Cardiac Cell Growth Supported By Biomimetic, Electrically-Conductive Polymer Substrate

Heart disease is the primary cause of mortality in the US, accountable for 25% of all deaths. Current therapies for heart disease do not regenerate damaged heart tissue. Developments in tissue engineering (TE) are leading to novel cell treatments to augment tissue repair.  Using pluripotent stem cells it is possible to generate contracting cardiomyocytes (CMs). However, current approaches result in CMs which have heterogeneous, immature electrical properties. We hypothesize that by growing CMs on an electrically-conductive material, which mimics the electrical properties of native heart tissue, the cells will be more homogeneous and have improved electrical properties. To test this, polypyrrole (PPy), an electrically-conductive polymer, was coated on polycaprolactone (PCL) to form PPy-PCL.  PPy-PCL has shown promise in neural TE applications. First, PCL was prepared by solvent-casting in DCM, flattened with a melt press, and punched into 20mm diameter scaffolds. PCL samples were then either treated with NaOH (3M; 0, 24, or 48 hours) to modulate hydrophobicity or coated with PPy. PPy-PCL was prepared via chemical polymerization of the PPy using ferric chloride as an oxidant. Materials were characterized through SEM, electrical-resistivity tests, and water contact angle (WCA) measurements.  A murine CM cell-line, HL-1s, were grown on PPy-PCL or on NaOH-treated PCL and cell viability, spread, and morphology were characterized using LIVE/DEAD assay and nuclear stains. PPy-PCL has a resistivity of 1.0 ± 0.4 kΩ compared to the uncoated-PCL which has infinite resistance. The NaOH-PCL saw a decreased WCA with increased NaOH-treatment. PCL that underwent 0, 24, and 48 hours of NaOH treatment had a WCA of 77 ± 3°, 35 ± 5°, and 24 ± 5° respectively. PPy-PCL had an effective WCA of 0° due to the super-hydrophilic nature of PPy. Adherent cells per area were: 290,000 ± 20,000 cells/cm², 160,000 ± 14,000 cells/cm², 360,000 ± 30,000 cells/cm², and 400,000 ± 40,000 cells/cm² for 0, 24, 48 hours of NaOH treatment and PPy-PCL respectively. Results indicate that PPy-PCL may offer a suitable, electrically-conductive, polymer substrate for use in cardiac TE. Future work will focus on characterization of cell-communication through analysis of electrical wave propagation, and protein expression, electrical stimulation of cells on the materials, and the effects of the materials on stem-cell differentiation into fully-functioning, homogeneous CMs.