KR20230012299A - Water-responsive linear shape memory hydrogel. method of manufacturing the same and use of the same - Google Patents

Abstract

The present invention relates to a memory hydrogel of a linear shape that can be reduced in length to a preset level when in contact with water, a manufacturing method thereof and uses thereof, wherein the memory hydrogel of the linear shape according to the present invention reacts very quickly upon contact with water and can be contracted to an original length within one minute, and can be freely controlled during an elongation process because the hydrogel is easy to control the deformation.

Description

Water-responsive linear shape memory hydrogel, manufacturing method thereof and use thereof {Water-responsive linear shape memory hydrogel. method of manufacturing the same and use of the same}

The present invention relates to a linear shape-memory hydrogel that reacts to water, a manufacturing method thereof, and a use thereof, and more particularly, to a linear shape-memory hydrogel capable of contracting in length to a predetermined level when in contact with water. It relates to a gel, its preparation method and its use.

Although many petrochemical products are widely used in real life today, the need to prepare for the steep price increase and future depletion of crude oil is emerging.

Therefore, in the production of functional plastics, studies to break away from fossil fuel dependence are attracting attention. One of them, hydrogel, is a polymer chain with a three-dimensional structure that is expanded by the absorption of water molecules, and is generally semi-solid. state can be defined.

Currently, it is used in various fields such as contact lenses, diapers, medical electrodes, and cell culture, but it is also true that the application range is limited due to its weak strength.

A shape memory hydrogel material can be temporarily transformed into a different shape, but returns to its original shape when exposed to external stimuli. Most of the conventional shape memory hydrogels that react to water have a long response time. It is slow, it is not easy to control the deformation, and the size is not large.

Therefore, there is a demand for the development of new shape-memory hydrogels with fast response time and easy deformation control.

Japanese Unexamined Patent Publication No. 2019-085483

The present inventors conducted research to solve the problems of the prior art as described above, and the hydrogel linear material prepared by completely drying in a stretched state shrinks to its original state before stretching when in contact with water. , It was found that the degree of deformation (shrinkage) can be precisely controlled by adjusting the degree of stretching, and the present invention was completed.

Accordingly, an object of the present invention is to provide a new shape memory hydrogel that has a fast reaction time, easy control of deformation, and reacts with water.

Another object of the present invention is to provide a new method for preparing a shape memory hydrogel that has a fast response time, easy control of deformation, and reacts with water.

Another object of the present invention is to provide a new use of shape memory hydrogel.

As a first embodiment to achieve the above object, the present invention provides a linear shape memory hydrogel comprising a dual cross-linked interpenetrating network (IPN) structure having covalent cross-linking and ionic cross-linking at the same time. do.

In one embodiment of the present invention, the shape memory hydrogel may be stretched.

In one embodiment of the present invention, the shape-memory hydrogel may be stretched to a length twice or more, preferably 2 to 6 times the original length before stretching, but is not limited thereto.

In one embodiment of the present invention, the degree of shrinkage of the shape-memory hydrogel can be controlled by adjusting the degree of elongation.

In one embodiment of the present invention, the shape memory hydrogel may have a polyacrylamide/calcium-alginate interpenetrating network structure, but is not limited thereto.

The present invention is a second embodiment to achieve the above object. The linear shape memory hydrogel according to the first embodiment is stretched and completely dried in the stretched state to form a linear shape that responds to water. A memory hydrogel is provided.

In one embodiment of the present invention, the linear shape memory hydrogel that reacts to water may be contracted to its original length before stretching upon contact with water, but is not limited thereto.

In one embodiment of the present invention, the stretching may be twice or more, preferably two to six times the original length, but is not limited thereto.

The present invention is a third embodiment for achieving the above object,

(a) obtaining a homogeneous solution by adding a crosslinking agent, a thermal initiator and a crosslinking accelerator to an aqueous solution containing a covalent crosslinking member and a monovalent ionic crosslinking member;

(b) adding the obtained solution to a tubular tube using a syringe; (c) Linear shape-memory hydrogel having a double cross-linked interpenetrating network structure having covalent cross-linking and monovalent ionic cross-linking at the same time by heating and polymerizing the tubular tube to which the solution is added, and cross-linking the covalent cross-linking members. obtaining a gel; and

(d) taking out the linear shape-memory hydrogel obtained in step (c) from the tubular tube and then immersing it in a divalent ionic crosslinking source; A method for preparing a shape memory hydrogel is provided.

