Biomedical Engineering Reference
In-Depth Information
tative model is self-assembly LB membranes made of amphiphilic PEG
derivatives or copolymers. Other typical models established with vari-
ous mechanisms include the thioalcohol-gold monolayer system based on
chemical affinity, and polyelectrolyte/polyion alternative multilayer sys-
tem including polylysine (polycation) and algin (a negatively charged
calcium-containing hydrogel) microcapsules [55-66].
4.
Matrix bulk blending
. Blends of material matrix and SMA in material bulk
are also used for biomaterial surface modification. The matrix-material
candidates are usually thermoplastic elastomers like polyurethane and
degradable glass-state scaffolds like PLA-PGA. For degradable scaf-
folds, any surface modification easily loses its function at the earliest
degradation of the surface layer; contrary to this, bulk blending is al-
ways capable of maintaining SMA present at the interface of degrad-
ing cracks. For blends in elastomers, using the elastomeric materials'
talent of environment-dependent “annealing” characteristics, SMA lo-
cational distribution and orientation are re-organizable by their self-
migration and re-assembly. Collaborating with the moveable macro-
molecular chains of the elastomeric matrix, the spontaneous SMA mi-
gration is driven by crystallo- or non-crystallo micro-phase separation
(between SMA and the matrix material) and oriented by SMA's am-
phiphilic surface-occupation tendency, which eventually achieves SMA
surface enrichment. During the whole procedure, three points of concern
are involved: the modulation of the micro-phase separation; the inter-
relationship between material mechanics and biocompatibility; and the
functional contribution by SMA size and chemical properties [67-75].
Firstly, the stability of SMA participation against phase separation needs
to be maintained by SMA-matrix crosslinking, but strictly avoiding the
loss of the matrix material's elastomeric characteristics. Thereby phys-
ical crosslinking, like H-bond connection/incorporation, is preferred.
Micro-phase separation in bulk inevitably leads to micro-domain sep-
aration on the surface, by which the number, species, and status of
binding proteins are varied, and consequently the material biocompat-
ibility as well as the bio-functionality is influenced. Investigations also
indicate that material mechanics and biocompatibility are frequently two
counter-factors to be optimized; and simultaneously, the equal contribu-
tions of SMA size, physical state, and chemical properties for material
biocompatibility are further emphasized. An H-bond grafting strategy
forpolyurethaneelastomersurfacemodificationviaSMA-matrixbulk
blending and its cardiovascular applications are thoroughly reviewed
in Sect. 2 [76-83].
