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We have developed a microfluidic platform for engineering cardiac microtissues in highly-controlled microenvironments. The platform is fabricated using direct laser writing (DLW) lithography and soft lithography, and contains four separate devices. Each individual device houses a cardiac microtissue and is equipped with an integrated strain actuator and a force sensor. Application of external pressure waves to the platform results in controllable time-dependent forces on the microtissues. Conversely, oscillatory forces generated by the microtissues are transduced into measurable electrical outputs. We demonstrate the capabilities of this platform by studying the response of cardiac microtissues derived from human induced pluripotent stem cells (hiPSC) under prescribed mechanical loading and pacing. This platform will be used for fundamental studies and drug screening on cardiac microtissues. 

Abstract Direct laser writing (DLW) via two‐photon polymerization is an emerging highly precise technique for the fabrication of intricate cellular scaffolds. Despite recent progress in using two‐photon‐polymerized scaffolds to probe fundamental cell behaviors, new methods to direct and modulate microscale cell alignment and selective cell adhesion using two‐photon‐polymerized microstructures are of keen interest. Here, a DLW‐fabricated 2D and 3D hydrogel microstructures, with alternating soft and stiff regions, for precisely controlled cell alignment are reported. The use of both cell‐adhesive and cell‐repellent hydrogels allows selective adhesion and alignment of human mesenchymal stem cells within the printed structure. Importantly, DLW patterning enables cell alignment on flat surfaces as well as irregular and curved 3D microstructures, which are otherwise challenging to pattern with cells. 

Abstract Direct laser writing via two‐photon polymerization (2PP) is an emerging micro‐ and nanofabrication technique to prepare predetermined and architecturally precise hydrogel scaffolds with high resolution and spatial complexity. As such, these scaffolds are increasingly being evaluated for cell and tissue engineering applications. This article first discusses the basic principles and photoresists employed in 2PP fabrication of hydrogels, followed by an in‐depth introduction of various mechanical and biological characterization techniques used to assess the fabricated structures. The design requirements for cell and tissue related applications are then described to guide the engineering, physicochemical, and biological efforts. Three case studies in bone, cancer, and cardiac tissues are presented that illustrate the need for structured materials in the next generation of clinical applications. This paper concludes by summarizing the progress to date, identifying additional opportunities for 2PP hydrogel scaffolds, and discussing future directions for 2PP research.