A Tri-Stimuli-Responsive Shape-Memory Material Using Host-Guest Interactions as Molecular Switches.

A thermo-, photo- and chemoresponsive shape-memory material is successfully prepared by introducing α-cyclodextrin (αCD) and azobenzene (Azo) into a poly(acrylate acid)/alginate (PAA/Alg) network. The tri-stimuli-responsive formation/dissociation of αCD-Azo acts as molecular switches freezing or increasing the molecular mobility. The resulting film herein can be processed into temporary shapes as needed and recovers its initial shape upon the application of light irradiation, heating, or chemical agent independently. Furthermore, the agar diffusion test suggests that the α-CD-Alg/Azo-PAA has good biocompatibility for L929 fibroblast-like cells.

Photoreversible polymer-surfactant micelles using the molecular recognition of α-cyclodextrin.

Photoreversible micelles were achieved by a combination of commercially available components sodium alginate (Alg), tetradecyltrimethylammonium bromide (TTAB), α-cyclodextrin (α-CD), and 4-(phenylazo)benzoic acid (PBA). Under visible light irradiation, α-CD interacted more favorably with PBA than with alkyl chains of TTAB. Therefore, polymer-surfactant micelles were formed by the self-assembly of Alg and TTAB through electrostatic attraction. After UV irradiation, micelles were disrupted because PBA in the cis form lost its ability to complex with α-CD, and then the latter was interacted with TTAB to prevent the association of alkyl chains of TTAB. On alternating irradiation of this quaternary system with UV and visible light, this reversible micellization process can be recycled many times.

pH-Switchable macroscopic assembly through host-guest inclusion.

A novel pH-switchable macroscopic assembly is reported using alginate-based hydrogels functionalized with host (α-cyclodextrin, αCD) and guest (diethylenetriamine, DETA) moieties. Since the interaction of αCD and DETA is pH sensitive, the host hydrogel and guest hydrogel could adhere together when the pH is 11.5 and separate when the pH is 7.0. Furthermore, this pH-controlled adhesion and dissociation shows a good reversibility. The host and guest polymers have good biocompatibility; therefore, this pH-sensitive macroscopic assembly shows great potential in biotechnological and biomedical applications.

Redox- and glucose-induced shape-memory polymers.

A novel redox-induced shape-memory polymer (SMP) is prepared by crosslinking ß-cyclodextrin modified chitosan (ß-CD-CS) and ferrocene modified branched ethylene imine polymer (Fc-PEI). The resulting ß-CD-CS/Fc-PEI contains two crosslinks: reversible redox-sensitive ß-CD-Fc inclusion complexes serving as reversible phases, and covalent crosslinks serving as fixing phases. It is shown that this material can be processed into temporary shapes as needed in the reduced state and recovers its initial shape after oxidation. The recovery ratio and the fixity ratio are both above 70%. Furthermore, after entrapping glucose oxidase (GOD) in the system, the material shows a shape memory effect in response to glucose. The recovery ratio and the fixity ratio are also above 70%.

pH-induced shape-memory polymers.

A novel pH sensitive shape-memory polymer (SMP) is prepared by cross-linking the ß-cyclodextrin modified alginate (ß-CD-Alg) and diethylenetriamine modified alginate (DETA-Alg): The pH reversible ß-CD-DETA inclusion complexes serve as a reversible phase, and the cross-linked alginate chains serve as a fixing phase. It is shown that this material can be processed into temporary shape as we needs at pH 11.5 and recover to its initial shape at pH 7. The recovery ratio and the fixity ratio were 95.7 ± 0.9% and 94.8 ± 1.1%, respectively. Furthermore, this material showed good degradability and biocompatibility. Because the shape transition pH value is quite close to that of our body fluid and this pH triggered shape-memory effect is convenient and safe to use, this material has a high potential for medical application.

Accelerating ESD-induced gastric ulcer healing using a pH-responsive polyurethane/small intestinal submucosa hydrogel delivered by endoscopic catheter.

Endoscopic submucosal dissection (ESD) is the standard treatment for early-stage gastric cancer, but the large post-operative ulcers caused by ESD often lead to serious side effects. Post-ESD mucosal repair materials provide a new option for the treatment of post-ESD ulcers. In this study, we developed a polyurethane/small intestinal submucosa (PU/SIS) hydrogel and investigated its efficacy for accelerating ESD-induced ulcer healing in a canine model. PU/SIS hydrogel possessed great biocompatibility and distinctive pH-sensitive swelling properties and protected GES-1 cells from acid attack through forming a dense film in acidic conditions in vitro. Besides, PU/SIS gels present a strong bio-adhesion to gastric tissues under acidic conditions, thus ensuring the retention time of PU/SIS gels in vivo. In a canine model, PU/SIS hydrogel was easily delivered via endoscopy and adhered to the ulcer sites. PU/SIS hydrogel accelerated gastric ulcer healing at an early stage with more epithelium regeneration and slight inflammation. Our findings reveal PU/SIS hydrogel is a promising and attractive candidate for ESD-induced ulcer repair.