Biomedical Engineering Reference
In-Depth Information
calization is physical coating (blends). Accordingly, the ideal SMA compound
for physical incorporation should be composed of at least three units: bio-
functional (end)group, spacer arm, and localizing anchor.
Bio-Functional Endgroup
As concluded in Sects. 1.2.1 and 1.3.1, smaller-sized endgroups with pertinent
expertise and appropriate efficiency would always serve the desired function-
ality better. The details will be depicted in this part of the review.
Spacer Arm
General principles of spacer arms have been thoroughly discussed in
Sect. 1.5.2. To fulfill the blood-contact applications in this study, polyethy-
lene glycol [PEG; or polyethylene oxide, PEO] is employed as the only
candidate for spacer arms. As a family of well-acknowledged biocompati-
ble compounds, PEG has numerous superior physicochemical, biochemical,
and biological properties. (1) PEG is highly water-soluble and also soluble
in vast numbers of organic solvents. Among the frequently used solvents,
ether and hexane are the only two non-solvents for PEG. This pleasant
solubility assures the simplicity and biocompatibility of most PEGylation
processes, including the treatments of isolation and purification. (2) PEG is
non-toxic and non-immunogenic. The low-molecular-weight PEG-derivatives
can be promptly metabolized by the host body. (3) PEG is highly hydrophilic
and PEG chains have high mobility and flexibility in compatible phases. If
introduced onto biomaterial surfaces, PEG chains are capable of creating
large thermodynamic exclusion volumes and simultaneously enhancing the
material-medium interface fluidity, as explicated in Sect. 1.5.2, which directly
favors the living immobilization of biological ligands by providing physical
mobility and hindering non-specific bindings. (4) All these superior prop-
erties of PEG can be conveniently rendered to its adjacent compounds or
groups via covalent conjugation (PEGylation) without affecting their original
characteristics [134-139].
Localizing Anchor
The design of the anchors totally depends on the proposed mechanism of
SMA-matrix material incorporation. In this study, 4,4
-methylene diphenyl
diisocyanate (MDI) is applied as the localizing anchor that physically bonds
to the PEU matrix material by mimicking the physical crosslink between PEU
hard blocks. Finally, the “ABCBA”-type SMA, named “MPEO”, is constructed
asshowninFig.1,inwhich“A”representsbio-functionalendgroups,“B”
represents the PEG spacer, and “C” represents the MDI anchor that also plays
the role of coupling groups for A-B moieties on both sides [76, 77].
