WO2017223261A2

WO2017223261A2 - Hydrogels, articles comprising hydrogels, and methods thereof

Info

Publication number: WO2017223261A2
Application number: PCT/US2017/038651
Authority: WO
Inventors: Corinne E. Lipscomb; Alexi J. YOUNG
Original assignee: 3M Innovative Properties Company
Priority date: 2016-06-23
Filing date: 2017-06-22
Publication date: 2017-12-28
Also published as: WO2017223261A3

Abstract

Described herein is a hydrogel having a water content of at least 10 wt%. The hydrogel is derived from an aqueous composition comprising: a hydrophilic monomer comprising at least one of (meth)acrylate and (meth)acrylamide; at least 0.1 wt% of a water-swellable clay; at least 0.1 wt% cellulose nanocrystals; and a photoinitiator. Also disclosed herein are methods of making hydrogels and articles thereof.

Description

HYDROGELS, ARTICLES COMPRISING HYDROGELS, AND METHODS THEREOF

TECHNICAL FIELD

[0001] Hydrogel compositions comprising both cellulose nanocrystals and a water-swellable clay are disclosed along with methods of making hydrogel compositions in a web-based process.

BACKGROUND

[0002] A hydrogel is a three-dimensional, hydrophilic or amphiphilic polymeric network capable of taking up large quantities of water. On contact with water, the hydrogel assumes a swollen hydrated state that results from a balance between the dispersing forces acting on hydrated chains and cohesive forces that do not prevent the penetration of water into the polymer network. The cohesive forces are most often the result of covalent crosslinking, but additionally may result from electrostatic, hydrophobic or dipole-dipole interactions.

[0003] When placed in an aqueous solutions, the hydrogels can imbibe water until they reach an equilibrium swelling point. Because of their high water content, hydrogels have been used for biomedical applications such as wound healing, drug delivery, in vitro cell culture, regenerative medicine, etc. SUMMARY

[0004] There is a desire for hydrogel compositions, which are lower cost that have similar or improved physical properties (e.g., mechanical strength and/or water retention). There is a desire to identify a hydrogel composition, which can be made via a web-based process.

[0005] In one aspect, a hydrogel is disclosed wherein the hydrogel has a water content of at least 10 wt%, and wherein the hydrogel film is derived from an aqueous composition, the aqueous composition comprising:

(a) a hydrophilic monomer comprising at least one of (meth)acrylate and

(meth)acrylamide ;

(b) at least 0.1 wt% of a water-swellable clay;

(c) at least 0.1 wt% cellulose nanocrystals; and

(d) a photoinitiator.

[0006] In another aspect, a method of making a hydrogel is disclosed. The method comprising: (i) obtaining an aqueous composition comprising:

(a) a hydrophilic monomer comprising at least one of (meth)acrylate and

(meth)acrylamide ; (b) at least 0.1 wt% of a water-swellable clay;

(c) at least 0.1 wt% cellulose nanocrystals; and

(d) a photoinitiator;

(ii) contacting the aqueous composition to a substrate; and

(iii) exposing the aqueous composition to radiation to at least partially cure the aqueous composition.

[0007] In another embodiment, a method of making a hydrogel film is disclosed, the method comprising:

(i) coating an aqueous composition onto a web at a first station, the aqueous composition comprising:

(a) a hydrophilic monomer comprising at least one of (meth)acrylate and

(meth)acrylamide ;

(b) at least 0.1 wt% of a water-swellable clay;

(c) at least 0.1 wt% cellulose nanocrystals; and

(d) a photoinitiator;

(ii) transporting the coated web to a second station; and

(iii) curing the coated web at the second station.

[0008] The above summary is not intended to describe each embodiment. The details of one or more embodiments of the invention are also set forth in the description below. Other features, objects, and advantages will be apparent from the description and from the claims.

DETAILED DESCRIPTION

[0009] As used herein, the term

"a", "an", and "the" are used interchangeably and mean one or more; and

"and/or" is used to indicate one or both stated cases may occur, for example A and/or B includes, (A and B) and (A or B);

"interpolymerized" refers to monomers that are polymerized together to form a polymer backbone;

"(meth)acrylate" refers to compounds containing either an acrylate or a methacrylate structure or combinations thereof;

"(meth)acrylamide" refers to compounds containing either an acrylamide or a methacrylamide structure or combinations thereof; and

"monomer" is a molecule which can undergo polymerization which then forms part of the essential structure of a polymer. [0010] Also herein, recitation of ranges by endpoints includes all numbers subsumed within that range (e.g., 1 to 10 includes 1.4, 1.9, 2.33, 5.75, 9.98, etc.).

[0011] Also herein, recitation of "at least one" includes all numbers of one and greater (e.g., at least 2, at least 4, at least 6, at least 8, at least 10, at least 25, at least 50, at least 100, etc.).

[0012] Hydrogel

[0013] A hydrogel is a network of hydrophilic polymer chains, which are dispersed in an aqueous medium. The water-swollen polymeric networks are rendered insoluble due to interactions (e.g., crosslinks) between polymer chains. When this network of hydrophilic polymers is placed in an aqueous solution, these systems often imbibe water until they reach an equilibrium swelling point. At this point, the enthalpy of mixing equals the restrictions imposed by the interactions (e.g., covalent bonding between chains, or non-covalent interactions (H- bonding, electrostatic, van der Waals) between chains) that hold the polymer chains together.

[0014] A hydrogel has the capacity to absorb many times (e.g. at least about 1.25, 1.5, 2, 2.5, 5, 10, or even 50 times, and potentially up to about 250 times) its own weight of aqueous fluid (e.g. water, biological fluid) in 24 hours.

[0015] The present disclosure is directed toward a hydrogel, an article, and methods thereof. In one embodiment, the hydrogels are made via a web-process, wherein long sheets or rolls of hydrogel are manufactured.

[0016] The hydrogel of the present disclosure has a water content of at least 10, 15, 20, 30, 40, or even 50 wt%. The hydrogel is derived from an aqueous composition comprising a hydrophilic monomer, a water-swellable clay, cellulose nanocrystals, and a photoinitiator. As will be discussed and shown herein, it has been discovered that by adding both a water-swellable clay and cellulose nanocrystals, an aqueous composition that can be coated and/or made in a web format can be achieved. Additionally and/or alternatively, adding both a water-swellable clay and cellulose nanocrystals, can provide hydrogels with improved physical properties (such as mechanical strength, water retention, etc.) can be achieved.

[0017] The hydrophilic monomer is a monomer that is soluble in water and/or may be miscible or partially miscible in water.

