Design of block-copolymer-based micelles for active and passive targeting

A self-consistent field study is presented on the design of active and passive targeting block-copolymeric micelles. These micelles form in water by self-assembly of triblock copolymers with a hydrophilic middle block and two hydrophobic outer blocks. A minority amount of diblock copolymers with the same chemistry is taken to coassemble into these micelles. At the end of the hydrophilic block of the diblock copolymers, a targeting moiety (TM) is present. Assuming that the rotation of the micelle towards the target is sufficiently fast, we can elaborate a single gradient cell model, wherein the micelle is in the center and the receptor (R) substrate exists on the outer plane of the spherical coordinate system. The distribution function of the targeting moiety corresponds to a Landau free energy with local minima and corresponding maxima. The lowest minimum, which is the ground state, shifts from within the micelle to the adsorbing state upon bringing the substrate closer to the micelle, implying a jumplike translocation of the targeting moiety. Equally deep minima represent the binodal of the phase transition, which is, due to the finite chain length, first-order like. The maximum in-between the two relevant minima implies that there is an activation barrier for the targeting moiety to reach the receptor surface. We localize the parameter space wherein the targeting moiety is (when the micelle is far from the target) preferably hidden in the stealthy hydrophilic corona of the micelle, which is desirable to avoid undesired immune responses, and still can jump out of the corona to reach the target quick enough, that is, when the barrier height is sufficiently low. The latter requirement may be identified by a spinodal condition. We found that such hidden TMs can still establish a TM-R contact at distances up to twice the corona size. The translocation transition will work best when the affinity of the TM for the core is avoided and when hydrophilic TMs are selected.