Hydrogel Chemistry in Expansion Microscopy: From Polyacrylamide to Next-Generation Swellable Polymers

Area of Science:

• Biomedical Imaging
• Polymer Chemistry
• Cell Biology

Background:

• Expansion microscopy (ExM) achieves nanoscale resolution using hydrogel-based physical specimen expansion.
• Early ExM relied on polyacrylamide (PAAm) hydrogels, facing limitations in expansion and fidelity.
• Significant advancements in hydrogel chemistry have addressed these limitations since 2015.

Purpose of the Study:

• To comprehensively review the evolution of hydrogel chemistry in ExM.
• To analyze how polymerization mechanisms, monomers, crosslinkers, and anchoring strategies impact gel performance.
• To guide researchers in selecting and optimizing hydrogels for ExM applications.

Main Methods:

• Literature synthesis of ExM hydrogel chemistry up to 2025.
• Critical analysis of polymerization, monomer composition, and crosslinker design.
• Evaluation of gel performance metrics: expansion factor, mechanical integrity, and spatial fidelity.

Main Results:

• Traces progression from PAAm to advanced dimethylacrylamide (DMAA) and click-chemistry tetra-gel systems.
• Highlights how specific polymer architectures influence expansion factor, isotropy, and biomolecular fidelity.
• Discusses emerging methods like single-shot expansion and microwave acceleration in relation to polymer chemistry.

Conclusions:

• Hydrogel chemistry is crucial for ExM performance, with ongoing innovation driving improved imaging capabilities.
• Understanding polymer parameters allows for tailored hydrogel selection for diverse ExM applications.
• Future polymer research holds promise for further advancements in ExM technology.