Managing active pharmaceutical ingredient raw material variability during twin-screw blend feeding.

Continuous powder feeding is a critical step in continuous manufacturing of solid dosage forms, as this unit operation should ensure the mass flow consistency at the desired powder feed rate to guarantee the process throughput and final product consistency. In this study, twin-screw feeding of a pharmaceutical formulation (i.e., blend) existing of a highly dosed very poorly flowing active pharmaceutical ingredient (API) leading to insufficient feeding capacity was investigated. Furthermore, the API showed very high batch-to-batch variability in raw material properties dominating the formulation blend properties. Formulation changes were evaluated to improve the flowability of the blends and to mitigate the impact of API batch-to-batch variability on the twin-screw feeding. Herewith, feeding evaluation tests and an extensive material characterization of the reformulated blends were performed to assess the impact of the formulation changes upon continuous twin-screw feeding. The transfer of the glidant from extra-granular to intra-granular phase allowed to improve the flowability of the blends. A sufficient feeding capacity for the downstream process and a mitigation of the impact of batch-to-batch variability of the API upon twin-screw feeding of the blends could be achieved. No effect of the formulation or of the API properties on the feeding stability was observed. The material characterization of the blends allowed identifying the material attributes which were critical for continuous twin-screw feeding (i.e., bulk density, mass charge and powder cohesiveness).

Raw material variability of an active pharmaceutical ingredient and its relevance for processability in secondary continuous pharmaceutical manufacturing.

Active Pharmaceutical Ingredients (API) raw material variability is not always thoroughly considered during pharmaceutical process development, mainly due to low quantities of drug substance available. However, synthesis, crystallization routes and production sites evolve during product development and product life cycle leading to changes in physical material attributes which can potentially affect their processability. Recent literature highlights the need for a global approach to understand the link between material synthesis, material variability, process and product quality. The study described in this article aims at explaining the raw material variability of an API using extensive material characterization on a restricted number of representative batches using multivariate data analysis. It is part of a larger investigation trying to link the API drug substance manufacturing process, the resulting physical API raw material attributes and the drug product continuous manufacturing process. Eight API batches produced using different synthetic routes, crystallization, drying, delumping processes and processing equipment were characterized, extensively. Seventeen properties from seven characterization techniques were retained for further analysis using Principal Component Analysis (PCA). Three principal components (PCs) were sufficient to explain 92.9% of the API raw material variability. The first PC was related to crystal length, agglomerate size and fraction, flowability and electrostatic charging. The second PC was driven by the span of the particle size distribution and the agglomerates strength. The third PC was related to surface energy. Additionally, the PCA allowed to summarize the API batch-to-batch variability in only three PCs which can be used in future drug product development studies to quantitatively evaluate the impact of the API raw material variability upon the drug product process. The approach described in this article could be applied to any other compound which is prone to batch-to-batch variability.

Electron holography on HfO2/HfO2-x bilayer structures with multilevel resistive switching properties.

Unveiling the physical nature of the oxygen-deficient conductive filaments (CFs) that are responsible for the resistive switching of the HfO2-based resistive random access memory (RRAM) devices represents a challenging task due to the oxygen vacancy related defect nature and nanometer size of the CFs. As a first important step to this goal, we demonstrate in this work direct visualization and a study of physico-chemical properties of oxygen-deficient amorphous HfO2-x by carrying out transmission electron microscopy electron holography as well as energy dispersive x-ray spectroscopy on HfO2/HfO2-x bilayer heterostructures, which are realized by reactive molecular beam epitaxy. Furthermore, compared to single layer devices, Pt/HfO2/HfO2-x /TiN bilayer devices show enhanced resistive switching characteristics with multilevel behavior, indicating their potential as electronic synapses in future neuromorphic computing applications.

Metal-Free CVD Graphene Synthesis on 200 mm Ge/Si(001) Substrates.

