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CO 2 levels in the atmosphere are increasing exponentially. The current climate change effects motivate an urgent need for new and sustainable materials to capture CO 2 . Porous materials are particularly interesting for processes that take place near atmospheric pressure. However, materials design should not only consider the morphology, but also the chemical identity of the CO 2 sorbent to enhance the affinity towards CO 2 . Poly(ionic liquid)s (PILs) can enhance CO 2 sorption capacity, but tailoring the porosity is still a challenge. Aerogel's properties grant production strategies that ensure a porosity control. In this work, we joined both worlds, PILs and aerogels, to produce a sustainable CO 2 sorbent. PIL-chitosan aerogels ( AEROPILs ) in the form of beads were successfully obtained with high porosity (94.6-97.0%) and surface areas (270-744 m 2 /g). AEROPILs were applied for the first time as CO 2 sorbents. The combination of PILs with chitosan aerogels generally increased the CO 2 sorption capability of these materials, being the maximum CO 2 capture capacity obtained (0.70 mmol g -1 , at 25 °C and 1 bar) for the CHT:P[DADMA]Cl 30% AEROPIL .

Sterilization is a quite challenging step in the development of novel polymeric scaffolds for regenerative medicine since conventional sterilization techniques may significantly alter their morphological and physicochemical properties. Supercritical (sc) sterilization, i.e. the use of scCO 2 as a sterilizing agent, emerges as a promising sterilization method due to the mild operational conditions and excellent penetration capability. In this work, a scCO 2 protocol was implemented for the one-pot preparation and sterilization of poly(ε-caprolactone) (PCL)/poly(lactic-co-glycolic acid) (PLGA) scaffolds. The sterilization conditions were established after screening against both Gram-positive (Staphylococcus aureus) and Gram-negative (Escherichia coli, Pseudomonas aeruginosa) vegetative bacteria and spores of Bacillus stearothermophilus, Bacillus pumilus and Bacillus atrophaeus. The transition from the sterilization conditions (140 bar, 39 °C) to the compressed foaming (60 bar, 26 °C) was performed through controlled depressurization (3.2 bar/min) and CO 2 liquid flow. Controlled depressurization/pressurization cycles were subsequently applied. Using this scCO 2 technology toolbox, sterile scaffolds of well-controlled pore architecture were obtained. This sterilization procedure successfully achieved not only SAL-6 against well-known resistant bacteria endospores but also improved the scaffold morphologies compared to standard gamma radiation sterilization procedures., (Copyright © 2021 The Authors. Published by Elsevier B.V. All rights reserved.)

Solid lipid microparticles (SLMPs) are attractive carriers as delivery systems as they are stable, easy to manufacture and can provide controlled release of bioactive agents and increase their efficacy and/or safety. Particles from Gas-Saturated Solutions (PGSS ® ) technique is a solvent-free technology to produce SLMPs, which involves the use of supercritical CO 2 (scCO 2 ) at mild pressures and temperatures for the melting of lipids and atomization into particles. The determination of the key processing variables is crucial in PGSS ® technique to obtain reliable and reproducible microparticles, therefore the modelling of SLMPs production process and variables control are of great interest to obtain quality therapeutic systems. In this work, the melting point depression of a commercial lipid (glyceryl monostearate, GMS) under compressed CO 2 was studied using view cell experiments. Based on an unconstrained D-optimal design for three variables (nozzle diameter, temperature and pressure), SLMPs were produced using the PGSS ® technique. The yield of production was registered and the particles characterized in terms of particle size distribution. Variable modeling was carried out using artificial neural networks and fuzzy logic integrated into neurofuzzy software. Modeling results highlight the main effect of temperature to tune the mean diameter SLMPs, whereas the pressure-nozzle diameter interaction is the main responsible in the SLMPs size distribution and in the PGSS ® production yield.

The increasing complexity in morphology and composition of modern biomedical materials (e.g., soft and hard biological tissues, synthetic and natural-based scaffolds, technical textiles) and the high sensitivity to the processing environment requires the development of innovative but benign technologies for processing and treatment. This scenario is particularly applicable where current conventional techniques (steam/dry heat, ethylene oxide, and gamma irradiation) may not be able to preserve the functionality and integrity of the treated material. Sterilization using supercritical carbon dioxide emerges as a green and sustainable technology able to reach the sterility levels required by regulation without altering the original properties of even highly sensitive materials. In this review article, an updated survey of experimental protocols based on supercritical sterilization and of the efficacy results sorted by microbial strains and treated materials was carried out. The application of the supercritical sterilization process in materials used for biomedical, pharmaceutical, and food applications is assessed. The opportunity of supercritical sterilization of not only replace the above mentioned conventional techniques, but also of reach unmet needs for sterilization in highly sensitive materials (e.g., single-use medical devices, the next-generation biomaterials, and medical devices and graft tissues) is herein unveiled., (© 2019 Wiley Periodicals, Inc.)

