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Jian Ping Gong, et al.

Fiber-Reinforced Soft Composite









http://www.sciencealert.com/scientists-invent-a-hydrogel-fabric-that-s-five-times-stronger-than-steel

Scientists Have Invented a Hydrogel Fabric That's 5 Times Stronger Than Steel

But you can still bend and stretch it.

by DAVID NIELD

Scientists have created a new hydrogel material reinforced with fibres that they say is up to five times harder to break than carbon steel – but still easy to bend and stretch.

That combination of properties means the new fabric could be used as the basis for artificial ligaments and tendons designed to help the body heal – or in manufacturing or fashion where a very tough but elastic material is needed.

Researchers from Hokkaido University in Japan developed the fabric, called fibre-reinforced soft composite (or FRSC), by combining hydrogels containing high levels of water with glass fibre fabric....

The end result is a material that's 25 times tougher than glass fibre fabric; 100 times tougher than hydrogels; and five times as strong as carbon steel, in terms of the energy required to break them...



https://www.oia.hokudai.ac.jp/blog/new-tougher-than-metal-fiber-reinforced-hydrogels/

New “tougher-than-metal” fiber-reinforced hydrogels

A team of Hokkaido University scientists has succeeded in creating “fiber-reinforced soft composites,” or tough hydrogels combined with woven fiber fabric. These fabrics are highly flexible, tougher than metals, and have a wide range of potential applications.

Efforts are currently underway around the world to create materials that are friendly to both society and the environment. Among them are those that comprise different materials, which exhibit the merits of each component.

Hokkaido University researchers, led by Professor Jian Ping Gong, have focused on creating a reinforced material using hydrogels. Though such a substance has potential as a structural biomaterial, up until now no material reliable and strong enough for long-term use has been produced. This study was conducted as a part of the Cabinet Office’s Impulsing Paradigm Change through Disruptive Technologies Program (ImPACT).

To address the problem, the team combined hydrogels containing high levels of water with glass fiber fabric to create bendable, yet tough materials, employing the same method used to produce reinforced plastics. The team found that a combination of polyampholyte (PA) gels, a type of hydrogel they developed earlier, and glass fiber fabric with a single fiber measuring around 10µm in diameter produced a strong, tensile material. The procedure to make the material is simply to immerse the fabric in PA precursor solutions for polymerization.

When used alone, the fiber-reinforced hydrogels developed by the team are 25 times tougher than glass fiber fabric, and 100 times tougher than hydrogels – in terms of the energy required to destroy them. Combining these materials enables a synergistic toughening. The team theorizes that toughness is increased by dynamic ionic bonds between the fiber and hydrogels, and within the hydrogels, as the fiber’s toughness increases in relation to that of the hydrogels. Consequently, the newly developed hydrogels are 5 times tougher compared to carbon steel.

“The fiber-reinforced hydrogels, with a 40 percent water level, are environmentally friendly,” says Dr. Jian Ping Gong, “The material has multiple potential applications because of its reliability, durability and flexibility. For example, in addition to fashion and manufacturing uses, it could be used as artificial ligaments and tendons, which are subject to strong load-bearing tensions.” The principles to create the toughness of the present study can also be applied to other soft components, such as rubber.

Fig2-Ionic bonds
figure2

Scanning Electron Microscopy (SEM) images of the fiber-reinforced hydrogels. The polymer matrix (arrows) filled the interstitial space in the fiber bundles and connected the neighboring fibers. (Huang Y. et al., Advanced Functional Materials, January 16, 2017)

Contacts:

Professor Jiang Ping Gong
Graduate School of Life Science
Hokkaido University
Email: gong[at]sci.hokudai.ac.jp

Naoki Namba (Media Officer)
Global Relations Office
Institute for International Collaboration
Hokkaido University
Tel: +81-11-706-8034
Email: pr[at]oia.hokudai.ac.jp



http://onlinelibrary.wiley.com/doi/10.1002/adfm.201605350/abstract
DOI: 10.1002/adfm.201605350
Advanced Functional Materials, January 16, 2017.

Energy-Dissipative Matrices Enable Synergistic Toughening in Fiber Reinforced Soft Composites

Yiwan Huang, et al.

