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

Abstract

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·H 2 O/DMSO was employed as a non-derivatizing solvent. Sequential dissolution of cellulose phosphates, casting, coagulation, solvent exchange, and scCO 2 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 scCO 2 drying. The low DS P values have no negative impact on pore size distribution, specific surface (S BET ≤ 310 m 2 g −1 ), porosity (Π 95.5-97 vol.%), or stiffness (Eρ ≤ 211 MPa cm 3 g −1 ). Considering the sterilization capabilities of scCO 2 , existing templating opportunities to afford dual-porous scaffolds and the good hemocompatibility of phosphorylated cellulose, TBAF·H 2 O/DMSO can be regarded a promising solvent system for the manufacture of cell scaffolding materials.

Hemocompatibility of cellulose phosphate aerogel membranes with potential use in bone tissue engineering

“…Microscopic evidence suggests that cellulose phosphates form somewhat denser networks at the expense of micron-size pores. Pore interconnectivity, pore volumes and pore size distributions, including the results of small-angle and wide-angle X-ray scattering (SAXS, WAXS) studies of similar samples have been reported elsewhere (Pircher et al, 2016;Schimper et al, 2018;Schimper et al, 2020). The reduced fraction of micron-sized pores is considered an advantage as it can impart enhanced robustness to the "walls" of large interconnected micron-size pores (50-500 μm) as present in dual-porous cellulosic scaffolds prepared from temporary templates of slightly fused PMMA or paraffin spheres (Pircher et al, 2015).…”

“…Cellulose phosphorylation was conducted as recently detailed ( Schimper et al, 2020 ). The amounts given in the following are sufficient for the preparation of 100 g cellulose phosphate.…”

“…In a concomitant attempt to further optimize the open macroporous cell wall architecture of dual-porous biocompatible cellulose scaffolds presented elsewhere ( Pircher et al, 2015 ), the scaffolding materials of this study were prepared following a recently proposed cellulose dissolution/coagulation protocol employing the hitherto rarely used cellulose solvent system tetrabutyl ammoniumfluoride/dimethyl sulfoxide/water (TBAF/DMSO/H 2 O) ( Pircher et al, 2016 ; Schimper et al, 2018 ). The thus obtained cellulose aerogels and cellulose phosphate aerogels ( Schimper et al, 2020 ) were tested for bioactivity (cd-Hap formation in simulated body fluid) and incubated with heparin anticoagulated whole human blood. Both blood and scaffolds were studied with regard to key parameters of hemostasis and inflammatory response.…”

False Morphology of Aerogels Caused by Gold Coating for SEM Imaging

“…Silica, silica-casein hybrid, silica-gelatin hybrid, Ca-alginate, polyimide, polyamide, Ca(II) crosslinked polyamide and cellulose aerogels were prepared using recipes previously published in the literature [ 20 , 21 , 22 , 39 , 40 , 41 , 42 , 43 , 44 , 45 ]. The essential summaries of the synthetic procedures are given in the Supplementary Materials .…”

Special Issue: Biopolymers in Drug Delivery and Regenerative Medicine

“…The obtained material was electroactive and allowed the release of dexamethasone by electrochemical stimulation, providing a stable system to be used in bioelectronic applications. Finally, cellulose phosphate aerogels for biomedical uses were developed by Schimper et al [ 11 ] through an environmentally friendly methodology based on the conversion of biomass into functional materials. The obtained derivatized cellulose aerogels can be beneficial for the design of dual-porous cell scaffolding materials with interconnected mesopores and micron-size pores.…”