Paper Number
AB11 

Session
Active and Biological Materials

Title
Rheological characterization of covalent adaptable thioester networks

Presentation Date and Time
October 12, 2021 (Tuesday) 10:15

Track / Room
Track 4 / Meeting Room C-D

Authors (Click on name to view author profile)

1. Desai, Shivani (Lehigh University, Chemical Engineering)
2. Carberry, Benjamin (University of Colorado at Boulder, Chemical Engineering)
3. Anseth, Kristi (University of Colorado, Boulder, Chemical engineering)
4. Schultz, Kelly M. (Lehigh University, Chemical and Biomolecular Engineering)

Author and Affiliation Lines (in printed abstract book)
Shivani Desai¹, Benjamin Carberry², Kristi Anseth² and Kelly M. Schultz^1
1Chemical and Biomolecular Engineering, Lehigh University, Bethlehem, PA 18015; ²Chemical Engineering, University of Colorado at Boulder, Boulder, CO

Speaker / Presenter 
Desai, Shivani

Keywords
experimental methods; biological materials; gels

Text of Abstract
Different types of cells have been shown to play an important role in repairing tissues during processes such as wound healing and tissue regeneration. Synthetic scaffolds are being developed as 3D cell culture platforms, which can be implanted into the body to deliver additional cells and enhance natural repair. Covalent adaptable networks have emerged as promising candidates for 3D cell culture platforms. These networks have adaptable cross-links that can break and reform in response to external stimuli, such as pH and shear. The ability to rearrange cross-links enables these networks to relax stress when encapsulated cells apply force to the network. This dynamic rearrangement mimics the native extracellular matrix (ECM) and permits complex cell functions including differentiation, spreading and proliferation. In this study, adaptable thioester networks are formed by photopolymerizing 8-arm PEG-thiol and PEGthioester di-norbornene. These thioester networks undergo rearrangement when excess thiols are available in the network. To design thioester networks for cell delivery applications, we first vary the amount of excess thiol in the network and use bulk rheology to measure stress relaxation of the networks. We then characterize network degradation with 100% excess thiol at physiological pH with multiple particle tracking microrheology (MPT). MPT measures Brownian motion of fluorescent probe particles embedded in the material and characterizes microstructural changes in the material. Using time-cure superposition we determine the critical relaxation exponent, n, which defines the sol-gel phase transition and also provides information about network connectivity. These results indicate that rearrangement causes phase transitions in the network over time. This work quantifies dynamic structural properties of thioester networks which informs the design of these scaffolds for specific tissue engineering applications and enhanced cell delivery.