Multimodal chromatography combining steric exclusion and cation exchange as an intermediate downstream step to purify yellow fever virus-like particles

Yellow fever (YF) is an hemorrhagic viral disease transmitted by infected mosquitoes, which is endemic in many African and Central/South American countries. The severe symptoms and the high mortality rate of the disease can have devastating effects in case an outbreak occurs in an area where the population is non-vaccinated. Before the current YF vaccine became available, outbreaks in cities like Barcelona (Spain) and Philadelphia (USA) led to the death of approximately 10% of the population. Recent outbreaks have shown that YF continues to be a major public health threat due to production capability issues and shortage of vaccine stockpiles, which even led to the use of an emergency fractional (1/5) dose in Africa in 2016 and in Brazil in 2018. Yellow fever virus-like particles (VLPs) represent an interesting alternative to develop a new YF vaccine. With the aim of developing an efficient and affordable process to purifiy yellow fever VLPs, in this work we developed a multimodal strategy combining cation exchange (CEX) and steric exclusion chromatography (SXC) under conditions where the product of interest does not bind to the CEX adsorber, whereas many contaminants do. In this way, the product of interest is retained just due to steric exclusion by the polyethylene glycol (PEG) added to the mobile phase. Product desorption can be achieved by decreasing PEG concentration, while contaminants remain bound to the adsorber and are eluted in the regeneration step. To the best of our knowledge, the application of such a multimodal strategy has not been published before. Please click Download on the upper right corner to see the full abstract

Hydrocyclones for single-use perfusion application

Hydrocyclones (HC) are very compact devices that promote solid-liquid separation under the action of a centrifugal field. Despite the small size, HCs have a large processing capacity and do not suffer from clogging. Therefore, several publications explored HCs as a potential cell retention device in perfusion applications in the last 20 years, but limited to non-disposable lab-scale bioreactors and to relatively low cell densities (up to ~10 million cells/mL). Even though the absence of moving parts may streamline the HC manufacturing, the performance of solid-liquid separation is highly dependent on the HC internal geometry. Said that, hydrocyclones can be produced by 3D printing, making them a promising alternative for the integration of cell retention devices in single-use bioreactor bags. The performance of hydrocyclones also depends on the attachment configuration to the bioreactor and cell concentration of the feed suspension. In this work, at first rapid batch tests were carried out to evaluate the impact of: (i) cell concentration; (ii) diameter of connector installed in the recirculation loop; and (iii) controlled harvest flow rate enabled by a peristaltic pump (520U model, Watson Marlow). The main response considered was their effect on HC separation efficiency. The stainless-steel HC2015 designed for mammalian cell separation (Pinto et al., 2008) was selected for the preliminary batch tests, and also used as a benchmark for plastic prototypes produced by 3D-printing techniques. Afterwards, the same HC2015 was installed in a 50-L single-use bag (XDR50 Xcellerex, GE Healthcare) specially customized for a perfusion cultivation with a mAb producer CHO cell line. The stainless-steel HC2015 when operating at 2.3 bar provided a total separation efficiency (Et) up to 96%, and a centrifugal separation efficiency (E´) of 82% for a CHO cell suspension at 24E6 viable cells per mL Concentrated cells recovered by the underflow port did not show decrease in viability compared to the feed suspension. The reduction of a TC connector size from 19.7 to 12.7 mm resulted in the total filling of the recirculation loop with liquid, disrupting the formation of the desirable umbrella-pattern discharge of the underflow and reducing cell retention. The use of a peristaltic pump to control the overflow flow rate equivalent to perfusion rates of 1 and 2 RV (reactor volume) per day in 40-L bioreactor working volume resulted in a reduction of the E´ values and a consequent increase of cell concentration in the harvest stream. The reduction in the separation efficiency was probably due to a disturbance of the liquid flow pattern inside the HC, since it was observed that the typical gas core coming out from the overflow was absent. These features were taken into account in the HC operation in the single-use 50-L perfusion bioreactor, and a cell concentration of 50E6 cells per mL was successfully achieved with a cell-specific perfusion rate (CSPR) as low as 20 pL per cell per day. The harvest stream consisted of a natural cell bleeding leaving the overflow outlet. Moreover, the lower cell viability and average diameter in the overflow evidenced the preferential retention of viable cells returning into the bioreactor, thus providing a healthier culture environment. A 3D-printed hydrocyclone with equivalent geometry to the stainless-steel HC2015 was made and presented slightly lower separation efficiencies. Further studies proposing materials with a smoother surface and investigating further 3D-printing techniques are currently ongoing. Pinto, R. C.V., Medronho, R. A., Castilho, L. R. (2008). Separation of CHO cells using hydrocyclones. Cytotechnology, 56(1), 57–67. doi:10.1007/s10616-007-9108-

