Method for preparing porous hydrogel through freezing-illumination

Abstract

The present invention discloses a freezing-illumination method for preparing porous gels, comprising the steps of: (a) synthesizing the gels containing dynamic exchangeable bonds; (b) illuminating the gels under frozen state by certain wavelength light source; (c) elevating the temperature and melt the ice crystals within the gels to get the porous structure. The dynamic exchangeable bonds existing in the gels include double/multi-sulfur bond, hydrazine bond, boronic ester bond. Catalyst is also included in the gel composition to activate the bond exchange reactions under illumination. This new method for preparing porous gels is easy to operate and suitable for most kinds of gels. Meanwhile, it can spatially control the pore structure within the gels by local illumination.

Claims

1. A freezing-illumination method for preparing a porous hydrogel, the method comprising the following steps in the following order: (a) synthesizing by polymerization a gel containing exchangeable bonds under room temperature or heating and using water as solvent; (b) freezing the gel containing exchangeable bonds to prepare a gel containing exchangeable bonds in a frozen state, and illuminating the gel containing exchangeable bonds in the frozen state by a light source so that the exchangeable bonds contained therein exchange; and (c) exposing to an elevated temperature the gel containing exchangeable bonds in the frozen state to melt ice crystals therein to obtain the porous hydrogel.

2. The method of claim 1, wherein the exchangeable bonds are selected from at least one of the following: bonds between two or more sulfur bonds, hydrazine bonds, boronic ester bonds, and host-guest interaction bonds.

3. The method of claim 1, wherein the porous hydrogel comprises a catalyst which can activate the exchangeable bonds when the catalyst is illuminated with a light source; and wherein the amount of the catalyst ranges 0.05-5% by weight of all dry ingredients in the porous hydrogel.

4. The method of claim 1, characterized in that: the exchangeable bonds are bonds between two or more sulfur atoms and the porous hydrogel further comprises a photo-radical initiator as a catalyst; or the exchangeable bonds are hydrazine bonds and the porous hydrogel further comprises a photo-base generator as a catalyst; or the exchangeable bonds are boronic ester bonds and the porous hydrogel further comprises a photo-acid generator as a catalyst; or the exchangeable bonds are host-guest interaction bonds and the porous hydrogel does not comprise a catalyst.

5. The method of claim 3, wherein addition of the catalyst includes in situ introduction during step (a) or diffusion into the gel containing exchangeable bonds after step (a).

6. The method of claim 1, wherein wavelength of the light source is 200-470 nm, and illuminating occurs for is 0.5 min-24 hours.

7. The method of claim 1, wherein the illuminating includes is uniform irradiation or local irradiation by a mask.

8. The method of claim 1, wherein, in step (b), freezing includes uniformly freezing or directionally freezing.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1: the image of laser scanning confocal microscope for example 1.

(2) FIG. 2: the image of laser scanning confocal microscope for example 2.

(3) FIG. 3: the image of laser scanning confocal microscope for example 3.

(4) FIG. 4: the image of laser scanning confocal microscope for example 4.

(5) FIG. 5: the image of laser scanning confocal microscope for example 5.

DETAILED EMBODIMENTS OF THE PRESENT INVENTION

(6) A further illustration of the invention is made with examples. However, the protection scope of the present invention is not limited by these examples.

Example 1 (Disulfide Bond)

(7) Materials: Acrylamide (AAm) and 2-hydroxy-4-(2-hydroxyethoxy)-2-methyl propiophenone (12959) purchased from J&K. N,N-bis(acryloyl) cystamine (BISAC) purchased from Alfa Aesar. Ammonium persulfate and N,N,N,N-tetramethylethylenediamine purchased from Sinopharm.

(8) Preparation: 500 mg acrylamide and 5 mg N,N-bis(acryloyl) cystamine were dissolved in 5 ml deionized water. After fully dissolved, 100 L ammonium persulfate and 10 L N,N,N,N-tetramethylethylenediamine were added into the solution. The solution was transferred to a sealed glass vessel quickly. 24 hour later, the resulting gel was immersed in a solution which contains the 2-hydroxy-4-(2-hydroxyethoxy)-2-methyl propiophenone (photo-catalyst) for 24 h. The gel was frozen by a cooling stage. Under the freezing condition, the gel was exposed by UV irradiation integrally for 5 min. After thawing, the gel swelled in the deionized water to obtain porous gels. The laser scanning confocal microscope was applied to characterize the pore structure of the obtained gel.

