Mixed Reversible Covalent Crosslink Kinetics Enable Precise, Hierarchical Mechanical Tuning of Hydrogel Networks

Volkan Yesilyurt; Andrew M Ayoob; Eric A Appel; Jeffrey T Borenstein; Robert Langer; Daniel G Anderson

doi:10.1002/adma.201605947

Mixed Reversible Covalent Crosslink Kinetics Enable Precise, Hierarchical Mechanical Tuning of Hydrogel Networks

Adv Mater. 2017 May;29(19). doi: 10.1002/adma.201605947. Epub 2017 Mar 15.

Authors

Volkan Yesilyurt^{1

2}, Andrew M Ayoob^{1

3

4}, Eric A Appel¹, Jeffrey T Borenstein⁴, Robert Langer^{1

2

5

6}, Daniel G Anderson^{1

2

5

6}

Affiliations

¹ David H. Koch Institute for Integrative Cancer Research, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA.
² Department of Anesthesiology, Boston Children's Hospital, Boston, MA, 02115, USA.
³ Program in Speech and Hearing Bioscience and Technology, Division of Medical Sciences, Harvard Medical School, Boston, MA, 02115, USA.
⁴ Center for Biomedical Engineering, Charles Stark Draper Laboratory, Cambridge, MA, 02139, USA.
⁵ Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA.
⁶ Harvard-Massachusetts Institute of Technology Division of Health Sciences and Technology, Institute for Medical Engineering and Science, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA.

PMID: 28295624
DOI: 10.1002/adma.201605947

Abstract

Hydrogels play a central role in a number of medical applications and new research aims to engineer their mechanical properties to improve their capacity to mimic the functional dynamics of native tissues. This study shows hierarchical mechanical tuning of hydrogel networks by utilizing mixtures of kinetically distinct reversible covalent crosslinks. A methodology is described to precisely tune stress relaxation in PEG networks formed from mixtures of two different phenylboronic acid derivatives with unique diol complexation rates, 4-carboxyphenylboronic acid, and o-aminomethylphenylboronic acid. Gel relaxation time and the mechanical response to dynamic shear are exquisitely controlled by the relative concentrations of the phenylboronic acid derivatives. The differences observed in the crossover frequencies corresponding to pK_a differences in the phenylboronic acid derivatives directly connect the molecular kinetics of the reversible crosslinks to the macroscopic dynamic mechanical behavior. Mechanical tuning by mixing reversible covalent crosslinking kinetics is found to be independent of other attributes of network architecture, such as molecular weight between crosslinks.

Keywords: Maxwell elements; boronic acids; dynamic covalent bonds; self-healing; stress relaxation.