Renata Adami

Design and production of gentamicin/dextrans microparticles by supercritical assisted atomisation for the treatment of wound bacterial infections

In this work, the supercritical assisted atomisation (SAA) is proposed, for the first time, for the production of topical carrier microsystems based on alginate-pectin blend. Gentamicin sulphate (GS) was loaded as high soluble and hygroscopic antibiotic model with poor flowability. Particularly, different water solutions of GS/alginate/pectin were processed by SAA to produce spherical microparticles (GAP) of narrow size (about 2 μm). GS loading was varied between 20% and 33% (w/w) with an encapsulation efficiency reaching about 100%. The micronised powders also showed high flow properties, good stability and constant water content after 90 days in accelerated storage conditions. The release profiles of the encapsulated drug were monitored using vertical diffusion Franz cells to evaluate the application of GAP microsystems as self-consistent powder formulation or in specific fibres or gels for wound dressing. All formulations showed an initial burst effect in the first 6h of application (40-65% of GS loaded), and in particular GAP4 produced with a GS/alginate/pectin ratio of 1:3:1, exhibited the ability to release GS continuously over 6 days. Antimicrobial tests against Staphylococcus aureus indicated that GS antibiotic activity was preserved at 6 days and higher than pure GS at 12 and 24 days for all SAA formulations, especially for GAP1.

Albumin/Gentamicin Microspheres Produced by Supercritical Assisted Atomization: Optimization of Size, Drug Loading and Release

In this work, the supercritical assisted atomization (SAA) is proposed, for the first time, not only as a micronization technology but also as a thermal coagulation process for the production of bovine serum albumin (BSA) microspheres charged with Gentamicin sulfate (GS). Particularly, different water solutions of BSA/GS were processed by SAA to produce protein microspheres with different size and antibiotic content. SAA precipitation temperature was selected in the range 100-130 °C to generate protein coagulation and to recover micronized BSA in form of hydrophobic aggregates; GS loading was varied between 10% and 50% (w/w) with an encapsulation efficiency which often reached 100%. In all cases, spherical and noncoalescing particles were successfully produced with a mean particle size of 2 µm and with a standard deviation of about ±1 µm. The microspheres also showed a good stability and constant water content after 60 days of storage. The release profiles of the entrapped drug were monitored using Franz cells to evaluate the possible application of the produced microspheres in wound dressing formulations. Particularly, the microspheres with a BSA/GS ratio of 4:1 after the first burst effect (of 40% of GS loaded) were able to release the GS continuously over 10 days.

In situ forming antibacterial dextran blend hydrogel for wound dressing: SAA technology vs. spray drying

This study focuses on designing microparticulate carriers based on high-mannuronic alginate and amidated pectin blend loaded with gentamicin sulphate able to move rapidly from dry to soft hydrogel. Supercritical assisted atomization was used to produce microparticles in form of dry powder and characteristics were compared with those obtained by spray-drying. Particles with very high encapsulation efficiency (approximately 100%) and small diameter (less than 2 μm) showed good flowability and high fluid uptake enabling wound site filling and limiting bacterial proliferation. Moisture transmission of the in situ formed hydrogel was about 95 g/m(2)h, ideal to avoid wound dehydration or occlusion phenomena. All formulations presented a burst effect, suitable to prevent infection spreading at the beginning of the therapy, followed by prolonged release (4-10 days) related to drug/polymers ratio. Antimicrobial tests showed stronger effect than pure GS over time (up-to 24 days) and the ability to degrade preformed biofilms, essential to properly treat infected wounds.

