Biomedical Engineering Reference
In-Depth Information
PLLA
dextran
proteins
self-assembly
degradation of
PLLA
Dex- g -OLLA
protein loaded
Dex- g -OLLA nanogel
release of proteins
from the nanogel
release of proteins
from the nanogel
Fig. 17 Protein loaded Dex- g -PLLA nanogel. Reprinted from [ 164 ] with permission
The SC nanogels had 70 nm mean diameter with narrow size distribution, signifi-
cantly lower critical aggregation concentration (CAC), and stronger thermodynamic
stability compared with those of the corresponding L -or D -isomer nanogels [ 163 ].
As described above, PEG has been frequently used in biomedical applications.
However, PEG is not biodegradable. Low molecular weight PEG (below
ca. 30,000 Da) can be excreted from kidneys, but such excretion is difficult for higher
molecular weight PEG. Therefore, it is valuable to provide biodegradable polymers
having PEG-like high biocompatibility, as well as biodegradability. Moreover,
PEG possesses reactive functional groups only at its termini, which results in a
lack of functionality in the main chain. PEG-based nanogels prepared by physical
crosslinking have not been reported. We reported the synthesis of PEG-like biode-
gradable polymers by polycondensation of dihydroxy bifunctional low molecular
weight PEG and an amino-protected Asp derivative, poly(Asp- alt -PEG). Poly(Asp-
alt -PEG)-capryl conjugates were synthesized as novel hydrophobically modified
biodegradable PEG copolymers. The poly(Asp- alt -PEG)-capryl conjugates formed
nanogels of approximately 15 nm in size by self-assembly at 20 C in aqueous media,
and the nanogel solutions displayed temperature-responsive phase transition. The
reversible transition of the nanogel solution was tunable in the range 19-55 C
by changing the introduced amounts of capryl units and the solution concentrations.
The nanogels gradually degraded within days in PBS at 37 C[ 262 ].
7 Supramolecular Biodegradable Systems
Supermolecular interlocked macromolecules have been paid much attention as
candidates of smart materials. Polyrotaxane (PRX) is a typical example. PEG/
cyclodextrin (CD)-based polyrotaxane was firstly reported by Harada and
coworkers by attachment of stoppers to pseudopolyrotaxane (pPRX) consisting of
a PEG and CDs [ 263 ]. Subsequently, many CD-based PRXs have been designed
and prepared as smart materials such as biomaterials, light-harvesting antennae,
insulating polymers,
stimuli-responsive molecular
shuttles etc.
[ 264 - 268 ].
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