Citronella oil (CO) has been reported to possess a mosquito-repellent action. However, its application in
topical preparations is limited due to its rapid volatility. The objective of this study was therefore to
reduce the rate of evaporation of the oil via microencapsulation. Microcapsules (MCs) were prepared
using gelatin simple coacervation method and sodium sulfate (20%) as a coacervating agent. The MCs
were hardened with a cross-linking agent, formaldehyde (37%). The effects of three variables, stirring
rate, oil loading and the amount of cross-linking agent, on encapsulation efficiency (EE, %) were studied.
Response surface methodology was employed to optimize the EE (%), and a polynomial regression model
equation was generated. The effect of the amount of cross-linker was insignificant on EE (%). The response
surface plot constructed for the polynomial equation provided an optimum area. The MCs under the optimized
conditions provided EE of 60%. The optimized MCs were observed to have a sustained in vitro
release profile (70% of the content was released at the 10th hour of the study) with minimum initial burst
effect. Topical formulations of the microencapsulated oil and non-microencapsulated oil were prepared
with different bases, white petrolatum, wool wax alcohol, hydrophilic ointment (USP) and PEG ointment
(USP). In vitro membrane permeation of CO from the ointments was evaluated in Franz diffusion cells
using cellulose acetate membrane at 32 C, with the receptor compartment containing a water–ethanol
solution (50:50). The receptor phase samples were analyzed with GC/MS, using citronellal as a reference
standard. The results showed that microencapsulation decreased membrane permeation of the CO by at
least 50%. The amount of CO permeated was dependent on the type of ointment base used; PEG base
exhibited the highest degree of release. Therefore, microencapsulation reduces membrane permeation
of CO while maintaining a constant supply of the oil.
Citronella oil (CO) has been reported to possess a mosquito-repellent action. However, its application intopical preparations is limited due to its rapid volatility. The objective of this study was therefore toreduce the rate of evaporation of the oil via microencapsulation. Microcapsules (MCs) were preparedusing gelatin simple coacervation method and sodium sulfate (20%) as a coacervating agent. The MCswere hardened with a cross-linking agent, formaldehyde (37%). The effects of three variables, stirringrate, oil loading and the amount of cross-linking agent, on encapsulation efficiency (EE, %) were studied.Response surface methodology was employed to optimize the EE (%), and a polynomial regression modelequation was generated. The effect of the amount of cross-linker was insignificant on EE (%). The responsesurface plot constructed for the polynomial equation provided an optimum area. The MCs under the optimizedconditions provided EE of 60%. The optimized MCs were observed to have a sustained in vitrorelease profile (70% of the content was released at the 10th hour of the study) with minimum initial bursteffect. Topical formulations of the microencapsulated oil and non-microencapsulated oil were preparedwith different bases, white petrolatum, wool wax alcohol, hydrophilic ointment (USP) and PEG ointment(USP). In vitro membrane permeation of CO from the ointments was evaluated in Franz diffusion cellsusing cellulose acetate membrane at 32 C, with the receptor compartment containing a water–ethanol
solution (50:50). The receptor phase samples were analyzed with GC/MS, using citronellal as a reference
standard. The results showed that microencapsulation decreased membrane permeation of the CO by at
least 50%. The amount of CO permeated was dependent on the type of ointment base used; PEG base
exhibited the highest degree of release. Therefore, microencapsulation reduces membrane permeation
of CO while maintaining a constant supply of the oil.
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