) bone fixator is proposed. Thanks to the shape memory effect, this device does not need any external tool for the fixation, as the anchorage is obtained only by the self-accommodation of the clip during the parent transformation. Calorimetry and thermo-mechanical tests were used to evaluate the phase transformation temperatures and to estimate the forces generated both during the fixing surgical procedure and after the surgical operation. An application on animal anatomical sample was also performed; an appropriate mechanical tightness as well as a good handiness has been found.

Update on the Design and Development of a TEG Cogenerator Device Integrated into Self-Standing Gas Heaters

Heating by gas combustion is widespread in residential and industrial environments, through the use of different types of systems and plants. A relevant case is that of gas stoves, where the heat-radiating unit operates autonomously with local gas feeding. A thermoelectric generator (TEG) can be integrated within this type of autonomous gas heater, for local production of electric power, so that devices requiring electric power can be added, where desired, without the need for any connection to the electrical grid. This approach can also lead to easier installation and operation, and eventually increases the overall efficiency. Following the development plan presented in a previous report, a new prototype of an autonomous gas heater for outdoor use has been implemented through the integration of an improved TEG device with a simple and robust design, which can be easily operated by the end-user. A small amount of heat is withdrawn and converted into electricity by the TEG, providing self-sustaining operation and, moreover, powering additional functions such as high-efficiency light-emitting diode lighting.

DSC and three-point bending test for the study of the thermo-mechanical history of NiTi and NiTi-based orthodontic archwires

It is a known fact that the NiTi orthodontic archwire is one of the first and most diffuse biomedical applications of shape memory alloys. In the last years, none deep study about orthodontic archwires has been conducted from the material point of view. In general, the clinical response is the principal aspect that has been investigated for this application. Nonetheless, the accurate mechanical and physical characterization of the archwires can be very important to add new developments to this biomedical product and to give a substantial contribution to the indispensable evolution that is crucial for better clinic results. In fact, the principal aspect that it is needed for further improvements is the study of the optimal force that does not cause damage to the surrounding tissues. According to this statement, a deep study about the thermo-mechanical characterization of several pseudoelastic commercial archwires used in the straight-wire low-friction techniques is presented. In detail, flexural mechanical tests in the three-point-bending configuration were conducted to assess the archwires unloading force, while differential scanning calorimetry was used to study the phase transition temperatures, and the thermo-mechanical history of each specimen. Both NiTi and NiTiCu commercial archwires were tested, and different geometries were considered. For all the archwires, an excellent repeatability of the results has been found. This series of characterizations provides a complete view of the thermo-mechanical properties of the material, and therefore it shows the possibility to modulate the functional properties developed by the device as a function of the biological field.

Design and Development of a TEG Cogenerator Device Integrated into a Self-Standing Natural Combustion Gas Stove

Heating by gas combustion, by use of different types of systems and plants, is widespread in residential and industrial environments. One example is the gas stove, the heat-radiating unit of which operates autonomously with a local gas feed and, possibly, electricity for an optional fan convector. A thermoelectric generator (TEG) can be integrated within this type of autonomous gas heater for local production of electric power, to support electrical auxiliaries, where desired, without the need for any connection to the electricity grid. This approach can lead to easier installation and operation and increases overall efficiency. A new prototype of an autonomous gas heater has been implemented by integration of a TEG device of simple and robust design, easily operated by the end user. A small amount of heat is withdrawn and converted into electricity by the TEG. This enables self-sustaining operation and, moreover, powers new ancillary functions (e.g. fan convector) without extra electrical requirements and no need for an electrical connection.

Can passive mobilization provide clinically-relevant brain stimulation? A pilot eeg and nirs study on healthy subjects

Lower limb rehabilitation is a fundamental part of post-acute care in neurological disease. Early commencement of active workout is often prevented by paresis, thus physical treatment may be delayed until patients regain some voluntary command of their muscles. Passive mobilization of the affected joints is mostly delivered in order to safeguard tissue properties and shun circulatory problems. The present paper investigates the potential role of early passive motion in stimulating cortical areas of the brain devoted to the control of the lower limb. An electro-mechanical mobilizer for the ankle joint (Toe-Up!) was implemented utilizing specially-designed shape-memory-alloy-based actuators. This device was constructed to be usable by bedridden subjects. Besides, the slowness and gentleness of the imparted motion, make it suitable for patients in a very early stage of their recovery. The mobilizer underwent technical checks to confirm reliability and passed the required safety tests for electric biomedical devices. Four healthy volunteers took part in the pre-clinical phase of the study. The protocol consisted in measuring of brain activity by EEG and NIRS in four different conditions: rest, active dorsiflexion of the ankle, passive mobilization of the ankle, and assisted motion of the same joint. The acquired data were processed to obtain maps of cortical activation, which were then compared. The measurements collected so far show that there is a similar pattern of activity between active and passive/assisted particularly in the contralateral premotor areas. This result, albeit based on very few observations, might suggest that passive motion provides somatosensory afferences that are processed in a similar manner as for voluntary control. Should this evidence be confirmed by further trials on healthy individuals and neurological patients, it could form a basis for a clinical use of early passive exercise in supporting central functional recovery.

