1. Paper Introduction 2014/01/17 Rika Ochi
Nature Communications, 2013, 4:2029, DOI: /ncomms3029
Photolatently modulable hydrogels using unilamellar titania nanosheets as photocatalytic crosslinkers
Mingjie Liu1, Yasuhiro Ishida1, Yasuo Ebina2, Takayoshi Sasaki2 & Takuzo Aida1,3
1 RIKEN Center for Emergent Matter Science.
2 National Institute for Materials Science, International Center for Materials Nanoarchitectonics,
3 Department of Chemistry and Biotechnology, School of Engineering,
The University of Tokyo,

2. Hydrogels ・Soft matter mainly composed of water
・Various applications are expected. ex) Drug release, 3D cell culture, actuator
・In general, hydrogels have low mechanical strength
Q. Wang, J. L. Mynar, M. Yoshida, E. Lee, M. Lee, K. Okuro, K. Kinbara & Takuzo Aida, Nature, 2010, 463, 339–343 .
Mechanical strong hydrogels
Clay nanosheets
ASAP
G3-binder
G3-binder
Physically crosslinking
G3-binder+ sodium polyacrylate (ASAP)
+ Laponite (Silicate)
[CNSs (negative)]/[G3-binder
(positive)]/[ASAP(negative)]
=18.0/2.0/6.0 mM;
Recently, two dimensional nanosheets (disk-shaped clay nanosheets)
have caught special attention as components of hydrogels.

3. This study
Photolatently reactive hydrogels which can be activated by light
Titania (Titanium oxide) : photocatalyst, nontoxic, biocompatible
Water-soluble vinyl　monomers
Hydroxyl radical
The use of unilamellar titania nanosheets (TiNSs)
as photocatalystic crosslinking points.

4. Preparation and thermo-response of hydrogel
Schematic illustration of TiNSs (0.4 wt%)-mediated photoinduced hydrogelation (l=260 nm, at 25 ℃ for 20 min) and pictures before and after the hydrogelation using IPAAm (10.0 wt%) as monomer

5. Thermoresponsive behavior of hydrogel
IPAAm/TiNSs (10.0/0.4 wt%)　at 25 and 40 ℃
In a patterned PDMS matrix
（50-mm-thick film ）
In a test tube
PDMS
Gel
PDMS= plastic
＠300 nm
Hydrogel sharply and reversibly changes, without any hysteresis, its optical transmittance in a very narrow temperature range of 32–33 ℃

6. Three-dimensional microstructure of hydrogel
ANS
Hydrophobic domain
10 mm
(e) A three-dimensional microstructure of the hydrogel constructed with its sliced two-dimensional images, obtained at 34 ℃ by confocal fluorescence laser scanning microscopy, where the sample was doped with a fluorescent probe (8-anilino-1-naphthalenesulphonic acid ammonium salt).
Submicron-sized tiny luminescent domains, which is advantageous for quick thermal shrinkage/swelling of polymer domains, certainly benefits from the mechanism of hydrogelation with photocatalytic TiNSs

7. Use as a thermoresponsive ion gate
(f) Ion conductivities of the hydrogel at different temperatures in the range 23–38 C at an applied cell voltage of 100mV, where the sample (IPAAm/TiNSs=10.0/0.4 wt%) was doped with LiClO4 (dopant, 500 mM).
Ion conductivity increased markedly at around the LCST.

8. Micropatterning of hydrogels
With poly(IPAAm)
With Ag nanocluster
500 mm
500 mm
Figure 3. (a) Schematic illustration of micropatterning with poly(IPAAm) and Ag nanocluster in a hydrogel matrix, prepared with DMAAm/TiNSs/Laponite (8.0/3.0/3.0 wt%), upon light exposure through a patterned photomask.). (d) Change in surface plasmonic absorbance (500 nm) with light exposure time of Ag nanocluster.
TiNSs are　immobilized at the crosslinking points therefore hardly diffuse inside the gel matrix.
→　Photo-micropatternig, microfabrication

9. Homo- and heterotropic conjugations of hydrogels
[DMAAm/TiNSs/Laponite] = 8.0/3.0/3.0 wt%
Light exposure (l>260 nm) for 20 min
Homotropic conjugation
Heterotropic conjugation
500%
550%
PDMS= plastic
・Repeatable use (healing of damaged part)
・Strong attachment
・Heterotropic conjugation possibly expand the potential of hydrogel

10. Thermoresponsive hydrogel actuator
Supplementary Figure S5. Thermoresponsive hydrogel actuator by lateral heterotropic conjunction of photolatently modulable hydrogel strips. (a) Schematic representation of a bimorph strip of laterally conjugated hydrogels with different thermoresponsive properties. The pink-colored and blue-colored layers were prepared with IPAAm/TiNSs (8.0/3.0 wt%) and DMAAm/TiNSs (8.0/3.0 wt%), respectively, in conjunction with Laponite (3.0 wt%). (b) Pictures of the bimorph strip at 25 (left) and 40 °C (right).
Lateral photochemical conjunction of two hydrogel strips with different thermo-responsive properties provides a soft actuator that operates by a temperature change.

11. Summary
・By using titania authors developed ‘photolatently modulable’ hydrogels that are readily preparable and also postmodulable
by light whenever needed.
・Consequently, TiNSs are immobilized at the crosslinking points in a polymer network and locally convert gelling water into hydroxyl radicals whenever exposed to light.
・This hydrogel would be useful for the development of materials.
ex) controlled drug release, semisynthetic enzymes, and three-dimensional tissue engineering.

12. strain–stress curve