Thixotropic cleaning suspension comprising hydrophilic polymer beads

Abstract

 A thixotyropic aqueous composition comprising a particulate hydrophilic polymer or copolymer or mixture thereof and a microcrystalline cellulose polymer.

Description

Background of the Invention

[0001] This invention relates to a stabilized aqueous suspension of polymeric particles having thixotropic viscosity properties, useful for cleaning contact lenses and other articles.

[0002] Phares et al, U.S. 3,884,826 (Barnes-Hind Pharmaceuticals, Inc.) describes the use of a cleaning preparation for hard contact lenses comprising a thixotropic gelling agent. No particulate polymer is described as being present. Su et al, U.S. 4,493,783 (Alcon Laboratories, Inc.) describes a cleaning preparation for contact lenses comprising spherical particles of certain hydrophobic polymers. The preparation may be a thixotropic ointment or gel.

[0003] This invention is cross referenced to US-A-4655957 which describes aqueous suspensions comprising beads of selected hydrophilic polymers suitable for cleaning contact lenses and other articles. This U.S. patent also teaches how to make these beads. No mention is made of agents providing thixotropic viscosity.

Summary of the Invention

[0004] In accordance with this invention, there is provided a stabilized composition for cleaning various articles, including contact lenses, the improvement comprising the inclusion of the combination of a particulate hydrophilic polymer or copolymer and a microcrystalline cellulose, preferably in the presence of an additional protective colloid. Typically, the composition for cleaning contact lenses will comprise an aqueous suspension having about 0.001 to about 25 weight percent of a particulate hydrophilic polymer and about 0.1 to 20 percent by weight of a blend of microcrystalline cellulose and protective colloid, in a buffered, isotonic solution containing one or more surfactants and optional preserving and sequestering agents.

[0005] The cleaning compositions of the invention are particularly efficacious for removing protein deposits from the surfaces of soft contact lenses, which have a great affinity for such deposits, without damaging the lenses.

Description of the Preferred Embodiments

[0006] More particularly, this invention relates to a stabilized composition comprising (A) particulate hydrophilic polymer or copolymer (or mixture thereof) and (B) microcrystalline cellulose, having utility as a facial scrub or heavy-duty hand cleaner, automotive or household cleaner, or contact lens cleaner. As described in US-A-4655957 cited above, it has been discovered that particulate hydrophilic polymers in aqueous suspension are effective cleaning agents. Stable suspensions of these hydrophilic polymer particles is difficult to achieve. The particles have an affinity for one another and agglomerate and settle out of suspension. The combination with microcrystalline cellulose of the present invention provides a highly thixotropic gel having a finite yield value, in which the large number of microcrystal particles in suspension form a mesh-like network which promotes better suspension stability of the hydrophilic polymer bead suspension. This results in a lower settling rate and prevents caking of the suspended particles of hydrophilic polymer. The finite yield value of the stabilized composition provides a composition which can be converted from a gel state to a pourable liquid state by the application of a finite amount of agitation to the composition. In actual use the gel-like suspension will be converted to a liquid-like consistency by shaking the container for ease of delivery, rubbing and rinsing. The composition will restore its gel-like characteristics by resting for a short period of time, because of its time-dependent viscosity characteristics.

[0007] Gels formed with microcrystalline celluloses such as Avicel® RC-591 are not sensitive to the presence of ionic ingredients as are gels formed with conventional thickeners such as Carbopol®.

[0008] The preferred particulate hydrophilic polymer is in the form of spherically shaped beads ranging in size from 0.1 to 10 micrometers in diameter and having an average size of about 0.2 to 0.5 micrometers. The particulate hydrophilic polymer is prepared by solution polymerization of selected monomers or comonomers in the presence of conventional crosslinkers, accelerators and initiators, as described in US-A-3,583,957 and in US-A-4,655,957. Examples are homopolymers or copolymers of poly(hydroxyalkyl methacrylates), poly(hydroxyalkyl acrylates) and poly(N-vinyl lactams). The amount of polymeric beads in suspension ranges from about 0.001 to about 25 weight percent, the preferred concentration from about 1 to about 10 percent.