[0018] In one embodiment, the monomer has a lipophilicity index less than or equal to 20. As used herein, the term "lipophilicity index" or "LI" refers to an index for characterizing the hydrophobic or hydrophilic character of a monomer. The lipophilicity index is determined by partitioning a monomer in equal volumes (1 : 1) of a non-polar solvent (e.g., hexane) and a polar solvent (e.g., a 75:25 acetonitrile-water solution). The lipophilicity index is equal to the weight percent of the monomer remaining in the non-polar phase after partitioning. Monomers that are more hydrophobic tend to have a higher lipophilicity index; similarly, monomers that are more hydrophilic tend to have a lower lipophilicity index. Measurement of lipophilicity index is further described in Drtina et al., Macromolecules, 29, 4486-4489 (1996). Examples of non-ionic monomers that have a sufficiently low lipophilicity index include, but are not limited to, hydroxyalkyl(meth)acrylates such as 2-hydroxyethylacrylate, 3-hydroxypropylacrylate, 2- hydroxyethylmethacrylate (e.g., LI is 1), and 3-hydroxypropylmethacrylate (e.g., LI is 2);

acrylamide (e.g., LI is less than 1) and methacrylamide (LI is less than 1); glycerol

monomethacrylate and glycerol monoacrylate; N-alkyl(meth)acrylamides such as N- methylacrylamide (e.g., LI is less than 1), N,N-dimethylacrylamide (e.g., LI is less than 1), N- methylmethacrylamide, and N,N-dimethylmethacrylamide; N-vinylamides such as N- vinylformamide, N-vinylacetamide, and N-vinylpyrrolidone; acetoxyalky(meth)acrylates such as

2-acetoxyethylacrylate and 2-acetoxyethylmethacrylate (e.g., LI is 9); glycidyl(meth)acrylates such as glycidylacrylate and glycidylmethacrylate (e.g., LI is 11); and vinylalkylazlactones such as vinyldimethylazlactone (e.g., LI is 15).

[0019] Hydrophilic monomers are known in the art and include vinyl monomers such as (meth)acrylates, and (meth)acrylamides.

[0020] Exemplary (meth)acrylate monomers include: acrylic acid (3-sulphopropyl) ester (SPA) and salts thereof, N,N-dimethylaminoethylmethacrylate and salts thereof, [2- (methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl) ammonium hydroxide, [2- (methacryloyloxy)ethyl]trimethylammonium chloride, 2-hydroxyethyl(meth)acrylate, hydroxypropyl(meth)acrylate, and polyethyleneglycolmono(meth)acrylate.

[0021] Exemplary (meth)acrylamide monomers include: N-substituted (meth)acrylamide derivatives, such as N-methylaerylamide, N-ethylacrylamide, cyelopropylacrylamide, N- isopropylacryiamide, N-metliylmethacryiamide, cyciopropylmethacrylamide. N- isopropylmetb acrylamide, diacetone acrylamide, hydroxyethyl acrylamide, 2-acrylamido-2- methylpropane sulphonic acid (AMPS) and salts thereof; and N,N-di-substituted

(meth)acrylamide derivatives, such as ,M-dimethylacrylamide, N,N- dimetliylaminopropyiacrylamide, N-methyl- -etliylacryiamide, -methyl-N- isopropylacrylami.de, N-raethyl-N-n-propylacrylamide, N,N-diethylacrylamide. N- acryloylpyrrolidine, N-aciyloylpiperidine, N-actyloyl-N'-methylhomopiperidine, and N-acryloyl- N'-methylpiperidine, N-acryloyl moφholine or a substituted derivative thereof and N,N dimethylaniinopropylmethaciylamide.

[0022] Other useful water soluble monomers include vinyl amides such as N-vinylacetamide, N- vinylformamide, N-vinylpyrrolidinone, and vinylpyridine.

[0023] In one embodiment, the vinyl monomers are substituted with acid or ionic groups (which may, for example, be salts of acid groups or tertiary ammonium groups). Such salts may include, for example, sodium, potassium, lithium, cesium, calcium, magnesium, zinc or ammonium salts or mixtures thereof. In one embodiment, the vinyl monomers comprise pendant sulphonic acid groups, and/or carboxylic acid groups.

[0024] Conventional cross-linking agents (i.e., compounds which covalently-bond polymer chains together) are suitably used to provide the necessary mechanical stability and to control the adhesive properties of the hydrogel. The amount of cross-linking agent required will be readily apparent to those skilled in the art such as from about 0.01, 0.05, or even 0.08% to about 0.5, 0.4, or even 0.3% by weight of the total polymerization reaction mixture. Typical cross-linkers comprise at least two polymerizable double bonds, and include tripropylene glycol diacrylate, ethylene glycol dimethacrylate, trimethylolpropane triacrylate, polyethylene glycol diacrylate

(polyethylene glycol (PEG) molecular weight between about 100 and about 4000, for example PEG400 or PEG600), and methylene bis acrylamide. In one embodiment, the composition is substantially free (i.e., less than 0.001, or even 0.01 wt%) of conventional cross-linking agents as in known in the art and disclosed, for example, in Haraguchi et al. in Macromolecules v. 36 (2003) p. 5732-5741.

[0025] The hydrophilic monomers in the present invention are preferably interactive with the water-sweliabie clay and cellulose nanocrystals when polymerized. Preferably, some of the hydrophilic monomers have functional groups which can forrn hydrogen bonds, ionic bonds, coordinate bonds, and/or covalent bonds with the water-swellable clay and cellulose nanocrystals. Examples of such functional groups include an amide group, an amino group, a hydroxy group, a tetram ethyl ammonium group, a silanol group, and an epoxy group.

[0026] Cellulose Nanocrystals

[0027] Cellulose nanocrystals are a particular type of cellulose particle. Cellulose nanocrystals are extracted as a colloidal suspension by acid hydrolysis of typically chemical wood pulps, but other cellulosic materials, such as bacteria, cellulose-containing sea animals (e.g. tunicate), or cotton can be used. Cellulose nanocrystals are constituted of cellulose, a linear polymer of beta (1 to 4) linked D-glucose units, the chains of which arrange themselves to form crystalline and amorphous domains.

[0028] Cellulose nanocrystals have a unique combination of characteristics such as high axial stiffness, high tensile strength, low coefficient of thermal expansion, thermal stability up to about

300 °C, high aspect ratio, low density, lyotropic liquid crystalline behavior, and shear thinning rheology in cellulose nanocrystal suspensions. Additionally, cellulose nanocrystals are renewable, sustainable, and carbon neutral, like the sources from which they are extracted.

[0029] The physical dimensions of cellulose nanocrystals can vary depending on the raw material used in the extraction. In one embodiment, the cellulose nanocrystal has an average cross-sectional distance (longest dimension of a cross-section of the cellulose nanocrystal, perpendicular to the length) of at least 2, 4, or even 5 nanometers (nm) and at most 10, 20, 30, or even 50 nm; and an average length (longest dimension of the cellulose nanocrystal) of at least 50, 75, or even 100 nm and at most 150, 200, 250, 500, 750, or even 1000 nm. The cross-sectional morphology of the nanocrystals is typically square, but can be rectangular, or rounded. Typically, the cellulose nanocrystals have a high aspect ratio (ratio of height versus length). In one embodiment, the cellulose nanocrystals have an aspect ratio of 10 to 100. The dimensions of the cellulose nanocrystals may be determined based on transmission electron microscopy (TEM), scanning electron microscopy (SEM), atomic force microscopy, or by other suitable means. Typically, the morphology is determined on dried samples.

[0030] Cellulose nanocrystals can also characterized by high crystallinity (e.g., at least 60%, 70%, 80%, 85%, or even 90%) approaching the theoretical limit of the cellulose chains. Hydrogen bonding between cellulose chains can stabilize the local structure in cellulose nanocrystals, and plays a key role in the formation of crystalline domains. Crystallinity, defined as the crystalline fraction of the sample can influence the physical and chemical behavior of cellulose nanocrystals.

