Cold Storage of Human Femoral Arteries for Twelve Months: Impact on Mechanical Properties.

OBJECTIVE: This biomechanical pre-clinical study aimed to assess the consequences on mechanical properties of long term cold storage (+2 to +8 °C) of arterial allografts. METHODS: Femoropopliteal arterial segments were collected from multiorgan donors and stored at +2 to +8 °C for twelve months in saline solution with added antibiotics. Mechanical characterisation was carried out using two different tests, with the aim of defining the physiological modulus and the maximum stress and strain borne by the sample before rupture. These characterisations were carried out after zero, six, and twelve months of storage for each sample (T0, T6, and T12, respectively). For comparison, the same tests were performed on cryopreserved femoropopliteal segments after thawing. RESULTS: Twelve refrigerated allografts (RAs), each divided into three segments, and 10 cryopreserved allografts (CAs) were characterised. The median (interquartile range [IQR]) Young's modulus was not statistically significantly different between the storage times for cold stored allografts: RAT0, 164 (150, 188) kPa; RAT6, 178 (141, 185) kPa; RAT12, 177 (149, 185) kPa. The median (IQR) Young's modulus of the CA group (153; 130, 170 kPa) showed no significant differences from the RA groups, irrespective of storage time. Furthermore, median (IQR) maximum stress and strain values were not significantly different between the different groups: for maximum stress: RAT0, 1.58 (1.08, 2.09) MPa; RAT6, 1.74 (1.55, 2.36) MPa; RAT12, 2.25 (1.87, 2.53) MPa; CA, 2.25 (1.77, 2.61) MPa; and for maximum strain: RAT0, 64% (50, 90); RAT6, 79% (63, 84); RAT12, 72% (65, 86); CA, 67% (50, 95). CONCLUSION: Cold storage for up to twelve months appears to have no impact on the mechanical characteristics of human arterial allografts. Therefore, this preservation method, which would greatly simplify routine care, seems feasible. Other indicators are being studied to verify the safety of this preservation process before considering its use in vivo.

Design Optimization of Printed Multi-Layered Electroactive Actuators Used for Steerable Guidewire in Micro-Invasive Surgery.

To treat cardiovascular diseases (i.e., a major cause of mortality after cancers), endovascular-technique-based guidewire has been employed for intra-arterial navigation. To date, most commercially available guidewires (e.g., Terumo, Abbott, Cordis, etc.) are non-steerable, which is poorly suited to the human arterial system with numerous bifurcations and angulations. To reach a target artery, surgeons frequently opt for several tools (guidewires with different size integrated into angulated catheters) that might provoke arterial complications such as perforation or dissection. Steerable guidewires would, therefore, be of high interest to reduce surgical morbidity and mortality for patients as well as to simplify procedure for surgeons, thereby saving time and health costs. Regarding these reasons, our research involves the development of a smart steerable guidewire using electroactive polymer (EAP) capable of bending when subjected to an input voltage. The actuation performance of the developed device is assessed through the curvature behavior (i.e., the displacement and the angle of the bending) of a cantilever beam structure, consisting of single- or multi-stack EAP printed on a substrate. Compared to the single-stack architecture, the multi-stack gives rise to a significant increase in curvature, even when subjected to a moderate control voltage. As suggested by the design framework, the intrinsic physical properties (dielectric, electrical, and mechanical) of the EAP layer, together with the nature and thickness of all materials (EAP and substrate), do have strong effect on the bending response of the device. The analyses propose a comprehensive guideline to optimize the actuator performance based on an adequate selection of the relevant materials and geometric parameters. An analytical model together with a finite element model (FEM) are investigated to validate the experimental tests. Finally, the design guideline leads to an innovative structure (composed of a 10-stack active layer screen-printed on a thin substrate) capable of generating a large range of bending angle (up to 190°) under an acceptable input level of 550 V, which perfectly matches the standard of medical tools used for cardiovascular surgery.

