Native state imaging and characterisation of tissue derived extracellular matrix hydrogels for regenerative medicine applications

The extracellular matrix (ECM) in native mammalian tissues provides a structural and functional framework to support tissue resident cells and promote cellular function. Mammalian tissues can be decellularised, to remove cellular antigens, that would otherwise incite an adverse immune response. These ECM derived biomaterials can be ground into small particulates, solubilised and polymerised to form hydrogels which reflect the biochemical complexity and bioinductive properties of the native matrix. ECM hydrogels contain highly complex structures, including proteins, growth factors, cryptic peptides and vesicles, within a hydrated environment.

ECM hydrogels have considerable utility as vehicles for cell delivery in regenerative medicine and as 3D substrates for in vitro cell culture, but the full potential has yet to be reached. To date, characterisation of ECM hydrogel structure has been limited to freeze-drying, removing water from the hydrogels, which is not representative of the native state. There is a need for new imaging modalities to inform both understanding of the ultrastructure of ECM hydrogels and interactions of cells seeded within these materials.

An alternative solution to freeze-drying is the rapid freezing of samples using cryogenic liquids to lock in the water, thereby preserving the structure of the hydrogel and its contents. By embracing cryogenic techniques such as cryo-Scanning Electron Microscopy, samples can be maintained once correctly preserved in their near native state. By using a Focused Ion Beam (FIB), samples can be cross-sectioned; sequential slicing and imaging in three dimensions will lead to better understanding of hydrogel ultrastructure and the impact this has on interactions with cells seeded within the hydrogel.