WO2008123996A1

WO2008123996A1 - Randomly collapsed nanostructures and uses thereof

Info

Publication number: WO2008123996A1
Application number: PCT/US2008/004278
Authority: WO
Inventors: Shu Yang; Dinesh Chandra
Original assignee: The Trustees Of The University Of Pennsylvania
Priority date: 2007-04-02
Filing date: 2008-04-02
Publication date: 2008-10-16

Abstract

This invention relates to methods and compositions for whitening teeth. Specifically, the invention relates to compositions and methods of whitening teeth using collapsed nanostructure arrays.

Description

P-9392-PC RANDOMLY COLLAPSED NANOSTRUCTURES AND USES THEREOF

GOVERNMENT INTEREST

[0001] This invention was supported, in part, by NSF grants No. DMR00-79909 and DMR-0548070. The government may have certain rights in the invention.

FIELD OF INVENTION

[0002] This invention is directed to methods and compositions for whitening teeth. Specifically, the invention relates to compositions and methods of whitening teeth using collapsed nanostructure arrays.

BACKGROUND OF THE INVENTION

[0003] Stained, yellowed or discolored teeth are almost inevitable due to the absorbent nature of dental material. Everyday activities such as smoking or other oral use of tobacco products, and eating, chewing or drinking certain foods and beverages (in particular coffee, tea and red wine) cause undesirable staining of surfaces of teeth. Staining can also result from microbial activity, including that associated with dental plaque. Even with regular brushing and flossing, years of chromogen accumulation can impart noticeable tooth discoloration.

[0004] Since the early 1980s, the tooth whitening industry has developed from only receiving tooth whitening treatments in a dental office to the scenario existing today in which numerous competitors sell over-the-counter tooth whitening systems including various delivery systems.

[0005] Professional dental treatments frequently include a tooth surface preparation such as acid etching followed by the application of highly concentrated bleaching solutions (e.g., up to 37% hydrogen peroxide) and/or the application of heat or light. These procedures provide rapid results, but are expensive, and often require several trips to the dentist..

[0006] Current home treatment methods include abrasive toothpastes, toothpastes that produce oxides, whitening gels for use with a dental tray and whitening strips. The effectiveness of such techniques depends on a variety of factors including the type and intensity of the stain, the type of bleaching agent, contact time of the bleaching agent on the teeth, the amount of available bleaching active in the composition, the ability of the bleaching agent to penetrate the tooth enamel, and consumer P-9392-PC compliance. Effectiveness of many of these treatments is adversely affected because of deficiencies in one or more factors relating to the composition and consumer compliance.

[0007] Accordingly, there is a need for improved compositions and methods for whitening teeth that s are capable of whitening the teeth rapidly and relatively inexpensively and that are able to be used at a lower concentration of peroxide, thus preventing tissue irritation, or causing tooth sensitivity.

SUMMARY OF THE INVENTION 0

[0008] In one embodiment, the invention provides a tooth whitening composition comprising a randomly collapsed array of polymeric nanostructures, whereby the air voids trapped between the collapsed array of polymeric nanostructures causes random light scattering. 5 [0009] In another embodiment, the invention provides a tooth whitening product, comprising: a strip of a material capable of being adapted to cover the front surface of one or more teeth; and a layer of a tooth whitening composition disposed on said strip of material, wherein said whitening composition comprises a randomly collapsed array of nanostructures, thereby affecting non-uniform light scattering that appears white. o

[00010] In one embodiment, the invention provides a method of making a randomly collapsed array of polymeric nanostructures, comprising: fabricating a master nanopillar array; generating a negative mold of the master; casting the mold with a liquid precursor of a polymer; hardening the polymer, thereby creating an array of polymeric nanostructures; removing the hardened polymer; and collapsing5 the polymeric nanostructures.

[00011] In another embodiment, the invention provides a method of whitening teeth, comprising adsorbing onto the surface of a tooth a strip of a material capable of being adapted to cover the front surface of one or more teeth; and a layer of a tooth whitening composition disposed on said strip of0 material, wherein said whitening composition comprises a randomly collapsed array of nanostructures, whereby the randomly collapsed array of nanostructures result in random light diffraction.

[00012] Other features and advantages of the present invention will become apparent from the following detailed description examples and figures. It should be understood, however, that the5 detailed description and the specific examples while indicating preferred embodiments of the invention are given by way of illustration only, since various changes and modifications within the P-9392-PC spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

[00013] The invention will be better understood from a reading of the following detailed description taken in conjunction with the drawings in which like reference designators are used to designate like elements, and in which:

Figure 1 shows a schematic illustration of the nanopillar dimensions;

Figure 2 shows (A) Schematic illustration of the replica molding steps from a Si master to a polymer replica using a PDMS mold. (B) Optical and SEM images of the non-collapsed and collapsed hydrogel nanopillar arrays from poly(2-hydroxyethyl methacrylate) (PHEMA);

Figure 3 shows SEM images of nanopillars at different processing steps of replica molding, (a-c) Silicon nanopillars masters, (d-f) PDMS molds replicated from corresponding silicon masters seen in Figure 2a-c. (g-i) Epoxy nanopillars molded from corresponding PDMS molds seen in Figure 2d-f. Feature dimensions: (a,d,g) cone-shape, h = 1 μm, d (tip) ) 300 nm, d (bottom) ) 680 nm, w= 1.32 μm; (b,e,h) circular cylinder, h = 9 μm, d = w= 500 nm; (c,f,i) square cylinder, h-9 μm, d=w=l μm;

Figure 4 shows cross-sectional SEM images of epoxy nanopillar array seen in Figure 3g-I;

Figure 5 shows a comparison of the fine features appeared in cone-shaped nanopillars from (a) silicon master and (b) its epoxy replica;

Figure 6 shows SEM images of molded nanopillars from (a) PDMS and (b) polyurethane with h=9 μ m and d=w=500 nm;

Figure 7 shows SEM images of various epoxy nanopillars (circular cylinders) with the same height, h-9 μm. (a) d =w=750 nm, (b) d =w=500 nm, (c) d =w =400 nm, and (d) d =400 nm, w =650 nm;

Figure 8 shows SEM images of partially restored epoxy nanopillars after the supercritical CO2 drying in comparison to the collapsed ones seen in Figure 7c,d. (a) h =9 μm, d= w= 400 nm, and (b) h= 9 μm, d= 400 nm, w= 650 nm; P-9392-PC Figure 9 shows the viscosity of PHEMA-PNIPAAm prepolymer vs. UV exposure time. UV intensity is 8.5 mW/cm2;

Figure 10 shows SEM images of epoxy nanopillars collapsed in different solvents;

Figure 11 shows SEM images of hydrogel pillars from copolymers of poly(methyl methacrylate-co- hydroxylethyl methacrylate) with different compositions and different topography after immersed in water and subsequently dried;

Figure 12 shows an average numbers of hydrogel pillars per cluster from copolymers of poly(methyl methacrylate-co-hydroxylethyl methacrylate) with different compositions and topography after immersed in water and subsequently dried.: and

Figure 13 shows whiteness of hydrogel pillars from copolymers of poly(methyl methacrylate-co- hydroxylethyl methacrylate) with different compositions and topography after immersed in water and subsequently dried.

DETAILED DESCRIPTION OF THE INVENTION

[00014] This invention relates in one embodiment to methods and compositions for whitening teeth. In another embodiment, provided herein are compositions and methods of whitening teeth using collapsed nanostructure arrays.

