Engineering of Thick Human Functional Myocardium via Static Stretching and Electrical Stimulation

Human cardiac-muscle patches (hCMPs) constructed from cardiomyocytes (CMs) that have been differentiated from human induced-pluripotent stem cells (hiPSCs) can fully replicate the genetic background of each individual patient and, consequently, can be used for personalized drug testing, disease modeling, and therapeutic applications. However, hCMPs produced via conventional techniques are relatively thin and typically contain hiPSC-CMs that are structurally and functionally more similar to CMs from fetal and neonatal hearts than from the hearts of adults. Here, we used our layer-by-layer (lbl) fabrication protocol to construct thicker (>2.1 mm), triple-layered hCMPs, and then evaluated hiPSC-CM maturity after ten days of standard culture (Control hCMPs), static stretching (Stretched hCMPs), or static stretching with electrical stimulation at 15 or 22 V (Stretched+15V or Stretched+22V hCMPs, respectively). Qualitative assessments of immunofluorescently stained hCMPs suggested that the expression and alignment of contractile proteins was greater in Stretched+22V hCMPs than in hCMPs from any other group, while quantitative assessment of mRNA abundance and protein expression via Western Blot analysis identified changes in patterns of gene expression that also suggested the Stretched+22V protocol significantly enhanced hCMP maturation. Images obtained via transmission electron microscopy indicated that static stretching and electrical stimulation were associated with dramatic increases in the development of Z-lines and gap junctions, and sarcomeres were significantly longer in hCMPs that underwent any of the maturation protocols than in Control hCMPs. Collectively, these observations confirm that our lbl fabrication protocol can be used to generate hCMPs of >2.1 mm thickness, and that hCMP maturity increased dramatically after just ten days of static stretching and electrical stimulation.