Impact of different tissue-simulating hydrogel compartments on in vitro release and distribution from drug-eluting stents.

In vitro drug release testing is an appropriate approach to identify critical parameters helping to predict drug release from drug-eluting stents (DES) prior to studying drug release behavior under in vivo conditions. Drug release and distribution from DES coated with a fluorescent model substance were studied in vitro using the vessel-simulating flow-through cell equipped with different long-term stable hydrogel compartments composed of agarose, polyacrylamide or poly(vinyl alcohol). The obtained experimental results were compared with the results of finite-element modeling obtained using experimentally determined diffusion coefficients and partition coefficients. In spite of differences regarding these parameters, experimental and mathematical data yielded only minor differences between the different gels regarding the release and distribution behavior and reasonable agreement between the modeling and the experiment was obtained. In an attempt to further elucidate the dosage form behavior, the diffusion coefficients in the gel as well as in the stent coating were systematically varied in the finite-element model. Changes in the diffusivity in the stent coating mainly impacted on the initial concentrations. Slower diffusion inside the hydrogel yielded a retarded elution from the stent coating and a higher model substance accumulation in the gel compartment at late time points.