In one embodiment of the present invention, the covalent cross-linking member may be at least one selected from acrylamide, methacrylate, acrylic acid, and hydroxylethyl methacrylate, but is not limited thereto.

In one embodiment of the present invention, the monovalent ionic crosslinking member may be at least one selected from sodium alginate, alginic acid, chitosan, and pectin, but is not limited thereto.

In one embodiment of the present invention, the divalent ionic crosslinking source may be at least one selected from calcium alginate, barium alginate, calcium chitosan, curri chitosan, calcium, pectin, and barium pectin, but is not limited thereto.

In one embodiment of the present invention, the crosslinking agent is N, N'-methylene bis (acrylamide), trimethylol ethane triacrylate, trimethylol propane triacrylate, pentaerythritol tetra acrylate, pentaerythritol tri acrylate, It may be at least one selected from dipentaerythritol pentaacrylate, dipentaerythritol hexaacrylate, caprolactone-introduced polyfunctional monomer, and triallyl isocyanurate, but is not limited thereto.

In one embodiment of the present invention, the thermal initiator may be at least one selected from ammonium persulfate, potassium persulfate, benzoyl peroxide, lauroyl peroxide, and t-butylperoxypivalate, but is not limited thereto.

In one embodiment of the present invention, the crosslinking accelerator may be at least one selected from N,N,N'N'-tetramethylethylenediamine, N-ethylethylenediamine, and N-(hydroxyethyl)ethylenediaminetriacetic acid. , but is not limited thereto.

In one embodiment of the present invention, the shape memory hydrogel may have a polyacrylamide/calcium-alginate interpenetrating network structure, but is not limited thereto.

As a fourth embodiment to achieve the above object, the present invention provides an actuator including the linear shape memory hydrogel according to the second embodiment.

As an embodiment of the present invention, since the linear shape memory hydrogel according to the second embodiment is a linear material that contracts when in contact with water, it can be applied to an actuator capable of reacting to water when attached to an existing polymer film. It may, but is not limited thereto.

As a fifth embodiment to achieve the above object, the present invention provides a self lifting system including the linear shape memory hydrogel according to the second embodiment.

As an embodiment of the present invention, when a mass is suspended and water is sprayed on the linear shape memory hydrogel according to the second embodiment, the mass can be lifted while the length is contracted, so it can be implemented as a self-lifting system. , but is not limited thereto.

As a sixth embodiment to achieve the above object, the present invention provides a chemical sensor including the linear shape memory hydrogel according to the second embodiment.

As an embodiment of the present invention, when the linear shape memory hydrogel according to the second embodiment is injected into a mixture of water and ethanol, the degree of recovery to the state before stretching is different depending on the mixing ratio of water and ethanol. , The chemical sensor may be used for measuring the ethanol content in a mixture of water and ethanol, but is not limited thereto.

The linear shape-memory hydrogel according to the present invention reacts very quickly upon contact with water, can be contracted to its original length within 1 minute, and has the advantage of being easily controlled in the stretching process due to easy control of deformation.

In addition, the linear shape-memory hydrogel according to the present invention has the advantage of being able to manufacture a shape-memory hydrogel linear material without the need for special equipment and tools and a long lead time.

Figure 1 shows a schematic diagram of the PAAm/Ca-alginate IPN hydrogel fiber synthesis procedure.
Figure 2 shows the absorption spectrum of the visible light region for the PAAm/Ca-alginate IPN hydrogel prepared in the form of a film.
Figure 3 shows the FTIR spectra of PAAm (red), Ca-alginate (blue) and PAAm/Ca-alginate IPN hydrogels.
Figure 4 shows the tensile stress-strain curves of PAAm/alginate IPN hydrogel fibers and PAAm hydrogel fibers prepared by the same method.
Figure 5 shows a schematic diagram of the preparation of water-responsive 1D hydrogels.
Figure 6 (a) shows the change in L _r / L ₀ value showing the shape recovery behavior of the 1D hydrogel for 20 minutes after being immersed in water, and (b) shows the change in stretching-drying-immersion repeated 10 times. It shows the shape recovery rate (R _r ) value after.
Fig. 7. DSC thermogram of 1D hydrogel, (a) in hydrogel state and (b) in completely dried state.
Figure 8 shows a schematic diagram of the shape recovery process for IPN hydrogel fibers, which includes drawing in DI water, drying, and dipping in deionized water.
Figure 9 (a) is a schematic diagram of the actuator based on the developed 1D hydrogel fiber and 3M tape, (b) shows a bending motion in response to water after being immersed in water for 1 minute, (c) is room temperature placed on filter paper soaked in water for 1 min.
10 is a photograph of a 1D hydrogel-based water-responsive self-lifting system capable of lifting weights of (a) 5 g and (b) 2 g.
11 (a) and (b) are photographs, (c) and (d) are SEM images, (a) and (c) are PAAm/Ca-alginate hydrogel fibers swollen in water, and (b ) and (d) show the PAAm/Ca-alginate hydrogel fibers after being immersed in pure ethanol for 5 minutes.
Figure 12 (a) shows the change in shape recovery rate (R _r ) value showing the shape recovery behavior of 1D hydrogels for 40 minutes after being immersed in water-ethanol mixtures with various ethanol contents ranging from 0.00 to 0.80. In this experiment, the 1D hydrogel was prepared by stretching the PAAm/Ca-alginate IPN hydrogel to twice its initial length (L ₀ ) and then completely drying it in the stretched state.
12(b) shows a plot of (1-Lr/L ₀ ) values after immersion in a water-ethanol mixture for 40 minutes as a function of ethanol volume fraction.
13 shows a plot of (1-L _r /L ₀ ) values as a function of ethanol volume fraction ranging from 0.00 to 0.20.

