TEXTURED APPLICATOR FOR APPLYING Ml CROP ARTICLES

This application claims priority from AU 2012905650 which is hereby incorporated ^' its entirety by reference.

TECHNICAL FIELD

This disclosure relates to an applicator for delivering elongate microparticles through a biological barrier. This disclosure particularly relates to an applicator for delivering elongate microparticles through a biological barrier for the purposes of transdermal delivery of compounds, such as bioactive compounds.

BACKGROUND ART

The oral administration of many drugs and other bioactive compounds is problematic due to the risk of degradation of the compounds in the gastrointestinal tract and/or elimination by the liver. Moreover, some drugs cannot effectively diffuse across the intestinal mucosa. Patient compliance may also be a problem, for example, in therapies requiring that pills be taken at particular intervals over a prolonged time.

Significant research has been conducted in recent years into the transport of drugs and therapeutic agents across biological barriers in the body, e.g., the skin, the oral mucosa, the blood-brain barrier etc. In the case where the biological barrier is skin, a major obstacle that must be overcome in developing effective transdermal delivery systems is the naturally low permeability of skin. Skin is a structurally complex, relatively thick membrane that provides an effective barrier to the entry of substances into the body. In normal human skin, the outer layer, the stratum corneum (SC), is approximately 10 to 20 μηι thick and consists of a stack of 15 to 25 flattened, cornified cells embedded in a matrix of intercellular lipid. However, in many pathological skin conditions, the SC can be many times thicker than normal skin. One function of the SC is to form a protective barrier, preventing the entry of hazardous environmental material and microorganisms into the body. Consequently, this layer is also the main barrier that must be overcome to deliver drugs or other therapeutic substances through the skin. Once across the SC, substances are then able to cross the viable epidermis and diffuse into the papillary dermis where they can enter the capillaries and be absorbed into the systemic circulation, enter lymphatic vessels or diffuse into the dermis and underlying tissue compartments.

Some bioactive compounds may be absorbed through the SC by topical application, e.g. by manually rubbing a preparation containing the compound into the skin. However, this technique is inefficient and is limited to absorption of relatively smaller bioactive compounds such as diclofinac.

One common technique for delivering drugs across a biological barrier such as skin is the use of a hypodermic needle, such as those used with standard syringes or catheters. The use of such needles generally causes pain; and may cause local damage to the skin at the site of insertion; bleeding, which increases the risk of disease transmission; and a wound sufficiently large to be a site of infection among many other disadvantages. Needle techniques also generally require administration by one trained in the use of needles. The needle technique also may be undesirable for long term, controlled continuous drug delivery.

Recent advances in transdermal delivery devices have included transdermal patches, which rely on diffusion of small molecules across the SC, and microneedle arrays, which pierce the SC to facilitate delivery of compounds. However, transdermal patches are not effective for delivering relatively large molecules which are not able to diffuse across the SC nor when the skin has a thick SC. Moreover, microneedle arrays have the

disadvantages of requiring supporting structures and/or applicators, which add to the complexity and cost of manufacture and use of such devices. Another disadvantage of transdermal patches and microneedle arrays is that their size necessarily limits the surface area for delivery of the bioactive compounds.

The applicant's copending patent application number PCT/AU2013/000670, the entire disclosure of which is incorporated herein by reference, discloses a method and composition for delivering a compound (such as a bioactive compound, cosmeceutical or cosmetic) through a biological barrier (eg skin) by applying a force (such as by massaging) to a composition comprising elongate micro particles and the compound on a surface of the barrier so that at least some of the elongate microparticles penetrate the biological barrier to facilitate delivery of the compound there through. This delivery method has the following advantages. By using elongate microparticles, which are discrete and independently moveable, as a means of penetrating the biological barrier, the need for a solid support can be obviated. The cost and complexity of manufacturing free elongate microparticles are therefore likely to be significantly less than those for (supported) microneedle arrays.

Moreover the delivery of compounds using the elongate microparticles is more effective than transdermal patches, particularly for relatively large molecules, by virtue of the penetration of the biological barrier by the elongate microparticles and attendant increase in permeability. In addition, in comparison with transdermal patches and microneedle arrays, the elongate microparticles are able to be applied, and thereby deliver compounds, over a large surface area due to the absence of the solid support. Without wishing to be limited by theory, it is believed that the penetration of the biological barrier by the elongate microparticles creates pathways for delivery of the compounds across the biological barrier. The compounds may be delivered through the pathways simultaneously with and/or subsequent to their creation. For example, the compound may be pushed through the biological barrier by the elongate microparticles as they create the pathways, and/or they may pass through the pathways subsequent to their creation, for example by being rubbed or massaged into a previously formed pathway.

Notwithstanding the above described advantages of applicant's copending patent application number PCT/AU2013/000670, it would be desirable to provide an applicator for applying the composition to the biological barrier, which would further enhance efficiency of penetration by the elongate microparticles and further improve delivery over large surface areas.

