Finding non-cytotoxic carrier materials that ensure a controlled release of an active hydrophobic drug over a long period of time is considered to be the “holy grail” in wound dressing applications. A team of researchers from Brazil and the USA report to have found a material that combines all of those desired characteristics.
The novel silica-polymer hybrid (SPH) aerogels, synthesized from silica nanoparticles, polyvinyl alcohol (PVA), polyacrylic acid (PAA), and water, were manufactured via freeze-drying and subsequent thermal treatment (see Figure below). While the freeze-drying ensured a complete removal of water, the ensuing thermal treatment at 160 °C facilitated the cross-linking between PVA and PAA, guaranteeing aerogel stability in aqueous media.

Schematic of manufacturing process of silica-polymer hybrid (SPH) aerogels.

Experiments conducted with dexamethasone (DEX), an agent used for the treatment of skin diseases, allergies, and rheumatic problems, showed that the SPH aerogels exhibit high drug encapsulation efficiencies, taking up around 75 % of DEX from an ethanol/water mixture within 24 hours. This feature was ascribed to the trapping of DEX molecules within the mesoporous silica nanoparticles.
The release rate of DEX from the aerogels was investigated by placing the loaded samples into a stirred phosphate buffered saline (PBS) solution at 37 °C and measuring the progression of the DEX concentration with time. These measurements showed that after an initial rapid discharge of DEX, the release rate leveled off, so that even after two months a steady drug discharge was obtained. This slow and prolonged release of DEX molecules was attributed to the polymer pore structure, limiting the mass transfer from the drug encapsulation site (silica nanoparticles) to the solution. Supporting this finding were results for SPH aerogels of a different constitution, which showed that a change in PVA:PAA ratio, yielding morphological modifications of the polymer pore network, leads to a significant change in drug release behavior.
In order to assess the biocompatibility and cytotoxicity of the synthesized material, the cell viability of vero cells and L929 fibroblasts was investigated in the presence of the SPH aerogels. This line of experiment showed that there is virtually no decrease in cell viability for either cell type after 72 hours, regardless of precursor selection.
The authors see potential applications of SPH aerogels in the treatment of skin burns or melanoma, which require wound dressing over extended periods of time. Furthermore, they see potential in tailoring the aerogel structures (e.g. with antibodies) to further extend their potential biological and medical applications.

More details: Follmann et al.; Multifunctional Hybrid Aerogels: Hyperbranched Polymer- Trapped Mesoporous Silica Nanoparticles for Sustained and Prolonged Drug Release, Nanoscale, December 2017. http://doi.org/10.1039/C7NR08464A

Coal fired power plants will play a substantial role in energy production for the majority of industrialized nations until at least the middle of this century. This is an issue since the large-scale combustion of carbon-based resources is a major contributor to the rising atmospheric CO₂ levels. In order to achieve the ambitious multilateral goals to lessen the detrimental effects of global warming by stabilizing the global CO₂ levels outlined in the Paris Agreement, the greenhouse gas emissions from coal fired power plants will need to be reduced drastically.

One way to achieve this reduction in emitted greenhouse gases without abandoning coal-based power production is the capturing and sequestration of emitted CO₂ (see graphic below). This can be done by retro-fitting existing power plants with carbon capture and storage (CCS) units, which remove carbon dioxide from flue gas, before storing it in a designated location. Most commonly, temperature-swing adsorption (TSA) processes, utilizing aqueous amine solutions as sorbents, are proposed for CO₂ capturing. However, the regeneration of the amine solution results in an energy penalty which drastically reduces the thermal efficiency of the power plant. Therefore, alternative sorbents requiring less energy for regeneration are under investigation.

Diagram of carbon capture and storage life cycle.
From: Scottish carbon capture and storage

In a joint effort, a project team consisting of Aspen Aerogels, the University of Akron, ADA-ES, and Longtail Consulting have synthesized and tested solid amine functionalized aerogels (AFA) in a bench scale fluidized bed reactor, in order to assess their potential for future application in CCS.

It was found that the AFAs synthesized by Aspen Aerogels showed promising CO₂ adsorption behavior and good stability over numerous adsorption-desorption cycles. On top of that, the novel solid sorbents possess significantly lower heats of reaction with CO₂ than commonly deployed liquid and solid sorbents. In a subsequent step, the AFAs were coated at the University of Akron, yielding pellets possessing a good cyclic stability in the presence of SO₂. The novel AFA pellets were then tested in a bench scale fluidized bed reactor to determine their physical properties (e.g. fluidizing gas velocities, void fraction, etc.) in such a reactor setup.

