During tissue sectioning, tissues containing bone or calcified lesions cannot be directly embedded in paraffin for sectioning. Due to the density difference between calcium and paraffin, intact sections are difficult to obtain. For calcium-containing tissues, decalcification should be carried out after fixation or simultaneously with fixation, followed by subsequent procedures including dehydration, clearing, wax infiltration, embedding and sectioning.There are various decalcifying reagents available, such as organic acids, inorganic acids, ethylenediaminetetraacetic acid (EDTA), and electrolytic decalcification methods. Among organic acids, formic acid and acetic acid are suitable for decalcification of bone marrow tissue. Formic Acid Decalcification Solution is a widely used decalcifier; however, its decalcification rate is relatively slow, so it is not applicable to dense cortical bone decalcification.
Formic Acid Decalcification Solution is mainly composed of formic acid and formalin,Advantages:① It delivers excellent nuclear staining effect;② It integrates decalcification and tissue fixation functions;③ It is suitable for decalcification of small tissue specimens and teeth.Disadvantages:① Slow decalcification speed, not recommended for routine specimen decalcification;② Not fit for dense cortical bone decalcification;③ Alkaline treatment with sodium sulfate solution is required after decalcification.
User-Supplied Materials:
1. PBS buffer, distilled water, 5% sodium sulfate solution
2. Heating device or microwave oven, dedicated glass containers for decalcification
Operating Procedures (For Reference Only):
1. Do not prepare overly thick bone tissue samples for decalcification; the recommended thickness is approximately 5 mm.
2. After tissue fixation, rinse the sample with PBS 3 times for 20 minutes each time.
3. Wash the tissue with distilled water 3 times for 20 minutes each time.
4. Immerse the tissue in Formic Acid Decalcification Solution at a volume ratio of 1:20~1:30 for decalcification over 3 to 10 days or longer. Replace with fresh decalcification solution if needed until the decalcification endpoint is reached. Most tissues finish decalcification within one week.
5. Rinse the tissue thoroughly with distilled water several times.
6. Immediately place the tissue into 5% sodium sulfate solution for alkaline neutralization treatment.
7. Flush the sample with running water for no less than 18 hours, then perform standard dehydration and embedding.
Precautions:
1. A 5 mm-thick bone tissue block generally completes decalcification within 3 to 10 days.
2. Ensure thorough decalcification to avoid insufficient or excessive treatment. Optimize decalcification duration to guarantee qualified sectioning while minimizing tissue damage caused by prolonged treatment.
3. Bone tissue shall be fixed prior to decalcification, or fixation and decalcification may be performed concurrently. Decalcification before fixation is forbidden to reduce tissue damage.
4. Check decalcification progress regularly. Over-decalcification will aggravate tissue damage and compromise staining results.
5. Wear a lab coat and disposable gloves during operation to ensure personal safety and health.
Appendix:
Determination of Decalcification Endpoint (Physical Method):Prick, pinch or clamp the tissue manually. Terminate decalcification once the bone tissue softens or no resistance is felt during needle puncture. This physical inspection may impair tissue architecture, so avoid excessive force or repeated testing.