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Pulsatile positive displacement pumps as ventricular assist devices were gradually replaced by rotary devices due to their large volume and high adverse event rates. Nevertheless, pulsatile ventricular assist devices might be beneficial with regard to gastrointestinal bleeding and cardiac recovery. Therefore, aim of this study was to investigate the flow field in new pulsatile ventricular assist devices concepts with an increased pump frequency, which would allow lower stroke volumes to reduce the pump size. We developed a novel elliptically shaped pulsatile ventricular assist devices, which we compared to a design based on a circular shape. The pump size was adjusted to deliver similar flow rates at pump frequencies of 80, 160, and 240 bpm. Through a computational fluid dynamics study, we investigated flow patterns, residence times, and wall shear stresses for different frequencies and pump sizes. A pump size reduction by almost 50% is possible when using a threefold pump frequency. We show that flow patterns inside the circular pump are frequency dependent, while they remain similar for the elliptic pump. With slightly increased wall shear stresses for higher frequencies, maximum wall shear stresses on the pump housing are higher for the circular design (42.2 Pa vs 18.4 Pa). The calculated blood residence times within the pump decrease significantly with increasing pump rates. A smaller pump size leads to a slight increase of wall shear stresses and a significant improvement of residence times. Hence, high-frequency operation of pulsatile ventricular assist devices, especially in combination with an elliptical shape, might be a feasible mean to reduce the size, without any expectable disadvantages in terms of hemocompatibility.

Bistable and multistable laminates are structural elements with more than one stable equilibrium configuration. The bistability makes them very interesting for the design of compliant mechanisms. However, these laminates are extremely sensitive to boundary conditions and attachment methods. It has been shown prior in the literature that restrictive boundary conditions can lead to the loss of bistability or unwanted deformation modes. This article develops attachment concepts that leverage the structural behavior changes caused by boundary conditions to expand the design space of bistable elements for structural applications. A systematic means of using the boundary conditions to improve the stability margins and load introduction of bistable tape springs is demonstrated. The stability margins and the achievable angles have been quantified using an analytical model previously developed by Guest and Pellegrino. Subsequently, high-fidelity finite element (FE) simulations are done in abaqus™ to determine the limits of the proposed method in terms of localization effects. Based on the analytical model and simulation outcomes, layup, size, and attachment points are determined, and two prototypes are fabricated, illustrating the effectiveness of the proposed method in expanding the design space of traditional bistable tape springs.

Main design objective of high-dynamic multiaxial testing machines is a high fundamental frequency. Carbon fiber reinforced polymers (CFRP) offer outstanding weight-specific properties and high design freedom. They are thus a promising choice for the development of novel testing machines. This paper investigates the challenges which are decisive for a successful implementation of the FRP technology. In order to assess the potential of the approach, an optimized CFRP testing machine is compared to a state-of-the-art metal design. Significantly improved performance at comparable costs indicates that the CFRP technology is a valuable asset to the design of complex low volume special-purpose machines.

Compliant structures have the capability to undergo large deformations without damage. For this reason, they represent an interesting solution for applications requiring shape adaptation. On the other hand, highly compliant directions in the structure can lead to large vibrations. The enhancement of the dissipation properties of these structures can prevent, or at least mitigate, the problem. This would result in systems offering an exceptional relation between the static and dynamic impedance. In this paper, a corrugated structure with adaptive damping properties is introduced. The structure relies on the double corrugation design, which offers high axial static compliance and extremely anisotropic static characteristics. In the dynamic regime, the vibration amplitude is reduced by exploiting the friction resulting from the electrostatic forces generated at the interfaces of a so-called electro-bonded laminate (EBL). A prototype of the enhanced corrugation is manufactured and tested. The dissipation properties of both the axial and the bending vibration modes are experimentally investigated. The results show that the dynamic structural response is significantly damped when a DC voltage is applied at the interface, thus highlighting the effectiveness of the used dissipation approach. Additionally, the applied voltage can be used as a tunable parameter to control the damping properties of the structures. The obtained adaptive system fulfills the dual function of providing highly anisotropic static compliance while introducing large adaptive dynamic impedance, thereby effectively decoupling the static and dynamic structural properties.

While much of the research on dielectric elastomer actuators used to concentrate on VHB 4910 as dielectric material, lately many new, specifically developed materials have come into focus. The acrylic VHB has been thoroughly characterized in a macro-scale agonist-antagonist configuration on an active hinge. This was carried out with the aim of using it on an airship, which was activated, undulating body and a fin and thus propelled in a fish-like manner. The concept was proved in flight, but still lifetime and viscosity of the actuators and the time-costing fabrication due to the necessary large pre-stretches of the dielectric membrane caused severe inconveniences. In order to evaluate the usability of other materials for this specific purpose, two other materials, a corrugated silicone with silver electrodes (by PolyPower) and an acrylic with interpenetrating network (IPN) developed by Pei et al. were characterized under similar conditions. The influence of the material on performance and design of the actuators and the conclusions for the use of the materials on the airship (and on applications with similar performance requirements) are presented.

Material based actuation with metallic fibers, for example shape memory alloys (SMA) is gaining popularity to replace the conventional bulky actuators used for shape morphing in aerospace sectors. However, Joule heating arising from electrical actuation of SMA affects the interfacial bonding between the SMA and the composite matrix and thus reduces the life span of the structure. Insulating the SMA from the composite matrix will tremendously increase the service life of these reconfigurable structures. Three-dimensional (3D) printing of functional elements during the fabrication phase of the composite structures permits the flexibility to form complex shaped reconfigurable lightweight aerospace components. Here, we present a novel technique to embed polymer encapsulated functional elements into structural composites. We use the direct-write (DW) technique to coat SMA with a polymer solution while simultaneously printing them onto carbon fiber prepreg. We develop high performance polymeric inks - polyetherimide and polycarbonate - compatible with the DW technique, the coating, as well as the composite. In addition to SMA, the technique can also be easily extended to embed various kinds of other functional fibers into composites, in any shape or form. Additionally, we also demonstrate the application of this technique to integrate SMA with polymeric structures towards actuators for robotics grippers or surgical tools. Successful demonstrators of our technique, in the form of SMA-CFRP hybrid and SMA-polymeric leaf-spring actuators are presented.