Analyzing the fluidization of a mixture of gas-sand-biomass using cfd techniques

Fluidization taking into account the presence of the material to be gasified is a differential addressed in this study. Accordingly the solid phase was composed of a binary mixture of sand and biomass. This paper deals with the numerical simulation of a gasifier bubbling fluidized bed using CFD for the system composed of gas - biomass – sand. In order to determine the best fluidization conditions, a factorial design 23 was carried out varying the biomass particle density and diameter and the biomass percentage in the solid phase. To perform the simulations, ANSYS CFX 15.0 was used, adopting an Eulerian approach coupled to the Kinetic Theory of Granular Flow. The k- ε turbulence model was adopted. Seventeen simulations were performed setting the gas superficial velocity to 0.38 m s-1. Based on the results of the factorial design, it was possible to qualitatively identify the tests to which the system reached a bubbling fluidization (1, 2, 5, 6, 9, 11, 12 and 14). The variable with the highest significance in the model equation was the diameter of the biomass particle. Volumetric fraction profiles of gas, sand and biomass were obtained to the 17 factorial design conditions as well as a model that predicts the bed expansion. The assay that reached greater bed height (0.50 m), staying on bubbling regime, was the one with 15% biomass particles with 375 m diameter and 85% sand, indicating those are good conditions for fluidization. Please click Additional Files below to see the full abstract

Spread pattern of the first dengue epidemic in the city of Salvador, Brazil

<p>Abstract</p> <p>Background</p> <p>The explosive epidemics of dengue that have been occurring in various countries have stimulated investigation into new approaches to improve understanding of the problem and to develop new strategies for controlling the disease. The objective of this study was to evaluate the characteristics of diffusion of the first dengue epidemic that occurred in the city of Salvador in 1995.</p> <p>Methods</p> <p>The epidemiological charts and records of notified cases of dengue in Salvador in 1995 constituted the source of data. The cases of the disease were georeferenced according to census areas (spatial units) and epidemiological weeks (temporal unit). Kernel density estimation was used to identify the pattern of spatial diffusion using the R-Project computer software program.</p> <p>Results</p> <p>Of the 2,006 census areas in the city, 1,400 (70%) registered cases of dengue in 1995 and the spatial distribution of these records revealed that by the end of 1995 practically the entire city had been affected by the virus, with the largest concentration of cases occurring in the western region, composed of census areas with a high population density and predominantly horizontal residences compared to the eastern region of the city, where there is a predominance of vertical residential buildings.</p> <p>Conclusion</p> <p>The pattern found in this study shows the characteristics of the classic process of spreading by contagion that is common to most infectious diseases. It was possible to identify the epicenter of the epidemic from which centrifugal waves of the disease emanated. Our results suggest that, if a more agile control instrument existed that would be capable of rapidly reducing the vector population within a few days or of raising the group immunity of the population by means of a vaccine, it would theoretically be possible to adopt control actions around the epicenter of the epidemic and consequently reduce the incidence of the disease in the city. This finding emphasizes the need for further research to improve the technology available for the prevention of this disease.</p

Novel, Meso-Substituted Cationic Porphyrin Molecule for Photo-Mediated Larval Control of the Dengue Vector Aedes aegypti

Dengue is a life-threatening viral disease of growing importance, transmitted by Aedes mosquito vectors. The control of mosquito larvae is crucial to contain or prevent disease outbreaks, and the discovery of new larvicides able to increase the efficacy and the flexibility of the vector control approach is highly desirable. Porphyrins are a class of molecules which generate reactive oxygen species if excited by visible light, thus inducing oxidative cell damage and cell death. In this study we aimed at assessing the potential of this photo-mediated cytotoxic mechanism to kill Aedes (Stegomyia) aegypti mosquito larvae. The selected porphyrin molecule, meso-tri(N-methylpyridyl),meso-mono(N-tetradecylpyridyl)porphine (C14 for simplicity), killed the larvae at doses lower than 1 µM, and at light intensities 50–100 times lower than those typical of natural sunlight, by damaging their intestinal tissues. The physicochemical properties of C14 make it easily adsorbed into organic material, and we exploited this feature to prepare an ‘insecticidal food’ which efficiently killed the larvae and remained active for at least 14 days after its dispersion in water. This study demonstrated that photo-sensitizing agents are promising tools for the development of new larvicides against mosquito vectors of dengue and other human and animal diseases