See the light hydrogel expands!

In nature, the light is converted into an optical drive system other capabilities, such as photosynthesis. Scientists inspired by natural light drive system, developed photosensitive material can be used in many catalytic functions, induction, adhesion, bio-engineering, drug delivery and soft robot. Compared with other stimuli, the light has more advantages, including immediate opening or closing signal, changing the wavelength, without direct contact with the substances. Photosensitivity hydrogels as biomaterials concern. Researchers have various photoactive component (e.g. photocleavable group, a photothermal agents and molecular light switch) incorporated into the hydrogel matrix, to adjust its physical, chemical and biological properties. Optical switch elements, e.g. azo benzene, aromatics, styrene, and derivatives thereof spiropyran after light treatment can be reversibly and selectively re-conformation. Photo-induced molecular conformational changes can drive macroscopic hydrogel. Spiropyran switchable between each form a closed loop spiropyran (SP) and open-loop form of cyanine (MC) two isomers, both isomers dipole moment, molecular size, polarity and net charges are different. There is no spiropyran containing a water-soluble polymerization sites may be reported examples, therefore, chemically bonded to the polymerization sites hydrogel network, using the light adjusting its physical properties are extremely important.


Recently, United States Northwestern University in Chicago, Illinois Simpson Cray Research Institute Samuel I.Stupp team in the [123 ] published in JACS 123] on [a \”Light-Driven Expansion of spiropyran Hydrogels\”, reported molecular design and chemical synthesis of the polymerizable water-soluble sulfonate-based spiropyran molecule, which molecule covalently connected to the hydrogel network, the resultant hydrogel has swelling behavior of light-induced. [Photo] Express 见光会膨胀的水凝胶!

1. The volume change of the hydrogel photo

Synthesis of a water-soluble methacrylate groups and sulfonate groups simultaneously containing polymerizable molecules of spiropyran. In the NIPAM monomer, BIS crosslinker and APS / TEMED presence of an initiator synthetic hydrogel.

The hydrogel containing the sulfonated spiropyran (1b-1d) of the light expands in volume after treatment in acidic water, and containing a non-Sulfonated spiropyran (1a) volume shrinkage hydrogel (FIG. 1A)

after the light. FIG. 1B Changes to prove that the illumination light and the expansion behavior of the sulfonated spiropyran charge related. For a more thorough understanding of such light expansion behavior of molecular dynamics (MD) simulation of coarse-grained (CG) model. SO3 groups can affect the interaction between the spiropyran molecule, the number of adjacent spiropyran molecule by calculating a first spiropyran solvated shell quantified (FIG. 1C). The results showed that the system containing 1a, and the MC SP isomerization reaction between the hydrophobic groups resulting in formation of clusters. System of sulfonated spiropyran (1b and 1d) the light in the charge increases, due to electrostatic repulsion not form clusters. 1a spiropyran interaction with water after irradiation is reduced, while the 1b and 1d increased, indicating photoinduced charge density reduction (or increase) helps the diffusion of water out of or into the gel from the gel ( Fig. 1d).

FIG. 1. (A) a water-soluble polymerizable spiropyran (molecular 1b-1d) design. (B) a graph measuring the change in volume before and after the respective different portions 1a-1d and the net charge amount of light. (C) Calculation of different molecules nearest adjacent SP MCH or coarse-grained simulation according to the open loop (top) and closed (bottom) of the probability map. (D) the average number of drops of water probability map. 见光会膨胀的水凝胶!
2. The pH value of the volume expansion of the light

The hydrogel light volume expansion can be adjusted, 1d hydrogel expansion ratio by changing the pH of the solution in the process as the light increasing the pH value is gradually increased (FIG. 2A). 1b-1c hydrogel has a similar tendency. OF disulfonated 1d to the same concentration of the aqueous solution at different pH values ​​in the UV-vis spectroscopy to explain this phenomenon FIG. Under dark conditions, MCH

