Controlled release from ordered microstructures formed by poloxamer block copolymers

The in vitro release kinetics of a low molecular weight hydrophilic drug from hydrogels consisting of Poloxamer poly(ethylene oxide)-poly(propylene oxide) block copolymer spherical micelles, and from tablets formulated from bulk (water-free) Poloxamer are reported. Sustained drug release has been achieved. Our experiments showed the drug release kinetics to depend on two contributions: (i) diffusion of the drug molecules through the water channels present in the gel microstructure (∼√t), and (ii) release concurrent with the erosion/ dissolution of the Poloxamer gel matrix (∼t). The drug release profiles determined experimentally for Poloxamer hydrogels were fitted to an equation which included both a diffusion and an erosion term. The two contributions were quantified and were correlated to the apparent diffusion coefficient of the drug in the gel matrix and to the erosion rate of the gel matrix. The matrix erosion rate was measured independently, and the drug released due to the erosion effect was thus estimated. The release of hydrophilic drug from Poloxamer tablets followed closely the erosion mechanism (zero order release kinetics), however, the diffusion mechanism was still active due to the formation of a thin hydrogel layer at the tablet surface. The interplay between the self-assembled microstructures present in Poloxamer block copolymer hydrogels and the drug molecules can be utilized in controlled delivery applications.