Good quality, complementary-metal-oxide-semiconductor (CMOS) technology compatible, 200 mm graphene was obtained on Ge(001)/Si(001) wafers in this work. Chemical vapor depositions were carried out at the deposition temperatures of 885 °C using CH4 as carbon source on epitaxial Ge(100) layers, which were grown on Si(100), prior to the graphene synthesis. Graphene layer with the 2D/G ratio ∼3 and low D mode (i.e., low concentration of defects) was measured over the entire 200 mm wafer by Raman spectroscopy. A typical full-width-at-half-maximum value of 39 cm-1 was extracted for the 2D mode, further indicating that graphene of good structural quality was produced. The study also revealed that the lack of interfacial oxide correlates with superior properties of graphene. In order to evaluate electrical properties of graphene, its 2 × 2 cm2 pieces were transferred onto SiO2/Si substrates from Ge/Si wafers. The extracted sheet resistance and mobility values of transferred graphene layers were ∼1500 ± 100 Ω/sq and µ ≈ 400 ± 20 cm2/V s, respectively. The transferred graphene was free of metallic contaminations or mechanical damage. On the basis of results of DFT calculations, we attribute the high structural quality of graphene grown by CVD on Ge to hydrogen-induced reduction of nucleation probability, explain the appearance of graphene-induced facets on Ge(001) as a kinetic effect caused by surface step pinning at linear graphene nuclei, and clarify the orientation of graphene domains on Ge(001) as resulting from good lattice matching between Ge(001) and graphene nucleated on such nuclei.

Growth and evolution of nickel germanide nanostructures on Ge(001).

Nickel germanide is deemed an excellent material system for low resistance contact formation for future Ge device modules integrated into mainstream, Si-based integrated circuit technologies. In this study, we present a multi-technique experimental study on the formation processes of nickel germanides on Ge(001). We demonstrate that room temperature deposition of ∼1 nm of Ni on Ge(001) is realized in the Volmer-Weber growth mode. Subsequent thermal annealing results first in the formation of a continuous NixGey wetting layer featuring well-defined terrace morphology. Upon increasing the annealing temperature to 300 °C, we observed the onset of a de-wetting process, characterized by the appearance of voids on the NixGey terraces. Annealing above 300 °C enhances this de-wetting process and the surface evolves gradually towards the formation of well-ordered, rectangular NixGey 3D nanostructures. Annealing up to 500 °C induces an Ostwald ripening phenomenon, with smaller nanoislands disappearing and larger ones increasing their size. Subsequent annealing to higher temperatures drives the Ni-germanide diffusion into the bulk and the consequent formation of highly ordered, {111} faceted Ni-Ge nanocrystals featuring an epitaxial relationship with the substrate Ni-Ge (101); (010) || Ge(001); (110).

Tailoring the strain in Si nano-structures for defect-free epitaxial Ge over growth.

We investigate the structural properties and strain state of Ge nano-structures selectively grown on Si pillars of about 60 nm diameter with different SiGe buffer layers. A matrix of TEOS SiO2 surrounding the Si nano-pillars causes a tensile strain in the top part at the growth temperature of the buffer that reduces the misfit and supports defect-free initial growth. Elastic relaxation plays the dominant role in the further increase of the buffer thickness and subsequent Ge deposition. This method leads to Ge nanostructures on Si that are free from misfit dislocations and other structural defects, which is not the case for direct Ge deposition on these pillar structures. The Ge content of the SiGe buffer is thereby not a critical parameter; it may vary over a relatively wide range.

The role of SiGe buffer in growth and relaxation of Ge on free-standing Si(001) nano-pillars.

We study the growth and relaxation processes of Ge nano-clusters selectively grown by chemical vapor deposition on free-standing 90 nm wide Si(001) nano-pillars with a thin Si(0.23)Ge(0.77) buffer layer. We found that the dome-shaped SiGe layer with a height of about 28 nm as well as the Ge dot deposited on top of it partially relaxes, mainly by elastic lattice bending. The Si nano-pillar shows a clear compliance behavior-an elastic response of the substrate on the growing film-with the tensile strained top part of the pillar. Additional annealing at 800 °C leads to the generation of misfit dislocation and reduces the compliance effect significantly. This example demonstrates that despite the compressive strain generated due to the surrounding SiO(2) growth mask it is possible to realize an overall tensile strain in the Si nano-pillar and following a compliant substrate effect by using a SiGe buffer layer. We further show that the SiGe buffer is able to improve the structural quality of the Ge nano-dot.

