Marine sponges of the subclass Keratosa originated on our planet about 900 million years ago and represent evolutionarily ancient and hierarchically structured biological materials. One of them, proteinaceous spongin, is responsible for the formation of 3D structured fibrous skeletons and remains enigmatic with complex chemistry. The objective of this study was to investigate the interaction of spongin with iron ions in a marine environment due to biocorrosion, leading to the occurrence of lepidocrocite. For this purpose, a biomimetic approach for the development of a new lepidocrocite-containing 3D spongin scaffold under laboratory conditions at 24 °C using artificial seawater and iron is described for the first time. This method helps to obtain a new composite as “Iron-Spongin”, which was characterized by infrared spectroscopy and thermogravimetry. Furthermore, sophisticated techniques such as X-ray fluorescence, microscope technique, and X-Ray diffraction were used to determine the structure. This research proposed a corresponding mechanism of lepidocrocite formation, which may be connected with the spongin amino acids functional groups. Moreover, the potential application of the biocomposite as an electrochemical dopamine sensor is proposed. The conducted research not only shows the mechanism or sensor properties of “Iron-spongin” but also opens the door to other applications of these multifunctional materials.

The structural biopolymer spongin in the form of a 3D scaffold resembles in shape and size numerous species of industrially useful marine keratosan demosponges. Due to the large-scale aquaculture of these sponges worldwide, it represents a unique renewable source of biological material, which has already been successfully applied in biomedicine and bioinspired materials science. In the present study, spongin from the demosponge Hippospongia communis was used as a microporous template for the development of a new 3D composite containing goethite [α-FeO(OH)]. For this purpose, an extreme biomimetic technique using iron powder, crystalline iodine, and fibrous spongin was applied under laboratory conditions for the first time. The product was characterized using SEM and digital light microscopy, infrared and Raman spectroscopy, XRD, thermogravimetry (TG/DTG), and confocal micro X-ray fluorescence spectroscopy (CMXRF). A potential application of the obtained goethite–spongin composite in the electrochemical sensing of dopamine (DA) in human urine samples was investigated, with satisfactory recoveries (96% to 116%) being obtained.

This study presents a novel approach to fabricating magnetic sponge-like composites by melting various types of steel onto three-dimensional (3D) carbonized spongin scaffolds under extreme biomimetic conditions. Spongin, a renewable marine biopolymer with high thermal stability, was carbonized at 1200 °C to form a turbostratic graphite matrix capable of withstanding the high-temperature steel melting process (1450–1600 °C). The interaction between molten steel vapors and the carbonized scaffolds resulted in the formation of nanostructured iron oxide (primarily hematite) coatings, which impart magnetic properties to the resulting composites. Detailed characterization using SEM-EDX, HRTEM, FT-IR, and XRD confirmed the homogeneous distribution of iron oxides on and within the carbonized fibrous matrix. Electrochemical measurements further demonstrated the electrocatalytic potential of the composite, particularly the sample modified with stainless steel 316L—for the hydrogen evolution reaction (HER), offering promising perspectives for green hydrogen production. This work highlights the potential of extreme biomimetics to create functional, scalable, and sustainable materials for applications in catalysis, environmental remediation, and energy technologies.

This experimental review discusses evolutionarily approved, naturally pre-designed skeletal architectures of marine keratosan sponges in the form of 3D scaffolds, which have garnered increasing interest in the fields of structural and functional biomimetics as well as in tissue engineering. It has been demonstrated that these renewable, ready-to-use natural scaffolds can undergo further modifications through specialized treatments such as metallization and carbonization, enabling the creation of functional biomaterials while maintaining the species-specific hierarchical 3D structure. The study presented remarkable findings, including the demonstration of the unique shape-memory behavior of these scaffolds even after two months of exposure to high mechanical pressure at temperatures exceeding 100 °C. Additionally, the cytocompatibility and biological performance of natural and carbonized (1200 °C) spongin scaffolds, derived from selected bath sponges, were comparatively investigated with respect to growth and proliferation of human MG-63 osteoblastic cells. Understanding whether carbonization universally enhances osteogenic capabilities or selectively amplifies the inherent architectural advantages remains to be critical for the rational design of sponge-derived scaffolds in bone and structural tissue engineering applications.

Naturally pre-structured three-dimensional (3D) scaffolds derived from commercial marine sponges represent renewable biomaterials with hierarchical, porous architecture optimized by evolution. For the first time, purified spongin scaffolds from Hippospongia communis sponges were functionalized via ion–plasma vacuum arc deposition of titanium, followed by high-temperature carbonization. The applied metallization process preserved the native open-cell 3D architecture of spongin while introducing an α-Ti nanostructured surface layer. Subsequent carbonization at 1200 °C led to the formation of turbostratic carbon and crystalline titanium carbide/oxycarbide phases, as confirmed by SEM, EDX, HRTEM, XRD, and Raman spectroscopy. The biological response of MG-63 osteoblast-like cells was evaluated using indirect cytocompatibility screening, Live/Dead confocal microscopy, WST-1 metabolic activity analysis, protein-normalized ALP-associated activity, and immunofluorescence staining of osteoblast- and adhesion-associated markers. MG-63 cells were selected to provide a bone-relevant osteoblast-like in vitro model for assessing cell–material interactions on Ti-containing spongin-based scaffolds. Ti–Spg and C–Ti–Spg scaffolds demonstrated enhanced cell coverage after 7 days of culture compared with native spongin. At day 14, C–Ti–Spg showed the highest protein-normalized ALP-associated activity together with the most extensive RUNX2-, OPN- and FAK-associated immunostaining pattern, supporting enhanced osteoblast-related activity and adhesion/matrix-associated cell–scaffold interactions under basal culture conditions. Complementary WST-1 metabolic readouts and FDA/PI confocal imaging did not indicate material-induced cytotoxicity, while WST-1 data were interpreted as relative metabolic indicators because colorimetric assays in 3D porous scaffolds can be influenced by reagent diffusion and scaffold architecture. This study demonstrates that naturally prefabricated 3D spongin scaffolds can be successfully metallized with Ti and converted into TiC-containing carbonized composites without loss of structural integrity or cytocompatibility. The combination of preserved hierarchical architecture with titanium-based surface chemistry provides a sustainable platform for the further development of bioinspired functional scaffolds for tissue engineering applications. Graphical abstract