Abstract

Tough hydrogels have shown strong potential as structural biomaterials. These hydrogels alone, however, possess limited mechanical properties (such as low modulus) when compared to some load-bearing tissues, e.g., ligaments and tendons. Developing both strong and tough soft materials is still a challenge. To overcome this obstacle, a new material design strategy has been recently introduced by combining tough hydrogels with woven fiber fabric to create fiber reinforced soft composites (FRSCs). The new FRSCs exhibit extremely high toughness and tensile properties, far superior to those of the neat components, indicating a synergistic effect. Here, focus is on understanding the role of energy dissipation of the soft matrix in the synergistic toughening of FRSCs. By selecting a range of soft matrix materials, from tough hydrogels to weak hydrogels and even a commercially available elastomer, the toughness of the matrix is determined to play a critical role in achieving extremely tough FRSCs. This work provides a good guide toward the universal design of soft composites with extraordinary fracture resistance capacity.



http://pubs.rsc.org/en/content/articlehtml/2015/mh/c5mh00127g
DOI: 10.1039/C5MH00127G
(Communication) Mater. Horiz., 2015, 2, 584-591

Extremely tough composites from fabric reinforced polyampholyte hydrogels

Daniel R. King, et al.

Ligaments are unique wet biological tissues with high tensile modulus and fracture stress, combined with high bending flexibility. Developing synthetic materials with these properties is a significant challenge. Hydrogel composites made from high stiffness fabrics is a strategy to develop such unique materials; however, the ability to produce these materials has proven difficult, since common hydrogels swell in water and interact poorly with solid components, limiting the transfer of force from the fabric to the hydrogel matrix. In this work, for the first time, we successfully produce extraordinarily tough hydrogel composites by strategically selecting a recently developed tough hydrogel that de-swells in water. The new composites, consisting of polyampholyte hydrogels and glass fiber woven fabrics, exhibit extremely high effective toughness (250[thin space (1/6-em)]000 J m−2), high tear strength (∼65 N mm−1), high tensile modulus (606 MPa), and low bending modulus (4.7 MPa). Even though these composites are composed of water-containing, biocompatible materials, their mechanical properties are comparable to high toughness Kevlar/polyurethane blends and fiber-reinforced polymers. Importantly, the mechanical properties of these composites greatly outperform the properties of either individual component. A mechanism is proposed based on established fabric tearing theory, which will enable the development of a new generation of mechanically robust composites based on fabrics. These results will be important towards developing soft biological prosthetics, and more generally for commercial applications such as tear-resistant gloves and bulletproof vests.



WO2016027383
COMPOSITE COMPRISING FABRIC AND POLYAMPHOLYTE HYDROGEL AND PREPARATION METHOD THEREOF

Inventor(s): GONG JIAN PING, et al.


A composite comprising a fabric and a polyampholyte hydrogel is provided. In the composite, the polyampholyte hydrogel is a hydrogel of a polymer bearing randomly dispersed cationic and anionic repeat groups and at least a part of the fabric is coated with the polyampholyte hydrogel. A method of preparation of the composite comprises steps (a) to (c): (a) providing a monomer mixture for preparation of a polyampholyte hydrogel; (b) immersing a fabric in the monomer mixture solution; and (c) polymerizing monomers in the monomer mixture solution to obtain a precursor of the composite.

DESCRIPTION

Field of The Invention

This invention relates to a composite comprising a fabric and a polyampholyte hydrogel and a method of preparation of the composite.

Discussion of The Background

Anterior Cruciate Ligament (ACL) reconstruction surgeries are one of the most common surgeries performed by orthopedic surgeons. To avoid using autographs or allographs, synthetic materials have been investigated as potential replacements.

Some materials which have been tested are Dacron, Marlex, Teflon, Nylon, and Carbon Fiber. [NP-2] It is important that the materials which are used can support the high load placed upon these ligaments. Carbon Fiber has been especially of interest as a replacement material because of its extremely high stiffness. Initial results with neat carbon fiber replacements were promising. [NP-3, 4] However problems were encountered, including fracture, fraying and spreading of carbon in the body, irritation and poor healing of the surrounding area, and accumulation of carbon in regional lymph nodes. [NP- 1,2, 5]

NP-1 : K. Miller, J. E. Hsu, L. J. Soslowsky, in Comprehensive Biomaterials, 2011, pp. 257-279.
NP-2: A. A. Amis, S. A. Kempson, J. R. Campbell, J. H. Miller, Journal of Bone and Joint Surgery 1988, 70-B, 628-634.
NP-3: D. H. R. Jenkins, B. McKibbin, Journal of Bone and Joint Surgery 1980, 62, 497-499.
NP-4: D. H. R. Jenkins, Journal of Bone and Joint Surgery 1978, 60-B, 520-522.
NP-5: S. Ramakrishna, J. Mayer, Composites Science and ... 2001, 61, 1189-1224.

