Paper Number
AB22 

Session
Active and Biological Materials

Title
Correlation of dynamic scaffold rheology with molecular release during material degradation

Presentation Date and Time
October 13, 2021 (Wednesday) 11:05

Track / Room
Track 2 / Ballroom 7

Authors (Click on name to view author profile)

1. Wu, Nan (Lehigh University, Chemical and Biomolecular Engineering)
2. Schultz, Kelly M. (Lehigh University, Chemical and Biomolecular Engineering)

Author and Affiliation Lines (in printed abstract book)
Nan Wu and Kelly M. Schultz
Chemical and Biomolecular Engineering, Lehigh University, Bethlehem, PA 18015

Speaker / Presenter 
Schultz, Kelly M.

Keywords
biological materials; gels; rheology methods

Text of Abstract
The goal of this work is to establish a quantitative correlation between molecular release and material degradation. We characterize a radical-initiated photopolymerized and a base-initiated Michael addition polymerized hydrogel, which form gels through distinct cross-linking reactions. Both scaffolds are cross-linked with the same degradable peptide, which enables degradation through the same enzymatic degradation reaction. A fluorescently labeled poly(ethylene glycol) is chemically conjugated to the scaffold and is released during enzymatic degradation. Real-time changes in scaffold rheological properties during degradation are measured using bulk rheology. Molecular release is measured by quantifying the fluorescence in the incubation liquid and the hydrogel scaffold. A complicating factor, described in the literature, is that shear may cause increased cross-linking after initiation of degradation resulting in an increase in storage modulus, which would change release profiles. We also test the hypothesis that shear induces additional cross-linking in degrading hydrogel scaffolds. To do this, enzymatic degradation is characterized using bulk rheology as materials undergo continuous or minimal shear and molecular release is measured when the material is incubated with and without shaking. We determine that shear does not change scaffold degradation or release regardless of gelation reaction. Instead, we determine that the type of hydrogel cross-linking reaction greatly affects both material degradation and molecular release. Hydrogel cross-linking by base-initiated Michael addition does undergo further cross-linking at the start of degradation, which results in minimal release. We correlate release with enzymatic degradation for both scaffolds. We determine that material storage modulus is indirectly correlated with release during degradation. These results indicate that rheological characterization is a useful tool to characterize and predict the release of molecules from degrading hydrogels.