Hereinafter, the present invention will be described in more detail through examples. However, the following examples are intended to illustrate the present invention, and the scope of the present invention is not limited thereto.

<Example>

As the compounds and materials used in the examples below, acrylamide (AAm), sodium alginate (Na-alginate), N,N'-methylene bis(acrylamide) (MBAA), ammonium persulfate (APS), N, N,N'N'-tetramethylethylenediamine (TEMED) and ethanol were purchased from Aldrich (USA).

Calcium chloride dihydrate (CaCl2.2H ₂ O) and methyl orange (4-[[(4-dimethylamino)phenyl]-azo]benzenesulfonic acid sodium salt) were purchased from Samcheon Chemical (Korea). Deionized water (DI) was purchased from SK Chemicals (Korea).

<Example 1> Synthesis of PAAm/Ca-alginate IPN hydrogel fibers

Reported in a previous study (Anal. Chim. Acta. 1131 80-9 (2020)); Following a two-step method similar to that described in Nature 489 133-6 (2012), PAAm/Ca-alginate IPN hydrogel fibers were synthesized.

A 5 g aqueous solution containing 1.8 g of acrylamide and 0.05 g of sodium alginate was prepared in a 20 ml vial. Then MBAA (0.1% by weight based on acrylamide) as a crosslinking agent, APS (1% by weight based on acrylamide) as a thermal initiator and 5 μl of TEMED as a crosslinking promoter of PAAm were added to obtain a homogeneous solution.

Then, using a syringe, the prepared aqueous solution was added to a PTFE tube having an inner diameter of 1 mm and a length of 2 cm. The filled tube solution was polymerized by heating at 60° C. for 1 hour, and acrylamide was cross-linked to obtain covalently cross-linked PAAM.

Then, the PAAm/Na-alginate hydrogel fibers were removed from the tube and immersed in a 0.5 M aqueous calcium chloride (CaCl ₂ ) solution at room temperature for 3 hours. In this process, Na-alginate was crosslinked by Ca ²⁺ to prepare PAAm/Ca-alginate IPN hydrogel fibers.

Thereafter, the prepared hydrogel fibers were washed with deionized water to remove unreacted residues. Finally, the hydrogel fibers were immersed in deionized water, washed and stored, and the deionized water was replaced every 12 hours for 3 days.

<Example 2> Fabrication of 1D hydrogel that reacts to water

Hydrogel fiber samples soaked in deionized water were clamped at 6 cm intervals. The clamp was then actuated so that the hydrogel fiber was stretched to three times its original length (18 cm).

After drying the stretched hydrogel sample at room temperature for 1 hour, the completely dried sample was removed from the clamp. For application to soft actuators, the stretched and dried 1D hydrogels were cut into appropriate sizes.

<Example 3> Ethanol sensing

In order to detect ethanol in a mixture of water and ethanol, a 1D hydrogel sample was prepared by the same stretching and drying method as described above. However, in this procedure, the clamps were operated so that the hydrogel fibers were stretched to twice their initial length, and allowed to dry completely at room temperature for 1 hour.

The prepared 1D hydrogel samples were immersed in water-ethanol mixtures prepared at various volume ratios. After 40 minutes, the hydrogel fibers were removed from the water-ethanol mixture and their length was measured.

