# Mechanics control the proliferation of diatoms entrapped in hydrogels

## TL;DR

This study shows how the mechanical properties of hydrogels affect the growth of diatoms, which is important for creating living materials in biotechnology.

## Contribution

The study reveals that residual stress in hydrogels regulates microorganism growth, offering new design guidelines for living materials.

## Key findings

- Residual stresses in agar hydrogels influence diatom proliferation.
- The interplay between cell pressure and hydrogel mechanics controls growth dynamics.
- Stress relaxation impacts the viability and division of entrapped diatoms.

## Abstract

The proliferation of microorganisms in hydrogels is crucial for the design of engineered living materials and biotechnological processes, and may provide insights into cellular growth in aquatic environments. While the mechanical properties of the gel have been shown to affect the division of entrapped cells, research is still needed to understand the impact and the origin of mechanical forces controlling the growth of microorganisms inside hydrogels. Using diatoms as model microorganisms, we investigate the viability, time to division and growth dynamics of cells entrapped in agar hydrogels with tuneable mechanical properties. Cell culture experiments, confocal optical microscopy and particle tracking velocimetry are performed to uncover the role of stress relaxation and residual stresses in the gel and how these affect diatom proliferation. Our experiments reveal that the interplay between the internal pressure of the dividing cell and the mechanical response of the hydrogel control the proliferation behaviour of the entrapped diatoms. By providing quantitative guidelines for the selection of hydrogels for the entrapment and growth of microorganisms, this study offers new insights on the design of living materials for established and emerging biotechnologies.

The growth of microorganisms entrapped in hydrogels is important for biotechnological and natural processes. Using diatoms in agar as model system, this study shows that residual stress regulates the growth of microorganisms inside hydrogels.