j. Cosmet. Sci., 50, 9-14 (January/February 1999)

The effectof preparationtechniqueon dropletsize in silicone emulsions V. GALLARDO, A. HERN.•NDEZ,A. PARERA,and M. A. RUIZ, Pharmacy and Pharmaceutical Technology Department, School of Pharmacy,University of Granada,E- 18071 Granada,Spain.

Accepted for publication December 15, 1998. Presented at the9th NationalCongress ofDermopharmacy, Granada,Spain,April 1998. Synopsis

A sunscreen formulation,a gel emulsionbasedon silicones, hasbeenpreparedthroughthe useof these polymers to manufacture emulsions at roomtemperature. Changes in dropletsizearestudiedin a formulationpreparedby two methods(at roomandat elevatedtemperature) usingthe microscopy technique.The influencesof time, temperature,and centrifugationare examined.We have concludedthat the roomtemperaturemanufacturing process providesemulsionswith a homogeneous dropletsizethat are slightly more stablethan thoseobtainedat elevatedtemperature. INTRODUCTION

Recentadvances in the preparationof topicalformulationshavedemonstrated the importanceof the vehiclein obtainingmaximumeffectiveness (1,2). The enormous developmentof siliconechemistryin recentyearshasgivenriseto numerouscompounds with everbetterproperties forusein pharmaceutics andparticularlyin dermocosmetics (3,4). Formulationswith thesecompounds canthereforebe foundin shampoos, hydratinggels, anti-agingcreams,non-fatemulsions,deodorants, antiperspirants, make-up,and especially sunscreenpreparations(5).

In the manytypesof cosmetics, the useof emulsions hasgrownthe mostin the lastfew years,thanksto state-of-the-arttechniquesand particularlyto the great advancesin research into raw materials.

We havecarriedout a detailedstudyof the variationin the preparationof emulsiongels basedon silicones,taking advantageof the fact that thesepolymerscan be used to prepareemulsionsat room temperature.Variationsin droplet size are studiedin a formulationpreparedwith the microscopy techniquein two ways:at roomor at elevated temperature.The influencesof time, temperature,and centrifugationarealsoexamined. EXPERIMENTAL

Silicone phase:DC-244 (tetramersilicone);SilbioneV-5 (pentamersilicone);DC-1401 (dimethiconol).

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Aqueous phase:Carbomer1382; triethanolamine(TEA); distilled water. So/atfilters:Isoamyl-p-methoxycinnamate (HeliopanE- 1000), butylmethoxydibenzoylmethane (Parsol 1789).

Preservative: Nipaguard: a mixture of sodium propyl and methyl hydroxybenzoate, 2-phenoxyethanol, and 2-bromo-2-nitropropane-l,3-diol. This combinationis a specific preservativefor solarfilters. So/vent: AlcoholbenzoicC12_15(FinsolVTN). Formulationcomposition: Isoamyl-p-methoxycinnamate 7% Butylmethoxydibenzoylmethane 1.5% DC-244 (tetramer silicone)

4%

SilbioneV-5 (pentamersilicone)

4%

AlcoholbenzoicC12_15

0.5 %

Triethanolamine

0.8 %

DC- 1401 (dimethiconol) Carhomer 1382 Distilled water

FORMULA

4%

Nipaguard BPX

3% 0.7% 78%

PREPARATION

The galenicalformulationwaspreparedby usingthe coldemulsifyingtechnique(6-8), consisting,in this instance,of the followingsteps: 1. The sunscreens are mixed with the solvent.The preservativeand the mixture of cyclomethicones arethen added,followedby the carbomer,water,andTEA. Finally, dimethiconolis addedand the emulsionis homogenized. 2. In the elevated-temperature preparationtechnique,the aqueousand the oily phases are raisedto a temperatureof about60øC beforemixing them together. 3. The preparations areheatedto 40-60øC and centrifugedto studytheir stability,in accordance with commonlyusedstabilitytest method. MICROPHOTOGRAPHIC

STUDY

Droplet sizeis expressed asthe sizeof globulesin the internalphaseanddependson the type and amount of surfactant,the techniqueof emulsification,the order in which componentsare added,etc.

Microphotography is an extremelyusefultechniquein stability studiesas it allows determinationof suchfactorsas creaming,coalescence, and recrystallization processes (9,10). A LavobalH, Carl ZeissJenamicroscope equippedwith a camerawasusedin this study(11). Photographs weretakenof sampleskept at roomtemperature,at 40øC, and at 60øC, aswell asof samplesthat werecentrifuged. RESULTS

AND

DISCUSSION

There wasscarcelyany differencein the organolepticcharacteristics of the formulations preparedat room or at elevatedtemperature,althoughover time the onespreparedat roomtemperatureseemedto haveslightly greaterstabilityparameters.This fact, combinedwith their easeof preparation,comprises a clearadvantage.

