Preparation Of Piezoelectric Composite Hydrogels And Study Of Piezoelectric Effect To Enhance The Osteochondral Repair

Articular cartilage disease is a common clinical disease.Since natural cartilage is vascular-free,its regeneration capacity is limited and the current treatment can not provide a complete solution for cartilage disease.Hydrogels perform well in osteochondral repair by combining them with external stimuli because of their three-dimensional structure similar to that of natural cartilage.However,the method of field stimulation has some difficulty,which limits their application.Therefore,hydrogels that can stimulate cell activity spontaneously are of concern.Inspired by the piezoelectric effect of collagen in cartilage tissue,this work would focus on the design of a biomimetic hydrogel.By introducing piezoelectric materials into hydrogel,piezoelectric properties of hydrogels can be endowed,thereby generating electrical signals under the stress field of hydrogels,to stimulate cell proliferation and differentiation,and promote tissue regeneration.In order to better verify the piezoelectric-enhanced repair mechanism of osteochondral,our strategy is to hope that the repair effect of the material itself is not so prominent otherwise it will cover up the repair effect brought by the piezoelectric effect.Therefore,we would choose the traditional polyvinyl alcohol hydrogel as the osteochondral repair materials.But,pure PVA hydrogel cannot obtain good osteochondral repair ability because of its low biodegradability and bioactivity.Therefore,we can better study the effect of piezoelectric performance on osteochondral repair and its mechanism of promoting cartilage formation in such PVA system.In this study,we thus used polyvinyl alcohol(PVA)as matrix material and added polyvinylidene fluoride(PVDF)to obtain PVA/PVDF piezoelectric hydrogels.The piezoelectric properties of the materials were elevated by the addition of nano-silver and meanwhile antibacterial properties were also endowed.When ethanol was used to remove the organic solvent,the swelling rate and compressibility of the material were also regulated.To better simulate osteochondral tissue,we designed and prepared a bilayer hydrogel where nano-silver wire was doped into the chondrogenic layer whilst nano-HA was doped into the osteogenic layer to mimic osteochondral tissue.The contents and results of this study are shown as follows:1.Preparation and characterization of PVA/PVDF piezoelectric hydrogels: Piezoelectric hydrogel was prepared by solution mixing method.The infrared characterization results showed that there was no chemical bonding between PVA and PVDF,and there were still piezoelectric β phase characteristic peaks.The results of piezoelectric test showed that the material had piezoelectric voltage and when the concentration of PVA and PVDF was15wt%,the value of piezoelectric voltage was 0.15 V.Swelling experiments showed that PVA15/PVDF15 composite material had a relatively low swelling ratio of about 60%,which was about 120 times lower than PVA pure hydrogel.Thus,PVA15%/PVDF15% hydrogel was used for the late experiments.2.Preparation and characterization of PVA/PVDF/Ag NWs piezoelectric hydrogels:When the Ag NWs was added into PVA/PVDF hydrogel,the piezoelectric voltage of the material was obviously increased to more than 0.3 V.The residual organic solvents were removed by ethanol and meanwhile the swelling and mechanical properties of the materials were also adjusted by ethanol.Subsequently,the physical and chemical properties of the material were analyzed by a series of characterization methods.The results showed that when the ethanol concentration was 70%,the swelling rate of the hydrogel was about 40%,and the compression modulus reached 0.42 MPa,which can match the level of natural articular cartilage well.The results showed good mechanical stability in the cyclic loading test.The results of DMA and SEM showed that the hydrogel had a three-dimensional network structure,and that the pore size of hydrogel was about 50 mm and that PVA and PVDF presented an obvious two-phase separation state.On this basis,nano hydroxyapatite(HA)was used to prepare double layer hydrogel.The results from the energy spectrum analysis showed that both silver nanowires and hydroxyapatite were evenly distributed in the material.3.Biological evaluation of piezoelectric hydrogels: After 7 days of co-culture of materials and cells,the proliferation activity of cells did not change obviously,and the cell morphology was normal.In vitro hemolysis test,the hemolysis rate of piezoelectric hydrogel was only 2%,and no hemolysis reaction occurred.In the antimicrobial experiments,the piezoelectric hydrogel showed excellent growth inhibition for E.coli and S.aureus(inhibition rate of 98%).4.Rabbit osteochondral defect model was used to evaluate the repair effect of piezoelectric hydrogel.The results showed that compared with PVA/HA hydrogel and blank group,piezoelectric hydrogel effectively promoted the regeneration of osteochondral defects.There was no obvious dent surface at the defect,the regenerated surface was smooth,the boundaries disappeared,and the surrounding tissues were well integrated,and the color of new tissues tended to be that of host tissues.