[00015] In one embodiment, provided herein are fabricated arrays of nanostructures from biocompatible hydrogels that in one embodiment, can be directly molded to the tooth surface to diffract blue light, which will compensate the yellow color of teeth. In another embodiment the bonding strength between hydrogel materials and the tooth surface is optimized. In another embodiment, provided herein is a fabricated high-aspect-ratio nanopillars, which in another embodiment, are purposely collapsed after molding onto the tooth surface. In another embodiment, collapsing the nanopillars produces random topography that results in non-uniform light scattering thereby appearing white (See Fig. 9B).

[00016] According to this aspect of the invention and in one embodiment, provided herein, is a tooth whitening composition, comprising a randomly collapsed array of polymeric nanostructures, whereby the collapsed array of polymeric nanostructures causes random light P-9392-PC scattering. In another embodiment, the nanostructure array used in the compositions and methods described herein, is made of biocompatible hydrogels.

[00017] In one embodiment, random scattering of light covering all the visible wavelengths thereby

₅ making surfaces appear white. In one embodiment, a network of nanoscale structures that are devoid of any periodicity will have a very different refractive index to the air that surrounds them allowing them to scatter light over the entire visible spectrum. In another embodiment, the term "collapsed" refers to the inability of a solid phase material to stand straight such that they either fall to the ground (ground collapse) due to the adhesion between the substrate and the polymer nanostructures, or stick too each other (lateral collapse) due to the adhesion between the polymer nanostructures. In one embodiment, the term "hydrogel" refers to a substance formed when an organic polymer (natural or synthetic) is set or solidified to create a three-dimensional open-lattice structure that entraps molecules of water or other solution to form a gel. The solidification can occur, e.g., by aggregation, coagulation, hydrophobic interactions, or cross-linking. In one embodiment, the hydrogels provided herein, rapidlys solidify to keep the nanostructures at the desired dimensions of aspect ratio and periodicity, but collapse randomly when exposed to water, allowing the scatter of light covering all visible wavelengths, appearing white. In another embodiment, the hydrogels used in the compositions and methods provided herein are also biocompatible, referring in one embodiment to being non toxic to tissues in contact with the hydrogel. In one embodiment, the hydrogels used in the methods and0 compositions provided herein are formulated from the monomers 2-hydroxyethyl methacrylate or (HEMA), ethylene glycol dimethacrylate (EGDMA), diethyleneglycol di methacrylate (DEGDMA), tetraethyleneglycol dimethacrylate (TE-EGDMA), polyurethane dimethacrylate (UDMA), tri(ethylene glycol) dimethacrylate (TEGDMA), and other dimethacrylates, acrylamide (Am), their copolymers, polyhedral oligomeric silsequioxane (POSS), epoxide POSS, dimethacrylate POSS, their copolymersS or a combination thereof in other embodiment.

[00018] In one embodiment a bright white is acheived by varying the feature size, aspect ratio, shape, and refractive index, crosslinking density and chemical composition (see e.g. Figure 11) of the hydrogel. The term "feature size" refers in one embodiment to the size of an individual structure in the0 array, or in another embodiment, the height of the nanopillar. In another embodiment, the shape of the nanostructures may be cylindrical in one embodiment, or in another embodiment the feature may be conical, or frusto-conical. In another embodiment, the shape may be pyramidal, or frusto-pyramidal or square in yet another embodiment. A person skilled in the art would readily recognize that the feature's geometrical shape is merely a factor in the optimization of the nanostructure, which willS depend on the monomers used to construct the hydrogel and other similar factors, but will not exceed the scope of the invention provided herein so long as the end result is a discrete nanostructure array as P-9392-PC described herein. In one embodiment, the feature size of the nanostructures used in the methods and compositions for tooth whitening described herein, is between about lOOnm to about 100 μm.

[00019] In one embodiment, varying the relative concentration of each monomer used to form the hydrogels and nanopillars, will affect their surface properties and the resulting average number of pillars in each collapsed cluster. A person skilled in the art would readily recognize that this feature could be used to modulate the degree of whiteness of the final composition. An example of the effect of monomer concentration on the average number of nanopillars per cluster is shown in Figure 12. In one embodiment, an optimal degree of whiteness may be achieved using a predetermined monomer concentration, which in another embodiment is a function of the feature size and shape as described herein. Accordingly and in another embodiment, the compositions and methods described herein further involve the determination of the optimal ratio of monomers used, to yield the highest degree of whiteness. In one embodiment, when the monomers are methyl methacrylate (MMA) and hydroxylethyl methacrylate (HEMA), the optimal concentration of MMA is 40% (see e.g. Figure 13, showing whiteness of hydrogel pillars from copolymers of poly(methyl methacrylate-co-hydroxylethyl methacrylate) with different compositions and topography after immersed in water and subsequently dried).

[00020] In one embodiment, the term "aspect ratio" refers to the ratio between the longest dimension of the feature and its shortest dimension. In one embodiment, the feature is square and the aspect ratio is between the height of the feature and its width, or in one embodiment, the feature is cylindrical and the aspect ratio is between the height of the feature and it diameter. In one embodiment, the aspect ratio of the feature used in the nanostructure arrays used in the compositions and methods provided herein, is between about 3 to about 25. In one embodiment the aspect ratio of the nanopillars is between about 3 and about 10. In another embodiment the aspect ratio of the nanopillars is between about 10 and about

15. In another embodiment the aspect ratio of the nanopillars is between about 15 and about 20. In another embodiment the aspect ratio of the nanopillars is between about 20 and about 25.

[00021] In one embodiment, bright white surface is obtained by optimizing the topography of the nanopillars array used in the compositions and methods provided herein. The term "topography" refers in one embodiment to the arrangement of the nanopillars on the surface of the array. In one embodiment, the number of nanopillars per unit area, or in another embodiment, the distance between adjacent pillars, or in another embodiment, the size of the pillars or their combination, would be varied to effect a different topography to the nanostructure array. P-9392-PC [00022] In one embodiment, bright white surface is effected using the compositions and methods provided herein, by varying the refractive index of the resulting array. This is affected in one embodiment by the choice of hydrogels used. In one embodiment, the refractive index of the nanostructures used in the methods and compositions for tooth whitening described herein, is between about 1.4 - 1.8.

[00023] In one embodiment, the compositions provided herein, are used in the methods for whitening teeth described herein. Accordingly, and in one embodiment, provided herein is a tooth whitening product, comprising: a strip of a material capable of being adapted to cover the front surface of one or more teeth; and a layer of a tooth whitening composition disposed on said strip of material, wherein said whitening composition comprises a randomly collapsed array of nanostructures, thereby affecting non-uniform light scattering that appears white. In one embodiment, the strip of material is sized to cover the front or labial/buccal surface of one or more teeth. In another embodiment, the strip of material is sized to cover the front surface of a plurality of teeth as well as at least some of the soft tissue adjacent those teeth. As used herein, the term "soft tissue" refers to one of the gingival margins. In another embodiment, the strip of material is sized to cover the front surface of a plurality of teeth, at least some soft tissue adjacent the plurality of teeth, and at least some of the back or lingual surface of the plurality to teeth. In one embodiment, the strip of material is sized to cover the front, six to eight teeth of the upper or lower rows of teeth that are visible when the wearer is smiling or either the maxillary dentition or the mandibular dentition. In another embodiment, the strip of material fits the entire upper or lower rows of teeth when positioned against the teeth.

