3D cell culture models (e.g. organoids, spheroids, micro-tissues) provide researchers with the ability to better mimic the in vivo environment compared to traditional 2D cell culture models. However, these more complex biological models present several challenges for researchers trying to characterize them via imaging as traditional high content imaging approaches are highly limited. For example, trying to image a 3D cell culture model with wide field or confocal microscopy results in significant characterization bias as light only penetrates a few cell layers into these models and thus the characterization is biased towards the cells on the exterior which are most exposed to nutrients and compound treatments.
This misrepresentation can be clearly seen from confocal imaging wherein the center of individual Z slices are typically dark which is due in many cases to optical attenuation and not a lack of cells or staining. However, some models of larger sizes will form necrotic cores and some researchers can have challenges with getting antibodies to penetrate deep into their models.
Another characterization problem with these 3D cell culture models is that while they are three-dimensional tissue-like constructs, they cannot be treated like traditional pieces of tissue and processed in accordance with traditional histopathology. The reason for this is that they are as small as 200 µm in diameter and are thus very easy to lose during the embedding and sectioning process. Furthermore, due to their size, many 3D cell culture models are typically embedded together to increase the probability that they can be found and subsequently sectioned. This creates several problems as this means that a 96 well plate will only yield eight slides if twelve models are pooled in order to get a single slide. Another problem is that the orientation of the slide is challenging to adjust and thus for 3D cell culture models which are heterogenous such as those that have cell sub-type polarity it is possible to take a section which is not representative of the sample.
At Visikol, we have developed several reagent, imaging and image analysis tools which allow us to side-step these problems through the use of tissue clearing combined with fluorescent labeling, high content confocal imaging and true 3D analysis. However, there are still many researchers who want to see traditional sections from 3D cell culture models and thus there is still a need for embedding, sectioning and traditional processing of these models. Therefore, Visikol has launched 3D cell culture histopathology services through which sections can be routinely collected from 3D cell culture models. These services include H&E, IHC and IF tissue labeling as well as slide scanning and digital pathology analysis.