The environmental impact of small-bowel capsule endoscopy.

INTRODUCTION: The environmental impact of endoscopy, including small-bowel capsule endoscopy (SBCE), is a topic of growing attention and concern. This study aimed to evaluate the greenhouse gas (GHG) emissions (kgCO2) generated by an SBCE procedure. METHODS: Life cycle assessment methodology (ISO 14040) was used to evaluate three brands of SBCE device and included emissions generated by patient travel, bowel preparation, capsule examination, and video recording. A survey of 87 physicians and 120 patients was conducted to obtain data on travel, activities undertaken during the procedure, and awareness of environmental impacts. RESULTS: The capsule itself (4 g) accounted for < 6 % of the total product weight. Packaging (43-119 g) accounted for 9 %-97 % of total weight, and included deactivation magnets (5 g [4 %-6 %]) and paper instructions (11-50 g [up to 40 %]). A full SBCE procedure generated approximately 20 kgCO2, with 0.04 kgCO2 (0.2 %) attributable to the capsule itself and 18 kgCO2 (94.7 %) generated by patient travel. Capsule retrieval using a dedicated device would add 0.98 kgCO2 to the carbon footprint. Capsule deconstruction revealed materials (e. g. neodymium) that are prohibited from environmental disposal; 76 % of patients were not aware of the illegal nature of capsule disposal via wastewater, and 63 % would have been willing to retrieve it. The carbon impact of data storage and capsule reading was negligible. CONCLUSION: The carbon footprint of SBCE is mainly determined by patient travel. The capsule device itself has a relatively low carbon footprint. Given that disposal of capsule components via wastewater is illegal, retrieval of the capsule is necessary but would likely be associated with an increase in device-related emissions.

Haptic Feedback Device Using 3D-Printed Flexible, Multilayered Piezoelectric Coating for In-Car Touchscreen Interface.

This study focuses on the development of a piezoelectric device capable of generating feedback vibrations to the user who manipulates it. The objective here is to explore the possibility of developing a haptic system that can replace physical buttons on the tactile screen of in-car systems. The interaction between the user and the developed device allows completing the feedback loop, where the user's action generates an input signal that is translated and outputted by the device, and then detected and interpreted by the user's haptic sensors and brain. An FEM (finite element model) via ANSYS multiphysics software was implemented to optimize the haptic performance of the wafer structure consisting of a BaTiO3 multilayered piezocomposite coated on a PET transparent flexible substrate. Several parameters relating to the geometric and mechanical properties of the wafer, together with those of the electrodes, are demonstrated to have significant impact on the actuation ability of the haptic device. To achieve the desired vibration effect on the human skin, the haptic system must be able to drive displacement beyond the detection threshold (~2 µm) at a frequency range of 100-700 Hz. The most optimized actuation ability is obtained when the ratio of the dimension (radius and thickness) between the piezoelectric coating and the substrate layer is equal to ~0.6. Regarding the simulation results, it is revealed that the presence of the conductive electrodes provokes a decrease in the displacement by approximately 25-30%, as the wafer structure becomes stiffer. To ensure the minimum displacement generated by the haptic device above 2 µm, the piezoelectric coating is screen-printed by two stacked layers, electrically connected in parallel. This architecture is expected to boost the displacement amplitude under the same electric field (denoted E) subjected to the single-layered coating. Accordingly, multilayered design seems to be a good alternative to enhance the haptic performance while keeping moderate values of E so as to prevent any undesired electrical breakdown of the coating. Practical characterizations confirmed that E=20 V/µm is sufficient to generate feedback vibrations (under a maximum input load of 5 N) perceived by the fingertip. This result confirms the reliability of the proposed haptic device, despite discrepancies between the predicted theory and the real measurements. Lastly, a demonstrator comprising piezoelectric buttons together with electronic command and conditioning circuits are successfully developed, offering an efficient way to create multiple sensations for the user. On the basis of empirical data acquired from several trials conducted on 20 subjects, statistical analyses together with relevant numerical indicators were implemented to better assess the performance of the developed haptic device.

