WO2008113109A1

WO2008113109A1 - Artificial substrate

Info

Publication number: WO2008113109A1
Application number: PCT/AU2008/000365
Authority: WO
Inventors: Gavin Greenoak
Original assignee: Australian Photobiology Testing Facility Pty Limited (Aptf)
Priority date: 2007-03-16
Filing date: 2008-03-14
Publication date: 2008-09-25

Abstract

An artificial substrate (20) adapted for use in testing of performance factors of topical lotions or creams, the substrate comprising one or more layers of polypropylene tape (22) bonded to a polypropylene film (24), wherein the polypropylene tape (22) has imprinted surface topography indentations therein.

Description

Artificial Substrate

Field of the Invention

The present invention relates to an artificial substrate adapted for use in testing of performance factors for topical lotions or creams. In particular, the present invention relates to an artificial substrate contoured to approximate human skin for testing of the ultraviolet light absorbing and transmitting characteristics of topical lotions and creams such as sunscreen.

Background of the Invention

Topical lotions and creams such as sunscreen are often laboratory tested during development to determine performance factors including the Sun Protection Factor (SPF) and ultra violet absorption and transmission characteristics. The testing can be conducted either 'in vivo' on human test patients or alternatively 'in vitro' on artificial substrates intended to mimic the characteristics and topography of human skin.

Human volunteers for in vivo testing of topical lotions and creams are exposed to high intensity ultra violet light (UV), which is a well established carcinogen in high doses. A further disadvantage concerns the complex nature of providing adequate solar simulation for human testing. On account of the necessary attenuation of artificial light source spectral emission using special filters, solar simulators can only achieve an approximation to sunlight. The differences lead to inaccuracies, and to significant overestimations of protection with products over SPF 30 (hence the ceiling set at 30+).

One known artificial substrate used for in vitro testing is known as MimSkin version 1.0 (Trade Mark). The substrate is made from inflexible quartz glass and has a topography derived from actual human skin casts. Whilst a number of sun-screening capability parameters can be measured with MimSkin version 1.0, the SPF measurements obtained with this substrate are generally unreliable. A further disadvantage is that MimSkin version 1.0 is very difficult to accurately produce and then reproduce.

Another known substrate used for in vitro testing is VITRO-SKIN (Trade Mark). This substrate contains both optimised protein and lipid components and is designed to have topography, pH, critical surface tension and ionic strength similar to human skin. VITRO-SKIN has been successfully applied to the measurement of SPF and UVA (long wave ultra violet rays) protection factors. Testing done on VITRO-SKIN is generally more reproducible than that performed in vivo on human skin, due to the consistent topography and wetting properties across each sheet. However, VITRO-SKIN requires a careful pre-hydration procedure, which in turn can lead to unreliable results. A further disadvantage is that VITRO-SKIN is prohibitively expensive.

Other known substrates are Transpore Tape and polymethylmethacrylate (PMMA) exist. However, they are not suitable for reproducibly measuring SPF.

Object of the Invention

It is an object of the present invention to overcome or ameliorate one or more of the above described disadvantages, or at least to provide a useful alternative to existing artificial substrates.

Summary of the Invention hi a first aspect, the present invention provides an artificial substrate adapted for use in testing of performance factors of topical lotions or creams, the substrate comprising one or more layers of polypropylene tape bonded to a polypropylene film, wherein said polypropylene tape has imprinted surface topography indentations therein.

Preferably the depth of the surface topography indentations is between about 95μm and lOOμm.

The polypropylene tape is preferably layered approximately 20 layers thick.

The thickness of the substrate is preferably between about 0.17mm and 0.29mm.

In a second aspect the present invention provides a method of preparing an artificial substrate adapted for use in testing of performance factors of topical lotions or creams, said method including the steps of: placing one or more layers of polypropylene tape on a polypropylene film; locating a mesh adjacent to a surface of the polypropylene tape; applying a force to said mesh and said polypropylene film, such that said mesh is impressed into said surface of the polypropylene tape; and releasing said force and removing said mesh to thereby leave imprinted surface topography indentations on said substrate.

