Clavicula

Hello! I'm new to cell culture, but I need to cultivate the Mle-12 cell line. For three months, I haven't been able to get more than 5-6 passages. With each passage, the number of dead cells increases. This is very frustrating, and unfortunately, I don't have any colleagues who can help me. Could you please tell me what's critical for this cell line and for lung epithelial cells in general? Are they more susceptible to overexposure to trypsin or mechanical stress? My protocol: 1. Pour off the old culture medium. 2. Wash with PBS (3 ml). 3. Add 1.5 ml of trypsin and wait 1 minute. While I wait, I tap the sides of the culture medium, otherwise the cells do not detach. 4. Pour in 3 ml of culture medium and wash the walls of the culture medium several times with a pipette until most of the cells detach. 5. Pour into a test tube and centrifuge for 5 minutes at 13,000. 6. Pour off the liquid and add 2 ml of new medium. 7. Pour 4 ml of new medium and 1 ml of cells into the new culture flask. 8. Mix the cells vigorously with a pipette about 20 times (if I don’t do this, they will remain stuck together). The first photo shows cells from passage 2-3. I do the passage every day at about the same time, but after a few days, the number of dead floating cells increases. And the second photograph is cells after 6 pass I will be very glad to receive any advice and will be happy to answer all questions.