Biomedical Engineering Reference
In-Depth Information
optimize interface microenvironments for better cell responses. As discussed
in previous sections, a major talent of MPEO-derived SMAs lies in their
ability of selectively binding and repulsing the molecular-scaled substances
approaching the interface. This ability is attributed to the characteristic of
MPEO-derivatives—the intramolecular coordination of functional ligand and
spacer-arms. The functional ligand provides desired cell affinity with speci-
ficity, which is enabled and associated by the spacers. Proper-sized spacers are
capable of unspecifically preventing any undesired adsorption that may harm
or dilute the ligand functionality. In the aqueous phase, the spacers are also
responsible for physically raising up the ligand and consequently increasing
the chance of reaching the receptors on EC surfaces. This coordinating mech-
anism demonstrates how molecular-leveled manipulation works for cellular
events [82, 83].
Technically, the ligands are incorporated to SMAs as endgroups of PEG
spacers, followed by a living immobilization onto PEU surfaces. The widely
acknowledged cell adhesion ligand, RGD tri-peptide is used as a positive con-
trol [31-36, 82, 83, 109, 115]. Mono-amino acids (AAs including acidic aspar-
tic acid [Asp, D], hydrophobic phenylalanine [Phe, F], neutral glycine [Gly,
G], and basic lysine [Lys, K] and arginine [Arg, R]) and their various com-
binations are respectively employed as functional ligands. Primary human
umbilical vein endothelial cells [HUVECs] are applied as the experimental
cells for transplantation. As exhibited in Fig. 8, successful endothelialization
is achieved on the basic AA-MPEO-decorated PEU surfaces. The performance
is comparable with the RGD-modified positive controls [82, 83].
3
Conclusions
This review recalls the advances in research on cardiovascular biomaterials,
starting from systematic investigations that are summarized centering on an
H-bond grafting model that is designed to facilitate surface modification of
blood-contact polyurethanes. The development of this model is initiated with
originality, and also benefits from ideas and methodologies drawn from com-
prehensive works from worldwide contributions. The entire project assem-
bles a series of self-contained studies covering aspects from prototype setup
through various blood-contact applications. H-bond grafting is an innovative
strategy functioning to conjugate SMAs with polyurethane matrix in non-
covalent ways such as the blending-coating process. The SMAs are designed
as a family of penta-blocked “ABCBA”-type oligomers. The “C”-blocks mimic
polyurethane hard blocks in structure, so that in blends of polyurethanes and
SMAs, the blenders incorporate each other via hydrogen bonds, which exactly
replicates the buildup of physical crosslinking points intrinsically existing in
polyurethane elastomers. Namely, the “C”-blocks act as H-bond grafting an-
