Preparation and application of adhesive, transparent and photocurable 3D printing citric acid chitosan hydrogel

Abstract

The invention relates to the field of hydrogel preparation, in particular to preparation and application of adhesive, transparent and photo-curable 3D printing citric acid chitosan hydrogel, and particularly relates to preparation and application of the adhesive, transparent and photo-curable 3D printing citric acid chitosan hydrogel which is prepared by the following steps: by taking acrylamide, chitosan and citric acid as raw materials, firstly preparing a citric acid chitosan prepolymer solution, and then adding a cross-linking agent and a low-cost photoinitiator to prepare CA-CS 3D printing ink. The adhesive, transparent and photocurable 3D printing citric acid chitosan hydrogel is prepared under the irradiation of second-level ultraviolet light. Chemical cross-linking of acrylamide and physical cross-linking of chitosan and citric acid form a mechanical network of the hydrogel, protons on citric acid provide conductivity for the gel, and rapid photocuring is achieved by regulating and controlling the concentration of a citric acid solution. The citric acid chitosan hydrogel disclosed by the invention also has piezoresistive sensing performance, transparency and adhesion performance, and also provides a new way for preparing the adhesive, transparent, stretchable and photocurable 3D printing citric acid chitosan hydrogel.

Description

Technical Field

[0001] The invention relates to the field of hydrogel preparation, and in particular to the preparation and application of an adhesive, transparent, photocurable 3D-printable citric acid chitosan hydrogel. Background Art

[0002] As a three-dimensional network structure material with high water content, hydrogel has been widely used in wearables, drug delivery, tissue engineering, soft robots and other fields due to its excellent biocompatibility, flexibility and adjustable physical and chemical properties. At the same time, with the development of photocuring 3D printing technology, the development of hydrogel materials suitable for photocuring 3D printing has become a research hotspot. However, traditional photocuring 3D printing hydrogels often require expensive initiators and long curing times, which makes it difficult to meet the needs of rapid prototyping and low-cost manufacturing. More importantly, it is difficult to prepare a gel that has both the ability to conform to the human body and visualize the state of human skin through 3D printing technology. Therefore, it is of great significance to develop a transparent, adhesive, low-cost and fast photocurable hydrogel.

[0003] Citric acid (CA) is a natural organic acid with three carboxyl and hydroxyl groups in its structure, which can form a stable physical cross-linking network with the functional groups of multifunctional biomacromolecules. In the rapid preparation of an adhesive, transparent, photocurable 3D-printable citric acid chitosan hydrogel, the hydroxyl and carboxyl groups of citric acid form physical cross-links by hydrogen bonding with the amino and hydroxyl groups in chitosan. This cross-linking method avoids the use of complex chemical reactions and toxic cross-linking agents, making the hydrogel safer and more environmentally friendly. In addition, citric acid is inexpensive and widely available, further reducing the cost of hydrogel preparation. Chitosan (CS) is a natural polysaccharide with a linear structure extracted from chitin, which has excellent biocompatibility, bioactivity and antibacterial properties. CS can not only form a stable network structure with citric acid through physical cross-linking, but also provide transparency and adhesion properties to the hydrogel, simplify the preparation process of the hydrogel, visualize the state of human skin and obtain better conformability.

[0004] Photocuring technology plays a key role in hydrogel 3D printing. Through the irradiation of ultraviolet light (365nm) or visible light, hydrogel can be rapidly cured and formed in a short time, thus meeting the requirements of 3D printing for rapid and precise material forming. However, photoinitiators with rapid initiation efficiency often require high manufacturing costs. Hydrogel materials based on citric acid and chitosan show excellent performance in the photocuring process: their transparency helps the penetration of ultraviolet light and ensures uniform curing; while the physically cross-linked network structure enhances the mechanical strength and stability of the material. The introduction of acrylamide gives the gel photocuring properties, and the rapid preparation of low-cost gels can be achieved through the reasonable selection of initiators and the concentration control of CA solutions. These characteristics make the hydrogel have broad application prospects in the fields of photocuring 3D printing of biomedical materials, flexible devices, and human-machine symbiosis.

