Biomedical Engineering Reference
In-Depth Information
shear conditions experienced by the constructs [44]. An alternate design features
the cell culture chamber linked to the media using Albuflow porous fiber bundles
(Fresenius Medical Care), and the reactor resulted in higher glucose availability
and slower lactate formation when compared to a non-perfused rotary culture of
lymphoblastoma cells [45]. It also resulted in a stable culture of human
hepatocytes with regard to liver function markers and cell growth when cells
were cultured on microcarrier beads for a bioartificial liver (BAL) [46]. In
addition, it was designed to function as a stand-alone, independently heated and
controlled device for potentially mobile applications with disposable tubes and
culture chambers.
In addition, the solid-state rotating bioreactor features the rotation of both
cylinders at the same rate, resulting in scaffold shear due to gravitational and
centrifugal forces within the volume. The volume of culture medium moves as a
solid body around the horizontal axis, which results in laminar flow and minimal
shear force on the constructs. These are especially useful for cell aggregation
systems because the very low hydrodynamic forces allow for lengthier cell-cell
interactions. In addition, their simplicity and efficacy translate well into large-
scale systems [47].
2.2.3.
Flow perfusion systems
The perfusion of media in a bioreactor can result in multiple desirable
phenomena: extensive nutrient transport into regions in the core of constructs, a
relatively narrow range of shear stresses, the ability to simply recycle media, and
a wide range of hydrodynamic conditions can be achieved by changing flow rate.
Generally the media is either perfused through a chamber in which the scaffold is
located or through the scaffold itself. The first design does provide continuous
recirculation of nutrients in the media, but it may not satisfy transport needs into
the construct itself. This is, however, an especially applicable bioreactor for use
with thin tissues, such as vascular grafts. In addition, it can then also provide
some mechanical conditioning similar to the pulsatile action of blood
in vivo
[67].
An option for thicker engineered tissues utilizing a porous scaffold is to
provide nutrients and oxygen to the core using fluid perfused through the
scaffold itself. Usually flow is restricted to one axis of the scaffold by placing the
scaffold into a cassette or holder. The scaffolds are then contained in a chamber
through which media is pumped. These scaffolds can be cultured in parallel by
using individual circuits of tubing connected to a multi-head peristaltic pump or
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