Cell viability refers to the overall health and survival capability of cells. It measures the proportion of living cells within a sample, providing a snapshot of their condition. This metric is a fundamental indicator used across various scientific and medical disciplines to understand cellular responses and overall well-being. Researchers assess cell viability to determine how cells are affected by different conditions or treatments.
What Cell Viability Represents
Cell viability extends beyond simply being alive; it indicates a cell’s ability to carry out its normal biological functions. Viable cells typically exhibit intact cell membranes, which act as barriers regulating what enters and exits the cell. They also possess active metabolic processes, such as energy production, necessary for growth and repair.
Viable cells also proliferate, meaning they can divide and reproduce under suitable conditions. This includes maintaining their physiological functions and responding appropriately to their environment. In contrast, non-viable cells, which are either dead or dying, often show compromised membrane integrity and reduced metabolic activity.
How Cell Viability Is Assessed
Scientists employ various methods to measure cell viability, each focusing on different aspects of cellular health. One common approach is the Trypan Blue exclusion assay, which relies on the principle that viable cells with intact membranes will exclude the dye, while dead cells with damaged membranes will absorb it and appear blue. This allows for direct counting of live versus dead cells.
Metabolic activity assays, such as the MTT or XTT assays, quantify cell health by measuring the activity of enzymes within the cells, particularly those in the mitochondria. Viable cells convert a colorless substrate into a colored product, with color intensity indicating metabolically active cells. Measuring adenosine triphosphate (ATP) content is another method, as ATP is an energy molecule produced by living cells. Higher ATP levels correlate with more viable cells.
Factors Affecting Cell Viability
Numerous factors, both internal and external, can influence a cell’s viability. Environmental conditions play a significant role, with temperature and pH levels needing to remain within optimal ranges for cells to function properly. Deviations can induce cellular stress, potentially reducing viability or causing cell death.
Essential nutrients and oxygen are crucial for cell health and survival. Insufficient supply impairs metabolic processes, decreasing viability. Toxic substances or certain drugs can damage cells, compromising their integrity and reducing survival. Cell type, age, and genetic makeup can also predispose cells to different levels of resilience or susceptibility to these factors.
Understanding “Good” Cell Viability
What constitutes “good” cell viability depends on the specific application or experimental objective; there is no universal percentage. For routine cell culture, high viability (often above 80-95%) is generally desired to ensure a healthy, growing cell population for experiments. This indicates a robust culture suitable for further research or expansion.
In drug development, viability interpretation shifts. When testing anti-cancer drugs, lower viability may be desired, indicating drug effectiveness in killing target cancer cells. Researchers seek compounds that reduce diseased cell viability while minimizing harm to healthy ones. This highlights how the objective dictates acceptable viability.
For regenerative medicine and cell-based therapies, maintaining a high percentage of viable cells is crucial for therapeutic success. Genetically modified cellular therapies often require a minimum viability of 70%. Cord blood products typically mandate at least 85% viability.
Before cryopreservation, cells intended for long-term storage should ideally have a viability greater than 90% to ensure a sufficient number of healthy cells survive the freezing and thawing process. Post-thaw viability for cryopreserved cells, particularly for stem cells, is often expected to exceed 90%, although some products might accept slightly lower if justified. These specific thresholds ensure the cells remain functional for their intended purpose, whether for research or clinical application.