Optimization of a compact air pressure actuated membrane
for inducing flow inside a bioreactor
Citation for published version (APA):
Neerincx, P. E., & Meijer, H. E. H. (2009). Optimization of a compact air pressure actuated membrane for inducing flow inside a bioreactor. Poster session presented at Mate Poster Award 2009 : 14th Annual Poster Contest.
Document status and date: Published: 01/01/2009 Document Version:
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Polymer Technology
Optimization of a Compact Air
Pressure Actuated Membrane for
Inducing Flow inside a Bioreactor
/department of mechanical engineering
P. E. Neerincx, H. E. H. Meijer Den Dolech, Eindhoven
Introduction
Tissue engineered heart valves constructed of cells of the pa-tient seeded on a degradable scaffold are cultured in bioreactors by using mainly mechanical loading like flow through the cul-tured valve to stimulate tissue development. To create flow in a compact and controlled way, a flexible, air pressure actuated and ultrasonic position measured membrane is used for displacing the culture medium, see Figure 1. The initially chosen spherical membrane geometrie failed, because stress relaxation lead to a difficult to measure tilting deformation.
Figure 1: Injection moulded bioreactor (left) and schematic repre-sentation of the air pressure actuated membrane which tilts during deformation and makes ultrasonic position measurement impossible (right).
Objective
The goal here is to design and realize a compact (diameter = 60 [mm] and a deflexion of minimal 40 [mm] to create a physiolog-ical pump volume of 80 [cc]), easy computer feedback control-lable flexible membrane which allows large deformations under low actuation pressures (+/- 30 KPa) without tilting deforma-tions to keep ultrasonic position measurement possible.
Approach
To reduce stress relaxation, it is suggested to mould the mem-brane in its neutral position (in-between totally inwards and out-wards) from where it can deform in a stable way. One obvious way to do this is to use a wavy pattern, see Figure 2 at the top. Marc Mentat [MSC Software] is used to compute the pump vol-ume and the stability of the wave shaped membrane, for differ-ent sets of membrane’s design parameters d, R and S [mm]. By slightly offsetting the midpoint of the membrane, we can com-pute and plot the reaction force during membrane loading in the computations and use this as a measure for stability (positive reaction force means stability).
Results
Figure 2 shows the results where the upper right corner is the ob-vious target. We start with increasing S (while d=1 and R=2,5) which increases pump volume at the same actuation pressure of +/- 30 [KPa] but destabilizes deformation, see arrow. Decreas-ing the wall thickness d also causes the deformation to become unstable. Increasing R results in a larger volume displacement but also in unstable deformations. Therefore decreasing R should
stabilize deformation and yield more pump volume which indeed is the case. Finally we decrease d (d, R, S = 0,75 / 1 / 2) resulting in a substantial increase of the pump volume (still at a actuation pressure of +/- 30 [KPa]) and a still acceptable sta-bility, which seems to be our ”optimum”. Figure 3 shows the difference in stability, volume displacement and actuation pres-sure of the most interesting parameter sets. Especially the the geometrie (0,75 / 1 / 2) which needs only +/-7 [KPa] actuation pressure for 80 [cc] volume displacement and behaves most lin-ear and stable and allows for easy feedback control. Concluding: the parameter set (0,75 / 1 / 2) is the best choice for our final membrane geometry.
Figure 2: Overview of the effect of parameter configurations on pump volume and stability force (bottom), membrane parameters (top left) and the final optimal membrane with d=0,75, R=1, S=2 (top right).
Figure 3: Stability force against volume displacement, showing that parameter sets with higher volume displacements are less stable (left) and the actuation pressure against volume displacement (right) of the final parameter sets of interests actuated with +/- 30 [KPa]. Contin-uous line represents the ”optimum”.