The surface topography indentations are preferably formed to a depth of between about 95μm and lOOμm.

The thickness of the substrate after said force is released is preferably between about 0.17mm and 0.29mm.

The method preferably further including the step of determining the suitability of said substrate by measuring the depth of the surface topography indentations after removing said mesh.

Preferably, the step of applying said force includes placing said mesh and said substrate in a vice and applying a torque of approximately 66Nm to a handle of said vice.

hi a third aspect, the present invention provides a method of evaluating a performance factor of a topical lotion or cream, said method including the steps of: placing one or more layers of polypropylene tape on a polypropylene film; locating a mesh adjacent to a surface of the polypropylene tape; applying a force to said mesh and said polypropylene film, such that said mesh is impressed into the surface of said polypropylene tape; releasing said force and removing said mesh to thereby leave imprinted surface topography indentations on said substrate; applying a neutral cosmetic base to said imprinted surface; applying said topical lotion or cream to said imprinted surface; exposing the substrate to ultra-violet light; and evaluating and recording the performance factor.

Preferably the surface topography indentations are formed to a depth of between about 95μm and lOOμm.

The thickness of the substrate after the force is released is preferably between about 0.17mm and 0.29mm. The performance factor is preferably SPF.

The substrate is preferably washed and dried after the application of the neutral cosmetic base.

The topical lotion is preferably applied to the substrate in dots which are subsequently spread evenly across the surface of the substrate, and the volume of topical lotion is 2 ±0.1 mg/cm².

The evaluated performance factor is preferably converted for comparison to results obtained in vivo testing.

In a fourth aspect, the present invention provides a topical lotion or cream SPF testing artificial substrate comprising one or more layers of polypropylene tape bonded to a polypropylene film, wherein said polypropylene tape has imprinted surface topography indentations with a depth of between about 95μm and lOOμm.

In a fifth aspect, the present invention provides an artificial substrate adapted for use in testing of performance factors of topical lotions or creams, the substrate comprising a layer of polypropylene, wherein said polypropylene has imprinted surface topography indentations therein.

In a sixth aspect, the present invention provides a method of preparing an artificial substrate adapted for use in testing of performance factors of topical lotions or creams, said method including the steps of: locating a mesh adjacent to a surface of a polypropylene substrate; applying a force to said mesh and said polypropylene substrate, such that said mesh is impressed into said surface of the polypropylene substrate; and releasing said force and removing said mesh to thereby leave imprinted surface topography indentations on said substrate.

In a seventh aspect, the present invention provides a method of evaluating a performance factor of a topical lotion or cream, said method including the steps of: locating a mesh adjacent to a surface of a polypropylene substrate; applying a force to said mesh and said polypropylene substrate, such that said mesh is impressed into the surface of said substrate; releasing said force and removing said mesh to thereby leave imprinted surface topography indentations on said substrate; applying a neutral cosmetic base to said imprinted surface; applying said topical lotion or cream to said imprinted surface; exposing the substrate to ultra-violet light; and evaluating and recording the performance factor.

In an eighth aspect, the present invention provides a topical lotion or cream SPF testing artificial substrate comprising a polypropylene layer, wherein said polypropylene layer has imprinted surface topography indentations with a depth of between about 95μm and lOOμm.

Preferably the substrate is formed from transparent polypropylene.

Preferably the substrate is formed from translucent polypropylene. More preferably, the percentage of UV transmission between 290 and 400nm is at least 60%.

