An Active Thermography approach for materials characterisation of thermal management systems for Lithium-ion batteries.

The aim of this work is an alternative non destructive technique for estimating the thermal properties of four different Thermal Management System (TMS) materials. More in detail, a thermographic setup realized with the Active Thermography approach (AT) is utilized for the purpose and the data elaboration follows the ISO 18755 Standard. As well known, Phase Changes Materials (PCMs) represent an innovative solution in the Thermal Management System (TMS) of Lithium-Ion batteries and, during the years, many solutions were developed to improve its thermal properties. As a matter of fact, parameters such as the internal temperature or heat exchanges impact on both efficiency and safety of the whole battery system. Consequently, the thermal conductivity was often chosen as a performance indicator of Thermal Management System (TMS) materials. In this work, both thermal diffusivity and thermal conductivity were estimated in two different testing conditions, respectively at room temperature and higher temperature conditions. The Active Thermography (AT) technique proposed in this activity has satisfactory estimated both thermal diffusivity and thermal conductivity of Thermal Management System (TMS) materials. An analytical model was also developed to reproduce the temperature experimental profiles. Finally, results obtained with AT approach were compared to those available from commercial datasheet and literature.

Neuromechanics of finger hangs with arm lock-offs: analyzing joint moments and muscle activations to improve practice guidelines for climbing.

Introduction: Climbing imposes substantial demands on the upper limbs and understanding the mechanical loads experienced by the joints during climbing movements is crucial for injury prevention and optimizing training protocols. This study aimed to quantify and compare upper limb joint loads and muscle activations during isometric finger hanging exercises with different arm lock-off positions. Methods: Seventeen recreational climbers performed six finger dead hangs with arm lock-offs at 90° and 135° of elbow flexion, as well as arms fully extended. Upper limb joint moments were calculated using personalized models in OpenSim, based on three-dimensional motion capture data and forces measured on an instrumented hang board. Muscle activations of upper limb muscles were recorded with surface electromyography electrodes. Results: Results revealed that the shoulder exhibited higher flexion moments during arm lock-offs at 90° compared to full extension (p = 0.006). The adduction moment was higher at 135° and 90° compared to full extension (p < 0.001), as well as the rotation moments (p < 0.001). The elbows exhibited increasing flexion moments with the increase in the arm lock-off angle (p < 0.001). Muscle activations varied across conditions for biceps brachii (p < 0.001), trapezius (p < 0.001), and latissimus dorsi, except for the finger flexors (p = 0.15). Discussion: Our findings indicate that isometric finger dead hangs with arms fully extended are effective for training forearm force capacities while minimizing stress on the elbow and shoulder joints. These findings have important implications for injury prevention and optimizing training strategies in climbing.

Engineering Graphene Wrinkles for Large Enhancement of Interlaminar Friction Enabled Damping Capability.

Graphene nanoplates are hoped-for solid lubricants to reduce friction and energy dissipation in micro and nanoscale devices benefiting from their interface slips to reach an expected superlubricity. On the contrary, we propose here by introducing engineered wrinkles of graphene nanoplates to exploit and optimize the interfacial energy dissipation mechanisms between the nanoplates in graphene-based composites for enhanced vibration damping performance. Polyurethane (PU) beams with designed sandwich structures have been successfully fabricated to activate the interlaminar slips of wrinkled graphene-graphene, which significantly contribute to the dissipation of vibration energy. These engineered composite materials with extremely low graphene content (∼0.08 wt %) yield a significant increase in quasi-static and dynamic damping compared to the baseline PU beams (by 71% and 94%, respectively). Friction force images of wrinkled graphene oxide (GO) nanoplates detected via an atomic force microscope (AFM) indicate that wrinkles with large coefficients of friction (COFs) indeed play a dominant role in delaying slip occurrences. Reduction of GO further enhances the COFs of the interacting wrinkles by 7.8%, owing to the increased effective contact area and adhesive force. This work provides a new insight into how to design graphene-based composites with optimized damping properties from the microstructure perspective.

Transcutaneously refillable, 3D-printed biopolymeric encapsulation system for the transplantation of endocrine cells.

Autologous cell transplantation holds enormous promise to restore organ and tissue functions in the treatment of various pathologies including endocrine, cardiovascular, and neurological diseases among others. Even though immune rejection is circumvented with autologous transplantation, clinical adoption remains limited due to poor cell retention and survival. Cell transplant success requires homing to vascularized environment, cell engraftment and importantly, maintenance of inherent cell function. To address this need, we developed a three dimensional (3D) printed cell encapsulation device created with polylactic acid (PLA), termed neovascularized implantable cell homing and encapsulation (NICHE). In this paper, we present the development and systematic evaluation of the NICHE in vitro, and the in vivo validation with encapsulated testosterone-secreting Leydig cells in Rag1-/- castrated mice. Enhanced subcutaneous vascularization of NICHE via platelet-rich plasma (PRP) hydrogel coating and filling was demonstrated in vivo via a chorioallantoic membrane (CAM) assay as well as in mice. After establishment of a pre-vascularized bed within the NICHE, transcutaneously transplanted Leydig cells, maintained viability and robust testosterone secretion for the duration of the study. Immunohistochemical analysis revealed extensive Leydig cell colonization in the NICHE. Furthermore, transplanted cells achieved physiologic testosterone levels in castrated mice. The promising results provide a proof of concept for the NICHE as a viable platform technology for autologous cell transplantation for the treatment of a variety of diseases.

Mechanical characterization and numerical simulation of a subcutaneous implantable 3D printed cell encapsulation system.

Cell transplantation in bioengineered scaffolds and encapsulation systems has shown great promise in regenerative medicine. Depending on the site of implantation, type of cells and their expected function, these systems are designed to provide cells with a physiological-like environment while providing mechanical support and promoting long-term viability and function of the graft. A minimally invasive 3D printed system termed neovascularized implantable cell homing and encapsulation (NICHE) was developed in polylactic acid for subcutaneous transplantation of endocrine cells, including pancreatic islets. The suitability of the NICHE for long term in vivo deployment is investigated by assessing mechanical behavior of both fresh devices under simulated subcutaneous conditions and NICHE retrieved from subcutaneous implantation in pigs. Both experimental and numerical studies were performed with a focus on validating the constitutive material model used in the numerical analysis for accuracy and reliability. Notably, homogeneous isotropic constitutive material model calibrated by means of uniaxial testing well suited experimental results. The results highlight the long term durability for in vivo applications and the potential applicability of the model to predict the mechanical behavior of similar devices in various physiological settings.