Single Emulsion Method Research Articles

Vitamin A microencapsulation within poly(methyl methacrylate)‐g‐polyethylenimine microspheres: Localized proton buffering effect on vitamin A stability

AbstractTo stabilize vitamin A in a cosmetic/dermatological formulation, we present here a new encapsulation method based on polymer microspheres having a localized “proton‐buffering” capacity. Poly(methyl methacrylate)‐g‐polyethylenimine (PMMA‐g‐PEI) was prepared by direct condensation grafting of PEI onto poly(methyl methacrylate‐co‐methyl acrylic acid). The reaction was confirmed by FT‐IR analysis showing the amide vibration at 1,550 cm−1. Elemental analysis indicated that the weight content of the grafted PEI was 1.6% (w/w). Vitamin A was encapsulated into PMMA‐g‐PEI microspheres by using an oil‐in‐water (O/W) single emulsion method. The presence of PEI moiety dramatically improved the chemical stability of vitamin A in microspheres. Vitamin A encapsulated within PMMA‐g‐PEI microspheres maintained 91% of its initial activity after 30‐day incubation at 40°C, while only maintaining 60% within plain PMMA microspheres. This study demonstrates that proton‐buffering within hydrophobic polymer matrix is a useful strategy for stabilizing “acid‐labile” active ingredients. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 517–522, 2004

PDLLA microspheres containing steroids: Spray-drying, o/w and w/o/w emulsifications as preparation methods

Hydrocortisone and its more soluble ester, hydrocortisone 21-a-cetate, have been incorporated into poly(D,L-lactic) acid (PDLLA) microspheres using single, double emulsion/solvent evaporation and by spray-drying techniques. This paper describes the characterization of the microparticles obtained (morphology, particle size distribution, drug content, yield of production, in vitro drug release behaviour) and a comparison of the results (drug loading, drug release, size of the microspheres) obtained from the different techniques used. These results demonstrate that by using a relatively more soluble ester of an insoluble steroid, hydrocortisone, the drug content within the microspheres can be increased, together with a high efficiency of loading, irrespective of the technique employed. In the case of hydrocortisone, spray-drying produces the highest loading and encapsulation eficiency compared to both single and double emulsion methods for microspheres of similar size (about 2–4—m) and suitable for lung delivery, but with lower yields (about 55% versus about 33%).