[0005] The 3D printable transparent, adhesive, low-cost, fast photocuring hydrogel prepared using citric acid and chitosan not only overcomes the multiple limitations of traditional materials, but also provides new possibilities for the future application of photocuring 3D printing technology. Summary of the invention

[0006] The invention overcomes the shortcomings of the prior art and provides a method for rapidly preparing an adhesive, transparent, and photocurable 3D-printable citric acid chitosan hydrogel. The method provides a first network through acrylamide covalent crosslinking, and citric acid and chitosan are physically crosslinked to provide a second network; the introduction of citric acid is used to dissolve chitosan and provide ionic conductivity for the gel, chitosan provides transparency and adhesive properties for the gel, and acrylamide gives the hydrogel photopolymerization ability. I2959 is selected as a low-cost photoinitiator, and the concentration of a CA solution is controlled to prepare a CA-CS 3D printing ink, so as to achieve second-level curing of an adhesive, transparent, and photocurable 3D-printable citric acid chitosan hydrogel.

[0007] The present invention is achieved through the following technical scheme: Preparation of an adhesive, transparent, photocurable 3D printable citric acid chitosan hydrogel, comprising the following steps: (1) Preparation of citric acid chitosan prepolymer solution Add chitosan to the citric acid solution, stir until completely dissolved to obtain a CA-CS solution; add acrylamide, an active monomer to be polymerized, to the CA-CS solution, stir to obtain a transparent citric acid chitosan prepolymer solution; (2) Preparation of CA-CS 3D printing ink At room temperature, a photoinitiator 2-hydroxy-2-methyl-1-[4-(2-hydroxyethoxy)phenyl]-1-propanone and a crosslinking agent N,N-methylenebisacrylamide were added to the citric acid chitosan prepolymer solution, and the mixture was stirred to obtain CA-CS 3D printing ink; (3) Preparation of adhesive, transparent, and photocurable 3D-printable citric acid chitosan hydrogel The CA-CS 3D printing ink was added into the 3D printing ink tube for photocuring 3D printing and cured under 365nm ultraviolet light to obtain an adherent, transparent, photocurable 3D printable citric acid chitosan hydrogel.

[0008] As a further improvement of the technical solution of the present invention, in step (1), the mass ratio of the monomer acrylamide to chitosan is 1-20:0.3, and the mass ratio of the monomer acrylamide to the citric acid in the citric acid solution is 1-5:1.

[0009] As a further improvement of the technical solution of the present invention, in step (2), the mass ratio of the photoinitiator 2-hydroxy-2-methyl-1-[4-(2-hydroxyethoxy)phenyl]-1-propanone to the cross-linking agent N,N-methylenebisacrylamide is 25:1.

[0010] As a further improvement of the technical solution of the present invention, the mass ratio of the cross-linking agent N,N-methylenebisacrylamide in step (2) to the monomer acrylamide in step (1) is 1:2000.

[0011] As a further improvement of the technical solution of the present invention, the CA-CS 3D printing ink obtained in step (2) needs to be stored at low temperature and away from light.

[0012] As a further improvement of the technical solution of the present invention, in the low-temperature and light-proof storage condition, the low temperature condition is 2-10°C.

[0013] As a further improvement of the technical solution of the present invention, in step (3), the curing temperature is room temperature and the curing time is 30s-30min.

[0014] The present invention also provides an application of an adhesive, transparent, photocurable 3D-printable citric acid chitosan hydrogel obtained by the above-mentioned preparation method as a piezoresistive sensor.