Some researchers have also attempted to use hydrogels as ligament replacements, but they lack the mechanical properties to support high loads. There is some mention in the patent literature of hydrogel and fabrics as prosthetics. [P-l, 2, 3, 4]

P-l : US Patent No. 6,629,997.
P-2: US Patent No. 6,187,043.
P-3: US Patent No. 6,027,744.
P-4: US Patent No. 4,919,667.

However the brittleness of traditional hydrogels may have prevented these methods from entering the market.

In addition to the application in ACL reconstruction surgeries, the applications listed below are those in which high toughness is desired, such as skin grafts, flexible tear resistant clothing, bandaging, bullet-proofing, etc.

In bandages, there is very little in the literature about fabric / hydrogel bandages, however there is some mention in the patent literature. In these systems fabric are used as support, and the hydrogel is used for wound closure, as they are generally non-toxic, consist mostly of water, and can promote wound healing. [P-5 to P-8]

P-5 : Absorptive wound dressing for wound healing promotion - 5,695,777 ;
P-6: Dressing material based on a hydrogel, and a process for its production -4,552,138 ;
P-7: Reinforced, laminated, impregnated, and composite-like materials as crosslinked polyvinyl alcohol hydrogel structures - 6,855,743;
P-8: Hydrogel Laminate, Bandages, and composites and methods for forming the same - 5,674,346

However, within these patents there is no obvious mention of utilizing these composite materials to make extremely tough or tear resistant bandages.

Fabric composites have been looked at and utilized before as high strength and toughness materials. Some of these are for ballistics and blast resistance.

P-9: Reinforced film for blast resistance protection - 8,039,102;
P-10: Impact resistive composite materials and methods for making same - 7,608,322;
P-l l : Body armor with improved knife-stab resistance formed from flexible composites - 7,288,493;
P-12: Ballistic-resistant article and process for making the same - 6,268,301;
P-13: Ballistic fabric laminates - 6,846,758;
P-14: Armor panel - 5,789,327;
P-15: Method for improving the energy absorption of a high tenacity fabric during a ballistic event - 5,595,809;
P-16: Lightweight armor and ballistic projectile defense apparatus - 8,375,839).

There are materials used for airbag technologies in vehicles.

P-17: Silicone composition for coating substrates made of textile material - 6,586,551 ;
P-18: Silicone coated textile fabrics - 6,354,620; etc.

Finally, some patents mention fabrics which exhibit high tear strength.

P-19: Textile-reinforced composites with high tear strength - 7,549,303;
P-20: Method of making a cut and abrasion resistant laminate - 6,280,546;
P-21 : Elastic composite structure - 7,153,789;
P-22: Composite elastic material - 6,706,364;
P-23: Cut resistant yarn, fabric and gloves - 5,119,512;
P-24: Fiber reinforced thermosetting resin compositions with coated fibers for improved toughness - 4,737,527;
P-25: Method of manufacture of silicone elastomer coated cloth - 4,478,895.

However in these examples, none of the composite materials utilize hydrogels, or any type of elastic materials which contain water. In many cases, the matrix material is thermosetting, which would result in the composite lacking any flexibility.

Recently, new polyampholyte (PA) hydrogels produced by Sun et. al. have shown the ability to maintain these features through a macromolecular architecture that also features self-healing, and one-pot synthesis abilities. [NP-6,7]

NP-6: T. L. Sun, T. Kurokawa, S. Kuroda, A. Bin Ihsan, T. Akasaki, K. Sato, M. A. Haque, T. Nakajima, J. P. Gong, Nature materials 2013, 12, 1-6.
NP-7: A. Bin Ihsan, T. L. Sun, S. Kuroda, M. A. Haque, T. Kurokawa, T.Nakajimac, J. P. Gong, J. Mater. Chem. B, 2013, 1 , 4555-4562

Previous work from the Crosby Research Group has shown that embedding soft elastomers with stiff fabrics can result in very interesting composite materials. [NP-8 to NP-10] Double network hydrogels devolved in the Gong Research Group have extremely high toughness, while having moderate ultimate tensile strength and low friction. [NP 11-14].

