Abstract: BACKGROUND: Conductive biomaterials are considered potential candidates for transmitting electrical signals for myocardial repair. Combining cell-based or cell-free strategies with conductive biomaterials to replenish cardiomyocytes and/or restore electrical signaling pathways is a promising approach for cardiac repair.
OBJECTIVE: To evaluate the effect of polypyrrole-chitosan conductive composite hydrogel on cardiac function in rats with myocardial ischemia-reperfusion injury.
METHODS: The polypyrrole-chitosan conductive composite hydrogel was prepared by chemical oxidative polymerization. The micromorphology, biocompatibility and conductivity of the hydrogels were characterized. Thirty adult SD rats were selected to establish a myocardial ischemia-reperfusion injury model by clamping the left anterior descending branch of the heart and then releasing it. After 21 days of modeling, the rats were divided into three groups by the random number table method: Normal saline was injected into the left ventricular infarction area and infarction margin area in the blank group. Chitosan hydrogel was injected into the left ventricular infarction area and infarction margin area in the ordinary hydrogel group. The polypyrrole-chitosan conductive composite hydrogel was injected into the left ventricular infarction area and infarction margin area, with 10 rats in each group. The corresponding time points after modeling were set, and cardiac mechanical function (echocardiogram, pressure-volume analysis), cardiac electrophysiology (electrocardiogram, programmed electrical stimulation, optical mapping technology, microelectrode array technology, eight-lead electrocardiogram, and electrical resistivity of the scar area) and cardiac histology were detected. 
RESULTS AND CONCLUSION: (1) There were a lot of pores on the surface of the conductive composite hydrogel, and the conductivity was (3.19±0.03)×10-3 mS/cm, which had good biocompatibility co-cultured with smooth muscle cells. (2) After 105 days of modeling, echocardiogram and pressure-volume analysis showed that compared with the blank group and the ordinary hydrogel group, the conductive composite hydrogel could significantly improve the contractile function of the heart of rats with myocardial ischemia-reperfusion injury. The results of electrocardiogram, programmed electrical stimulation, optical mapping technology, microelectrode array technology, eight-lead electrocardiogram, and electrical resistivity of the scar area examination at 105 days after modeling displayed that, compared with the blank group and the ordinary hydrogel group, the conductive composite hydrogel could significantly improve the electrical conduction function of the heart of rats with myocardial ischemia-reperfusion injury and reduce the occurrence of arrhythmia. Masson staining of heart tissue at 105 days after modeling exhibited that there were different degrees of fibrosis in the myocardial infarction area of the three groups. Compared with the normal saline group and the ordinary hydrogel group, the conductive hydrogel group had more normal myocardial tissue and less fibrosis in the myocardial infarction area. (3) The results verify that polypyrrole-chitosan conductive composite hydrogel may promote the repair of infarcted heart after ischemia-reperfusion injury by increasing the electrical conduction velocity of infarct scar area tissue, increasing scar thickness, enhancing synchronous cardiac contraction, and reducing damaged tissue. 

Key words: conductive biomaterial, polypyrrole, chitosan, hydrogel, ischemia-reperfusion injury, cardiac tissue engineering