Growth and relaxation processes in Ge nanocrystals on free-standing Si(001) nanopillars.

We study the growth and relaxation processes of Ge crystals selectively grown by chemical vapour deposition on free-standing 90 nm wide Si(001) nanopillars. Epi-Ge with thickness ranging from 4 to 80 nm was characterized by synchrotron based x-ray diffraction and transmission electron microscopy. We found that the strain in Ge nanostructures is plastically released by nucleation of misfit dislocations, leading to degrees of relaxation ranging from 50 to 100%. The growth of Ge nanocrystals follows the equilibrium crystal shape terminated by low surface energy (001) and {113} facets. Although the volumes of Ge nanocrystals are homogeneous, their shape is not uniform and the crystal quality is limited by volume defects on {111} planes. This is not the case for the Ge/Si nanostructures subjected to thermal treatment. Here, improved structure quality together with high levels of uniformity of the size and shape is observed.

Characterisation of surface-modified solid lipid nanoparticles (SLN): influence of lecithin and nonionic emulsifier.

Solid lipid nanoparticles (SLN), an alternative colloidal drug delivery system to polymer nanoparticles, emulsions and liposomes, are generally produced by high pressure melt-emulsification. However, the harsh production process is not applicable for formulations containing shear and temperature sensitive compounds. For that reason, subsequent adsorptive SLN loading might be a promising alternative. The aim of the present study was the development and characterisation of surface-modified SLN for adsorptive protein loading by variation of both the lipid matrix and the emulsifier concentration in the continuous phase. Variations in SLN composition resulted in particle sizes between 674 and 61 nm corresponding to specific surfaces of 4.5 m(2)/g and 48.9 m(2)/g and zeta potentials between -23.4 mV and -0.9 mV. In dependence of SLN surface properties, albumin payload ranged from 2.5 to 15%. Thermoanalysis, X-ray diffraction and electron microscopy revealed anisometrical and crystalline particles. In vitro cytotoxicity was low in terms of both haemolysis, which was between 1 and 2%, and neutral red test (NRT) showing a half lethal dose between 1.1 and 4.6%.

Thermal analysis of the crystallization and melting behavior of lipid matrices and lipid nanoparticles containing high amounts of lecithin.

Lipid nanoparticles (LNP) based on triglycerides containing high amounts of the amphiphilic lipid lecithin have been proposed as a promising alternative drug delivery system with regard to drug loading capacity. Aim of the present study is to evaluate the influence of lecithin within the lipid matrix (LM) on the crystallization behavior by thermoanalysis and wide angle X-ray diffraction (WAXD). The crystallinity of LM and LNP is mainly determined by the triglyceride content. However, lecithin influences the crystallization behavior significantly. WAXD shows an accelerated polymorphic transition of the LM to the beta-modification upon storage with increasing lecithin content. Both, the melting point and the crystallization temperature are not affected by the lecithin concentration and are comparable to recrystallized triglyceride bulk. However, the crystallinity indices (CI) of LM show a general decrease by 10% suggesting an incomplete crystallization. For the formation of LNP at least 10% lecithin is necessary and all systems are present in the stable beta-modification. In comparison to the undispersed LM, the crystallization temperature of LNP is significantly decreased by about 20 degrees C whereas the melting point is reduced by about 5 degrees C only. Melting enthalpy is comparable to the untreated triglyceride bulk and elevated in comparison to the undispersed LM. Isothermal heat-conduction microcalorimetry (IMC) enables the determination of crystallization kinetics after fitting of the heat flow volume according to the Avrami equation.