For example, the crystallinity of cellulose nanocrystals directly influences the accessibility for chemical derivatization, swelling and water-binding properties.

[0031] The surfaces of the cellulose nanocrystals typically comprise a plurality of hydroxyl groups. In a preferred embodiment, the surface of the cellulose nanocrystals are not modified as these hydroxyl groups are thought to assist in water retention of the hydrogel composite.

However, these hydroxyl groups can be modified to achieve different surface properties (surface functionalization), which modifications can be used to adjust the self-assembly and dispersion of the cellulose nanocrystals within the composite, and to control interfacial properties in composites. For example, various amounts of the cellulose hydroxyl groups can be conjugated to or replaced by other chemical moieties such as carboxyl groups, carboxyalkyl groups, alkylsulfonic acid groups, phosphate groups, sulfate groups, and the like. The modifications thus alter the charge density of the cellulose nanocrystal surface. For example, selective oxidation of the primary alcohol (RCH₂OH) group on the cellulose surface to a carboxylic acid (RCO₂H) provides acidic groups, which can optionally be used to couple to amine groups (RNH₂), optionally attached to other chemical moieties, forming a conjugated moiety (via an amide bond).

In another example, two nearby carboxyl groups can be treated with a base to form carboxylate anions (RCO2 ), which in turn can be ionically bridged by a divalent cation such as Ca⁺² or Mg⁺². Chemical functionalization of the material can be used to optimize the properties for various applications. [0032] The density of the cellulose nanocrystals is less than 1.6, 1.4, 1.2, or even 1.1 g/cm³ at ambient conditions.

[0033] The zeta potential measures the potential difference existing between the surface of a solid particle immersed in a conducting liquid (e.g. water) and the bulk of the liquid of the cellulose nanocrystal surface. The cellulose nanocrystals have a zeta potential higher (i.e., less negative) than -50, -45, -40, -35, -30, or even -25 mV based on dynamic light scattering.

[0034] The cellulose nanocrystals typically have a pH of less than 7.5, 7.0, 6.5, or even 6.0 and greater than 4.5, 5.0, or even 5.5 when measured at ambient conditions.

[0035] Based on the processing to form the cellulose nanocrystals, residual sulfur may be present. In one embodiment, the cellulose nanocrystals comprise greater than 0.01% and less than

1, 0.8, 0.5, 0.1 or even 0.05% sulfur content. An exemplary method to determine sulfur content is inductively coupled plasma.

[0036] Cellulose nanocrystals may be obtained, for example, from CelluForce, Montreal, Canada; Melodea Ltd., Israel; American Process Inc., Atlanta, GA; Blue Goose Biorefineries Inc., Saskatoon, Canada; and the USDA Forest Products Laboratory, Madison, WI via the University of Maine.

[0037] In the present disclosure, the cellulose nanocrystals are present in an amount of at least 0.1 % wt of the total aqueous composition (100 wt%). In one embodiment, the amount of cellulose nanocrystal in the aqueous composition is at least 0.1, 0.3, 0.5, or even 1 wt%; and at most 5, 6, 8, 10, 15, or even 20 wt% versus the total weight of the aqueous composition.

[0038] Water-swellable Clay

[0039] Clay can be added to a hydrogel composition to enhance the mechanical properties in the composites comprising large amounts of water. In one embodiment, the clay can be used to adjust the viscosity of the hydrogel prior to curing. The water-swellable clay of the present disclosure is a clay mineral capable of swelling and uniformly dispersing in water or a mixed solvent of water and an organic solvent. A water-swellable clay which will hydrate in the presence of water can be used.

[0040] In one embodiment, the water-swellable clay is an inorganic clay mineral capable of uniformly dispersing in a molecular form (single layer) or level close thereto in water. More specifically, the water-swellable clay may contain sodium as an interlay er ion.

[0041] Bentonite is sodium bentonite which is basically a hydratable montmorillomite clay of the type generally found in the Black Hills region of South Dakota and Wyoming. This clay has sodium as a predominant exchange ion. However, the bentonite may also contain other cations such as magnesium and iron. There are cases wherein a montmorillomite predominant in calcium ions can be converted to a high swelling sodium variety through a well known process called "peptizing" . The clay may also be any member of the dioctahedral or trioctahedral smectite group or mixtures thereof. Examples are Beideliite, Montronite, Hectorite, Sepiolite and Samonite. Attapulgite and Kaolin clay also are beneficiated when re-wetted and re-dried.

[0042] Laponite clay refers generally to a synthetic, layered silicate clay that has a layer structure in the form of disc-shaped crystals when dispersed in water. Macromolecules of the laponite clay have a disc-shaped crystal similar to bentonite and hectorite, but are more than one order of magnitude smaller in size. In contrast to clays with a large (e.g. , greater than 100) aspect ratio (ratio of length to height) that tend to aggregate in a face-to-face lamellar fashion, laponite clay tends to form partially delaminated disordered aggregates through edge-to-edge interactions. Laponite clay may have, without limitation, an aspect ratio of between about 10 and about 80, or between about 15 and about 50, or between about 20 and about 40, or between about 25 and about 35. in one embodiment, the laponite clay has an aspect ratio of about 30. It will be understood that these aspect ratios represent averages. The surface of the crystal may have a negative charge of about 50-55 mmol- 100 g^~l. The edges of the crystal may have small, localized positive charges that are about 4-5 mmol - 100 g^~\ Laponite clay may have a physical surface area over about 900 nr -g^"1, Laponite clay may comprise about 8% by weight water that may be released from its crystal structure at temperatures above about 150° C. Commonly known laponite clays encompassed by the disclosure include without limitation those that comprise: lithium, magnesium, and sodium silicate; those that comprise lithium, magnesium, sodium silicate, and tetrasodium pyrophosphate; those that comprise sodium, magnesium, and those that comprise fluorosilicate; and sodium, magnesium, fluorosilicate, and tetrasodium pyrophosphate.

[0043] in one embodiment, the diameter of the disc-shaped crystal in the laponite clay may be from about 1 nanometer (nm) to about 300 nm, from about 5 nm to about 150 nm, or from about 10 nm to about 100 nm. In one embodiment, the diameter of the disc-shaped crystal is from about 15 nm to about 50 nm . In another embodiment, the diameter of the disc-shaped crystal is from about 20 nm to about 40 nm, or from about 25 nm to about 35 nm, or about 25 nm, or about 35 nm.

[0044] In one embodiment, the thickness of the disc-shaped crystal in the laponite clay may be from about 0.1 nm to about 3 nm, from about 0.5 nm to about 1.5 nm, or from about 0.8 nm to about 1.2 nm. in one embodiment, the thickness of the disc-shaped crystal is from about 0.8 nm to about 1 nm. In another embodiment, the thickness of the disc-shaped crystal is about 0.92 nm. In one embodiment, the density of laponite clay is between about 2.5 and about 2.55 gm/cm³, or about 2.53 gm/cm³.

