Near-infrared responsive three-component supramolecular hydrogels of peptide, agarose and upconversion nanoparticles.

Self-assembled, low molecular weight hydrogels are of particular interest for the development of responsive materials because they exhibit tunable viscoelasticity, high water content, and shear-thinning behavior, which make them suitable for various applications as biomimetic materials. Moreover, such hydrogels are quite easy to prepare. Here, a three-component gel is prepared by adding the peptide AAP-FGDS to an agarose polymer network. The photoresponsive peptide hydrogel exhibits excellent reversible properties. The photoisomerization of the peptide is enabled by lanthanide-doped upconversion nanoparticles (UCNP) added as a third component in the gel. UCNP can convert excitation in the near infrared (NIR) range into emission of higher energy through the process of upconversion. Irradiation with an NIR laser dissolves the self-assembled three-dimensional network structure of the peptide, resulting in a softer hydrogel. The three-component supramolecular gel can potentially be used for in vivo applications considering the fact that (unlike harmful UV light) NIR light can penetrate deeply into tissue.