Photolabile networks for tissue
engineering applications
Degradable hydrogels synthesized through
free-radical chain polymerizations of
multifunctional macromolecular monomers are
increasingly used as cell encapsulation
platforms for tissue regeneration and as drug
delivery devices. Controlling degradation of the
hydrogel is important for these applications and
is typically achieved by synthetically
incorporating hydrolytically or enzymatically
degradable blocks within the gel-forming
macromers, where the rate of degradation is
pre-determined by the initial macromer chemistry
and cannot be easily altered in situ.
Here, a novel photolabile poly(ethylene
glycol)-based (PEG) macromolecular monomer was
used to synthesize hydrogels that degrade upon
light exposure, allowing real-time and spatial
control of degradation. Ethyl
4-(4-(1-hydroxyethyl)-2-methoxy-5-nitrophenoxy)butanoic
acid (photoscissile group, PS) was incorporated
into a PEG-based monomer (PEG Mn~3400
g/mol) to create PS-b-PEG-b-PS
diacrylate. Upon exposure to light (UV or
visible), this macromolecular monomer undergoes
photolytic cleavage to release PEG and acrylic
acid. Photolabile copolymer networks of PS-b-PEG-b-PS
diacrylate and PEG monoacrylate (Mn~375
g/mol) were created by redox-initiated
polymerization (15 wt% monomer in water). The
networks were subsequently irreversibly degraded
with 365-nm or 405-nm light (10 or 20 mW/cm2)
and characterized by following mass loss and
shear modulus with time. Gel degradation was
controlled temporally by varying light exposure
and spatially by photolithography to demonstrate
the utility of these photolabile materials for
externally tuning hydrogel properties in real
time.
|
