Author Description

Characterizing dynamic rheological properties and structural changes during hydrogel degradation is critical in the design of these materials for drug delivery applications. In order to advance hydrogel design in targeted, controlled released drug delivery applications, our work focuses on developing techniques to precisely characterize real-time hydrogel degradation and determine degradation mechanisms in response to biologically relevant stimuli. In this work, two types of stimuli-responsive hydrogels are investigated, covalent adaptable hydrogels (CAHs) and biodegradable polymer-peptide hydrogels.We characterize covalent adaptable hydrogel degradation in response to changes in pH that mimic those in the gastrointestinal (GI) tract. This work aims to inform design of CAHs as a new vehicle for oral drug delivery. The specific CAH we are characterizing is a pH-responsive hydrogel that consists of 8-arm star poly(ethylene glycol) (PEG)-hydrazine that self-assembles with 8-arm star PEG-aldehyde creating covalent adaptable hydrazone bonds. We use μ2rheology, which is an experimental platform that allows us to change the incubation fluid environment to mimic pH changes in the GI tract and simultaneously characterize real-time scaffold degradation. μ2rheology is multiple particle tracking microrheology (MPT) in a microfluidic device. MPT is well-suited to characterize the material rheological evolving without perturbing their structure in a complex microenvironment. MPT measures the Brownian motion of fluorescent probe particles embedded in the material to extract rheological properties. Our two-layer microfluidic device enables consecutive fluid exchange around a single sample with minimal sample loss. Using μ2rheology, we characterize CAH degradation at a single pH (pH 4.3, 5.5 and 7.4), with a single pH exchange (pH 4.3 to 7.4 and pH 7.4 to 4.3) and during transient changes in pH which mimic the pH in the entire GI tract. Using time-cure superposition (TCS), the super