Preparation And Osteogenic Activity Of Chitin Whisker Composite Liquid Crystal Hydrogels

The liquid crystal(LC)property and viscoelasticity of natural bone ECM play a decisive role in guiding cell behavior,conducting cell signal and regulating mineralization.Under certain conditions,the aqueous suspension of chitin whisker(CHW)can exhibit a typical cholesteric LC texture similar to that of liquid crystalline collagen,which forms the framework of natural bone.However,the suspension of the CHW has the defect of unstable nature.In recent years,hydrogels have been widely used to prepare bone tissue repair materials with the viscoelasticity mimicking natural bone ECM.However,the rate of stress relaxation of chemical crosslinked hydrogels is slow.In addition,bone tissue engineering scaffold materials should have connected pore structure and appropriate porosity,while 3D-printed PLLA scaffolds have controllable porosity,but they are faced with defects such as inadequate osteogenic activity.Based on the above considerations and analysis,in this paper,the LC properties of CHW are highly utilized to construct the composite bone tissue engineering scaffold materials with LC properties and viscoelasticity that mimicking natural bone ECM.Centering on this research purpose,the following research works has been carried out:1.First,CS solution was introduced into CHW aqueous suspension and the LC mixed suspension was prepared by ultrasonic treatment.Then,the CHW/CS LC composite hydrogels with different ratios of CHW and CS were prepared using geniping as a crosslinking agent.The results indicated that the introduction of CS not only did not destroy the LC properties of CHW,but also greatly improved its mechanical properties.A freezing/salt solution treatment strategy was further adopted,and the chemical and physical dual-crosslinked CHW7.5CS0.8-I LC composite hydrogel with a certain fold structure on the surface was prepared.The as-prepared composite hydrogel not only showed good birefringence,but also had certain resilience and more obvious stress relaxation behavior.In addition,the mechanical properties of the composite hydrogel were further improved,and the maximum Young modulus is up to 46.58 ± 1.38 k Pa.Cell experiments in vitro showed that the LC properties and viscoelasticity of the composite hydrogels can effectively improve and influence the adhesion,proliferation and osteogenic differentiation of mouse bone marrow mesenchymal stem cells(BMSCs)through cell-matrix interaction based on mechanical transduction.2.In order to better simulate the 3D structure and properties of natural bone,PLLA scaffolds were fabricated by using 3D printing,which was further surface modified by polydopamine(PDA)to obtain PLLA-PDA scaffolds.Then,the CHW/CS LC hydrogel precursor was successfully perfused into the holes of the PLLA-PDA scaffold based on vacuum impregnation and chemical crosslinking.Then the orientation channel structure of LC hydrogel in the scaffold was fabricated by freeze casting/freeze drying technology.On this basis,the as-prepared PP-CHW/CS-P composite scaffold was treated with phytic acid solution to endow the composite scaffold with oriented dual-crosslinked LC hydrogel,moreover,the effects of phytic acid solution with different concentrations on the properties of the as-prepared composite scaffold were investigated.The results showed that the structure of gel network affects the LC properties and mechanical properties of composite scaffolds.By using 10% phytic acid solution physical crosslinking LC hydrogel in the composite scaffold,the as-prepared PP-CHW/CS-P-10% composite scaffold can not only retain its good orientation structure and LC properties,but also further improve its mechanical properties,and the composite scaffold showed the maximum compressive strength of 14.0995 ± 0.23122 MPa,and the maximum Young’s modulus of 176.7715 ± 0.40234 MPa under dry condition.3.Based on the research in the previous chapter,the antibacterial activity of the PP-CHW/CS-P-10% composite scaffold was further tested,moreover,BMSCs were used to conduct cell experiments on PP-CHW/CS-P-10% composite scaffold in vitro.The results showed that phytic acid treatment endowed the composite scaffold with strong antibacterial activity.Moreover,the introduction of CHW/CS LC hydrogel network and phytic acid can effectively improve the cell adhesion behavior and promote cell proliferation and osteogenic differentiation on the composite scaffold.In addition,the PP-CHW/CS-P-10% composite scaffold has an oriented layered structure that can induce highly oriented cell growth.