Fixativa

Fixativa, or fixatives, are chemical agents used to preserve biological tissues, cells, or other materials by stabilizing their structure and halting decay. They achieve this by cross-linking proteins, denaturing enzymes, dehydrating, or otherwise immobilizing cellular components, thereby maintaining morphology for further analysis or observation.

In histology and pathology, fixatives preserve tissue samples before embedding and staining. Common agents include formaldehyde (often used as formalin), paraformaldehyde, glutaraldehyde, methanol, and ethanol. The choice depends on the intended analyses: formaldehyde is widely used for light microscopy, while glutaraldehyde is favored for electron microscopy. Bouin’s and Zenker’s solutions are older formulations that combine fixatives with other components to enhance preservation.

For electron microscopy, osmium tetroxide is frequently used as a post-fixative to preserve lipids and provide contrast, often in combination with aldehyde fixatives.

In art conservation, fixatives are used to secure drawing media such as charcoal or graphite to paper, reducing smudging and facilitating handling. These sprays or coatings may contain polymers and resins. While useful, some fixatives can alter tonal qualities or interact with pigments, so choices depend on the medium and desired permanence.

Safety and handling are important, as many fixatives are hazardous. Formaldehyde is carcinogenic; glutaraldehyde can irritate the skin and eyes; osmium tetroxide is toxic; picric acid can be explosive when dry. Work with fixatives typically requires proper ventilation, protective equipment, and adherence to safety guidelines.

See also topics include histology, tissue processing, electron microscopy, and conservation science.