Biomedical Engineering Reference
In-Depth Information
poly(acrylic acid) (PAA) [
74
,
75
] Liu et al. reported the free radical polymerization
of PNIPAAm grafted to methylcellulose (MC) using ammonium persulfate and
N,N,N′,N′-tetramethyl ethylene diamine as an initiator [
76
]. The sol-gel transition
of the thermogels occurs within a minute with tunable transition temperature based
on the composition of the copolymer. Recently, controlled radical polymerization
techniques such as atom transfer radical polymerization (ATRP) have allowed for
new block architectures as well as modulation of the thermogel behavior. Recently,
Kitazawa et al. reported the synthesis of a thermosensitive triblock copolymer, con-
sisting of poly(benzyl methacrylate) as the terminal blocks and poly(methyl meth-
acrylate) as the middle block, by ATRP [
77
]. This polymer exhibits a thermogelling
effect in an ionic liquid and shows an extremely high gelation temperature of
above 100 °C. Abandansari et al. reports the synthesis of a pentablock polymer of
PNIPAAm-PCL-PEG-PCL-PNIPAAm, which was synthesized by combining ring-
opening polymerization and ATRP [
78
]. Li et al. synthesized a class of thermogels
for the delivery of cardiosphere-derived cells (CDCs) [
79
]. The hydrogels were
based on a central polycaprolactone unit with flanking PNIPAAm, poly(2-hydrox-
yethyl methacrylate) and poly(dimethyl-
ʳ
-butyrolactone acrylate) (Fig.
3
). Atom
transfer radical polymerization was utilized for the fabrication of well-defined ther-
mogelling polymers. These polymer solutions formed semi-solid gels within 5 s.
3.2.3 Synthetic Gels Prepared by the Formation of Poly(Urethane)S
The formation of multiblock copolymers with high molecular weights is the basis
for the preparation of thermogelling copolymers with extremely low gelation
concentrations. Typically, this is prepared by a one-pot reaction of poly(ethylene
glycol) as the first block, poly(propylene glycol) as the second block, and a third
block polymer of choice. Without the third block, the thermogelling effect is also
observed [
80
]. However, based on the different requirements such as degradation
stability, hydrophobicity of the block copolymer, and drug release profile of the
thermogel, the third block can be used to tune the thermogel properties. Over the
past 7 years, several blocks have been utilized including poly[(R)-3-hydroxybu-
tyrate] (PHB) [
81
-
83
], PLA [
84
], PCL [
85
,
86
] poly(ethylene butylene) [
87
,
88
]
and poly(trimethylene carbonate) [
89
]. Recently, Park et al. reported the synthe-
sis of thermogelling polymers with functional groups in the backbone to allow for
bio-functionalization to enhance cell-materials interactions [
90
]. Here, an amine-
functionalized ABA block copolymer, poly(ethylene glycol)-poly(serinol hexam-
ethylene urethane) (ESHU) with one free primary amine group on every repeating
unit was synthesized. The polyurethane unit functions as the hydrophobic block
and PEG acts as the hydrophilic block. Serinol is a serine derivative with two
hydroxyl groups and one amine group; the hydroxyl groups allow for conjugation
with the isocyanate groups to form the urethane linkages and the amino group can
be used for further functionalization. The amino group was first protected during
the urethane formation. This protected amino group was reacted to form a bio-func-
tionalized ESHU with IKVAVS peptide which shows rapid thermogelling property.
Search WWH ::
Custom Search