Curved by Design: Applying Microfluidic Principles for Nonplanar and Planar Suspended Tissue Patterning to the Development of Bladder Models with Tunable Mechanics

ABSTRACT Cells in vivo exist in a complex environment where they receive chemical and physical cues from neighboring cells and the extracellular matrix. Suspended, three dimensional (3D) cell culture enables the study of mechanical signals in a controlled in vitro setting where cells can exert forces on the extracellular matrix, and mechanical stimulation can be externally applied. In addition to mechanical cues, tissues in vivo also exhibit spatial heterogeneity and nonplanar topography. To facilitate the development of suspended 3D cell culture models with both spatial and geometric complexity, we previously introduced Suspended Tissue Engineering with Assemblable Microfluidics (STEAM). STEAM is an accessible, modular platform that utilizes fluidic patterning to create multiregional planar and nonplanar suspended cell-embedded 3D tissues. Herein, we further characterize the STEAM dome platform by developing a theoretical model that explains some experimental considerations necessary for successful two-region patterning in a nonplanar construct. We highlight a brief biological application of the planar and nonplanar STEAM platforms by creating simple but physiologically relevant model systems for the bladder, a sphere-like organ with concentric tissue layers and a central lumen that dynamically expands and contracts during filling and voiding. We demonstrate that the suspended configuration of the planar bladder smooth muscle tissue patch induces inherent tension, which can be increased by further straining the tissues; both result in muscle cell alignment along the axis of stretch as shown by a clear peak at 90° in a radial sum analysis of the two dimensional Fast Fourier Transform of images with fluorescent signal from myosin heavy chain 11 immunostaining. Further, we utilize the nonplanar STEAM platform with a human urothelial cell line (HBLAK) and primary bladder smooth muscle cells (HBdSMC) to create a bladder wall model, resulting in a domed, bilayered tissue. STEAM integrates patterning precision, mechanical functionality, and customizability to actualize an accessible and low cost alternative to generate spatially and geometrically complex suspended tissues.