Injectable HA/PEG Hydrogels Prepared Via Strain-promoted Azide-Alkyne Click Reaction

In situ injectable hydrogels have received extensive attention recently,since they are formed by injecting the solutions of gel precursors through minimally invasive operation.The preparation of injectable hydrogels are divided into two categories:physical cross-linking and chemical cross-linking.For the selection of these two methods,the mechanical strength and biological safety of the hydrogels prepared by them should be taken into consideration.The mechanical strength of physical cross-linked hydrogels are usually not strong enough,and most of the chemical crosslinking methods have their own defects in biocompatibility.So,a simple,efficient and biocompatible cross-linking reaction system is essential.Strain-promoted alkyne-azide cycloaddition(SPAAC)reaction is a bio-friendliy orthogonal reaction,thus becomes one of the best choices for the preparation of injectable hydrogel materials.Ideally,the raw materials used to prepare injectable hydrogels should be water-soluble and non-toxic.The gel obtained is preferred to be degraded when disease healing or tissue regeneration has been completed.Hyaluronic acid(HA),a ubiquitous polysaccharide in human body,is critical to cell and tissue function and doesn’t cause immune reaction.As a biological material,its safety has been tested for long-term clinical use.What’s more,there are lots of hydroxyl and carboxyl fimctional groups on the molecular chain of HA,which makes it easy to go through with chemical modification.Therefore,HA is selected to be the skeleton polymer of the hydrogels in this paper.In Chapter 1,the progress of research on injectable hydrogels,SPAAC click chemistry and the materials to fabricate hydrogels were reviewed.In Chapter 2,inectable HA/PEG hybrid hydrogels were prepared by strain-promoted azide-alkyne cycloaddition(SPAAC)click chemistry.First,through the efficient reaction of amino and carboxyl groups in aqueous phase,HA molecular chain was successfully modified with cyclooctyne to prepare the Cyclooctyne-HA which was a key to the hydrogel.Then,four azide modified PEG were synthesized by using sodium azide to attack the-OMs group.All the products were confirmed by NMR,GPC and so on.Then,a series of gels with different concentrations were fabricated by simply mixing the solutions of two gel precursors.The gel time was tested by a tube method,and at the same time,their mechanical properties were tested to analyse and compare the effects of the concentration of gel precursors and the ratio of functional groups on the gel properties.Results showed that the shortest gelation time was 5 minutes.SEM scanning electron microscopy showed that all hydrogels exhibited an internal three-dimensional network structure and the pore sizes were ranging from 5 to 100 μm.In addition,the hydrogels had good resistance to enzyme degradation.It took eleven days to degrade in PBS solution with the presence of 50 U/mL of hyaluronidase.And the compressive strength could reach 185 kPa,showing the excellent mechanical properties of hydrogels.Finally,the gel precursor solutions were mixed with COS-7 cells to carry out three-dimensional cell culture experiments.The results showed a good growth and high proliferation rate of cells,which confirmed the good biocompatibility of the gels.Therefore,the HA/PEG injectable hydrogels have great potential for biomedical applications such as controlled release,injection cosmetic and tissue engineering.