Femtosecond laser preparation of resin embedded samples for correlative microscopy workflows in life sciences

Characterization of human trabecular bone across multiple length scales using a correlative approach combining X-ray tomography with LaserFIB and plasma FIB-SEM

Three-dimensional correlative multimodal and multiscale imaging is an emerging method for investigating the complex hierarchical structure of biological materials such as bone. This approach synthesizes images acquired across multiple length scales, for the same region of interest, to provide a comprehensive view of the material structure of a sample. Here, we develop a workflow for the structural analysis of human trabecular bone using a femtosecond laser to produce a precise grid to facilitate correlation between imaging modalities and identification of structures of interest, in this case, a single trabecula within a volume of trabecular bone. Through such image registration, high resolution X-ray microscopy imaging revealed fine architectural details, including the cement sheath and bone cell lacunae of the selected bone trabecula. The selected bone volume was exposed with a combination of manual polishing and site-specific femtosecond laser ablation and then examined with plasma focused ion beam-scanning electron microscopy. This reliable and versatile correlation approach has the potential to be applied to a variety of biological tissues and traditional engineered materials. The proposed workflow has the enhanced capability for generating highly resolved and broadly contextualized structural data for a better understanding of the architectural features of a material spanning its macroscopic to nanoscopic levels.

Exploration of fs-laser ablation parameter space for 2D/3D imaging of soft and hard materials by tri-beam microscopy

Tri-beam microscopes comprising a fs-laser beam, a Xe+ plasma focused ion beam (PFIB) and an electron beam all in one chamber open up exciting opportunities for site-specific correlative microscopy. They offer the possibility of rapid ablation and material removal by fs-laser, subsequent polishing by Xe-PFIB milling and electron imaging of the same area. While tri-beam systems are capable of probing large (mm) volumes providing high resolution microscopical characterisation of 2D and 3D images across exceptionally wide range of materials and biomaterials applications, presenting high quality/low damage surfaces to the electron beam can present a significant challenge, especially given the large parameter space for optimisation. Here the optimal conditions and artefacts associated with large scale volume milling, mini test piece manufacture, serial sectioning and surface polishing are investigated, both in terms of surface roughness and surface quality for metallic, ceramic, mixed complex phase, carbonaceous, and biological materials. This provides a good starting place for those wishing to examine large areas or volumes by tri-beam microscopy across a range of materials.

Integrating cellular electron microscopy with multimodal data to explore biology across space and time

Biology spans a continuum of length and time scales. Individual experimental methods only glimpse discrete pieces of this spectrum but can be combined to construct a more holistic view. In this Review, we detail the latest advancements in volume electron microscopy (vEM) and cryo-electron tomography (cryo-ET), which together can visualize biological complexity across scales from the organization of cells in large tissues to the molecular details inside native cellular environments. In addition, we discuss emerging methodologies for integrating three-dimensional electron microscopy (3DEM) imaging with multimodal data, including fluorescence microscopy, mass spectrometry, single-particle analysis, and AI-based structure prediction. This multifaceted approach fills gaps in the biological continuum, providing functional context, spatial organization, molecular identity, and native interactions. We conclude with a perspective on incorporating diverse data into computational simulations that further bridge and extend length scales while integrating the dimension of time.