W/O/W 다중유화법과 용매 증발법을 이용한 L-ascorbic acid

microcapsules의 제조

이가영, 최성욱, 김중현*, 김우식*

연세대학교 화학공학과 기능성초미립자공정연구실

Preparation of Microcapsules Containing L-Ascorbic Acid by

W/O/W Multiple Emulsification and Solvent Evaporation Method

Ga-Young Lee, Sung-Wook Choi, Jung-Hyun Kim*, Woo-Sik Kim*

Nanosphere Procecess and Technology Laboratory,

Department of Chemical Engineering, Yonsei University

Introduction

Nowadays the use of L-ascorbic acid is not limited to agents which enrich vitamin C as an essential nutritive element, but is extending in various applications. More particularly, because of the chemical structure and physiological activities, L-ascorbic acid is useful as a souring agent, reductant antioxidant, bleaching agent and stabilizer in various chemical reagents, foods and beverages; in pharmaceuticals for susceptive diseases such as preventive and remedy for viral diseases, bacterial inhibitor in cosmetics including skin-refining agent and skin whitening agent. L-ascorbic acid has a strong anti-oxidation activity, promoting biosynthesis of collagen and proliferation of fibroblast. Especially, it is very effective in inhibiting melanin-formation and thereby can be employed in topical applications for purpose of preventing an abnormal pigmentation such as freckle. The objectives of the current investigations were to optimize a encapsulated particle preparation process to produce PCL (poly-caprolactone) microcapsules containing L-ascorbic acid (pure vitamin C), based on a W/O/W multiple emulsification and solvent evaporation method. All emulsified systems provided protection L-ascorbic acid, as its degradation rate, which increased with increasing pH, was slower in emulsified systems than in aqueous solutions. However, ascorbic acid is easily decomposed by oxidation in an aqueous base to cause a reduction of activity during long-term storage.

Theory

Microencapsulation of active compounds is a certain application of the prospective drug delivery systems because it has obvious advantages, biological activity, controlling the core-material release rate, decreasing the administration frequency, and so on. Especially, it is very important for cosmetics. The science and technology of microencapsulation is a good example of how one can extrapolate ban application from a field other than cosmetics. Then methods of microencapsulation were also related to pharmaceuticals, veterinary applications, food, copying systems, laundry products, agricultural uses, pigments, and other lesser known uses. Generally, microencapsulation has many advantages such as (1) to control odor or taste, (2) to alter solubility, (3) to delay volatilization, (4) to prevent incompatibilities, (5) to handle toxic materials, (6) to enhance flow characteristics, (7) to produce sustained or slow release medication, (8) to protect inner compounds from moisture, heat, or  oxidation. There are many methods for microencapsulation such as coarcervation polymerization, in-situ polymerization, interfacial polymerization, spray encapsulation, W/O or O/W microemulsion and W/O/W or O/W/O multiple emulsion. In the present study, we studied preparation of PCL microcapsules containing L-ascorbic acid by W/O/W multiple emulsification and solvent evaporation method, the aim was to formulate W/O/W multiple emulsions as potential cosmetic or topical vehicles for L-ascorbic acid, using nonionic emulsifiers and to evaluate the oxidative stability of the L-ascorbic acid over time in these formulations. It was studied nowadays that several O/W microemulsion, O/W and W/O emulsion and a W/O/W multiple emulsion prepared using non-ionic, non-ethoxylated, skin-compatible emulsifiers. Wherein, the highest protection of L-ascorbic acid was when dissolved in the inner aqueous phase of the W/O/W multiple emulsion. Multiple W/O/W emulsions are vesicular systems in which very small water droplets are entrapped within oil drops, themselves dispersed in an aqueous phase. They have potential uses as drug and cosmetic vehicles, as they might protect encapsulated substances and enable incompatible substances to be incorporated in the same formulation; moreover, prolonged action after administration can be expected.

