Histological Fixation Process and Fixatives

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Tissue monitoring generally includes the stages of fixation, dehydration, clearing, hardening (infiltration), paraffin blocking/paraffin(emmeding), sectioning, water removal, routine staining, and mounting. Fixation is the basic and first step in the microscopic examination of tissues. The histotechnical process, which includes components such as detection, tissue tracking and staining, basically aims to capture and visualize the state of the relationships between tissue parts inside and outside the cell and various cells at a certain time as close as possible to the living state. Maintaining the natural structure of the tissue is important for the follow-up phase. The main feature of a good fixative should protect the sample and make the macromolecules insoluble without changing the chemistry of the sample studied and allowing it to be examined as closely as possible to its living state. In histological tissue analysis including light microscope and electron microscope techniques, an appropriate fixation method is selected for each study. Detection solutions are classified in terms of content. The most commonly used fixative in light microscopic follow-up procedures is 10% formaldehyde. For the electron microscope, the gluteraldehyde-osmium tetraoxide binary is widely used for fixation purposes. Gluteraldehyde acts more slowly and is more expensive than formaldehyde. Formalin is obtained by dissolving formaldehyde in water. In addition, the fixed samples can be stored in the solution for months. With a successful fixation process, the structural properties of the tissue are preserved and thus it is possible to examine the tissue as closely as possible. Thus, better quality sections are obtained from the tissue samples taken. For this reason, it will be more efficient to interpret well-fixed samples by photographing them. In this review, which was created by using various sources, the elements to be considered for an ideal fixation were determined and it was aimed to provide an overview of successful fixation for light microscope and electron microscope.