Cultivation Platforms Research Articles

Techno-economic assessment of open microalgae production systems

Microalgae represents a promising feedstock due to inherent advantages such as high solar energy efficiencies, large lipid fractions, and utilization of various waste streams including industrial flue gas. This study directly evaluates and compares the economic viability of biomass production from two different open cultivation platforms, 1) algal turf scrubbers and 2) open raceway ponds. Modular sub-process models were developed and leveraged for the economic comparison of the systems on the metric of harvested biomass. The system boundary was expanded to include downstream processing for the production of renewable diesel through thermochemical conversion for a comparison of the production platforms on a cost per gallon of fuel. Economic results of the two production pathways show a biomass production cost for the algal turf scrubber of $510tonne−1 and $8.34 per gallon for fuel. Open raceway pond results give a biomass cost of $673tonne−1 and a fuel cost of $6.27 per gallon. Sensitivity analysis show productivity and culture stability to be critical factors in the economic viability. Multiple scenarios are presented with baseline results directly compared to literature and highlight the need for robust growth modelling.

Bioreactors for high cell density and continuous multi-stage cultivations: options for process intensification in cell culture-based viral vaccine production.

With an increasing demand for efficacious, safe, and affordable vaccines for human and animal use, process intensification in cell culture-based viral vaccine production demands advanced process strategies to overcome the limitations of conventional batch cultivations. However, the use of fed-batch, perfusion, or continuous modes to drive processes at high cell density (HCD) and overextended operating times has so far been little explored in large-scale viral vaccine manufacturing. Also, possible reductions in cell-specific virus yields for HCD cultivations have been reported frequently. Taking into account that vaccine production is one of the most heavily regulated industries in the pharmaceutical sector with tough margins to meet, it is understandable that process intensification is being considered by both academia and industry as a next step toward more efficient viral vaccine production processes only recently. Compared to conventional batch processes, fed-batch and perfusion strategies could result in ten to a hundred times higher product yields. Both cultivation strategies can be implemented to achieve cell concentrations exceeding 107 cells/mL or even 108 cells/mL, while keeping low levels of metabolites that potentially inhibit cell growth and virus replication. The trend towards HCD processes is supported by development of GMP-compliant cultivation platforms, i.e., acoustic settlers, hollow fiber bioreactors, and hollow fiber-based perfusion systems including tangential flow filtration (TFF) or alternating tangential flow (ATF) technologies. In this review, these process modes are discussed in detail and compared with conventional batch processes based on productivity indicators such as space-time yield, cell concentration, and product titers. In addition, options for the production of viral vaccines in continuous multi-stage bioreactors such as two- and three-stage systems are addressed. While such systems have shown similar virus titers compared to batch cultivations, keeping high yields for extended production times is still a challenge. Overall, we demonstrate that process intensification of cell culture-based viral vaccine production can be realized by the consequent application of fed-batch, perfusion, and continuous systems with a significant increase in productivity. The potential for even further improvements is high, considering recent developments in establishment of new (designer) cell lines, better characterization of host cell metabolism, advances in media design, and the use of mathematical models as a tool for process optimization and control.

Production of human pluripotent stem cell therapeutics under defined xeno-free conditions: progress and challenges.

Recent advances on human pluripotent stem cells (hPSCs), including human embryonic stem cells (hESCs) and induced pluripotent stem cells (hiPSCs) have brought us closer to the realization of their clinical potential. Nonetheless, tissue engineering and regenerative medicine applications will require the generation of hPSC products well beyond the laboratory scale. This also mandates the production of hPSC therapeutics in fully-defined, xeno-free systems and in a reproducible manner. Toward this goal, we summarize current developments in defined media free of animal-derived components for hPSC culture. Bioinspired and synthetic extracellular matrices for the attachment, growth and differentiation of hPSCs are also reviewed. Given that most progress in xeno-free medium and substrate development has been demonstrated in two-dimensional rather than three dimensional culture systems, translation from the former to the latter poses unique difficulties. These challenges are discussed in the context of cultivation platforms of hPSCs as aggregates, on microcarriers or after encapsulation in biocompatible scaffolds.

