*Article* **Collagen from the Marine Sponges** *Axinella cannabina* **and** *Suberites carnosus***: Isolation and Morphological, Biochemical, and Biophysical Characterization**

**Leto-Aikaterini Tziveleka 1, Efstathia Ioannou 1, Dimitris Tsiourvas 2, Panagiotis Berillis 3, Evangelia Foufa <sup>1</sup> and Vassilios Roussis 1,\***


Academic Editors: Azizur Rahman and Tiago H. Silva Received: 22 April 2017; Accepted: 25 May 2017; Published: 29 May 2017

**Abstract:** In search of alternative and safer sources of collagen for biomedical applications, the marine demosponges *Axinella cannabina* and *Suberites carnosus*, collected from the Aegean and the Ionian Seas, respectively, were comparatively studied for their insoluble collagen, intercellular collagen, and spongin-like collagen content. The isolated collagenous materials were morphologically, physicochemically, and biophysically characterized. Using scanning electron microscopy and transmission electron microscopy the fibrous morphology of the isolated collagens was confirmed, whereas the amino acid analysis, in conjunction with infrared spectroscopy studies, verified the characteristic for the collagen amino acid profile and its secondary structure. Furthermore, the isoelectric point and thermal behavior were determined by titration and differential scanning calorimetry, in combination with circular dichroism spectroscopic studies, respectively.

**Keywords:** *Axinella cannabina*; *Suberites carnosus*; sponges; marine collagen
