Biomedical Engineering Reference
In-Depth Information
previously developed bioreactor for 4 days after 48 hours in static culture [69].
The hybrid matrix displayed desirable mechanical characteristics over hydrogels
of only collagen or fibrin, and the cyclically strained samples performed better
than statically cultured samples. A similar method utilizing shear rather than
strain was employed by Shirota
et al.
to determine the potential of human
endothelial progenitor cells (EPCs) from circulating peripheral blood to line
microporous polyurethane grafts coated with a photoreactive gelatin layer. After
seeding the EPCs to the construct statically for 4 days, hydrodynamic shear stress
was applied using a circulatory loop. This apparatus yielded a flow rate of 60
mL/min, which resulted in a calculated shear stress of 30 dyne/cm
2
for 12 hours.
This simple system resulted in elongated EPCs which were aligned in the
direction of flow. The cells were tightly adhered and appeared in a confluent
monolayer, similar to native artery.
Tissue engineered vascular grafts can be made more physiologically
analogous by incorporating two pivotal types of cells into a perfused vascular
engineering graft, both smooth muscle and endothelial cells. Jeong
et al.
used a
hybrid scaffold of jellyfish collagen with poly(lactide-co-glycolide) (PLGA)
fibers to demonstrate the benefits of both a hybrid biomaterial and a dynamic
culture system [70]. Tubular scaffolds were formed by molding and drying
collagen gels, then electrospinning PLGA fibrous layers on the abluminal
surface. First, rabbit aorta smooth muscle cells were seeded by injection and held
under static conditions in a pulsatile perfusion bioreactor for 2 days. Then, the
scaffolds were subjected to pressure flow of 25 mmHg with a pulse of 1 Hz for
14 days. After the SMC culture, rabbit endothelial cells were seeded into the
lumen and allowed to adhere for 90 minutes before the flow rate was increased
gradually up to 0.1 mL/s over 7 days. The perfusion was found to significantly
influence cell alignment in the direction parallel to flow when compared to the
randomly aligned static cultures. This alignment appears in arteries
in vivo
and is
critical for the contractile functions of these cells [71].
The emphasis for most tissue engineered products is to culture the proper cell
types
in vitro
prior to implantation of the functional tissue. Tillman
et al.
demonstrated this using conditioning of poly(
ō
-caprolactone) (PCL) and collagen
hybrid electrospun scaffolds seeded with both endothelial and smooth muscle
cells in a pulsatile perfusion bioreactor for a total of 9 days [72]. The cells
adhered to the surface of the graft even under the physiological pulsatile
conditions and resulted in a structure similar to native vessel. When exposed to
an
in vivo
sheep blood model, the ECs lining the luminal surface of the
conditioned grafts only showed minimal platelet adherence, key for
in vivo
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