Environmentally Sustainable Chitin-Based Composite Structures Isolated from Lichens: Physicochemical Characterization and Biointerface Evaluation

Lichens are complex symbiotic organisms composed of fungi and photosynthetic partners such as algae or cyanobacteria. While numerous bioactive compounds have been extracted from lichens, their insoluble, structural polymeric materials remain largely unexplored. In this study, the structural components of four lichen species—Xanthoparmelia pulla, Rhizoplaca chrysoleuca, Diploschistes scruposus, and Umbilicaria nylanderiana—were isolated through sequential demineralization, deproteinization, and decolorization processes to obtain sustainable biopolymeric matrices. The isolated materials were characterized using FTIR, XRD, TGA, SEM, and EDS analyses. The combined physicochemical analyses supported the presence of chitin-containing structural polysaccharides together with residual mineral components and revealed species-dependent differences in the chemical, crystalline, thermal, morphological, and elemental characteristics of the isolated materials. XRD analysis further revealed distinct diffraction profiles and contributions from residual crystalline mineral phases, particularly CaCO₃. SEM observations indicated species-dependent differences in surface morphology, while EDS confirmed the presence of C, N, O, Si, and Ca elements. The MTT assay revealed species-, concentration-, and time-dependent differences in L929 cell viability. Materials derived from X. pulla and R. chrysoleuca showed comparatively favorable cellular responses, whereas D. scruposus and U. nylanderiana caused significant reductions in cell viability. These findings provide comparative physicochemical and cellular-response data on lichen-derived structural materials and support their further investigation as naturally derived materials for potential biointerface applications.