(425 nm) and absorption intensity with increasing the pH is lowered (FIG. 2B), while higher pH values ​​described, SP 2- and the MCH – equilibrium reaction between SP 2- to move. By tracking OF MCH (425 nm) and the absorption intensity change SP 2- (225 nm) is used to represent the equilibrium reaction (FIG. 2C). 1d hydrogelAfter spontaneous expansion of the secondary light-induced expansion gum (2D, a red circle) occurs at a higher pH solution in the light. The reverse order of two stimuli are applied to the same gel, to obtain the same final expansion coefficient (2D, a blue triangle). while the pH value and the light stimulation produced a faster swelling kinetic (2D, a black square). The light amount of isomerization are the critical parameters of the degree of expansion, the expansion capacity of an optical switch with the increase ratio increases.

FIG. 2. (A) 1d hydrogels swell kinetics of light at different pH values. (B) dark spiropyran (1d) UV-vis spectra at different pH values. (C) SP2- MCH- and absorbance change curve over time. (D) expansion kinetics 1d hydrogel combinations in different stimuli. 见光会膨胀的水凝胶!
3 light different expansion LCST polymer hydrogel performance

of the light is adjusted through the degree of expansion (FIG. 3A) controllable to select an LCST of different polymers (DEGMA and OEGMA) . At constant spiropyran compound concentration, pH and room temperature, LCST of the polymer is inversely proportional to the light expanded 1d containing a hydrogel (FIG. 3B). Since the LCST polymers used were all higher than room temperature, the low degree of curl LCST polymer chains collapse ratio higher LCST polymer chain. After illumination, the charge density increases, the water into the polymer network, collapsed polymeric chain extension, resulting in a large expansion ratio (Figure 3C). Conversely, fewer high LCST polymer chain wound at room temperature showed only minimal expansion due photoisomerization.

FIG 3. (A) molar ratio of the synthesis of photosensitive polymer having an LCST different DEGMA and by changing the OEGMA. (B) 1d photoinduced hydrogel expands its LCST. Expansion effect a schematic view (C) of different light-induced LCST hydrogel. 见光会膨胀的水凝胶!
4. Phototaxis programming hydrogel receiving phototactic inspired plants, developed a series of phototropic hydrogel network (FIG. 4A). As shown in FIG 4B, 1a hydrogel shrink uniformly bent to the light source, this system is a photopositive (PP). And a monomer-1d 1b Synthetic hydrogels expansion bend in the light from the light source, such as bending behavior opposite negative chemotaxisGloss (NP). Because photons continued to spread in the hydrogel, PP and NP will eventually return to its original shape. Using different spiropyran (FIG. 4C) to change the network or the LCST polymeric backbone (FIG. 4D) and the height of the adjustable bending angle of NP. Compared with 1b and 1c, 1d hydrogel having a higher charge density after irradiation, so that the maximum bending angle, bending the fastest (Fig. 4E). When given spiropyran molecule (1b), low LCST due to the large expansion of the gel to exhibit a large bending angle and the bending speed faster (Fig. 4F). FIG. 4G show three different types of the four curved NP – maximum bending angle after the recovery period straight. Since a plurality of molecules and polymers spiropyran skeleton Alternatively, a combination of different networks and the polymer spiropyran series programmable bending angle and the driving dynamics.
FIG 4. (A) a schematic view of the positive and negative chemotaxis aqueous hydrogel of light. (B) contains a sulfonated spiropyran (1a) and PNIPAM backbone photopositive hydrogel. Negative (C) contains a sulfonated spiropyran (1b-1d) and PNIPAM backbone Phototaxis hydrogel. (D) containing different 1b and poly (DEGMA -co-OEGMA) bent hydrogel. Diagram (E) Photo hydrogels curved corner C and illumination time. Diagram (F) D picture hydrogel bending angle illumination time. The maximum bending angle of the light (G) image hydrogel D – dark cycle. 见光会膨胀的水凝胶!