The above references to the background art do not constitute an admission that the art forms a part of the common general knowledge of a person of ordinary skill in the art. The above references are also not intended to limit the application of the applicator or method as disclosed herein.

SUMMARY OF THE DISCLOSURE

In a first aspect, there is disclosed an applicator for applying elongate microparticles to a biological barrier so that at least some of the elongate microparticles penetrate the biological barrier, the applicator including a microtextured surface configured to engage and orientate the elongate microparticles at an angle to facilitate penetration of the biological barrier. In a second aspect, there is provided a method for applying elongate microparticles to a biological barrier so that at least some of the elongate microparticles penetrate the biological barrier, including the step of using an applicator including a microtextured surface to engage and orientate the elongate microparticles at an angle to facilitate penetration of the biological barrier.

Throughout the specification, any reference to microparticles should be understood to be a reference to elongate microparticles unless the context makes clear otherwise.

The following discussion will focus on the use of the applicator for applying elongate microparticles to skin, but it is to be understood that the present disclosure extends to use with other biological barriers, such as mucosa or keratin based biological barriers such as nails.

The applicator is an implement for use in applying the elongate microparticles, but is not a permanent support for the elongate microparticles. The elongate microparticles are provided separately from the applicator head. Some of the elongate microparticles may temporarily adhere to the microtextured surface of the applicator head during and following use. However, after delivery of the elongate microparticles, the applicator is removed.

The elongate microparticles can be applied to the skin to assist in delivery of a compound. The compound may be a bioactive compound (such as a pharmaceutical (including an excipient), protein, peptide or vaccine), a pigment, a cosmeceutical, a neutraceutical or a cosmetic. The compound can be a formulation. The formulation can be a controlled release formulation. In one embodiment, at least some of the elongate

microparticles themselves are a solid form of the compound e.g. a drug or an excipient.

In one embodiment, the compound is coated on at least some of the surfaces of at least some of the microparticles. When the compound is coated on the elongate

microparticles, the compound is delivered with the microparticles as they penetrate the biological barrier. The compound can be coated on the surface of at least some of the microparticles by mixing them with the compound and then e.g. freeze or air drying the microparticles.

In one embodiment, the compound can comprise or include nanoparticles or sub- micron particles. The nanoparticles or sub-micron particles can be metal particles. The metal particles can be gold particles. The nanoparticles or sub-micron particles can have a diameter in the range of from about 1 to about 600 nm, such as from 1 to about 100 nm. The nanoparticles or sub-micron particles can have a diameter in the range of from about 100, 200, 300, 400, 500 or 600 nm.

The microparticles may be included in a composition which also includes the compound for delivery through the skin. The elongate microparticles and the compound can be applied to an area of the skin and the microtextured surface of the applicator can be manually rubbed or massaged over that area.

In an embodiment of the applicator, the microtextured surface of the applicator may be treated with a compound (such as by being coated with a compound) intended to be delivered through the skin. Accordingly, during use of this embodiment to apply the microparticles to the skin, the compound can be simultaneously delivered during

microparticle penetration. In another embodiment, the microtextured surface of the applicator may be treated with a compound and the elongate microparticles.

In an embodiment, the elongate microparticles are applied to the skin in a first step in the absence of a compound. The elongate microparticles are thought to form microchannels in the skin as they penetrate the skin under the manual force applied by the applicator surface. In a second, subsequent step a compound can be applied to the skin (with or without massaging or rubbing of the compound); and at least some of the compound can penetrate through the microchannels formed in the skin thereby delivering the compound.

In a third aspect, there is provided a method for delivering a compound through a biological barrier including

providing a plurality of elongate microparticles and the compound,

providing an applicator including a microtextured surface for engaging and orientating the elongate microparticles at an angle to facilitate penetration of the biological barrier,

applying a manual force to the surface of the biological barrier using the applicator so that at least some of the elongate microparticles penetrate the biological barrier and thereby facilitate delivery of the compound through the biological barrier.

In one embodiment of the method, the elongate microparticles are provided in a composition and the particles and composition are applied concurrently to the biological barrier by the applicator. In another embodiment, the elongate microparticles are applied by the applicator to the biological barrier before the compound is provided. In this embodiment, the method further includes the step of applying the compound to the surface of the biological barrier over at least a part of the area in which the elongate microparticles penetrated the barrier. According to a fourth aspect of the present invention there is provided a kit comprising: the applicator according to the first aspect of the invention; elongate

microparticles for penetration through a biological barrier under a force applied by the applicator; and a compound for delivery through the biological barrier. The above description relating to the first, second and third aspects of the invention applies equally to the fourth aspect of the invention.

