Solid lipid microparticles (SLM) containing juniper oil as anti-acne topical carriers: preliminary studies

Solid lipid microparticles (SLM) were used as carriers of juniper oil and proposed for the topical treatment of acne vulgare. The formulations were obtained by the o/w emulsification method. Compritol and Precirol were employed as lipidic materials. Emulsions containing 1.5% (w/w) of lipophilic phase (lipid and oil) and two different lipid to oil ratios (1:1 and 2:1) were prepared. Blank particles were also prepared, as a comparison. The SLM were characterized in terms of encapsulation efficiency, size, and morphology. The particle size stability in aqueous dispersions was monitored over one month. Evaporation of volatile compounds of oil from microparticles by weight loss was investigated. The qualitative composition of Juniper oil before and after the encapsulation process was determined by gas chromatography (GC) and gas chromatography/mass spectrum (GC/MS) analyses. The antimicrobial activity of the oil encapsulated into the lipid microparticles against P. acnes was studied as contact time assay and compared to the activity of the oil not encapsulated. The emulsification method here described was a good technique for the encapsulation of essential oils. Percentage yields of production and encapsulation efficiencies were higher for Compritol preparations than for these prepared using Precirol. All preparations were characterized by similar particle size distributions (dvs about 3-4 microm) regardless of lipid type and lipid to oil ratios. Microscopy observations showed that the microparticles in aqueous dispersions had almost spherical shape, independently from their composition. The scanning electron microscopy (SEM) analyses showed that when the particles were dried, they had an irregular shape and a rough surface. The SLM dispersions based on Compritol revealed particle size stability over the investigated period of 30 days. In contrast, an increase of the mean dimensions in the preparations containing Precirol was observed. A low loss of volatile oil compounds owing to evaporation from dry particles was found in all preparations. This indicated that the microparticles were able to substantially maintain the oil loaded inside their lipidic structure, reducing its volatility. Some modifications of composition were found in the oil encapsulated in SLM with respect to the juniper oil raw material, but these modifications did not decrease the antibacterial activity of the oil. The SLM here described are promising carriers for the development of anti-acne topical formulations containing Juniper oil.