In vitro comparison of harvesting site effects on cardiac extracellular matrix hydrogels.

Cardiac extracellular matrix (cECM) derived hydrogel has been investigated to treat myocardial infarction through animal studies and clinical trials. The tissue harvesting site commonly selects porcine left ventricle (LV) because heart attack majorly takes place in LV. However, little is known about whether the region of cardiac tissue harvesting is critical for downstream applications. In this work, in vitro studies to compare cECM hydrogels derived from adult porcine whole heart (WH), LV, and right ventricle (RV) were performed. The cECM from WH has similar chemical composition compared with cECM from LV and RV. All three types of cECM hydrogels share many similarities in terms of their microstructure, gelation time, and mechanical properties. WH-derived cECM hydrogels have larger variations in storage modulus (G') and complex modulus (G*) compared with the other two types of cECM hydrogels. Both human cardiomyocytes and mesenchymal stem cells could maintain high cell viability on all hydrogels without significant difference. In terms of above results, the cECM hydrogels from WH, LV and RV exhibited similarity in material properties and cell response in vitro. Thus, future fabrication of cECM hydrogels from WH would increase the yield, which would decrease processing time and production cost.

A microfluidic device for noninvasive cell electrical stimulation and extracellular field potential analysis.

We developed a device that can quickly apply versatile electrical stimulation (ES) signals to cells suspended in microfluidic channels and measure extracellular field potential simultaneously. The device could trap cells onto the surface of measurement electrodes for ES and push them to the downstream channel after ES by increasing pressure for continuous measurement. Cardiomyocytes, major functional cells in heart, together with human fibroblast cells and human umbilical vein endothelial cells, were tested with the device. Extracellular field potential signals generated from the cells were recorded. We found that under electrical stimulation, cardiomyocytes were triggered to alter their field potential, while non-excitable cells were not triggered. Hence this device can noninvasively distinguish electrically excitable cells from electrically non-excitable cells. Results have also shown that increased cardiomyocyte cell number led to increased magnitude and occurrence of the cell responses. This relationship could be used to detect the viable cells in a cardiac tissue. Application of variable ES signals on different cardiomyocyte clusters has shown that the application of ES clearly boosted cardiomyocytes electrical activities according to the stimulation frequency. In addition, we confirmed that the device can apply ES onto and detect the electrical responses from a mixed cell cluster; the responses from the mixed cluster is dependent on the ratio of cardiomyocytes. These results demonstrated that our device could be used as a tool to optimize ES conditions to facilitate the functional engineered cardiac tissue development.