In one embodiment of the kit, the elongate microparticles and the compound are provided together in a composition or formulation. In one embodiment of the kit, the elongate microparticles comprise the compound (e.g. the elongate microparticles are a solid form of a drug). At least some of the elongate microparticles can be at least partially coated with the compound. In another embodiment of the kit, at least a portion of the applicator surface is coated with the compound. The kit can be provided together with instructions for use. The applicator can be held in the hand of an operator and the microtextured surface can be manually massaged or rubbed over the area of skin to which the elongate microparticles should be applied. The manual massaging or rubbing can facilitate at least some of the elongate microparticles to penetrate the skin. In an embodiment, the applicator includes a body and an applicator head on which is provided the microtextured surface. In another embodiment, the applicator comprises a glove or a finger cot including the microtextured surface on a finger tip region thereof.

In another embodiment, the applicator includes microtexturing on both the head and body thereof. For example, the applicator may be substantially cylindrical in shape. The cylindrical applicator can have a body in the form of a shaft and a head in the form of a tip of the shaft. The cylinder can have a microtextured surface on the shaft and the tip. In one embodiment, the cylindrical applicator may be a rod or a baton. This embodiment is suitable for use where the biological barrier is provided within a body cavity and the applicator is inserted into the body cavity during use. At least the portion of the shaft intended for insertion can comprise a microtextured surface. The body cavity can be, for example, a vaginal tract. The applicator is intended for manual use; however, there may be mechanical and/or electronic integration within the applicator. For example, there could be mechanical agitation of the microtextured surface of the applicator. The agitation can be vibration and/or oscillation. The applicator could include a sonophoresis or electrophoresis probe or something similar that provides a 'non-invasive' force to enhance delivery. Any agitation may work in conjunction with the manual massaging or rubbing application technique.

The hand-held applicator may further comprise a force controller. The force controller enables the user to vary the force with which the applicator is manually applied to the skin such that an optimal force for penetration of the skin may be achieved. The force controller may also include an applied force meter which indicates to the user when the optimal manual force is achieved. The force applied by the applicator surface to the elongate microparticles is a force within a range that can be applied manually by a human operator. In an embodiment, the force may be greater than 0.01 Newtons, such as a minimum of 0.1 Newtons. In an embodiment, the applied force is at least 0.2 Newtons. In one embodiment, the applied force is 2.5 Newtons. The maximum force may be 10 Newtons.

The inventors have found that the elongate microparticles show much greater epidermal / dermal penetration when they are applied using the applicator than when simply applied manually without an applicator, e.g. by rubbing with a finger. As used herein, the term "microtextured" means that the surface has raised and/or lowered surface features on the micrometers to millimeter scale.

In an embodiment, the textured surface includes angled faces that define spaces for receiving the elongate microparticles during use of the applicator. The angled faces may be flat or curved. In use of the applicator of this embodiment, at least an end region of each elongate microparticle is received in a space such that at least one angled face engages the end of the elongate microparticle and defines the orientation of the elongate microparticle. The spaces may be each defined by one or more angled faces. In one embodiment, the spaces may be defined between protrusions on the textured surface. The protrusions may comprise a series of laterally spaced elongate or discrete microprotrusions or microridges wherein each protrusion or ridge provides two or more generally inwardly angled faces. A first face can engage the end of a elongate microparticle and an adjacent second face can define the orientation of the elongate microparticle. There can be bases or valleys formed between the ridges.

In another embodiment, the spaces may be defined by recesses in the textured surface. The recesses may comprise a series of laterally spaced elongate or discrete microrecesses. The microrecesses may be a series of dimples. In one embodiment, each recess provides two or more inwardly angled faces. One of the faces can engage the end of a elongate microparticle and the other can define the orientation of the elongate

microparticle. Preferably, the microtextunng geometry is such that the elongate

microparticles cannot be received into and trapped in the texturing e.g. spaces between the faces. The face that defines the orientation of the elongate microparticle may be angled and dimensioned to provide support for at least an end section of the elongate microparticle. In this embodiment, at least the end section of the elongate microparticle may extend across the width of the face. The width of the face may therefore be less than the minimum length of the elongate microparticles so that each microparticle can extend beyond the face and penetrate the biological barrier during use of the applicator. The width of this face may be a minimum of 8 microns. The maximum width of this face may be 1 mm.

There may be some geometries of microtexturing that are optimal for engaging and orienting individual elongate microparticles and other geometries of microtexturing that are optimal for engaging aggregates of elongate microparticles. The types of microtexturing on the surface of the applicator may differ over the surface. The types of microtexturing may differ to provide optimal penetration of single particles and aggregates of particles. Single particles may be best orientated by relatively small features in the microtexturing. In one embodiment, a peripheral circumferential edge of a generally cylindrical applicator surface may have a first geometry of microtexturing and top surface of the cylinder may have a different geometry of microtexturing.

