Gelatin Nano-coating for Inhibiting Surface Crystallization of Amorphous Drugs


Inhibit the fast surface crystallization of amorphous drugs with gelatin nano-coatings.



The free surface of amorphous films of indomethacin or nifedipine was coated by a gelatin solution (type A or B) and dried. The coating’s effect on surface crystallization was evaluated. Coating thickness was estimated from mass change after coating.



For indomethacin (weak acid, pKa = 4.5), a gelatin coating of either type deposited at pH 5 and 10 inhibited its fast surface crystal growth. The coating thickness was 20 ± 10 nm. A gelatin coating deposited at pH 3, however, provided no protective effect. These results suggest that an effective gelatin coating does not require that the drug and the polymer have opposite charges. The ineffective pH 3 coating might reflect the poor wetting of indomethacin’s neutral, hydrophobic surface by the coating solution. For nifedipine (weak base, pKa = 2.6), a gelatin coating of either type deposited at pH 5 inhibited its fast surface crystal growth.



Gelatin nano-coatings can be conveniently applied to amorphous drugs from solution to inhibit fast surface crystallization. Unlike strong polyelectrolyte coatings, a protective gelatin coating does not require strict pairing of opposite charges. This could make gelatin coating a versatile, pharmaceutically acceptable coating for stabilizing amorphous drugs.

Electro microscope pictures of coated and uncoated crystals
(a)Crystalgrowthonthe free surface of amorphous IMC at 313K.(b)Sameas(a),buta10nm thick gold coating was applied to the surface of IMC at time zero. Under the same condition, no crystal growth was observed.

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