Based on those findings, Longtail Consulting modeled the hydrodynamic and heat transfer properties of the solid aerogel sorbent in the fluidized bed reactor and finalized the process requirements. Subsequently, a techno-economic analysis (TEA) of the entire CO₂ capturing unit (assuming 90 % capturing efficiency) fitted to a coal fired, supercritical steam cycle power plant producing 550 MW_e was performed. Despite offering a promising behavior from a technological perspective, the TEA revealed that utilizing novel AFA sorbents results in approx. 20 % higher levelized electricity costs. This finding was mainly attributed to the fact that the attrition of the material during fluidization was unknown, yielding high variable costs for the selected scenario. Additionally, a relatively high apparent particle density inside the fluidized be reactor led to a  massive pressure drop, causing a surge in auxiliary electricity input.

In light of these findings, the project team concluded that further testing under practical conditions and simultaneous optimization of the AFAs will be essential to make solid sorbents an economical alternative to state-of-the-art aqueous amines.

As the need for creative solutions to reduce greenhouse gas emissions is only increasing, it is promising to see that the vast potential of aerogels is being explored to address climate change. Whether or not solid sorbents can be successfully utilized in TSA in an economically reasonable way may prove to be one of the key factors determining the success of CCS.

Full Report: https://doi.org/10.2172/1349123

Read more at: https://www.osti.gov/scitech/biblio/1349123

Because of their unique characteristics, graphene aerogels are attractive materials for a wide range of applications. However, due to their micro-fibrous structure, strength and resilience, which are both desired properties, are generally considered to be mutually exclusive. By employing a bidirectional freeze-drying technique, researchers from the Zhejiang University (China) have successfully manufactured monolithic graphene aerogels uniting both properties.

Comparison of lamellar structure of thalia dealbata stem (left) and graphene aerogel (right)

In order to achieve those exceptional characteristics, the micro-scale architecture of the aerogels was based on the structure of a thalia dealbata stem, which is able to provide sufficient strength to support the plants leaves and blossoms while enduring powerful external forces (e.g. strong winds). The mimicking of this special three-dimensional lamellar structure consisting of bridged layers (see Figure above), yielded aerogel structures exhibiting strength and resilience simultaneously (see Figure below).

Images of fresh cubic graphene aerogel before compression (left), graphene monolith compressed by >6000 times its own weight (middle), recovered aerogel after compression (right).

When compared to a graphene aerogel exhibiting a random structure, the biomimetic aerogel showed a significant superiority in recovery behavior after being strained. Furthermore, the authors found that the aerogel architecture and hence the mechanical properties of the graphene structures can be further optimized by tuning the precursor composition.

The fabrication of such firm and robust structures could be play a pivotal role in establishing graphene aerogels in sensing applications. Additionally, the manufacturing technique reported by the authors can potentially be extended to other materials in order to obtain tailored micro-architectures.

More details: Miao Yang et al.; Biomimetic Architectured Graphene Aerogel with Exceptional Strength and Resilience, ACS Nano, 2017, 11 (7), pp 6817–6824. https://doi.org/10.1021/acsnano.7b01815

Read more at: https://www.forbes.com/sites/samlemonick/2017/07/31/plant-inspires-super-strong-aerogel/#2b9b35b96415

The Hamburg based startup Aerogelex has received the ETPN (European Technology Platform for Nanomedicine) Award 2017 for Best Nanomedicine Product/Deal at the Bio-Europe 2017. The awards committee was impressed by Aerogelex’s biopolymer aerogels for wound dressing, pharmaceutical, and life science applications.

Best Nanomedicine Product/Deal 2017 Awardee Aerogelex founder
Dr. Raman Subrahmanyam, Best Nanomedicine Early Clinical Stage Project
Awardee Dr. Su Metcalfe, and ETPN Chairman Patrick Boisseau

Aerogelex’s goal is to facilitate the implementation of aerogels in cosmetic, food, pharmaceutical, and thermal applications by transferring their wealth of knowledge about aerogels and aerogel manufacturing to partners who see value in the performance aerogels can offer.  Aerogelex will partner with companies and research groups to solve the materials and processing challenges associated with bringing aerogels and aerogel-based materials to market.

