Synthesis And Flurescence Visualized Degradationof UV-crosslinkable Chitosan

Hydrogel scaffoldsplay an important role in tissue engineering and regenerative medicine.Serving as one of biomaterial scaffolds,hydrogels are generally regarded as biocompatible materials because their high water content and soft nature render them similar to natural extracellular matrices and minimize tissue irritation and cell adherence.Furthermore,their porous structure,along with their water content,is suitable properties to accommodate high loads of water-soluble compounds,such as therapeutically active proteins and peptides.Chitosan is a biodegradable and natural biomaterial with amino groups,which has been widely used in tissue engineering and drug delivery owing to its biodegradability by lysozyme,biocompatibility,antibacterial activity and hemostatic ability.However,there are some challenges associated with chitosan for its applications in tissue engineering,such as poor solubility in neutral pH solution and lack of UV crosslinking and thermo-responsive ability.So we facilely designed a hydrosoluble,UV crosslinkable chitosan derivative by N-acylation and further endowwith thermo-responsive ability.In this doctoral dissertation,we employed carbon nanodots(CNDs)with low photobleaching,red emission and good biocompatibility as fluorescent indicator for real-time and non-invasive visual in vitro/in vivo degradation of hydrogels.The limit of existing chitosan includes: 1.could not dissolve in neutral pH solution;2.could not be UV crosslinked.In this study,we facilely synthesized a hydrosoluble,UV crosslinkable and injectable chitosan by single-step N-acylation.The degree of substitution(DS)of methacryloyl groupswas positively correlated to the ratio of MA used in acylation reaction,which could be controlled by regulating ratio of anhydride to amino groups.The solubility of N-MAC in neutral pH solution increased to 27.6 mg/m L with DS increasing to 28.4%.N-MAC hydrogel was obtained via photopolymerization of carbon–carbon double bonds under(30s)UV irradiation.UV-crosslinkable chitosan exhibits good biocompatibility.Patterned cell-laden microgels with on-demand regular geometric shapes and complex logos were fabricated via lithography.Injectable and rapid transdermal curing hydrogels were developed via skin-penetrable UV-crosslinking strategy within mice subcutaneous space.UV-crosslinkable chitosan hydrogels stimulated a relatively slight acute inflammatory response but did not transformed into chronic inflammation,and could afford good biocompatibility.Hydroxyapatite(HA)/UV-crosslinkable chitosan hydrogelwas prepared by mixing chitosan with HAand sequentiallyapplying for UV irradiation.The high HA content in composite hydrogel benefited the acceleration of bone regeneration.To endow UV-crosslinkable chitosan with thermo-responsive ability,a novel UV-crosslinkable and thermo-responsive chitosan was designed by grafting with poly N-isopropylacrylamide(PNIPAM)and acetylation of methacryloyl groups.The thermo-responsive unit PNIPAM endowed chitosan hydrogel with temperature triggered volume shrinkage and reversible swelling/de-swelling behavior.DOX release rate was accelerated and approximately 40 times higher than that from non-irradiated hydrogels.The UV-crosslinkable and thermal-responsive hydrogel served as in situ forming hydrogel-based drug depot is developed for NIR-triggered localized on-demand release.To date,synthetic yield of CNDs via hydrothermal carbonization is quite low(<50%).We report here the synthesis of CNDs derived from chitosancontaining carbon-carbon double bond and small molecule containing carbon-carbon double bond/chitosan.The CNDs exhibited a constant increase in synthetic yield(increase to 85.9%)and content dependent feature.Hence the concept of carbon-carbon double bonds boosting ultrahigh-yield synthesis of CNDs provides a promising strategy to be employed as carbonaceous nanodrug aiming at preventing and curing ageing and age-related diseases.These CNDs exhibited a high quantum yield and wide emission wavelengths(400~550 nm)as a consequence of nitrogen incorporation.We further demonstrate applications of CNDs as probes for heavy metal ion detection.The CNDs offered potential as mercury ion sensors with detection limit of 80 n M.A smartphone APP based on CNDs was developed providing a portable and low cost detection platform for detection of heavy metal ions contamination.CNDs could be uptaked and metabolism mainlythrough the digestive system in zebrafish.The CNDs exhibit outstanding protective effect against oxidative stress viadown-regulating exogenous and endogenous ROS generation.We employed CNDs with low photobleaching,red emission and good biocompatibility as fluorescent indicator for visual in vitro/in vivo degradation of hydrogels.The embedded CNDs in hydrogels did not diffuse outside in the absence of hydrogel degradation.We had acquired similar degradation kinetics between gravimetric and visual determination,and established mathematical equation to quantitatively depict in vitro degradation profile of hydrogels.Based on the in vitro data,we developed a visual platform that could quantitatively depict in vivo degradation behavior of new injectable biomaterials by real-time and non-invasive fluorescence tracking.This fluorescence-related visual imaging methodology holds great potentials for rational design and convenient in vivo screening of biocompatible and biodegradable injectable hydrogels in tissue engineering.