[0015] The technical solution provided by the present invention has the following advantages compared with the prior art: The present invention uses acrylamide, chitosan and citric acid as raw materials, first prepares a citric acid chitosan prepolymer solution, then adds a crosslinking agent and a low-cost initiator to prepare CA-CS 3D printing ink, and prepares an adhesive, transparent, and photocurable 3D-printable citric acid chitosan hydrogel under ultraviolet light irradiation in seconds. The chemical crosslinking of acrylamide and the physical crosslinking of chitosan and citric acid constitute the mechanical network of the hydrogel, the protons on the citric acid provide conductivity for the gel, and rapid photocuring is achieved by regulating the concentration of the citric acid solution. The preparation process of the present invention is simple, low-cost, and the preparation time is 30s-30min. The citric acid chitosan hydrogel also has piezoresistive sensing performance, transparency and adhesion performance, and also provides a new way for adhesive, transparent, stretchable, and photocurable 3D-printable citric acid chitosan hydrogel. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.

[0017] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0018] Figure 1 This is a schematic diagram of the preparation process of the adhesive, transparent, stretchable, and photocurable 3D-printable citric acid chitosan hydrogel described in the present invention.

[0019] Figure 2 The schematic diagram of the tensile properties of an adhesive, transparent, stretchable, photocurable 3D printable citric acid chitosan hydrogel prepared in Example 1 of the present invention shows that the citric acid chitosan hydrogel in Example 1 of the present invention has good tensile properties and can reach 10 times of the original length.

[0020] Figure 3 This is a schematic diagram of the adhesion performance of an adhesive, transparent, stretchable, photocurable 3D printable citric acid chitosan hydrogel prepared in Example 1 of the present invention. As can be seen from the figure: the adhesion performance of the citric acid chitosan hydrogel in Example 1 of the present invention to flower petals, plastics, and steel.

[0021] Figure 4 The transparency of the adhesive, transparent, stretchable, photocurable 3D-printable citric acid chitosan hydrogel prepared in Example 1 of the present invention allows the details of the flower to be clearly observed.

[0022] Figure 5The conductivity comparison diagram of an adhesive, transparent, stretchable, photocurable 3D printable citric acid chitosan hydrogel prepared in Examples 1-2 of the present invention. The citric acid chitosan hydrogels of the present invention all have high conductivity. The comparison shows that compared with Example 2, the high concentration CA solution in Example 1 gives the gel a greater conductivity.

[0023] Figure 6 A schematic diagram of the response of an adhesive, transparent, stretchable, photocurable 3D-printable citric acid chitosan hydrogel prepared in Example 1 of the present invention to finger bending in a strain sensor. As can be seen from the figure: the gel prepared in Example 1 can accurately detect human body movement and effectively and reliably output sensing signals.

[0024] Figure 7 This is a stress-strain curve comparison diagram of an adhesive, transparent, stretchable, photocurable 3D printable citric acid chitosan hydrogel prepared in Examples 1 and 2 of the present invention. Comparison description: Compared with Example 2, the high concentration CA solution in Example 1 imparts better mechanical properties to the gel. DETAILED DESCRIPTION

[0025] In order to more clearly understand the above-mentioned objectives, features and advantages of the present invention, the scheme of the present invention will be further described below. It should be noted that the embodiments of the present invention and the features in the embodiments can be combined with each other without conflict.

[0026] In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention may also be implemented in other ways different from those described herein; it is obvious that the embodiments in the specification are only part of the embodiments of the present invention, rather than all of the embodiments.

[0027] The present invention provides a specific embodiment of the preparation of an adhesive, transparent, photocurable 3D printable citric acid chitosan hydrogel, comprising the following steps: (1) Preparation of citric acid chitosan prepolymer solution Add chitosan to the citric acid solution, stir until completely dissolved to obtain a CA-CS solution; add acrylamide, an active monomer to be polymerized, to the CA-CS solution, stir to obtain a transparent citric acid chitosan prepolymer solution; (2) Preparation of CA-CS 3D printing ink At room temperature, a photoinitiator 2-hydroxy-2-methyl-1-[4-(2-hydroxyethoxy)phenyl]-1-propanone and a crosslinking agent N,N-methylenebisacrylamide were added to the citric acid chitosan prepolymer solution, and the mixture was stirred to obtain CA-CS 3D printing ink; (3) Preparation of adhesive, transparent, and photocurable 3D-printable citric acid chitosan hydrogel The CA-CS 3D printing ink was added into the 3D printing ink tube for photocuring 3D printing and cured under 365nm ultraviolet light to obtain an adherent, transparent, photocurable 3D printable citric acid chitosan hydrogel.