[0045] Useful water-swellable clays include: synthetic hectorite Nao.3(Mg,Li)3Si40io(OH)2], sapomte [Cao.25(Mg,Fe)3((Si,Al)40io)(OH)2-n(H₂0)], montmonllonite [(Na,Ca)o.33(Al,Mg)2(Si40io)(OH)2-«H₂0], laponite [Na ^{÷ 07} H Si Alg^I.i, : ){>,, (OH)₄] ^"'07 j, and synthetic mica.

[0046] The aqueous compositions of the present disclosure comprise at least 0.1 %wt of the water-swellable clay versus the total weight of the aqueous composition. In one embodiment, the amount of water-swellable clay in the aqueous composition is at least 0.3, 0.5, or even 1 wt%; and at most 5, 6, 8, 10, 15, or even 20 wt% versus the total weight of the aqueous composition.

[0047] Photoinitiator

[0048] Photoinitiators for radical polymerization of the aqueous composition are classified in the art as cleavage (Type I) and hydrogen-abstraction (Type II) initiators. A Type I initiator, upon absorption of radiation (e.g., light), spontaneously undergoes "alpha-cleavage", yielding the initiating radical immediately. A Type II initiator is a photoinitiator which, when activated by actinic radiation, forms free radicals by hydrogen abstraction from a second (H-donor) compound to generate the actual initiating free radical. This second compound is called a polymerization synergist or co-initiator.

[0049] Type I and Type II photoinitiators are known in the art. These photoinitiators may not however, have sufficient water solubility to be used in the aqueous hydrogel compositions of the present disclosure. To improve the solubility of the photoinitiator, as is known in the art, the photoinitiator can be derivatized with a (more) hydrophilic group, the counter ion can be adjusted to improve the compound's water solubility, and/or a co-solvent can be used to aid the dissolution of the photoinitiator in the aqueous composition.

[0050] Examples of Type I photoinitiators are benzoin derivatives; benzoin ethers (such as benzoin methyl ether and benzoin propyl ether); methylolbenzoin and 4-benzoyl-l,3-dioxolane derivatives; benzilketals; dimethylhydroxyacetophenone; substituted a-ketols (such as 2-methyl- 2-hydroxy propiophenone); alpha, alpha-dialkoxyacetophenones; alpha-hydroxy alkylphenones; alpha-aminoalkylphenones; acylphosphine oxides; bisacylphosphine oxides; acylphosphine sulphides; halogenated acetophenone derivatives; and the like. Exemplary Type I photoinitiators include: 4-[2-(4-moφholino)benzoyl-2-dimethylamino]-butylbenzenesulfonate salt, and phenyl- 2,4,6-trimethyl-benzoylphosphinate salt. Suitable salts include, for example, sodium and lithium cations. A commercial example of suitable Type I photoinitiator is available from BASF SE, Ludwigshafen, Germany, under the trade designation: "IRGACURE 2959" (2-hydroxy-4'-(2- hydroxyethoxy)-2 -methyl propiophenone) .

[0051] Examples of Type II photoinitiators are modified benzophenones, benzils, and thioxanthones.

[0052] Exemplary Type II photoinitiators include those of the structure:

Formula (I) where m is 0 or 1; n is 1, 2, 3, or 4; p is 0 or 1; and L is an alkylene group comprising from 1 to 4 carbons and having a hydroxyl group. In one embodiment, L is -CH(OH)CH2-. Exemplary photoinitiators of Formula (I) include:

sodium salt).

[0053] Examples of Type II photoinitiators include those of the structure:

Formula (II)

where n is 1, 2, 3, or 4; and X is comprising -N(CH₃)3S0₃CH₃ , and -CH(0H)-(CH₂)_P-N(CH₃)3C1 where p is 1, 2, 3, or 4 . Exemplary photoinitiators of Formula (II) include:

[0054] Examples of Type II photoinitiators include those of the structure:

Formula (III)

Wherein R is -alkyl sulfonate comprising 1, 2, 3, or 4 carbon atoms (e.g., CttSC Na) or a tertiary amine salt comprising at 3, 4, 5, 6, or even 7 carbon atoms (e.g., -0Η2Ν(Ο¾)3 CI).

[0055] Examples of Type II photoinitiators include those of the structure:

Formula (IV)

wherein R comprises a carboxylic acid or a tertiary amine and salts thereof. Exemplary R groups include -COOH, or -CH(0H)CH₂N(CH₃)₃C1.

[0056] Exemplary water-soluble Type II photoinitiators include: 4-(3- sulfopropyloxy)benzophenone and 2-(3-sulfopropyloxy) thioxanthene-9-one, and 2-, 3-, and 4- carboxybenzophenone .

[0057] In one embodiment, the photoinitiators are water-soluble, which means that at ambient conditions (e.g., 23 °C), the photoinitiator has a solubility of at least 0.01, 0.1, 0.25, 0.5, 1, 2, 5 or even 8 % by weight in water.

[0058] In one embodiment, the aqueous composition comprises at least 0.01, 0.05, 0.1, or even 0.5 wt %; and at most 1, 2, 4, or even 5 wt % of the photoinitiator based on the total weight of the aqueous composition.

[0059] In the aqueous compositions, lowering the pH and/or increasing the ionic strength of the aqueous composition can impact the orientation of the clay, thereby increasing the viscosity of the aqueous composition. As known in the art, if the pH is lowered too much (e.g., pH of less than 3, or even 2) or the ionic strength is too high, the clay can flocculate compromising the physical properties (e.g., decreasing the hydrogel integrity, causing cloudiness, decreasing of storage modulus, etc.) of the hydrogel. [0060] In one embodiment, the pH of the aqueous composition comprising the hydrophilic monomer, the water-swellable clay, the cellulose nanocrystals, a photoinitiator, and optional additional components, may be adjusted. Acids used to adjust the pH of the composition include those known in the art. Exemplary acids include: hydrochloric, perchloric, sulfuric, nitric, chloric, phosphoric, acetic, citric, acrylic, butyric, etc. The amount of acid used will vary depending on the strength (e.g., pKa) of the acid, the buffering capacity of the composition, and the pH of the hydrogel composition prior to the addition of the acid. For example, a strong acid (e.g., an acid that is completely dissociated in aqueous solution) may require a small amount to be used, while a weaker acid would require a larger amount to achieve the same pH value. For example, if the composition has a high buffering capacity, a greater amount of acid would be needed to change the pH.

[0061] In one embodiment, salts, such as sodium chloride, can be used to increase the aqueous composition's ionic strength and impact the viscosity.

[0062] Additional Components

[0063] The aqueous composition of the present invention may include one or more additional ingredients, which may be added prior to the curing (i.e., polymerization, grafting, and/or crosslinking) of the aqueous composition or after curing to impact the aesthetics and/or performance of the resulting hydrogel coating. It is generally preferred that substantially all of the final ingredients of the hydrogel are present in the aqueous composition, and that - apart from minor conventional conditioning or, in some cases, subsequent modifications caused by the sterilization procedure - substantially no chemical modification of the hydrogel takes place after completion of the polymerization reaction.