Solvent injection as a new approach for manufacturing lipid nanoparticles--evaluation of the method and process parameters.

Lipid nanoparticles (LNP) can be prepared by rapidly injecting a solution of solid lipids in water-miscible solvents or a water-miscible solvent mixture into water. The aim of the present study was to evaluate the potential of this method for the preparation of LNP and the physicochemical characterization of the particles produced by this method. The results show that solvent injection is a potent and versatile approach for LNP preparation. Acetone, ethanol, isopropanol and methanol are suitable solvents in contrast to ethylacetate with which no LNP could be prepared. The obtained particle sizes (z-average) were between 80 and 300 nm depending on the preparation conditions. Up to 96.5% of the employed lipid was directly transformed into LNP. The LNP formation process seems to be diffusion controlled. Physicochemical characterization of the particles by differential scanning calorimetry (DSC), transmission electron microscopy and X-ray diffraction analysis reveals a distinct decrease in crystallinity of the colloidal lipid in comparison to the bulk lipid. Furthermore, DSC analysis of LNP hints at a delayed recrystallization of the colloidal lipid and the presence of two modifications. Therefore, a certain physical instability of the LNP has to be considered.

Solubilization of bromhexine hydrochloride in aqueous lecithin dispersions. Physicochemical characterization of interactions between drug and carrier.

In aqueous systems bromhexine hydrochloride (Br-HCl) has a poor solubility (4.54 mg/g) and displays no amphiphilic character e.g. self association. Therefore the drug is molecularly dispersed in water until the solubility product of Br-HCl is exceeded. Solubilization of Br-HCl is linearly increased on addition of lecithin; calculations show that 10 mg Phospholipon 90G (P 90G) enable solubilization of additional 1.25 mg Br-HCl after the solubility product of Br-HCl has been exceeded. This means that four to five phospholipid molecules are needed for the solubilization of one drug molecule. Ternary systems with P 90G concentrations up to 20% have a lamellar microstructure. The systems are multilamellar vesicle dispersions as polarisation microscopy, transmission electron microscopy and small-angle X-ray diffractometry suggest. Furthermore, Br-HCl solubilization leads to a significant reduction of the interlamellar distance d and increases the elastic properties of the systems. 31P NMR data provide evidence that Br-HCl is solubilized within the lipophilic part of the phospholipid bilayer.

In vivo biocompatibility and biostability of modified polyurethanes.

Modified segmented polyurethanes were examined for biostability and biocompatibility using an in vivo cage implant system for time intervals of 1, 2, 3, 5, and 10 weeks. Two types of materials were used: polyether polyurethanes and polycarbonate polyurethanes. Two unmodified polyether polyurethanes (PEUU A' and SPU-PRM), one PDMS endcapped polyether polyurethane (SPU-S), and two polycarbonate polyurethanes (SPU-PCU and SPU-C) were investigated in this study. Techniques used to characterize untreated materials were dynamic water contact angle, stress-strain analysis, and gel permeation chromatography. Cellular response was measured by exudate analysis and by macrophage and foreign body giant cell (FBGC) densities. Material characterization, postimplantation, was done by attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) in order to quantify biodegradation and scanning electron microscopy (SEM) to qualitatively describe the cellular response and biodegradation. The exudate analysis showed that the acute and chronic inflammatory responses for all materials were similar. Lower FBGC densities and cell coverage on SPU-S were attributed to the hydrophobic surface provided by the PDMS endgroups. The polycarbonate polyurethanes did not show any significant differences in cell coverage or FBGC densities even though the macrophage densities were slightly lower compared to polyether polyurethanes. By 10 weeks, biodegradation in the case of PEUU A' and SPU-PRM was extensive as compared to SPU-S because the PDMS endcaps of SPU-S provided a shield against the oxygen radicals secreted by macrophages and FBGCs and lowered the rate of biodegradation. In the case of polycarbonate polyurethanes, the oxidative stability of the carbonate linkage lowered the rate of biodegradation tremendously as compared to the polyether polyurethanes (including SPU-S). The minor amount of biodegradation seen in polycarbonate polyurethanes at 10 weeks was attributed to hydrolysis of the carbonate linkage.

