阅读说明：本技术 一种双层水凝胶、制备方法及其应用 (Double-layer hydrogel, preparation method and application thereof ) 是由 刘爱萍 董鹏丽 程琳 张智钦 房彬 于 2020-03-20 设计创作，主要内容包括：一种双层水凝胶、制备方法及其应用,所述水凝胶的制备包括以下步骤：配置N-异丙基丙烯酰胺-黏土前驱液注入模具中交联作为第一层,之后,在其表面加条纹模具且注入同种前驱液作为第二层,利用液面分层和界面渗透原理,前驱液滴加不同种类的醇,控制醇的种类和渗透的时间；然后低温紫外辐射交联聚合,去离子水浸泡预处理,得到垂直方向上不同梯度的双层水凝胶。本发明的方法原料易得,操作简单,重复性好,且可通过低温紫外辐射交联的方法来固定这种特殊结构。此外,由于其特殊的双层孔结构,在高于其最低相变温度的同一环境中可同时实现对物体的抓取和释放行为,从而可在相同环境中实现对物体的位移。(A double-layer hydrogel, a preparation method and application thereof, wherein the preparation of the hydrogel comprises the following steps: preparing N-isopropylacrylamide-clay precursor liquid, injecting the N-isopropylacrylamide-clay precursor liquid into a mold to be crosslinked to form a first layer, then adding a stripe mold on the surface of the N-isopropylacrylamide-clay precursor liquid, injecting the same precursor liquid to form a second layer, dropwise adding different types of alcohol into the precursor liquid by utilizing the liquid level layering and interface permeation principles, and controlling the types of the alcohol and the permeation time; then carrying out low-temperature ultraviolet radiation crosslinking polymerization and deionized water soaking pretreatment to obtain the double-layer hydrogel with different gradients in the vertical direction. The method has the advantages of easily obtained raw materials, simple operation and good repeatability, and the special structure can be fixed by a low-temperature ultraviolet radiation crosslinking method. In addition, due to the special double-layer hole structure, the grabbing and releasing actions of the object can be realized simultaneously in the same environment higher than the lowest phase transition temperature, so that the displacement of the object can be realized in the same environment.)

1. A preparation method of a double-layer hydrogel is characterized by comprising the following steps: the method comprises the following steps:

step (1): preparing a precursor solution:

adding the preparation raw materials into the dispersion medium, and uniformly stirring under a dark condition until the preparation raw materials are completely dissolved to obtain a transparent precursor solution; the preparation method comprises the following steps of preparing raw materials, wherein the raw materials comprise a polymerization reaction monomer, a chemical cross-linking agent, a photoinitiator and a pore-forming agent, the polymerization reaction monomer is N-isopropyl acrylamide, the chemical cross-linking agent is synthetic hectorite, the photoinitiator is 1-hydroxycyclohexyl phenyl ketone, and the pore-forming agent is different alcohols;

step (2): injecting into a mold:

injecting the precursor liquid obtained in the step (1) into a plastic circular mold, placing the plastic circular mold on a horizontal table top, and then carrying out low-temperature ultraviolet radiation crosslinking on the precursor liquid in the plastic circular mold for 3-5 minutes;

and (3): adding a pore-forming agent:

adding a stripe mask on the precursor liquid subjected to low-temperature ultraviolet radiation crosslinking in the step (2), then continuously adding the precursor liquid prepared in the step (1) into the stripe mask, then taking a proper amount of pore-forming agent by using an injector or a dropper, slowly dripping the pore-forming agent on the surface of the precursor liquid in the stripe mask, enabling the mold not to move again, and standing for 6min or 8min after the pore-forming agent is added; then, the permeation time of the upper layer liquid of the precursor liquid on the stripe mask is controlled by adopting the principles of two-layer liquid layering and interface permeation, so that the diameter of the hole is controlled, and an asymmetric structure of two layers of holes is formed; obtaining the hydrogel precursor solution after diffusion treatment;

and (4): low-temperature ultraviolet radiation crosslinking:

and (4) carrying out low-temperature ultraviolet radiation crosslinking on the hydrogel precursor liquid in the step (3), after the hydrogel precursor liquid is completely crosslinked, soaking and washing non-crosslinked substances by using deionized water to obtain the vertical-direction double-layer non-uniform porous hydrogel, thus obtaining the double-layer hydrogel.

