3D Printing Of High Strength Biohybrid Gradient Hydrogel Scaffolds For Efficient Repair Of Osteochondral Defect

In this work,a high strength thermoresponsive supramolecular copolymer hydrogel was synthesized by one-step copolymerization of dual hydrogen bonding monomers,N-acryloyl glycinamide and N-[tris?hydroxymethyl?methyl]acrylamide.The NAGA/THMMA copolymer hydrogel?PNT hydrogel?demonstrated temperature sensitive reversible gel?sol transition and shear-thinning behaviors.Copolymerization of THMMA could mitigate the hydrogen bonding interactions of PNAGA,thus resulting in a decrease of extrusion temperature on one hand,and aid in stabilizing swelling of the hydrogels on the other hand.Further,in biomimicking articular cartilage-subchondral bone architecture,a bilayer biohybrid gradient hydrogel scaffold with gradient compositions of TGF-?1 loaded on the top layers and?-TCP incorporated on the bottom layers was fabricated by a one-step thermal-assisted extrusion printing technique.The resultant gradient scaffold maintained the high fidelity and resolution of architecture,featuring highly interconnected porosity and desirable mechanical properties as well as excellent biocompatibility.The introduction of?-TCP not only improved the physicochemical properties of the scaffolds,but also stimulated the proliferation,ALP activities and differentiation of hBMSCs.Meanwhile,loading TGF-?1 improved the growth and chondrogenic differentiation of the hBMSCs.In vivo animal evaluation further verified that the biohybrid gradient hydrogel scaffolds could simultaneously promote the regeneration of both cartilage and subchondral bone within osteochondral defects.Further,we constructed a biodegradable high-strength hydrogel that could be3D-printed to bioscaffolds that could provide a mechanical support in the early stage of osteochondral repair,and be eventually degraded with the growth of the new tissue.First,inspired by stimuli-responsive remarkable changes in consistency?hardening,softening,autolysis?of sea cucumbers,we synthesized a supramolecular polymer?SP?hydrogel directly by photoinitiated aqueous polymerization of N-acryloyl 2-glycine monomer containing one amide and one carboxyl group on the side chain.The protonation/deprotonation as well as the ability to complex metal cations of carboxyl groups,confered a number of unique properties to PACG hydrogel,including pH/ion responsiveness,self-healing properties,and autolysis.Then,we combined ACG with methacrylated gelatin?GelMA?to construct a hydrogen bonding strengthened P?ACG/GelMA?hydrogel,which had better mechanical properties and biocompatibility,and could be degraded by collagenase.The incorporation of GelMA made the ACG/GelMA printable and UV light irradiation could stabilize the 3D printed scaffolds.To enhance the repair efficacy of osteochondral defect,we printed biohybrid gradient hydrogel scaffolds with loading Mn²⁺and bioactive glass?BG?on the top layers and the bottom layers,respectively.The animal experiment is underway to determine the in vivo repair effect.The 3D printing technique in conjunction with the high performance hydrogels may extend the application scope of noncovalent bonding reinforced-hydrogels,offering a promising strategy for integrated repair of osteochondral defects.