High-strength Photoresponsive Hydrogels With Integrated Functions

In the present study, hydrogen bonding strengthened hydrogels withphotosensitivity, termed as P(OEGMA-co-VDT-co-SPAA)(POVSP for short), wereprepared by UV light-initiated copolymerization of2-vinyl-4,6-diamino-1,3,5-triazine(VDT), oligo(ethylene glycol) methacrylate (OEGMA) and a spiropyran-containingmonomer (SPAA) which was prepared as reported method. Both the tensile strengthand compression strength went up with the increase in VDT content due to themultiple hydrogen bondings of diaminotriazine residues, which acted as additionalphysical crosslinking. The UV-visible absorbance spectra before and after UV(365nm) irradiation showed the photosensitivity of POVSP hydrogel. The contactangles of POVSP hydrogels decreased after UV irradiation, indicating the increasedsurface hydrophilicity caused by the isomerization of SPAA moieties; furtherirradiation of visible light could make the contact angles return to the initial values.After UV irradiation for15min, the adhered L929cells could detach from POVSPhydrogel surfaces caused by the increase in hydrophilicity. Furthermore, selectivedetachment of cells could be realized by UV light illumination on the specifiedregions of gel surface. Hydrogen bonding between diaminotriazines were shown totightly anchor the PVDT/pDNA complex nanoparticles on the gel surface, wherereverse gene transfection was achieved. Following up with UV irradiation triggeredthe unharmful detachment of gene-modified cells from the gel surface. The resultsdemonstrated that the transfection efficiency increased with the increment of VDTcontent in hydrogels.Another photosensitive hydrogel P(AAm-co-VDT-co-SPAA)(PAVSP for short)with excellent mechanical properties was synthesized by white light-initiatedcopolymerization of acrylamide (AAm), VDT and SPAA. The tensile andcompressive properties were enhanced with the increment of VDT content.Incorporating AAm was shown to improve the mechanical strength significantly inthe whole range of VDT/AAm ratios due to the synergistic hydrogen bondings both inbetween amides and in between diaminotriazines. The hydrogel showed goodbiocompatibility and the cell adherence rate was higher than POVSP hydrogels. Sincethe reversible isomerization of spiropyran could cause the reversible change in hydrophilicity on hydrogel surface, the cell adhesion and light induced detachmentcould be repeated by alternating visible and UV light irradiation, indicating thereusability of PAVSP hydrogels as a wet soft platform for cell culture and unharmfuldetachment. The effect of fibronectin modification on cell adherence rate anddetachment efficiency was also examined. As for gene transfection, fibronectin waspre-adsorbed on the hydrogel surface to enhance the transfection efficiency.Additionally, after fibronectin coating a new method called “sandwich-like genetransfection” was adopted and much higher efficiencies were obtained. Following upwith UV illumination caused the unharmful detachment of gene infected cells to ahigher extent. The PAVSP hydrogel holds potential as a robust platform for operatinggene delivery and controlled harvest of desired seed cells for tissue engineering.