2.6.2. In Vitro Resistance to Enzymatic Degradation

In vitro biodegradation of F1 and F3 derived SCMs and nc-SCMs was evaluated by incubation at 37 ◦C with native fetal bovine serum (FBS) for 15 day and by collagenase digestion for 6 days. The results showed that all of the membranes were completely intact after both of the treatments. This indicates a strong resistance of the marine biomaterials to enzymatic degradation at physiological conditions, even for the not crosslinked versions nc-SCM-F1 and nc-SCM-F3 (not shown). Conversely, a parallel incubation of a commercial mammalian collagen membrane (Bio-Gide®, Geistlisch Pharma, Wolhusen, Switzerland), which is usually employed in dental surgery, showed a complete collagenase digestion after 6 days incubation. Furthermore, after FBS treatment, all of the SCMs (crosslinked or not) resulted visibly opaque (Figure 6A) as compared to the negative controls that were incubated in phosphate buffered saline (PBS). Other than opaque, FBS-treated membranes also appeared to be thicker than their controls in PBS, as observed by optical stereomicroscope (Figure 6B). Both features, i.e., opacity and thickness, were likely due to the serum protein adsorption onto the membrane surfaces.

**Figure 6.** SCM serum interaction and water absorbing capacity. (**A**) SCM-F1 incubated in 1 mL of FBS (left) or PBS (right) for 15 day at 37 ◦C; (**B**) Stereo-microscope observation of SCM-F1after incubation for 15 days at 37 ◦C in FBS (left) or PBS (right); scale bar, 50 micrometer; (**C**) Not cross-linked (nc-SCM) and cross-linked SCM derived from F1 and F3 fibrillar extracts after soaking in PBS for 1 h.
