Challenges in tracing material flow passing a loss-in-weight feeder in continuous manufacturing processes

Loss-in-weight feeders are an integral part of most continuous manufacturing processes, ensuring a constant mass flow. The feeders cause a significant degree of back-mixing in such lines. Understanding back-mixing is essential for the treatment of disturbances. However, feeders refilled semi-continuously contradict the common theory assuming steady-state. This study aims at understanding dynamic back-mixing and related phenomena. Low filling levels of a feeder are investigated using a fluorescent tracer. These investigations prove an impact of the addition of material probably caused by a non-uniform draw-in of the screws and dead material in the hopper. In turn, the dead material accounts for up to 50 % of the material in the hopper. Possible evidence of dead zones at higher filling levels and in feeders from literature are discussed additionally. Steady-state models from literature are extended to represent the observations and back-mixing at all filling levels. This extension reduces the root-mean-squared deviation of the model from the experimental data by 41%. The model predicts different responses to similar disturbances depending on the filling. This state-dependent back-mixing and the observed dead zones are challenging for diverting non-conforming material and material traceability. Therefore, these phenomena should be considered in selecting and operating feeders.

Tracking raw material flow through a continuous direct compression line Part I of II: Residence time distribution modeling and sensitivity analysis enabling increased process yield

Continuous manufacturing (CM) offers advantages in quality and space-time yield compared to common batch manufacturing. However, higher yield losses due to the start-up procedure make a broad application uneconomical. This work discusses the possibility of reducing yield losses by adjusting the degree of back-mixing. Back-mixing of nonconforming material from disturbances or start-up will result in the contamination of subsequent material. Therefore, higher degrees of back-mixing cause the discharge of additional material. Choosing an advantageous setting of operational parameters may be a simple way to change the degree of back-mixing. Based on direct compression, this work demonstrates the identification of promising parameters. Therefore, step-change experiments using color-marked material in the feeder, blender, and tablet press quantify the impact of three operational parameters per device. Models for the devices and the entire process result from those measurements. Subsequently, a global variance-based sensitivity analysis identifies the most influential parameters. As a result, adjusting the minimal filling level of the feeder and the rotational feed frame speed of the tablet press reduces back-mixing by more than 30%. At high costs of the raw materials, the resulting savings can significantly improve the economic performance of CM compared to batch manufacturing.

Influence of thermally induced structure changes in diluted β-lactoglobulin solutions on their surface activity and behavior in foam fractionation

Surface activity is an intrinsic protein feature, leading to the capability of aqueous protein solutions to form foam. This feature provides opportunities for downstream processing, such as usage of foam fractionation for purification. In order to investigate the impact of the surface activity on the performance of the foam fractionation process, protein solutions with different surface activity were produced by different thermal denaturation of aqueous β-lactoglobulin solutions. The effectiveness of the denaturation procedure was verified with circular dichroic spectroscopy, and the impact on surface activity was determined via dynamic surface tension measurement. The increased surface activity resulted in higher foamate flow rates. Furthermore, the effects could be correlated with secondary structure changes and with the dynamic surface pressure. The new result of this study is that the effect of the denaturation of a protein on foam fractionation depends on the protein concentration. At the lower feed concentration, effects became visible, which could not be observed at the higher concentration.

Correlating the phase settling behavior of aqueous-organic solvent systems in a centrifugal partition chromatograph

The prediction of the performance of a Centrifugal Partition Chromatography (CPC) is a difficult but desirable task. The partitioning of the sample, as well as the fluid dynamical phenomena dispersion, coalescence, and stationary phase retention have to be individually understood. Therefore, the phase settling behavior of different aqueous-organic solvent systems and with this, the dependency of the stationary phase retention in CPC was investigated in this study. On the one hand, batch settling experiments were performed, and the settling velocity of aqueous-organic solvent systems was investigated. With this it was possible to correlate the stationary phase retention in CPC in both operating modes. For descending mode operation a high settling velocity of the lower phase and for ascending mode a high settling velocity of the upper phase is needed for a stable operation and a high stationary phase retention. On the other hand, the dimensionless numbers Capillary number (Ca) and Morton number (Mo) were used to generate a universally applicable correlation for the stationary phase retention in ascending mode. It was shown, that a high stationary phase retention correlates with low values of Ca and Mo, whereas the influence of Mo is neglectable in the parameter space investigated. Within this correlation, the individual influence of each influencing parameter on the stationary phase retention was included. Moreover, this correlation was compared to descriptions for descending mode given in literature. With this it was shown that the minimal stationary phase retention is correlatable to the point of phase inversion.