[0009] The cellulose polymers useful in the present invention are colloidal forms of microcystalline cellulose. An example is Avicel® RC-591, supplied by FMC Corp., a dry blend of 89 percent microcrystalline cellulose and 11 percent sodium carboxymethyl cellulose. Typically in the resulting dispersion approximately 60 percent of the particles of microcrystalline cellulose are less than 0.2 micrometers in size. Preferably the microcrystalline cellulose is blended with a protective hydrophilic colloid as a means of preventing agglomeration and facilitating dispersion. Examples of suitable protective colloids are sodium carboxymethyl cellulose, xanthan gum, hydroxypropylmethylcellulose and methylcellulose. When a protective colloid is added to microcrystalline cellulose gels, the soluble polymer particles absorb on the microcrystalline cellulose particles. As the proportion of protective colloids is increased, the composition becomes less thixotropic and the yield value decreases. Preferably the concentration of protective colloids to aid dispersion should be in the range of about 0.1 percent to 20 percent by weight of the dry blended microcrystalline cellulose polymer powder prior to its addition to the thixotropic suspension. Additional protective colloid may be added during preparation of the aqueous suspension to assist in dispersing the particles and preventing agglomeration. Preferably the concentration of the blended polymer (microcrystalline cellulose and protective colloids) employed to provide the thixotropic suspension of the invention should be in the range of about 0.1 percent to 20 percent by weight of the solution.

[0010] The formulation includes a carrier such as water or isotonic saline solution to which one or more additives such as surfactants, preservatives, stabilizers, buffers, tonicity adjusters and thickening agents may be added. Preferred nonionic surfactants for this invention include ethylene oxide/propylene oxide surfactants, for example poloxamers and their block copolymers or tetrafunctional initiators such as ethylenediamine, e.g. poloxamine 1107 (tradename Tetronic® 1107) and ethoxylated cocoamide (tradename Amidox® C5) in concentrations ranging from 0.01 percent to 10 percent, with the preferred concentration being 1 to 5 percent. Additional nonionic surfactants for this invention may be selected from the polyethylene glycol esters of fatty acids (e.g., coconut) or polyoxyethylene or polyoxypropylene ethers of higher alkanes (C₁₂-C₁₈). Examples of suitable nonionic surfactants include polysorbate (20) (tradename Tween® 20), polyoxyethylene (23) lauryl ether (tradename Brij® 35), polyoxyethylene (40) stearate (tradename Myrj® 52) and polyoxyethylene (25) propylene glycol stearate (tradename Atlas® G 2612). Other nonionic surfactants suitable for use in this invention can be readily ascertained, in view of the foregoing description, from McCutcheon's Detergents and Emulsifiers, North American Edition, McCutcheon Division, MC Publishing Co., Glen Rock, New Jersey 07452, U.S.A., 1980.

[0011] Preservative agents in an amount from 0.00001 to 0.5 weight percent may be added to inhibit bacterial growth in the composition. Suitable examples of such agents include thimerosal, sorbic acid, phenylmercuric salts (e.g., nitrate, borate, acetate, chloride, or gluconate), 1,5-pentanedial, the polymers and water-soluble salts of hexamethylene biguanides, and benzalkonium chloride. Cocamidopropylbetaine (tradename Amphosol® CA) is an example of a suitable amphoteric surfactant which functions as a preservative in this composition. For this invention, the preferred concentration of Amphosol® is 0.25 percent.

[0012] In addition to the active ingredients previously described, buffers, optional tonicity agents, sequestering agents, and humectants are included in contact lens cleaners. Suitable buffers include sodium or potassium citrate, citric acid, boric acid, sodium bicarbonate, sodium borate, and various mixed phosphate buffers including combinations of Na₂HPO₄, NaH₂PO₄, and KH₂PO₄. Generally, buffers may be used in amounts ranging from about 0.05 to 2.5% with the preferred concentration being 0.1 to 1.5%. Glycerol or propylene glycol in a preferred concentration of 1.5% are suitable tonicity agents. Sequestering agents such as ethylenediaminetetracetic acid (EDTA) and its disodium salt (disodium edetate) may be added in amounts ranging from 0.001 to 2.0%.

[0013] The composition is generally used by applying it to a surface, rubbing the surface with the composition, and rinsing or wiping the cleansed surface. The method of use of the cleaning preparation for contact lenses comprises removing the lenses from he eyes, shaking the preparation to convert it to a liquid-like consistency, applying the shaken preparation to the lenses, rubbing, and thereafter rinsing the lenses with a solution such as preserved saline solution. In an alternate cleaning method, the cleaning preparation may be applied to a pad or a sponge which may be used to scrub the surface to be cleaned.

[0014] The following examples are illustrative only and should not be construed as limiting the invention. All parts and percentages referred to herein are on a weight percent basis.

