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 DSP (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 DSP values have no negative impact on pore size distribution, specific surface (SBET ≤ 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.
Highlights
Amplifying efforts towards a more bio-based economy have recently revived the urge for novel smart processes capable of efficiently transforming biomass or its constituents into functional materials.Molecules 2020, 25, 1695; doi:10.3390/molecules25071695 www.mdpi.com/journal/moleculesAmong the broad variety of biopolymers, cellulose is probably the most valuable renewable resource, since it is an abundant unique source of energy, chemicals, and materials
Based on the finding that the non-derivatizing solvent system tetrabutylammonium fluoride / dimethylsulfoxide (TBAF/DMSO) affords the formation of small particles, and finely substructured cellulose II networks [32], we extended the exploration of this solvent for processing different types of pulp into cellulose aerogels [36]
This study investigates the utilization of TBAF·xH2 O/DMSO for the preparation of cellulose phosphate aerogels since the latter have shown promise as cell scaffolding materials
Summary
Amplifying efforts towards a more bio-based economy have recently revived the urge for novel smart processes capable of efficiently transforming biomass or its constituents into functional materials. Besides dual-porous architecture, appropriate nanotopology, surface chemistry, electrical charge density, mechanical properties, or availability of growth factors are further important prerequisites [26] This is complemented by purity and preservation of chemical integrity of cellulose throughout processing into the desired cell scaffolding materials. Cross-linked aerogels obtained from cellulose nanocrystals carrying a low count of phosphate halfester groups on their surface were reported to fulfil many requirements of viable bone tissue scaffolds [21] This complements the results of earlier attempts aiming at the preparation of cellulose II phosphate aerogels via shaping and coagulation of cellulose phosphates from Lyocell dopes, i.e., using the solvent system N-methylmorpholine-N-oxide (NMMO)/water. The exploratory work was expected to provide data for developing a cellulose phosphate 3D printing approach for cell scaffolding materials
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