2. The method of claim 1, wherein the bilayer hydrogel is prepared by: the dispersion medium in the step (1) comprises dye and water.

3. The method of claim 1, wherein the bilayer hydrogel is prepared by: the different alcohols in the step (1) comprise ethanol, methanol, glycerol and n-amyl alcohol.

4. The method of claim 1, wherein the bilayer hydrogel is prepared by: the low-temperature ultraviolet radiation crosslinking comprises ultraviolet lamp illumination and a low-temperature environment, wherein the ultraviolet wavelength of the ultraviolet lamp is 365nm, and the ultraviolet illumination is carried out in a three-time circulation alternating mode so as to avoid incomplete crosslinking.

5. The method of claim 4, wherein the bilayer hydrogel is prepared by: the total uv light exposure time was 10 minutes to ensure complete crosslinking.

6. The method of claim 1, wherein the bilayer hydrogel is prepared by: the heterogeneous porous structure in the double-layer heterogeneous porous structure hydrogel is obtained by adopting the principles of two-layer liquid layering and interface permeation.

7. The method of claim 6, wherein the bilayer hydrogel is prepared by: the heterogeneous porous structure controls the size of formed holes and the number of large holes in the vertical direction by controlling the layering of two layers of liquid and the time of interfacial permeation, and simultaneously, the holes formed after the dropwise addition of ethanol, methanol and n-amyl alcohol are distributed according to a gradient which is smaller and smaller from top to bottom due to the direction and respective concentration of the dropwise added liquid, and the holes formed after the dropwise addition of glycerol are smaller and smaller from top to bottom.

8. A bilayer hydrogel produced by the method of producing a bilayer hydrogel according to any one of claims 1 to 7, wherein: the double-layer hydrogel has the lowest phase transition temperature of 31-33 ℃, so that the double-layer hydrogel is placed in water higher than the lowest phase transition temperature, the double-layer hydrogel loses water and shrinks, the double-layer hydrogel is placed in water lower than the lowest phase transition temperature, and the double-layer hydrogel absorbs water and expands.

9. The bilayer hydrogel of claim 8, wherein: after the alcohol liquid is dripped into the double-layer hydrogel, the double-layer hydrogel has a loose macroporous structure on one side of the dripped alcohol liquid, and has a compact small-hole structure on one side close to the bottom of the plastic mold, so that the difference of two side holes forms an asymmetric structure, and further the double-layer hydrogel forms the difference of water loss shrinkage or water absorption expansion in water at the lowest phase transition temperature or in water at the lowest phase transition temperature, and finally the double-layer hydrogel can be bent and restored in different water and can be stably circulated for many times.

10. Use of a bilayer hydrogel according to claim 9, wherein: the double-layer hydrogel is made into a gripper model, a thin wire or an iron wire and the gripper hydrogel are made into a flexible gripper, the flexible gripper is placed in the water with the temperature higher than the lowest phase transition temperature to grip an object, the object can be displaced in different degrees in the same environment, on the other hand, if the flexible gripper is placed in the water with the temperature higher than the lowest phase transition temperature to grip the object, the object can be released when the flexible gripper is placed in the water with the temperature lower than the lowest phase transition temperature, and the two kinds of gripping can be circulated for many times.

Technical Field

The invention relates to the technical field of structural design and application of hydrogel materials, in particular to a double-layer hydrogel, a preparation method and application thereof.

