I've been preparing the ocular film (0.5 cm x 0.5 cm) of Prednisolone sodium phosphate based on polyvinyl alcohol (PVA). When I prepared the blank film using PVA, it was totally transparent with adequate mechanical strength. As soon as I added the API (7mg/film), the film had crystalline edges and it adhered to the surface tightly after drying. It was really difficult to peel the film and was too brittle. Both PVA and API are freely soluble in water; thus distilled water was used as the solvent system. The solubility of Prednisolone sodium phosphate is around 250mg/ml. When I prepared the total volume 5 ml, it had 151.2 mg of API on it. What might be the reasons for crystal formation and brittle nature of the film? I would really appreciate your answer. Thank you.
The reason maybe inhomogeneous distribution of the components across the film. During drying the API maybe segregating to the edge via a combination of crystallization and coffee ring effect observed in evaporating drops
The edge appears to be related to the "coffee ring effect" where the accumulation of PVA or PVA/API composites lead to the formation of the edges. If it is too brittle, try a few freeze thaw cycles to induce the crystalite formation in PVA.
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