Abstract
Hydrogels with photo-responsive mechanical properties have found broad biomedical applications, including delivering bioactive molecules, cell culture, biosensing, and tissue engineering. Here, using a photocleavable protein, PhoCl, as the crosslinker we engineer two types of poly(ethylene glycol) hydrogels whose mechanical stability can be weakened or strengthened, respectively, upon visible light illumination. In the photo weakening hydrogels, photocleavage leads to rupture of the protein crosslinkers, and decrease of the mechanical properties of the hydrogels. In contrast, in the photo strengthening hydrogels, by properly choosing the crosslinking positions, photocleavage does not rupture the crosslinking sites but exposes additional cryptical reactive cysteine residues. When reacting with extra maleimide groups in the hydrogel network, the mechanical properties of the hydrogels can be enhanced upon light illumination. Our study indicates that photocleavable proteins could provide more designing possibilities than the small-molecule counterparts. A proof-of-principle demonstration of spatially controlling the mechanical properties of hydrogels was also provided.
Highlights
In the Pho-Weak mutant, one of the cysteine residues is at the 54th position, while the other is attached to the C-terminal end (Figure 1A and Supplementary Figure 1)
We explore the use of light to control the mechanical properties of PhoCl-polyethylene glycol (PEG) hydrogels in 2D
Here we demonstrated the use of a photocleavable protein, PhoCl, as crosslinkers, and multiple-armed PEG as backbones to prepare photo-responsive hydrogels
Summary
Photo-switchable proteins have been widely used in many fields, including super resolution imaging, optogenetics, fluorescent sensors, and recently as switchable crosslinkers for the engineering of photo-responsive hydrogels (Christie, 2007; Rogan and Roth, 2011; Shcherbakova et al, 2012, 2015; Nienhaus and Nienhaus, 2014; Guntas et al, 2015; Koetting et al, 2015; Niopek et al, 2016; Coquelle et al, 2018). Comparing to other environment-responsive hydrogels, photoresponsive hydrogels have drawn considerable interest (Murphy et al, 2007; Yuan et al, 2008; Gillette et al, 2010; Patterson and Hubbell, 2010; Davis et al, 2011; Yoshikawa et al, 2011; Burdick and Murphy, 2012; Stowers et al, 2015; Abdeen et al, 2016; Han and Lin, 2016), because their mechanical properties can be remotely and non-invasively controlled upon light illumination (Kloxin et al, 2009; Guvendiren and Burdick, 2012; Rosales et al, 2015; Kim et al, 2019; Nowak and Ravoo, 2019; Wu et al, 2019). Generally, most photo-responsive hydrogels are based on the switch between oligomeric and monomeric states of proteins upon light illumination. For example, the reversible change between tetramers and monomers of Dronpa145N can lead to photo-controlledPhoto-Responsive Hydrogels gel-sol transition or reversible change of the stiffness of the hydrogels (Lyu et al, 2017; Xin et al, 2017). Similarly, the switch between dimeric and monomeric states of cyanobacterial phytochrome 1 can lead to the reversible softening and strengthening of the hydrogels, which allowed dynamic control of the migration of immune cells and mechanotransduction of stem cells (Hörner et al, 2019). The change between dimeric and monomeric states of UVR8-1 led to the design of hydrogels for photo-controlled protein delivery and cell separation (Zhang et al, 2015). Green light induced tetrameric to monomeric transition of the C-terminal adenosylcobalamin binding domain (CarHC) can cause the dissolution of the hydrogels for the stem cell/protein release (Wang et al, 2017). Recently, it was shown that the photo-induced conformational change of LOV2 domains can be used to dynamically control the mechanical properties of the corresponding proteins (Liu et al, 2018). This method is unique in that it does not involve oligomeric photo-switchable proteins but utilize the change of crosslinker length. It is desirable to explore new operation mode of photo-controllable hydrogels based on photo-responsive proteins.
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