The effect of strain state on the biostability of a poly(etherurethane urea) elastomer.

The effect of deformation state on degradation of a PEUU without added stabilizers was examined in an oxidative environment that simulates the in vivo biodegradation of the polymer. Polymer tubes were stressed uniaxially and biaxially over glass mandrels and treated in 20% hydrogen peroxide/0.1 M cobalt chloride solution for 12 days at 37 degrees C. The amount of degradation was determined from the ATR-FTIR peak height of the amorphous aliphatic ether absorbance at 1110 cm-1. If a uniaxial stress was applied, degradation was inhibited and the amount of surface ether remaining after treatment increased linearly with strain. If the stress was biaxial, the amount of degradation was not reduced unless the strain was greater than 200%. Decreased degradation correlated with the amount of soft-segment orientation. The decreased degradation rate was attributed to compaction of the polyether phase by orientation, which resulted in lower permeability to oxidative agents, particularly oxygen. Macroscopic damage was confined to a thin peeling surface layer if the stress was uniaxial. In comparison, biaxially stressed PEUU ruptured.

Comparison of two antioxidants for poly(etherurethane urea) in an accelerated in vitro biodegradation system.

Vitamin E (+/-alpha-tocopherol) was recently investigated as an antioxidant for implanted poly(etherurethane urea) (PEUU) elastomers. In that work, vitamin E prevented chemical degradation of biaxially strained PEUU up to 5 weeks implantation, and prevented pitting and cracking of the PEUU surface for the duration of the 10-week cage implant study. The promising results of the in vivo studies motivated a detailed comparison of vitamin E with Santowhite, the standard antioxidant used in PEUU elastomers. To evaluate vitamin E and Santowhite as antioxidants in PEUU, an accelerated in vitro treatment system was used that mimics the in vivo degradation of PEUUs. Vitamin E was even more effective than Santowhite in preventing pitting and cracking to the biaxially strained PEUU elastomers. The inhibition of ether oxidation was greater with vitamin E than with Santowhite when compared by equivalent concentrations and molar concentrations, respectively. It is hypothesized that the increased effectiveness of vitamin E in this system, compared to Santowhite, is due to differences in antioxidant mechanism(s). Vitamin E is more efficient in preventing PEUU oxidation than Santowhite because its phenoxy radical is more stable and it can terminate more than one chain per vitamin E molecule.

Role of oxygen in biodegradation of poly(etherurethane urea) elastomers.

It is generally accepted that biodegradation of poly(etheruethane urea) (PEUU) involves oxidation of the polyether segments on the surface where leukocytes are adhered. The influence of dissolved oxygen, which is known to control oxidation of polymers in more traditional environments, was explored in this study. Specimens treated in vitro with hydrogen peroxide-cobalt chloride for 12 days exhibited a brittle, degraded surface layer about 10 microm thick. Attenuated total reflectance-Fourier transform infrared spectroscopy of the surface revealed that the ether absorbance at 1110 cm(-1) gradually decreased with in vitro treatment time to 30% of its initial value after 12 days. In contrast, 6 days in vitro followed by 6 days in air produced a decrease to 12% of the initial volume. Therefore, removing a specimen from the in vitro solution after 6 days and exposing it to air for the remainder of the 12 days actually resulted in more oxidation than leaving it in the in vitro solution for the entire 12 days. These results suggest that PEUU degrades by an autooxidation mechanism sustained by oxygen. By successfully modeling the depth of the surface degraded layer with a diffusion-reaction model, it was demonstrated that PEUU biodegradation is controlled by diffusion of oxygen into the polymer.

Vitamin E as an antioxidant for poly(etherurethane urea): in vivo studies. Student Research Award in the Doctoral Degree Candidate Category, Fifth World Biomaterials Congress (22nd Annual Meeting of the Society for Biomaterials), Toronto, Canada, May 29-June 2, 1996.