Design and development of a thermoelectric cogeneration device integrated in autonomous gas heaters

An autonomous heat-radiating gas heater for commercial outdoor environments has been selected as a test case for implementing cogeneration in autonomous gas heaters and stoves, permitting its installation and operation without the need of a connection to the electrical network. A thermoelectric generator (TEG) was selected for this purpose[1], designed for converting an amount of the produced heat into electrical power for auxiliary (ventilation, battery recharge) or ancillary functions (high efficiency LED illumination). The design approach, the layout and structure of the TEG are discussed, as well as the constraints for its integration in the existing gas heater. Design features and main components are examined: hot side heat collector for capturing heat from the flame; thermoelectric module (TEGM) technology and model selection; natural convection heat radiator at cold side; analysis and optimization of the thermal chain; TEGs assembly and its design as a whole. A prototype has been built and tested,...

A new design of a Nitinol ring-like wire for suturing in deep surgical field.

The present work proposes a new suturing procedure based on self-accommodating suture points. Each suture point is made of a commercial NiTi wire hot-shaped in a single loop ring; a standard suture needle is then fixed at one end of the NiTi suture. According to this simple geometry, several NiTi suture stitches have been prepared and tested by tensile test to verify the closing force in comparison to that of commercial sutures. Further experimental tests have also been performed on anatomic samples from animals to verify the handiness of the NiTi suture. Moreover, surface quality of sutures has been carefully investigated via microscopy. Results show that the NiTi suture expresses high stiffness and a good surface quality. In addition, the absence of manual knotting allows for a simple, fast and safe procedure.

Temperature-modulated differential scanning calorimetry for the study of reversing and nonreversing heat flow of shape memory alloys

The measurement of the thermophysical parameters associated with the thermoelastic martensitic transformation (TMT) of shape memory alloys (SMAs) is fundamental for the correct simulation of the process describing the outcome of SMA actuation. In particular, there are two important energy components during a TMT: the first one is a reversing form related to the nucleation and accommodation of martensite twin boundaries upon cooling, and it is restored when the martensite is heated up to austenite finishing transformation temperature. The second one is represented by a nonreversing form associated with the movement of the grain interfaces, with the defect forming and with the work raised when a plastic transformation occurs. This nonreversing component is dissipated in the form of heat and internal frictional work. Standard differential scanning calorimetry (DSC) measures the sum of these two contributions; therefore, DSC is not able to identify the reverse component that is the one useful in simulation and mathematical modeling of the SMA actuation. Temperature-modulated DSC (MDSC) is really able to separate the two energy forms by the superimposition of a sinusoidal temperature signal to the standard DSC linear temperature ramp. In this paper, MDSC is used to investigate the evolution of reversing and nonreversing heat flows of several NiTi and NiTi-based wires and sheets depending on the microcrystalline state. Observations on the reversing specific heat capacity trend are also drawn.

Study of pseudoelastic systems for the design of complex passive dampers: Static analysis and modeling

This work presents an experimental and numerical analysis of several parallel systems of NiTi pseudoelastic wires. Standard tensile tests were accomplished to evaluate the global damping capacity, the energy dissipated per cycle and the maximum attenuated force in a static condition. Besides, a numerical model was implemented to predict the damping response of more complex pseudoelastic arrangements. It was found a damping capacity upper limit of 0.09 regardless the number and the length of the NiTi components. In addition, it was found that the energy dissipated per cycle is related to the strain and to the number of the NiTi components; furthermore, the system composed of NiTi wires with different length allows for an elastic region that is related to the numbers of wires and that presents a modulation of the stiffness. Finally, the proposed numerical model allows a precise design of complex pseudoelastic combinations as it is able to represent the rhombohedral characteristic.