The increase in the world demand of bone and cartilage replacement therapies urges the development of advanced synthetic scaffolds for regenerative purposes, not only providing mechanical support for tissue formation, but also promoting and guiding the tissue growth. Conventional manufacturing techniques have severe restrictions for designing these upgraded scaffolds, namely, regarding the use of organic solvents, shearing forces, and high operating temperatures. In this context, the use of supercritical fluid technology has emerged as an attractive solution to design solvent-free scaffolds and ingredients for scaffolds under mild processing conditions. The state-of-the-art on the technological endeavors for scaffold production using supercritical fluids is presented in this work with a critical review on the key processing parameters as well as the main advantages and limitations of each technique. A special stress is focused on the strategies suitable for the incorporation of bioactive agents (drugs, bioactive glasses, and growth factors) and the in vitro and in vivo performance of supercritical CO2-processed scaffolds.

This review provides a concise overview of up-to-date developments in the processing of neat poly(lactic acid) (PLA), improvement in its properties, and preparation of advanced materials using a green medium (CO2 under elevated pressure). Pressurized CO2 in the dense and supercritical state is a superior alternative medium to organic solvents, as it is easily available, fully recyclable, has easily tunable properties, and can be completely removed from the final material without post-processing steps. This review summarizes the state of the art on PLA drying, impregnation, foaming, and particle generation by the employment of dense and supercritical CO2 for the development of new materials. An analysis of the effect of processing methods on the final material properties was focused on neat PLA and PLA with an addition of natural bioactive components. It was demonstrated that CO2-assisted processes enable the control of PLA properties, reduce operating times, and require less energy compared to conventional ones. The described environmentally friendly processing techniques and the versatility of PLA were employed for the preparation of foams, aerogels, scaffolds, microparticles, and nanoparticles, as well as bioactive materials. These PLA-based materials can find application in tissue engineering, drug delivery, active food packaging, compostable packaging, wastewater treatment, or thermal insulation, among others. [ABSTRACT FROM AUTHOR]

The atmospheric concentration of CO 2 is rising at an alarming pace, creating a pressing need for new and sustainable materials capable of capture and conversion. Poly(ionic liquid)s (PILs) are particularly effective catalysts for processes at or near atmospheric pressure. PILs industrial application poses challenges due to the low porosity of PIL, the limited batch conversion capacity, and the difficulties in reuse. To overcome these limitations, we herein propose the use of AEROPILs catalysts obtained from the integration of PILs in chitosan-based aerogels. These cost-effective highly porous materials have unique and tuneable porous properties making them not only ideal sustainable CO 2 sorbents but also promising heterogeneous catalysts. While AEROPILs show moderate yields for CO 2 conversion in batch mode, high catalytic activity was achieved when AEROPILs were used to catalyse the CO 2 cycloaddition reaction to epoxides in packed-bed reactors operated under continuous flow. The catalytic activity and stability were maintained over 60 h without activity loss, and high productivity (space-time yield of 21.18 g prod h−1 L−1). This research reveals the pioneering use of AEROPILs to efficiently upcycle CO 2 into cyclic carbonate under a continuous flow setup. [Display omitted] • Novel AEROPILs formulations have been optimised for CO 2 conversion. • Cyclic carbonates were obtained with 81 % yield and 90 % selectivity in batch. • AEROPILs remained active for 5 successive catalytic cycles in batch. • In continuous flow AEROPILs exhibited a productivity of 21.18 g prod h−1 L−1. • In continuous flow AEROPILs remained stable for over 60 h. [ABSTRACT FROM AUTHOR]

