Preparation Of Magnetic Injectable Self-healing CS/SH Secondary Hydrogel And Study Of Its Self-healing Mechanis

Intervertebral disc degeneration is a long-term irreversible process caused by a variety of factors.Currently,there are many treatments for low back pain caused by intervertebral disc degeneration.However,none of them can entirely solve the continuing intervertebral disc degeneration,let alone restore and rebuild the structure and function of the affected intervertebral disc.Nevertheless,when the nucleus pulposus tissue has just undergone degeneration at the early stage of intervertebral disc degeneration,hydrogels loaded with seed cells of differentiation potential can be injected into the nucleus pulposus tissue of the diseased intervertebral disc through minimally invasive surgery to replace the nucleus pulposus cells that have undergone degeneration.This newly reported strategy helps to delay the degeneration of nucleus pulposus and even rebuild the nucleus pulposus tissue and restore the normal structure and function of nucleus pulposus tissue.However,injectable self-healing hydrogels currently being used for nucleus pulposus tissue engineering still meet various problems,such as low mechanical properties,easy cell leakage,low cell proliferation,and differentiation rate originated from toxic crosslinking agents and easy infection.To the above problems,chitosan and sodium hyaluronate were selected as the main raw materials to provide biocompatibility and part of antibacterial properties in this work.Additionally,rod-like zinc oxide（R-Zn O）and magnetic rod-like zinc oxide（R-MZn O）were introduced into the samples to strengthen the antibacterial properties.Then,magnetic injectable self-healing hydrogels for tissue engineering of nucleus pulposus were easily prepared by a two-step method without toxic crosslinking agent and any modification of raw materials.The composition,structure and magnetism of the obtained samples were characterized.The mechanical properties,swelling properties,degradation properties and antibacterial properties of the materials were finely tested.The main research contents and results are as follows:（1）Using chitosan（CS）and sodium hyaluronate（SH）for preparing primary polyelectrolyte hydrogel,the suitable concentration of the two components was explored out to be 1%while the mixing ratio to be 2:1.The polyelectrolyte hydrogel is freeze-dried and grounded into powder.During the preparation of secondary gels,the properties of hydrogels were regulated by changing the concentration of calcium chloride and lyophilized gel powder.It is found that when the concentration of calcium chloride is 0.125M,the concentration of lyophilized gel powder is 8.5%,the gelation time of hydrogel is 8.8min,the compressive strength is 0.103Mpa when the deformation is 70%,the injection is smooth and complete,and the self-healing can be completed in12h,and the degradation and swelling rate are low,which can meet the use requirements of the core pulpoile material.Therefore,8.5%hydrogel has the best comprehensive performance.It is found that when the concentration of calcium chloride is 0.125M,the concentration of lyophilized gel powder is 8.5%,the gelation time of hydrogel is 8.8min,the compressive strength is 0.103Mpa when the deformation is 70%,the injection is smooth and complete,and the self-healing can be completed in 12h,and the degradation and swelling rate are low,which can meet the use requirements of the core pulpoile material.Therefore,8.5%hydrogel has the best comprehensive performance.（2）R-Zn O was prepared by hydrothermal method with the addition of zinc nitrate hexahydrate and ammonium carbonate,and polyethylene glycol 6000 for assistance.Then,the surface of R-Zn O was modified and make it negatively charged to be wrapped by nano-ferric oxide that had intrinsically had positive charges on the surface through electrostatic interaction.The products were named R-MZn O.Scanning electron microscope（SEM）was used to analyze the morphology of the sample,X-ray diffractometer（XRD）was used to analyze the composition and crystal structure of the sample,and X-ray photoelectron spectroscopy（XPS）was used to analyze the elemental composition and chemical valence state of the sample.The magnetic properties of the samples were analyzed by magnetic response performance（VSM）.The results showed that the prepared zinc oxide has rod-like structure,and the surface of zinc oxide was rough.XRD showed that hexagonal zinc oxide and ferric oxide were successfully prepared.XPS results showed that the elements of R-Zn O and R-MZn O are Zn,O,and Fe.The position of lattice oxygen peak in O1s of R-Zn O and R-MZn O were of clear difference,indicating the interaction between Zn O and Fe₃O₄.（3）During the preparation of secondary hydrogels,doping R-Zn O or R-MZn O can not only improve the mechanical properties of hydrogels,but also improve the antibacterial performance of hydrogels.The antibacterial performance of hydrogels was the best when the addition amount is 0.3%,and the antibacterial performance of R-MZn O is better than that of R-Zn O.（4）The hydrogels prepared in this paper showed no cytotoxicity to rat bone marrow mesenchymal stem cells.