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Nanostructure of Fully Injectable Hydrazone-Thiosuccinimide Interpenetrating Polymer Network Hydrogels Assessed by Small-Angle Neutron Scattering and dSTORM Single-Molecule Fluorescence Microscopy.

ACS applied materials & interfaces (2017-11-14)
Trevor Gilbert, Richard J Alsop, Mouhanad Babi, José Moran-Mirabal, Maikel C Rheinstädter, Todd Hoare
ABSTRACT

Herein, we comprehensively investigate the internal morphology of fully injectable interpenetrating networks (IPNs) prepared via coextrusion of functionalized precursor polymer solutions based on thermoresponsive poly(N-isopropylacrylamide) (PNIPAM) and nonthermoresponsive poly(vinyl pyrrolidone) (PVP) by reactive mixing using kinetically orthogonal hydrazone and thiosuccinimide cross-linking mechanisms. Small-angle neutron scattering, probing both the full IPN as well as the individual constituent networks of the IPN using index-matching, suggests a partially mixed internal structure characterized by PNIPAM-rich domains entrapped in a clustered PVP-rich phase. This interpretation is supported by super-resolution fluorescence microscopy (direct stochastic optical reconstruction microscopy) measurements on the same gels on a different length scale, which show both the overall phase segregation typical of an IPN as well as moderate mixing of PNIPAM into the PVP-rich phase. Such a morphology is consistent with the kinetics of both gelation and phase separation in this in situ gelling system, in which gelation effectively traps a fraction of the PNIPAM in the PVP phase prior to full phase separation; by contrast, such interphase mixing is not observed in semi-IPN control hydrogels. This knowledge has significant potential for the design of an injectable hydrogel with internal morphologies optimized for particular biomedical applications.

MATERIALS
Product Number
Brand
Product Description

Sigma-Aldrich
N-Vinylformamide, 98%
Sigma-Aldrich
1-Vinyl-2-pyrrolidinone, contains sodium hydroxide as inhibitor, ≥99%
Sigma-Aldrich
N-Isopropylacrylamide, ≥99%
Sigma-Aldrich
Acrylic acid, anhydrous, contains 200 ppm MEHQ as inhibitor, 99%
Sigma-Aldrich
Cysteamine, ≥98.0% (RT)