Experimental Study On The Functional Recovery Of Cardiac Ischemia-Reperfusion Injury In Rats Of Injectable Conductive Hydrogel Polypyrrole-Chitosan

Objective:To investigate the effectiveness and mechanism of conductive hydrogel polypyrrole-chitosan（PPY-CHI）in the treatment of cardiac function recovery after left ventricular ischemia-reperfusion in rats.Methods:Using ferric chloride hexahydrate as redox agent,polypyrrole was grafted onto the biological material chitosan by one-step redox method,and glutaraldehyde was used as crosslinking agent for agglutination to construct a conductive composite PPY-CHI hydrogel,which was controlled by 2%CHI hydrogel alone.In vitro,the conductivity of the composite PPY-CHI was detected by cyclic voltammetry.Adjust the dosage of glutaraldehyde and observe the gelling agglutination time of PPY-CHI and CHI.In a2.5cm Petri dish,PPY-CHI and CHI were formed into 2mm thick sheets,dried and dehydrated,and their ultrastructure was observed by scanning electron microscopy.In vivo,a rat IRI model was prepared by programmed blockade and reperfusion of the left ventricular anterior descending branch,and surface II lead ECG and ultrasound were used to evaluate whether the modeling was successful.After successful modeling,the animals were randomly divided into 3 groups（PPY-CHI group,CHI group,Saline group n=10）,and 200ul PPY-CHI,CHI and Saline were injected into infarction and surrounding areas.At 14,28,42,56,70 and 84 days after treatment,echocardiography was used to evaluate the changes of cardiac mechanical function,and ECG was used to observe the electrophysiological changes of the heart.At the end of the experiment,the change level of cardiac pump function was detected by the pressure volume curve,and the tissue resistance of myocardial infarction and limbic region between different groups was measured by four-probe resistance meter.The action potential level of different regions was detected by the 8-head electrode catheter on the surface of the heart.Fluorescent electric standard detection technology was used to detect the longitudinal conduction rate of the left ventricular body surface.Induced arrhythmia stimulation measures the ability and severity of arrhythmias resistance in different treatment groups.A cardiac specimen was collected,cut into a 2 mm transverse cutting ring,measured the lateral size of the left ventricular end-diastolic stage,and the fiber content of the anterior wall of the left ventricle was measured by Mason staining to assess the level of ventricular remodeling.Results:1.PPY-CHI aqueous solution can be synthesized by one-step redox method,which is generally observed as black,and hydrogel can be formed by adding glutaraldehyde;The conductivity of PPY-CHI is（3.19±0.03）×10^-3m S/cm.CHI conductivity is（1.19±0.13）×10^-3m S/cm.The gel time of both is about 30s;Biocompatibility confirmed:SMC was cultured on the two materials without difference,similar to conventional dishes,with good biocompatibility.The ultrastructure showed that the surface void of PPY-CHI was large,which was conducive to cell fixation.2.The rat cardiac IRI model can be induced by sequential clamping of the left anterior descending branch of the left crown,and the US shows that the left ventricular EF%is less than 30%,and the ECG shows wide malformed QRS wave on the ECG and ST segment elevation.3.After treatment,the recovery of cardiac function in different treatment groups changed differently with time.In the PPY-CHI group at 14,28,42,56,70,and 84 days after transplantation:EF values increased by 22%at 84 days after transplantation.FS values increased by 34%at 84 days post-transplantation.LVIDs decreased by 6%at 84days post-transplantation;CHI group:EF value did not change significantly increased by7%84 days after transplantation.FS value increased by 3%84 days after transplantation;The value of LVIDs increases slowly.Saline group:EF values decreased or did not change.The FS value is almost unchanged.The value of LVIDs is increasing.The P-V volume curve shows that the EF value of the PPY-CHI group is about 45%higher than that of the CHI group and the Saline group.The dp/dt max in the PPY-CHI group was twice that of the CHI group.The dp/dt max in the PPY-CHI group was 3 times that of the Saline group.The dp/dt min in the PPY-CHI group was 3 times that of the CHI group/Saline group.The EDV in the PPY-CHI group was 6%shorter than that in the CHI group.EDV in the PPY-CHI group was 17%shorter than in the Saline group.The ESV of the PPY-CHI group was 18%shorter than that of the CHI group.ESV was shortened by 27%in the PPY-CHI group compared with the Saline group.4.After treatment,cardiac electrophysiological changes in different treatment groups.In terms of ECG:the QRS interval in the PPY-CHI group was shortened by 28%.The QRS interval was shortened by 14%in the CHI group.The QRS interval in the Saline group was shortened by 3%.The QT interval in the PPY-CHI group was shortened by 25%.The QT interval in the CHI group was shortened by 7%.The QT interval in the Saline group continued to prolong;QTc interval:the QTc interval was shortened by 23%in the PPY-CHI group;The QTc interval in the CHI group was shortened by 6%.The QTc interval was extended by 3%in the Saline group.In vivo tissue resistance:the resistance of myocardial infarction scar area in the PPY-CHI group was about 20%lower than that in the CHI group and the Saline group.The 8-lead voltage detection on the surface of myocardium showed that the voltage amplitude of the infarct scar area of the PPY-CHI group/the voltage amplitude of the normal area was about twice that of the CHI group and the Saline group.Fluorescence electric label measurement:the electrical conduction velocity of PPY-CHI group was 636mm/s,which was 18%faster than that of CHI group and 31%faster than that of Saline group.The PES score showed that the PPY-CHI group was 2.75±1.79,the CHI group was 6±1.15,and the Saline group was5.29±1.16.the PPY-CHI group had lower scores and stronger anti-arrhythmia.The PPY-CHI treatment group had the characteristics of low tissue resistance,high local voltage,fast conduction velocity,low PES score,and good recovery of cardiac mechanical function and electrophysiological function.5.The histological level showed that the left ventricle in the PPY-CHI treatment group had the shortest diameter in the diastolic period,less collagen fiber components in the tissue,and low ventricular remodeling.Conclusion:PPY-CHI hydrogels can be successfully synthesized by one-step redox method with high in vitro conductivity and biocompatibility.When injected into the fibrotic scar area and marginal area of the ischemic heart,it can significantly improve the mechanical and electrophysiological function of the heart,and the main possible mechanism is to reduce the tissue resistance of the scar area and integrate the infarct area with normal myocardial tissue electrical conduction.PPY-CHI hydrogels provide a new strategy for the use of cardiac tissue engineering techniques to repair cardiac ischemia-reperfusion injuries.