<Example 4> Characterization

The absorbance spectrum of the IPN hydrogel was recorded using a UV-Vis spectrophotometer (Cary 50, Agilent). Fourier transform infrared (FTIR) spectrum was recorded in the wavelength range of 500 to 4000 cm ^-1 using an attenuated total reflection Fourier transform infrared spectrometer (ATR-FTIR, Thermo Nicole 5700).

Tensile stress-strain curves (tensile stress-strain curves) were measured at a constant stroke speed of 60 mm ^-1 using a universal testing machine (EZ-SX, Shimadzu). Differential Scanning Calorimetry (DSC) measurements were performed using a Differential Scanning Calorimeter (Q400, TA Instruments) under N ₂ protection. The sample was heated and cooled at a rate of 10° C. min ⁻¹ .

The microscopic shape of the hydrogel was observed using a field emission scanning electron microscope (JSM-6700F, JEOL). The hydrogel sample, which was maximally swollen by immersion in deionized water at room temperature, was freeze-dried under vacuum at -70 °C until all water was inside.

For shape observation, the lyophilized hydrogel sample was coated with gold for 30 seconds.

<Experimental Example 1> Synthesis of PAAm/Alginate IPN Hydrogel Fiber

Tough PAAm/alginate hydrogel fibers were prepared based on synergetic reinforcement using covalently crosslinked PAAm and ionically crosslinked alginate.

First, acrylamide (AAm) and Na-alginate were dissolved in deionized water, and then AAm initiator (APS), crosslinking agent (MBAA) and crosslinking accelerator (TEMED) were added to the aqueous solution and mixed homogeneously. Next, the mixed solution was rapidly injected into a PTFE tube using a syringe. A PTFE tube containing the mixed solution was heated at 60° C. for 1 hour to synthesize PAAm/Na-alginate hydrogel through free radical polymerization and cross-linking of AAm together with MBAA inside.

Until this process proceeded, the Na-alginate was well dispersed in the PAAm hydrogel and was not cross-linked.

Then, the PAAm/Na-alginate hydrogel was expelled from the tube by injecting deionized water into a tube with a syringe and then immersing in an aqueous calcium chloride solution.

In this process, the alginate chains were ionically cross-linked by Ca ²⁺ cations linking the alginate networks to each other. This prepared a homogeneous hydrogel fiber.

A schematic diagram of the synthesis process for obtaining PAAm/alginate IPN hydrogel fibers is shown in Figure 1, which shows the hydrogel fibers immersed in an aqueous solution. Since the IPN hydrogel synthesized in this example is transparent in the visible region (see Fig. 2), the hydrogel fiber was dried with methyl orange prior to immersion to increase its visibility in water.

The FTIR spectra of the obtained PAAm/Ca-alginate hydrogel fibers were observed and characterized by comparing the presence of absorption bands in the FTIR spectra of pure PAAm and pure Ca-alginate hydrogels.

The PAAm hydrogel has a stretching vibration of NH at a peak of 2922 cm ^-1 , a peak of 1652 cm ^-1 for C = O stretching, Two peaks were shown at 3327 and 2922 cm ^-1 corresponding to a peak at 1601 cm ^-1 for NH transformation and a peak at 1117 cm ^-1 for planar vibration of NH2.

The Ca-alginate hydrogel had peaks at 3228 cm ^-1 as well as 1601 cm ^-1 (unbalanced COO-stretching) for OH stretching, peaks at 1410 cm ^-1 (CH strain) and 1019 and 934 cm ^-1 (CO stretch) showed a peak. The peak at 811 cm ^-1 was due to the mannuronic acid residue of alginate.

The spectrum of the PAAm/Ca-alginate hydrogel synthesized in this example showed typical absorption bands of PAAm and Ca-alginate hydrogels (see Fig. indicates that it is composed.

Tensile tests were performed to investigate the mechanical properties of hydrogel fibers and the resulting stress.

Strain curves are shown in FIG. 4 . The tensile strength of the PAAm/alginate IPN hydrogel fiber (408 kPa) was greatly improved compared to the PAAm IPN hydrogel fiber (174 kPa) prepared by the same method.

It was found that the strain at fracture increased from 331% to 426%, and the tensile modulus and toughness significantly increased. It was confirmed that the IPN structure was formed with the improved mechanical properties as described above.