[0064] Such additional ingredients include additives known in the art, including, for example, water, organic plasticizers, surfactants, polymeric material (hydrophobic or hydrophilic in nature, including proteins, enzymes, naturally occurring polymers and gums), synthetic polymers with and without pendant carboxylic acids, electrolytes, osmolytes, pH regulators, colorants, chloride sources, bioactive compounds and mixtures thereof. In some embodiments, the additional ingredients may serve more than one purpose. For example, glycerol may serve as an organic plasticizer and an osmolyte.

[0065] In one embodiment, an additional polymer may be added. The polymer can be a natural polymer (e.g. xanthan gum), synthetic polymer (e.g. polyoxypropylene-polyoxyethylene block copolymer or poly-(methyl vinyl ether alt maleic anhydride)), or any combination thereof. In one embodiment, a rheology modifying polymer may be incorporated into the aqueous composition at levels typically up to about 10% by weight of total polymerization reaction mixture, e.g. from about 0.2% to about 10% by weight. Such polymer(s) may include polyacrylamide, poly-sodium 2-acrylamido-2-methylpropane sulfonate (NaAMPS), polyethylene glycol (PEG),

polyvinylpyrrolidone (PVP) or carboxymethyl cellulose.

[0066] In one embodiment, a bioactive compound may be added. The term "bioactive compounds" is used to mean any compound or mixture included within the hydrogel for some effect it has on living systems, whether the living system be bacteria or other microorganisms or higher animals such as the patient. Bioactive compounds that may be mentioned include, for example, pharmaceutically active compounds, antimicrobial agents, antiseptic agents, antibiotics and any combination thereof. The hydrogel may incorporate antimicrobial agents, for example, those active against such organisms as Staphylococcus aureus and Pseudomonas aeruginosa. Antimicrobial agents may, for example, include: sources of oxygen and/or iodine (e.g. hydrogen peroxide or a source thereof and/or an iodide salt such as potassium iodide); antimicrobial metals, metal ions and salts, such as, for example, silver-containing antimicrobial agents (e.g. colloidal silver, silver oxide, silver nitrate, silver thiosulphate, silver sulphadiazine, or any combination thereof), hypochlorous acid; or any combination thereof.

[0067] In one embodiment, agents for stimulating the healing of wounds and/or for restricting or preventing scarring may be incorporated into the hydrogel. Examples of such agents include growth factors such as TGF (transforming growth factor), PDGF (platelet derived growth factor), KGF (keratinocyte growth factor, e.g. KGF-I or KGF-2), VEGF (vascular endothelial growth factor), IGF (insulin growth factor, optionally in association with one or more of IGF binding protein and vitronectin); cell nutrients; glucose; an anabolic hormone or hormone mixture such as insulin, triiodothyronine, thyroxine or any combination thereof; or any combination thereof.

[0068] In one embodiment, the aqueous composition further comprises a humectant such as polyethylene glycol, polyethylene glycol-co-polypropylene oxide copolymers, partially hydrolyzed polyvinyl acetate, polyvinyl pyrrolidone, glycerol or glycerol derivative,

methylcellulose or other cellulose derivative, polyoxazoline, and natural gums. The amount of humectant added can vary based on the type used. For example typically no more than 30%, 40%, 50% or even 60% by weight of glycerol can be added.

[0069] In one embodiment, one or more plasticizers, preferably one or more organic plasticizer is added. The one or more organic plasticizer, when present, may suitably comprise any of the following either alone or in combination: at least one polyhydric alcohol (such as glycerol, polyethylene glycol, or sorbitol), at least one ester derived therefrom, at least one polymeric alcohol (such as polyethylene oxide) and/or at least one mono- or poly-alkylated derivative of a polyhydric or polymeric alcohol (such as alkylated polyethylene glycol). Glycerol is a preferred plasticizer. An alternative preferred plasticizer is the ester derived from boric acid and glycerol. When present, the organic plasticizer may comprise up to about 45%, for example up to about 35%, for example up to about 25%, for example up to about 15%, by weight of the hydrogel composition.

[0070] In one embodiment, the aqueous composition comprises a compatible surfactant.

Surfactants can lower the surface tension of the mixture before polymerization and thus aid processing. The surfactant or surfactants may be non-ionic, anionic, zwitterionic or cationic, alone or in any mixture or combination. The surfactant may itself be reactive, i.e. capable of participating in the hydrogel-forming reaction. The total amount of surfactant, if present, is suitably up to about 10% by weight of the aqueous composition, preferably from about 0.05% to about 4% by weight. The surfactant may, for example, comprise at least one propylene oxide/ethylene oxide block copolymer, for example such as that supplied by BASF Corp.,

Florham Park, NJ under the trade designation "PLURONIC P65" and "PLURONIC L64" block copolymer.

[0071] Additional osmolyte(s) may be included to modify the osmolality of the hydrogel.

Osmolytes may be ionic (e.g. electrolytes, for example salts which are readily soluble in the aqueous phase of the hydrogel to increase the ionic strength of selected cations or anions and hence the osmolality of the hydrogel). By selecting the ions present in an ionic osmolyte, and particularly by selecting the cation so as to correspond or not with cationic counterions in the monomer(s) of the hydrogel, the ionic strength of certain anions (e.g. chloride) can be varied with fine control, without substantially changing the ionic strength of cations already present in very large amounts as counterions of the monomer(s). Osmolytes may be organic (non-ionic), for example organic molecules which dissolve in or intimately mix with the aqueous phase of the hydrogel to increase the osmolality of the hydrogel deriving from non-ionic species in the aqueous phase. Such organic osmolytes include, for example, water-soluble sugars (e.g. glucose, fructose and other monosaccharides; sucrose, lactose, maltose and other disaccharides; or any combination of mono- and di-saccharides), and polyhydric alcohols (e.g. glycerol and other polyhydroxylated alkanols).

[0072] In addition to water, in one embodiment, a water miscible organic solvent may be used.

Examples of such organic solvents include methanol, acetone, methyl ethyl ketone and tetrahydrofuran. The mixing ratio of water to the organic solvent can be optionally selected within a range wherein the water swelling clay can be homogeneously dispersed.

[0073] In one embodiment, the aqueous composition is substantially free of water miscible solvent, in other words, the aqueous composition comprises less than 5%, 1% or even 0.5% by weight of organic solvent versus the weight of the aqueous composition.

[0074] Preparation [0075] The aqueous composition comprising: monomers, clay, cellulose nanocrystals, water, initiator, and any additional components, may be prepared using techniques known in the art. Advantageously, the aqueous compositions of the present disclosure may be processed in a coatable format, wherein the aqueous composition is mixed, coated, and then cured to form the hydrogel. Such preparations can result in thin layers and/or films of hydrogel.

[0076] In one embodiment, the aqueous compositions of the present disclosure have a viscosity such that they can be applied onto a surface and stay sufficiently in place before curing. For example, in a web-type manufacture, the aqueous composition can be applied onto a web (i.e., substrate) at a first station and then passed along to a second station, wherein the aqueous composition is cured to form the hydrogel. After curing, the web comprising the hydrogel can then be subsequently processed, for example, the hydrogel may be rolled into a spool, additional layers of materials may be applied to the hydrogel to form an article, the web of hydrogel may be cut into smaller sections, etc.

[0077] The viscosity of a coatable aqueous composition is typically at least 1,000 or 2,000 cps (centipoise) ranging up to 100,000 cps at 25°C. In some embodiments, the viscosity is no greater than 75,000; 50,000; or 25,000 cps.

