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Disease research and drug screening platforms require in vitro model systems with cellular cues resembling those of natural tissues. Fibrillar alignment, occurring naturally in extracellular matrices, is one of the crucial attributes in tissue development. Obtaining fiber alignment in 3D, in vitro remains an important challenge due to non-linear material characteristics. Here, we report a cell-compatible, shear stress-based method allowing to obtain 3D homogeneously aligned fibrillar collagen hydrogels. Controlling the shear-stress during gelation results in low strain rates, with negligible effects on the viability of embedded SH-SY5Y cells. Our approach offers reproducibility and tunability through a paradigm shift: The shear-stress initiation moment, being the critical optimization parameter in the process, is related to the modulus of the developing gel, whereas state of the art methods often rely on a predefined time to initiate the alignment procedure. After curing, the induced 3D alignment is maintained after the release of stress, with a linear relation between the total acquired strain and the fiber alignment. This method is generally applicable to 3D fibrillar materials and stress/pressure-controlled setups, making it a valuable addition to the fast-growing field of tissue engineering. Controlling fiber alignment in vitro 3D hydrogels is crucial for developing physiologically relevant model systems. However, it remains challenging due to the non-linear material characteristics of fibrillar hydrogels, limiting the scalability and repeatability. Our approach tackles these challenges by utilizing a stress-controlled rheometer allowing us to monitor structural changes in situ and determine the optimal moment for applying a shear-stress inducing alignment. By careful parameter control, we infer the relationship between time, induced strain, alignment and biocompatibility. This tunable and reproducible method is both scalable and generally applicable to any fibrillar hydrogel, therefore, we believe it is useful for research investigating the link between matrix anisotropy and cell behavior in 3D systems, organ-on-chip technologies and drug research. [Display omitted] [ABSTRACT FROM AUTHOR]

The research area of nonlinear topologies of conjugated polymers (CPs) became a topic of growing interest due to their unique optoelectronic properties compared to CPs with linear topologies. Nonetheless, the field of the third-order nonlinear optical response (TONO) is still largely unexplored, although, theoretically, nonlinear CPs should give a higher TONO response. Therefore, linear CPs and a trigonal nonlinear CP were synthesized via a combination of a controlled chain-growth polymerization, post-polymerization reactions and a click reaction. Afterward, the TONO response of the CPs was investigated with the highly sensitive third-harmonic scattering technique using solvatochromism experiments. In contrast to what was expected, trigonal nonlinear CPs do not possess a higher TONO response compared to their linear counterparts. • Conjugated polymers. • Third-order nonlinear optical response. • Third harmonic scattering. • Kumada catalyst transfer condensative polymerization. • Nonlinear topologies. [ABSTRACT FROM AUTHOR]