On the Road to Biopolymer Aerogels—Dealing with the Solvent

Abstract

Aerogels are three-dimensional ultra-light porous structures whose characteristics make them exciting candidates for research, development and commercialization leading to a broad scope of applications ranging from insulation and catalysis to regenerative medicine and pharmaceuticals. Biopolymers have recently entered the aerogel foray. In order to fully realize their potential, progressive strategies dealing with production times and costs reduction must be put in place to facilitate the scale up of aerogel production from lab to commercial scale. The necessity of studying solvent/matrix interactions during solvent exchange and supercritical CO2 drying is presented in this study using calcium alginate as a model system. Four frameworks, namely (a) solvent selection methodology based on solvent/polymer interaction; (b) concentration gradient influence during solvent exchange; (c) solvent exchange kinetics based on pseudo second order model; and (d) minimum solvent concentration requirements for supercritical CO2 drying, are suggested that could help assess the role of the solvent in biopolymer aerogel production.

Preparation of Biopolymer Aerogels Using Green Solvents

“…However, direct soaking in a bath with pure ethanol or other organic solvents leads to significant irreversible shrinkage. To avoid this drawback, stepwise solvent exchange is performed 5,9 4. Production of Aerogels by Supercritical CO 2 Drying 1.…”

Hybrid Alginate‐Based Cryogels for Life Science Applications

“…This solvent exchange affects the gel structure resulting in some shrinkage [24] and makes the loading of the scaffolds with active principles (drugs, cells etc.) Water cannot directly be extracted from hydrogels due to its very low solubility in sc-CO 2 at pressures and temperatures typically used for aerogel preparation (10 -15 MPa, 303 -333 K).…”

“…Instead, water in the hydrogel has to be exchanged with an organic solvent prior to drying (solvent exchange step). This solvent exchange affects the gel structure resulting in some shrinkage [24] and makes the loading of the scaffolds with active principles (drugs, cells etc.) problematic.…”

A redox strategy to tailor the release properties of Fe(III)-alginate aerogels for oral drug delivery

“…The drying procedure was initiated only when the ethanol content reached min. 98.5 V/V% to ensure single phase conditions during subsequent supercritical drying (Subrahmanyam et al, 2015). The samples were dried with supercritical CO 2 at 45°C and 140 bar using a continuous flow process in a high pressure autoclave, as described elsewhere (Goncalves et al, 2016;Smirnova, Mamic, & Arlt, 2003).…”

“…Highly porous aerogels can be relatively simply prepared from metal ion crosslinked alginate hydrogels (Garcia-Gonzalez, Quignard, Valentin, & Di Renzo, 2008;Subrahmanyam, Gurikov, Dieringer, Sun, & Smirnova, 2015;Tkalec, Kranvogl, Uzunalic, Knez, & Novak, 2016). Similarly to the hydrogels, these aerogels are versatile biomaterials which were recently introduced into the field of drug delivery research Veronovski, Novak, & Knez, 2012).…”