Bacterial cellulose produced by the gram-negative bacterium Gluconacetobacter xylinum was found to be an excellent native starting material for preparing shaped ultra-lightweight cellulose aerogels. The procedure comprises thorough washing and sterilization of the aquogel, quantitative solvent exchange and subsequent drying with supercritical carbon dioxide at 40 degrees C and 100 bar. The average density of the obtained dry cellulose aerogels is only about 8 mg x cm(-3) which is comparable to the most lightweight silica aerogels and distinctly lower than all values for cellulosic aerogels obtained from plant cellulose so far. SEM, ESEM and nitrogen adsorption experiments at 77 K reveal an open-porous network structure that consists of a comparatively high percentage of large mesopores and smaller macropores.

Ultra-lightweight cellulose aerogels can be obtained in three steps: (1) preparation of a cellulose solution in molten N-methylmorpholine-N-oxide monohydrate (NMMO·H2O) at 110–120°C and casting of the viscous mass into moulds; (2) extraction of the solidified castings with ethanol to initiate cellulose aggregation and to remove NMMO·H2O so that the fragile, fine-porous texture of cellulose II is largely retained; and (3) drying of the lyogel using supercritical carbon dioxide (scCO2). According to this approach, cellulosic aerogels were prepared from eight commercial cellulosic materials and pulps and analysed for selected chemical, physicochemical and mechanical parameters. The results reveal that all aerogels obtained from 3% cellulose containing NMMO·H2O melts had a largely uniform mesoporous structure with an average pore size of ∼9–12 nm, surface area of 190–310 m2 g-1, and specific density of 0.046–0.069 g cm-3, but rather low mechanical stability expressed as compressive yield strain of 2.9–5.5%. All samples showed viscoelastic behaviour, with Young's modulus ranging from ∼5 to 10 N mm-2. Doubling the cellulose content in the NMMO·H2O melt from 3% to 6% increased Young's modulus by one order of magnitude. Shrinkage of the fragile cellulose bodies during scCO2 drying was still considerable and is subject to further investigations. Influencing parameters such as scCO2 pressure, cellulose content, regenerating solvent and the number of regenerating baths were optimised.

Cellulosic aerogels are intriguing new materials produced by supercritical drying of regenerated cellulose obtained by solvent exchange of solid Lyocell moldings. From Nmethylmorpholine-N-oxide (NMMO) solutions with cellulose contents between 1 and 12%, dimensionally stable cellulose bodies are produced, in which the solution structure of the cellulose is largely preserved and transferred into the solid state, the material having densities down to 0.05 g cm -3 and surface areas of up to 280 m 2 g -1 . In this study, several aspects of cellulosic aerogel production are communicated: the stabilization of the cellulose solutions against degradation reactions by agents suitable for later extraction and drying, a reliable extraction and drying procedure by supercritical carbon dioxide, the advantages of DMSO/NMMO in this procedure as a solvent/non-solvent pair, and some data on the physical properties of the materials.

Bacterial cellulose aerogels overcome the drawback of shrinking during preparation by drying with supercritical CO2. Thus, the pore network of these gels is fully accessible. These materials can be fully rewetted to 100% of its initial water content, without collapsing of the structure due to surface tension of the rewetting solvent. This rehydration property and the high pore volume of these material rendered bacterial cellulose aerogels very interesting as controlled release matrices. Supercritical CO2 drying, the method of choice for aerogel preparation, can simultaneously be used to precipitate solutes within the cellulose matrix and thus to load bacterial cellulose aerogels with active substances. This process, frequently termed supercritical antisolvent precipitation, is able to perform production of the actual aerogel and its loading in one single preparation step. In this work, the loading of a bacterial cellulose aerogel matrix with two model substances, namely dexpanthenol and L‐ascorbic acid, and the release behavior from the matrix were studied. A mathematical release model was applied to model the interactions between the solutes and the cellulose matrix. The bacterial cellulose aerogels were easily equipped with the reagents by supercritical antisolvent precipitation. Loading isotherms as well as release kinetics indicated no specific interaction between matrix and loaded substances. Hence, loading and release can be controlled and predicted just by varying the thickness of the gel and the solute concentration in the loading bath.

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Shaped cellulosic aerogels-as the 'young' generation succeeding the well-established silica and synthetic polymer-based aerogels-are intriguing materials that feature properties similar to those of their antecessors combined with the additional advantages and characteristics of the re-growing biopolymer cellulose. Reinforced shaped cellulosic aerogels consisting of two interpenetrating networks of cellulose and silica were prepared from shaped cellulose solutions by (1) regenerating (reprecipitating) cellulose with ethanol, (2) subjecting the obtained shaped alcogels to sol-gel condensation with tetraethoxysilane as the principal network-forming compound, and (3) drying the reinforced cellulose bodies with supercritical carbon dioxide. The influence of different types of cellulose and sol-gel forming parameters on porosity, cellulose integrity, and silica content were studied by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), gel permeation chromatography (GPC), and nitrogen adsorption at 77 K. The results of SEM and EDX confirmed the presence of silicon inside the obtained cellulosic aerogel. GPC of the cellulosic matrix prior and after silica coating showed no alteration of the molecular weight distribution for most of the samples, confirming a far-reaching preservation of cellulose's chemical integrity throughout the modification procedure. Nitrogen adsorption experiments at 77 K revealed that the micro-and meso-pore characteristics were largely retained throughout silica modification.

Hemocompatible, shaped cellulose phosphate aerogels were obtained from phosphorylated cellulosic pulps of low degree of phosphorylation (DSP≤0.20) by dissolution in stabilized NMMO×H2O, shaping, reprecipitation with ethanol and subsequent scCO2 drying. The novel aerogels were found to be promising materials for cell scaffolding and bone grafting. Special features include their interconnected and spread porosity, highly porous surface and microstructure, good hemocompatibility, and suitable hydroxyl apatite-binding environment. Adsorption of Ca2+ ions to the phosphate groups did not invert the negative inflammatory response observed after phosphorylating cellulose, but increased platelet-dependent parameters of hemostasis.