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.
[research]
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 
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).
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.
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.
