*4.4. Removal of Spicules from Insoluble Collagen*

In order to remove the siliceous spicules, InSC was treated with an HF solution (10% *v*/*v*) for 20 min at room temperature. The exact conditions were standardized using siliceous spicules isolated as previously described [73]. The material was rinsed with distilled-deionized water until pH ~ 6 was reached and the HF-treated spicule-free collagen (SF-InSC) was isolated by centrifugation at 12,000× *g* for 20 min and subsequently lyophilized.