Background

Hydrogels have a variety of stimulus-responsive properties, with water contents similar to those of biological soft tissues. Therefore, the hydrogel has wide potential application value in the fields of biomedicine and soft robots. Hydrogels can undergo reversible changes in response to external stimuli, such as water-loss contraction and water-absorption expansion, but these changes are often indiscriminately and uncontrollable. Therefore, the hydrogel needs to be structurally designed to have an anisotropic structure, so that the deformation can be controlled.

In recent years, smart hydrogels have attracted a great deal of interest because they undergo drastic changes in volume or other properties in response to external stimuli (e.g., changes in temperature, pH, humidity, specific ions or molecules, ionic strength, or electric field strength). Due to its stimulus response characteristics, intelligent hydrogels play an increasingly important role in numerous applications such as intelligent actuators, for scaffolds for tissue engineering, switches on and off of chemical reactions, carriers for drug delivery, biosynthetic matrices, artificial muscles and soft biomimetic machines. The stimulus responsive deformation motion of the smart hydrogel includes expansion/contraction and bending/unbending. The expansion/contraction is caused by the presence of swelling/contraction of the hydrogel in all respects; while buckling/unbending is the result of different sizes of hydrogels expanding/contracting non-uniformly in different directions. The bending/unbending motion of smart hydrogels depends on many parameters, such as the shape and size of the hydrogel, and the inhomogeneous structure. A stimulus-responsive hydrogel is a hydrogel that can make a bending/non-bending response to an environmental stimulus, and has received much attention because of its high application prospects in many biomimetic application fields (such as soft carriers, manipulators, and crawlers). Among stimuli-responsive hydrogels, temperature-responsive hydrogels are most attractive because temperature changes are easily controlled as an external stimulus. In many practical applications, such as temperature-controlled flexible robots, temperature-sensitive hydrogels must have significant flexural properties and good mechanical properties. To date, researchers have made numerous attempts at this point with good results and have developed several temperature responsive hydrogels with bending response characteristics. Due to the non-uniform internal structure of the hydrogel, an asymmetric response to temperature can cause significant bending/unbending deformation of the hydrogel. By establishing an asymmetric cross-linking degree distribution on the hydrogel or multi-layered structure, a temperature-reactive hydrogel with a non-uniform structure is prepared. By controlling the preparation conditions of the hydrogel at the reaction temperature, a non-uniform crosslinked structure can be obtained. Therefore, designing and controlling the heterogeneous structure of the hydrogel actuator is the key to controlling its actuation behavior. The traditional method is to gradually polymerize a passive polymer hydrogel and an active polymer hydrogel to form a double-layer structure. Generally, the bilayer structure of different types of hydrogels shows slower bending/non-bending deformation for different responses, and can realize the grabbing and releasing of objects under different environments, but the bending angle is limited to a certain extent, and after certain repeated driving, especially under the condition of large-scale bending, the two layers have the tendency of layering along a weak interface, thereby affecting the driving performance, so that a great challenge still faces to the structural performance, and meanwhile, a difficult problem is still existed in how to realize the movement of objects under the same environment.

Therefore, aiming at the complex operation of the multilayer hydrogel and the incapability of realizing quick response, the double-layer hydrogel which is simple, easy to synthesize, low in cost, quick in response and capable of deforming in the same environment is provided according to the principles of liquid level layering and interface permeation.

Disclosure of Invention

Aiming at the problems in the prior art, the invention provides a double-layer hydrogel, a preparation method and application thereof.

The purpose of the invention is realized by the following technical scheme on one hand:

a preparation method of the bilayer hydrogel comprises the following steps:

step (1): preparing a precursor solution:

adding the preparation raw materials into the dispersion medium, and uniformly stirring under a dark condition until the preparation raw materials are completely dissolved to obtain a transparent precursor solution; the preparation method comprises the following steps of preparing raw materials, wherein the raw materials comprise a polymerization reaction monomer, a chemical cross-linking agent, a photoinitiator and a pore-forming agent, the polymerization reaction monomer is N-isopropyl acrylamide, the chemical cross-linking agent is synthetic hectorite, the photoinitiator is 1-hydroxycyclohexyl phenyl ketone, and the pore-forming agent is different alcohols;