Characterization and correlation of mobile phase dispersion of aqueous-organic solvent systems in centrifugal partition chromatography

To reach a high separation efficiency using Centrifugal Partition Chromatography (CPC), the fluid dynamical behavior of the liquid-liquid two-phase systems must be clearly understood. The fluid dynamics, namely the dispersion, the coalescence, and the stationary phase retention, have a high impact on a separation. Especially the mobile phase dispersion influences the mass transfer during a separation. In this study, the mobile phase dispersion of different aqueous-organic solvent systems was characterized for ascending and descending mode via video analysis. Thereby the influence of the physical properties of the solvent systems, the operating parameters, and the geometry of the chamber inlet was investigated systematically using dimensional analysis. With the help of the dimensionless numbers Ohnesorge number (Oh_CPC), Eötvös number (Eo_CPC), and Weber number (We_CPC) the impact of the solvent system, the plant parameters, and the operating parameters on the mobile phase dispersion could be described. Inside the three dimensional area, spanned by the dimensionless numbers, each state of mobile phase dispersion (undispersed, low dispersed, highly dispersed, and atomized) could be allocated to an individual region for both operating modes. Moreover, differences in mobile phase deflection depending on the operating mode and a possible reason for these were described.

Correlating physical properties of aqueous-organic solvent systems and stationary phase retention in a centrifugal partition chromatograph in descending mode

The performance of the Centrifugal Partition Chromatography (CPC) as a liquid-liquid chromatographic technique depends strongly on the two-phase solvent system used. Thereby the individual influence of the retention of the stationary phase, the coalescence, and the dispersion of the mobile phase in the chambers must be understood to select appropriate solvent systems and reach high separation efficiencies. In this study, an optical measurement system was used to investigate the influence of the physical properties of the Arizona solvent systems on the stationary phase retention in descending mode. Therefore, physical properties like density, viscosity, and interfacial tension were measured as well as the stationary phase retention. Using dimensionless numbers, a correlation between the stationary phase retention and the influencing parameters could be determined. The correlation was validated using data from the literature. Additionally, the solvent systems were modified by additives to identify the validity of the correlation. It was proven that the dimensionless numbers Capillary number (Ca) and Morton number (Mo) can be used to predict the stationary phase retention of other liquid-liquid solvent systems as well as for different operating conditions.

Simulation of continuous low pH viral inactivation inside a coiled flow inverter

Continuous production of monoclonal antibodies is gaining more and more importance. To ensure continuous flow through the entire process as well as viral safety, continuous viral clearance needs to be investigated as well. This study focuses on low pH viral inactivation inside a coiled flow inverter (CFI). Computational fluid dynamics (CFD) simulation is used to gain further insight into the inactivation process inside the apparatus. The influence of viruses in comparison to different tracer elements on the residence time distribution (RTD) behavior is investigated. Finally, the viral inactivation kinetics are implemented into the CFD simulation and real process conditions are simulated. These are compared to experimental results. To the authors' knowledge, this study represents the first successful simulation of continuous viral inactivation inside a CFI. It allows the detailed analysis of processes inside the apparatus and the prediction of experimental virus study results and will therefore contribute to the effective planning of future validation studies.

Recovery of Natural α-Ionone from Fermentation Broth

Recently, the market value of aromas has constantly been rising. Because the supply from natural feedstock is limited, the biotechnological production has received more interest. Thus far, only a few attempts have been made to produce α-ionone, a valued essential aroma of raspberry, biotechnologically. This study reports a production process for enantiopure (R)-α-ionone from lab scale (2-150 L) with typical titer of 285 mg/L broth to industrial scale (up to 10 000 L) with a titer up to 400 mg/L broth, focusing on the development of a downstream process with a maximized yield at minimized effort. The developed recovery consists of solid-liquid extraction from the biomass at φ = 0.4 g of n-hexane/g of biomass for 90 min at ambient temperature and adsorption from the aqueous supernatant at Φ = 0.5 g of Diaion HP-20/mg of α-ionone, followed by desorption at Ψ = 30 g of n-hexane/g of Diaion HP-20. Altogether, natural α-ionone could be gained in substantial quantity and purity of >95%.

Simulation of pH level distribution inside a coiled flow inverter for continuous low pH viral inactivation

The continuous production of monoclonal antibodies (mAbs) with the help of disposable equipment poses one of the future major changes in the pharmaceutical industry. Consequently, continuous viral clearance needs to be developed as well. The coiled flow inverter (CFI) was successfully implemented in the continuous downstream as a residence time module for low pH viral inactivation. As the elution profile of the upstream continuously operated protein A chromatography results in fluctuating pH values, the pH level distribution inside the CFI is highly relevant. This study presents a detailed investigation of pH level distribution inside the CFI at varying inlet conditions with the help of computational fluid dynamics simulation. The simulation model was validated first with the help of experimental data. Afterwards, the model was used for further investigations. It was determined that with a pH sine curve as input, the duration until steady state at the outlet requires two times the minimum residence time of the apparatus. Moreover, it could be observed that the CFI itself offers a progressive dampening effect on the pH level distribution. Afterwards, different forms of the sine curve representing different operation modes of the continuous protein A chromatograph were tested to evaluate this dampening capability. It became clear that the switch time has the highest influence on the resulting pH of the outlet stream and should be considered for process development. Finally, the radial pH profiles at different positions inside the CFI were determined. This once again revealed the high radial mixing capability of the CFI and its influence on the resulting product stream.

