Highly Reproducible Tissue Positioning with Tapered Pillar Design in Engineered Heart Tissue Platforms

We present a novel design of elastic micropillars for tissue self-assembly in engineered heart tissue (EHT) platforms. The innovative tapered profile confines reproducibly the tissue position along the main micropillar axis, increasing the accuracy of tissue contraction force measurement. Polydimethylsiloxane-based pillars were designed and fabricated by wafer-level molding in an hourglass shape, with symmetric tapering producing a restriction for tissue movement in the middle of the pillars’ length. Confinement efficacy of the new geometry was validated by comparing the tissue performance in straight versus tapered (75° or 80° tapering angle) micropillars. While in all three cases compact tissues formed successfully, for both tapered designs the functionality assays evidenced yield increase from 15% to 100%, higher spatial tissue confinement, and correspondingly higher accuracy and smaller dispersion in measurements of tissue contraction force.

Introduction

Engineered heart tissue (EHT) models have demonstrated valuable potential to reproduce the (patho)physiology of human cardiac tissue in vitro [1]. They are composed of cardiomyocytes (CMs) and non-cardiomyocyte cells within an extracellular matrix (ECM), which self-assemble into tissue-like constructs around two or multiple elastic anchoring points, here called (micro)pillars. For a platform meant to culture EHTs, the design of substrate, the shape and number of elastic pillars, and their mechanical properties are crucial for tissue formation. In our previous miniature EHT platform based on polydimethylsiloxane (PDMS) [2], the cell-gel mixture self-assembled into a tissue-like construct around a pair of micropillars with uniform, rectangular cross-section within an elliptic microwell. However, tests showed that such straight pillar geometry is not optimal for long-term tissue culture, as tissues tend in time to increase the contraction force and move upwards towards the pillars' tip, eventually jumping off and detaching from the pillars in extreme cases. Variation in tissues' adherence position along the pillars hampers precise and consistent measurements of tissue contractile parameters. To address this issue, herein we introduce a tailored tapering in pillar design to constrain the tissue on a precisely defined position along the pillars' length.