Linearly elastic polyacrylamide (PAA) hydrogels have been widely used in mechanosensing studies because they are biocompatible, capable of a wide range of functionalization, and have tunable mechanical properties. However, the in vivo microenvironments of living tissues are viscoelastic, and these purely elastic substrates may not produce a physiologically relevant cellular response. Herein, we use a stereolithography (SLA)-based additive manufacturing technique to make viscoelastic PAA substrates with tunable mechanical properties and study cellular response. We fabricated three PAA substrates of different complex moduli by SLA and embedded fluorescent markers during the additive manufacturing of the substrates that show a homogeneous and uniform structural composition throughout, which conventional manufacturing techniques cannot produce. Rheological studies show a viscoelastic behavior with a 5−10% loss moduli compared to their elastic moduli, which mimics actual living tissues. Single live cells were seeded on these dissipative PAA substrates to establish cell mechanosensing behavior between cell traction, cytoskeletal prestress, and cell spreading. As the substrate moduli were increased, an accompanying increase in cellular traction and prestress was observed, but not cell spreading. This suggests that cell spreading can be decoupled from traction and intracellular prestress in physiologically relevant environments. As the cellular response on real tissue like viscoelastic materials remains largely unknown, additively manufactured PAA will fill the gap and can be used in a myriad of mechanosensing studies very precisely and accurately due to their superior reproducibility.

Additive manufacturing of viscoelastic polyacrylamide substrates: A new era for mechanobiology studies

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