NP-8: M. D. Bartlett, A. B. Croll, D. R. King, B. M. Paret, D. J. Irshick, A. J.Crosby, Advanced Materials 2012, 24, 1078-1083.
NP-9: S. A. Pendergraph, M. D. Bartlett, K. R. Carter, A. J. Crosby, ACS Applied Materials & Interfaces 2012, 4, 6640-5.
NP-10: D. R. King, M. D. Bartlett, C. A. Gilman, D. J. Irschick, A. J. Crosby, in prep 2013.
NP-11 : J. P. Gong, Y. Katsuyama, T. Kurokawa, Y. Osada, Advanced Materials 2003, 15, 1155-1158. Revised 12/17/12 4
NP-12: J. P. Gong, T. Kurokawa, T. Narita, G. Kagata, Y. Osada, G Nishimura, M. Kinjo, Journal of the American Chemical Society 2001, 123, 5582-5583.
NP-13: T. Tominaga, N. Takedomi, H. Biederman, H. Furukawa, Y. Osada, J. P.Gong, Soft Matter 2008, 4, 1033.
NP-14: K. Yasuda, J. P. Gong, Y. Katsuyama, A. Nakayama, Y. Tanabe, E. Kondo, M. Ueno, Y. Osada, Biomaterials 2005, 26, 4468-4475.

Utilizing a fabric and PA hydrogel composite could allow for high loads (from the fiber) while the PA hydrogel could prevent wear and rejection from the body. Incorporating these new hydrogels into fabric will allow for new materials with unique properties that are currently lacking in the literatures and patents.

Brief Description of The Drawings

The present invention will be described in the following text by the exemplary, non-limiting embodiments shown in the figures, wherein:

Figure 1 is a computer-aided drawing of one embodiment of the composites of the present invention. Left: a side view; right: a projection view.

Figure 2 is an image of testing setup for the tearing test.

Figure 3 is a tearing test result showing tear strength at breakage on one embodiment of the composite of the present invention. Comparison of a neat glass fiber fabric, a PA hydrogel, a combination of the fabric and a SN hydrogel, the SN hydrogel.

Figure 4 shows force vs. displacement curve for 20 mm wide samples of the composite of the present invention, a neat glass fiber fabric, a combination of the fabric and a SN hydrogel.

Figure 5 shows microscopy images of glass fiber fabric and PA hydrogel between the fibers of the fabric of one embodiment of the composite of the present invention.

Figure 6 is a microscopy image showing deformation in the tearing region of the fabric (macro scale)

Figure 7 is a tensile stress-strain measurement result on one embodiment of the composite of the present invention.

Figure 8 is a tensile stress-strain measurement result on a neat glass fabric.

wo1wo2wo3  wo4

wo5 wo6

Descriptions of The Embodiments

The following preferred specific embodiments are, therefore, to be construed as merely illustrative, and not limitative of the remainder of the disclosure in any way whatsoever. In this regard, no attempt is made to show structural details of the present invention in more detail than is necessary for the fundamental understanding of the present invention, the description taken with the drawings making apparent to those skilled in the art how the several forms of the present invention may be embodied in practice.

This invention relates to a composite comprising a fabric and a PA hydrogel which is relatively soft and viscoelastic. The fabric can be a woven fabric or unwoven fabric and the unwoven fabric can be a knitted fabric. A woven fabric is obtained by producing the interlacing of warp fibers and weft fibers in weave styles, such as plain, twill, or satin styles and so on. A woven fabric is preferred because the integrity of the woven fabric is maintained by the mechanical interlocking of the fibers, and their drape, surface smoothness and stability can be controlled by the weave styles based on the design requirements.

The fabric can be made from inorganic material fibers, organic material fibers, biomaterial fibers or a mixture thereof. Inorganic material fibers are composed of inorganic chemical compounds, based on natural elements, which are resistant to high temperatures and high mechanical strength. Examples of the inorganic material fibers include glass fibers, carbon fibers, ceramics fibers and metals fibers. These inorganic materials fibers are commonly applied infields that require high performance materials, such as building materials, protective clothing, parts of airplanes, spaceships, and so on. Organic material fibers are made from synthesized polymers or small molecules, which are polymerized into long linear chains. Examples of the organic material fibers include synthetic polymer fibers such as nylon fibers, aramid fibers, polyalkylene fibers such as polyethylene fibers, polypropylene fibers. These organic material fibers with high mechanical performance and thermal stability are reinforced in the polymer matrix, which are applied in fields such as the automotive industry, railways, aerospace, and so on. Biomaterial fibers are made from plants and animals, which are low cost, low density, high toughness, renewable and biodegradable. Examples of biomaterial fibers include cellulose fibers and cotton fibers. These biomaterials fibers are widely reinforced with a polymer matrix in the textile, and automotive industries. The fabric is preferably comprised of long fibers. Woven and non-woven fabrics that are commercially available can be used. The fabric can be in a form of a sheet, a tape, a strip, a tube, a rod, and so on. The preferred composite is produced by the fabric with hydrophilic surface, such as glass fiber, and PA hydrogel.