Development and Optimization of 3D-Printed Flexible Electronic Coatings: A New Generation of Smart Heating Fabrics for Automobile Applications.

Textile-based Joule heaters in combination with multifunctional materials, fabrication tactics, and optimized designs have changed the paradigm of futuristic intelligent clothing systems, particularly in the automobile field. In the design of heating systems integrated into a car seat, conductive coatings via 3D printing are expected to have further benefits over conventional rigid electrical elements such as a tailored shape and increased comfort, feasibility, stretchability, and compactness. In this regard, we report on a novel heating technique for car seat fabrics based on the use of smart conductive coatings. For easier processes and integration, an extrusion 3D printer is employed to achieve multilayered thin films coated on the surface of the fabric substrate. The developed heater device consists of two principal copper electrodes (so-called power buses) and three identical heating resistors made of carbon composites. Connections between the copper power bus and the carbon resistors are made by means of sub-divide the electrodes, which is critical for electrical-thermal coupling. Finite element models (FEM) are developed to predict the heating behavior of the tested substrates under different designs. It is pointed out that the most optimized design solves important drawbacks of the initial design in terms of temperature regularity and overheating. Full characterizations of the electrical and thermal properties, together with morphological analyses via SEM images, are conducted on different coated samples, making it possible to identify the relevant physical parameters of the materials as well as confirm the printing quality. It is discovered through a combination of FEM and experimental evaluations that the printed coating patterns have a crucial impact on the energy conversion and heating performance. Our first prototype, thanks to many design optimizations, entirely meets the specifications required by the automobile industry. Accordingly, multifunctional materials together with printing technology could offer an efficient heating method for the smart textile industry with significantly improved comfort for both the designer and user.

Design Rules of Bidirectional Smart Sensor Coating for Condition Monitoring of Bearings.

This paper reports a novel monitoring technique of bearings' bidirectional load (axial and radial) based on a smart sensor coating, which is screen printed onto the surface of a cross-shaped steel substrate. To ensure the accuracy and stability of measurement as well as the durability of the printed coating, the developed prototype is built according to design rules commonly used in electronic circuits. The finite element model (FEM) is used to predict the mechanical property of the tested substrate under either unidirectional or bidirectional loads. Regarding the output voltage of the piezoelectric sensor, experimental results are revealed to be well-corelated to the numerical simulation. It is pointed out that the output signal generated from the sensor (electrode) could be particularly affected due to the capacitive parasite coming from the conductive tracks (CTs). Such a phenomenon might be reduced by printing them on the dielectric layer rather than on the piezocomposite layer. The study also investigates a highly anisotropic shape of electrodes (rectangular instead of circle), indicating that the orientation of such electrodes (axial or radial) does affect the output measurement. To sum up, the high performance of a sensor network coating depends not only on the ultimate characteristics of its own materials, but also on its structural design. Such an issue has been rarely reported on in the literature, but is nonetheless crucial to achieving reliable condition monitoring of bearings, especially for multidirectional loads-a key signature of early failure detection.

Molten-State Dielectrophoretic Alignment of EVA/BaTiO3 Thermoplastic Composites: Enhancement of Piezo-Smart Sensor for Medical Application.

