In the past few years, the output of formaldehyde in my country has been increasing year by year, which is consistent with the development of my country's textile industry and building materials industry, which shows that formaldehyde will still be the darling of my country's chemical industry for a long time in the future. According to relevant experts, in recent years, my country has successfully developed formaldehyde-free non-iron finishing agents and formaldehyde-free environment-friendly urea-formaldehyde resins. Price hinders the replacement process of formaldehyde.
The key to the effective fixation of formaldehyde is the formation of cross-linked chains between protein end groups. The groups involved in the immobilization of proteins by formaldehyde are mainly amino, imino and amido groups, peptides, guanidino groups, hydroxyl groups, SH and aromatic rings. The reaction of formaldehyde with tissue proteins is diverse and complex because it can combine with a variety of different functional groups, forming bridges between them in most cases. Formaldehyde has this cross-linking function, which is also its disadvantage. In the tissue fixed with formaldehyde, immunohistochemistry is required, and enzymatic digestion or thermal antigen retrieval method is often advocated to make the protein and formaldehyde cross-linked aldehyde bond Broken open to facilitate subsequent staining. Formaldehyde can be made into a simple or mixed fixative. The easiest and easiest way to master it is to take 10ml of formaldehyde and add 90ml of water, which is 10% formalin. Of course, the requirements for the fixative used now are more stringent. For these, it is best to use buffered formalin fixative, which will facilitate the need for subsequent immunohistochemical staining.
From a histological point of view, formaldehyde is a good fixative. It has many advantages: less tissue shrinkage, less damage, and good preservation of inherent substances; uniform fixation and strong penetration; Tissue elasticity is beneficial for slicing; it can preserve fat and lipid substances; the cost is low. Although formaldehyde has the above advantages, it is relatively speaking, no substance can be perfect, and it also has many disadvantages: the content of impurities, such as methanol, can passivate enzymes and affect the reaction; The fixative becomes acidic and affects staining; it can produce formalin pigment, which affects observation; it cannot fix uric acid and carbohydrates; it is easy to volatilize and pollute the environment, which can cause the specimen to dry up; it can exist on the fixed tissue for a long time. Some people have done experiments. After the tissue is fixed with formaldehyde and washed in running water for 5 hours, there is still a considerable amount of formaldehyde combined with protein, but it needs to be washed with running water for a long time (24 days of washing). It is impossible to remove the formaldehyde on the tissue. Because it is impossible for clinical biopsy to have such a long time to wash the tissue. Therefore, it should be pointed out that in the subsequent technical operations, special attention should be paid to the presence of formaldehyde, We must find a way to remove it, otherwise it will affect all kinds of dyeing, and even lead to failure.