HeartWare HVAD Flow Estimator Accuracy for Left and Right Ventricular Support.

This study investigated the accuracy of the HeartWare HVAD flow estimator for left ventricular assist device (LVAD) support and biventricular assist device (BiVAD) support for modes of reduced speed (BiVAD-RS) and banded outflow (BiVAD-B). The HVAD flow estimator was evaluated in a mock circulatory loop under changes in systemic and pulmonary vascular resistance, heart rate, central venous pressure, and simulated hematocrit (correlated to viscosity). A difference was found between mean estimated and mean measured flow for LVAD (0.1 ± 0.3 L/min), BiVAD-RS (-0.1 ± 0.2 L/min), and BiVAD-B (0 ± 0.2 L/min). Analysis of the flow waveform pulsatility showed good correlation for LVAD (r2 = 0.98) with a modest spread in error (0.7 ± 0.1 L/min), while BiVAD-RS and BiVAD-B showed similar spread in error (0.7 ± 0.3 and 0.7 ± 0.2 L/min, respectively), with much lower correlation (r2 = 0.85 and r2 = 0.60, respectively). This study demonstrated that the mean flow error of the HVAD flow estimator is similar when the device is used in LVAD, BiVAD-RS, or BiVAD-B configuration. However, the instantaneous flow waveform should be interpreted with caution, particularly in the cases of BiVAD support.

Influence of Powder Loading Fraction on Properties of Bonded Permanent Magnets Prepared By Selective Laser Sintering.

Production of bonded permanent magnets (PMs) by processing a mixture of neodymium-iron-boron (Nd-Fe-B) (spherical and flake) and polyamide-12 powders using selective laser sintering (SLS) has focused on increasing the magnetic powder loading fraction to improve the magnetic performance of PMs. However, when using SLS to produce PMs from mixed feedstock, the likelihood of the areas between the magnetic particles being infiltrated by the liquefied binder inducing particle bonding is reduced as binder content is reduced. This decreases mechanical strength and introduces upper limits to the attainable loading fraction of the magnetic powder. The present study investigated the mechanical properties and provided an insight into the residual induction, of loading fractions between 10% and 90% of spherical and flake powders when producing PMs using SLS. The maximum attainable loading fractions were 80%/vol and 70%/vol for the flake and spherical powders, respectively. The PMs produced from the flakes reached a maximum density and residual induction at 50%/vol loading fraction. The PMs produced from spherical powder reached maximum density and residual induction at 70%/vol loading fraction; however, a knee point at 30%/vol loading fraction demonstrated only minor improvements to density (8.8%) and residual induction (13.4%) with further increases in loading fraction. Although PMs produced from flakes demonstrated superior mechanical properties, the elastic modulus and strain limit rapidly decreased with increases in powder loading fraction for both powder types. This study demonstrated the application-specific balance between mechanical and magnetic strength that must be considered when producing PMs by using SLS.

Development and validation of a low-cost polymer selective laser sintering machine.

Due to manufacturer implemented processing parameter restrictions and the cost prohibitive nature of selective laser sintering (SLS) machines, researchers have limited opportunities to explore the processing of new materials using this additive manufacturing (3D printing) process. Accordingly, this article aimed to overcome these limitations by describing the build and operation of a customizable low-cost polymer SLS machine. The machine boasts a three piston powder bed with the center build piston heated by PID controlled ceramic heaters. Thermal energy for powder consolidation was provided via a 2.44 W solid state diode laser which was mechanically traversed using stepper motor driven belt drives. New layers of powder were deposited by a counter-rotating roller system. The SLS machine was controlled by executing G-code in Mach3 allowing full customization of processing parameters. The machine demonstrated the production of parts from polyamide-12 reaching densities of 918 ± 9 kg/m3 while achieving an elastic modulus of 358.36 ± 3.04 MPa and elongation at break of 11.13 ± 0.02%. With part properties similar to those achievable with a commercial machine, this low-cost SLS machine could be a vital tool in assisting researchers to explore the processing of new materials.

Open-source automated centrifugal pump test rig.

Design methods for large industrial pumps are well developed, but they cannot be relied upon when designing specialised miniature pumps, due to scaling issues. Therefore, the design and development phase of small pumps demand numerous experimental tests to ensure a viable prototype. Of initial interest is hydraulic design in the form of pump performance and efficiency curves. This project aimed to produce an automated test rig capable of generating both the performance (P-Q - pressure vs. flow rate) and efficiency curves that are reliable and repeatable. The apparatus is largely customizable and suitable for a range of smaller pump sizes. The pump impeller and volute were 3D printed, allowing for design flexibility and rapid prototyping and testing. The test loop was automated which allowed the flow rate to be incremented from 0 L/min to the maximum flow rate. At each step the pressure, flow rate, voltage and current were recorded to generate the P - Q and efficiency curves. Repeatability results showed low variations of ±3 mmHg (400 Pa) in pressure and ± 2% in hydraulic efficiency. The given setup can be used to compare and evaluate the hydraulic performance of various pump designs.