Holographic Display-Based Control for High-Accuracy Photolithography of Cellular Micro-Scaffold With Heterogeneous Architecture

Engineered 3-D tissues that replicate composite in vivo architectures have shown great potential for use in biomedical research. Cell-encapsulated hydrogel microscaffolds have been applied widely as basic building blocks to construct these artificial tissues. However, the accurate reproduction of heterogeneous hierarchical structures and different regional mechanical properties inside a single integrated microscaffold that mimics physiologically relevant complex tissues presents a major challenge. Here, we propose a novel fabrication control algorithm to achieve high-accuracy photolithography of microscaffolds that recapitulate the high fidelity of native tissues by adjusting a 3-D digital mask using holographic imaging feedback. By performing digital holographic reconstruction to express the hydrogel photocuring process in a matrix form and presetting the curing duration for each discrete point, the 3-D digital mask was predefined to represent the required customized microscaffold. During fabrication, the ultraviolet exposure area was divided into microscaled grids with relatively uniform irradiance to control the photocuring process discretely for every local region in the entire architecture. The holographic imaging feedback allowed the curing duration of each grid to be adjusted in real time, which enabled the accurate reproduction of a 3-D construct integrated with different microstructural morphologies and mechanical properties. Finally, poly(ethylene glycol) diacrylate and gelatin methacrylate, as typical biomaterials, were used to fabricate the heterogeneous hierarchical microscaffold. The structural accuracy was improved from 65 to 12 μm and Young's modulus was controlled flexibly in 27.9 ± 3.5-91.2 ± 3.5 kPa range. With different local mechanical properties, cell migration in the microscaffold from soft to stiff areas is observed successfully.