Figure 4.

Click chemistry has been used to concentrate systemic drugs at the site of interest,^25,95 which can be accomplished in several ways. (Top) Hydrogels functionalized with a molecule such as DBCO can be injected into a localized tissue site. Subsequent injection with azide-tagged therapeutics enables concentration at the hydrogel site via the click reaction. (Bottom) Cells can also be labeled with azide groups to directly target the cells themselves. Subsequent injection with therapeutics labeled with the complimentary click group, in this case DBCO, results in concentration at the membranes of the cells expressing azides followed by subsequent uptake. (A color version of this figure is available in the online journal.)