Long-Term Improvement Of Cardiac After Chronic Myocardial Infarction With Injectable Conductive Hydrogel PPY-CHI

Objective:To investigate the long-term effectiveness and possible mechanism of injectable conductive hydrogel chitosan and Polypyrrole-Chitosan（PPY-CHI）in promoting functional recovery after myocardial infarction in rats.Methods:The conductive aqueous solution PPY-CHI was synthesized by one-step redox method,and the conductive hydrogel was formed by glutaraldehyde cross-linking method with 2%chitosan（CHI）as the control;the conductive properties and electrical conduction damage rate of PPY-CHI were determined by four-probe method and its electrochemical properties were studied;the biocompatibility was studied by co-culture with NRVMs and detection of cell number and expression levels of marker proteins Cx-43 and SARC.In vivo,an SD-rats myocardial infarction（MI）model was formed by ligation of the anterior descending branch of the left ventricle,and four weeks later,cardiac function was assessed by ultrasound.LVFS less than 25%MI rats were randomly divided into three groups,and equal volumes of PPY-CHI,CHI hydrogel and saline were injected into the infarct and marginal zone.Echocardiography was used to assess LVEF,LVFS,and LVIDd changes with time at4,8,12 and 22 weeks after transplantation.At the end of treatment,cardiac tissue resistance was assessed by four probes,heart specimens were harvested,immunofluorescence staining was applied to detect capillary density and assess the pro-angiogenic ability of PPY-CHI,and Masson staining was applied to detect the collagen content of the LV anterior wall and assess the level of ventricular remodeling.Results:1、Successful aggregation of pyrrole monomers into polypyrrole and riveting on a chitosan backbone in a redox reaction containing Fe Cl₃,with glutaraldehyde enabling the formation of PPY-CHI conductive hydrogels;2、PPY-CHI agglutination time was（26.4±2.19）s,which was not different from CHI;PPY-CHI and CHI conductivity were（15.54±2.19）x10^-3S/cm and（2.79±0.74）x10^-3S/cm,respectively,with statistically significant differences;at 0.5cm,1.0cm,1.5cm,and 2.0cm distances voltage values were PPY-CHI:（76.58±9.39）m V,（69.88±10.71）m V,（60.12±11.26）m V,（53.64±10.58）m V,CHI:（30.8±3.20）m V,（18.34±1.74）m V,（11.74±1.87）m V,（5.98±1.41）m V,respectively,and the differences were statistical significance that PPY-CHI has great electrical conductivity and low loss of electrical signal during its internal conduction;3、NRVMs could adhere and grow on PPY-CHI containing,CHI coated culture dishes,and their cell numbers,rhythmic beating,CX-43 and SARC expression levels did not differ explicitly from those on conventional culture dishes,showing great biocompatibility;4、The left ventricular anterior descending branch line embolus ligation method could successfully construct a rat MI model,and PPY-CHI and CHI hydrogel could be transplanted into the infarct and borderline areas by intracardiac injection.At 22weeks post-transplantation,LVEF,LVFS,and LVIDd increased in the PPY-CHI group compared to post-infarct:（16.6±1.82）%,（10.64±0.55）%,and（2.208±0.02）mm,respectively,and LVEF,LVFS,and LVIDd increased in the CHI group compared to post-infarct:（10.4±6.88）%,（3.8±1.64）%,and（3.35±0.03）mm,and LVEF,LVFS,and LVIDd in the Saline group increased compared to post-infarction:（5.2±5.59）%,（1.2±1.92）%,（3.63±0.15）mm,respectively;5、At the end of the experiment,the ratio of resistance value at myocaardial ibfarction site to marginal region in the groups of PPY-CHI,CHI and Saline groups were:（92.74±6.21）%,（92.53±5.24）%,and（81.25±6.02）%,respectively,and immunofluorescence staining showed that the percentage of fluorescence intensity in the three groups:（8.22±1.06）%,（6.73.11±0.36）%,and（4.21±0.99）%,respectively,and Masson staining showed that the percentage of collagen in the three groups:（25.63±0.40）%,（19.11±0.69）%,and（14.59±0.79）%;The above data suggest that PPY-CHI has lower tissue resistance and significantly increased capillary density and scar debulking wall thickness compared to the Saline and CHI groups.Conclusion:The injectable conductive hydrogel has great injectability,conductivity and biocompatibility,and is a good carrier for cell growth.Intramyocardial injection of PPY-CHI can continuously reduce the resistance of scar tissue,promote angiogenesis,reduce the tissue resistance of scar area and inhibit ventricular remodeling,promote the repair of cardiac function after chronic myocardial infarction,and point out a new strategy for the prevention and treatment of chronic ischemic cardiomyopathy.