DYNAMIC CELL CULTURE METHODS FOR FUNCTIONALIZED BIOMATERIALS - Biologically-Responsive Hybrid Biomaterials - page 386

patency of grafts. In addition, the structural integrity of 7 out of 8 (87.5%)
unseeded constructs of the same materials successfully maintained pulsatile
arterial flow up to 1 month after implantation in vivo .
In a similar way, Zhang et al. used silk-based vascular grafts seeded with
human coronary artery smooth muscle cells and human aortic endothelial cells
sequentially with a Matrigel® coating between to mimic the basement membrane
[73]. The silk and Matrigel® together increased endothelium coverage and
retention when in dynamic flow. In addition, the dynamic flow conditions
resulted in improved cell proliferation and alignment, extracellular matrix
production, and cell phenotype. Flow rate in the peristaltic pumped perfusion
system was increased from 5 to 35 mL/min over 7 days, and then maintained at
35 mL/min for up to another 7 days. The expression of mRNA for SMC
contractile markers was between 3.9 and 15.3 fold higher for the dynamic
cultures at days 7 and 14. Maintaining the contractile phenotype of the SMCs in
vitro is an important obstacle for vascular graft engineering [74,75]. An
additional exciting prospect for this system is its ability to be further modified by
the facile attachment of RGD-peptides or other peptides or proteins, a method
previously determined feasible [76,77]. It is clear that by combining hybrid
vascular scaffolds with co-culture in a dynamic setting, the most structurally and
functionally successful tissue engineered vascular graft can be achieved on an
individual basis of requirements [78]. In addition, by focusing on specific peptide
sequences incorporated into a biomimetic material, it has been shown possible to
reduce thrombogenicity of an ECM graft while still promoting endothelial cell
attachment and culture on the biomaterial surface [79].This research is an
indication of the direction for hybrid vessel grafts where bioresponsive surfaces
can promote attachment and proliferation of desired cells while avoiding the
responses of undesired cell types.
3.1.2. Heart valves
Tissue engineering of heart valves can be complex due to their precise
mechanical function and forceful fluid environment [65]. In addition, the
specialized cellular and ECM components need the ability to be remodeled in
response to changes in mechanical forces, just as a heart valve in vivo adjusts
[80]. The usefulness of a bioreactor becomes clear in conditioning tissues to
withstand and function in the physiological environment. Previously, tissue
engineered heart valve bioreactors have been shown to induce extracellular
matrix formation, increase structural integrity, improve cell organization and