Poly(etherurethane) elastomers are useful materials in medical devices because of their mechanical properties and biocompatibility. However, it is necessary to stabilize these elastomers against the oxidation of their ether soft segments. Synthetic antioxidants such as Santowhite and Irganox are often satisfactory; however, particularly for biomedical applications, it was of interest to test the natural antioxidant vitamin E in poly(etherurethane urea) (PEUU) elastomers in vivo. The alpha-tocopherol form of vitamin E was added to PEUU at 5% by weight. Biaxially strained PEUU specimens with and without vitamin E were tested in vivo in the cage implant system. The influence of vitamin E on PEUU biostability was analyzed by attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy and scanning electron microscopic (SEM) characterization of the PEUU surface. ATR-FTIR results showed that vitamin E prevented chemical degradation of the PEUU surface up to 5 weeks implantation, and at 10 weeks 82% of the ether remained. In contrast, without an antioxidant, only 18% of the ether remained after 10 weeks. No surface pitting or cracking was observed by SEM on PEUU with vitamin E; PEUU without antioxidant ruptured owing to extensive pitting and cracking. It was concluded that the antioxidant properties of vitamin E prevented oxidation of strained PEUU elastomers in vivo. The influence of vitamin E on PEUU biocompatibility was characterized by exudate leukocyte counts, density of leukocytes adherent to the PEUU, and morphology of adherent leukocytes. These results indicated decreased leukocyte counts in the exudate and less active adherent cells on the PEUU with vitamin E compared to PEUU without antioxidant. A proposed cell-polymer feedback system demonstrates how vitamin E improves both biostability and biocompatibility of PEUU elastomers in vivo.

Oxidative biodegradation mechanisms of biaxially strained poly(etherurethane urea) elastomers.

As part of ongoing studies in polyurethane biostability and biodegradation, we have investigated an in vitro system to test strained poly(etherurethane urea) (PEUU). Recently, we utilized this system to reproduce in vivo stress cracking in strained Pellethane. In this study, strained PEUU was tested to determine whether it degrades through a common mechanism with Pellethane and to further examine the steps involved in this degradation. Biaxially strained PEUU elastomers were treated with an alpha 2-macroglobulin (alpha 2-Mac) protein solution followed by an oxidative H2O2/CoCl2 treatment. Characterization of the strained PEUU specimens was performed with attenuated total reflectance-Fourier transform infrared spectroscopy, scanning electron microscopy (SEM), electron spectroscopy for chemical analysis, and contact angle analysis. The results from these characterization techniques provide conclusive evidence that biodegradation of PEUU and Pellethane occurs through a common mechanism. Chemical changes to the PEUU include cleavage of the polyether soft segments and urethane linkages, leaving the hard segment domains unaffected. SEM analysis shows that this chain cleavage leads to the development of severe pitting and cracking of the PEUU surface. In addition, the in vitro degradation accurately reproduces the in vivo degradation chemically and physically. This result verifies that the primary species responsible for biodegradation of PEUUs, in vivo, are hydroxyl and/or hydroperoxide radicals. alpha 2-Mac pretreatment increases the rate of degradation compared to direct treatment in H2O2/CoCl2. As the PEUU soft segment chains are cleaved, the degradation products are extracted into the treatment solution or environment. Finally, a new biodegradation mechanism of PEUUs is presented that involves crosslinking of the polyether soft segments.

An organizational typology for self-help groups.

Those investigating the nature and functioning of self-help groups have been handicapped by the lack of a conceptual framework to bridge the diversity among such groups as well as to clarify the boundaries between consumer-owned and professionally owned groups. This paper describes a typology that classifies local units of these groups in terms of differences and similarities in their organizational structures. Rooted in organizational theory, it has two dimensions: external dependence upon resources and internal extent of experiential authority. Using it, the authors identified five types of groups, referred to as Unaffiliated, Federated, Affiliated, Hybrid, and Managed. The typology was validated with actual groups.