Brief Description of the Drawings

A preferred embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

Fig. 1 shows a substrate according to the present invention during production;

Fig. 2 is a chart showing the transmittance of polypropylene tape arranged in different numbers of layers;

Fig. 3 shows a torque being applied to the substrate in a vice;

Fig. 4 shows the arrangement of spots of lotion applied to the substrate;

Fig. 5 is a chart indicating the transmittance of the finished substrate;

Fig. 6 is a chart indicating the transmittance of isolated human epidermis; Fig. 7 shows the surface profile of a wire mesh; and

Fig. 8 is a chart showing the spectral irradiance of Labsphere and APTF. Detailed Description of the Preferred Embodiment

Fig. 1 shows an embodiment of an artificial substrate 20 according to the present invention. The substrate 20 is made from tape 22, such as office adhesive work tape marketed under the brand "Office Works" which is bonded to a piece of polypropylene film 24 having a thickness of 170μm.

The tape 22 is clear and typically 24mm in width. Fig. 2 shows a graph indicating the light transmittance of the tape 22. The legend refers to the number of scans (x5) and transmittance through one layer of tape.

The substrate 20 is formed with tape 22 which is layered in approximately 20 layers until the total thickness of the tape 20 is approximately 700μm. Each layer of tape is between 50 and 55 microns thick. The polypropylene film 24 to which the tape is bonded has a thickness of approximately 170μm.

hi an alternative embodiment, the substrate 20 is formed from a single sheet of polypropylene having a thickness of 0.25mm ± 0.04mm. The substrate may be formed from either transparent or translucent polypropylene. For the latter, the percentage of UV transmission between 290 and 400nm is at least 60%.

The preparation of the substrate 20 is as follows:

To prepare the base for the substrate 20, a polypropylene film 24 is cut into pieces,

(60x30mm), using a metal ruler and knife. There are two readily available thicknesses of the polypropylene film 24 which are 300 and 375 microns.

A measurement is then made and recorded with respect to the thickness of the polypropylene film 24. The polypropylene film 24 should be kept free of dust.

The tape 22 is cut as a segment from a roll of such tape 22. The segment is cut to the centre of the roll and the cardboard core is removed and discarded. The circumferential length of the segment is approximately 70mm.

The user may then put on magnifying glasses and may also use a light magnifier. This assists the user in visualising the substrate 20 preparation process.

The user then uses a scalpel, and estimates and very carefully separate the top layer of tape to the depth of 740 microns from one corner end of the length of tape. From the comer end where the user started, the scalpel is slid down the 24mm width of the tape. This essentially opens one end of the tape.

5 The estimated 740 micron thickness piece of tape is separated from the base, sufficiently to permit the measurement of the thickness of the layer with a micrometer.

If the tape 22 is found to be the correct thickness, (i.e. 740microns,or within 5-lOmicrons more than 740), it is peeled away from the base very carefully, only touching the outero edges.

Once the tape 22 has been peeled away the thickness is remeasured with the micrometer, keeping the micrometer away from the edges and checking the thickness in at least two places, for uniformity. If the thickness of the tape 22 is between 730-750 microns, thens the tape 22 can be used. If not, it is discarded and the process is repeated.

The tape 22 is placed over and manually bonded to the polypropylene film 24. From the middle of the tape 22 and the polypropylene film 24, the user presses down, while sliding the finger along the edge of tape 22 and film 24. The user should avoid pockets of air0 being trapped between the tape 22 and the film 24.

The substrate 20 is then placed on a flat piece of wood. By placing a square rule over one edge and using a knife, the user cuts along that edge, to provide a straight cut both through the tape 22 and the film 24 so that they both basically become one edge of the substrateS 20. Measuring from the same edge, the length of the substrate 20 to a distance of 37mm is marked. The substrate 20 is then cut to 37 mm in length.

