Construction Of High-Strength Pva Hydrogel Fibers With Tendon-Like Modulus And Study On Their Application In Tendon Stress Monitoring

Tendons connect the body’s bones and muscles at the joint,to help assisting and stabilizing the joint,and are therefore often subject to high levels of stressful movement.Such tissue exhibits a slow metabolism,low oxygen consumption,low vascular and cellular distribution.When injury occurs at tendon,the recovery period takes longer.Meanwhile,it is quite difficult to quantitatively assess the load on the tendon during this period in a timely manner,making it highly susceptible to secondary injury.Implanting strain sensors that match the mechanical properties of the tendon into the damaged tissue,which can take up the stress and at the same time sensitively monitor the mechanical stimulus signals at the tendon site,is an effective strategy to address above problems.Traditional clinical tendon repair materials are PET fibers,which do not have intrinsic conductivity and cannot realize intelligent sensing.Mechanical sensing properties can be imparted by coating methods,which would be accompanied with stability problems of the coating.Hydrogel materials are widely used in the field of tissue engineering due to their good biocompatibility and unique three-dimensional network structure.However,due to the high water content,hydrogels are much weaker than tendons and cannot satisfy the requirements for mechanical properties（tensile strength of tendon:～10 MPa,Young’s modulus:374.24±106.12k Pa）,and small strain sensing（tendons generally<5%）when implanted in tissues.Most of the current research has only focused on the strength,strain sensitivity,or fiber forming of hydrogels,while few reports on the preparation of hydrogel fibers that combine excellent mechanical strength,high sensitivity at small strain,implant stability,and biocompatibility.In this study,polyvinyl alcohol（PVA）,a water-soluble polymer rich in hydroxyl groups,was used as the hydrogel substrate and graphene oxide（GO）as the conductive filler to achieve in-situ fiber formation in capillary was achieved through"freeze-thaw cycle".The mechanical strength of hydrogel fibers was further enhanced after salting out.Hydrogel fibers with high strength,anti-swelling property and good resilience were obtained.Scanning electron microscopy,Fourier infrared spectroscopy,X-ray diffraction and mechanical testing were employed to investigate the structure and comprehensive performance of the hydrogels.According to the changes in the structure of hydrogel fibers,the interaction between ions and polymers was clarified.The results show that the utilization of freezing and salting out cycles can effectively reduce the hydration capacity of PVA,thus promoting the formation of hydrogen bonds between polymer molecular chains.With the increase of crystallinity and cross-linking density,outstanding mechanical and anti-swelling properties of hydrogel fiber were realized.On such basis,after the introduction and reduction of GO,such hydrogel fibers exhibits better sensing sensitivity at small strain.When GO addition was 0.8 wt%,the corresponding fibers P-2.5 Na₃Cit/0.8 GO possessed the tensile strength of 8.38±0.51 MPa and Young’s modulus of 1.20±0.09 MPa,which were of the order of magnitude of the mechanical properties of the damaged tendon.In addition,the P-2.5 Na₃Cit/0.8 GO hydrogel has low strain detection（0-5%）and high sensing sensitivity（1.12）,satisfying the requirements of high strength and low strain monitoring.Besides,cytocompatibility experiments,in vitro repair model tests and in situ monitoring of in vivo implantation were conducted in collaboration with Huashan Hospital.The results showed that the fiber sensor exhibits excellent biocompatibility and in situ sensing stability,providing a new strategy for monitoring tendon repair and subsequent treatment.