Aerogels from Cellulose Phosphates of Low Degree of Substitution: A TBAF·H₂O/DMSO Based Approach

Biopolymer aerogels of appropriate open-porous morphology, nanotopology, surface chemistry, and mechanical properties can be promising cell scaffolding materials. Here, we report a facile approach towards the preparation of cellulose phosphate aerogels from two types of cellulosic source materials. Since high degrees of phosphorylation would afford water-soluble products inappropriate for cell scaffolding, products of low DS_P (ca. 0.2) were prepared by a heterogeneous approach. Aiming at both i) full preservation of chemical integrity of cellulose during dissolution and ii) utilization of specific phase separation mechanisms upon coagulation of cellulose, TBAF·H₂O/DMSO was employed as a non-derivatizing solvent. Sequential dissolution of cellulose phosphates, casting, coagulation, solvent exchange, and scCO₂ drying afforded lightweight, nano-porous aerogels. Compared to their non-derivatized counterparts, cellulose phosphate aerogels are less sensitive towards shrinking during solvent exchange. This is presumably due to electrostatic repulsion and translates into faster scCO₂ drying. The low DS_P values have no negative impact on pore size distribution, specific surface (S_BET ≤ 310 m² g^-1), porosity (Π 95.5-97 vol.%), or stiffness (Eρ ≤ 211 MPa cm³ g^-1). Considering the sterilization capabilities of scCO₂, existing templating opportunities to afford dual-porous scaffolds and the good hemocompatibility of phosphorylated cellulose, TBAF·H₂O/DMSO can be regarded a promising solvent system for the manufacture of cell scaffolding materials.