Synthesis And Characterization Of Photoresponsive Hydrogel

Photoresponsive hydrogels can be described as intelligent polymer materials that contain photo switchable moleculers in the hydrogel crosslinking network structure and colour changes in response to light. Photoresponsive hydrogels have received considerable attention from scientists due to their potential applications in various fileds such as optical storage and memory devices, display and communications systems, molecular switches and unit, ion and molecule detection, drug delivery, fluorescence labeling, etc."Click chemistry", especially copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC), was shown as a great success in fabricating various functional and well-defined hydrogels because of its fast reaction process, high efficiency, reliability, no by-products, good stability and selectivity. Therefore, it has its own superiority in fabricating devices for drug delivery and regenerative medicine. Spiropyran (SP) has a reversible structure which consists of two orthogonal aromatic rings connected by a carbon atom of sp3 hybridization. Upon the irradiation of ultraviolet light, the original colorless and hydrophobic SP undergoes the cleavage of C=O bond, forming a colorful and hydrophilic merocyanine (MC). Since this process is often reversible and repeatable, the photo-reactive groups are attractive and useful in diverse forms to functionalize hydrogels in a broad range of applications. Moreover, MC can complex with metal cations via the phenolate oxygen atom, which has been attached more attentions on the design of photochromic sensors for detecting heavy metal ions. Taking the above advantages of SP moieties, photo-responsive hydrogels were prepared and their association with peptides or other macro molecules could be controlled by light to construct a photo-responsive hydrogel system.In the present study, novel hydrogels with extremely high strength, reversible photoresponsive and excellent biocompatible properties were prepared. The functional hydrogels (PEG-SP) with biocompatibility were synthesized from a well-defined poly (ethylene glycol) polymer with spiropyran groups at a given position via Cu (I)-catalyst Azide-Alkyne Cycloaddition (CuAAC) reaction. The molecular structures of the sequential intermediates for hydrogel preparation were verified by*HNMR, FT-IR and UV-Vis. The amphipathic functional hydrogels (PPG-PEG-SP) were synthesized from well-defined poly (ethylene glycol) polymer with spiropyran groups and (PPG9(C=CH))7 via Cu (I)-catalyst Azide-Alkyne Cycloaddition (CuAAC) reaction. The mechanical property, swelling ratio, compression strength, surface hydrophilicity, and biocompatibility of the resulting hydrogel were characterized. Before and after UV light irradiation, the contact angle, swelling ratio and optical property of the hydrogels have a change. Furthermore, their possessed excellent biocompatibility as demonstrated by their performance in an in vivo porcine subcutaneous implantation environment. No inflammation was observed and they got along well with the adjacent tissue. The above features indicate that photoresponsive hydrogels are promising as an implantable matrix for potential applications in biomaterial.