Mechanics of Biohybrid Valveless Pump-bot

Engineering living systems is a rapidly emerging discipline where the functional biohybrid robotics (or ‘Bio-bots’) are built by integrating of living cells with engineered scaffolds. Inspired by embryonic heart, we presented earlier the first example of a biohybrid valveless pump-bot, an impedance pump, capable of transporting fluids powered by engineered living muscle tissues. The pump consists of a soft tube attached to rigid boundaries at the ends, and a muscle ring that squeezes the tube cyclically at an off-center location. Cyclic contraction results in a net flow through the tube. We observed that muscle force occasionally buckles the tube in a random fashion, i.e., similar muscles do not buckle the tube consistently. In order to explain this anomaly, here we develop an analytical model to predict the deformation and stability of circular elastic tubes subjected to a uniform squeezing force due to a muscle ring (like a taught rubber band). The prediction from the model is validated by comparing with experiments and finite element analysis. The non-linear model reveals that the circular elastic tube cannot buckle irrespective of muscle force. Buckling state can be reached and sustained by bending and folding the tube before applying the muscle ring. This imperfection may appear during assembly of the pump or from non-uniform thickness of the muscle ring. This study provides design guides for developing advanced biohybrid impedance pumps for diverse applications.

Design and Analysis of a Valveless Impedance Pump for a Direct Sodium Borohydride–Hydrogen Peroxide Fuel Cell

A valveless impedance pump is designed and applied for the first time to supply the liquid fuels for a direct sodium borohydride–hydrogen peroxide fuel cell (DBHPFC). This valveless pump consists of an amber latex rubber tube, which is connected at both ends to rigid stainless-steel tubes of different acoustic impedance, and a simple actuation mechanism with a small direct control (DC) motor and a cam combined. The cam is activated by the motor and periodically compresses the elastic tube at a position asymmetrical from the tube ends. The traveling waves emitted from the compression combine with the reflected waves at the impedance-mismatched rubber tube/stainless-steel tube interfaces. The resulting wave interference creates a pressure gradient and generates a net flow. When connected to a DBHPFC with an active area of 25 cm2, the pump can deliver the fuel at a maximum pumping rate of 30 ml/min, resulting in corresponding DBHPFC maximum power and a current of 13.0 W and 25.5 A, respectively. The specific power, volumetric power density, and back work ratio of the DBHPFC with this pumping method have been proven superior to those of the other pumping configuration with peristaltic pumps. This valveless impedance pump is mechanically simply and less susceptible to corrosion, and it can reduce the volume and weight of fuel cell systems to a measurable extent. The experimental results demonstrate the feasibility of the device for practical DBHPFC applications.

Experimental Study on Net Flow Rate Generation Inside Closed Loop Mechanical Circulatory System Using Impedance Pump

This present study focused on the performance of net flow rate inside closed loop mechanical circulatory system with single and double pinching impedance pumps which generates a unidirectional flow of fluid around closed loop of soft viscoelastic tubing. The experimental setup consisted of viscoelastic tubing connected between two ends of rigid tube which was compressed rhythmically or squeezed asymmetrically at various frequencies by motorized pinching. Hence, net flow of fluid around the tubing can occur without valves. Experiment was done on two different fluid, namely Newtonian and Non-Newtonian. Result showed that the flow rate inside closed loop system for non-Newtonian fluid and Newtonian fluid were in good agreement with each other. Single pinching showed a lower flow rate compared to double pinching at higher frequency. The results could be used as a model for a new Mechanical Circulatory Support System used by cardiac patients. Factors influencing the performance of valveless impedance pump was also explained.

Performance Evaluation of a Resonant-integrated Pumping System

Impedance pump is a simple valve-less pumping mechanism; it offers a low energy, low noise alternative at both macro- and micro-scale devices. It is also demonstrated to be a promising new technique for producing and amplifying net flow. There have been research studying the effects of series-connected impedance pump, where an increase in net flow is exhibited. In this study, an integrated system of conventional pump and impedance pump is introduced. This paper describes the performance evaluation of this integrated pumping system, with emphasis on the amount of amplification induced as a function of Womersley number (normalized excitation frequency) and normalized pressure head. Due to the nature of the resonant valve-less impedance pump, the integrated pumping system exhibits similar behaviour and characteristics as an impedance pump, such as the pulsatile nature of net flow. Results show positive outcomes where maximum amplification of 91.7% is demonstrated at resonance.

Experimental Analysis of Impedance-Driven Reverse Flow Dynamics

Impedance pump is a type of valveless pumping device, in which it utilizes a bio-inspired mechanism for pumping of fluid based on resonant wave interactions along a flexible media. By inducing a periodic asymmetrical compression on the flexible media will produce a unidirectional flow within the system. The impedance pump has many beneficial characteristics which make it an effective driving mechanism, especially for micro-fluidic systems. In addition, the wave-based mechanism through which pumping occurs infers many benefits in terms of simplicity of design and manufacturing. Adjustment of simple parameters such as the excitation frequency or compression location will reverse the direction of flow, providing a very versatile range of flow outputs. This paper describes the experimental analysis of such impedance-driven flow with emphasis on dynamical study of the reverse flow in open-loop environment. In this study, tapered section with converging steps is introduced at both ends of the flexible media to amplify the reverse flow. Study conducted shows that the reverse peak flow is rather significant with estimate of 23% lower than the forward peak flow. The flow dynamics on the other hand has shown to exhibit different characteristics as per the forward peak flow.

MEASUREMENT OF FLOW IN CIRCULAR ELASTIC TUBE

Impedance pump is a simple valveless pumping mechanism which typically used in viscosity measurement device to assist pumping of fluid. It is typically connected to an elastic tube in a circulatory system of a more rigid tube. In conventional mechanical circulatory support systems using rotary pump, the pumping mechanism was exposed to turbulent stresses. Hence, this may cause damage to blood cells flowing through the impeller. There has been initial work on finding alternative solution using the impedance pump system. However, substantial findings are not yet sufficient to fully understand the mechanism. The purpose of this research is to extend the investigation on impedance pump by specifically looking at the effect of structural parameters on the elastic tube and the flow behaviour. In this study, a closed loop impedance pump system was set up to demonstrate blood flow circulatory system where the mixture of glycerine and water was used as the working fluid. Three variables were regulated namely voltage, tube thickness, and tube length was used in order to get the flowrate of the working fluid. Based on the results, it was found that tube thickness of 1 mm and a length of 200 mm had produced the highest flowrate in the region 75 ml/min.

Experimental Study on the Effect of Pinch Parameters and Fluid Viscosity to Flow in Closed Loop Impedance Pump

This paper aims to analyse the performance of impedance pump that uses energy mismatch to drive fluid flow. The experimental setup mainly focus to establish the relationship between the fluids flow rates in elastic tube section connected between two ends of solid tube and pinch mechanism location as well as fluid viscosity. Measurement of fluid flow rate or representation of its velocities resulting from the pumping mechanism is measured using two different supply voltage and constant pincher width. These measured parameters resulting from the pinch mechanism of the elastic tube section were varied at different pinch location along itsx-axis direction; divided into two main cases namely (1) 2 V and (2) 3 V at 40 mm to 140 mm pinch location. From the voltage variation, it is found that the maximum flow rate given by voltage 3.0 V at pinch location 40 mm while for the effect of viscosity, the highest flow rate is 93 ml/min. The profiles obtained revealed the characteristic of valve less pump to be the new model of new Ventricular Assist Device use in cardiac patient as well as further explanation about the factor that influence the characteristic of elastic tube.