Bioresorbable polyelectrolyte amphiphiles as nanosized carriers for lipophilic drug solubilization and delivery

Starting from drug carriers and drug-delivery systems described in the literature, this article examines more specifically those that are relevant to the field of nanocarriers composed of a degradable hydrophilic polyelectrolyte backbone with pendent hydrophobes arranged to form comb-like co-polymers. Advantage is taken of the nanosized, lipophilic pocket-bearing multimolecule aggregates formed in aqueous media by such amphiphilic polyelectrolytes to accommodate water-insoluble drug molecules according to a phenomenon named macromolecular microencapsulation. Comments are also made on the criteria to be fulfilled by nanosized polymeric drug carriers. These carriers require a size or molar mass high enough to avoid renal excretion and thus be retained in the body for longer periods of time than the free drug. Since they nevertheless have to be eliminated from the body (bioresorption), they must be degraded at the end of use. In situ degradation is an important criterion that is taken into account by using special polyelectrolytes that belong to the class of the so-called "artificial biopolymers". Artificial biopolymers are made of pro-metabolite units than generate metabolite upon degradation, thus resulting in metabolisation of degradation end-products if intermediates are not excreted before. Aggregates of amphiphilic polyanions derived from malic acid, citric acid, L-lysine and L-serine are presented to support the concept of macromolecular microencapsulation. Comparison is made with non-polyelectrolytic systems with similar structures.