[00024] In one embodiment, the layer of the tooth whitening composition is a homogeneous, uniform and continuous layer. In another embodiment the thin layer is non-uniform, non-continuous, and/or heterogeneous. In one embodiment, the thin layer is a laminate or separated layers of components, an amorphous mixture of components, separate stripes or spots or other patterns of different components, or a combination of these nanostructures as described herein. The tooth whitening composition of the present invention can be provided in the form of a viscous liquid, paste, gel, solution, or any other state or phase that can form a thin layer. The tooth whitening composition can be provided in the form of a gel with a viscosity between about 200 and about 1 ,000,000 cps at low shear rates (approximately one seconds '). In another embodiment, the viscosity is between about 100,000 and about 800,000 cps or between about 150,000 and about 700,000 cps. In yet another embodiment, the viscosity is between about 300,000 and about 700,000 cps.

[00025] In one embodiment, the tooth whitening composition also has a yield stress. Yield stress is the amount of force on a material required before the material begins to move. The yield stress must be P-9392-PC high enough so that the tooth whitening composition described herein, for whitening teeth, is able to form a thin layer and also to handle the disturbances caused by manufacturing, handling, and storage. The yield stress of the tooth whitening composition is between about 2 Pascals and about 3000 Pascals, or in another embodiment, between about 20 Pascals and about 2000 Pascals, or in another embodiment, between about 200 Pascals and about 1500 Pascals, or in another embodiment, between about 400 Pascals and about 200 Pascals. In one embodiment additional constituents are added to the tooth whitening composition such as water in one embodiment, or gelling agents, humectants, pH adjusting agents, stabilizing agents, desensitizing agents, plasticizers, cross likning agents or their compbination in other embodiments of the product described herein.

[00026] Suitable gelling agents useful in the present invention include "Pemulen" made by B. F. Goodrich Company, carboxypolymethylene, carboxymethyl cellulose, carboxypropyl cellulose, hydroxyethyl cellulose, poloxamer, Laponite, carrageenan, Veegum, carboxyvinyl polymers, and natural gums such as gum karaya, xanthan gum, Guar gum, gum arabic, gum tragacanth, and mixtures thereof. The preferable gelling agent for use in the present invention is carboxypolymethylene, obtained from B. F. Goodrich Company under the tradename "Carbopol". Particularly preferable Carbopols include Carbopol 934, 940, 941 , 956, 971, 974, 980, and mixtures thereof. Particularly preferred is Carbopol 956. Carboxypolymethylene is a slightly acidic vinyl polymer with active carboxyl groups.

[00027] Other suitable gelling agents include both polymers with limited water solubility as well as polymers lacking water solubility. Suitable limited water solubility adhesives include: hydroxy ethyl or propyl cellulose. Adhesives lacking water solubility include: ethyl cellulose and polyox resins. Another possible adhesive suitable for use in the instant composition is polyvinylpyrrolidone with a molecular weight of about 50,000 to about 300,000. Still another possible adhesive suitable for use in the instant composition is a combination of Gantrez and the semisynthetic, water-soluble polymer carboxymethyl cellulose.

[00028] A pH adjusting agent may also be added to make the composition safe for oral tissues. These pH adjusting agents, or buffers, can be any material that is suitable to adjust the pH of the composition. Suitable materials include sodium bicarbonate, sodium phosphate, sodium hydroxide, ammonium hydroxide, potassium hydroxide, sodium stannate, triethanolamine, citric acid, hydrochloric acid, sodium citrate, and combinations thereof. The pH adjusting agents are added in sufficient concentrations so as to adjust the pH of the composition to between about 3 and about 10, preferably between about 4 and about 8.5, and more preferably between about 4.5 and about 8. The pH P-9392-PC adjusting agents are generally present in an concentration between about 0.01 % and about 15% and preferably between about 0.05% and about 5%, by weight of the composition.

[00029] Suitable stabilizing agents include benzoic acid, salicylic acid, butylated hydroxytoluene, tin salts, phosphates, and others. Suitable bleach activators include trichloroisocyanuric acid and the phosphates, such as tetrasodium pyrophosphate.

[00030] Desensitizing agents may also be used in the tooth whitening composition. These agents may be preferred for consumers who have sensitive teeth. Desensitizing agents include potassium nitrate, citric acid, citric acid salts, strontium chloride, and combinations thereof. Potassium nitrate is a preferred desensitizing agent. Other agents which provide the benefit of reduced tooth sensitivity are also included in the present invention. Typically, the concentration of a desensitizing agent is between about 0.01% and about 10%, preferably between about 0.1% and about 8%, and more preferably between about 1 % and about 7% by weight of the tooth whitening composition.

[00031] In one embodiment, the term "swelling index" refers to the free volume of the interior of a polymer, as a parameter for indicating the swelling degree of gel by solvent. The swelling index of the nanostructures used in the compositions and methods for teeth whitening described herein, decreases as the cross-linking density increases, and it increases as the cross-linking density decreases. In another embodiment, the cross-linking density varies according to the amount of the cross-linkers charged thereto when the nanostructure array is prepared, and impact resistance of the molded collapsed nanostructure is improved as the swelling index is increased by the use of a small amount of the cross-linkers. In one embodiment, the whitening composition provided herein, used in the methods described herein, has a crosslinker concentration of between about 1-30% (w/w).

[00032] In one embodiment, the teeth whitening compositions and products provided herein, are made using the methods described herein. Accordingly and in one embodiment, provided herein is a method of making a randomly collapsed array of polymeric nanostructures, comprising: fabricating a master nanopillar array; generating a negative mold of the master; casting the mold with a liquid precursor of a polymer; hardening the polymer, thereby creating an array of polymeric nanostructures; removing the hardened polymer; and collapsing the polymeric nanostructures.

[00033] In another embodiment, the nanopillars of the master nanopillar array in the method of making a randomly collapsed array of polymeric nanostructures are conical, frusto-conical, cylindrical, square, or their combination. In one embodiment, the step of generating a negative mold of the master array is carried out by covering the master array with a liquid phase of a mold polymer. In another P-9392-PC embodiment, the liquid phase is a melt, an emulsion, a solution, or a suspension of the mold polymer.

In one embodiment, the mold polymer is epoxy, polycarbonate and the like.

[00034] In another embodiment, provided herein is a method of making a randomly collapsed array of

5 polymeric nanostructures, comprising: fabricating a master nanopillar array; generating a negative mold of the master; casting the mold with a liquid precursor of a polymer; hardening the polymer, thereby creating an array of polymeric nanostructures; removing the hardened polymer; and collapsing the polymeric nanostructures, whereby in one embodiment the step of generating a negative mold of the master array is carried out by covering the master array with a liquid phase of a mold polymer, ando whereby in another embodiment, the step of hardening the mold polymer or the casting polymer in another embodiment, comprises heating, UV light curing, drying removing solvent, concentrating or a combination thereof.