There may be smooth areas on the surface of the applicator which do not comprise microtexturing. The microtexturing on the surface of the applicator can be in a range of from about 1 to 100 %. In an embodiment, at least about 75, 77, 80, 85, 90 or 95 % of the applicator surface comprises microtexturing, with the areas between the microtexturing being substantially smooth. In an embodiment, the surface of the applicator comprises 100% microtexturing with no smooth areas. Different amounts of microtexturing can deliver different doses of a compound. In one embodiment, at a given concentration of a compound in a composition or formulation, different amounts of microtexturing can be selected to control dose delivery. For example, 95 % microtexturing of the surface of the applicator may provide 95 % of the available dose of a compound of the composition; while 50 % of microtexturing on the surface of the applicator may provide 50 % of the available dose of a compound in the composition. It is hypothesised that following application of the elongate microparticles there is negligible disruption to the skin due to the micro-sized diameter of the particles and the skin's elastic properties. It is believed that the microchannels formed by the elongate microparticles close following their penetration (similar to with microneedle arrays). This attribute of quick closure of pathways created by the elongate microparticle following application is beneficial when considering potential foreign substance (microbial) infiltration.

At least that part of the applicator comprising the textured surface is constructed from material that is harder than skin as otherwise the elongate microparticles embed in the applicator rather than in the skin.

The microtexturing on the surface of the applicator can engage and align the elongate microparticles. It is thought that the bases or valleys within the textured surface are the most common areas that provide resistance to the elongate microparticles when pushing them into the skin.

In some embodiments, the material of the applicator surface can be chosen or adapted to be attractive to the elongate microparticles in order to engage and orient them. For example, the material of the applicator may differ in any bases, valleys or depressions within the mictrotexturing to provide attraction in those areas. The attraction can be provided in the form of adhesive and/or magnetic materials. If portions of the microtexturing are attractive, it may be possible to attract elongate microparticles to the applicator head and have them aligned by e.g. the ridges in the texturing.

In an embodiment, the material from which the microtexturing is formed is soft and/or malleable. A soft material may allow for deeper penetration of the elongate microparticles. If the material from which the microtexturing is formed is too hard, some of the elongate microparticles may be broken e.g. by snapping, which is undesirable. The material may comprise a UV curable polymer.

The microtextured surface of the applicator can be formed by any method that results in surface microtexturing. The method can be 3D printing, photolithography or deep reactive ion etching.

In some embodiments, it is advantageous if the microparticles penetrate the biological barrier at an angle. The angle can be sufficiently oblique to allow the microparticle to penetrate the stratum corneum, but not so deep that the microparticle penetrates the dermis (i.e. the nerve bed is in the dermal layer). The significance of an angled penetration profile can also be that the microparticles can create microchannels with a greater surface area for delivery of a bioactive or other compound when compared to perpendicular or 90 degree penetration (relative to the skin). This can mean that the delivery method of embodiments of the present invention is advantageous over prior art devices such as microneedles and gas jet injectors. It is thought that an angled penetration of the elongate microparticles can disrupt a greater region of viable epidermis, increasing its permeability yet being minimally invasive by minimizing damage to the dermal-epidermal junction, dermal capillaries and pain receptors.

The angled faces on the microtextured surface may be orientated such that during use of the applicator, the elongate microparticles may be orientated at an acute angle with respect to the skin surface to facilitate penetration of the biological barrier. In an

embodiment, the elongate microparticles may be orientated, such as to penetrate the skin at an angle of greater than 0 and less than about 45 degrees, such as in the range of from about 5 to about 30 degrees, for example in the range of from about 7 to about 25 degrees. It is expected that the angle of penetration will rarely be greater than 45 degrees. The angle could be greater than 45 degrees if the elongate microparticles are clumped, or if the skin is deformed around the applicator. For example, skin with degraded collagen and elastin (e.g. aged skin) could potentially deform around the applicator and during massaging the particles could penetrate at close to perpendicular (90 degrees).

In a fifth aspect, there is provided an applicator for facilitating penetration of elongate microparticles into a biological barrier, the applicator including a microtextured surface configured to engage and orientate the elongate microparticles during penetration of the biological barrier at an angle of greater than 0 degrees and less than about 45 degrees. The textured surface may have a generally convex, concave, rectangular, v-shaped or other profile during use. In one embodiment, the microtextured surface is generally convex. Experimentation with different applicator designs has found that a generally convex textured surface better aligns particles in an orientation that allows them to penetrate the skin than either, for example, a smooth convex surface or a concave textured surface, which can result in poor penetration. Due to the elastic nature of skin, it stretches and moves when force is applied to it. It is therefore believed that a generally convex profile allows optimal contact between the textured surface and the skin when the applicator is manually pressed against the skin. In one embodiment, the portion of the applicator comprising the

microtextured surface may be made from a deformable material that can start as concave and become convex upon the application of force.

In an embodiment, the elongate microparticles comprise a material having sufficient strength and rigidity to withstand an applied force of at least 13MPa. The elongate microparticles may comprise silica. However, other suitable materials may also be used, such as metals, semi-metals such as silicon, plastics, (e.g. biocompatible polymers,) cellulose derived materials or ceramic materials. Silica is conveniently used due to its relative low cost, suitable mechanical properties, biocompatibility and availability. In one embodiment, as described above, the elongate microparticle is itself formed from a solid drug or excipient.