[0078] In one embodiment, the water-swellable clay can be used to increase the viscosity of the aqueous solution to render a coatable aqueous composition.

[0079] In one embodiment, the cellulose nanocrystals can be used to increase the viscosity of the aqueous solution to render a coatable aqueous composition.

[0080] The coatable aqueous composition may be coated on a suitable substrate and polymerized by exposure to actinic radiation. Suitable substrates include: polymeric films, woven and nonwoven polymeric substrates, glass, ceramic, and combinations thereof. Exemplary polymeric films include: polyurethane films, polyamide films, polyurea films, and films containing synthetic block copolymer rubbers such as Polystyrene-Woc -polybutadiene-Woc -polystyrene (SBS),

Polystyrene-Woc -polyisoprene-Woc -polystyrene (SIS), and styrenic block copolymers with a hydrogenated midblock of styrene-ethylene/butylene-styrene (SEBS) or styrene- ethylene/propylene-styrene (SEPS). In one embodiment, the substrate is a removable liner, comprising a release agent, which is used to decrease the adhesion of the hydrogel to the substrate. In one embodiment for wound applications, the substrate may comprise a backing layer or a release layer and any desired sheet support member that may be interposed between the release layer and the hydrogel composition, or embedded within the hydrogel composition.

[0081] In one embodiment, the aqueous composition is initially applied onto a substrate (e.g., a web or sheet), the aqueous compositions can be applied by methods such as roller coating, flow coating, dip coating, spin coating, spray coating, bar coating, gravure coating, knife coating, and die coating. Thickness of the resulting coating layer can vary depending on the application. For example, in in vivo applications (e.g., stents), the thickness of the coating layer can range from at least 10 nm or even 100 nm to at most 1 micrometer (μιη), 10 μιη, or even 100 μιη. For example, in wound care applications, the thickness of the coating layer can range from at least 0.1 millimeters (mm), 0.25 mm or even 0.5 mm to at most 2 mm, 3 mm, or even 10 mm.

[0082] The aqueous composition can be polymerized by various techniques, yet is preferably polymerized by radiation-initiated free radical polymerization, including using electron beam, gamma, and especially ultraviolet (UV) light radiation. Any ultraviolet light source, as long as part of the emitted light can be absorbed by the photo-initiator or photo-initiator system, may be employed as a radiation source, such as, a high or low pressure mercury lamp, a cold cathode tube, a black light, an ultraviolet LED, an ultraviolet laser, and a flash light. Of these, the preferred source is one exhibiting a relatively long wavelength UV-contribution having a dominant wavelength of 300-400 nm. Specifically, a UV-A light source is preferred due to the reduced light scattering therewith resulting in more efficient interior curing. UV radiation is generally classed as UV-A, UV-B, and UV-C as follows: UV-A: 400 nm to 320 nm; UV-B: 320 nm to 290 nm; and UV-C: 290 nm to 100 nm. Relatively low light intensity sources such as blacklights, which provide generally 10 milliWatts/centimeter² (mW/cm²) or less (as measured in accordance with procedures approved by the United States National Institute of Standards and Technology as, for example, with a UVIMAP UM 365 L-S radiometer manufactured by

Electronic Instrumentation & Technology, Inc., in Sterling, VA) over a wavelength range of 280 to 400 nanometers; and relatively high light intensity sources such as medium pressure mercury lamps which provide intensities generally greater than 10 mW/cm², preferably 15 to 450 mW/cm². Intensities can range from 0.1 to 150 mW/cm², preferably from 0.5 to 100 mW/cm², and more preferably from 0.5 to 50 mW/cm². The monomer component(s) can also be polymerized with high intensity light sources as available from Fusion UV Systems Inc. UV light to polymerize the monomer component(s) can be provided by light emitting diodes, blacklights, medium pressure mercury lamps, etc. or a combination thereof.

[0083] When the film is a monolithic film, the thickness of the (e.g. radiation) cured film is typically at least 10, 15, 20, or 25 μπι (1 mil) to 500 μπι (20 mils) thickness. In some embodiments, the thickness of the (e.g. radiation) cured film is no greater than 400, 300, 200, or

100 μπι. When the film is a film layer of a multilayer film, the multilayer film typically has the thickness just described. However, the thickness of the film layer may be less than 10 μπι.

[0084] Because photoinitiation is discontinued when the activation source is turned off, advantageously, the use of the photopolymerization method would enable control of the polymerization and/or curing of the hydrogel. For example, polymerization to achieve a coatable viscosity may be conducted such that the conversion of monomers to polymer is up to about 30%. Polymerization can be terminated when the desired conversion and viscosity have been achieved by removing the light source and by bubbling air (oxygen) into the solution to quench propagating free radicals.

[0085] After completion of the polymerization/cure, a hydrogel is formed. In one embodiment, the hydrogels of the present disclosure are a film, meaning that they are a sheet of material, having an opposed first and second major surfaces defining a thickness of the film, wherein the thickness of the hydrogel is less than the width of the film. In one embodiment, the thickness of the hydrogel is at least 0.01, 0.025, 0.5, or even 0.1 mm and no more than 0.5, 1, 1.5, 2, or even 2.5 mm.

[0086] In one embodiment, the hydrogel of the present disclosure comprises at least 0.1, 0.3, 0.5, or even 1 wt%; and at most 5, 6, 8, 10, 15, or even 20 wt% cellulose nanocrystals versus the total weight of the hydrogel.

[0087] In one embodiment, the hydrogel of the present disclosure comprises at least 0.1, 0.3, 0.5, or even 1 wt%; and at most 5, 6, 8, 10, 15, or even 20 wt% of water swellable clay versus the total weight of the hydrogel.

[0088] In one embodiment, the hydrogel is sterilized for biological use. The product is preferably sterilized in conventional manner. The sterilized hydrogel may be used immediately, e.g. to provide a skin-adhesive layer in an article, or a top release layer may be applied to the composite for storage and transportation of the composite.

[0089] The water content absorbed by the resulting hydrogel can be a function of the monomers used, for example hydroxyethyl(methacrylate) and vinyl pyrrolidone and glycerol methacrylate and acrylamide monomers can be used to form hydrogels with high water content. Acid- containing monomers such as (meth)acrylic acid and 2-acrylamido-2-methylpropanesulfonic acid provide ionic character at pH above 4 and contribute to large amounts of water absorption.

[0090] The storage modulus in an indication of the stiffness of a material. In one embodiment, the hydrogels of the present disclosure have a storage modulus (G') of at least 3000, 4000, 5000, 7000, 8000, or even 9000 dynes/centimeter² ; and at most 15000, 20000, 30000, 40000, 50000, or even 60000 dynes/centimeter² when measured at 37°C.

[0091] The hydrogel sheet may be part of a multi-layer composite, including further layers such as further hydrogels and/or other polymers and/or other sheet support members. For example, a breathable (air and/or moisture permeable) polymeric film (e.g. polyurethane), which may, if desired, be present as a foam, may overlie the hydrogel sheet or composite on the major face of the sheet or composite directed away from the lesion in use. The breathable polymeric film may be, or may constitute part of, the backing layer. [0092] The hydrogel composition and other sheet components as desired may preferably be provided with a release layer (e.g. of non-stick paper or plastic, such as siliconised paper or plastic) to protect one or both major face of the sheet prior to use.