<Experimental Example 2> Preparation of 1D hydrogel that reacts to water

The synthesized IPN hydrogel fiber was very tough enough to be stretched more than 5 times the initial length when a tensile force was applied in the longitudinal direction (see FIG. 5). When the tensile force was removed, the stretched hydrogel fiber sample returned to its original size. However, when the fiber was completely dried in the drawn state, the order in the drawn state was maintained.

Interestingly, when fully dried in the stretched state, it quickly returned to its original state upon contact with water. In order to investigate the characteristics of these shaping clothes in detail, as shown in FIG. 5, a series of experiments including stretching, drying and shrinking processes were performed.

First, PAAm/Ca-alginate IPN hydrogel fiber samples stored in deionized water were removed and both ends were clamped between two clamps. Then, the hydrogel fiber was stretched in the longitudinal direction to be three times the initial length (L ₀ ). The stretched hydrogel fibers were dried for 1 hour at room temperature while fixed on a lamp. After completely drying the sample, the 1D hydrogel remained stretched without contraction even after being removed from the clamp.

The length of the 1D hydrogel measured after removal (L _s ) was exactly three times the initial length (L ₀ ). When the 1D hydrogel sample was immersed in deionized water, it absorbed water and recovered to its original length. The hydrogel length (L _r ) after immersion in deionized water varied with the immersion time. It continued to shrink to almost 80% of its initial length (L ₀ ) within the first minute. However, it was found that the 1D hydrogel sample gradually swelled in water after 1 minute and recovered to its original length before stretching after being immersed for 20 minutes.

To show the shape recovery behavior of the 1D hydrogel, after being immersed in water for more than 20 minutes, the ratio of L ₀ to L 0 of the _hydrogel was plotted as a function of immersion time in water. As can be seen in (a) of FIG. 6, the ratio of L _r to L ₀ decreased to 0.8 1 minute after being immersed in water.

These results indicate that the pre-stretched dry 1D hydrogel experienced a rapid order change (shrinkage) within 1 min upon contact with water. The ratio of L _r to L ₀ continued to increase with the immersion time of 1 minute or more, and reached 1.0 after almost 20 minutes. In this example, shape recovery (R _r ) was determined using the following equation.

R _r = L _r20 / L ₀ × 100

Here, L _r20 is the length of the hydrogel after being immersed in water for 20 minutes, and L ₀ is the original length of the hydrogel before stretching.

The shape recovery process including stretching, drying, and shrinkage was repeatedly tested, and the R _r value calculated after each cycle is shown in FIG. 6(b).

During repeated tests including 10 cycles of stretching-drying-shrinking, R _r did not change significantly, indicating that the 1D hydrogel exhibits excellent durability during stretching and shrinking processes.

The mechanism for the water-induced shape recovery behavior of pre-stretched dry PAAm/Ca-alginate IPN hydrogel fibers can be explained as follows. The hydrogel fiber synthesized in this example has excellent mechanical properties because it has two polymer networks with an interpenetrating structure.

-12℃, 도 7의 (a)).In the hydrogel state, the bonds between the polymer chains are weak because hydrogen bonds are mainly formed with water and polar groups of the PAAm polymer and alginate. In addition, a high percentage of free water can act as a plasticizer, and all these factors lower the glass transition temperature of the hydrogel (Tg

-12°C, Fig. 7 (a)).

As a result, the polymer chain is in a rubbery state. The hydrogel fibers, which are then in a good elastomeric state, are easily stretched and return to their original order when the force is removed.

142℃, 도 7의 (b))를 크게 증가시킬 수 있다. 따라서, 1D 하이드로젤은 고분자 사슬이 유리 상태이기 때문에, 힘이 제거된 후에도 연신 상태로 잔존하고. 수축 응력은 고분자 사슬에 저장된다.However, when the hydrogel fiber is dried in a stretched state and the water is completely removed, hydrogen bonds are formed between the polar group of PAAm and the alginate chain, which can act as a crosslinking point, and the Tg (Tg

142° C., FIG. 7 (b)) can be greatly increased. Therefore, since the polymer chains in the 1D hydrogel are free, they remain stretched even after the force is removed. Shrinkage stress is stored in the polymer chain.

When the pre-stretched dry hydrogel fibers come into contact with water and absorb it, hydrogen bonds are re-formed between the water and the polymer chains. Therefore, the hydrogen bonds between the polymer chains formed in the dry state are broken. The properties of the polymer chain are restored from the glass state to the rubber state, and the polymer chain cannot temporarily maintain the shape of the fixed elongated state.

