A Novel Culture System Shows that Stem Cells Can be Grown in 3D and Under Physiologic Pulsatile Conditions for Tissue Engineering of Vascular Grafts
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Oscar Abilez, M.D.,*,†,1 Peyman Benharash, M.D.,*,† Mahncy Mehrotra,*,† Emiko Miyamoto, B.S.,*,‡ Adrian Gale, B.S.,*,§ Jean Picquet, M.D.,*,† Chengpei Xu, M.D., Ph.D.,*,† and Christopher Zarins, M.D.,*,†

As cardiovascular disease has become more prominent, various methods to develop better vascular grafts came into light in tissue engineering. This study specifically tests for a culture system that would successfully grow and differentiate embryonic stem cells into endothelial, smooth muscle, and fibroblast cells that can be assembled into vascular grafts. Because the nature of vascular system requires pulsatile condition due to the pumping of heart and blood pressure, the authors have designed a new bioreactor system that incorporates flow with regular pulses above a 3D culture of stem cells.

The particular experiment consisted of PBS solution flowing on top of a culture system at a pre-assigned rate and pressure controlled through a computer. A CCD camera gathers pictures and video files that observe the displacement of cells within the 3D scaffold. The displacement and the unison in movement signify the ability of mESC (mouse embryonic stem cell) to successfully differentiate into vascular cells. Two controls were tested along with stem cells in 3D Matrigel matrix: a positive control with beads in 3D Matrigel and a negative control with stem cells in 2D culture.

The results somewhat showed similarity with a regular fluid flow mechanism. Due to the shear stress on only the top of the culture, a gradient of maximum displacement was observed; the cells / beads that were closest (the top-most layer of culture) to the PBS flow moved the furthest along with the flow, while those on the bottom barely changed its position. Cells in 2D system were completely washed away, assuring that in pulsatile condition, only 3D scaffold enables stem cells to maintain its unison and hence function to differentiate.

The drawback of this experiment was in the approximation of the applied shear stress. The fluid used for the flow and the geometrical dimension of the culture system in the experiment did not accurately represent the actual condition in vascular system of a mouse, in terms of shear stress calculation. However, this problem can be easily fixed in later experiments by substituting a solution that better describes the system and changing the dimension of 3D scaffold when designing one.

The significance of this study is that it is one of the first and successful researches to attempt tissue engineering using stem cells, and not already differentiated cells. The autologous stem cells would significantly reduce the problems faced with the ongoing vascular grafts (i.e. material availability and immunological rejection). The combination of stem cell research with tissue engineering, such as this one, seems to be promising.