[0093] Because of their high water content, hydrogels are often inherently biocompatible. Thus, these articles may be used in wound dressings or in devices/articles (e.g., stents) meant for contact with biological tissues.

[0094] In one embodiment, the hydrogel of the present disclosure is used in a wound dressing comprising a hydrogel. In another embodiment, the hydrogel of the present disclosure is used in a wound dressing comprising a hydrogel disposed on a backing, with optionally a breathable polymeric applied on the opposing side of the hydrogel.

[0095] Exemplary embodiments of the present disclosure, include, but are not limited to the following:

[0096] Embodiment 1. A hydrogel wherein the hydrogel has a water content of at least 10 wt%, and wherein the hydrogel is derived from an aqueous composition, the aqueous composition comprising:

(a) a hydrophilic monomer comprising at least one of (meth)acrylate and

(meth)acrylamide ;

(b) at least 0.1 wt% of a water-swellable clay;

(c) at least 0.1 wt% cellulose nanocrystals; and

(d) a photoinitiator.

[0097] Embodiment 2. The hydrogel of any one of the previous embodiments, further comprising a cross-linking agent.

[0098] Embodiment 3. The hydrogel of any one of the previous embodiments, wherein the cellulose nanocrystals have an average length less than 300 nm.

[0099] Embodiment 4. The hydrogel of any one of the previous embodiments, wherein the cellulose nanocrystals have an average cross-sectional dimension of less than 20 nm.

[00100] Embodiment 5. The hydrogel of any one of the previous embodiments, wherein the aqueous composition comprises 0.001 to 5 % by weight of the photoinitiator.

[00101] Embodiment 6. The hydrogel of any one of the previous embodiments, wherein the photoinitiator is a water soluble photoinitiator.

[00102] Embodiment 7. The hydrogel of any one of the previous embodiments, wherein the photinitiator comprises at least one of: 2 -hydroxy -4'-(2-hydroxyethoxy)-2 -methyl propiophenone, 4-(3-sulfopropyloxy)benzophenone, 2-(3-sulfopropyloxy) thioxanthen-9-one, carboxybenzophenone, and salts thereof.

[00103] Embodiment 8. The hydrogel article of any one of the previous embodiments, wherein the water-swellable clay comprises at least one of laponite, synthetic hectorite, and montmorillonite .

[00104] Embodiment 9. The hydrogel of any one of the previous embodiments, wherein the aqueous composition comprises 0.5-20% by weight of the water-swellable clay.

[00105] Embodiment 10. The hydrogel of any one of the previous embodiments, wherein the hydrogel has a thickness of at least 0.1 mm.

[00106] Embodiment 11. The hydrogel of any one of the previous embodiments, wherein the aqueous composition further comprises an additive comprising at least one of polyethylene glycol, polyethylene glycol-co-polypropylene oxide copolymers, partially hydrolyzed polyvinyl acetate, polyvinyl pyrrolidone, glycerol, glycerol derivative, methylcellulose, other cellulose derivative, polyoxazoline, and natural gums.

[00107] Embodiment 12. The hydrogel of any one of the previous embodiments, wherein the hydrogel further comprises an antimicrobial agent.

[00108] Embodiment 13 An article comprising the hydrogel of any one of embodiments 1- 12, wherein the article is a wound dressing, or a stent coating.

[00109] Embodiment 14. A method of making a hydrogel, the method comprising:

(i) obtaining an aqueous composition comprising:

(a) a hydrophilic monomer comprising at least one of (meth)acrylate and

(meth)acrylamide ;

(b) at least 0.1 wt% of a water-swellable clay;

(c) at least 0.1 wt% cellulose nanocrystals; and

(d) a photoinitiator;

(ii) contacting the aqueous composition to a substrate; and

[00110] Embodiment 15. The method of embodiment 14, wherein the radiation is by UV radiation.

[00111] Embodiment 16. A method of making a hydrogel film, the method comprising: (i) at a first station, coating an aqueous composition onto a web, the aqueous composition comprising:

(a) a hydrophilic monomer comprising at least one of (meth)acrylate and

(meth)acrylamide ; (b) at least 0.1 wt% of a water-swellable clay;

(c) at least 0.1 wt% cellulose nanocrystals; and

(d) a photoinitiator;

(ii) transporting the coated web to a second station; and

(iii) curing the coated web at the second station to form the hydrogel film.

[00112] Embodiment 17. The method of embodiment 16, further comprising transporting the hydrogel film to a third station, where the hydrogel film is wound onto a roll.

[00113] Embodiment 18. The method of any one of embodiments 16-17, wherein the web comprises a release layer and the aqueous composition is coated onto a release layer.

[00114] Embodiment 19. The method of embodiment 18, wherein a polyurethane film is disposed onto the hydrogel film, opposite the release layer.

EXAMPLES

[00115] Unless otherwise noted, all parts, percentages, ratios, etc. in the examples and the rest of the specification are by weight, and all reagents used in the examples were obtained, or are available, from general chemical suppliers such as, for example, Sigma-Aldrich Company, Saint Louis, Missouri, or may be synthesized by conventional methods.

[00116] These abbreviations are used in the following examples: g = grams, rpm = revolutions per minute, min = minutes, °C = degrees Celsius, and mW= milliWatt.

DM Ac Am N,N-Dimethylacrylamide, obtained from Sigma-Aldrich

Company, St. Louis, MO.

[00117] TEST METHODS

[00118] Water Loss by Thermal Gravimetric Analysis (TGA)

[00119] Samples were stored in foil bags until just prior to testing. Upon removal from a foil storage bag, samples were evaluated for water content using a Model Q5000IR

Thermogravimetric Analyzer (TA Instruments, New Castle, DE) under an isothermal condition of 37° C (99° F) for 210 minutes in air. The weight loss is report as a % change from the initial weight.

[00120] Storage Modulus (G') by Rheological Analysis

[00121] Samples were stored in foil bags until just prior to testing. Upon removal from a foil storage bag, samples were evaluated for storage modulus (G') using a Model AR-G2

Rheometer (TA Instruments, New Castle, DE) equipped with a water trap and parallel plates having a diameter of 20 millimeters. A 1.0 millimeter gap, a shear rate of 1 radian/second, and a heating rate of 5° C/minute between 0° and 100° C were used as test parameters and modulus were measured. It was observed that above 60° C the storage modulus rose sharply due to loss of water.

[00122] Handling Properties

[00123] Hydrogel film samples were evaluated for their handling properties by die cutting pieces, removing the release liners, and using the free-standing, self-supporting films for evaluation of water loss and modulus. If the films could be cut, liners removed, and samples placed in the test equipment without losing their integrity they were graded as "Pass". If the films broke, cracked, or failed in other ways they were graded as "Fail".