[00035] In one embodiment, the term hardening refers to any action that will enable the mold5 comprising the imprinted nanostructure used for teeth whitening described herein, to be able to support their own weight, these nanopillars which in certain embodiments may vary in feature size, density, uniformity, shape or a combination thereof, to maintain their shape upon introduction of the liquid precursor used to fabricate the nanostructure array used in the compositions and products for teeth whitening described herein. Accordingly and in one embodiment, the step of casting the mold with ao liquid precursor of a polymer, comprises filling the mold with a melt, an emulsion, a solution, or a suspension of a polymer. In one embodiment, the precursor polymer is a biocompatible hydrogel formulated from the monomers 2-hydroxyethyl methacrylate (HEMA), ethylene glycol dimethacrylate

(EGDMA), diethyleneglycol dimethacrylate (DEGDMA), tetraethyleneglycol dimethacrylate (TE-

EGDMA), polyurethane dimethacrylate (UDMA), tri(ethylene glycol) dimethacrylate (TEGDMA),₅ and other dimethacrylates, acrylamide (Am), their copolymers, polyhedral oligomeric silsequioxane

(POSS), epoxide POSS, dimethacrylate POSS, their copolymers or a combination thereof.

[00036] In another embodiment, provided herein is a method of making a randomly collapsed array of polymeric nanostructures, comprising: fabricating a master nanopillar array; generating a negativeo mold of the master; casting the mold with a liquid precursor of a polymer; hardening the polymer, thereby creating an array of polymeric nanostructures; removing the hardened polymer; and collapsing the polymeric nanostructures, whereby the step of collapsing comprises reducing the polymer's

Young's modulus (E) to be lower than the critical elastic modulus for a ground collapse, ( £^* )•

Elasticity refers in one embodiment, to the property of the nanopillar described herein, which causes it₅ to be restored to its original shape after distortion. Distortion may occur in one embodiment due to gravitational forces acting on the features or nanopillars of the nanostructures used in the P-9392-PC compositions, products and methods provided herein. In one embodiment, the term "Young's modulus" refers to the ratio of the stress to the strain, of the material. In one embodiment, Young's modulus is used to predict the elongation or compression of an object as long as the stress is less than the yield strength of the material.

[00037] In one embodiment, provided herein is a method of making a randomly collapsed array of polymeric nanostructures, comprising: fabricating a master nanopillar array; generating a negative mold of the master; casting the mold with a liquid precursor of a polymer; hardening the polymer, thereby creating an array of polymeric nanostructures; removing the hardened polymer; and collapsing the polymeric nanostructures, whereby the step of collapsing comprises reducing the polymer's Young's modulus (E) to be lower than the critical elastic modulus for a lateral collapse (E_L ^* ).ln one embodiment, Ground collapse refers to the collapse of the nanopillars to the ground, which can be attributed to either the nanopillar' s own weight or the surface adhesive force. In another embodiment, Lateral collapse refers to adhesion among nanopillars when they are too close to each other. Lateral collapse refers in another embodiment to a surface phenomena controlled by adhesive forces. In one embodiment, collapsing the nanostructures used in the compositions and products provided herein, and that are used in the methods described herein is effected by contacting the cast biocompatible polymer with a plasticizer. The term "plasticizer", refers in one embodiment to the ability of the added agent to reduce Tg, or in another embodiment, to increase the free volume or swelling index of the amorphous state.

[00038] In one embodiment, the nanostructures produced using the methods provided herein, are used in the methods of teeth whitening provided herein, accordingly and in one embodiment, provided herein is a method of whitening teeth, comprising adsorbing onto the surface of a tooth a strip of a material capable of being adapted to cover the front surface of one or more teeth; and a layer of a tooth whitening composition disposed on said strip of material, wherein said whitening composition comprises a randomly collapsed array of nanostructures, whereby the randomly collapsed array of nanostructures result in random light diffraction. In one embodiment, any of the strips described hereinabove, are used in the method for whitening teeth provided herein. In one embodiment, the non- collapsed nanostructures used in the compositions and products provided herein, diffracts blue light.

[00039] In one embodiment, provided herein is a method of whitening teeth, comprising adsorbing onto the surface of a tooth a strip of a material capable of being adapted to cover the front surface of one or more teeth; and a layer of a tooth whitening composition disposed on said strip of material, wherein said whitening composition comprises a randomly collapsed array of nanostructures, whereby the randomly collapsed array of nanostructures result in random light diffraction, whereby adsorbing P-9392-PC comprises etching the enamel surface of the tooth with acid; and applying a liquid hydrogel precursor to the acid etched surface. Acid etch enamel before applying the liquid hydrogel precursor. In one embodiment, a 10% solution of phosphoric acid is placed on the enamel portions of the tooth for fifteen seconds to introduce rough surface. In another embodiment, the liquid hydrogel precursor flows s in and fill the valleys and bond to the enamel.

[00040] In one embodiment, provided herein is a method of whitening teeth, comprising adsorbing onto the surface of a tooth a strip of a material capable of being adapted to cover the front surface of one or more teeth; and a layer of a tooth whitening composition disposed on said strip of material, wherein

I₀ said whitening composition comprises a randomly collapsed array of nanostructures, whereby the randomly collapsed array of nanostructures result in random light diffraction, whereby adsorbing comprises chemical adhesion of enamel and dentin, by adding metallic polyakenoate salts, thereby partially dissolving the hydroxyapetite and chelating hydroxyapetite; and cross linking the dissolved hydroxyapetite with the hydrogel. In one embodiment, hydrogel precursor is formulated by adding

15 metallic polyakenoate salts, which partially dissolves the hydroxyapetite and chelates hydroxyapetite by replacing phosphate ions. In another embodiment, the crosslinking of hydrogel and tooth structure gives excellent chemical bonding strength.

[00041] In another embodiment, provided herein is a method of whitening teeth, comprising chemical

20 adhesion of enamel and dentin, by adding metallic polyakenoate salts, thereby partially dissolving the hydroxyapetite and chelating hydroxyapetite; and cross linking the dissolved hydroxyapetite with the hydrogel. as a layer of a tooth whitening composition disposed on said strip of material, wherein said whitening composition comprises a randomly collapsed array of nanostructures, whereby the randomly collapsed array of nanostructures result in random light diffraction and further comprising

25 the step of nucleating the whitening composition with calcium phosphate.

[00042] In one embodiment, the compositions and products used for teeth whitening described herein comprises hydroxyapetite impregnated in the nanostructure array.

30 [00043] In one embodiment, templated mineralization of calcium phosphate on is effected onto the hydrogel surface. In another embodiment, the aforementioned mineralization refers to mineral nucleation and growth occurring at room-temperature. In one embodiment, a master with arrays of nanostructures, is patterned based on the methods provided herein for making the nanostructures followed by replica molding into desired hydrogel system. In one embodiment, soft lithography is a

35 used pattern feature sizes ranging from 30 nm to 100 μ m over a large strip area. P-9392-PC [00044] In one embodiment, the size and shape of the hydroxyapatite crystals (Ca₅(PO₄)₃θH) grown in the hydrogels described herein are optimized to give a bright whitening effect when refracting light. In another embodiment, the size and shape of the calcium phosphate crystals grown in the hydrogels described herein are optimized to give a bright whitening effect when refracting light. In one 5 embodiment, degree of supersaturation of the initial Calcium Phosphate solution, or in other embodiments pH of the Hydrogel, temperature, feed rate, presence of other ions capable of acting as heterogeneous nucleation centers and their concentration, or their combination are used to yield an optimal crystal size and shape of hydroxyapatite, thereby enabling crystal size of between about 300 to about 900 nm. 0

[00045] The term "about" as used herein means in quantitative terms plus or minus 5%, or in another embodiment plus or minus 10%, or in another embodiment plus or minus 15%, or in another embodiment plus or minus 20%. s [00046] The following examples are presented in order to more fully illustrate the preferred embodiments of the invention. They should in no way be construed, however, as limiting the broad scope of the invention.

