Biocompatible micro tweezers for 3D hydrogel organoid array mechanical characterization

Abstract

This study presents novel biocompatible Polydimethylsiloxane (PDMS)-based micromechanical tweezers (μTweezers) capable of the stiffness characterization and manipulation of hydrogel-based organoids. The system showed great potential for complementing established mechanical characterization methods such as Atomic Force Microscopy (AFM), parallel plate compression (PPC), and nanoindentation, while significantly reducing the volume of valuable hydrogels used for testing. We achieved a volume reduction of ~0.22 μl/sample using the μTweezers vs. ~157 μl/sample using the PPC, while targeting high-throughput measurement of widely adopted micro-mesoscale (a few hundred μm-1500 μm) 3D cell cultures. The μTweezers applied and measured nano-millinewton forces through cantilever’ deflection with high linearity and tunability for different applications; the assembly is compatible with typical inverted optical microscopes and fit on standard tissue culture Petri dishes, allowing mechanical compression characterization of arrayed 3D hydrogel-based organoids in a high throughput manner. The average achievable output per group was 40 tests per hour, where 20 organoids and 20 reference images in one 35 mm petri dish were tested, illustrating efficient productivity to match the increasing demand on 3D organoids’ applications. The changes in stiffness of collagen I hydrogel organoids in four conditions were measured, with ovarian cancer cells (SKOV3) or without (control). The Young’s modulus of the control group (Control—day 0, E = 407± 146, n = 4) measured by PPC was used as a reference modulus, where the relative elastic compressive modulus of the other groups based on the stiffness measurements was also calculated (control-day 0, E = 407 Pa), (SKOV3-day 0, E = 318 Pa), (control-day 5, E = 528 Pa), and (SKOV3-day 5, E = 376 Pa). The SKOV3-embedded hydrogel-based organoids had more shrinkage and lowered moduli on day 0 and day 5 than controls, consistently, while SKOV3 embedded organoids increased in stiffness in a similar trend to the collagen I control from day 0 to day 5. The proposed method can contribute to the biomedical, biochemical, and regenerative engineering fields, where bulk mechanical characterization is of interest. The μTweezers will also provide attractive design and application concepts to soft membrane-micro 3D robotics, sensors, and actuators.

Fibrillogenesis in collagen hydrogels accelerated by carboxylated microbeads

“…Pure collagen hydrogels were prepared using nine parts of collagen and one part of 10X PBS, adjusting the pH of the mixture to 7.4 with NaOH 0.1 N [21]. The collagen mixture and all reagents were kept at 4 • C to prevent gelation.…”

A Low‐Cost, User‐Friendly Rheo‐Optical Compression Assay to Measure Mechanical Properties of Cell Spheroids in Standard Cell Culture Plates

“…Further experimental advances to characterize cell spheroids mechanical behavior, such as the Young's modulus and characteristic relaxation times, include other techniques, such as isotropic compression by osmotic pressure, [26,27] atomic force microscopy (AFM), [28,29] micro-indentation, [30] tweezers, [31] cavitation rheology [32,33] and elastography. [34,35] Each of these methods has its own strengths and limitations, and their results, in terms of Young's modulus, can vary, depending on the specific technique used, as shown in Table S1 (Supporting Information) for different immortalized cell lines and human biopsies.…”