Dear friend Gita Parviz

The decrease in density of your pure nanofibers after drug loading could be due to the fact that the drug molecules are occupying some of the space between the fibers. This could lead to an increase in the distance between the fibers and hence a decrease in density. Another possible explanation is that the drug molecules could be interacting with the fibers themselves, leading to a change in their structure and hence a change in their density (Polymeric Nanofibers....).

I hope this helps! Let me know if you have any other questions.

Source:

(1) Polymeric Nanofibers for Drug Delivery Applications: A ... - Springer. https://link.springer.com/article/10.1007/s10856-022-06700-4.

(2) Nanofibers: New Insights for Drug Delivery and Tissue Engineering. https://pubmed.ncbi.nlm.nih.gov/28017155/.

(3) Drug loading and delivery using nanofibers scaffolds - PubMed. https://pubmed.ncbi.nlm.nih.gov/27188394/.