Science in Images: Tissue Mimics

If you ask most people, they have an opinion on the use of animals in research. Despite the need for animals in some situations, there are many scenarios where viable alternatives do exist.

Imaged below are hydrogels: soft-solids consisting of over 90% water. Hydrogels are already heavily utilised in research, from tissue engineering to drug delivery.

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Hydrogels are great candidates for tissue mimics and in turn, the replacement of animals in some experiments. The properties of the gel can be individually tailored and designed such that the strength, charge and other characteristics are similar to a tissue sample.

In this case the hydogel is comprised of agarose, a polysacharide (carbohydrate), whose long chains make up the framework around which the water resides.

Hydrogels with similar properties to brain tissue were fabricated and used to test a large number of MRI contrast agents: the final therapeutic use is as an agent for labelling stem cells, for implantation into the brain, for cell therapy.

For cellular therapy to be effective, we need to know if cells remain in the correct location and are performing the correct function. One way to do is to label them before implantation, so we can image them with an MRI.

Samples of contrast agent are prepared and injected into the gel, before they are imaged. By using hydogels in this way, we can test many combinations of contrast agents quickly, cost-effectively and without the use of animals.

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Science in Images: Fluorescent Staining of Mesenchymal Stem Cells

Mouse mesenchymal stem cells, incubated with polymer nanoparticles encapsulating the dye coumarin_6 (green) and the enzyme Cellulase (red).

Cells are incubated in chambers on a glass slide. During incubation endocytosis occurs: cells uptake the nanoparticles into them.

Cells have a mass of surface receptors, which can allow for very specific uptake. The uptake of nanoparticles by cells in this way can have huge implications for medical treatments, such directed chemotherapy.

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After the cells have been incubated for around 24 hours, they are fixed and stained with further dyes, so the cytoskeleton (purple) and the nucleus (blue) of the cell can be seen. The first image shows a low magnification of the cells.

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The next image is a Z-stack confocal image. In other words, multiple images of the cell were taken at different spacing in the Z-direction, to get slices throughout the cell. The Centre image shows the XY direction, or the cell parallel to the glass slide. The images below and beside this show the ZY and the ZX of the cell, or the perpendicular directions. What we can see using this technique is exactly where both the nanoparticles and the enzyme are within the cell.

Science in Images: Prussian Blue Staining

Rat mesenchymal stem cells, extracted from bone marrow, and labelled with Iron Oxide nanoparticles, before re-implantation. The image shows a section of the brain, stained with Eosin (pink) and then Prussian blue (blue/purple).

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Prussian blue is a common histology stain; used to detect the presence of iron. The stain uses solutions of potassium ferrocyanide and hydrochloric acid to stain tissue. Iron deposits are then stained as blue or purple.