M. Alnaief

Amino functionalised Silica-Aerogels for CO2-adsorption at low partial pressure

Effective adsorption of CO2 at low partial pressures is required for many technical processes, such as gas purification or CO2 removal in closed loop environmental control systems. Since the concentration of CO2 in such applications is rather low, a high adsorption capacity is a required property for the adsorbent. Silica aerogels possessing an open pore structure, a high porosity and a high surface area, have a great potential for utilisation as CO2 adsorbents. Nonetheless in order to reach high adsorption capacities, silica aerogels should be functionalised, for instance by amino functionalisation. In this work, two different functionalisation methods were applied for the generation of amino functionalised aerogels: co-condensation during the sol-gel process and post-treatment of the gel. The co-condensation functionalisation allows the introduction of up to 1.44 wt.% nitrogen into the aerogel structure with minor reductions in surface area, leading however only to minor increases in the adsorption capacity at low partial pressures. The post functionalisation of the gel causes a greater loss in surface area, but the CO2 adsorption capacity increases, due to the introduction of higher amounts of amino groups into the aerogel structure (up to 5.2 wt.% nitrogen). Respectively, 0.523 mmol CO2/g aerogel could be adsorbed at 250 Pa. This value is comparable with the adsorption capacity at this pressure of a standard commercially available adsorbent, Zeolite 13X.

Enhancement of griseofulvin release from liquisolid compacts

The potential of hydrophilic aerogel formulations and liquisolid systems to improve the release of poorly soluble drugs was investigated using griseofulvin as model drug. The in vitro release rates of this drug formulated as directly compressed tablets containing crystalline griseofulvin were compared to aerogel tablets with the drug adsorbed onto hydrophilic silica aerogel and to liquisolid compacts containing the drug dissolved or suspended in PEG 300. Furthermore, the commonly used carrier and coating materials in liquisolid systems Avicel® and Aerosil® were replaced by Neusilin®, an amorphous magnesium aluminometasilicate with an extremely high specific surface area of 339 m²/g to improve the liquisolid approach. Both the liquisolid compacts containing the drug dissolved in PEG 300 and the aerogel tablets showed a considerably faster drug release than the directly compressed tablets. With liquisolid compacts containing the drug suspended in PEG 300, the release rate increased with rising fraction of dissolved drug in the liquid portion. It could be shown that Neusilin® with its sevenfold higher liquid adsorption capacity than the commonly used Avicel® and Aerosil® allows the production of liquisolid formulations with lower tablet weights.

Tableting properties of silica aerogel and other silicates.

Context: In solid oral dosage forms silicates are commonly used as glidants in low concentration. However, due to their large specific surface area, silicates may also be used as carrier materials for drugs. Moreover, silicates allow amorphisation of drugs by co-grinding or processing with supercritical fluids. Objective: The aim of this study was to investigate the physical and the tableting properties of Silica Aerogel (special type of silica with an extremely large specific surface area), Neusilin® US2 (magnesium aluminometasilicate), Florite® (calcium silicate) and Aerosil® 200 (colloidal silica). Materials and methods: Powder blends of Avicel® PH102 (microcrystalline cellulose) and different amounts of the respective silicate were compacted and analyzed for their tabletability (tensile strength vs. compaction pressure) as well as their Heckel plot. Results and discussion: With Neusilin® the tabletability appeared to be independent of the silicate concentration, whereas with Florite® an increasing silicate concentration led to a higher tensile strength. In contrast, the addition of Silica Aerogel and Aerosil® resulted in a decrease of the tensile strength. With Aerosil® a maximum tolerable concentration of 20% [w/w] was determined. Plastic deformation of all powder blends decreased with increasing silicate concentration. This effect was most pronounced with Aerosil® and least with Florite®. Conclusion: Tablets with acceptable tensile strength were obtained with all plain silicates except for Aerosil®. Therefore, these silicates may be used in tablet formulations, e.g. as carrier materials for liquid or amorphous drugs.

Effect of processing parameters on preparation of carrageenan aerogel microparticles

The aim of this work is to produce aerogel microparticles using a biocompatible polymer. Commercial available carrageenan suitable for gelation was used as a precursor for gel preparation. Microspherical carrageenan gel particles were obtained by applying emulsion technology. The gel was converted to an aerogel using supercritical carbon dioxide extraction process. Several process parameters were investigated for their effect on the final properties of the produced aerogel. The produced aerogel particles were characterized for their textural properties using gas sorption analysis. For complete understanding the following characterization techniques were employed: FTIR, PXD, TGA, SEM, Zeta sizer, particles density and particle size distribution. In conclusion, biodegradable aerogel micro-spherical particles based on three different commercial available carrageenan were produced. Depending on the process parameters the surface area of the produced aerogel ranged between 33 and 174m2/g, the average pore volume and pore sized were 0.35±0.11cm3/g and 12.34±3.24 respectively. The produced porous material shows potential characteristic for drug delivery application.

Investigation of Carrageenan Aerogel Microparticles as a Potential Drug Carrier

Carrageenan is an anionic polysaccharide offering many advantages to be used in drug delivery applications. These include availability, thermo-stability, low toxicity, and encapsulating properties. Combination of these properties with aerogel properties like large surface area and porosity make them an ideal candidate for drug adsorption and delivery applications. Emulsion-gelation technique was used to prepare carrageenan gel microparticles with supercritical CO2 for drying and loading purposes. Ibuprofen has been selected as a model drug for drug loading inside. The prepared microparticles were characterized using particle size analysis, X-ray diffraction, differential scanning calorimetry, Fourier transform infrared spectroscopy, density measurements, surface area, and porosity measurements. Finally, dissolution was applied to the loaded preparations to test in vitro drug release. Ibuprofen was successfully loaded in the amorphous form inside the prepared microparticles with a significant enhancement in the drug release profile. In conclusion, prepared carrageenan aerogel microparticles showed an excellent potential for use as a drug carrier.