Investigating the Kinetics and Structure of Network Formation in Ultraviolet-Photopolymerizable Starch Nanogel Network Hydrogels via Very Small-Angle Neutron Scattering and Small-Amplitude Oscillatory Shear Rheology

Abstract

While photopolymerization has been broadly used to fabricate hydrogels, the kinetics of the structural evolution of such hydrogels during photopolymerization and how the kinetics relate to ultimate hydrogel properties are not well-understood. Herein, small-amplitude oscillatory shear rheology (bulk scale) and time-resolved very small-angle neutron scattering (vSANS, microscale) are used in tandem to investigate the kinetics of the photopolymerization of methacrylated starch building blocks with different concentrations, charges (cationic (+), anionic (−), or neutral (0)), and morphologies (soluble branched starch, starch nanoparticles, or combinations thereof). Starch nanoparticles (SNPs) enabled the fabrication of much denser hydrogels than soluble starch but took longer to gel due to the reduced conformational mobility of the polymerizable methacrylate groups on the SNPs. The addition of charge (cationic or anionic) increases the bulk gelation time while significantly reducing the observed changes in the fluid scale and correlation length, suggesting less covalent crosslinking and inherent SNP deformation during photogelation; indeed, the fluid exponent analysis suggests that charged SNPs deswell upon crosslinking, consistent with the behavior of microgels in colloidal crystals, while uncharged SNPs swell due to competition between inter-and intraparticle crosslinking. The combination of shear rheology and vSANS measurements can thus inform the design of new photopolymerizable hydrogels with targeted comprehensive properties.

Gelatin-Based Hybrid Hydrogels as Matrices for Organoid Culture

“…The slower cross-linking of CSNB-GelSH in comparison with DexNB-GelSH might be caused by the negatively charged nature of chondroitin sulfate in combination with negatively charged gelatin above its iso-electric point (IEP) of 4.8–5.0, which leads to a slower approaching of the polymer chains due to repulsive forces. , The latter phenomenon was described by Majcher et al They executed research on the cross-linking kinetics of starch in uncharged, cationic, and anionic forms. Both the charged derivatives significantly increased the photoinduced gelation time . However, all thiol-NB hydrogels exhibited faster cross-linking kinetics compared to GelMA.…”

“…Both the charged derivatives significantly increased the photoinduced gelation time. 34 However, all thiol-NB hydrogels exhibited faster cross-linking kinetics compared to GelMA. The latter was described before by Van Damme et al 35 comparing the kinetics of GelMA with GelNB-GelSH hydrogels.…”

“…28 The degree of substitution when adding 0.5, 1, 2, and 4 equiv was, respectively, 12, 34, 68, and 93%, with respect to the disaccharide repeating units. The building blocks are from now onward referred to as CSNB (12), CSNB (34), CSNB(68), and CSNB(93). It should be noted that the DS of DexNB is defined as the percentage of modified monosaccharide units since dextran consists of anhydroglucose (i.e., monosaccharide) repeating units.…”

Advances in Small Angle Neutron Scattering on Polysaccharide Materials

“…Time-resolved small angle scattering is often applied for the analysis of structural changes and rheological properties of hydrogel systems. A recent study focused on the effect of photopolymerization synthesis method on the kinetics of the network morphology of Starch hydrogels [ 51 ]. Evolution of the network formation was captured through repeated alternating steps of very small-angle neutron scattering (vSANS) measurements and exposure of samples to UV light.…”