In an embodiment the elongate microparticles are dimensioned to penetrate through a stratum corneum of skin. The dimensions may vary depending on the material of the elongate microparticles. The elongate microparticles may have a high aspect ratio. The aspect ratio

(length:width) may be at least about 10: 1 , such as at least about 15: 1. In some

embodiments the aspect ratio may be greater than 20: 1. The upper limit on aspect ratio may be about 200: 1 , such as about 150: 1. In some embodiments, the maximum aspect ratio is about 100: 1.

In one embodiment the length of the elongate microparticles is at least about 20 μηι and preferably at least about 50 μηι. The maximum length of the elongate microparticles may be about 800 μηι and is preferably about 500 μηι. In an embodiment the length of the elongate microparticles is in the range of from about 20 μηι to about 500μηι. The average length of the microparticles may be greater than about 75 μηι, such as greater than about 90 μηι. The average length may vary from about 90 to about 510 μηι.

In an embodiment the maximum width or diameter of the elongate microparticles is about 100 μηι and may be about 50 μηι or less, preferably less than about 40 μηι and more preferably is less than about 20 μηι. For some materials, the width may be less than about 12μηι, such as in the range of from about 5 to 10 μηι, in the case of silica.

In an embodiment, the elongate microparticles are substantially uniform in size. At least about 50%, and preferably at least about 70% of the elongate microparticles, may have lengths within about 80% of the median length. In an embodiment, at least about 80% of the elongate microparticles have lengths within about 80% of the median length.

In an embodiment the elongate microparticles may be hollow, solid or a combination thereof. The elongate microparticles may have a variety of shapes or profiles whilst still having a high aspect ratio. For example, the elongate microparticles can have a cross- sectional shape that is substantially circular, square, triangular or other. The elongate microparticles can be a mixture of the different types described.

In an embodiment at least some of the elongate microparticles have one or more substantially flat ends. In an embodiment at least some of the elongate microparticles have a tapered end geometry. The microparticles preferably have an end angled at less than about 180° and may be less than about 20° such as less than about 10°.

In an embodiment at least some of the elongate microparticles have one or more substantially convex ends.

In an embodiment the end surface area of the elongate microparticles may be a maximum of about 2000 square micrometers. The applicator surface can cause penetration of from about 1 to about 100 particles per mm ² . In some embodiments, the applicator ssuurface can cause penetration of about 40,

50, 60, 70 or 80 elongate microparticles per mm ² .

The applicator can cause penetration of the elongate microparticles to a depth of at least 40 μηι, such as up to 50 μηι, preferably up 60 μηι. The elongate microparticles do not tend to penetrate deeper than 60 μηι after application. This may be due to the dermal collagen acting as a physical penetration barrier to the elongate microparticles.

An average of up to about 15%, such as between 10 to 15 % of the elongate microparticles provided to the skin may penetrate into the dermis.

The number of elongate microparticles in the body will decrease over time as they are expelled from the body. It is expected that the elongate microparticles will be completely expelled from the body after about 1 , 2 or 3 weeks. The potential mechanism of elongate microparticle elimination could be associated with natural skin turn-over (desquamation). In humans, over approximately three weeks, new skin cells (keratinocytes) are generated within the stratum basale. The keratinocytes migrate upwards forming the cellular viable epidermis. As the cells migrate closer to the surface of the skin they begin to terminally differentiate (lose their cell nuclei) and flatten. This process renews the stratum corneum and aids in the natural removal of foreign bodies within the skin.

BRIEF DESCRIPTION OF THE DRAWINGS

Notwithstanding any other forms which may fall within the scope of the applicator and method as set forth in the Summary, specific embodiments will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 shows a side view of a first applicator embodiment.

Figure 2 (a) is a close up schematic view of different embodiments of the

microtextured surface.

Figure 2 (b) is an embodiment of the applicator in which the head can change from concave to convex upon the application of a force.

Figures 3 (a) and (b) show photomicrographs of the textured surface on the head of the first applicator embodiment.

Figure 3 (c) is a second applicator embodiment in the form of a cylindrical baton. Figure 4 (a) is a schematic showing an elongate microparticle (EMP) engaged and oriented by respective angled faces on the microtextured surface.

Figure 4 (b) is a schematic showing an elongate microparticle penetrating the skin at

45°.

Figure 5 is a schematic illustration comparing the use of a textured applicator head with a smooth applicator head.

Figure 6 shows photomicrographs of textured and smooth applicator heads and the respective skin penetration of NaF. Figure 7 is an SEM image of a microtextured applicator surface (100% of the surface is textured), a partially textured applicator surface (77% of the surface is textured; 23% of the surface comprises smooth area) and a smooth applicator surface (0% texturing); the graph shows the corresponding skin penetrations of NaF with different amounts of microtexturing with and without elongate microparticles;

Figure 8 is a graph showing the dependency of skin penetration depth on the angle of the elongate microparticles to the skin surface.

