Engineering cardiac microenvironments for func onal drug safety screening

Cardiotoxic side effects of non‐cardiovascular pharmaceutical agents reported in the late 1980’s resulted in the safety and efficacy testing guidelines that is used today to evaluate the risk of adverse cardiac effects. However, the current testing method relies on single ion channel testing which has low specificity and results in unnecessary dismissal of potential new drug candidates.

Attrition of drug candidates in the late development phases is associated with high costs in addition to the inconvenience to patients missing out on potential useful pharmaceuticals. The use of human induced pluripotent stem cells (hiPSCs) is heavily explored to reach a more human relevant testing model.

Both single cell testing with a multiple ion channel approach and the development of engineered cardiac tissues in vitro are explored. Engineered cardiac tissues benefits from increased physiological relevance compared to single cell testing as the development potential of stem cell derived cardiomyocytes increases in a 3D environment.

Further, engineered cardiac tissues rely on the response from a syncytium of cells with an increased physiological response resembling that of the adult myocardium. This work focuses on the formation of engineered cardiac tissues by developing a cell seeding multiassay platform (MAP) with room for multiple in vitro tissues cultured in parallel.

The manufacturing approach uses a novel stereolithographic 3D printing approach to produce MAPs in a compliant non‐toxic material. MAPs contain mechanical microenvironments to promote tissue formation including vertical flexible posts with tunable stiffness. Characterization of mechanical properties gives the opportunity to support easy read‐out of tissue contraction force using optical tracking.

When a cell‐loaded scaffold material with muscle mimicking stiffness is seeded into the designed MAPs, engineered tissues self‐assemble around the flexible posts to form a defined in vitro tissue. Mouse myoblast cells form a confined tissue strip within 3 days of culture with uniaxially aligned cells.

The tissue formation can be tracked by following the deflection of the flexible posts during tissue compaction. Upon culturing cardiac progenitor cells inside MAPs the resulting engineered cardiac tissues are synchronously beating suggesting that cellular connections are formed between cells. The contraction force of the cardiac tissues causes the posts to deflect and offer optical read‐out of tissue contraction force.

Engineered cardiac tissues response to electrical stimulation and allows continuous pacing at 1 Hz for up to 2 weeks. Extended culture time of engineered cardiac tissues under these conditions reveal an increased contraction force with time in culture. MAPs show promising results for formation of engineered cardiac tissues using a manufacturing method with upscaling potential for industrial use.

Engineered cardiac tissues develops inside MAPs to form cellular connection and shows possibility for functional read‐out. Further work is needed to show functionality of cardiotoxicity testing using pharmaceutical drugs known to have a high sensitivity with current testing methods.