By keeping the substrate 20 straight along the edge provides an easy point of reference, if required. Especially when putting the substrate 20 in a profiler. 0

A steel mesh 26 (having a texture as shown in Fig. 7) having a size of 40 perforations per inch (15.7/cm), and being formed from a wire diameter of 0.224mm, and aperture size of .041mm is placed against a surface of the substrate 20 in contact with the tape 22, and the mesh 26 and substrate 20 are then sandwiched between two steel plates 28. The two steel plates 24 are then placed in a vice and a force is applied to the handle of the vice with a torque wrench, as shown in Fig. 3, until 66Nm is reached. The steel plates 28 and the sandwiched mesh 26 and substrate 20 are left in the vice under pressure for 5 minutes, such that the mesh 26 is pressed into the surface of the tape 22. The vice is then released and the substrate 20 is left for another 5 minutes.

The finished substrate 20 has a topography on one side to a depth of between 60μm to 1 lOμm. The mesh 26 is derived from casts of actual human skin, such that the imprinted surface topography indentations created by the mesh 26 on the substrate 20 resemble human skin.

The ultra violet transmittance of the finished substrate 20 is shown in Fig. 5, which is in contrast to the transmittance of human epidermis as shown in Fig. 6.

The substrate 20 profile is then measured and a preferred substrate is selected with a topography imprint depth of 95-100μm. At least 3 regions of the profile should be measured to ensure that the topography depth is consistent across the substrate 20. The depth measurements can be undertaken using either a confocal laser microscope or a profilometer (Tencor PlO)

The thickness of the substrate 20 after the application of the surface texturing with the mesh 26 is within the range of 0.17mm to 0.29mm.

The substrate 20 is then pre-treated with a neutral cosmetic base such as Aquase Cream and left for 15 minutes. The pre-treated substrate 20 is then washed gently with water and detergent, rinsed and air dried.

The use of the substrate 20 in testing the SPF of a lotion or cream will now be described. Sunscreen, or another product to be tested is then applied in a number of spots to the profiled surface of the substrate 20 with a small spatula. The arrangement of the spots is shown in Fig. 4. The spots of sunscreen are then rubbed into the substrate 20 with the finger stall of a surgical glove. The sunscreen is applied in the quantity of 2 ±0.1 mg/cm², and it is rubbed in approximately 20 times with a force of 250-30Og to obtain a uniform thickness. Accordingly, for a substrate dimensioned 24mm x 30mm, 14.4mg of sunscreen is required. The treated substrate 20 is then exposed to ultra-violet light from a metal halide lamp for a time period based upon the estimated SPF of the sunscreen. The SPF is then determined with Labsphere, and the obtained data is converted to in vivo results.

The SPF of the in vivo result is matched with corrected SPF with solar simulation spectral irradiance, and the real SPF is the SPF after UV exposure, but before correcting, because it is calculated with sun light. The SPF is calculated using the CIE (Committee Internationale L'Eclairage) Action Spectrum for sunburn erythema in humans, the UV transmission through the test sample (from 290 - 400 nm), and a recognised Standard Sun spectrum (Melbourne, or Alberqueque). The equations for this calculation are well established.

An advantage is that the SPF measured not only correlates well with in vivo derived values but can be corrected (for deficiencies in solar simulating light sources) to provide a more accurate SPF value with respect to actual use in sunlight.

A further advantage is that this substrate is inexpensive, flexible, disposable, and has the same UV transmission profile as human skin.

Although the invention has been described with reference to specific examples, it will be appreciated by those skilled in the art that the invention may be embodied in many other forms.

Claims

The claims:

1. An artificial substrate adapted for use in testing of performance factors of topical lotions or creams, the substrate comprising one or more layers of polypropylene tape bonded to a polypropylene film, wherein said polypropylene tape has imprinted surface topography indentations therein.

2. An artificial substrate adapted for use in testing of performance factors of topical lotions or creams, the substrate comprising a layer of polypropylene, wherein said polypropylene has imprinted surface topography indentations therein.

3. The substrate of claim 1 or claim 2, wherein the depth of the surface topography indentations is between about 95μm and lOOμm.