SILICONE-BASED

EMULSION

GELS

Figure 1. The samplepreparedat room temperature.

Figure 2. The samplepreparedat elevatedtemperature.

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Sampleat roomtemperature

diameter pm Figure 3. Diagramof sizedropletsin Figure 1. MICROSCOPY

STUDY

Photographs weretakenof samples keptat roomtemperature, at 40øC,andat 60øCover time. Figure 1 showsthe samplepreparedat room temperature,and Figure 2 the one preparedat elevatedtemperature.It is apparentthat there is little differencein the Sample at elevated temperature

.:-'.•

." ?:

3

4

..

.'"'•.'

:•'."r4 .t"5

•':,:

'" ,

$

6

7

8

9

10

Diameter pm Figure 4. Diagramof sizedropletsin Figure2.

11

12

13

SILICONE-BASED

EMULSION

Table

GELS

13

I

Comparisonof StatisticalParametersfor Room-Temperatureand Elevated-Temperature Formulas Room-temperature Statisticalparameters

Number of droplets(N) Averagediameterby number(Dn, lam) Averagediameterby weight (Dw) Averagediameterby volume(Dv) Averagediameterby area(Ds) Averagediameter(Dz) Polydispersive index (PDI) Standard deviation (SD) Geometric standard deviation (GSD) Coefficient of variation % (CV)

Elevated-temperature

formula

formula

231

357

2.81

2.81

7.O9 3.96

7.6 4.O9

3.35

3.41

8.27

8.89

2.52

2.7

1.82 1.76 64.81

1.93 1.77 68.42

dropletsizebetweenthesetwo preparations. Figures3 and4 presentthe resultsfrom the determinationof the dropletsizein both photographs, applyinga statisticalprocess (see Table I). Note that the averagediameter is around 2.8 !am, with a slightly higher polydispersive indexfor the heatedsample.The percentage of the coefficientof variation is alsohigher in sample2. All thesevaluessupportthe conclusions drawn from the organolepticanalysisof the preparations,in that the differencesbetweenthe two methodsareminimal, but slightlyfavorthe formulationmanufactured at roomtemperature. After beingsubjectedto extremetemperatureconditions(60øCfor overa week)and to centrifugation(10,000 rpm for 30 min), slight coalescence canbe observed,with droplets tending to clump and occasionally increasingin size (Figure 5).

&

.

Figure 5. The sampleafter centrifugation.

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CONCLUSION

The emulsionmanufactured at roomtemperaturehasorganolepticcharacteristics similar to thoseof the emulsionpreparedat elevatedtemperature,while its stability is slightly better, leading to the conclusionthat the room-temperaturepreparationtechniqueis preferablein silicone-based emulsions.

ACKNOWLEDGMENT

We thank ChristineMarie Laurin for translatingthe original manuscriptinto English.

REFERENCES

(1) G. Dahms,Choosing emollientsandemulsifiers for sunscreen products,Cosmet. Toi/etr.109(11),45-54 (1994). (2) D. T. Floyd, Formulationof sun protectionemulsionswith enhancedSPF response,Cosmet. Toi/etr. 112, 55-63 (1997). (3) A.J. Disapioand M. S. Starch,"Using Siliconesin Topical Products,"in TopicalDrug DeliveryFormulations (MarcelDekker,New York, 1990), pp. 389-409. (4) J. Smid-Korbar,J. Krist, and S. Srcic,Polydimethylsiloxane oil in ointments,Pharm.J. Slovenia, 37, 86-90 (1986). (5) M. A. Ruiz, A. Hernandez,A. Parera,and V. Gallardo,Dimethylsiloxanepolymers:Vaporizationrate test/freezingtemperatures,J. SocCosmet. Chem.46, 175-180 (1995). (6) C. Cabeza,Derivadosorganomodificados de silicona.Formulaciones cosm6ticas en emulsiones. Elaboraci6nde emulsiones en frio. Aplicaciones. NCP, 173, 17-24 (1990). (7) A.J. DisapioandM. S. Starch,New silicones emulsifiertechnology, Cosmet. Toi/etr.96, 55-57 (1981).

(8) P. HameyerandC. Bould,Organosilicone W/O emulsifiers, Man•f Chem.,20, 23-25 (1990). (9) R. Franquesa et al., Estabilidadde medicamentos A.E.F.I. (1985). (10) B. Artalejo,C. Fauli, and A. Del Pozo,Preformulaci6n de emulsiones: Estudioconductim6trico, Ind. Farm. 7/8, 91-99 (1987).

(11) C. Phyllis,Am. Perf•m.Cosmet., 4, 77 (1962).