Micronization of Lysozyme by Supercritical Assisted Atomization

Supercritical Assisted Atomization (SAA) has been used to produce lysozyme microparticles. Lysozyme has been micronized using water, buffered water at pH 6.2 and water–ethanol mixtures at different volume percentages. Precipitated lysozyme particles were spherical, with a narrow particle size distribution (PSD) ranging from 0.1 to 4 µm. The concentration of lysozyme in the liquid solvent mixture had a nonlinear effect on the particle distribution, with an increase of the X0.9 from about 1 to 3 µm varying the enzyme concentration from 5 to 20 mg/mL. Precipitation temperature was set as low as possible to avoid enzyme degradation. High‐performance liquid chromatography analysis showed no degradation of lysozyme and the enzyme activity, measured by turbidimetric enzymatic assay, only slightly decreased after SAA processing. Depending on the process conditions lysozyme retained from 95% to 100% of the biological activity compared to the untreated enzyme. Biotechnol. Bioeng. 2009; 104: 1162–1170.

Production of cromolyn sodium microparticles for aerosol delivery by supercritical assisted atomization.

The purpose of this study was to produce cromolyn sodium (CS) micrometric particles with controlled particle size (PS) and PS distribution (PSD) suitable for aerosol delivery, using a supercritical fluids-based process. CS was micronized using the supercritical assisted atomization (SAA) technique at different solute concentrations in water and different precipitation temperatures. Two techniques were used to measure PS and PSD of produced particles: scanning electron microscopy image analysis and laser scattering analysis. The 2 techniques were compared to provide a complete description of the powder obtained. High-performance liquid chromatography analysis was used to verify the absence of degradation of CS after micronization; differential scanning calorimetry, thermogravimetric analysis (TGA), and X-ray analysis were performed to study the effect of operative conditions on the crystalline structure and on the water content of SAA micronized particles. The CS particles obtained were spherical, with a volumetric percentage of particles with a diameter ranging between 1 and 5 µm of 50% to 66%. The precipitation temperature had no significant effect on PSD, but high drying temperatures led to product degradation. Increasing the concentration of CS in water solution produced an increase in PS of the micronized particles. TGA showed that the micronized CS had a different hydration state than the untreated CS did. The micronized product was stable after 12 months of storage, and no modifications in structure, morphology, or crystallinity were detected. In conclusion, SAA is an efficient technique for micronization of CS, and stable spherical amorphous particles suitable for aerosol delivery can be produced.

Supercritical Assisted Atomization: Polyvinylpyrrolidone as Carrier for Drugs with Poor Solubility in Water

Supercritical assisted atomization (SAA) is an efficient technique to produce microparticles and composite microspheres formed by polymers and pharmaceutical compounds. In this work polyvinylpyrrolidone (PVP) was proposed as carrier for pharmaceutical compounds that show a poor solubility in water medium. Indeed, this polymer is hydrosoluble and can be generally used to enhance the dissolution rate of hydrophobic compounds when finely dispersed in it. However, it is difficult to obtain coprecipitates with a uniform dispersion of the active molecule using other micronization techniques. The experiments were performed using ethanol as solvent; SAA plant was operated at 40°C and 76 bar in the saturator and 70°C and 1.6 bar in the precipitator. Three different dexamethasone/polymer weight ratios were selected: 1/2, 1/4, and 1/8. Produced composite particles showed a regular, spherical shape and a mean diameter ranging from about 0.8 to 1 μm, depending on the polymer/drug weight ratio. Dissolution analysis demonstrated that microparticles containing a lower drug amount show a higher dissolution rate.

Alginate beads as a carrier for omeprazole/SBA-15 inclusion compound: A step towards the development of personalized paediatric dosage forms.

The treatment of gastro-esophageal reflux disease (GERD) shows several issues among paediatric patients. This work aims to the formulation of enteric alginate beads loaded with omeprazole (OME) allowing age- and weight-related personalized dosages in children. OME was entrapped in SBA-15 mesoporous compound, characterized and loaded into alginate beads by prilling at different OME and alginate concentrations. The beads resulted of homogeneous size, spherical morphology and very consistent in drug loading and distribution. Formulations demonstrated limited swelling and release (about 10%) in simulated gastric fluid (SGF) after 2h and a prolonged release in simulated intestinal fluid (SIF), till 6h, due to a mixed diffusion-case II transport mechanism. The beads were superior to the market product, which showed lower release in SGF but immediate dissolution in SIF. The high alginate beads uniformity and release properties make them a potential novel tool for a personalized treatment of GERD in children.

