We have already discussed the use of bioreactors in tissue engineering, particularly bone tissue engineering. After analyzing the contribution of the rotating wall vessel bioreactor and the spinner flask, we will now examine a new type of culture system: the flow perfusion bioreactor.
Let’s find out together what its advantages and critical issues are.
Flow perfusion bioreactor, what it is and how it works
The paper “Design of a Flow Perfusion Bioreactor System for Bone Tissue-Engineering Applications” (Gregory N. Bancroft, Vassilios I. Sikavitsas, Antonios G. Mikos) suggests that the flow perfusion bioreactor is an ideal solution for developing bone tissue equivalents.
According to the paper, the flow perfusion bioreactor would overcome the limitations of the spinner flask bioreactor.
To better understand this point, it is necessary to take a step back.
In our article about spinner flask bioreactors for bone tissue engineering (inseriamo qui un link ad articolo su spinner flasks), we had described how this type of bioreactor offered promising performance for cell culture of three-dimensional polymeric scaffolds with MSCs.
However, we also pointed out some critical issues; first, the limitation of nutrient transport in the culture fluid, which was limited only to cells exposed outside the scaffold.
The flow perfusion bioreactor can potentially overcome this limitation. By using a pump that continuously perfuses the culture medium through the porous network of the scaffold, it would indeed be possible to ensure external and internal mixing of the culture fluid.
In other words, in a flow perfusion bioreactor, fluid flow occurs through the scaffold instead of being limited to just the edges, improving nutrient delivery.
To demonstrate this, colleagues Gregory N. Bancroft, Vassilios I. Sikavitsas, Antonios G. Mikos built a flow perfusion bioreactor in order to identify the best design for bone tissue engineering.
The resulting culture system is essentially composed of two parts:
- individual flow chambers, which are the culture chambers within which the scaffolds are placed;
- the flow system circuit consists of reservoirs and a peristaltic pump that is used to pump the liquid medium inside the culture chamber.
Basically, the whole system works like this: fluid is drawn from a first reservoir by the action of the peristaltic pump.
At this point, the culture fluid enters the flow chamber through a top hole and, once pumped inside, flows through the scaffold and out the bottom, with a directional flow from top to bottom.
The outflowing fluid flows to the second reservoir. Then, under the effect of gravity, it returns to the first tank, completing the circuit.
Advantages and critical issues of flow perfusion bioreactors in bone tissue engineering
The flow perfusion bioreactor offers several advantages:
- mitigates external and internal diffusion limitations;
- provides nutrients and gases to the cells in the scaffold;
- ensures a more homogeneous distribution of cells and mineral deposits in the scaffolds than spinner flask bioreactors.
However, flow perfusion bioreactors must meet certain key characteristics to ensure these conditions.
As reported by Gregory N. Bancroft, Vassilios I. Sikavitsas, Antonios G. Mikos, “there are several requirements for a successful flow perfusion system design.”
In particular, the system must distribute flow through the scaffolds, minimizing the nonperfusion flow surrounding each cultured scaffold. If it fails to do so, the entire system offers little advantage over the aforementioned spinner flask bioreactor.
The other critical issue remains the high shear stress applied to the cultured cells, a problem already encountered in spinner flask bioreactors.
Is there an alternative to flow perfusion bioreactors for bone tissue engineering?
For the past several years, the Cellex team has been working to propose an alternative that can mitigate the limitations of flow perfusion bioreactors and spinner flasks for developing tissue engineering constructs.
This alternative is called BioAxFlow, a bioreactor designed specifically for Tissue Engineering.
The bioreactor is based on advanced fluid dynamics based on four main components:
- a base integrating inlet and outlet ports for controlled media flow;
- a cylindrical chamber;
- scaffold stand for scaffold placement;
- a cap with two openings for vent caps and two sampling ports.
In BioAxFlow, during the seeding process, a cell suspension is injected into the main chamber where the scaffolds are located and placed on the corresponding stand. This is done in an automated process that maximizes cell utilization and ensures even scaffold distribution.
The flow generated within it ensures continuous movement of the medium. In this way, the scaffolds are constantly surrounded and perfused by a cell culture medium, being exposed to nutrients and growth factors.
In addition, within BioAxFlow, minimal mechanical shear stress is applied to the cultured cells, which is ensured precisely by advanced fluid dynamics.
Sources
“Formation of three-dimensional cell/polymer constructs for bone tissue engineering in a spinner flask and a rotating wall vessel bioreactor”, Vassilios I. Sikavitsas, Gregory N. Bancroft, Antonios G. Mikos, 2001
“Design of a Flow Perfusion Bioreactor System for Bone Tissue-Engineering Applications”, Gregory N. Bancroft, Vassilios I. Sikavitsas, Antonios G. Mikos, 2003
“A fluid dynamics-model system for advancing Tissue Engineering and Cancer Research studies: Dynamic Culture with the innovative BioAxFlow Bioreactor”, Giulia Gramigna, Federica Liguori, Ludovica Filippini, Maurizio Mastantuono, Michele Pistillo, Margherita Scamarcio, Antonella Lisi, Giuseppe Falvo D’Urso Labate, Mario Ledda, 2025