Construction Of BMSCs-laden Injectable Hydrogels And Their Applications In Cartilage Tissue Engineering

Cartilage defects caused by injuries or common diseases seriously threaten human health.There are no blood vessels or nerves in adult cartilage which greatly limit the self-healing after cartilage injury.Lately,cartilage tissue engineering(CTE)provides a promising method to repair the damaged tissues by integrating cells,biomaterial scaffolds and growth factors.Among all the biomaterial scaffolds,injectable hydrogels have attracted enormous interests because of their superior properties,including their extracellular matrix(ECM)-like structures,good bioactivity and in situ formation with minimum invasion.Bone marrow mesenchymal stem cells(BMSCs)are one of the most commonly used stem cells for biomedical applications.Therefore,this study developed several injectable hydrogel systems,and their potential applications in CTE were also investigated.Chapter 1 summarized the clinical treatments for cartilage repair as well as the current strategies for fabricating injectable hydrogels in TE.Chapter 2 fabricated a BMSCs-laden injectable hydrogel system via enzyme-catalyzed crosslinking of hyaluronic acid-tyramine(HA-TA)and collagen type I-tyramine(Col-TA)for cartilage regeneration.HA and Col are important components of ECM which are regarded as ideal biomaterials for TE applications.However,Col is insoluble in water which greatly limits its applications in TE.To address this limitation,the amine groups of Col were changed into carboxyl groups through modification with SAH,and the obtained Col-SAH showed excellent water solubility.In addition,HA was introduced to decrease the degradation rate of this system.The results illustrated that this hydrogel could gelate within several seconds.Afterward,combining with transforming growth factor-?1(TGF-?1),this injectable hydrogel system could effectively promote the regeneration of cartilage both in vitro and in vivo.However,this kind of hydrogel system still possessed some drawbacks,for example,the mechanical property was relatively poor,and H2O2 might cause certain toxicity which partly limited the applications in CTE.Chapter 3 fabricated a fast-forming BMSCs-encapsulated double network(DN)hydrogel via ultrasonically induced SF and bioorthogonal reaction crosslinking.Recently,bioorthogonal reactions have attracted considerable attentions in biomedical filed,and they occur between specific groups under physiological conditions.In addition,DN hydrogels possess excellent mechanical properties in comparison with the traditional single network hydrogels.In this study,bioorthogonal pairs(2-cyanobenzothiazole(CBT)and cysteine(Cys))were modified onto 4-arm poly(ethylene glycol)(PEG)which allowed the 4-arm PEG to crosslink within several seconds.Meanwhile,SF was induced to form the ?-sheet structure via ultrasonication to further improve the mechanical properties of the hydrogels.The results suggested that this BMSCs-laden DN hydrogel showed excellent mechanical strength and provided a suitable microenvironment for BMSCs survival,growth and differentiation in vitro.In addition,together with TGF-?1,the quantity and quality of the in vivo restored cartilage were significantly improved.However,such a kind of hydrogel still possessed some shortcomings,for example,the addition of DTT might have a certain impact on the activity of cells which needed further optimization.Chapter 4 developed an injectable Col-PEG-SF DN hydrogel system with both good biological and mechanical properties.Col-Norbornene(Nb)and PEG-Tetrazine(Tz)were synthesized to rapidly form the Col-PEG hydrogel which could gelate within several seconds based on the bioorthogonal reaction between Nb and Tz.Meanwhile,SF was ultrasonically induced to form the SF hydrogel via ?-sheet structure.The results demonstrated that Col-PEG-SF DN hydrogel po-ssessed excellent biocompatibility,short gelation time and good mechanical properties,which was suitable for cartilage repair.Moreover,this BMSCs-laden DN hydrogel together with TGF-?1 could efficiently promote the regeneration of cartilage both in vitro and in vivo.Compared to the hydrogels above,the Col-PEG-SF DN hydrogel possessed several advantages,for example,no catalyst was needed in this system which endowed the hydrogel with excellent biocompatibility,moreover,the mechanical property was also enhanced which makes it appealing for CTE applications.