[0028] In one embodiment provided by the present invention, the mass ratio of the monomer acrylamide to chitosan in step (1) is 1 to 20:0.3, preferably, the mass ratio of the monomer acrylamide to chitosan is 2 to 15:0.3, and further preferably, the mass ratio of the monomer acrylamide to chitosan is 2 to 10:0.3. The mass ratio of the mass of the monomer acrylamide to the citric acid in the citric acid solution is 1 to 5:1. The specific method for preparing the citric acid solution is: adding CA to water and stirring until completely dissolved. In this embodiment, the concentration of the citric acid solution is 21.8 mg / mL-60 mg / mL. Before adding chitosan to the citric acid solution, it is necessary to place the stirred and dissolved citric acid solution for half an hour before adding chitosan, in order to cool the citric acid solution to room temperature and promote the physical crosslinking of CA and CS. The citric acid in the present invention helps to dissolve chitosan and provide physical crosslinking points and ionic conductivity for subsequent crosslinking reactions.

[0029] In another embodiment provided by the present invention, in step (2), the mass ratio of the photoinitiator 2-hydroxy-2-methyl-1-[4-(2-hydroxyethoxy)phenyl]-1-propanone to the cross-linking agent N,N-methylenebisacrylamide is 25:1.

[0030] In one embodiment provided by the present invention, the mass ratio of the cross-linking agent N,N-methylenebisacrylamide in step (2) to the monomer acrylamide in step (1) is 1:2000.

[0031] In another embodiment provided by the present invention, the CA-CS 3D printing ink obtained in step (2) needs to be stored at low temperature and away from light. Compared with other chitosan 3D printing inks, the chitosan 3D printing ink obtained by the preparation method of the present invention is colorless and transparent, has good dispersibility, and can shorten the light curing time to seconds by adjusting the CA concentration in the printing ink. At the same time, the use of a low-cost initiator can effectively save the cost of the 3D printing ink, and can be quickly formed into a citric acid chitosan hydrogel with transparent adhesion properties.

[0032] Furthermore, in the low temperature and light-proof storage condition, the low temperature condition is 2-10° C. The light-proof storage can be performed by placing the printing ink in a brown light-proof container.

[0033] Preferably, in step (3), the curing temperature is room temperature and the curing time is 30 s-30 min.

[0034] The present invention also provides the use of the adherent, transparent, photocurable 3D-printable citric acid chitosan hydrogel as a piezoresistive sensor.

[0035] The specific embodiments of the present invention are described in detail below.

[0036] The chemical materials used in the present invention are: acrylamide, citric acid, N,N-methylenebisacrylamide, chitosan, 2-hydroxy-2-methyl-1-[4-(2-hydroxyethoxy)phenyl]-1-propanone, deionized water, and quality purity and precision control are performed. The combined dosage is as follows: in grams, milliliters, millimeters, centimeters 3 Is the unit of measurement.

