The lymphatic system is critically important for immune surveillance, lipid absorption and, in general, the mass transport from the interstitium (space between cells and matrix proteins) back into the cardiovascular (venous) circulation . The lymphatic vascular system consists of two main categories of vessel: initial lymphatics, which admit interstitial fluid to become lymph (lymph absorption) and are non-muscular, and collecting lymphatics, which have muscular walls enabling propulsion of lymph (lymph propulsion) . In combination, one-way valves and contractions enable pumping of lymph, and also lymph suction from the initial lymphatic network upstream. One possible consequence of inadequate lymph transport is lymphedema, in which protein-rich interstitial fluid accumulates in the tissues, leading to inflammation, fatty tissue proliferation, fibrosis and tissue swelling.
There is currently no optimal treatment for lymphedema. Manual therapy or compression garments only provide temporary relief; new surgical techniques are still under investigation. In this project, we explore the use of a piezoelectric peristaltic micropump as a component of surgical treatment.
One of the most straightforward configurations in micropumps is the integration of an actuator with two microvalves. In the first step of this project, the focus has been on selecting the correct design of the microvalves and to regulate the dimensions of the device in order to obtain the desired flow rate of the lymph flow.
Aim of the thesis
In this thesis, the student will simulate the 3D Micropump performance with COMSOL Multiphysics.
The micropump (Fig 1) will be modelled using a novel piezoelectric material as the actuator (PVDF-TrFE). Furthermore, PDMS (an elastic polymer) will be used to simulate a valveless configuration , the channel compartment and the housing. Currently, the design of a single chamber with multiple
actuators has been simulated (Fig. 1). However, a single chamber micropump is not able to provide the desired performances to overcome the lymphatic blockage.
Figure 1. Design of the single chamber multiactuator micropump. Blue: the fluid compartment; green: the PDMS membarne and in red the piezoelectric actuators. Approprtiate sequential activations pumps the liquid from left to right.
An effective method to obtain a desirable flow rate and back pressure without increasing the voltage is to construct multi-chamber pumps. Multi-chamber can be build either in parallel or serial connections (Fig. 2) .
Figure 2. (a) Single chamber configuration with only one piezoelectric actuator; (b) Multi-chamber parallel configuration with two piezoelectric actuators. Adapted from Azarbadegan et al. (c) Multi-chamber configuration in a serial configuration, adapted from Liu et al.
The tasks of the student would include:
A working prototype of a single chamber micropump will be available by September 2021. The student will have the chance to contribute to the experimental validation and performance assessment of the prototype.