Biomedical Engineering Reference
In-Depth Information
but unfortunately prone to causing thrombosis. Since it is still unrealistic for
synthetic materials to produce a completely bio-inert product, both the pros
and cons reflected from the interactions between material and blood com-
ponents must be balanced for an optimal outcome. Research maintained the
adoption of superior polymers as implant scaffolds, but gradually improved
the strategy by pursuing active involvement of biological factors that may lead
the host reactions to tend positively for the expected purpose. One of the
model approaches is surface immobilization of proteinic ligands. Currently,
the ultimate goal is to develop bio-absorbable artificial vascular implants that
may take the responsibility of maintaining vascular biomechanics and in-
tegrity, simultaneously guiding and participating in vascular regeneration,
until they are eventually replaced in whole or in part by new vascular tissues.
Accordingly, the ideal fabrication of vascular implants is proposed to be an in
vitro integration of tissue-engineered cellular precursors and bio-absorbable
substrates that are hybridized with guider proteins for host cell ingrowth and
precursor renewal [102-105].
Surface-engineered endothelialization for artificial cardiovascular im-
plants can be achieved either by allogenic EC seeding or inducing host EC
reoccupation. These two strategies may work separately or in coordination.
Allogenic Endothelial Cell Seeding
The original idea of biomaterial surface endothelialization via in situ growth
of allogenic EC was first established in 1978. Afterwards, the primary tech-
nical barriers for in vitro EC culture were gradually conquered, covering the
whole procedure of cell culture from cell harvest, seeding to cell develop-
ment, and also resolves the maintenance of the endothelial phenotype on
artificial surfaces, namely, prevention of dedifferentiation or desquamation.
Animal experiments indicate a better fluency of blood flow in the endothe-
lialized artificial vascular system compared to its untreated control. Further
investigation also reveals the anti-infective contribution by endothelializaion.
However, for clinical applications, the greatest disadvantage of allogenic EC
transplantation is the low cell density. The seeded cells cannot sufficiently in-
tegrate with the implant surface to build up a full and continuous coverage.
To overcome this problem, attempts have been made at in vitro expansion of
allogenic cells until confluence and then performing implantation, or relying
on the employment of microvascular EC that is endowed with superior pro-
liferation capacity. Nevertheless, significant drawbacks still exist in the form
of the extra complication of the cell culture process and the requirement of
secondary surgery. They both produce extra toleration of patients and also
increase the chance of contamination and infection [106-108].
Inducing Host Endothelial Cell Reoccupation
Theoretically, specific EC growth factors are capable of stimulating the over
ECM ingrowth of capillary vessels and thereby promoting endothelialization
