Optical Clearing of Skeletal Muscle Bundles Engineered in 3-D Printed Templates

Many techniques for engineering and interrogating three-dimensional (3-D) muscle bundles from animal- or patient-derived myoblasts have recently been developed to overcome the limitations of existing in vitro and in vivo model systems. However, many approaches for engineering 3-D muscle bundles rely on specialized and time-consuming techniques, such as photolithography for fabrication and cryosectioning for histology. Cryosectioning also limits visualization to a single plane instead of the entire 3-D structure. To address these challenges, we first implemented a consumer-grade 3-D-printer to rapidly prototype multiple templates for engineering muscle bundles. We then employed our templates to engineer 3D muscle bundles and identify template geometries that promoted bundle survival over three weeks. Subsequently, we implemented tissue clearing, immunostaining, and confocal imaging to acquire z-stacks of intact muscle bundles labelled for myogenic markers. With this approach, we could select the imaging plane on-demand and visualize the intact 3-D structure of bundles. However, tissue clearing did cause some tissue degradation that should be considered. Together, these advances in muscle tissue engineering and imaging will accelerate the use of these 3-D tissue platforms for disease modeling and therapeutic discovery.