Thiele, J. | Search bioRxiv

bioRxiv2024

A precision microgel platform to direct vascular morphogenesis in vitro

The dynamic organization of tissue development is reciprocally controlled by localized gradients of morphogens emanating from distinct clusters of cells that act as signaling centers1. While microgels2,3 have shown promise to recapitulate this process in engineered tissue constructs, their capacity to tailor morphogen distribution in space and time remained limited4-7. Here, we introduce a library of sulfated glycosaminoglycan (sGAG)-based microgels that offer unprecedented control over morphogen affinity (GUIDe, Gel Units to Instruct Development), thus enabling precise formation of concentration gradients. Multiparametric adjustment of the microgel charge patterns resulting from sGAG ionization was key to programmable morphogen release. The potential of our microgel system to guide tissue morphogenesis is demonstrated through the local administration of VEGF gradients in a microgel-in-gel in vitro vasculogenesis model and in hiPSC-derived kidney organoid cultures. Our micromaterials-based methodology offers valuable new options to mimic and modulate morphogen signaling centers, thereby advancing tissue/organ development research.

bioengineering↗

bioRxiv2018

Standardized microgel beads as elastic cell mechanical probes

Cell mechanical measurements are gaining increasing interest in biological and biomedical studies. However, there are no standardized calibration particles available that permit the cross-comparison of different measurement techniques operating at different stresses and time-scales. Here we present the rational design, production, and comprehensive characterization of poly-acylamide (PAAm) microgel beads mimicking biological cells. We produced mono-disperse beads at rates of 20 - 60 kHz by means of a microfluidic droplet generator, where the pre-gel composition was adjusted to tune the beads elasticity in the range of cell and tissue relevant mechanical properties. We verified bead homogeneity by optical diffraction tomography and Brillouin microscopy. Consistent elastic behavior of microgel beads at different shear rates was confirmed by AFM-enabled nanoindentation and real-time deformability cytometry (RT-DC). The remaining inherent variability in elastic modulus was rationalized using polymer theory and effectively reduced by sorting based on forward-scattering using conventional flow cytometry. Our results show that PAAm microgel beads can be standardized as mechanical probes, to serve not only for validation and calibration of cell mechanical measurements, but also as cell-scale stress sensors.\n\nSignificance StatementOften vastly different cell mechanical properties are reported even for the same cell type when employing different measurement techniques. This discrepancy shows the urgent need for standardized calibration particles to cross-compare and validate techniques. Microgel beads can serve this purpose, but they have to fulfil specific requirements such as homogeneity, sizes and elasticities in the range of the cells, and they have to provide comparable results independent of the method applied. Here we demonstrate the standardized production of polyacrylamide microgel beads with all the features an elastic cell-mimic should have. These can not only be used as method calibration particles, but can also serve as cell-scale sensors to quantify normal and shear stresses exerted by other cells and inside tissues, enabling many new applications.

biophysics↗