EXAMPLES o Materials and Methods:

Replica Molding of High-Aspect-Ratio Polymer Nanopillars

[00047] The replica molding technique involves three processing steps as illustrated in Figure 2: (1) fabrication of a patterned Si master with desired dimensions using 248-nm photolithography; (2) generating a negative PDMS replica from the original Si master as a mold; and (3) casting a liquid5 precursor against the PDMS mold, followed by curing and peeling off to obtain the patterned polymeric structures.

Fabrication of High-Aspect-Ratio Silicon Masters

[00048] An array of square or dot structures was photopatterned on 200-mm singlecrystal silicon0 wafers using 248-nm photolithography to create 4 mm x 10 mm fields. The resist pattern was transferred into Si using a high-density inductively coupled plasma (ICP) etching tool following a procedure to fabricate high-aspect-ratio silicon nanopillars. As shown in Figure 3a-c, three different shapes of high-aspect-ratio silicon nanopillars were fabricated, including cone-shape as well as circular and square cylinders. The width (or diameter) d of the nanopillars ranged from 300 nm to 15 μm, the height h ranged from 7 to 9 μm, and the spacing w between pillars ranged from 400 nm to

1.32 μm, respectively. For cone-shaped nanopillars (Figure 3a), the height h is 7 μm and the diameters P-9392-PC d at tip and bottom of the pillar are 300 and 680 nm, respectively. For purposes of calculation, the bottom diameter that gives an aspect ratio of 10.3 was used. For the circular cylinders, the height h is kept as 9 μm, and the diameters d are 400, 500 (Figure 3b), and 750 nm, respectively, resulting in an aspect ratio of 22.5, 18, and 12, respectively. For square cylinders, the height & is 9 μm and the width d is 1 μm with an aspect ratio of 9 (Figure 3c).

Replica Molding to Polymeric Nanopillars

[00049] Three types of nanopillars were prepared, (i) PDMS nanopillars: The as-produced PDMS mold was cleaned by DI water, 2-propanol, acetone, and oxygen plasma sequentially. It was then silanized with (tridecafluoro- l,l,2,2-tetrahydrooctyl)trichlorosilane for at least 2 h to ensure ease of peeling off the mold. The liquid PDMS prepolymer mixture was poured over the mold and covered with a glass slide on the top, followed by curing in an oven at 80 ⁰C for 2 h. (ii) Polyurethane nanopillars: UV- curable polyurethane (NOA 68, Norland Products, Inc.) was poured on the PDMS mold and exposed to a UV light (UVP Blak-Ray) for 10 min with a glass slide covering the top. (iii) Epoxy resin nanopillars: Epoxy resin DER 354 (Dow Chemical) was mixed with 3 wt % Cycracure UVI 6976 (Dow Chemical) as cationic photoinitiators. The viscous solution was degassed for 1 h and then was allowed to sit at least 2 min to ensure complete filling of the nanoporous PDMS mold before UV exposure for -15 min. After curing, all polymer nanopillars were carefully peeled off from the PDMS mold and investigated by SEM.

Supercritical CO2 Drying

[00050] Supercritical CO2 has low surface tension and high diffusivity. Supercritical drying has been used in photolithography and MEMS to prevent pattern collapse caused by capillary forces during drying. This technique was used to restore the collapsed high-aspect-ratio nanopillars. The collapsed nanopillars were first soaked in methanol solution, followed by ultra-sonification for 20 min to encourage the separation between the touched pillars. The wet sample was then transferred into the supercritical drier chamber (SAMDRI-PVT-3D from tousimis) and filled with liquid CO2. The methanol was purged from the chamber under a continuous flash of liquid CO2. After several purge- flash cycles to completely remove methanol, the chamber was heated above the critical point of CO2 (31.1 ⁰C, 7382 kPa) and maintained for 5 min before slowly venting to the atmosphere.

Characterization

[00051] Static contact angles between the liquid prepolymers and PDMS were measured using a goniometer equipped with a CCD camera averaged over 3 spots. Scanning electron microscopy (SEM) images were obtained on FEI Strata DB235 Focused Ion Beam under voltage of 8 keV. A spot size of

3 was chosen for high resolution and detailed topographical information. All samples were coated with P-9392-PC a thin layer of platinum. The dimension of nanopillars was measured using the preinstalled software on SEM.

Example 1: Fabrication of High- Aspect-Ratio Nanopillar Arrays by Replica Molding.

[00052] To fabricate the high-aspect-ratio silicon masters with good control of feature size, uniformity, and vertical profiles, high etch rates are necessary. Thus, inductively coupled plasma (ICP) etching was chosen over other common plasma sources, such as reactive ion etching (RIE). Figure 3a-c shows SEM images illustrating deep through-wafer etching with aspect ratios ranging from 9 to 18. The Si masters are then replica molded to various polymer nanopillars through corresponding PDMS molds. The use of PDMS molds is inexpensive, and multiple copies can be replicated from the original master; each PDMS mold can be reused many times without deformation, which makes it attractive for many applications. As seen in Figure 3d-f, the PDMS nanoporous membranes replicated from Si masters maintained the integrity over a large area. In the molding process, filling of the nanopores with liquid precursors is capillary-force-controlled. The complete filling time t can be estimated as:

2ηjι^" t =

Rv ^f cos Θ (Equ. 1)

[00053] where TJs is the viscosity of the liquid epoxy resin, R is the hydraulic radius of the nanopore, γ is the surface tension at the liquid/air interface, and θ is the contact angle between the liquid and the surface of the capillary. A lower contact angle (i.e., higher wettability) of liquid on the PDMS mold is preferred for complete filling at a shorter period of time. For example, the viscosity of liquid epoxy resin ηs is -4000 cps at 25 ⁰C, the surface tension γis ~40 mN/m, and the contact angle between the liquid epoxy resin and the PDMS mold is 57° (see Table 1). For the deepest nanopores (h=9 μm), the required complete filling time of epoxy is estimated as -0.1 s, which is much shorter than the time we used in the experiment, typically > min. Similarly, the required complete filling time of PDMS and polyurethane nanopillar arrays is less than Is. It is important to point out that Equ 1 ignores possible air trapped by the introduction of liquid precursors. Nevertheless, no air bubbles were observed in the fabricated nanopillars, and polymers fully penetrated the mold. Since PDMS is well-known for its high oxygen permeability, it is likely that air readily dissolves into the PDMS mold. Epoxy nanopillars replicated from the corresponding silicon masters with different shapes and dimensions (Figure 3a-c) were exemplified in Figure 3g-i. Up to an aspect ratio of 18, densely patterned cylindrical epoxy nanopillars (e.g., h =9 μm, d=500 nm, and w=500 nm, see Figure 3h) were found stable without any pattern collapse (Table 1). P-9392-PC Table I: Physical Properties of PDMS (RTV615), Polyurethane (NOA68). and Epoxy Resin

(DER-354)

PDMS polyurethane epoxy resin

Young' s modulus, E (MPa) 1.7 ± 03^β 138⁶ ~3000* viscosity at 25 ⁰C (cps/ 4000 5000 3500-4500 surface tension, γ_s ( mN/m) 19.8^f ~40 ~40 contact angle (θ) (⁰Y 70 42 57

[00054] The cross-sectional view (Figure 4) clearly shows that the epoxy nanopillars have the same height as the original silicon masters, 7 μm and 9 //m for the cone-shaped and cylindrical nanopillars, respectively. It is interesting to note that a closeup view of the cone-shaped Si nanopillars reveals fine ring features (see Figure 5a) generated during the anisotropic etching process. In the corresponding epoxy nanopillars, such ring features were faithfully replicated (Figure 5b), which further illustrates the high fidelity of replica molding from epoxy resin.