Influence of Supercritical Antisolvent Micronization Parameters on Nalmefene HCl Powder Characteristics

Supercritical antisolvent precipitation (SAS) is a promising technique for the micronization of pharmaceutical compounds. Like all the manufacturing processes, SAS might induce solid-state modifications, the formation of undesired polymorphic forms or degradation products and the presence of solvent residues in the final product. In this work, the influence of SAS process parameters on nalmefene HCl powder characteristics was investigated. Ethanol was used as the liquid solvent and supercritical carbon dioxide as antisolvent. Micronization experiments were performed at pressures of 130 and 150 bar, in the temperature range 40–67°C, and CO2 molar fraction was between 0.95 and 0.97. Amorphous particles and particles with different degrees of crystallinity and different sizes were obtained by varying the antisolvent molar fraction at different operating conditions. High-performance liquid chromatography and headspace gas chromatography analyses were performed to verify the purity of the micronized product and the absence of residual ethanol. The structural characteristics of micronized nalmefene HCl particles were studied by differential scanning calorimetry, X-ray powder diffraction and thermogravimetry analyses. The micronization process did not induce degradation of the compound and a product with a solvent residue less than 2 p.p.m. was obtained. The process induced the modification of nalmefene HCl from hydrated to anhydrous form; at particular conditions a solvate form was also obtained.

pH-sensitive polymersomes: controlling swelling via copolymer structure and chemical composition

Abstract pH-sensitive vesicles used as drug delivery systems (DDSs) are generally composed of protonable copolymers. The disaggregation of these nanoparticles (NPs) during drug release implies the dispersion of positively charged cytotoxic polyelectrolytes in the human body. To alleviate such issue, we synthesised A(BC)n amphiphilic block copolymers with linear (n = 1) and branched (n = 2) architectures to obtain pH-sensitive vesicles capable of releasing drugs in acidic conditions via controlled swelling instead of disaggregation. We obtained this feature by fine-tuning the relative amount of pH-sensitive and hydrophobic monomers. We studied pH-driven swelling by measuring NPs size in neutral and acidic conditions, the latter typical of tumours or inflamed tissues (pH∼6) and lysosomes (pH∼4.5). Dynamic light scattering (DLS) and zeta potential data provided useful indications about the influence of architecture and chemical composition on NPs swelling, stability and polycation release. Results demonstrated that vesicles made of linear copolymers with ∼22–28% in mol of protonable monomers in the ‘BC’ block swelled more than other species following a pH change from pH 7.4 to pH 4.5. We finally evaluated the cytotoxicity of vesicles composed of linear species, and paclitaxel (PTX) release from the latter in both cancer and normal cells.

Impact of intermolecular drug-copolymer interactions on size and drug release kinetics from pH-responsive polymersomes

Abstract pH-sensitive polymersomes are produced from amphiphilic copolymers of the type mPEG-b-(PMMA-ran-PDMAEMA) obtained via ATRP, so that mPEG with molecular masses of 2k and 5kDa forms the corona of a hydrophobic double layer with 22–28% molar content in protonable DMAEMA. Vesicles obtained via dialysis were loaded with curcumin, 2-naphthole, paclitaxel (PTX) and ampicillin sodium salt, and the release kinetics of the latter studied via UV-vis spectrometry as a function of pH. Overall, the release profiles clearly indicated a dopant-sensitive kinetics and, likely, mechanism depending on molecule-copolymer interactions. Infrared spectrometry highlighted the formation of hydrogen bonds and salt bridges that may be responsible for these findings; support for the formation of the latter are obtained comparing the IR spectrum for ampicillin doped-vesicles with the anharmonic vibrational transition of model salt bridges. Importantly, DLS data indicated that our vesicles appeared to remain stable even at pH 4.4 after 48 h and completely releasing ampicillin. The release profiles of co-loaded curcumin/PTX with ampicillin also suggest that desorption rates of water-soluble species can be modulated by the presence of hydrophobic molecules in the double layer, at least at pH 7.4 and 6.4.