Preparation Of Ultrathin Hydrogel Films Via Layer By Layer "Click" Chemistry

Ultrathin hydrogel films have been paid more and more attention due to their promising applications on sensors, advanced delivery system and surface functionalization of materials. Compared with macro-hydrogels, ultrathin hydrogel films possess faster response and more widespread practical values.Usually, hydrogel films are fabricated by spin-casting with hydrogel precursors, and subsequent crosslinking. It is a simple method but with serious limitations. It can be only used on the specific substrate such as smooth plane. In addition, it’s difficult to control the thickness of hydrogel films below micron scale.A facile strategy was used to fabricate ultrathin hydrogel films via the combination of layer by layer (LbL) technique and "click" chemistry. The hydrogel precursors were synthesized by polycondensation and then were used to prepare ultrathin hydrogel films via LbL thiol-ene "click" reaction under human physiological condition without any metal catalyst or light irradiation.The ultrathin hydrogel films were characterized by UV-vis absorption spectra which showed the intensity increased with the number of bilayer numbers. Also, the thickness of the hydrogel films showed a linear growth by ellipsometry and the hydrogel films grew at a regular speed of averaging 2.8 nm per bilayer. The results demonstrated that the method LbL "click" chemistry allowed excellent control over the thickness of the ultrathin hydrogel films.A series of hydrogel precursors were synthesized with either multi-ene or multi-thiol and specific constituent for different applications. For example, the precursor POEGDMAM which containing quaternary ammonium salt was used to prepare a kind of antibacterial hydrogel films which exhibited excellent antibacterial activity against both Staphylococcus aureus and Escherichia coli which was enhanced by the growing numbers of layers. This kind of biocompatible antibacterial ultrathin hydrogel films is a promising candidate for biomedical applications. Also, the hydrogel films were used to be a drug carrier for controlled release. Model drug camptothecin was grafted onto one of the hydrogel precursors. A sustained release can be obtained in hours as the degradation of the hydrogel films.In brief, the combination of layer by layer (LbL) technique and "click" chemistry is a facile strategy to fabricate ultrathin hydrogel films with a variety of functions which were expected to be highly sensitive and provide a wide prospection in actual application compared with traditional hydrogels...