Intracellular calcium response of Sf-9 insect cells exposed to intense fluid forces

Induction of mammalian cell death by simple shear and extensional flows

In this work we investigated whether the type of shear flow, to which cells are exposed, influences the initiation of cell death. It is shown that mammalian cells, indeed, distinguish between discrete types of flow and respond differently. Two flow devices were employed to impose accurate hydrodynamic flow fields: uniform steady simple shear flow and oscillating extensional flow. To distinguish between necrotic and apoptotic cell death, fluorescence activated cell sorting and the release of DNA in the culture supernatant was used. Results show that Chinese Hamster Ovaries and Human Embryonic Kidney cells will enter the apoptotic pathway when subjected to low levels of hydrodynamic stress (around 2.0 Pa) in oscillating, extensional flow. In contrast, necrotic death prevails when the cells are exposed to hydrodynamic stresses around 1.0 Pa in simple shear flow or around 500 Pa in extensional flow. These threshold values at which cells enter the respective death pathway should be avoided when culturing cells for recombinant protein production to enhance culture longevity and productivity.

Effects of hydrodynamic and interfacial forces on plant cell suspension systems

Plant cells are perceived to be sensitive to the hydrodynamic environment in conventional bioreactors. Heightened sensitivity, relative to most bacterial cultures, is frequently attributed to larger plant cell sizes, extensive vacuolization and aggregation patterns. Early studies of shear sensitivity focused on cell lysis and/or loss of viability. More recently, an extensive array of sub-lethal responses has been identified. A fuller understanding of these sub-lytic effects may assist in the optimization of large-scale cultivation conditions. This paper reviews recent work on the hydrodynamic shear sensitivity of plant cell systems, under cultivation conditions and in purpose-built shearing devices. The relevance of different approaches to the characterization of the intensity of a given hydrodynamic environment is discussed. Indicators of cell response to hydrodynamic stress are evaluated. The potential significance of cellular defense mechanisms, observed in response to mechanical stimulants, is identified.

The engineering effects of fluids flow on freely suspended biological macro-materials and macromolecules

The manufacture of many biotechnologically important products requires consideration of the physical breakage and biochemical degradation pathways at all stages during processing, storage and transportation. The engineering flow environment in most items of bioprocess equipment has long been recognised as a key factor in determining these pathways and is the focus of the present review. Because of its industrial significance, the detrimental effects of the engineering flow environment on freely suspended bioparticles have been the subject of many scientific investigations over the past few decades. There is a general consensus of opinion that fluid shear and elongational stresses are the two main breakage pathways of relevance to processing of most biomaterials. An additional degradation pathway has also been identified involving significant losses of biological activity of macromolecules at gas-liquid, gas-solid and liquid-liquid interfaces. In such cases, the engineering flow field is shown to have a secondary role in determining the kinetics of inactivation. An equally important consideration in the optimisation of the relevant unit operations is the biomechanical integrity of the flow sensitive material. The biomechanical and biorheological parameters that determine the integrity of biomaterials are poorly defined, their evaluations present future research challenges and are of immediate engineering significance.

Observations on the shear damage to different animal cells in a concentric cylinder viscometer

A clear distinction is made between damage to the population of cells and damage to individual cells on exposure to shear stress. Work on mechanical damage to animal cells in suspension is reported for six different cell lines. Precisely controlled shears of 1 Pa, 10 Pa, and 100 Pa were generated in a viscometer and distortions in morphology of the cells-for instance, the formation of transient pores, cytoplasmic extrusions, and ghost-cell membranes-are presented with photographic evidence. Low shears are shown to be just as damaging as the higher shears, although the type of damage is different. It follows that bioreactors should be operated at intermediate shear levels for optimal yield. A mechanism to account for the unexpected stability of animal cells at intermediate levels of shear is presented.