Authors: Cole A. DeForest and Kristi S. Anseth
Journal: Angewandte Chemie International Edition
Affiliation: Chemical & Biological Engineering, University of Colorado and the Howard Hughes Medical Institute
Hydrogels have become an important category of materials for studying cell growth and development. Scientists are able to control a variety of their properties and also introduce biochemical epitopes that allow control over the cellular environment and stimuli. In this paper the authors combine two different chemical reactions in order to reversibly control the presence of a stimulus. Additionally, they use their system to create gradients of biological cues within a hydrogel.
In order to construct this system, the authors take advantage of two chemical reactions that are known to be biocompatible and also controllable by the presence of certain wavelengths of light – the reaction of a carbon-carbon double bond and a thiol (controlled by a photoinitiator) and the degradation of an o-nitrobenzyl ether using UV light. They synthesized a molecule that contained both groups and has biological relevance using solid-phase peptide synthesis.
The authors synthesized a hydrogel that had alkenes available to react with the thiols in the peptide they synthesized. They introduced the peptide into the hydrogel during swelling and the amount of peptide attached to the hydrogel was controlled by the length of exposure to the light or the concentration of the photoinitiator.
They were able to attach peptides in concentrations that are biologically relevant. The authors could then expose the gel to a different wavelength of light that cleaves the o-nitrobenzyl ether which allows for the release of the peptide. The authors showed that the cleavage follows a first order degradation and determined the rate constant. Using this data they were able to determine that more than 97% of the peptide is removed after ten minutes of exposure to 20 mW cm-2 of light. With this information it is possible to calculate the amount of peptide released at a given length of irradiation.
Additionally, the researchers were able to control where the peptide adhered to the gel using masked light. They were able to pattern the gels both two dimensionally and three dimensionally, creating a double helix of attached peptide with the ability to selectively remove one helix by controlling the cleavage reaction. In addition to this type of patterning, they were also able to create gradients of peptide within the gel.
The authors also conducted cell studies in which they demonstrated their ability to control the adhesion of cells using their new synthetic tools. They predict that they will be able to develop a deeper understanding of how cells interact with the extracellular matrix and further cell-delivery techniques that can be used in regenerative medicine.