4. The substrate of claim 1 or 2, wherein the polypropylene tape is layered approximately 20 layers thick.

5. The substrate of claim 1 or claim 2, wherein the thickness of the substrate is between about 0.17mm and 0.29mm.

6. The substrate of claim 1 or 2, wherein the substrate is formed from transparent polypropylene.

7. The substrate of claim 1 or 2, wherein the substrate is formed from translucent polypropylene.

8. The substrate of claim 1 or 2, wherein the percentage of UV transmission between 290 and 400nm is at least 60%.

9. A method of preparing an artificial substrate adapted for use in testing of performance factors of topical lotions or creams, said method including the steps of: placing one or more layers of polypropylene tape on a polypropylene film; locating a mesh adjacent to a surface of the polypropylene tape; applying a force to said mesh and said polypropylene film, such that said mesh is impressed into said surface of the polypropylene tape; and releasing said force and removing said mesh to thereby leave imprinted surface topography indentations on said substrate.

10. A method of preparing an artificial substrate adapted for use in testing of performance factors of topical lotions or creams, said method including the steps of: locating a mesh adjacent to a surface of a polypropylene substrate; applying a force to said mesh and said polypropylene substrate, such that said mesh is impressed into said surface of the polypropylene substrate; and releasing said force and removing said mesh to thereby leave imprinted surface topography indentations on said substrate.

11. The method of claim 9 or 10, wherein the surface topography indentations are formed to a depth of between about 95 μm and lOOμm.

12, The method of claim 9 or 10, wherein the thickness of the substrate after said force is released is between about 0.17mm and 0.29mm.

13. The method of claim 9 or 10, further including the step of determining the suitability of said substrate by measuring the depth of the surface topography indentations after removing said mesh.

14. The method of claim 9 or 10, wherein the step of applying said force includes placing said mesh and said substrate in a vice and applying a torque of approximately 66Nm to a handle of said vice.

15. A method of evaluating a performance factor of a topical lotion or cream, said method including the steps of: placing one or more layers of polypropylene tape on a polypropylene film; locating a mesh adjacent to a surface of the polypropylene tape; applying a force to said mesh and said polypropylene film, such that said mesh is impressed into the surface of said polypropylene tape; releasing said force and removing said mesh to thereby leave imprinted surface topography indentations on said substrate; applying a neutral cosmetic base to said imprinted surface; applying said topical lotion or cream to said imprinted surface; exposing the substrate to ultra-violet light; and evaluating and recording the performance factor.

16. A method of evaluating a performance factor of a topical lotion or cream, said method including the steps of: locating a mesh adjacent to a surface of a polypropylene substrate; applying a force to said mesh and said polypropylene substrate, such that said mesh is impressed into the surface of said substrate; releasing said force and removing said mesh to thereby leave imprinted surface topography indentations on said substrate; applying a neutral cosmetic base to said imprinted surface; applying said topical lotion or cream to said imprinted surface; exposing the substrate to ultra-violet light; and evaluating and recording the performance factor.

17. The method of claim 15 or 16, wherein the substrate is washed and dried after the application of said neutral cosmetic base.

18. The method of claim 15 or 16, wherein the topical lotion is applied to the substrate in dots which are subsequently spread evenly across the surface of the substrate, and the volume of topical lotion is 2 ±0.1 mg/cm².

19. The method of claim 15 or 16, wherein the performance factor is converted for comparison to results obtained in vivo testing.

20. The method of claim 15 or 16, wherein the performance factor is SPF.

21. A topical lotion or cream SPF testing artificial substrate comprising one or more layers of polypropylene tape bonded to a polypropylene film, wherein said polypropylene tape has imprinted surface topography indentations with a depth of between about 95μm and lOOμm.

22. A topical lotion or cream SPF testing artificial substrate comprising a polypropylene layer, wherein said polypropylene layer has imprinted surface topography indentations with a depth of between about 95 μm and lOOμ.