Hydrogel drug delivery platforms are the subject of a robust and burgeoning industry. In 2021, hydrogel-based drug delivery commanded a 6.4-billion-dollar market that is projected to grow to 10.4 billion by 2027. Drug release from hydrogels is mainly dictated by the tunable network pore size relative to the size of the cargo and thus, occurs passively. Stimuli-responsive hydrogels offer great advantages as they respond to various external environmental cues. Light is a particularly attractive stimulus as it affords spatiotemporal control over the release of cargo from hydrogels. Herein, we describe photo-responsive, oligoviologen-crosslinked hydrogels (Fig. 1) in which negatively charged molecular cargo was loaded electrostatically and released on command through a photoinduced electron-transfer (PET) process involving photoirradiation of an integrated Aza-BODIPY photocatalyst with red light (660 nm). The photoexcited Aza-BODIPY then transfers an electron to the oligoviologen-based crosslinkers, resulting in a one-electron reduction of the viologen subunits (V2+ to V●+). This reversible V2+ to V●+ transition has been leveraged in various applications such as electrochromism, molecular machines, etc., however, in our functional materials, the Aza-BODIPY is regenerated by a sacrificial reductant, triethanolamine (TEOA), and the anionic cargo is free to diffuse away as a TEOA radical cation salt. At the end of this PET cycle, the viologen radical cation is reoxidized back to its dicationic oxidation state upon exposure to ambient O2. Over time, with constant irradiation, this dynamic photoredox process results in continuous viologen reduction/oxidation, and the release of the cargo in its entirety is possible. In my presentation, I will discuss our efforts to apply this unique photoredox-based method of cargo release in the context of antimicrobial applications.

Electrostatic loading and photoredox-based release of antibiotics from oligoviologen-crosslinked hydrogels using red light and a BODIPY photocatalyst

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