Therefore, it was observed that the 1D hydrogel was contracted by the shrinkage stress stored in the polymer chain and restored to its original order. A schematic diagram of the shape recovery mechanism of the 1D hydrogel is shown in FIG. 8 .

<Experimental Example 3> One-way soft actuator based on 1D IPN hydrogel

As described above, since the 1D hydrogel prepared in the present invention has easy shape deformation and excellent shape recovery characteristics, it responds quickly to stimuli and is mechanically sufficiently robust to be used repeatedly. This water responsive deformation property of 1D hydrogels motivated the inventors to develop an intelligent actuator system that responds to contact with water.

We prepared a 1D hydrogel that reacts to water and a simple one-way actuator that can bend when it touches water. More specifically, a 2 cm 1D hydrogel prepared by the method described in FIG. 5 was attached to the center of a 3M tape as shown in FIG. 9 (a).

Both ends of the 1D hydrogel were fixed to the tape by folding the tape. The prepared samples were immersed in deionized water at room temperature. As described above, as the 1D hydrogel absorbs water, it shrinks back to its original shape. As the 1D hydrogel is deformed, that is, reduced to its original length before being stretched, the actuator sample can be arcuately bent and deformed within 1 minute (Fig. 9(b)).

In addition, the 1D hydrogel-based actuator can operate by absorbing surrounding water without being immersed in water. The actuator sample prepared in (a) of FIG. 9 was carefully placed on a water-soaked filter paper with the hydrogel facing down 1D. As in the case of operation by immersion in water, it can be seen that the sample containing the hydrogel fibers was deformed and bent into an arcuate shape after about 1 minute (Fig. 9(b)). Most of the water-responsive actuators were prepared by attaching a material that absorbs water and swells towards the non-water-reactive material, which absorbs water and bends in one direction upon contact.

However, since the 1D hydrogel-based actuator developed in this example can be easily fabricated using 3M tape, it is inexpensive and readily available. In addition, since it can work by absorbing the water present in the surroundings, it does not need to be immersed in water.

By using the programmable deformation characteristics of 1D hydrogels that react to water, a self-lifting system can be designed. As can be seen in FIG. 10, a weight of 5 g was suspended using the 1D hydrogel prepared by the method of FIG. 5. Then, water was rapidly sprayed several times using a spray gun in the direction of the 1D hydrogel at room temperature.

As the 1D hydrogel fibers absorbed the sprayed water, they gradually contracted and the weight increased (Fig. 10(a)), which means that the self-lifting system worked well. After water spray, the hydrogel fiber could lift a 5 g weight up to 3.5 cm in 3 minutes. As shown in (a) of FIG. 10, after that, the length of the hydrogel fibers did not decrease any more. In a subsequent experiment using a 2g weight, it was observed that the weight could rise up to 5.5 cm after 3 minutes of water spray (Fig. 10(b)).

These results show that a self-lifting system that reacts to water can be manufactured without special equipment or complicated processes using the synthesized 1D hydrogel.

<Experimental Example 4> 1D IPN hydrogel-based ethanol sensing platform

It is particularly important in attempts to determine the concentration of ethanol in water in the food and beverage industry. In water-ethanol mixtures, instrumental analytical methods such as high-performance liquid chromatography, gas chromatography and Fourier transform infrared spectroscopy are widely used to quantify the ethanol content.

While these methods yield accurate results, they require expensive special equipment, highly trained personnel, and time-consuming sample preparation that are not suitable for point-of-care analysis. As such, a significant challenge remains to develop a simple, inexpensive, and portable detection method for quantifying the relative amounts of ethanol in water-ethanol mixtures.

Since the solubility of PAAm and alginate in ethanol is much lower than that in water, the water released from the hydrogel cannot be replaced with ethanol, and the volume of the hydrogel decreases when it is immersed in ethanol. 11(a) and (b) show PAAm/Ca-alginate IPN fibers of 3 cm length swollen in water and immersed in pure ethanol. The length of the fiber decreased from 3 cm to 2.3 cm, and the thickness significantly decreased after soaking for 5 minutes (Fig. 11 (a) and (b)).

When the water-swollen PAAm/Ca-alginate IPN fibers were investigated through SEM analysis, the porous 3D network structure, a highly porous 3D network structure was observed, indicating that the IPN hydrogel fibers contained a significant amount of water. means (Fig. 11(c)). Conversely, no pores were observed on the surface of the samples immersed in ethanol, indicating that the Heidlgel fibers released a significant amount of water when immersed in ethanol.

