Controlled release of testosterone and estradiol-17 β from biodegradable cylinders
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A controlled release device for the hormones, testosterone and estradiol-17 β, was developed by coating a melt extruded hormone/poly (ϵ-caprolactone) cylinder with pure polylactide. Since testosterone and estradiol-17β have much higher permeabilities in poly (ϵ-caprolactone) than in polylactide, they primarily permeate through the open ends of the cylinder, with little release through the polylactide wall. By changing the cylinder length, the release rate and duration could be adjusted. The release followed Pick's diffusion equation for a drug loading below its solubility in poly (ϵ-caprolactone) or Higuchi's equation for a drug loading above the solubility. The diffusion coefficients of testosterone and estradiol-17β in poly (ϵ-caprolactone) were estimated as (8.31 ±3.12) × 10−18 and (0.728 ± 0.250) × 10−18 cm2/s, respectively.