Preparatory Examples

EXAMPLES I, II AND III

[0015] Aqueous contact lens cleaning compositions are prepared having the following formulations.

1 Supplied by BASF Wyandotte Corp.

2 Supplied by Stepan Chemical Co.

3 A cocoamidopropylbetaine supplied by Stepan Chemical Co.

4 Poly(2-hydroxyethylmethacrylate) beads of mean size 0.2-2.0 micrometer prepared as in Example I of US-A-4655957

5 Poly(hexamethylene biguanide)

6 Dry blended of 89% microcrystalline cellulose and 11% sodium carboxymethyl cellulose.

[0016] The above formulations were prepared by first mixing the Avicel® RC-591 with one-quarter of the total water, which was then heated to 50-90°C. The hydroxypropylmethylcellulose was then added with agitation until all particles are thoroughly wetted. An additional one-quarter of the water was added, and the solution cooled to 20-25°C. The hydrogel beads were then added with low-speed mixing to avoid foaming, followed by the sodium chloride, disodium edetate, boric acid, sodium borate, Tetronic® 1107, Amidox® C5 and Amphosol® CA. Mixing was continued until the components were completely dissolved. The composition was sterilized at 121°C for at least 30 minutes, cooled to room temperature with constant stirring, and then the PHMB was added in the form of a 55 ppm aqueous solution.

Summary

[0017] The preparations are stable physically, chemically and microbiologically. They are non-cytotoxic and non-irritating to the eye. They are compatible with hydrophilic soft contact lenses, and at the same time are effective cleaners. No caking of the suspended beads is observed upon standing. The preparations can be dispensed as low viscosity liquids after shaking the container, and spread easily on the objects to be cleaned and recover their viscosity upon standing after use. A similar comparison preparation also containing hydrogel beads but thickened with 0.5 percent of a conventional anionic thickener, Carbomer® 940, a polyacrylic acid supplied by B.F. Goodrich, was made. This comparative preparation did not recover its thixotropic viscosity upon standing after use, and thus lacked the bead dispersion stability of the present invention.

Claims

1. A thixotropic suspension comprising: (A) 0.001 to 25 weight percent of a bead shaped particulate hydrophilic cross-linked vinyl-type homopolymer or copolymer; (B) about 0.2 to 20 percent by weight of a microcrystalline cellulose polymer; and (C) water.

2. The thixotropic suspension of Claim 1 in which said bead shaped particulate hydrophilic cross-linked vinyl type homopolymer or copolymer is selected from the group consisting of poly(hydroxyalkylmethacrylate), poly(hydroxyalkylacrylate) and poly(N-vinyl lactam) and mixtures thereof.

3. The thixotropic suspension of Claim 1 further comprising a protective hydrophilic colloid as a means of controlling the thixotropic viscosity of said suspension where said protective hydrophilic colloid is present between 0.1 and 20 weight percent of the combined weight of said protective hydrophilic colloid and said microcrystalline cellulose polymer (B).

4. The thixotropic aqueous suspension of Claim 3 in which the protective hydrophilic colloid is selected from the group consisting of sodium carboxymethylcellulose, xanthan gum, hydroxypropylmethylcellulose and methylcellulose.

5. The thixotropic suspension of Claim 3 in which the concentration of the blend of microcrystalline cellulose and protective hydrophilic colloid ranges from about 0.1 percent to 20 percent by weight of the suspension.

6. The thixotropic suspension of Claim 1 which further comprises one or more surfactants chosen from the group consisting of nonionic and amphoteric type surfactants.

7. The thixotropic suspension of Claim 5 which further comprises one or more surfactants chosen from the group consisting of nonionic and amphoteric type surfactants.

8. The thixotropic suspension of Claim 6 which further comprises an additive chosen from the group consisting of preservatives, stabilizers, buffers, tonicity agents and thickening agents.

9. The thixotropic suspension of Claim 7 which further comprises an additive chosen from the group consisting of preservatives, stabilizers, buffers, tonicity agents and thickening agents.

10. A method for cleaning various articles including automobiles, tiles, countertops, tubs, vinyl and leather surfaces which method comprises applying the composition of Claim 1 to the surface, rubbing the surface with said composition, and rinsing the cleaned surface.

11. A method for cleaning contact lenses which method comprises applying the composition of Claims 1-5 to a contact lens, rubbing the lens with the said composition and thereafter rinsing the lens.