Example 2 (Boronic Ester Bond)

(9) Materials: m-acrylamido phenylboronic acid, and the structure was as follow:

(10) ##STR00001##

(11) N-[Tris(hydroxymethyl)methyl]acrylamide was purchased from Alfa Aesar, and the structure as follow:

(12) ##STR00002##

(13) Acrylamide (AAm) was purchased from J&K. Ammonium persulfate and N,N,N,N-tetramethylethylenediamine were purchased from Sinopharm. Diphenyliodonium nitrate was purchased from Aladdin.

(14) Preparation: 446 mg acrylamide, 60 mg m-acrylamido phenylboronic acid and 55 mg N-[Tris(hydroxymethyl)methyl]acrylamide were dissolved in the 5 ml deionized water. After fully dissolved, 100 L ammonium persulfate and 10 L N,N,N,N-tetramethylethylenediamine were added into the solution. The solution was transferred to a sealed glass vessel quickly. 24 hours later, the resulting gel was immersed in a solution which contains the diphenyliodonium nitrate (control the pH=10) for 24 hours. The gel was frozen by a cooling stage. Under the freezing condition, the gel was exposed by UV irradiation integrally for 5 min. After thawing, the gel swelled in the water to obtain porous gels. The laser scanning confocal microscope was applied to characterize the pore structure of the porous gel.

Example 3 (Hydrazine Bond, Locally Illumination)

(15) Materials: Polyethylene glycol was terminated by benzoyl hydrazine (Mn=2000), and the structure was as follow.

(16) ##STR00003##

(17) Tris[(4-aldehyde-phenoxy)-methyl] ethane, and the structure was as follow:

(18) ##STR00004##

(19) Tetraphenylborate quaternary ammonium (Photobase generator).

(20) Preparation: 45.4 mg polyethylene glycol terminated by benzoyl hydrazine and 5.8 mg Tris[(4-aldehyde-phenoxy)-methyl] ethane were dissolved in the 1.0 ml dimethylsulfoxide. After fully dissolved, 0.5 L acetic acid was added into the solution. The solution was transferred to a sealed glass vessel quickly. 24 hours later, the resulting gel was immersed in a solution which contains the photobase generator (control the pH<6) for 24 hours. The gel was frozen by a cooling stage. Under the freezing condition, the gel was exposed by UV irradiation using a photo mask with a SCI pattern for 5 min. After thawing, the gel swell in the water to obtain porous gels. The laser scanning confocal microscope was applied to characterize the pore structure of the porous gel.

Example 4 (Host-Gust Interaction)

(21) Materials: Acrylamido cyclodextrin, and the structure was as follow:

(22) ##STR00005##

(23) Acrylamido azobenzene, and the structure was as follow:

(24) ##STR00006##

(25) Acrylamide (AAm) purchased from J&K. Ammonium persulfate and N,N,N,N-tetramethylethylenediamine purchased from Sinopharm.

(26) Preparation: 100 mg acrylamide, 60 mg acrylamido cyclodextrin and 10 mg acrylamido azobenzene were dissolved in the 5 ml deionized water. After fully dissolved, 100 L ammonium persulfate and 10 L N,N,N,N-tetramethylethylenediamine were added into the solution. The solution was transferred to a sealed glass vessel quickly. 24 hour later, the resulting hydrogel was immersed in the deionized water for 24 hours. The hydrogel was frozen by a cooling stage. Under the freezing condition, the hydrogel was exposed by UV irradiation integrally for 5 min. After thawing, the hydrogel swelled in the water to obtain the porous hydrogels. The laser scanning confocal microscope was applied to characterize the pore structure of the porous gel.

Example 5 (Hydrophobic Monomer)

(27) Materials:

(28) butyl methacrylate (BA) purchased from sigma-aldrich and phenyl bis(2,4,6-trimethylbenzoyl)-phosphine oxide (819) purchased from J&K. N,N-bis(acryloyl) cystamine (BISAC) purchased from Alfa Aesar.

(29) Preparation: 500 mg butyl methacrylate and 5 mg N,N-bis(acryloyl) cystamine were dissolved in 5 ml dimethyl sulfoxide. After fully dissolved, 4 mg ammonium persulfate and 10 L N,N,N,N-tetramethylethylenediamine were added into the solution. The solution was transferred to a sealed glass vessel quickly. 24 hours later, the resulting gel was immersed in a dimethyl sulfoxide solution which contains the phenyl bis(2,4,6-trimethylbenzoyl) phosphine oxide (photo-catalyst) for 24 hours. The gel was frozen by a cooling stage. Under the freezing condition, the gel was exposed by UV irradiation integrally for 5 min. After thawing, the gel swelled in the dimethyl sulfoxide to obtain porous gels. The laser scanning confocal microscope was applied to characterize the pore structure of the obtained gel.