Multispectral image analysis for algal biomass quantification

This article reports a novel multispectral image processing technique for rapid, noninvasive quantification of biomass concentration in attached and suspended algae cultures. Monitoring the biomass concentration is critical for efficient production of biofuel feedstocks, food supplements, and bioactive chemicals. Particularly, noninvasive and rapid detection techniques can significantly aid in providing delay-free process control feedback in large-scale cultivation platforms. In this technique, three-band spectral images of Anabaena variabilis cultures were acquired and separated into their red, green, and blue components. A correlation between the magnitude of the green component and the areal biomass concentration was generated. The correlation predicted the biomass concentrations of independently prepared attached and suspended cultures with errors of 7 and 15%, respectively, and the effect of varying lighting conditions and background color were investigated. This method can provide necessary feedback for dilution and harvesting strategies to maximize photosynthetic conversion efficiency in large-scale operation.

Micropatterning of Hydrogels on Locally Hydrophilized Regions on PDMS by Stepwise Solution Dipping and in Situ Gelation

This study presents a simple but highly versatile method of fabricating picoliter-volume hydrogel patterns on poly(dimethylsiloxane) (PDMS) substrates. Hydrophilic regions were prepared on hydrophobic PDMS plates by trapping and melting functional polymer particles and performing subsequent reactions with partially oxidized dextran. Small aliquots of a gelation solution were selectively trapped on the hydrophilic areas by a simple dipping process that was utilized to make thin hydrogel patterns by the in situ gelation of a sol solution. Using this process, we successfully formed calcium alginate, collagen I, and chitosan hydrogels with a thickness of several micrometers and shapes that followed the hydrophilized regions. In addition, alginate and collagen gel patterns were used to capture cells with different adhesion properties selectively on or off the hydrogel structures. The presented strategy could be applicable to the preparation of a variety of hydrogels for the development of functional biosensors, bioreactors, and cell cultivation platforms.

A Multi-Platform Flow Device for Microbial (Co-) Cultivation and Microscopic Analysis

Novel microbial cultivation platforms are of increasing interest to researchers in academia and industry. The development of materials with specialized chemical and geometric properties has opened up new possibilities in the study of previously unculturable microorganisms and has facilitated the design of elegant, high-throughput experimental set-ups. Within the context of the international Genetically Engineered Machine (iGEM) competition, we set out to design, manufacture, and implement a flow device that can accommodate multiple growth platforms, that is, a silicon nitride based microsieve and a porous aluminium oxide based microdish. It provides control over (co-)culturing conditions similar to a chemostat, while allowing organisms to be observed microscopically. The device was designed to be affordable, reusable, and above all, versatile. To test its functionality and general utility, we performed multiple experiments with Escherichia coli cells harboring synthetic gene circuits and were able to quantitatively study emerging expression dynamics in real-time via fluorescence microscopy. Furthermore, we demonstrated that the device provides a unique environment for the cultivation of nematodes, suggesting that the device could also prove useful in microscopy studies of multicellular microorganisms.

Engineering cell platforms for myocardial regeneration

Introduction: Various engineered ‘cell-platforms’ have been reported in recent years for the possible treatment of myocardial infarction (MI) and end-stage heart failure. These engineered platforms rely on two key factors: cells and/or biomaterial scaffolds for the regeneration of the infarcted heart tissue.Areas covered: Two major cell-platform approaches are described and broadly categorized as ‘injectable cell platforms’ and ‘patch-based cell platforms’. The recent advancements in these cell-platforms in terms of their relative successes in-vivo as well as their clinical feasibility are summarized. Natural as well as synthetic scaffolds, with or without the cellular component, are compared with cell based therapy alone. This review focuses on achievements, as well as the gaps that are presently checking any progress towards producing clinically relevant panacea for myocardial regeneration.Expert opinion: Cardiac and induced pluripotent stem cells will probably be the focus of future research. The combined cell-biomaterial scaffold therapy is superior to cell therapy alone. Nevertheless, encouraging pre-clinical successes have limited translation into clinical practice due to limited cell survival post transplantation, inadequate construct thicknesses for human-sized hearts and the traditional use of ‘flat (2D) tissue culture’ techniques. The development of complementary dynamic 3D cultivation platforms will probably lead to improved outcomes and enable fast screening of various therapeutic approaches.