Effect of drying methods on Acetobacter xylinum bacterial cellulose aerogels and cryogels

Bacterial cellulose (BC) pellicles were produced from Acetobacter xylinum using a simple, additive-free, and low-cost static cultivation method consistent with sustainable and green bioprocessing principles. Two post-synthesis drying routes were compared: supercritical carbon dioxide (scCO₂) drying following acetone solvent exchange and direct lyophilization without chemical additives or pre-freezing. The resulting BC aerogels and cryogels were characterized by SEM, confocal microscopy, BET analysis, FTIR spectroscopy, EDS, and geometrical evaluation with a particular emphasis on nanostructure, porosity, and network integrity. scCO₂-dried BC aerogels exhibited a well-preserved three-dimensional nanofibrillar network, achieving a BET surface area (123 m²/g), large pore volume (0.36 cm³/g), and an average pore diameter of 10 nm. Confocal microscopy revealed higher surface roughness (Rz up to ~ 58 μm), reflecting a more developed and heterogeneous surface topography. Lyophilized BC cryogels showed lower surface area (51 m²/g) and pore volume (0.13 cm³/g); however, SEM and confocal analyses indicated that the nanofibrillar network and three-dimensional architecture were largely retained, with only localized fibril aggregation and reduced roughness (~ 28-30 μm). EDS confirmed high chemical purity in scCO₂-dried aerogels, while minor inorganic traces detected in cryogels were attributed to residual components from the tea-based culture medium. Although scCO₂ drying provided slightly superior structural preservation and textural properties, the porous architecture remained comparable between the two methods. Overall, additive-free BC pellicles produced by static cultivation and processed via limited pre-freezing followed by lyophilization provided a structurally comparable and more sustainable alternative, offering a practical balance between textural performance and processing simplicity. These findings underscore the potential of simplified drying strategies for the sustainable fabrication of BC-based porous materials without compromising structural functionality.     .