[0037] Acrylamide: AM solid 99.5% Citric Acid: CA Solid 99.5% N,N-Methylenebisacrylamide: MBAA solid 99.5% Chitosan: CS solid 98% 2-Hydroxy-2-methyl-1-[4-(2-hydroxyethoxy)phenyl]-1-propanone: I2959 solid solid 99.5% Deionized water: H2O liquid 99.99% Example 1

[0038] A method for preparing an adhesive, transparent, stretchable, and photocurable 3D-printable citric acid chitosan hydrogel comprises the following steps: (1) Preparation of citric acid chitosan prepolymer solution Add 1.2g±0.001g of citric acid to 5.5±0.001 mL of deionized water and stir until dissolved to obtain a citric acid (CA) solution; after standing for half an hour, add 0.3g±0.001g of chitosan (CS) to the citric acid solution and stir until completely dissolved to obtain a CA-CS solution. Add 4.0g±0.001g of the active monomer to be polymerized acrylamide (AM) to the CA-CS solution and stir to obtain a transparent and clear citric acid chitosan prepolymer solution; (2) Preparation of CA-CS 3D printing ink 0.05 g ± 0.001 g of photoinitiator I2959 and 0.002 g ± 0.001 g of cross-linking agent N, N-methylenebisacrylamide (MBAA) were added to the citric acid chitosan solution containing the reactive monomers, and the mixture was stirred evenly to obtain CA-CS 3D printing ink, which was then stored at 4 degrees Celsius away from light.

[0039] (3) Preparation of adherent, transparent, photocurable 3D-printable citric acid chitosan hydrogel 3.2 ± 0.001 mL of CA-CS 3D printing ink was added into the 3D printing ink tube for 3D printing and cured at room temperature for 30 s under 365 nm UV light to obtain an adherent, transparent, and photocurable 3D printable citric acid chitosan hydrogel.

[0040] (4) Detection, testing, analysis, and characterization The piezoresistive properties and electrical conductivity of an adhesive, transparent, stretchable, photocurable 3D-printable citric acid chitosan hydrogel were tested and analyzed.

[0041] The Keithley DMM6500 digital multimeter was used to perform piezoresistive sensing performance analysis and conductivity testing of an adhesive, transparent, stretchable, photocurable 3D-printed citric acid chitosan hydrogel.

[0042] Conclusion: The adhesive, transparent, photocurable 3D printable citric acid chitosan hydrogel in the present invention was successfully prepared, which has both transparent adhesion, conductivity and stretchability, and can be used for the subsequent preparation of sensors for humanoid robots. Example 2

[0043] A method for preparing an adhesive, transparent, stretchable, and photocurable 3D-printable citric acid chitosan hydrogel comprises the following steps: (1) Preparation of citric acid chitosan prepolymer solution Add 1.2g±0.001g of citric acid to 20.0±0.001 mL of deionized water and stir until dissolved to obtain a citric acid (CA) solution; after standing at room temperature for half an hour, add 0.3g±0.001g of chitosan (CS) to the citric acid solution and stir until completely dissolved to obtain a CA-CS solution. Add 4.0g±0.001g of the active monomer to be polymerized acrylamide (AM) to the CA-CS solution and stir to obtain a transparent and clear citric acid chitosan prepolymer solution; (2) Preparation of CA-CS 3D printing ink 0.05 g ± 0.001 g of photoinitiator I2959 and 0.002 g ± 0.001 g of cross-linking agent N, N-methylenebisacrylamide (MBAA) were added to the citric acid chitosan solution containing the reactive monomers, and the mixture was stirred evenly to obtain CA-CS 3D printing ink, which was then stored at 4 degrees Celsius away from light.

[0044] (3) Preparation of adhesive, transparent, and photocurable 3D-printable citric acid chitosan hydrogel 3.2 ± 0.001 mL of CA-CS 3D printing ink was added into the 3D printing ink tube for 3D printing and cured at room temperature for 20 min under 365 nm UV light to obtain an adherent, transparent, and photocurable 3D printable citric acid chitosan hydrogel.

[0045] By comparing Examples 1 and 2, it can be seen that, when other preparation conditions are the same, a high-concentration CA solution can shorten the photocuring time. Comparative Example 1

[0046] A method for preparing chitosan hydrogel comprises the following steps: The preparation steps were exactly the same as those in Example 1, except that CA was not added in step (1). Comparative Example 2

[0047] A method for preparing citric acid chitosan hydrogel comprises the following steps: The preparation steps are exactly the same as those in Example 1, except that AM is not added in step (1).

