Fig. 2. Polymer nanoparticle (PNP) hydrogel formulation and rheological properties. (a) PNP hydrogels are dynamic networks formed from supramolecular interactions between a dodecyl-modified (hydroxypropyl)methyl cellulose (HPMC-C12) network and self-assembled nanoparticles composed of poly(ethylene glycol)-block-poly(lactic acid) (PEG-PLA) block copolymers. Drug cargo can be easily loaded into the hydrogel by incorporation into the buffer. Formulation nomenclature is denoted by network polymer wt%: nanoparticle wt%. (b) Gelation occurs by physically mixing stock solutions of the polymer and nanoparticles to form a homogeneous hydrogel (nanoparticle solution artificially colored blue). (c) Storage (G′) and loss (G′′) moduli and (d) viscosity as a function of shear rate were measured for two different PNP formulations (data adapted from Meis, et al.27). (e) A 2:10 PNP hydrogel is injected through a 21G needle and rapidly forms a robust depot upon injection. (f) Step shear tests were performed by alternating between low (0.1 rad s−1) and high (10 rad s−1) shear rates after preconditioning for 90 seconds. (g) Yield stresses (indicated by dotted lines) were determined from a stress-controlled sweep.