Dry powder inhalers (DPIs) have gained increasing clinical acceptance in the local treatment of lung diseases due to their ability to meet the evolving needs of patients while avoiding environmental concerns. However, some formulations for DPIs still encounter performance limitations in terms of aerodynamic properties and achievement of therapeutic doses. Innovative aerogel powder formulations for DPIs processed using combined supercritical CO 2 (scCO 2)-based technologies can overcome these limitations, especially in the case of poorly water-soluble drugs. The loading of hydrophobic drugs into aerogels can be optimized through a thorough understanding of the physicochemical properties of the formulation and the scCO 2 processing conditions. In this study, drug-loaded alginate aerogel particles were prepared by combining gelation-emulsification techniques and scCO 2 -based technologies. Beclomethasone dipropionate (BDP), a hydrophobic corticosteroid, was incorporated into the aerogel matrix by scCO 2 impregnation. The influence of contact time, initial amount of drug, and use of co-solvents on the efficiency of scCO 2 impregnation were studied. The kinetics of the BDP adsorption process was modelled to elucidate the time required for the drug to attain equilibrium concentration under specific operating conditions. Nitrogen adsorption-desorption and helium pycnometry revealed particles with large surface area (>200 m2/g) and porosity (ca. 90%). The resulting aerogels had excellent aerodynamic properties at relevant BDP doses, as confirmed by in vitro lung deposition tests. Ex vivo permeability tests with porcine lung tissues evidenced that BDP released from the inhaled formulation could penetrate the bronchial tissue. [Display omitted] • Green CO 2 technologies are promising to produce DPIs with good performance. • Co-solvents and impregnation contact time have a great effect on drug loading. • Modelling of the SCF-assisted impregnation kinetics indicates that drug loading is regulated by diffusion aided by co-solvent. • Two simultaneous first-order drug release profiles were modelled for the pattern of inhaled particles. • BDP released from the alginate aerogel matrix penetrates the bronchial lung tissue. [ABSTRACT FROM AUTHOR]

Compressed CO 2 foaming allows for obtaining porous solid drug-loaded scaffolds for regenerative medicine under mild conditions and in the absence of organic solvents. However, a precise process design and optimization as well as certain modifications of the technology are still needed to tackle certain limitations like the control of the porosity of scaffolds from certain low molecular weight biopolymers. Besides, stability under storage is a critical quality attribute to define the usefulness of scaffolds. In the particular case of bone scaffolds, the information on this regard is still very limited and strongly dependent on each particular composition and architecture. In order to gain an insight into this issue, scaffolds composed of poly(lactic- co -glycolic acid) (PLGA) and poly(ε-caprolactone) (PCL) as polymeric matrix, with and without pre-gelified starch (St) as release-controlling agent and dexamethasone (DXMT) as bioactive compound were designed and prepared by a modified compressed CO 2 foaming technique (26 °C, 60 bar) and assessed regarding stability under storage. The scaffolds were stored at 25 °C and 65% relative humidity (zone II ICH-climatic conditions for Europe, USA and Japan) for up to three months to determine the effect of storage on the structural, physicochemical and mechanical properties, and DXMT release. Changes in the scaffolds point out the importance of stability assays and storage conditions. Namely, a decrease in the viscoelastic moduli of the scaffolds and a faster degradation rate were observed after prolonged storage periods. DXMT release from the scaffolds was erosion-controlled and thus modified for scaffolds stored for longer time periods. [ABSTRACT FROM AUTHOR]

CO2 levels in the atmosphere are increasing exponentially. The current climate change effects motivate an urgent need for new and sustainable materials to capture CO2. Porous materials are particularly interesting for processes that take place near atmospheric pressure. However, materials design should not only consider the morphology, but also the chemical identity of the CO2 sorbent to enhance the affinity towards CO2. Poly(ionic liquid)s (PILs) can enhance CO2 sorption capacity, but tailoring the porosity is still a challenge. Aerogel's properties grant production strategies that ensure a porosity control. In this work, we joined both worlds, PILs and aerogels, to produce a sustainable CO2 sorbent. PIL-chitosan aerogels (AEROPILs) in the form of beads were successfully obtained with high porosity (94.6–97.0%) and surface areas (270–744 m2/g). AEROPILs were applied for the first time as CO2 sorbents. The combination of PILs with chitosan aerogels generally increased the CO2 sorption capability of these materials, being the maximum CO2 capture capacity obtained (0.70 mmol g−1, at 25 °C and 1 bar) for the CHT:P[DADMA]Cl30%AEROPIL. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, we investigated on the preparation of three zeolite encapsulated-trityl cations (trityl, dimethoxytrityl and methoxytrityl) using supercritical CO2 (scCO2) as the processing media. Since the studied trityl cations had a size larger than the diameter of the zeolite channels, the fabrication was based on a ship-in-a-bottle procedure using benzene, benzaldehyde, anisole, diphenylcarbinol and benzophenone as building blocks. The different cations were prepared by nucleophilic substitution, using the inner supercage of the acid zeolite as both a microreactor and a negative counterion for the trityl cation. The obtained impregnated samples were purified by cleaning with a continuous flow of scCO2. Loaded amounts of ca. 8 wt.% were obtained following the supercritical procedure. The successful formation of the cation was confirmed by using optical spectroscopies, such as UV–vis diffuse reflectance and FTIR spectroscopies. [Copyright &y& Elsevier]