step (2): injecting into a mold:

injecting the precursor liquid obtained in the step (1) into a plastic circular mold, placing the plastic circular mold on a horizontal table top, and then carrying out low-temperature ultraviolet radiation crosslinking on the precursor liquid in the plastic circular mold for 3-5 minutes;

and (3): adding a pore-forming agent:

adding a stripe mask on the precursor liquid subjected to low-temperature ultraviolet radiation crosslinking in the step (2), then continuously adding the precursor liquid prepared in the step (1) into the stripe mask, then taking a proper amount of pore-forming agent by using an injector or a dropper, slowly dripping the pore-forming agent on the surface of the precursor liquid in the stripe mask, enabling the mold not to move again, and standing for 6min or 8min after the pore-forming agent is added; then, the permeation time of the upper layer liquid of the precursor liquid on the stripe mask is controlled by adopting the principles of two-layer liquid layering and interface permeation, so that the diameter of the hole is controlled, and an asymmetric structure of two layers of holes is formed; obtaining the hydrogel precursor solution after diffusion treatment;

and (4): low-temperature ultraviolet radiation crosslinking:

and (4) carrying out low-temperature ultraviolet radiation crosslinking on the hydrogel precursor liquid in the step (3), after the hydrogel precursor liquid is completely crosslinked, soaking and washing non-crosslinked substances by using deionized water to obtain the vertical-direction double-layer non-uniform porous hydrogel, thus obtaining the double-layer hydrogel.

Further, the dispersion medium in the step (1) includes a dye and water.

Further, the different kinds of alcohols in step (1) include ethanol, methanol, glycerol, and n-pentanol.

Further, the low-temperature ultraviolet radiation crosslinking comprises ultraviolet lamp illumination and a low-temperature environment, wherein the ultraviolet wavelength of the ultraviolet lamp is 365nm, and the ultraviolet illumination is carried out in a three-cycle alternating mode so as to avoid incomplete crosslinking.

Further, the total uv exposure time was 10 minutes to ensure complete crosslinking.

Further, the heterogeneous porous structure in the double-layer heterogeneous porous structure hydrogel is obtained by adopting the principles of two-layer liquid layering and interface permeation.

Furthermore, the heterogeneous porous structure controls the size of the formed holes and the number of large holes in the vertical direction by controlling the layering of two layers of liquid and the time of interfacial permeation, and simultaneously, due to the direction and the respective concentration of the dropwise added liquid, the holes formed after the dropwise added ethanol, methanol and n-amyl alcohol are distributed in a gradient manner from top to bottom and are smaller and smaller, and the holes formed after the dropwise added glycerol are smaller and smaller from top to bottom.

The other aspect of the object of the invention is realized by the following technical scheme:

the double-layer hydrogel is prepared by the preparation method of the double-layer hydrogel, the lowest phase transition temperature of the double-layer hydrogel is 31-33 ℃, so that the double-layer hydrogel is placed in water higher than the lowest phase transition temperature, the double-layer hydrogel loses water and shrinks, the double-layer hydrogel is placed in water lower than the lowest phase transition temperature, and the double-layer hydrogel absorbs water and expands.

In one embodiment, after the alcohol liquid is dripped into the double-layer hydrogel, the double-layer hydrogel has a loose macroporous structure on one side of the dripping alcohol liquid, and has a compact small pore structure on one side close to the bottom of the plastic mold, so that the difference of the two side pores forms an asymmetric structure, and then the double hydrogels form the difference of water loss shrinkage or water absorption expansion in water with the temperature higher than the lowest phase transition temperature or in water with the temperature lower than the lowest phase transition temperature, finally the double-layer hydrogel can be bent and restored in different water, and can be stably circulated for multiple times.

