Biomedical Engineering Reference
In-Depth Information
11.4.3.1
Heart Tissue Engineering
Engineered heart tissue can form a thick myocardium after implantation on
myocardial infarcts in immune-suppressed rats [
1432
]. When evaluated 28 days
later, engineered heart tissue shows neither undelayed electrical coupling to
the native myocardium, arrhythmia, nor dilation. Cardiomyocytes seeded onto
mechanically conditioned, perfused, porous scaffolds can conduct action potentials
and beat synchronously, but the scar hinders a proper integration of implanted cells.
Cell sheet technology applied to a monolayer of adipose tissue-derived, pluripo-
tent, mesenchymal (non-hematopoietic) stem cells allows the repair of scarred
myocardium after myocardial infarction in rat hearts [
1433
]. Engrafted mesenchy-
mal stem cells prevent wall thinning in the scar area and improve the cardiac
function.
Composite matrices can be used for heart valve engineering. Enzymatically de-
cellularized porcine aortic valves that are impregnated with biodegradable polymer
by a stepwise exchange provide a scaffold for heart valve tissue engineering with
complete endothelialization [
1434
]. Ovine cell seeding of decellularized porcine
heart valves (with almost complete preservation of the extracellular matrix) is
improved under pulsatile flow conditions [
1435
].
Preliminary numerical experiments have been carried out to study the content
and orientation of collagen fibers
24
of the loaded aortic valve [
1437
]. In an isotropic
cusp, the fiber orientation is driven by the principal strain directions. The remodeling
depends on the transvalvular pressure, fiber stiffness, initial fiber direction (close to
the principal strain directions in this work), and loading conditions.
11.4.3.2
Vascular Tissue Engineering
Sheet-based tissue engineering, using fibroblasts and endothelial cells, without
smooth myocytes and exogenous biomaterials, can form cylindrical blood vessels,
characterized by a composite multilayered wall with vasa vasorum [
1438
].
Arterial stenoses and lumen blockage by clots locally or emboli remotely can
be treated by bypass grafting surgery. Autologous grafts (internal mammary artery,
saphenous vein) are used in most patients. Synthetic grafts can also be utilized. To
reduce the failure rate of synthetic (polytetrafluoroethylene) grafts due to thrombosis
and scar within graft lumen, biocompatible, durable biosynthetic grafts have been
made. Synthetic tubes are coated by an adhesion matrix (fibronectin) and endothelial
cells on its interior surface. Endothelial cells are genetically changed to overexpress
24
The cardiac extracellular matrix is mainly composed of collagenous fibers. The fiber network
is involved in the distribution of forces generated in the heart. Studies on collagen synthesis
by cardiac fibroblasts show that the ratio of collagen-3 to collagen-1 increases in mechanically
stretched cells [
1436
]. Collagen-3 mRNA level increases in response to cyclic mechanical stretch
in 12 h, whereas collagen-1 mRNA concentration does not change.
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