Abstract
In this short review, drug delivery systems, formed by polysaccharide-based (i.e., agarose, alginate, and chitosan) aerogels, are analyzed. In particular, the main papers, published in the period 2011–2020 in this research field, have been investigated and critically discussed, in order to highlight strengths and weaknesses of the traditional production techniques (e.g., freeze-drying and air evaporation) of bio-aerogels with respect to supercritical CO2 assisted drying. Supercritical CO2 assisted drying demonstrated to be a promising technique to produce nanostructured bio-aerogels that maintain the starting gel volume and shape, when the solvent removal occurs at negligible surface tension. This characteristic, coupled with the possibility of removing also cross-linking agent residues from the aerogels, makes these advanced devices safe and suitable as carriers for controlled drug delivery applications.
Highlights
The results indicated that a slower release of ketoprofen was achieved increasing PEG diacrylate concentration, since it lowered aerogel permeability when it was immersed in an aqueous solution
Burst effect associated to CS-based aerogel was eliminated after graphene oxide (GO) addition Cryogels with enhanced antibacterial action against S. aureus The same amount of drug was incorporated into the gel using supercritical impregnation instead of organic solvents High specific surface area
Not all the solubilised drug in supercritical CO2 (SC-CO2) was absorbed onto the aerogel, and the non-absorbed drug can precipitate in form of nanoparticles Cryogels and xerogels showed a condense structure; Burst effect was detected during the drug release from aerogel ethylenediamine-modified agarose (ETAGR) had a lower cross-linking density than unmodified AGR and, for this reason, burst effect was detected during the drug release test Sucrose particles could be present on the gel CS aerogel showed a collapsible cell structure
Summary
Pharmaceutical industry is evolving from traditional drug delivery systems, in which a biopolymeric matrix is used to provide weight, volume and flowability, toward new formulations, in which a biopolymer is adopted as drug performance enhancer in terms of release time and bioavailability (Agüero et al, 2017; Yuan et al, 2018; Shi et al, 2019; Wei et al, 2020; Liu et al, 2021). According to Takeshita et al (2020a), a low affinity between the polymer forming the gel and the substituting solvent induces the formation of an aerogel-like structure during the solvent exchange itself and a drastic shrinkage of the gel To minimize this phenomenon, some guidelines can be followed: (i) to select an organic solvent at high affinity with the biopolymer (Takeshita et al, 2020a); (ii) to perform a multi-step solvent exchange (García-González et al, 2011; Baldino et al, 2019), at increasing percentage by volume of the solvent substituting water. They demonstrated that, thanks to this process, it was possible to obtain a complete removal of GTA from CS gels: the supercritical mixture (CO2 + ethanol) showed a high affinity toward GTA, favoring its removal from the samples For this reason, SC-CO2 drying can be considered a promising process to purify chemically cross-linked CS aerogels, to be used for pharmaceutical applications.
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