Experimental

L-ascorbic acid was purchased from Ones company. PCL, gelatin and hes- peridin were purchased from Aldrich Chemical Co., USA. Span 80 and Tween 20/40/60/80/85 were obtained from Duksan pure chemicals Co., Korea. PVA (1500 of polymerization degree), Sodium chloride, Dichloromethane and trichloromethane were from also Duksan pure chemicals Co., Korea. All water used in the experiments was produced by Elgastats UHQ system, UK. We tested basic chemical property for reduced activity of L-ascorbic acid to make fundamental data. In this experiment, L-ascorbic acid was dissolved in buffer solution with various antioxidant such as hesperidin and sodium chloride, which was evaluated at room temperature for one month. Reduced activity was evaluated by UV absorbance at 266nm. Experimental of fitting for standard curve was evaluated at each concentration of standard testing samples such as 0.005 g/l, 0.01 g/l, 0.02g/l, 0.03g/l, 0.04g/l, 0.05g/l. Then each sample was added into 0.0025% sodium chloride or hesperidin or their mixture as antioxidant. In the present study, microcapsules containing L-ascorbic acid was prepared by multiple emulsion. The W/O/W multiple emulsification was prepared by a two step procedure as stated at the beginning of this suggestion: in the first step the primary W/O emulsion was obtained by mixing L-ascorbic acid and sodium chloride used core materials in inner water phase, which L-ascorbic acid was dissolved in DDI water with sodium chloride used as antioxidant. PCL was used as shell material of the microcapsules. Dichlomethane and tri- chloromethane were used as continuous oil phase in the primary water-in oil emulsion. The oil continuous phase was prepared as 4.0g of PCL dissolved in 98ml of dichloromethane. Then Inner aqueous solution was dispersed into oil phase with W/O emulsifiers, agitating at 4000 rpm by means of homogenizer for 10 min. In the second step, the primary emulsion was poured into a dispersion of secondary O/W emulsifiers under homogenizing. The solvent of prepared multiple emulsion was evaporated by vacuum drier at 25.9oC. Finally, the produced microcapsules were collected by centrifugation at 5000rpm for 10 min.

Results and discussion

Microencapsulation of L-ascorbic acid with PCL by a W/O/W multiple emulsification and solvent evaporation technique carried out. Various factors affecting microencapsulation, i.e.. type of various emulsifiers or stabilizers such as Span 80, Tween series, gelatin and PVA, their concentration in each step, type of oil continuous phase in W/O primary emulsion, PCL concentration, agitation speed and agitator type were studied. Digradation rate, particle size, entrapped encapsulation efficiency, stability test were investigated. It was shown that maximum stability of the primary W/O emulsion indicated HLB 6.975 using 75% (w/w) of Span 80 and 25% (w/w) of Tween 80 without any additives. The 20% (w/w) emulsifier was most effective to stabilize the primary W/O emulsion. In the secondary (W/O)/W emulsion, degree of dispersion was more stable as decreasing precipitation ratio and particle size, which was not much related with HLB of secondary emulsifier, contrary to the primary W/O emulsion. Then, final emulsion could be more stabilized by adding PVA, Pluronic, gelatin or its blending with Tween series. Mostly, it was more stable as increasing emulsifier or stabilizer content. While, in that case of using PVA, it was less stable as increasing its concentration. PCL microcapsules were successfully produced in W/O/W emulsion, and spherical particle mean size of the microcapsules containing L-ascorbic acid was in the range of 2-10 mm.

References

1. Herstein Morris, US Patent 5,902,591 (1999)

2. T. J. Kim, Y. S. Kim et al, Korean J. Food Sci. Tech., 399, 28 (1996).

3. Yamamoto Itaru et al., US Patent 5,767,149 (1998)

4. M. Gallarate, M. E. Carlotti et al, Int J. Pharm., 233-241, 188 (1999).

7. M. A. Benoit, B. Banas, J. Gillard, Int J. Pharm,73-75, 184 (1999).

8. I. S. Arvanitoyannis, Totally and Partially Biodegradable Polymer Blends Based on Natural and Synthetic Macromolecules, Marcel Decker, Inc., Greece (1999).

9. D. R. Chen et al, Polymer Degradation and Stability, 455-459, 67(2000).