Example 2: Polymer Stiffness affects the Stability of Nanopillar Arrays

[00055] Because of the low modulus of PDMS, the aspect ratio of the stable PDMS nanopillar is limited to 6, above which the PDMS nanopillars will ground collapse or lateral collapse. Ground collapse refers to the collapse of the nanopillars to the ground, which can be attributed to either the nanopillar's own weight or the surface adhesive force. Lateral collapse refers to adhesion between nanopillars when they are too close to each other. It is anticipated that the stiffness of the molded materials will play a critical role in the success of replica molding of high-aspect-ratio nanopillars. To prove the principle of concept, two more molding materials from PDMS (RTV 615) and polyurethane (NOA 68), respectively were investigated, and compared the replication results to that from epoxy. The physical dimension and shape of the master and mold are kept the same as the epoxy nanopillars, and the replication results for nanopillars from PDMS and polyurethane are shown in Figure 6. All PDMS nanopillars (aspect ratio >9) were found ground collapsed (Figure 6a), whereas lateral collapse occurred in polyurethane nanopillars when the aspect ratio was above 12 (Figure 6b, Table 3). These results are in sharp contrast to the behavior of high-aspect-ratio epoxy nanopillars, which collapse laterally above the aspect ratio of 18. To better understand the nature of mechanical instability in the high-aspect-ratio polymer nanopillars, experimental results were compared with theoretical prediction. There are two established models to explain the ground collapse. Hui et al. (Langmuir 2002, 18, 1394.) have assumed that the nanostructures fall under their own weight, whereas Roca-Cusachs and co- workers believe that gravitational force is not the major force when the feature size is on the order of micro- and nanometers but rather the adhesion forces should be taken into account. Based on Hui's P-9392-PC model that the nanopillar ground collapses under its own weight, the critical elastic modulus of ground collapse, E_g ^* , can be estimated as:

^E& 7.837/ ₍E,u.2)

[00056] where / ) ΛJ//64 for a circular cylinder, and q=pgπd²/4 is the weight per unit length of the cylinder. When the elastic modulus E of the polymers is greater than E_g ^* , no ground collapse should occur. For circular cylinders with h=9 μm, d=w=500 nm, the calculated critical elastic modulus of ground collapse, £^* , is 57 Pa, which is much smaller than the elastic modulus of PDMS, £'=1.7+0.3

MPa. According to the gravitational collapsing theory all fabricated PDMS nanopillars should be stable, which is in contrast to the experimental results. If ground collapse is mainly caused by adhesion force to the ground, the critical elastic modulus of ground collapse can be described by:

2"^Q3^3/4(1 - /)^] V²W

&^df² (Equ 3)

[00057] where W is work of adhesion, and V is the Poisson ratio. Given the work of adhesion of PDMS

(W=44 mN/m) and the Poisson ratio V=0.5, £^* is estimated as 36.9 MPa for circular cylinders with h=9 μm and d=w=500 nm, which is much greater than the elastic modulus of PDMS. Thus, ground collapse of these PDMS nanopillars is expected and was observed experimentally.

[00058] As deduced from the SEM images and theoretical prediction, high-aspect- ratio PDMS nanopillars were confirmed to undergo ground collapse by adhesion force. Similar calculation has been applied to polyurethane and epoxy nanopillars. For nanopillars with the largest aspect ratio (22.5 for h=9 μm, d=w=400 nm), E_g ^* is estimated as ~117 MPa, smaller than both the elastic moduli of the polyurethane (E=I 38 MPa) and epoxy (E=3000 MPa). Consistent with the prediction from the adhesion theory, no ground collapse was observed for all polyurethane and epoxy nanopillars.

[00059] Instead, lateral collapse occurred when the aspect ratio was above 12 and 18 for polyurethane and epoxy nanopillars, respectively. Using the lateral collapse theory established by Hui et al., the critical elastic modulus of lateral collapse for nanopillars with circular cross-sections was estimated:

P-9392-PC [00060] where γ_s is the surface energy of the nanopillar material. If the elastic modulus of the molded nanopillars E is greater than E_L ^* , there is no lateral collapse. For the collapsed polyurethane nanopillars (see Figure 6b), h=9 μm, rf=w=500 nm, and E_L ^*= 2300 MPa, which is much larger than the elastic modulus of the polyurethane, E =138 MPa. Therefore, lateral collapse of the polyurethane S nanopillars was expected and confirmed experimentally. In contrast, epoxy nanopillars with the same shape, dimension, and surface energy as the above polyurethane nanopillars were expected to be stable since E epoxy ~ 3000 MPa was much greater than E_L ^* and was confirmed experimentally (Figure 7b).

[00061] The comparison between three molding materials implies that material stiffness plays ano important role in the stability of polymer nanopillars and the nature of mechanical failure. When the polymers are very soft and the elastic modulus of polymers, E, is less than the critical elastic modulus of ground collapse, E_g ^* , ground collapse caused by the surface adhesive force will occur. To overcome the ground collapse, polymers with larger modulus are preferred. Lateral collapse becomes dominant if the polymer's elastic modulus E is less than the critical elastic modulus of lateral collapse, E_L ^* . 5 Example 3: Critical Aspect Ratio of Lateral Collapse

[00062] Besides stiffness, other factors such as pillar feature size, density, aspect ratio, and surface energy of molding materials, will affect the fidelity of fabrication of high-aspect-ratio nanopillars. On the basis of an existing model the critical aspect ratio of lateral collapse from nanopillars with twoo different shapes wascalculated:

(Equ. 5, for Cylindrical Pillars)

(Equ.6, for Orthogonal Pillars) [00063] Tables 2 and 3 compare the calculated critical aspect ratios vs the experiment results from epoxy and polyurethane nanopillars, respectively. The results in Table 2 indicate that the experimental5 results of epoxy nanopillars agree well with the theoretical prediction. No lateral collapse was observed when the aspect ratio of nanopillars is smaller than the calculated critical aspect ratio; the nanopillars are stable and can be replicated with high fidelity (see Figure 7a,b). When the nanopillars become very tall and the aspect ratios exceed their corresponding critical values, the nanopillars become unstable and lateral collapse occurs. For example, the two epoxy nanopillars shown in Figure0 7c,d (h=9 μm, w=d=400 nm, and h=9 μm, J=400 nm, w=640 nm, respectively) have an aspect ratio of 22.5, which is greater than their critical aspect ratios, 17.3 and 22, respectively; thereby, lateral P-9392-PC collapse was observed for both nanopillars. In the case of polyurethane nanopillars, the experimental results also agree well with the theoretical prediction with the exception of two structures: the square pillars with d=w=\ μm and the cylindrical pillars with d=w=l 50 nm, which are predicted to be unstable but are found experimentally to be stable. The discrepancy between experiment and theory might be attributed to the softer nature of polyurethane. It is worth noting that epoxy nanopillars with h=9 μm and d=w=500 nm, which have an experimental aspect ratio (18) close to the calculated critical value (18.6), show no apparent collapse after molding. However, lateral collapse could be easily induced later when they were in contact with water, which has a high surface tension of 72.8 mN/m. This implies that it is possible to manipulate the stability of nanopillars by the surface tension of solvents, which will allow to collapse the nanopillars.