These results indicate that the swelling behavior of the PAAm/Ca-alginate hydrogel in a mixture of water and ethanol is different from that of pure water.

When the 1D hydrogel prepared in this example is immersed in a mixture of water and ethanol, it tends to selectively absorb only water molecules. Considering the result that the 1D hydrogel presented above contracts by absorbing water, the present inventors found that the 1D hydrogel can show different shape recovery behaviors depending on the content of ethanol in the mixture of water and ethanol, and based on the shape recovery behavior Therefore, it was assumed that the determination of the ethanol fraction in a mixture of water and ethanol was possible. In order to investigate the effect of the ethanol fraction of the water-ethanol mixture, 1D hydrogel samples prepared by the same stretching and drying process were prepared.

However, in this process, the clamp was operated to stretch the hydrogel fiber to twice its initial length (not to three times its initial length) and then dried completely at room temperature. This is because the difference in shape recovery behavior according to the ethanol content in the mixture of water and ethanol occurs more in the 1D hydrogel sample, which can increase the sensitivity of the sensing platform.

Next, the 1D hydrogel samples were immersed in water-ethanol mixtures of various mixing ratios, and the shape recovery behavior of the hydrogel fibers was observed for more than 40 minutes. In all ratios of water and ethanol mixture conditions, when the immersion time was longer than 40 minutes, the length of the hydrogel fiber did not undergo any further change.

Figure 12 (a) shows the shape recovery behavior of 1D hydrogels immersed in a mixture of water and ethanol for 40 minutes at various mixing ratios.

When the ethanol content in the mixture of water and ethanol was less than 40%, the shape recovery behavior was almost the same. In this case, the hydrogel continued to shrink for the first 5 minutes after immersion, rapidly changed its length, and then gradually swelled from 5 to 40 minutes. While the ethanol content was increased to 60% and 70%, contraction continued to increase at 10 and 30 minutes, respectively, after which little change in length occurred. When the 1D hydrogel was immersed in a water-ethanol mixed solution containing 80% ethanol, there was little change in length for more than 40 minutes.

The 1D hydrogel in pure water completely recovered to its original length, as observed in previous experiments, and after 40 min, the length of the hydrogel fiber (L _r ) almost matched the initial length (L ₀ ). However, as shown in (a) of FIG. 12, the hydrogel showed different L _r /L ₀ values depending on the ethanol content of the mixed solution after 40 minutes.

More specifically, as the volume ratio of ethanol in the mixture of water and ethanol increased, the length recovered after immersion (L _r ) gradually decreased. These results clearly show that the volume fraction of ethanol in the water-ethanol mixture has a dramatic effect on the shape recovery behavior of the 1D hydrogels, and is consistent with our expectations.

This dependence can be analyzed quantitatively using the (1-L _r /L ₀ ) value of the 1D hydrogel after immersion in a mixture of water and ethanol for 40 min. The (1-L _r /L ₀ ) value was plotted as a function of the ethanol volume fraction, which almost linearly depended on the ethanol volume fraction at the ethanol volume fraction of 0.0-0.7 (FIG. 12(b)).

The resulting 1D hydrogel can potentially be used for the development of a new chemical sensing platform for detecting ethanol in a mixture of water and ethanol.

0.9973)은 도 13의 실험 데이터에 선형을 적용했을 때 얻어졌는데, x와 y는 각각 에탄올 부피 분율과 (1-L_r/L₀) 값을 나타낸다.In particular, it was shown that the (1-L _r /L ₀ ) value depended on the ethanol volume fraction in a very linear manner in the range of 0.0 to 0.2 (FIG. 13). Equation y = 0.299x (regression coefficient

0.9973) was obtained when a linearity was applied to the experimental data in FIG. 13, where x and y represent the ethanol volume fraction and (1-L _r /L ₀ ) values, respectively.

The value of the limit of detection (LOD) was calculated by the equation LOD=3σ/m _s (where m _s and σ are the slope of the linear fit and the standard deviation of the blank sample, respectively) and found to be approximately 0.036.

Table 1 below compares previously reported methods for the detection of ethanol in a mixture of water and ethanol.