Figure 9 is a graph showing the delivery amounts of aminolevulinate (ALA) coated elongate microparticles delivered with the applicator, as compared to ALA delivered without the presence elongate microparticles.

Figure 10 is a graph showing the delivery amounts of NaF in a two stage application process in which elongate microparticles are applied to the skin first, followed by separate application of NaF.

Figure 11 is a graph showing the densities of nanoparticle penetration using no microparticles, short microparticles and long microparticles.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

Referring firstly to Figure 1 , a first embodiment of an applicator 10 for applying elongate microparticles to a biological barrier is shown. The applicator includes a body 12 suitable for being held in a user's hand and a removable applicator head 14 on which is provided a textured surface 16. The textured surface 16 has a generally convex profile 18. The applicator head 14 is provided on the end of a biased shaft 20. The biased shaft 20 is spring biased to an extended position (as shown). Upon application of a manually applied force to the applicator head 14 (such as when manually pressed against a patient's skin during use e.g. by massaging or rubbing), the shaft 20 is depressed (not shown) to a retracted position. The shaft 20 may include a scale thereon (not shown) indicating the amount of depression corresponding to the required amount of force for penetration of elongate microparticles through the skin layer during use.

Figure 2(a) (top row) is a close up schematic view of the applicator surface 16 of the embodiment in Figure 1 as it contacts with the skin. Three different micro-textured profiles are shown. The first type of texturing (leftmost image) comprises microridges or microsteps. The middle image shows a second type of texturing in the form of dimples (cross-sections of the dimples are seen). The rightmost image shows microchannels with a triangular cross- section. Figure 2(b) (bottom row) shows that an applicator 110 can have a flexible concave head 114 which becomes convex as pressure is applied to biased shaft 120. In the leftmost image, the head 114 is concave; as the spring deforms the head 1 14 it flattens (middle image); and as the spring applies more pressure the head 1 14 becomes concave. The variation in shape of the applicator head is advantageous in that the concave shape allows microparticles to be gathered and retained therein before modifying the shape to convex to allow rubbing or massaging the microparticles into the skin.

Figures 3 (a) and (b) show photomicrographs of the textured surface 216 (at respective different magnifications and orientations) on the head 214 of the first applicator embodiment 210. The textured surface 216 includes a series of laterally spaced elongate microridges 222 each providing two generally inwardly (with respect to the applicator head) angled faces 224 and 226. Figure 4 (a) shows how angled face 224 can orient the elongate microparticle 227; and how angled face 226 can engage the elongate microparticle 227. Engagement face 226 can apply a force to the elongate microparticle 227 to cause it to penetrate the skin. Successive microridges 222 are ~200μηι apart, as is evident from Figure 3 (a). Figure 3 (b) shows that the elongate microridges 222 are regularly divided into segments 228. The segmented character of the elongate microridges may assist in orientating the elongate microparticles by locating the ends of the elongate microparticles between segments during use. In Figure 4 (b) it can be seen that the elongate microparticle 227 can penetrate the skin at e.g. about 30°. It should be understood that Figures 4 (a) and (b) are schematic only and are not to scale.

Figure 3 (c) is a photomicrograph of another embodiment of an applicator 310 having a body in the form of a shaft 312 and a head 314 with a tip. The applicator 310 is in the form of a baton. The baton has a microtextured surface 316 along shaft 312 and over tip 314.

Figure 5 is a schematic illustration comparing the use of a textured applicator head (b) of the disclosure (e.g. the applicator of Figure 1) with a smooth surfaced applicator head (a). The smooth surfaced applicator head does not receive or orientate the elongate microparticles 430 for optimal skin penetration. In contrast, the textured applicator head 410 includes a series of laterally spaced elongate microridges 422 each providing two generally inwardly angled faces 424 and 426 that define spaces 432 for receiving the elongate microparticles 430 during use of the applicator. At least an end region 434 of each elongate microparticle 430 is received in the space 432 such that at least one angled face 424 engages the end 436 of the elongate microparticle 430 and the other angled face 426 defines the orientation of the elongate microparticle 430. The elongate microparticles 430 are orientated at an angle within a desired range to facilitate penetration of the biological barrier comprising skin 440.

Examples

Non-limiting Examples of methods employing embodiments of the applicator of the invention will now be described. Throughout the examples, any reference to microparticles should be understood to be a reference to elongate microparticles unless the context makes clear otherwise.

Example 1A

Data has been obtained that shows that the skin penetration of sodium fluorescein (NaF) is significantly enhanced when loaded elongate microparticles containing the dye are delivered using an applicator having a textured applicator head (such as illustrated in Figure 3) as compared with using an applicator head having a smooth texture.

