Photoresponsive hydrogel networks using melanin nanoparticle photothermal sensitizers

Photoreconfigurable and photodegradable polymeric networks have broad utility as functional biomaterials for many applications in medicine and biotechnology. The vast majority of these functional polymers are synthesized using chemical moieties that may be cytotoxic in vivo. Materials synthesized from these substituents also pose unknown risk upon implantation and thus will encounter significant regulatory challenges prior to use in vivo. This work describes a strategy to prepare photodegradable hydrogel networks that are composed of well-characterized synthetic polymers and natural melanin pigments found within the human body. Self-assembled networks of poly(l-lactide-co-glycolide)-poly(ethylene glycol) ABA triblock copolymers are doped with melanin nanoparticles to produce reconfigurable networks based on photothermal phase transitions. Self-assembled hydrogel networks with melanin nanoparticles exhibit a storage modulus ranging from 1.5 ± 0.6 kPa to 8.0 ± 7.5 kPa as measured by rheology. The rate of UV-induced photothermal heating was non-monotonic and varied as a function of melanin nanoparticle loading. A maximum steady state temperature increase of 20.5 ± 0.30 °C was measured. Experimental heating rates were in close agreement with predictions based on attenuation of light in melanins via photothermal absorption and Mie scattering. The implications of melanin nanoparticles on hydrogel network formation and light-induced disintegration were also characterized by rheology and dynamic light scattering. Taken together, this class of photoreconfigurable hydrogels represents a potential strategy for photodegradable polymers with increased likelihood for clinical translation.