Dielectrophoresis has recently been used for developing high performance elastomer-based structured piezoelectric composites. However, no study has yet focused on the development of aligned thermoplastic-based piezocomposites. In this work, highly anisotropic thermoplastic composites, with high piezoelectric sensitivity, are created. Molten-state dielectrophoresis is introduced as an effective manufacturing pathway for the obtaining of an aligned filler structure within a thermoplastic matrix. For this study, Poly(Ethylene-co Vinyl Acetate) (EVA), revealed as a biocompatible polymeric matrix, was combined with barium titanate (BaTiO3) filler, well-known as a lead-free piezoelectric material. The phase inversion method was used to obtain an optimal dispersion of the BaTiO3 within the EVA thermoplastic matrix. The effect of the processing parameters, such as the poling electric field and the filler content, were analyzed via dielectric spectroscopy, piezoelectric characterization, and scanning electron microscopy (SEM). The thermal behavior of the matrix was investigated by thermogravimetric analysis (TGA) and differential scanning calorimetry analysis (DSC). Thermoplastic-based structured composites have numerous appealing advantages, such as recyclability, enhanced piezoelectric activity, encapsulation properties, low manufacturing time, and being light weight, which make the developed composites of great novelty, paving the way for new applications in the medical field, such as integrated sensors adaptable to 3D printing technology.

Extrusion-Based 3D Printing of Stretchable Electronic Coating for Condition Monitoring of Suction Cups.

Suction cups (SCs) are used extensively by the industrial sector, particularly for a wide variety of automated material-handling applications. To enhance productivity and reduce maintenance costs, an online supervision system is essential to check the status of SCs. This paper thus proposes an innovative method for condition monitoring of SCs coated with printed electronics whose electrical resistance is supposed to be correlated with the mechanical strain. A simulation model is first examined to observe the deformation of SCs under vacuum compression, which is needed for the development of sensor coating thanks to the 3D printing process. The proposed design involves three circle-shaped sensors, two for the top and bottom bellows (whose mechanical strains are revealed to be the most significant), and one for the lip (small strain, but important stress that might provoke wear and tear in the long term). For the sake of simplicity, practical measurement is performed on 2D samples coated with two different conductive inks subjected to unidirectional tensile loading. Graphical representations together with analytical models of both linear and nonlinear piezoresistive responses allows for the characterization of the inks' behavior under several conditions of displacement and speed inputs. After a comparison of the two inks, the most appropriate is selected as a consequence of its excellent adhesion and stretchability, which are essential criteria to meet the target field. Room temperature extrusion-based 3D printing is then investigated using a motorized 3D Hyrel printer with a syringe-extrusion modular system. Design optimization is finally carried out to enhance the surface detection of sensitive elements while minimizing the effect of electrodes. Although several issues still need to be further considered to match specifications imposed by our industrial partner, the achievement of this work is meaningful and could pave the way for a new generation of SCs integrated with smart sensing devices. The 3D printing of conductive ink directly on the cup's curving surface is a true challenge, which has been demonstrated, for the first time, to be technically feasible throughout the additive manufacturing (AM) process.

Investigation of Blood Coagulation Using Impedance Spectroscopy: Toward Innovative Biomarkers to Assess Fibrinogenesis and Clot Retraction.

This study focused on a coagulation assessment based on the novel technique of blood-impedance-magnitude measurement. With the impedance characterization of recalcified human blood, it was possible to identify two significative biomarkers (i.e., measurable indicators) related to fibrin formation (1st marker) and clot retraction (2nd marker). The confocal microscopy of clotting blood provided a complete visual analysis of all the events occurring during coagulation, validating the significance of the impedance biomarkers. By analyzing the impedance phase angle (Φ) of blood during coagulation, as well as those of the clot and serum expelled after retraction, it was possible to further clarify the origin of the 2nd marker. Finally, an impedance-magnitude analysis and a rotational thromboelastometry test (ROTEM®) were simultaneously performed on blood sampled from the same donor; the results pointed out that the 1st marker was related to clotting time. The developed technique gives rise to a comprehensive and evolutive insight into coagulation, making it possible to progressively follow the whole process in real time. Moreover, this approach allows coagulation to be tested on any materials' surface, laying the ground for new studies related to contact coagulation, meaning, thrombosis occurring on artificial implants. In a near future, impedance spectroscopy could be employed in the material characterization of cardiovascular prostheses whose properties could be monitored in situ and/or online using effective biomarkers.