Enhanced release of small molecules from near-infrared light responsive polymer-nanorod composites.

Stimuli-responsive materials undergo structural changes in response to an external trigger (i.e., pH, heat, or light). This process has been previously used for a range of applications in biomedicine and microdevices and has recently gained considerable attention in controlled drug release. Here, we use a near-infrared (NIR) light responsive polymer-nanorod composite whose glass transition temperature (T(g)) is in the range of body temperature to control and enhance the release of a small-molecule drug (<800 Da). In addition to increased temperature and resulting changes in molecule diffusion, the photothermal effect (conversion of NIR light to heat) adjusts the composite above the T(g). Specifically, at normal body temperature (T < T(g)), the structure is glassy and release is limited, whereas when T > T(g), the polymer is rubbery and release is enhanced. We applied this heating system to trigger release of the chemotherapeutic drug doxorubicin from both polymer films and microspheres. Multiple cycles of NIR exposure were performed and demonstrated a triggered and stepwise release behavior. Lastly, we tested the microsphere system in vitro, reporting a ∼90% reduction in the activity of T6-17 cells when the release of doxorubicin was triggered from microspheres exposed to NIR light. This overall approach can be used with numerous polymer systems to modulate molecule release toward the development of unique and clinically applicable therapies.