The other aspect of the object of the invention is realized by the following technical scheme:

the double-layer hydrogel is applied, wherein the double-layer hydrogel is made into a grip model, thin wires or iron wires and the grip model are used as flexible grips, the flexible grips are placed in water with the temperature higher than the lowest phase transition temperature to grip an object, the object can be displaced in the same environment in different degrees, on the other hand, if the flexible grips are placed in water with the temperature higher than the lowest phase transition temperature to grip the object, the object can be released when the flexible grips are placed in water with the temperature lower than the lowest phase transition temperature, and the two kinds of grips can be circulated for many times.

The invention has the beneficial effects that:

according to the invention, the double-layer hydrogel is prepared by adopting a liquid level layering and interface permeation method, so that the preparation process of the double-layer hydrogel is simplified, the cost is saved and the quick response is realized; meanwhile, the phenomenon that the traditional double-layer hydrogel interface is easy to tear and delaminate is greatly improved by adopting the same hydrogel in the double layers; on the other hand, because the diffusion and the permeability coefficient of different alcohols are different, the size of the formed holes and the number of large holes in the vertical direction can be controlled by controlling the permeation time, meanwhile, because of the dropping direction and the respective concentration of liquid, the holes formed after the dropping of ethanol, methanol and n-amyl alcohol are distributed according to a gradient which is gradually reduced from top to bottom, and the holes formed after the dropping of glycerol are gradually reduced from top to bottom, so that the non-uniform structure of the single-layer hydrogel is realized, the purposes of generating different degrees of bending in water with the temperature higher than the lowest phase transition temperature of the water, grabbing an object, generating recovery in water with the temperature lower than the lowest phase transition temperature of the water and releasing the object are achieved.

Drawings

FIG. 1 is a structural diagram of a two-layer heterogeneous porous hydrogel preparation structure according to the present invention;

FIG. 2 is a schematic diagram of the dropping of pore-forming agent on the surface of the precursor liquid and a schematic diagram of the diffusion after dropping:

FIG. 3 is a schematic representation of the front and back sides of a hydrogel obtained after cross-linking of a precursor solution according to the present invention;

FIG. 4 is a scanning electron microscope image of the upper surface, the lower surface and the cross section of the n-amyl alcohol induced double-layer heterogeneous porous hydrogel;

FIG. 5 is scanning electron micrographs of the upper, middle and lower parts of the section of the n-pentanol-induced double-layer heterogeneous porous hydrogel according to the present invention;

FIG. 6 is a scanning electron microscope image of the upper surface, the lower surface and the cross section of the methanol-induced double-layer heterogeneous porous hydrogel of the present invention;

FIG. 7 is scanning electron micrographs of the upper, middle and lower portions of a section of a methanol-induced two-layer heterogeneous porous hydrogel according to the present invention;

FIG. 8 is a scanning electron microscope image of the cross section of the hydrogel with double-layer heterogeneous porous structure induced by n-amyl alcohol in different periods of time according to the invention;

FIG. 9 is a graph showing the tensile properties of a two-layer heterogeneous cellular hydrogel according to the present invention;

FIG. 10 is a graph showing the curvature statistics of the hydrogel with a two-layer heterogeneous porous structure according to the present invention:

FIG. 11 is a diagram showing the physical driving of the whole hydrogel (without stripes) after different diffusion times of the upper liquid of the hydrogel with a double-layer nonuniform porous structure of the invention:

FIG. 12 is a graph showing the physical bending of the hydrogel after stripes of different angles in the two-layer nonuniform porous structure hydrogel of the present invention:

FIG. 13 is a diagram of a gripping action of the double-layered non-uniform porous hydrogel as a flexible gripper in the same environment;

FIG. 14 shows a two-layer hydrogel with non-uniform porous structure as a flexible gripper for gripping in different environments.

Detailed Description

The present invention will be described in detail with reference to specific examples. The following examples will assist those skilled in the art in further understanding the present invention, but are not intended to limit the present findings in any way. It should be noted that variations and modifications can be made by persons skilled in the art without departing from the spirit of the invention. All falling within the scope of the present invention.