# TiFM2.0 – versatile mechanical measurement and actuation in live embryos

## TL;DR

TiFM2.0 is a tool that measures and manipulates mechanical forces in live embryos to study how tissues shape during development.

## Contribution

TiFM2.0 introduces a double-probe system with improved precision and accessibility for mechanical experiments in embryos.

## Key findings

- TiFM2.0 enables bidirectional mechanical experiments in embryos.
- The system was used to study mechanical heterogeneities in chicken embryos.
- Simplified protocols allow easier replication of TiFM systems in labs.

## Abstract

During development, spatial-temporally patterned tissue-level stresses and mechanical properties create diverse tissue shapes. To understand the mechanics of small-scale embryonic tissues, precisely controlled sensors and actuators are needed. Previously, we reported a control-based approach named tissue force microscopy (TiFM1.0), which combines dynamic positioning and imaging of an inserted cantilever probe to directly measure and impose forces in early avian embryos. Here, we present an upgraded system (TiFM2.0) that uses interferometer positioning to minimise probe holder footprint, enhancing accessibility and imaging signal. This new design enables a double-probe configuration for bidirectional stretching, compression and stress propagation experiments. As proof-of-concept, we showcase a variety of examples of TiFM2.0 applications in chicken and zebrafish embryos, including the characterisation of mechanical heterogeneities important for the morphogenesis of the chicken posterior body axis. We also present simplified designs and protocols for the replication of TiFM systems with minimal custom engineering for developmental biology labs.

Summary: Precisely-controlled, sensitive cantilevers measure and perturb tissue forces and mechanical properties in their native locations in live embryos, providing a useful tool to study tissue mechanics that underlie morphogenesis.