Micro-textured curved applicator heads were printed using a 3D-printer. Autodesk Inventor Professional 2012 was used to draw the applicator and applicator heads. The file was exported as a stereolithography (STL) file. The applicator was 3D-printed using a V- Flash® FTI 230 Desktop Modeler (3D Systems®, USA). The UV-crosslinking resin consisted of a proprietary V-Flash® FTI-GN Material. Post processing was done using the company's protocol.

50 μΙ_ of a NaF solution was gently mixed with 5 mg of elongate microparticles manufactured in accordance with applicant's copending patent application

PCT/AU2013/000670 and available under the trademark Foroderm™. The mixture was placed on the surface of the skin of the volar forearm and gently massaged manually using the hand held applicator (either smooth or textured, respectively) for 30 s with 0.25 N of force. Excess NaF was wiped off followed by rinsing and drying of the skin prior to imaging by confocal microscopy. Scanning electron microscopy was used to image the applicator heads post treatment.

The results of Example 1 are shown in Figure 6. The top left and right

photomicrographs respectively show a smooth surfaced applicator head and the resulting small amount (11 , 143 +/- 2,747 total pixel intensity) of NaF (dye) penetration into the skin using the smooth textured applicator head. The middle left and right photomicrographs respectively show a textured applicator head and the resulting significantly higher amount (28, 100 +/- 2763 total pixel intensity, which is significantly greater (p = 0.0017, student t-test) of NaF penetration into the skin i.e. much greater than that produced by a smooth surface applicator head. The bottom photomicrograph shows the surface of the skin after application of elongate microparticles containing NaF dye using a smooth applicator head. As can be seen, the elongate microparticles are deposited on the skin surface, indicating lack of penetration into the skin. Example 1 B

The same procedures as in Example 1 A were followed. In this example, cylindrical shaped solid silica elongate microparticles (EMP) with an aspect ratio of 33 ± 22, a diameter of 9.3 ± 0.9 μηι and a length of 303.4 ± 208.7 μηι were chosen. Although the lengths have a broad profile, the bulk of the population consists of a high aspect ratio (28 ± 1 1) with 50 % of the EMPs having a length between 120.1 and 483.2 μηι.

Microtextured curved applicator heads were printed using a 3D-printer in order to compare the delivery efficacy of a textured head (Figure 7(a)) with a similarly shaped partially-textured head (Figure 7(b)) and a smooth applicator head (Figure 7(c)). The partially-textured surface of the applicator head consisted of both smooth and textured regions (23 ± 1 % of the projected area was smooth) with the same morphology as the fully textured head. The graph in Figure 7 shows that when used to deliver sodium fluorescein, the 100% micro-textured applicator head resulted in high intensity fluorescent signal within human skin (total pixel intensity of 13,830 ± 3,715). It was observed that the level of sodium fluorescein decreased when a partially textured applicator head was used (total pixel intensity of 10,494 ± 2,203). The 24 % reduction in signal was similar to the 23% decrease in texturing. The smooth applicator head resulted in a significant 41 % decrease in signal (total pixel intensity of 5,564 ± 1 , 174) compared to the 100% textured applicator (p < 0.0001). These results suggest micro-texturing of the applicator head has a significant influence on microparticle application. Also shown in the graph of Figure 7 are the results of application of NaF by the same applicators in the absence of elongate microparticles. It is clear that penetration of NaF is superior when applied using elongate microparticles and an applicator. Example 2

A separate investigation using excised pig skin demonstrated that the angle at which the elongate microparticles are applied to the skin determines the amount of skin penetration of the elongate microparticles. 50 μΙ_ of the NaF solution was gently mixed with 5 mg of elongate microparticles. The mixture was placed on the surface of excised pig skin and gently manually massaged using the textured applicator for 30 s with 0.25 N of force. Excess NaF was wiped off followed by rinsing and drying of the skin prior to imaging by confocal microscopy. Statistical analysis was done using GraphPad Prism 5.03. The results are shown in Figure 8. The graph shows that a more acute angle to the skin results in less penetration than a more obtuse angle.

The angle of inserted elongate microparticles was observed in the pig skin using reflectance confocal microscopy and this angle was used as a proxy for the angle of initial penetration.

The results indicate that the use of a textured applicator head results in enhanced delivery of payloads to the skin. The texturing aligns the elongate microparticles for optimal penetration into the skin. The elongate microparticles penetrated the skin at an angle of 15.11 +/- 7.71 degrees with respect to the skin surface. Potentially by tailoring the angle of the textured ridges on the applicator head, the elongate microparticles can be tailored to have specific penetration angles. This is important because as shown in Figure 8, the penetration depth of the elongate microparticles is significantly correlated to the penetration angle.

