Nanocontainers formed by self-assembly of poly(ethylene oxide)-b-poly(glycerol monomethacrylate) -: Drug conjugates

The synthesis, self-assembly behavior, and delivery properties of poly(ethylene oxide)-b-poly(glycerol monomethacrylate)- (PEO-b-PG2MA-) drug conjugates is herein described. Double hydrophilic PEO-b-PG2MA copolymers synthesized by atom transfer radical polymerization (ATRP), using a PEO-based macroinitiator, were used for post-polymerization conjugation to the hydrophobic nonsteroidal anti-inflammatory agent indomethacin (IND). IND contents ranging from 15 to 49% w/w(p) were attached to the same polymer precursor via Steglich esterification, leading to amphiphilic block copolymer-drug conjugates (PEO-b-(PG2MA-IND)). Dynamic light scattering (DLS) and transmission electron microscopy (TEM) experiments revealed that PEO-b-(PG2MA-IND) copolymer chains self-assemble into spherical nanoparticles in water, whose hydrodynamic size (2R(H) = 24-100 nm) and morphology (micelles or vesicles) are dictated by both the amount of IND and the PG2MA block length. Interestingly, such a particular system was also proven to be able to stabilize, transport and deliver physically encapsulated (free) IND (F-IND). The maximum F-IND loadings ranged from 13 to 20% w/w(p), thus reaching remarkable IND payloads (i.e., covalently bound B-IND + physically entrapped F-IND) as high as 58% w/w(p). However, self-organization for F-IND loaded samples with more than 50% w/w(p) IND originated vesicular morphologies instead of micelles and provoked a huge increase in the size of the objects. The release of IND is a pH-dependent process, which is governed by intrinsic molecular characteristics of F-IND (aqueous dissociation behavior) and pH-sensitivity of ester linkages in the conjugates. At approximately neutral pH, the ester bound linkages are stable and the diffusion of F-IND out of the carrier is favored, whereas sustained release with slow kinetics takes place under acidic pH conditions.