(531b) Synthesis and Characterization of Hyaluronic Acid and Heparin Thiol-Ene Hydrogels for the Spatial Sequestering of Bioactive Signals

Authors: 
Darling, N. J., University of California Los Angeles
Segura, T., University of California Los Angeles
Polymer scaffolds serve
a central role in the field of tissue engineering by directing cellular
processes based on the mechanical as well as biochemical properties
Hyaluronic acid (HA), a non-sulfated glycosaminoglycan (GAG) distributed
throughout connective, epithelial, and neural tissue, plays a role in wound
healing and angiogenesis. HA hydrogels are widely utilized to create
scaffolds for tissue repair and to study cell behavior in vitro. Though
these materials are commonly synthesized via Michael addition chemistry, we
have found that these chemistries lead to hydrogels that have local areas of
high and low crosslinking as a result of inappropriate mixing and fast gelation
kinetics (Figure A). This heterogeneity leads to inconsistent cell behavior
through the gel and between gels of the same condition.  To circumvent this
limitation, we report on light activated thiol-ene HA hydrogels, which can be
thoroughly mixed prior to gelation. In addition, we report on the incorporation
of heparin, through the same thiol-ene chemistry allowing for dosing of heparin
within an HA gel. Heparin (HP), an important glycosaminoglycan (GAG) capable of
sequestering growth factors and protecting them from proteolysis, mediates the
spatial presentation of both bound and soluble growth factors in vivo
and is utilized here in vitro to control the presentation and release of
growth factors. We show synthesis of norbornene-functionalized
HA (HA-Norb) and norbornene functionalized heparin (Hep-Norb) (Figure B) using
completely aqueous chemistry avoiding the need to transfer HA and Hep
to the organic phase. As expected, we find that the initiator type and degree
of crosslinking influences the mechanical properties of the gels. We find that
the ability to dose in Hep
is critical to allow extensive cellular spreading and migration
(Figure
B) through out the scaffold indicating that through modulating growth factor
presentation and retention, we can guide cell behaviour. This new hydrogel
material more closely mimics the ECM of tissues with substantial GAG content
such as the brain.

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