Bioprocess optimization for purification of chimeric VLP displaying BVDV E2 antigens produced in yeast Hansenula polymorpha

Chimeric virus-like particles (VLP) are known as promising tools in the development of safe and effective subunit vaccines. Recently, a technology platform to produce VLP based on the small surface protein (dS) of the duck hepatitis B virus was established. In this study, chimeric VLP were investigated displaying the 195 N-terminal amino acids derived from the glycoprotein E2 of the bovine viral diarrhea virus (BVDV) on their surface. Isolation of the VLP from methylotrophic yeast Hansenula polymorpha was allowed upon co-expression of wild-type dS and a fusion protein composed of the BVDV-derived antigen N-terminally fused to the dS. It was shown the VLP could be purified by a process adapted from the production of a recombinant hepatitis B VLP vaccine. However, the process essentially depended on costly ultracentrifugation which is critical for low cost production. In novel process variants, this step was avoided after modification of the initial batch capture step, the introduction of a precipitation step and adjusting the ion exchange chromatography. The product yield could be improved by almost factor 8 to 93 ± 12 mg VLP protein per 100 g dry cell weight while keeping similar product purity and antigenicity. This allows scalable and cost efficient VLP production.

Display of malaria transmission-blocking antigens on chimeric duck hepatitis B virus-derived virus-like particles produced in Hansenula polymorpha

BACKGROUND

Malaria caused by Plasmodium falciparum is one of the major threats to human health globally. Despite huge efforts in malaria control and eradication, highly effective vaccines are urgently needed, including vaccines that can block malaria transmission. Chimeric virus-like particles (VLP) have emerged as a promising strategy to develop new malaria vaccine candidates.

METHODS

We developed yeast cell lines and processes for the expression of malaria transmission-blocking vaccine candidates Pfs25 and Pfs230 as VLP and VLP were analyzed for purity, size, protein incorporation rate and expression of malaria antigens.

RESULTS

In this study, a novel platform for the display of Plasmodium falciparum antigens on chimeric VLP is presented. Leading transmission-blocking vaccine candidates Pfs25 and Pfs230 were genetically fused to the small surface protein (dS) of the duck hepatitis B virus (DHBV). The resulting fusion proteins were co-expressed in recombinant Hansenula polymorpha (syn. Pichia angusta, Ogataea polymorpha) strains along with the wild-type dS as the VLP scaffold protein. Through this strategy, chimeric VLP containing Pfs25 or the Pfs230-derived fragments Pfs230c or Pfs230D1M were purified. Up to 100 mg chimeric VLP were isolated from 100 g dry cell weight with a maximum protein purity of 90% on the protein level. Expression of the Pfs230D1M construct was more efficient than Pfs230c and enabled VLP with higher purity. VLP showed reactivity with transmission-blocking antibodies and supported the surface display of the malaria antigens on the native VLP.

CONCLUSION

The incorporation of leading Plasmodium falciparum transmission-blocking antigens into the dS-based VLP scaffold is a promising novel strategy for their display on nano-scaled particles. Competitive processes for efficient production and purification were established in this study.

Establishment of a yeast-based VLP platform for antigen presentation

Background

Chimeric virus-like particles (VLP) allow the display of foreign antigens on their surface and have proved valuable in the development of safe subunit vaccines or drug delivery. However, finding an inexpensive production system and a VLP scaffold that allows stable incorporation of diverse, large foreign antigens are major challenges in this field.

Results

In this study, a versatile and cost-effective platform for chimeric VLP development was established. The membrane integral small surface protein (dS) of the duck hepatitis B virus was chosen as VLP scaffold and the industrially applied and safe yeast Hansenula polymorpha (syn. Pichia angusta, Ogataea polymorpha) as the heterologous expression host. Eight different, large molecular weight antigens of up to 412 amino acids derived from four animal-infecting viruses were genetically fused to the dS and recombinant production strains were isolated. In all cases, the fusion protein was well expressed and upon co-production with dS, chimeric VLP containing both proteins could be generated. Purification was accomplished by a downstream process adapted from the production of a recombinant hepatitis B VLP vaccine. Chimeric VLP were up to 95% pure on protein level and contained up to 33% fusion protein. Immunological data supported surface exposure of the foreign antigens on the native VLP. Approximately 40 mg of chimeric VLP per 100 g dry cell weight could be isolated. This is highly comparable to values reported for the optimized production of human hepatitis B VLP. Purified chimeric VLP were shown to be essentially stable for 6 months at 4 °C.

Conclusions

The dS-based VLP scaffold tolerates the incorporation of a variety of large molecular weight foreign protein sequences. It is applicable for the display of highly immunogenic antigens originating from a variety of pathogens. The yeast-based production system allows cost-effective production that is not limited to small-scale fundamental research. Thus, the dS-based VLP platform is highly efficient for antigen presentation and should be considered in the development of future vaccines.