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The most commonly used fixative in histology is formaldehyde. It is usually used as a 10% neutral buffered formalin (NBF), that is approx. 3.7%–4.0% formaldehyde in phosphate buffer, pH 7. Since formaldehyde is a gas at room temperature, formalin – formaldehyde gas dissolved in water (~37% w/v) – is used when making the former fixative.
Formaldehyde (/ f ɔːr ˈ m æ l d ɪ h aɪ d / ⓘ for-MAL-di-hide, US also / f ə r-/ ⓘ fər-) (systematic name methanal) is an organic compound with the chemical formula CH 2 O and structure H−CHO, more precisely H 2 C=O.
The most widely used fixative for light microscopy is 10% neutral buffered formalin, or NBF (4% formaldehyde in phosphate buffered saline). [ 13 ] [ 12 ] [ 9 ] For electron microscopy, the most commonly used fixative is glutaraldehyde , usually as a 2.5% solution in phosphate buffered saline . [ 9 ]
Paraformaldehyde can be depolymerized to formaldehyde gas by dry heating [2] and to formaldehyde solution by water in the presence of a base, an acid or heat. The high purity formaldehyde solutions obtained in this way are used as a fixative for microscopy and histology. The resulting formaldehyde gas from dry heating paraformaldehyde is flammable.
The use of plastination allowed the use of many body parts such as muscle, nerves, bones, ligaments, and central nervous system to be preserved. [ 21 ] The University of Texas Health Science Center at San Antonio was the first school in the United States to use this technique to prepare gross organ specimens for use in teaching. [ 22 ]
Drug delivery systems have been around for many years, but there are a few recent applications of drug delivery that warrant 1. Drug delivery to the brain: Many drugs can be harmful when administered systemically; the brain is very sensitive to medications and can easily cause damage if a drug is administered directly into the bloodstream.
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Here, the first priority is for long-term preservation, not presentation. As such, medical embalmers use anatomical wetting fluids that contain concentrated formaldehyde (37–40%, known as formalin) or glutaraldehyde and phenol, and are made without dyes or perfumes. Many embalming chemical companies make specialized anatomical embalming fluids.