The mechanism of separating gel
The serum separation gel is composed of hydrophobic organic compounds and silica powder. It is a thixotropic mucus colloid. Its structure contains a large number of hydrogen bonds. Due to the association of hydrogen bonds, a network structure is formed. Under the action of centrifugal force, the network structure is destroyed and changed. For a fluid with low viscosity, when the centrifugal force disappears, it re-forms a network structure, which is called thixotropy. That is, under the condition of constant temperature, a certain mechanical force is applied to the mucus colloid, which can change from a high-viscosity gel state to a low-viscosity sol state, and if the mechanical force disappears, it will return to the original high-viscosity gel state. The phenomenon of gel and sol interconversion resulting from the action of mechanical forces was first named by Freundlich and Petrifi. Why does the interaction between gel and sol occur due to the action of mechanical force? Thixotropy is because the structure of the separating gel contains a large number of hydrogen bond network structures. Specifically, the hydrogen bond not only forms a single covalent bond, but also forms a weak hydrogen bond with other negatively charged molecules under certain conditions. At room temperature, the hydrogen bond is relatively easy to be cut off to cause recombination. The silica surface has silyl hydroxyl groups (SiOH) to form SiO molecular aggregates (primary particles), which are linked by hydrogen bonds to form chain-like particles. The chain silica particles and the particles of the hydrophobic organic compound constituting the separating gel further form hydrogen bonds to generate a network structure and constitute gel molecules with thixotropy.
The specific gravity of the separating gel is maintained at 1.05, the specific gravity of the serum is about 1.02, and the specific gravity of the blood clot is about 1.08. When the separating gel and the coagulated blood are centrifuged in the same test tube, the hydrogen chain network structure in the silica aggregate is caused by the centrifugal force applied to the separating gel. After being destroyed, it becomes a chain-like structure, and the separating gel becomes a substance with low viscosity. The blood clot heavier than the separating gel moves to the bottom of the tube, and the separating gel reverses, forming three layers of blood clot/separating gel/serum at the bottom of the tube. When the centrifuge stops rotating and loses the centrifugal force, the chain particles of the silica aggregates in the separation gel form a network structure again by hydrogen bonds, restore the initial high viscosity gel state, and form an isolation layer between the blood clots in the serum.
Post time: Mar-11-2022