In the composite of this invention, at least a part of the surface of the fabric is coated with the PA hydrogel. The PA hydrogel can be coated on either surface of the fabric or both surface of the fabric partially or fully. The PA hydrogel is a hydrogel of a polymer bearing randomly dispersed cationic and anionic repeat groups.

The PA hydrogel is selected from the group consisting of random polymers obtained by random polymerization of a cationic monomer and an anionic monomer. The cationic monomer is selected from the group consisting of monomers having an amino group, preferably a quarternized amine group. Examples of the cationic monomer include the monomer selected from the group consisting of 3-(methacryloylamino)propyltrimethylammonium chloride (MPTC), acryloyloxethyltrimethylammonium chloride (DMAEA-Q), methacrylatoethyl trimethyl ammonium chloride (MTAC) and 4-vinylpyridine chloride (4-VPC).

The anionic monomer is selected from the group consisting of a sulfonate group, a sulfonic acid group, a carboxylate group, a carboxyl acid group, a phosphate group, and a phosphoric acid group. Examples of the anionic monomer include the monomer selected from the group consisting of sodium p-styrenesulfonate (NaSS), anionic 2-acrylamido-2-methylpropanesulfonic acid (AMPS), sodium 4-styrenecarboxylic acid (NaSA), acrylic acid(AA), sodium acrylate, methacrylic acid(MAA), and ethylene glycol 1-methacrylate 2-phosphate.

One example of the PA hydrogels is P(NaSS-co-MPTC) hydrogels, randomly copolymerized from concentrated aqueous solutions of oppositely charged monomers, sodium p-styrenesulfonate (NaSS) and 3-(methacryloylamino)propyltrimethylammonium chloride (MPTC). One example of the P(NaSS-co-MPTC) hydrogels exhibits high strength (tensile fracture stress ob . 1.8 MPa), high extensibility (tensile fracture strain eb = 7.4), and high toughness (tearing energies T = 4000 J m<"2>). The PA hydrogels are self-recoverable due to the non-covalent ionic bonds. In addition to these excellent mechanical properties, these PA hydrogels have excellent biocompatibility and anti-biofouling properties. [NP-6].

Another example of a PA hydrogels is the PA P(NaSS-co-DMAEA-Q) hydrogels synthesized from sodium p-styrenesulfonate (NaSS) and acryloyloxethyltrimethylammonium chloride (DMAEA-Q). DMAEA-Q is relatively hydrophilic in comparison with the cationic monomer MPTC.

The chemical structures of monomers are shown below:

Cationic monomers: MPTC, DMAEA-Q;

Anionic monomers: NaSS, AMPS.

1

Other examples of PA hydrogels are the P(NaSS-co-MTAC4) and P(NaSS-co-VPC) systems synthesized by using methacrylatoethyl trimethyl ammonium chloride (MTAC) or 4-vinylpyridine chloride (4-VPC) as a cationic monomer. Chemical structures of the cationic monomers for the PA hydrogels are shown below:

2

NaSA

3

The above PAs are those developed from linear PAs by employing the ionic bond as a reversible sacrificial bond that breaks and reforms dynamically. [NP-6, 7] Owing to the random distribution, the opposite charges on the PAs form multiple ionic bonds of wide distribution in strength. The strong bonds work as permanent cross-linkers, imparting the elasticity of the hydrogel. The weak bonds are fragile and they break under stress, serving as reversible sacrificial bonds. Upon rupture of the weak bonds, the globule polymer chains unfolded, serving as hidden length. These two processes dissipate energy and impart toughness to the hydrogel. The PA hydrogels used in the present invention are supramolecular hydrogels and contain about 50 wt% water, yet are very tough and viscoelastic. An illustration of PA networks with ionic bonds of different strength is shown below. The strong bonds serve as permanent crosslinking points, and the weak bonds act as reversible sacrificial bonds that rupture under deformation.

Neutral PAs form globule structures in aqueous medium by formation of ionic bonds, which leads to phase separation. It is better to determine the optimized charge ratio of the precursor solution to form the neutral PA. The effects of the monomer concentration Cm and the chemical cross-linker density C (CMBAA in case MBAA is used as the chemical cross-linker) on the behavior of the PA is considered when the PA hydrogel is prepared. These two parameters are crucial to control the phase separation of the system. It is preferred that a phase diagram of formulation in the Cm-CMBAA space can be constructed in advance and homogenous hydrogel phase is determined. The mechanical properties of PA hydrogels are dependent on the combinations of the ionic monomer pairs. There is a tendency of that more hydrophilic monomers produced softer and stretchable gels and vice versa.

