Dynamic 3D Patterning of Biochemical Cues by using Photoinduced Bioorthogonal Reactions

Hydrogels: soft matters in photomedicine

Photodynamic therapy (PDT), a shining beacon in the realm of photomedicine, is a non-invasive technique that utilizes dye-based photosensitizers (PSs) in conjunction with light and oxygen to produce reactive oxygen species to combat malignant tissues and infectious microorganisms. Yet, for PDT to become a common, routine therapy, it is still necessary to overcome limitations such as photosensitizer solubility, long-term side effects (e.g., photosensitivity) and to develop safe, biocompatible and target-specific formulations. Polymer based drug delivery platforms are an effective strategy for the delivery of PSs for PDT applications. Among them, hydrogels and 3D polymer scaffolds with the ability to swell in aqueous media have been deeply investigated. Particularly, hydrogel-based formulations present real potential to fulfill all requirements of an ideal PDT platform by overcoming the solubility issues, while improving the selectivity and targeting drawbacks of the PSs alone. In this perspective, we summarize the use of hydrogels as carrier systems of PSs to enhance the effectiveness of PDT against infections and cancer. Their potential in environmental and biomedical applications, such as tissue engineering photoremediation and photochemistry, is also discussed.

Caged peptides to control enzymatic activity within hydrogel scaffolds

Enzyme-assisted 3D lithography: A peptide substrate for transglutaminase factor XIII (FXIIIa) can be caged with a photo-deprotectable group and immobilized to the hydrogel framework. The substrate can be decaged by using multiphoton light to anchor cell-signaling motifs in a spatial specific manner.

Sequential "click" - "photo-click" cross-linker for catalyst-free ligation of azide-tagged substrates

Heterobifunctional linker allows for selective catalyst-free ligation of two different azide-tagged substrates via strained-promoted azide-alkyne cycloaddition (SPAAC). The linker contains an azadibenzocyclooctyne (ADIBO) moiety on one end and a cyclopropenone-masked dibenzocyclooctyne (photo-DIBO) group on the other. The first azide-derivatized substrate reacts only at the ADIBO end of the linker as the photo-DIBO moiety is azide-inert. After the completion of the first SPAAC step, photo-DIBO is activated by brief exposure to 350 nm light from a fluorescent UV lamp. The unmasked DIBO group then reacts with the second azide-tagged substrate. Both click reactions are fast (k = 0.4 and 0.07 M(-1) s(-1), respectively) and produce quantitative yield of ligation in organic solvents or aqueous solutions. The utility of the new cross-linker has been demonstrated by conjugation of azide functionalized bovine serum albumin (azido-BSA) with azido-fluorescein and by the immobilization of the latter protein on azide-derivatized silica beads. The BSA-bead linker was designed to incorporate hydrolytically labile fragment, which permits release of protein under the action of dilute acid. UV activation of the second click reaction permits spatiotemporal control of the ligation process.

Porous alginate hydrogel functionalized with virus as three-dimensional scaffolds for bone differentiation

In regenerative medicine, a synthetic extracellular matrix is crucial for supporting stem cells during its differentiation process to integrate into surrounding tissues. Hydrogels are used extensively in biomaterials as synthetic matrices to support the cells. However, to mimic the biological niche of a functional tissue, various chemical functionalities are necessary. We present here, a method of functionalizing a highly porous hydrogel with functional groups by mixing the hydrogel with a plant virus, tobacco mosaic virus (TMV), and its mutant. The implication of this process resides with the three important features of TMV: its well-defined genetic/chemical modularity, its multivalency (TMV capsid is composed of 2130 copies of identical subunits), and its well-defined structural features. Previous studies utilizing the native TMV on two-dimensional supports accelerated mesenchymal stem cell differentiation, and surfaces modified with genetically modified viral particles further enhanced cell attachment and differentiation. Herein we demonstrate that functionalization of a porous alginate scaffold can be achieved by the addition of viral particles with minimal processing and downstream purifications, and the cell attachment and differentiation within the macroporous scaffold can be effectively manipulated by altering the peptide or small molecule displayed on the viral particles.