Oxidized Cladophora nanocellulose derivatives : Functionalization towards biocompatible materials

Nanocellulose is a promising candidate for biomedical applications because of its enhanced mechanical properties, increased surface area and greater porosity compared to bulk cellulose. This thesis investigates the functionalization of Cladophora nanocellulose and evaluates the influence of these modifications on physicochemical properties and biocompatibility of the material. An electrochemically assisted TEMPO-mediated oxidation setup produced cellulose materials with varying degrees of carboxyl groups. This approach allowed control of the charge applied during the process and adjustment of the carboxylation. Carboxylated nanocellulose membranes had smaller surface area and total pore volume and a more compact structure than the membranes of the unmodified material. Moreover, the introduction of carboxyl groups resulted in membranes with an aligned fiber pattern; the alignment and aggregation of the fibers tended to increase with higher degrees of oxidation. Cytocompatibility studies using fibroblasts and osteoblastic cells have shown that the bioinert Cladophora nanocellulose membranes can be rendered bioactive by the introduction of carboxyl groups. Nevertheless, at least 260 µmol g-1 carboxyl groups are required to obtain nanocellulose membranes that promote cell adhesion and spreading comparable to those observed when cells are cultured on tissue culture material. In parallel, a periodate oxidation produced 10-20 µm 2,3-dialdehyde cellulose beads with very smooth and compact surfaces. This material was sulfonated up to 50% of the aldehyde groups, resulting in charged, porous structures that maintained the spherical shape. The mesoporous assembly could be tailored by altering the degree of sulfonation, which also produced variations in surface charge, ζ-potential, specific density, surface area and thermal stability. Because the physicochemical properties make these sulfonated beads potential candidates for immunosorption and blood-related applications, they were further characterized regarding hemocompatibility. In vitro studies showed that both sulfonated beads and unmodified Cladophora nanocellulose did not present hemolytic activity. The pro-coagulant activity of the sulfonated beads was significantly lower than that of the unmodified nanocellulose; however, the material’s modifications did not diminish the activation of the complement system. The results presented in this thesis show that it is possible to tailor the biocompatibility of Cladophora nanocellulose by introducing chemical modifications to its structure and by carefully tuning its physicochemical properties