Abstract: Nanometric inorganic pigments are widely used as fillers for hybrid composite materials. However, these nanometric powders are hydrophilic in nature and their surface must be functionalized before use. In this work, titanium dioxide (TiO2) nanoparticles were coated using silane coupling agents with alkyl functionality. A supercritical carbon dioxide (scCO2) method was used for surface silanization. Five alkylalkoxysilanes with different alkyl chain length and structure were studied: methyltrimethoxy, isobutyltriethoxy, octyltriethoxy, octyldimethylmethoxy and octadecyltrimethoxysilane. The microstructure and thermal stability of deposited monolayers were characterized using thermogravimetric analysis, ATR–IR spectroscopy, transmission electron microscopy, wettability characterization and low-temperature N2 adsorption/desorption analysis. The use of scCO2 as a solvent provided an effective approach to functionalize individual inorganic nanoparticles due to the enhanced diffusivity of the solution molecules in the aggregates interparticle voids. The trifunctional silanes employed here yielded surfaces with better thermal stabilities and greater hydrophobicities than the used monofunctional silane. [Copyright &y& Elsevier]

The effects of surface treatment of nanometric titanium dioxide (TiO2) powder with octyltriethoxysilane on the hydrophobicity of the inorganic nanoparticles have been investigated. Thermogravimetric analysis (TGA), attenuated total reflection infrared spectroscopy (ATR-IR), laser scattering and specific BET-surface area and pore volume measurements were used as characterization techniques. The TiO2 nanoparticles were treated with solutions of supercritical carbon dioxide (scCO2) as solvent and silane molecules. A thermal resistant polysiloxane structure was formed on the TiO2 surface. The mesoporosity of the aggregates of TiO2 was preserved after the supercritical silanization process. The dispersibility of TiO2 in an organic hydrophobic phase (petroleum) was enhanced after the surface treatment. Optimization and modelling of the silanization process in scCO2 media was performed using experimental design. Reaction pressure (P), temperature (T) and processing time (t) were chosen as potential variables that may influence the process. A two-level full factorial design involving 23 experiments was carried out to extract information concerning significant effects and interactions. Results showed that changes in the values of the process variables lead to variations in particle size distribution and porosity of the silanized samples. [ABSTRACT FROM AUTHOR]

The article discusses a study on various L- Polylactic acid (PLA) polymers that range from low to high molecular weight processed at various crystallization conditions. The study addressed the interaction of supercritical carbon dioxide (SCCO2)-drug (triflusal) solutions with low-molecular weight L-PLA to prepare a drug delivery system based on impregnation of the drug in the L-PLA matrix with SCCO2) as solvent.

Abstract: This study aims to analyze the effects of supercritical carbon dioxide (SCCO2) on the carbonation of Portland cement pastes, with and without mineral addition. The process is based on the advantages of the low viscosity and surface tension of SCCO2 that allow the complete wetting of complex substrates with intricate geometries, including internal surfaces of agglomerates such of these found in cement pastes. The supercritical treatment alters the bulk chemical and structural properties of cement pastes by accelerating natural carbonation reactions, while at the same time it reduces both free and bound water. The observed overall effects of supercritical carbonation on Portland cement pastes were the neutralization of pore water alkalinity, the formation of calcium carbonate and the reduction in the Ca/Si ratio of the calcium silicate hydrate (CSH) gel. Moreover, the massive precipitation of calcium carbonate inside microcracks after supercritical treatment caused the refinement of the microstructure, thus, reducing water permeability to a large extent. Supercritical carbonation method can be completed in few hours, rendering it technically interesting. This work also contributes to the idea of increasing the durability of concrete by means of a preventive hydrophobic supercritical treatment against water ingress. A generic SCCO2 method for concrete silanization is proposed here. [Copyright &y& Elsevier]

Abstract: In order to effectively exploit the remarkable properties of fine particles to form hybrid nanostructured composites with applications in the biomedical area, one essential step is their surface functionalization. The overall objective of the present work was to use supercritical carbon dioxide (scCO2) for the design of the surface of inorganic particles by depositing thin and ultrathin films. Two scCO2 routes were proposed to modify the surface of micro- (SiO2, 5μm) and nanometric (TiO2, 20–30nm) oxide particles: antisolvent methods for polymers that are non-soluble in CO2 (polymethylmethacrylate), and the use of compressed CO2 as a solvent for modifiers with certain solubility in scCO2 (octadecylsilane, salicylic acid). In the antisolvent technique, solid particles were dispersed in a solution containing the polymer and mixed with scCO2; polymer precipitation, induced by the presence of CO2, occurred preferentially onto the available surface offered by the oxide particles. For CO2-soluble modifiers, the molecules were transferred from the compressed phase to the surface of the solid particles by diffusion; reactivity between adequate moieties permitted to form covalently grafted films. Vibrational ATR-FTIR spectroscopy was used to evaluate potential interactions between samples components. The wettability of the produced systems was analyzed by dispersion experiments in water and toluene. [Copyright &y& Elsevier]