P-9392-PC

[00064]

Table 2. Comparison of Calculated Critical Aspect Ratios and Experimental Results of Epoiy Nanopillar Arrays nanopillar dimension aspect ratio stability nan opillar shape rf(nm) Λ (/<m) »i i_'(nra) calculated critical value experimental result predicted observed circular cylinder 750 9 750 21 3 12 stable stable circular cylinder 500 9 500 1S.6 IS stable stable circular cylinder 400 9 400 17.3 22.5 unstable unstable circular cylinder 400 9 650 22 22.5 unstable unstable cone-shape" 680 7 1320 2S.7 10.3 stable stable square cylinder 1000 9 1000 12.4 9 stable stable

" Bottom diameter is used for calculation

Table 3. Comparisoi i of Calculated Critical Aspect Ratios and Experimental Results of Pohurelliane Nanopillar Arrays nanopillar dimension aspect ratio stability nanopillar shape tf(nm) Λ (//in) >ι i' (niτi) calculated critical value experimental result predicted observed circular cylinder 750 9 750 S.I 12 unstable stable circular cylindei 500 9 500 7 IS unstable unstable circular cylinder 400 9 400 6.5 22.5 unstable unstable circular cylinder 400 9 650 HA 22.5 unstable unstable cone-shape" 680 7 1320 10.9 10.3 stable stable square cylinder 1000 9 1000 6 9 unstable stable

" Bottom diameter is used tor calculation.

P-9392-PC

Example 4: Once collapsed, Nanopillar Arrays will substantially remain so

[00065] It is well-known that high surface tension of the developer will cause pattern collapse in high-aspect-ratio photoresist structures. SupercriticalCO2 that has nearly zero surface tension has been used to reduce the capillary force during drying to maintain the integrity of the resist patterns. Previously, this method was used to fabricate highly porous 3D polymeric microstructures with high aspect ratios. Here an attempt was made to use methanol/supercritical CO2 drying to restore the collapsed nanopillars. As seen in Figure 7c,d, before the solvent treatment, epoxy nanopillars with an aspect ratio of 22.5 are not stable and laterally collapsed: every six or more nanopillars adhere to each other to form bundles and the pattern lost initial grating color. The collapsed nanopillars were first immersed in methanol (?*=22.6 mN/m) to reduce the adhesion force between nanopillars. After ultra-sonification for 20 min, the color of nanopillar arrays changed from opaque to green, indicating at least some restoration of the nanopillars in methanol. The wet nanopillars were then treated with supercritical CO2 drying. Afterward, most of the originally collapsed nanopillars stand straight with every two or three nanopillars lightly touching on the tips (see Figure 8). Increased spacing (w=1.6d, Figure 8b) offers a slight improvement of the separation between nanopillars. This suggests that if the polymer nanopillars have collapsed already, varying the surface tension of solvent may not be sufficient to overcome the inelastic distortion. Even partially restored, the nanopillars are found to be metastable since their aspect ratio is already above the critical threshold.

Example 5: Patterning hydrogel nanopillars by soft lithography

[00066] Nanopillars of poly(2-hydroxy ethyl methacrylate-N-isopropyl acrylamide) (PHEMA-NIPAAm) were fabricated by a two step process: 1 ) partial prepolymerization and 2) photocrosslinking the prepolymers in PDMS mold.

[00067] Experimental details: For preparation of prepolymer mixture, 2.5 g HEMA with 20 wt% NIPAAm was mixed with 0.625 ml of water. 3 wt% Irgacure 1 173 was added as initiator. The mixture was exposed to UV light (8.5 mW/cm 2 ) for 3 minutes to obtain a viscous, random copolymer of the above two components. The viscosity of the partially polymerized copolymer for various exposure time can be seen in Figure 3. We found control P-9392-PC

of the prepolymer viscosity was critical to the success of molding the hydrogel nanostructures. Only when the viscosity is high enough, . 4.4x104 cps, we were able to replica the nanopillars into the hydrogels.

[00068] Before molding, 1 wt% ethylene glycol dimethacrylate (EGDMA) as crosslinker and 2 wt% Irgacure 1 173 as initiator were added to the viscous solution, stirred vigorously with a glass stir bar and then degassed in a dessicator for proper mixing. Using silicon with cone shaped nanopillars as master, inverse PDMS mold was created according to the procedure seen in Fig. 2. A droplet of liquid mixture was then placed on the PDMS mold, followed by UV curing to create the hydrogel nanopillars seen in Fig. 2b.

[00069] Depending on the mechanical strength (e.g. Young's moldulus) of the cured polymer and solvent used, it was anticipated that nanopillars will collapse into different shapes, which may affect their whiteness. For example, while the PHEMA nanopillars fabricated above collapsed immediately when exposed to water, the poly (ethylene glycol dimethacrylate) (PEGDMA) nanopillars, where were fabricated in the similar fashion, did not collapse in water but collapsed when exposure to ethanol. This is because the PEGDMA is a harder material compared to PHEMA. In addition, PEGDMA is highly crosslinked, therefore, is not swollen by water and maintains its high Young's modulus in water. In contrast, PHEMA is swollen by water, thus, effectively lower its Young's modulus in water and collapsed. However, in ethanol, the solvent swells the PEGDMA and decreases its mechanical strength, thus leading to the collapse.

[00070] Separately, observations were made indicating that different collapsed patterns in epoxy nanopillars exist when exposed to solvents with different solvent quality (Fig. I I ), which can be attributed to both the capillary force during solvent drying and the plasticizing effect by the solvent.

Example 6: Template-driven mineralization of calcium phosphate on hvdrogel surface

[00071] A new layer of dentin-like minerals, that is calcium phosphate is grown on the surface of the hydrogels, which ultimately whitens the tooth and enhances the bonding strength and mechanical strength of the molded nanostructures. Template-driven nucleation and mineral growth on hydrogel scaffold has been studied for bonelike composites. By incubating poly(2- P-9392-PC

hydroxyethyl methacrylate) (PHEMA) together with hydroxyapatite (HA) solution and hydrolysis of the PHEMA hydrogels, extensive calcification is observed. PHEMA hydrogels are hydrolyzed at room temperature and hydroxyapatite is calcified on molded hydrogel surface. The underlying nano- and microstructured templates (both the topography and the s chemical functionality of the hydrogel materials) direct the crystal nucleation and growth, the morphology of the calcium phosphate apatite over the time, and its effect to the light scattering. This template-driven mineralization technique provides an efficient approach toward dentin-like composites with high mineral-hydrogel interfacial adhesion strength.

io [00072] Having described preferred embodiments of the invention with reference to the accompanying drawings, it is to be understood that the invention is not limited to the precise embodiments, and that various changes and modifications may be effected therein by those skilled in the art without departing from the scope or spirit of the invention as defined in the appended claims.