[00124] EXAMPLES

[00125] Examples 1-4 and Comparative Example 1

[00126] Various poly(acrylic acid) hydrogels (PAA Hydrogels) were prepared as follows using the amounts shown in Table 1 below. Deionized water (where used) was added to an 8 ounce glass jar which was then placed on a magnetic stirrer and a magnetic stir bar placed therein. The stir bar was rotated at approximately 600 revolutions/minute (rpm). Next, XLG Clay (where used), and CNC, 20.1 grams of AA containing 0.1 grams of 12959 (0.5 wt%), and 2.5 grams of an aqueous solution containing 2 wt% of MBA (0.05 g MBA) were added slowly in the sequence given with continued stirring. After thoroughly mixing, the resulting sols were allowed to stand for up to 18 to 24 hours in order to build viscosity. If an increase in viscosity was not observed, then an aqueous solution containing 10 wt% of citric acid was added in 1.0 milliliter increments with mixing until a coatable viscosity was obtained. The samples were then coated between two release liners using a notchbar coater having a gap setting of 508 micrometers (0.020 inches) greater than the combined thickness of the release liners and cured by exposure to a UVA light source having a UVA peak emission wavelength of between 350 and 400 nanometers from both sides for five minutes to provide a total UVA energy of 2.4 Joules/square centimeter. Immediately after UVA curing, the hydrogel film samples were placed in foil bags, and the bags were heat sealed shut until further use. The film samples were later evaluated for water loss, storage modulus, and handling properties as described above.

Table 1 : PAA Hydrogel Compositions

Table 2

[00127] Looking at, for example, CE1 and E3 in Table 2, a similar level of water retention was obtained when a combination of cellulose nanocrystals and clay was used versus cellulose nanocrystals alone. However, E3, used less than half the total amount of filler (cellulose nanocrystals and clay) than CE 1. Similarly, the same or higher modulus values were obtained between CE 1 and E3 even though E3 used less than half the total amount of filler. Further, handling of the hydrogels was acceptable even though the total amount of filler was less when a combination of cellulose nanocrystals and clay was used.

[00128] Examples 5-7 and Comparative Examples 2 and 3

[00129] Various poly(dimethylacrylamide) hydrogels (PDMA Hydrogels) were prepared and evaluated as described for Examples 1-4 and Comparative Example 1 using the amounts shown in Table 4 below with the following modifications. 6.0 grams (10 wt%) of DMAcAm was used in place AA; 0.75 grams of the MBA solution was used, and 0.03 grams (0.05 wt%) of 12959 was employed in the sequence given. Finally, 0.23 grams of a 10 wt% aqueous solution of citric acid in deionized water was added slowly with continued mixing. Next, the sols were allowed to stand in order to build viscosity. The gap setting was 1524 micrometers (0.060 inches) greater than the combined thickness of the release liners and UVA exposure was from one side for 20 minutes to provide a total UVA energy of 4.8 Joules/square centimeter. Immediately after UVA curing, the hydrogel film samples were placed in foil bags and heat sealed shut until further use. The film samples were later evaluated for water loss, modulus, and handling properties as described above.

[00130] Comparative Example 4 was prepared as follows using the amounts shown in Table 3 below. Deionized water was added to an 8 ounce glass jar which was then placed on a magnetic stirrer and a magnetic stir bar placed therein. The stir bar was rotated at approximately 600 revolutions/minute (rpm). Next, CNC, 20.1 grams of DMAcAm containing 0.1 grams of 12959 (0.5 wt%), and 2.5 grams of an aqueous solution containing 2 wt% of MBA (0.5 g MBA) were added slowly in the sequence given with continued stirring. After thoroughly mixing, the resulting sol was allowed to stand for up to 18 to 24 hours in order to build viscosity. An increase in viscosity was not observed in this sample. An aqueous solution containing 10 wt% of citric acid was added in 1.0 milliliter increments to increase viscosity. However, a coatable viscosity was not obtained after 5 aliquots of citric acid solution and therefore, this aqueous solution was not processed (e.g., cured) or tested further.

Table 3 : PDMA H dro el Com ositions

Did not achieve a coatable viscosity Table 4

[00131] As shown in Table 4 for the acrylamide-containing hydrogels, increased levels of water retention were obtained when a combination of cellulose nanocrystals and clay was used versus clay alone. Comparing CE 3 with E6 or E7, a similar level of water retention was obtained when a combination of cellulose nanocrystals and clay was used versus cellulose nanocrystals alone. For acrylamide hydrogels, higher modulus values were obtained when a combination of cellulose nanocrystals and clay was used versus when either the clay or cellulose nanocrystals were used alone. Handling was acceptable in the examples even though the total amount of filler was less than when a combination of cellulose nanocrystals and clay was used.

[00132] Foreseeable modifications and alterations of this invention will be apparent to those skilled in the art without departing from the scope and spirit of this invention. This invention should not be restricted to the embodiments that are set forth in this application for illustrative purposes. To the extent that there is any conflict or discrepancy between this specification as written and the disclosure in any document mentioned or incorporated by reference herein, this specification as written will prevail.

Claims

What is claimed is:

1. A hydrogel wherein the hydrogel has a water content of at least 10 wt%, and wherein the

hydrogel is derived from an aqueous composition, the aqueous composition comprising:

(e) a hydrophilic monomer comprising at least one of (meth)acrylate and

(meth)acrylamide ;

(f) at least 0.1 wt% of a water-swellable clay;

(g) at least 0.1 wt% cellulose nanocrystals; and

(h) a photoinitiator.

2. The hydrogel of any one of the previous claims, further comprising a cross-linking agent.

3. The hydrogel of any one of the previous claims, wherein the cellulose nanocrystals have an average length less than 300 nm.

4. The hydrogel of any one of the previous claims, wherein the cellulose nanocrystals have an average cross-sectional dimension of less than 20 nm.

5. The hydrogel of any one of the previous claims, wherein the photinitiator comprises at least one of: 2-hydroxy-4'-(2-hydroxyethoxy)-2-methyl propiophenone, 4-(3- sulfopropyloxy)benzophenone, 2-(3-sulfopropyloxy) thioxanthen-9-one, carboxybenzophenone, and salts thereof.

6. The hydrogel of any one of the previous claims, wherein the aqueous composition comprises 0.5-20% by weight of the water-swellable clay.

7. The hydrogel of any one of the previous claims, wherein the hydrogel has a thickness of at least 0.1 mm.

8. An article comprising the hydrogel of any one of claims 1-7, wherein the article is a wound dressing, or a stent coating.

9. A method of making a hydrogel, the method comprising:

(i) obtaining an aqueous composition comprising: (e) a hydrophilic monomer comprising at least one of (meth)acrylate and (meth)acrylamide ;

(f) at least 0.1 wt% of a water-swellable clay;

(g) at least 0.1 wt% cellulose nanocrystals; and

(h) a photoinitiator;

(ii) contacting the aqueous composition to a substrate; and

10. A method of making a hydrogel film, the method comprising:

(i) at a first station, coating an aqueous composition onto a web, the aqueous composition comprising:

(e) a hydrophilic monomer comprising at least one of (meth)acrylate and

(meth)acrylamide ;

(f) at least 0.1 wt% of a water-swellable clay;

(g) at least 0.1 wt% cellulose nanocrystals; and

(h) a photoinitiator;

(ii) transporting the coated web to a second station; and

(iii) curing the coated web at the second station to form the hydrogel film.