Aerogelex is currently open to partnership with individuals and companies who looking to establish a foothold in biopolymer aerogels, or who are interested in using supercritical drying in their manufacturing process. Businesses that partner with Aerogelex will get access to an aerogel production plant where aerogel prototypes can be manufactured and optimized. After a successful pilot phase, partnering companies will learn how to manufacture aerogels on a large scale in order to establish their own expertise.

To get a glimpse of the technological opportunities that supercritical drying and biopolymer aerogels offer, curious minds can purchase the first official product from Aerogelex on BuyAerogel.com. The ”AeroEggs” up for sale are unique aerogels made from hard-boiled eggs that reveal the endless possibilities that aerogels can offer.

Full video of Nanomedicine Award ceremony with presentation from Aerogelex founder Dr. Raman Subrahmanyam:  https://www.youtube.com/watch?v=P6JXJBrQVfY&list=PLjyB2R13BJCv4XVHoxm1TsZL_VkZiELDk

Increasing atmospheric CO₂ levels and dwindling fossil fuel resources have motivated the search for sustainable and renewable sources of energy. Hydrogen is considered to be an environmentally friendly alternative to common fossil fuels, as it does not emit environmentally harmful greenhouse gases upon combustion. Therefore, the quest for an efficient and sustainable way of generating hydrogen on a large scale is in full swing.

Supercritical water gasification (SCWG) of biomass is one such renewable hydrogen production technique that is currently being investigated. Due to the unique properties of supercritical water (e.g. high diffusivity, miscibility with gases) the process promises high energy conversion efficiencies. However, a suitable catalyst for the reaction, ensuring high H₂ yields while suppressing coke and tar formation, has remained elusive. Researchers from the University of Western Ontario (Canada) have recently synthesized a Ru-Ni-Al₂O₃ catalyst which has shown promise for the SCWG process.

Synthesis of the catalyst required the formation of a clear solution which was achieved by mixing the aluminum support in isopropanol at 75 °C followed by the addition of nitric acid. Thereafter, the metallic precursors (nickel nitrate and ruthenium acetylacetonate) were added to the sol to initiate the aging process. After completion of the gel formation, the liquids contained in the porous structure were extracted via low temperature supercritical drying with CO₂. In a last step the samples were calcined and reduced at 600 °C to obtain the ready-to-use aerogel catalysts (see Figure below).

Schematic of Ru-Ni-Al₂O₃ aerogel catalyst production technique

The Ru-Ni-Al₂O₃ aerogel, synthesized via this process, exhibited a higher specific surface area and pore volume when compared to impregnated or xerogel Ru-Ni-Al₂O₃ catalysts. These superior structural features significantly enhanced the hydrogen yields during SCWG, due to the increase in available active surface area. Furthermore, the porous aerogel morphology was also shown to decrease unwanted coke formation on the catalyst surface. A comparison of Ni-Al₂O₃ and Ru-Ni-Al₂O₃ aerogel catalysts revealed that the promoting nature of ruthenium (Ru) leads to superior catalytic activities for the bimetallic composite. Additionally, the utilization of Ru further decreased coke formation during the gasification reaction.

In order to assess the cyclic stability of the aerogel structures Ni-Al₂O₃ and Ru-Ni-Al₂O₃ catalysts were employed in three consecutive SCWG reactions. Both structures showed signs of deactivation (e.g. decrease in surface area), however, even during the third experimental run a decent catalytic activity was observed for both structures. For example, the recycled Ru-Ni-Al₂O₃ aerogel exhibited only slightly smaller hydrogen yields than the fresh Ru-Ni-Al₂O₃ xerogel and the fresh impregnated Ni-Al₂O₃ catalysts.

Although numerous projects aiming at the development of renewable energy generation processes are in progress, we are still a long way from a fully formed strategy to replace fossil fuels globally. Therefore, technical advancements paving the way to a more sustainable future are essential. This study has shown that aerogels could play an integral role in propelling alternative processes such as supercritical water gasification to market maturity.

More details: Md. Zakir Hossain, Muhammad B.I. Chowdhury, Anil Kumar Jhawar, Paul A. Charpentier; Supercritical water gasification of glucose using bimetallic aerogel Ru-Ni-Al₂O₃ catalyst for H₂ production, Biomass and Bioenergy Volume 107, December 2017, Pages 39-51. https://doi.org/10.1016/j.biombioe.2017.09.010