Biomedical Engineering Reference
In-Depth Information
rary shape by physical crosslinks such as crystallites; and (ii) netpoints—
precursors that determine the permanent shape of the polymer [301].
A biodegradable copolymer formed from oligo(
-caprolactone)diol and
oligo(
p
-dioxanone) diol has been shown to be an excellent suture material,
as illustrated in Fig. 9. Here, the loose knots formed from fiber-like forms of
this copolymer are used for wound closure where the knots tighten upon an
increase in temperature, and thereafter keep the wound lips together under
the right stresses for better healing [300].
Photoresponsive shape memory polymers are created by incorporating
cinnamic groups which could be deformed to attain a temporary shape by
UV light illumination at ambient temperatures. The un-deformed shape of
these polymers can be recovered by exposing them to UV light with a dif-
ferent wavelength at ambient temperature [305]. The use of UV light as an
external stimulus obviates the need for temperature changes, as required in
the case of temperature-sensitive shape memory polymers.
Recently Thorton et al. designed chemically crosslinked alginate hydrogels
into a compressed form for a noninvasive administration of the cells-scaffold
system into the defect site. The inserted hydrogel is then swollen in vivo to
re-gain its original equilibrium swollen shape [306]. Here, the initially com-
pressed hydrogels regain their permanent shape through swelling and not
through any external stimuli. This attempt therefore shows the feasibility of
ε
Fig. 9
A fiber of a thermoplastic shape-memory polymer was programmed by stretching
about 200%. After forming a loose knot, both ends of the suture were fixed. The photo
series shows, from
top
to
bottom
, how the knot tightened in 20 swhenheatedto40
◦
C.
(Reprinted with permission from Lendlein A, Langer R (2002) Science 269:1673, copyright
2002 AAAS)