The polymers are obtained by random copolymerization of a cationic monomer and an anionic monomer and a neutral monomer. The addition of the neutral monomer can adjust the stiffness and toughness of the samples. Examples of the neutral monomer include acrylamide based monomers such as acrylamide (AAm), N-isopropylacrylamide (NIPAM), dimethylacrylamide (DMAAm); vinyl based monomers such as vinyl acetate, vinyl pyridine, styrene; alkylacrylate based monomers such as methylmethacrylate; hydroxyalkyl acrylate based monomers such as hydroxyethylacrylate; and fluorine containing unsaturated monomers such as trifluoroethyl acrylate.

Synthesis of PA hydrogels and preparation of the Composite

PA hydrogels are synthesized using a one-step random copolymerization of an anionic monomer and a cationic monomer. Using a one-step random copolymerization, the composite of the present invention can be manufactured in one step.

The present invention further relates to a method of preparation of a composite comprising a fabric and a polyampholyte hydrogel. The method comprises the following steps (a) to (c).

(a) providing a monomer mixture for preparation of a polyampholyte hydrogel;

(b) immersing a fabric in the monomer mixture solution; and

(c) polymerizing monomers in the monomer mixture solution to obtain a precursor of the composite.

(a) Provision of a monomer mixture

The monomer mixture can be a mixed aqueous solution of an anionic monomer and a cationic monomer and the aqueous solution is prepared by mixing the monomers with water. The monomer concentration, Cm, influences the behavior of the resulting PA and the preparation of the PA hydrogels. The monomer concentration, Cm, means the total concentration of the anionic monomer and a cationic monomer. The monomer concentration, Cm, is desirably in a range from 1 to 5 mol/L, preferably range from 1.5 to 2.5 mol/L in order to prepare PA hydrogels enabling to provide a tough and stiff, yet<'>flexible composite.

In addition, molar fraction of the anionic monomer F influences the behavior of the resulting PA and the preparation of the PA hydrogels. The molar fraction of the anionic monomer F means a molar fraction of the anionic monomer to the total of the anionic monomer and a cationic monomer. The molar fraction of the anionic monomer F is desirably in a range from 0.4 to 0.6, preferably in a range from 0.5 to 0.54 in order to prepare PA hydrogels that provide tough and stiff, yet flexible composites.

The mixed aqueous solution can further contain a polymerization initiator and/or a cross-linking agent and/or a salt. The polymerization initiator can be ultraviolet initiator such as 2-oxoglutaric acid, sodium

4-[2-(4-morpholino)benzoyl-2-dimethylamino]butylbenzenesulfonate, and phenacylpyridinium oxalate. The concentration of the polymerization initiator can be set in view of the kind of the monomers and the preferable initiator concentration is, but not limited to, in a range from 0.01 mol% to lmol% against to total monomer concentration.

The cross-linking agent is preferably a chemical cross-linker having two or more of (meth)acrylate groups in a molecule such as N, N'-methylenebis (acrylamide) (MBAA) and ethyleneglycoldimethacrylate. N, N'-methylenebis (acrylamide) (MBAA) is preferred when an (meth)acrylate based monomer is used. Ethyleneglycoldimethacrylate is preferred when a vinyl monomer such as NaSS and 4-VPC is used. The cross-linking agent can be used in combination or alone. The concentration of the cross-linking agent can vary in view of the monomers and the preferable concentration is, but not limited to, in a range of 0.1mol% to 10mol% against to total monomer concentration.

The salt can be an inorganic salt. Examples of the inorganic salt include an alkali metal salt such as LiCl, NaCl, KC1, CsCl, CaCl2, MgS04, K2S04, or MgCl2. The concentration of the salt can vary in view of the kind of the monomers and the monomer concentration Cm and is not limited specifically but is in a range of 0.1M to 2M, for example. The usage of salt can reduce the viscosity of the mixed aqueous solution and obtain the homogeneous samples. However, the higher the salt concentration, the higher the burden of removal of the salt after polymerization.

