Liposomes are lipid-based delivery systems that can improve the delivery and bioavailability of incorporated drugs, particularly those with poor water solubility. One of the drawbacks, however, is the limited physical and chemical stability of liposomes in aqueous dispersions. Their stability can be improved by converting them into a dry form by spray drying, with the addition of sugars as protective agents.
Liposomes were prepared from hydrogenated soy phosphatidylcholine and cholesterol using the thin-film method. Our goal was to investigate whether the preparation could be transferred from a small scale to a five-fold larger scale while maintaining the ratios of the input components before converting the dispersions into a stable dry powder by spray drying using lactose, trehalose, or sucrose.
Liposomes were evaluated before and after drying by measuring vesicle size, polydispersity index, and zeta potential, while the size distribution of the dry particles was determined by laser diffraction. Scaling up did not substantially alter the properties of the vesicles, confirming the successful transfer of the procedure. Despite their nearly neutral surface charge, the dispersions remained physically stable for at least 24 hours.
Among the three tested sugars, lactose and trehalose provided good protection of the vesicles during spray drying, as the liposomes returned to the nanometre range with narrow size distribution after reconstitution. Sucrose proved unsuitable under the drying conditions used, which we attribute to its lower glass transition temperature compared with the other two sugars. The lipid-to-sugar ratio of 1:10 was determined to be the most suitable.
Subsequently, resveratrol, a lipophilic polyphenol with poor water solubility, was incorporated into the liposomes as a model drug. Its incorporation did not substantially change the vesicle size, while the trehalose formulation provided the highest drying yield and the lowest polydispersity index after reconstitution.
The results confirmed that liposomes can be prepared on a five-fold larger scale and converted by spray drying into a stable dry form with preserved vesicle properties after reconstitution, although not all sugars proved equally suitable under identical drying conditions.
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