This paper presents an analytical model to determine a closed form mathematical representation for the output displacement of a displacement amplification compliant mechanism used for energy harvesting. A symmetric five-bar compliant mechanism with right-circular and corner-filleted flexure hinges was mathematically modeled and its displacement was determined using the Castigliano energy theorem. The stresses within the flexure joints, the weakest points in the mechanism body, were calculated. The mathematical model expresses both the displacement amplification and the stresses as functions of the design parameters and the load caused by the harvester. The developed model can be used to optimize the mechanism dimensions for maximum harvested power, while minimizing its structural stresses. The mechanism was also modeled numerically using finite element methods; both the analytical and numerical models were verified experimentally. The mathematical model of the mechanism was integrated with a model representing a piezoelectric energy harvester to calculate the open-circuit voltage. As a proof of concept, experiments were performed using an unimorph piezoelectric cantilever at low-frequency (less than 1 Hz) harmonic excitation inputs. The measured open-circuit voltage was found to be in agreement with that calculated using the proposed model, when integrated with the model representing the piezoelectric beam. The power generated by the piezoelectric harvester, equipped with the proposed displacement amplification mechanism, was more than a hundred times that without amplification.

Fetal aqueductal stenosis (AS) is one of the most common causes of congenital hydrocephalus, which increases intracranial pressure due to partial or complete obstruction of cerebrospinal fluid (CSF) flow within the ventricular system. Approximately 2–4 infants per 10,000 births develop AS, which leads to progressive hydrocephalus, which enlarges the head often necessitating delivery by cesarean section. Most babies born with AS are severely neurologically impaired and experience a lifetime of disability. Therefore, a new device technology for venticuloamniotic shunting is urgently needed and has been studied to ameliorate or prevent fetal hydrocephalus development, which can provide a significant impact on patients and their family’s quality of life and on the decrease of the healthcare dollars spent for the treatment. This study has successfully validated the design of shunt devices and demonstrated the mechanical performance and valve functions. A functional prototype shunt has been fabricated and subsequently used in multiple in vitro tests to demonstrate the performance of this newly developed ventriculoamniotic shunt. The shunt contains a main silicone-nitinol composite tube, a superelastic 90° angled dual dumbbell anchor, and an ePTFE valve encased by a stainless-steel cage. The anchor will change its diameter from 1.15 mm (collapsed state) to 2.75 mm (deployed state) showing up to 1.4-fold diameter change in human body temperature. Flow rates in shunts were quantified to demonstrate the valve function in low flow rates mimicking the fetal hydrocephalus condition showing “no backflow” for the valved shunt while there is up to 15 mL/h flow through the shunt with pressure difference of 20 Pa. In vivo ovine study results show the initial successful device delivery and flow drainage with sheep model.

Nitinol is an excellent candidate material for developing various self-expanding endovascular devices due to its unique properties such as superelasticity, biocompatibility and shape memory effect. A low-energy laser joining technique suggests a high potential to create various large diameter Nitinol endovascular devices that contain complex geometries. The primary purpose of the study is to investigate the effects of laser joining process parameters with regard to the mechanical and biocompatible performance of Nitinol stents. Both the chemical composition and the microstructure of the laser-welded joints were evaluated using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). In vitro study results on cytotoxicity demonstrated that the joining condition of 8 Hz frequency and 1 kW laser power showed the highest degree of endothelial cell viability after thermal annealing in 500°C for 30 min. Also, in vitro study results showed the highest oxygen content at 0.9 kW laser power, 8 Hz frequency, and 0.3 mm spot size after the thermal annealing. Mechanical performance test results showed that the optimal condition for the highest disconnecting force was found at 1 Hz frequency and 1 kW power with 0.6 mm spot size. Two new endovascular devices have been fabricated using the optimized laser joining parameters, which have demonstrated successful device delivery and retrieval, as well as acute biocompatibility.

In this paper, we introduce a symmetric five-bar compliant mechanism for the displacement amplification of mechanical vibration. When the proposed mechanism is connected to an energy harvester, input excitation vibrations to the mechanism are amplified, which leads to an increase in harvested power. The mechanism is composed of both rigid links and flexure hinges, which enable deflection. The flexure hinges we use are either of the right-circular, or the corner-filleted types. The mechanism is analyzed using a pseudo-rigid-body-model, where flexure hinges are substituted with rotational springs. We developed an analytical model of the displacement amplification, which was validated both experimentally and numerically using a finite element model. Our model reveals that the displacement amplification is a function in design parameters, such as the geometry of the mechanism, the flexure hinges stiffness, in addition to the load caused by the harvester. The effects of the flexure hinge dimensions on the flexure hinges stiffness, and thus on displacement amplification were investigated. Preliminary experiments indicate the success of our proposed mechanism in amplifying small excitation harmonic inputs and generation of power.