Silk Microspheres Prepared by Spray-drying of an Aqueous System

Scoured silk fibre was dissolved in a solution of calcium chloride in water and ethanol. After dialysis against purified water, theophylline as model drug was added to the solution. Silk microspheres prepared after spray-drying were round but somewhat wrinkled; their diameter was 5 μm (approx.). According to powder X-ray diffractometry, and FTIR and Raman spectroscopy, fibroin and theophylline were amorphous in the microsphere. The microspheres formed gels immediately after soaking in purified water and in Japanese Pharmacopoeia XIII solutions 1 (pH 1.2) and 2 (pH 6.8); the gels dissolved slightly in these aqueous media. In this way we have developed a new drug carrier for sustained release without the use of poisonous organic solvents or glutaraldehyde.