(b) Immersion of a fabric into the monomer mixture solution; A cell for preparation of the composite is comprised of, but not limited to, a pair of plates such as glass plates facing each other and the thickness between the plates is controlled by a spacer thickness. This spacing is, but not limited to, desirably in a range from 0.001 mm to 10 mm, preferably in a range from 0.01 mm to 5.0 mm, and more preferably in a range from 0.1 mm to 1.0 mm. The plates and the spacer are selected from the material inert with the mixed aqueous solution and the spacer can be a silicone spacer, for example, with a prescribed thickness. The thickness of the spacer decides the thickness of the composite. A fabric is placed in the space made by the plates. This fabric can be woven or knit or unwoven and may range in thickness from 0.001 mm to 1 mm in thickness, and may consist of a plain, twill, or satin weave. The mixed aqueous solution is added into the channel in which the fabric has been placed. The fabric can be placed nominally in the center of the space, or preferentially towards an edge or surface such as 60/40, 70/30, 80/20, etc. distribution of the PA on each side of the fabric. Alternatively, the composite may be prepared by coating the fabric with the mixed aqueous solution on either or both sides of the fabric surface. The coating may be applied by spraying, dipping, knife-over-roll, or other traditional fabric coating methods.

(c) Polymerization of the monomers to obtain a precursor of the composite The mixed aqueous solution is cured, for example, by irradiation of ultraviolet light when an ultraviolet initiator is used. Wavelength of the ultraviolet light can be determined in view of the ultraviolet initiator. The irradiation can be conducted in an inert atmosphere, such as argon atmosphere, at an ambient temperature or an increased temperature for 1 minute to 24 hours, preferably from 1 hour to 12 hours, and more preferably from 8 hours to 12 hours, which is adjusted by the power of ultraviolet light. This reaction can take place at an ambient temperature or an increased temperature in an inert atmosphere such as an argon or nitrogen atmosphere. The composite consisted of fabric and PA can be prepared with the thickness from 0.001mm to 10mm controlled by the size of spacer.

In this method, the cationic and anionic monomers are essentially copolymerized randomly in the PA hydrogels. The random structure of the copolymer can be confirmed using a Ή-NMR reaction kinetics study, for example.

After polymerization, the as-prepared gel is immersed in water to reach equilibrium and to wash away the residual chemicals after one week, for example. The amount of the water is not limited specifically and it is preferred to confirm the equilibrium state and disappearance of the residual chemicals in the gel. During this process, the mobile counter-ions of the ionic copolymer as well as the salt used, are removed from the gel, and the oppositely charged ions on the copolymer form stable ionic complexes either through intra- or interchain interactions.

Polymerization conditions and structural features and mechanical properties of various PA hydrogels are shown in the table below.

Table 1
t1

* Cm and / represent the total ionic monomers concentration (mol/L) and the charge fraction of the anionic monomer, respectively, in the precursor solution used to synthesize the gels. The parameters cw, E, ab, eb, Wb, tan5, and R are the water content, Young's modulus, fracture stress, fracture strain, work of extension at fracture, loss factor (10 Hz and strain 0.5%), and shock-absorbing ratio, respectively, at room temperature. 7s is the softening temperature determined by the peak of loss factor of the gels.

A computer-aided drawing of one embodiment of the composites of the present invention is shown in Figure 1. Left side is a side view of the composite and right side is a projection view. One embodiment of the composites of the present invention exhibits toughness two orders of magnitude higher than traditional hydrogels (SN gel) (Gc 4800 J/m<2>vs 10 J/m<2>). In addition, one embodiment of the composites of present invention exhibits dramatic increase in toughness. For the case of a 20 mm wide strip of the composite comprised of woven glass fiber and PA gel, a Gc value (105,000 J/m<2>) can be obtained which is an additional two orders of magnitude greater than the neat PA gel, and 4 orders of magnitude higher than a traditional SN gel. (See Figure 3).

Interestingly, unlike most composites where combining two materials results in an averaging of their mechanical properties, in this case the tear strength is much greater than either materials when tested independently. Also when the control SN gel and fabric was tested, a noticeable decrease in tear strength was observed, which reinforces that this special combination of PA gel and fabric is necessary to see a great increase in tear strength (See the following Examples).

The composite of the present invention can be employed for medical treatment for example for ligament reconstruction surgeries such as Anterior Cruciate Ligament (ACL) reconstruction surgeries. The composite of the present invention can also be employed for bandages, skin grafts, flexible tear resistant clothing or bullet-proofing.

There are many ways this invention improves over the prior art. When used as internal prostheses, fabrics have many issues with regards to tearing, failing, and degrading. Often to prevent this, these stiff substrates would be coated in elastomers. However elastomers often result in a bodily response which can lead to infection or rejection. The coating material, the PA hydrogel, used here contains primarily of water and is non-toxic, and resists cell adhesion.