[0048] The presence of insoluble matter in Comparative Example 1 indicates that CA plays a role in dissolving CS, making the gel transparent, the protons of CA can improve the conductivity of the gel, and the full dissolution of CS helps to improve the adhesion of the gel and form a second network to improve the mechanical properties. Comparative Example 2 cannot be formed under ultraviolet light, indicating that AM is a light-sensitive component in the 3D printing ink, and without the addition of AM, a hydrogel with mechanical properties cannot be obtained by photocuring.

[0049] The above is only a specific implementation of the present invention, which enables those skilled in the art to understand or implement the present invention. Although detailed descriptions are given with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions recorded in the aforementioned embodiments, or replace some or all of the technical features therein by equivalents; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments, and they should all be covered by the protection scope of the claims.

Claims

1. Preparation of an adhesive, transparent, photocurable 3D printable citric acid chitosan hydrogel, characterized in that: The following steps are involved: (1) Preparation of citric acid chitosan prepolymer solution Add chitosan to the citric acid solution and stir until completely dissolved to obtain a CA-CS solution; Adding active monomer acrylamide to be polymerized into the CA-CS solution and stirring to obtain a transparent citric acid chitosan prepolymer solution; (2) Preparation of CA-CS 3D printing ink At room temperature, a photoinitiator 2-hydroxy-2-methyl-1-[4-(2-hydroxyethoxy)phenyl]-1-propanone and a crosslinking agent N,N-methylenebisacrylamide were added to the citric acid chitosan prepolymer solution, and the mixture was stirred to obtain CA-CS 3D printing ink; (3) Preparation of adhesive, transparent, and photocurable 3D-printable citric acid chitosan hydrogel The CA-CS 3D printing ink was added into the 3D printing ink tube for photocuring 3D printing and cured under 365nm ultraviolet light to obtain an adherent, transparent, photocurable 3D printable citric acid chitosan hydrogel.

2. The preparation of an adhesive, transparent, photocurable 3D printable citric acid chitosan hydrogel according to claim 1, characterized in that: In step (1), the mass ratio of the monomer acrylamide to chitosan is 1-20:0.3, and the mass ratio of the monomer acrylamide to the citric acid in the citric acid solution is 1-5:

1.

3. The preparation of an adhesive, transparent, photocurable 3D printable citric acid chitosan hydrogel according to claim 1, characterized in that: In step (2), the mass ratio of the photoinitiator 2-hydroxy-2-methyl-1-[4-(2-hydroxyethoxy)phenyl]-1-propanone to the crosslinking agent N,N-methylenebisacrylamide is 25:

1.

4. The preparation of an adhesive, transparent, photocurable 3D printable citric acid chitosan hydrogel according to claim 1, characterized in that: The mass ratio of the cross-linking agent N,N-methylenebisacrylamide in step (2) to the monomer acrylamide in step (1) is 1:2000.

5. The preparation of an adhesive, transparent, photocurable 3D printable citric acid chitosan hydrogel according to claim 1, characterized in that: The CA-CS 3D printing ink obtained in step (2) needs to be stored at low temperature and away from light.

6. The preparation of an adhesive, transparent, photocurable 3D printable citric acid chitosan hydrogel according to claim 5, characterized in that: In the low temperature and light-proof storage condition, the low temperature condition is 2-10°C.

7. The preparation of an adhesive, transparent, photocurable 3D printable citric acid chitosan hydrogel according to claim 1, characterized in that: In step (3), the curing temperature is room temperature and the curing time is 30 s-30 min.

8. Use of an adherent, transparent, photocurable 3D printable citric acid chitosan hydrogel obtained by the preparation method according to any one of claims 1 to 7 as a piezoresistive sensor.

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