Comment by Y_Y

You are quite right, seems like there are unbreakable matrices that require chemical action:

https://www.jsr.org/hs/index.php/path/article/download/4787/...

Suitable chemical methods:

https://www.sciencedirect.com/science/article/abs/pii/S01418...

https://pmc.ncbi.nlm.nih.gov/articles/PMC10157874/