The composite of the present invention has various utilities. Wound care would benefit from this invention, because the PA hydrogels could create extremely resilient and tear resistant bandages. In the composite of the present invention, the fabric is used as support and the PA hydrogel is used for wound closure, as they are generally non-toxic, consist mostly of water, and can promote wound healing.

Examples

The present invention will be described in detail below based on examples. However, the present invention is not limited to the examples.

1. Materials

Sodium p-styrenesulfonate (NaSS), Methyl chloride quarternized N, N-dimethylamino ethylacrylate (DMAEA-Q), Acrylamide (AAm), 2-oxoglutaric acid and N, N'-methylenebis (acrylamide) (MBAA) were purchased from the Wako company (Japan). Fabric (S-Glass 4-Harness Satin Weave) (4HS) were purchased from the ACP composite company. In the 4HS, the fill yarn passes over three warp yarns and under one. All of the chemicals were used as purchased without further purification.

2. Methods

2- 1. Synthesis of materials

Polyampholyte hydrogels (PA) were synthesized using the one-step random copolymerization of an anionic monomer NaSS and a cationic monomer DMAEA-Q. A mixed aqueous solution with the prescribed monomer concentration (Cm=2.0 mol/L) and molar fraction of the anionic monomer (F=0.52), 0.1mol% ultraviolet initiator, 2-oxoglutaric acid, 0.1mol% chemical crosslinker MBAA (in a concentration relative to the total monomer concentration), and 0.5M NaCl was poured into a reaction cell. The cell was consisted of a pair of glass plates with 10 mm (L)x l0 mm (w)x lmm(d), where the thickness was controlled by the silicone spacer thickness. The reacted system was irradiated with 365-nm ultraviolet light for 8h in the atmosphere of argon.

Polyacrylamide hydrogels (PAAm) were produced from the polymerization of 2 mol/L acrylamide monomer, 0.1mol% 2-oxoglutaric acid and 1.0mol% chemical crosslinker MBAA (relative to the total monomer concentration) under the UV light.

PA gel/fabric composite were produced by the similar described polymerization process. The fabric 4HS with approximately 0.3 mm thickness were fixed to the center of reaction cell prior to injecting the reaction solution. To produce the PA gel/fabric composite, the polymerization was carried out after filling the PA solution with the same composition to the reaction cell.

Similar to the PA gel/fabric composite production, the PAAm/fabric composite was synthesized by the AAm solution and fabric 4HS. [0059]

After polymerization, the as-prepared gel was immersed in a large amount of water for 1 week to allow the gel to reach equilibrium and to wash away the residual chemicals and counter-ions.

2-2. Characterization

Tearing test:

The tearing test was performed to characterize the toughness in air using a commercial test machine (Instron Cat. No 2752-005). The image of testing setup for the tearing test is shown in Figure 2. The test samples were cut to rectangular shape with 40 mm (L) x 20-100 mm (w)<χ>0.5-1.3 mm (t). A cut was made 20 mm along the length, at the center of the width of the sample, to create two arms. The two arms of a test piece were clamped, and then the upper arm was pulled upward at constant velocity 50 mm/min while the tearing force F was recorded. The tearing energy T was calculated at a constant tearing force F using the relation T = 2F/w, where w is the thickness of the sample. The results are shown in Figure 3 and 4. Figure 3 shows tear strength at breakage and Figure 4 shows force vs. displacement curve for 20 mm wide samples of the composite of the present invention, a neat glass fiber fabric, a combination of the fabric and a SN hydrogel. Figure 5 shows microscopy images of glass fiber fabric and PA hydrogel between the fibers of the fabric of the sample, A is an image of fibrillation in the matrix gel and B is an image of fracture of the fibrils, which is hypothesized to dissipate energy. Figure 6 is a microscopy image showing deformation in the tearing region of the fabric (macro scale).

Tensile test:

The tensile stress-strain measurements were performed using a tensile-compressive tester (Tensilon RTC-1310A, Orientec Co.) at a deformation rate of 10 mm/min in air. The test was carried out on samples with rectangle shape with the size (25 mm (L) x 20 mm (w)<χ>0.85 mm (d). In order to prevent the slipping of the sample at the end of the clamp during the tensile test, polyethylene terephthalate (PET) plates with 2 mm (L) x 2 mm (w)<χ>3mm (d) adhere the ends of samples was used by super glue cyanoacrylate. The PET plates were gripped by the clamp during the tensile test. The results are shown in Figures 7 (composite) and 8 (neat glass fabric). The strength of the materials exceeded the strength of the mounting grips, and the ultimate properties of these materials exceed the results presented. [0062]




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