Example 3

Force effects on microparticle application were explored using sodium fluorescein delivery in human skin. The cross-sectional heat map images (not shown) of representative regions within a treatment site show that with 0 N application force applied to elongate microparticles by an applicator on the surface of the skin, the amount of fluorescence signal detected was minimal and was restricted to the surface of the skin. A manual force of 0.1 N applied by an applicator to elongate microparticles on the skin resulted in a significant increase in signal, which remained relatively constant with additional forces up to 0.5 N. However, a 2.5 N application force applied by an applicator to elongate microparticles on the skin resulted in an increase in signal and uniformity (adjusted p = 0.0006). Example 4

50 μΙ_ of 0.01 mCi/mL ¹⁴ C-5-aminolevulinic acid hydrochloride was gently mixed with 5 mg of elongate microparticles manufactured in accordance with applicant's copending patent application PCT/AU2013/000670 and available under the trademark Foroderm™. Following mixing the elongate microparticles were dried at ambient conditions in a fume hood. The elongate microparticles were then applied to the skin using an applicator in accordance with an embodiment of the present invention. In order to provide a comparison, ALA was applied to the skin directly (i.e. without the use of elongate microparticles at all). Figure 9 shows that there was a 2.6 fold improvement in the delivery of aminolevulinate (ALA) across the skin when elongate microparticles (EMP) were used as a vehicle as compared to ALA applied to the skin in the absence of microparticles. Example 5

The graph of Figure 10 shows the results of applying elongate microparticles (EMPs) before the application of NaF. Elongate microparticles were massaged or rubbed into the surface of the skin using an applicator in accordance with the present invention. Excess elongate microparticles were then removed from the skin. Sodium fluorescein (NaF) was then applied to the area of the skin in which elongate microparticles had penetrated. The NaF was applied using the applicator to massage or rub the skin. The x-axis of the graph on Figure 10 shows different time periods (30, 60, 90, 120 s) over which NaF was massaged into the skin into the particle pretreated areas. A control was undertaken involving 120 seconds of massage of NaF using the applicator over an area in which there was no pretreatment with microparticles. It is clear that the use of microparticles elongate increased NaF penetration into the skin.

Example 6

The elongate microparticles were used to deliver NaF labelled 50 micron

nanoparticles into the skin. The graph of Figure 11 shows the delivery densities of nanoparticles to the upper layers of the skin using no microparticles, long microparticles and short microparticles. Short microparticles had a mean length 27.5 ± 9.8 μηι with 50% of the population having a mean length between 20.9 μηι and 32.6 μηι. Long microparticles had a mean length of 301.0 ± 209.5 μηι, with 50% of the population having a mean length between 118.0 μηι and 477.7 μηι.

The graph shows that long microparticles resulted in the highest signal (i.e. the highest density of nanoparticles in the skin). The labelled nanoparticles were detected by measuring the amount of NaF (dye) fluorescence. This corresponded to the visual observation. Short microparticless resulted in a similar intensity of nanoparticles signal on the surface of the skin as the application of nanoparticles without elongate microparticles. However, below the stratum corneum the signal was higher than without them.

Long microparticles resulted in significantly enhanced delivery of nanoparticles compared to without microparticles (p = 0.0093) using the Mann-Whitney test.

It was found that unlike smaller drug molecules, nanoparticles result in limited diffusion. This is shown by the 'pocketed' delivery profile, where the nanoparticles remain in close proximity to the microparticles. As the microparticles penetrate the skin layers, the nanoparticles accumulate within the elongate microparticle deposition sites.

Example 7

In a separate experiment it was demonstrated that long length elongate

microparticles (EMP) can also boost the penetration of EMP through mucosal skin surfaces. EMP used in this experiment varied in length (mean, 301.0±209.5μηι) such that 50 % of the microparticle population had a length between 1 18.0 and 477 μηι. In these in vivo mouse experiments, a 10μΙ quantity of sodium fluorescein (1 mg/ml) was pipetted into the vaginal tracts of mice. In one group of mice, dye application occurred only after prior application of a small quantity of EMP (5mg). The dye solution was gently massaged with a rod-like applicator. Such an applicator is shown in Figure 3(c). Vaginal tracts were removed at sacrifice and mounted for cryosectioning. When sodium fluorescein was applied to the mucosa in the absence of EMP, minimal fluorescence was observed within the tissue sections. However, when sodium fluorescein was administered in conjunction with EMP there was a significantly greater fluorescence signal detected throughout the surface of the epithelium. Analysis of the signal intensity demonstrated that the EMP assisted sodium fluorescein to penetrate within the epithelim to about 60μηι. This is more than 4 times deeper within the epithelium compared to delivery in the absence of EMP. This suggests that EMP can enhance the delivery of agents across both mucous containing and non- mucous containing skin or membrane and are useful for facilitating delivery to inaccessible surfaces (e.g. vaginal tract).

Whilst a number of specific applicator and method embodiments have been described, it should be appreciated that the applicator and method may be embodied in many other forms.

In the claims which follow, and in the preceding description, except where the context requires otherwise due to express language or necessary implication, the word "comprise" and variations such as "comprises" or "comprising" are used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the apparatus and method as disclosed herein.