Abstract: Precipitated calcium carbonate (PCC) is conventionally produced through the gas–solid–liquid carbonation route, which consists on bubbling gaseous CO2 through a concentrated calcium hydroxide (Ca(OH)2) slurry. However, atmospheric carbonation processes are slow and have low carbonation efficiency. A novel technology based on the combination of supercritical carbon dioxide (scCO2) and ultrasonic agitation is described here for the preparation of high-yield PCC. The combination of both techniques has demonstrated to produce outstanding improvement for the conversion of Ca(OH)2 to the stable calcite polymorph of calcium carbonate (CaCO3). These experiments were carried out at 313K and 13MPa using a high-pressure reactor immersed in an ultrasounds cleaner bath. The process kinetics and the characteristics of the precipitated particles using ultrasonic agitation were compared with those obtained under similar experimental conditions using mechanical stirring and non-agitated systems. The crystal characteristics of the samples obtained using the three different agitation techniques were characterized by X-ray diffraction and scanning electron microscopy. [Copyright &y& Elsevier]

Abstract: scCO2 technology was used for the impregnation of microporous zeolites with organic molecules. Specifically, faujasite Y was impregnated with 1,3,5-triphenyl-2-pentene-1,5-dione that after reacting with the acid sites of the zeolite large cavities, formed the 2,4,6-triphenylpyrylium cation. Since the triphenylpyrylium cation has a size higher than the diameter of the zeolite channels, the fabrication method was considered as a ship-in-a-bottle procedure. To optimize the loading, different pressures and temperatures were tested in both the diffusion and cyclisation steps used in the impregnation supercritical process. The obtained impregnated samples were purified either by conventional Soxhlet extraction with dichloromethane or by cleaning with a scCO2 continuous flow. Loaded amounts of ca. 4–7wt% were obtained following the supercritical procedure, which resulted more time-effective than the conventional procedure based in the use of organic solvents. Samples obtained were analyzed by thermal analysis, UV–vis and IR spectroscopy and characterization of surface area and micropore volume. [Copyright &y& Elsevier]

Abstract: A supercritical carbon dioxide (SCCO2) antisolvent technique was used for the precipitation of several biopolymers into fibers organized in a three-dimensional network. The work was first focused on separately processing either a biodegradable (polycaprolactone or polylactic acid) or a non-biodegradable (polymethylmetacrylate) homopolymer. Second, we established that the antisolvent supercritical technique can be also used to make fibrous networks of blends constitute by non-biodegradable and biodegradable polymers (polymethylmetacrylate/polycaprolactone). The influence of several operating variables (e.g., liquid solution concentration or flow rate and nozzle design) on the polymers morphology and properties was evaluated. For all studied systems, fibers with a rough textured surface and an extremely high surface area in the order of 100–400m2 g−1 were precipitated. Prepared materials have potential applications in tissue engineering, since they have intrinsic advantages from a biomimetic approach. [Copyright &y& Elsevier]

The subdivision behavior of polymeric tablets produced with the well-known polymers Soluplus® (SOL), polyvinyl pyrrolidone co-vinyl acetate (PVPVA) and hydroxypropyl methylcellulose (HPMC) was evaluated in this study. The polymeric tablets were submitted to different post-treatments (aging, thermal and exposure to compressed gaseous carbon dioxide) and its mechanical, spectroscopic and microstructure properties were assessed. SOL tablets showed the best results for tablet subdivision, particularly, the mean mass variation (3.9%) was significantly lower than the other two polymeric tablets (7.2% and 9.1% for PVPVA and HPMC, respectively), and showed better results than common tablets produced from powder matrices (7–14%). SOL tablets were also more sensitive to the different post-treatments applied, which reduced the mass loss and friability from 1.5% and 0.8%, respectively, to values close to zero and without altering their porosity. The thermal treatment of PVPVA tablets, in turn, also led to similar subdivision results, with mass loss of 0.3% and friability of 0.02%. In contrast, the granules of HPMC presented compaction difficulties making its tablets unsuitable for the subdivision process, even after additional post-treatment. Polymeric matrices with uniform internal structure and appropriate mechanical strength are the key to a better adaptation for the tablet subdivision. [ABSTRACT FROM AUTHOR]