In Table 1 above, [1] is Anal. Methods. 7 4138-44 (2015), [2] Microchem. J. 147 437-43 (2019), [3] in Sensors Actuators, B Chem. 206 119-25 (2015), [4] Microchem. J. 121 107-11 (2015), [5] Opt. Rev. 22 385-392 (2015). [6] is Ind. Eng. Chem. Res. 58 17833-41 (2019), [7] in Anal. Methods. 8

4028-36 (2016).

by the method proposed in the present invention. Ethanol can be detected in a wide range of concentrations using the current system (0.0-0.7). However, the LOD values were found to be relatively low from previously reported ones (Table 1). The developed method is also inexpensive, portable, safe to use and handle, environmentally friendly, and detectable with the naked eye.

The present inventors believe that the sensing platform proposed in the present invention can be a promising alternative for a point-of-care test to detect ethanol in a mixture of water and ethanol.

Claims (19)

A linear shape memory hydrogel comprising a double cross-linked interpenetrating network structure having covalent cross-links and ionic cross-links at the same time.
The linear shape-memory hydrogel according to claim 1, wherein the shape-memory hydrogel is stretched.
The linear shape-memory hydrogel according to claim 2, wherein the shape-memory hydrogel is stretched to a length twice or more than its original length before stretching.
The linear shape-memory hydrogel according to claim 1, wherein the degree of contraction is controlled by adjusting the degree of elongation of the shape memory hydrogel.
The linear shape memory hydrogel according to claim 1, wherein the shape memory hydrogel has a polyacrylamide/calcium-alginate interpenetrating network structure.
A linear shape-memory hydrogel that reacts to water, obtained by stretching the linear shape-memory hydrogel according to any one of claims 1 to 5 and completely drying it in the stretched state.
The linear shape memory hydrogel that reacts to water according to claim 6, wherein the water-responsive linear shape-memory hydrogel shrinks to its original length before stretching upon contact with water.
[Claim 7] The linear shape memory hydrogel that responds to water according to claim 6, wherein the stretching is at least twice the original length.
(a) obtaining a homogeneous solution by adding a crosslinking agent, a thermal initiator and a crosslinking accelerator to an aqueous solution containing a covalent crosslinking member and a monovalent ionic crosslinking member;
(b) adding the obtained solution to a tubular tube using a syringe;
(c) Linear shape-memory hydrogel having a double cross-linked interpenetrating network structure having covalent cross-linking and monovalent ionic cross-linking at the same time by heating and polymerizing the tubular tube to which the solution is added, and cross-linking the covalent cross-linking members. obtaining a gel; and
(d) taking the linear shape memory hydrogel obtained in step (c) out of the tubular tube and then immersing it in a divalent ionic cross-linking source; the linear shape memory according to claim 1 Manufacturing method of hydrogel.
10. The method of claim 9, wherein the covalent cross-linking member is at least one selected from acrylamide, methacrylate, acrylic acid, and hydroxylethyl methacrylate.
10. The method of claim 9, wherein the monovalent ionic crosslinking member is at least one selected from sodium alginate, alginic acid, chitosan and pectin,
The divalent ionic crosslinking source is a linear shape memory hydrogel, characterized in that at least one selected from calcium alginate, barium alginate, calcium chitosan, curry chitosan, calcium, pectin and barium pectin Manufacturing method.
10. The method of claim 9, wherein the crosslinking agent is N, N'-methylene bis (acrylamide), lymethylol ethane triacrylate, trimethylol propane triacrylate, pentaerythritol tetra acrylate, pentaerythritol tri acrylate, Method for producing a linear shape memory hydrogel, characterized in that at least one selected from dipentaerythritol pentaacrylate, dipentaerythritol hexaacrylate, caprolactone-introduced polyfunctional monomer and triallyl isocyanurate .
10. The linear shape memory hydrogel according to claim 9, wherein the thermal initiator is at least one selected from ammonium persulfate, potassium persulfate, benzoyl peroxide, lauroyl peroxide and t-butylperoxypivalate. Manufacturing method of.
10. The method of claim 9, wherein the crosslinking accelerator is at least one selected from N,N,N'N'-tetramethylethylenediamine, N-ethylethylenediamine, and N-(hydroxyethyl)ethylenediaminetriacetic acid. A method for producing a linear shape memory hydrogel.
10. The method according to claim 9, wherein the shape memory hydrogel has a polyacrylamide/calcium-alginate interpenetrating network structure.
An actuator comprising the linear shape memory hydrogel according to claim 6.
A self-lifting system comprising the linear shape memory hydrogel according to claim 6.
A chemical sensor comprising the linear shape memory hydrogel according to claim 6.
19. The chemical sensor according to claim 18, which is for measuring the ethanol content in a mixture of water and ethanol.

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