title: Mixed Reversible Covalent Crosslink Kinetics Enable Precise, Hierarchical Mechanical Tuning of Hydrogel Networks.
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 pKadifferences 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.
authors.affiliation: David H. Koch Institute for Integrative Cancer Research, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA.|Department of Anesthesiology, Boston Children's Hospital, Boston, MA, 02115, USA.
authors.forename: Volkan
authors.initials: V
authors.lastname: Yesilyurt
authors.affiliation: David H. Koch Institute for Integrative Cancer Research, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA.|Program in Speech and Hearing Bioscience and Technology, Division of Medical Sciences, Harvard Medical School, Boston, MA, 02115, USA.|Center for Biomedical Engineering, Charles Stark Draper Laboratory, Cambridge, MA, 02139, USA.
authors.forename: Andrew M
authors.initials: AM
authors.lastname: Ayoob
authors.affiliation: David H. Koch Institute for Integrative Cancer Research, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA.
authors.forename: Eric A
authors.initials: EA
authors.lastname: Appel
authors.affiliation: Center for Biomedical Engineering, Charles Stark Draper Laboratory, Cambridge, MA, 02139, USA.
authors.forename: Jeffrey T
authors.initials: JT
authors.lastname: Borenstein
authors.affiliation: David H. Koch Institute for Integrative Cancer Research, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA.|Department of Anesthesiology, Boston Children's Hospital, Boston, MA, 02115, USA.|Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA.|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.
authors.forename: Robert
authors.initials: R
authors.lastname: Langer
authors.affiliation: David H. Koch Institute for Integrative Cancer Research, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA.|Department of Anesthesiology, Boston Children's Hospital, Boston, MA, 02115, USA.|Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA.|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.
authors.forename: Daniel G
authors.initials: DG
authors.lastname: Anderson
keywords: Maxwell elements; boronic acids; dynamic covalent bonds; self-healing; stress relaxation