I₅

Claims

P-9392-PCWhat is claimed is:

1. A tooth whitening composition comprising a randomly collapsed array of polymeric nanostructures, whereby the collapsed array of polymeric nanostructures causes random light scattering.

2. The composition of claim 1 , wherein the nanostructure array is made of biocompatible hydrogels.

3. The composition of claim 1 , wherein the non-collapsed nanostructure array diffracts blue light.

4. The composition of claim 1 , wherein the nanostructure array is comprised of nanopillars.

5. The composition of claim 4, wherein the nanopillars have an aspect ration of between about 3 to about 25

6. The composition of claim 1, wherein the whitening composition has a feature size between about lOOnm to about 100 μm.

7. The composition of claim 1, wherein the whitening composition has an aspect ratio of between about 3 to about 10.

8. The composition of claim 1, wherein the whitening composition has refractive index of between about 1.4 - 1.8 .

9. The composition of claim 2, wherein the hydrogels are formulated from the monomers 2-hydroxyethyl methacrylate (HEMA), ethylene glycol dimethacrylate (EGDMA), diethyleneglycol dimethacrylate (DEGDMA), tetraethyleneglycol dimethacrylate (TE- EGDMA), polyurethane dimethacrylate (UDMA), tri(ethylene glycol) dimethacrylate (TEGDMA), and other dimethacrylates, acrylamide (Am), their copolymers, polyhedral oligomeric silsequioxane (POSS), epoxide POSS, dimethacrylate POSS, their copolymers or a combination thereof.

10. A tooth whitening product, comprising: a strip of a material capable of being adapted to cover the front surface of one or more teeth; and a layer of a tooth whitening composition disposed on said strip of material, wherein said whitening composition comprises a randomly collapsed array of nanostructures, thereby affecting non-uniform light scattering that appears white.

1 1. The product of claim 10, wherein the nanostructure array is made of biocompatible hydrogels. P-9392-PC

12. The product of claim 10, wherein the non-collapsed nanostructure array diffracts blue light.

13. The product of claim 10, wherein the nanostructure array is comprised of nanopillars.

14. The product of claim 13, wherein the nanopillars have an aspect ration of between about 3 to about 25.

15. The product of claim 10, wherein the whitening composition has a feature size between about lOOnm to about 100 μm.

16. The product of claim 10, wherein the whitening composition has an aspect ratio of between about 3 to about 10.

17. The product of claim 10, wherein the whitening composition has refractive index of between about 1.4 - 2.0.

18. The product of claim 10, wherein the whitening composition has a crosslinker concentration of between about 1-30 wt%.

19. A method of making a randomly collapsed array of polymeric nanostructures, comprising: a. fabricating a master nanopillar array; b. generating a negative mold of the master; c. casting the mold with a liquid precursor of a polymer; d. hardening the polymer, thereby creating an array of polymeric nanostructures; e. removing the hardened polymer; and f. collapsing the polymeric nanostructures.

20. The method of claim 19, whereby the nanopillars are conical, frusto-conical, cylindrical, square, or their combination.

21. The method of claim 19, whereby the step of generating a negative mold of the master array is carried out by covering the master array with a liquid phase of a mold polymer.

22. The method of claim 20, whereby the liquid phase is a melt, an emulsion, a solution, or a suspension of the mold polymer.

23. The method of claim 21 , further comprising hardening of the liquid phase of the mold polymer.

24. The method of claim 23, whereby hardening comprises heating, UV light curing, drying removing solvent, concentrating or a combination thereof.

25. The method of claim 19, whereby the nanopillars vary in feature size, density, uniformity, shape or a combination thereof. P-9392-PC

26. The method of claim 19, whereby the step of casting the mold with a liquid precursor of a polymer, comprises filling the mold with a melt, an emulsion, a solution, or a suspension of a polymer.

27. The method of claim 19, whereby the step of hardening the polymer comprises heating, 5 UV light curing, drying removing solvent, concentrating or a combination thereof thereby creating an array of amorphous polymeric nanostructures.

28. The method of claim 19, whereby the step of collapsing comprises reducing the polymer's Young's modulus (E) to be lower than the critical elastic modulus for a gravitational collapse ( E_g ^* ) 0

29. The method of claim 19, whereby the step of collapsing comprises reducing the polymer's Young's modulus (E) to be lower than the critical elastic modulus for a lateral collapse ( E_L ^* )

30. The method of claim 19, whereby the polymer is formulated from the monomers 2- hydroxyethyl methacrylate (HEMA), ethylene glycol dimethacrylate (EGDMA),s diethyleneglycol dimethacrylate (DEGDMA), tetraethyleneglycol dimethacrylate (TE-

EGDMA), polyurethane dimethacrylate (UDMA), tri(ethylene glycol) dimethacrylate (TEGDMA), and other dimethacrylates, acrylamide (Am), their copolymers, polyhedral oligomeric silsequioxane (POSS), epoxide POSS, dimethacrylate POSS, their copolymers or a combination thereof. o 31. The method of claim 19, whereby the non-collapsed nanostructure array diffracts blue light.

32. The method of claim 19, wherein the nanopillars have an aspect ration of no less than 3.

33. The method of claim 19, whereby the collapsed nanostructure array has a feature size 5 between about lOOnm to about 100 μm.

34. The method of claim 19, whereby the collapsed nanostructure array has an aspect ratio of between about 3 to about 10.

35. The method of claim 19, whereby the collapsed nanostructure array has refractive index of between about 1.4 - 2.0. 0

36. An array of randomly collapsed nanostructures made by the method of claim 19.

37. A method of whitening teeth, comprising adsorbing onto the surface of a tooth a strip of a material capable of being adapted to cover the front surface of one or more teeth; and a layer of a tooth whitening composition disposed on said strip of material, wherein P-9392-PC

said whitening composition comprises a randomly collapsed array of nanostructures, whereby the randomly collapsed array of nanostructures result in random light diffraction.

38. The method of claim 37, whereby the nanostructure array is made of biocompatible hydrogels.

39. The method of claim 37, whereby the non-collapsed nanostructure array diffracts blue light.

40. The method of claim 37, whereby the nanostructure array is comprised of nanopillars.

41. The method of claim 40, whereby the nanopillars have an aspect ration of between about 3 and about 25.

42. The method of claim 37, whereby the whitening composition has a feature size between about lOOnm to about 100 μm.

43. The method of claim 37, whereby the whitening composition has an aspect ratio of between about 3 to about 10.

44. The method of claim 37, whereby the whitening composition has refractive index of between about 1.4 - 1.8.

45. The method of claim 37, wherein the whitening composition has a crosslinker concentration of between about 1 -30 wt%.

46. The method of claim 37, comprising the array of randomly collapsed nanostructures of claim 35.

47. The method of claim 37, whereby adsorbing comprises etching the enamel surface of the tooth with acid; and applying a liquid hydrogel precursor to the acid etched surface.

48. The method of claim 37, whereby adsorbing comprises chemical adhesion of enamel and dentin, by adding metallic polyakenoate salts, thereby partially dissolving the hydroxyapetite and chelating hydroxyapetite; and cross linking the dissolved hydroxyapetite with the hydrogel.

49. The method of claim 37, whereby the whitening composition comprises hydroxyapetite impregnated in the nanostructure array.

50. The method of claim 48, further comprising the step of nucleating the whitening composition with calcium phosphate.