# Ex vivo

Ex vivo (Latin for 'out of the living') refers to experiments or measurements performed on biological materials—such as tissues, organs, or cells—that have been removed from an organism and maintained under conditions that, to some extent, mimic their natural environment. This approach preserves the functional viability and structural integrity of the extracted materials for a limited time, enabling the study of biological processes in a controlled setting. While certain ex vivo techniques have been employed since the early 20th century, their formalization and refinement as a research methodology accelerated in the mid-20th century. Ex vivo studies are widely applied in medical research, pharmacology, and biotechnology, serving as an intermediate method between in vitro (test tube) experiments and in vivo (whole-organism) studies. They provide a balance between experimental control and physiological relevance, allowing for investigations that may be ethically or technically impractical in living subjects.

## Definition

Ex vivo, meaning 'out of the living' in Latin, refers to biological studies conducted on tissues, organs, or cells that have been removed from an organism and maintained in a controlled environment outside the body. An intermediate approach between in vitro studies, which use isolated cells in artificial conditions, and in vivo studies, which occur within a living organism, ex vivo methods preserve functional viability and structural integrity of the extracted biological materials for a limited timeframe. As these materials are subject to degradation over time, the controlled environment typically encompasses regulated temperature, nutrient supply, oxygenation, and humidity, often facilitated through cell culture media or specialized chambers.
Ex vivo models are used in research scenarios that require a level of organizational complexity beyond what in vitro systems can achieve, while reducing the variables inherent in whole-organism studies. In dermatological research, for example, human skin organ culture (hSOC) is used to investigate wound healing, drug penetration, and toxicology, leveraging the preservation of skin architecture, including appendages. Skin explants from surgical procedures are used to assess initial tissue responses to laser treatments, providing insights into early-stage physiological changes. However, ex vivo models do not replicate long-term or systemic effects.

## Techniques

Ex vivo research uses specialized techniques to sustain tissues or cells outside their natural environment while preserving their functional integrity. In ex vivo organ perfusion, whole organs—such as the heart or lungs—are maintained in a functional state by circulating solutions that mimic physiological blood flow. This method enables researchers to investigate organ-level responses to drugs, disease states, or environmental changes under controlled conditions. In contrast, traditional organ culture typically involves maintaining organ sections or small fragments in static or semi-static conditions without active perfusion.
Another widely used technique is organotypic slice cultures, where thin sections of organs are maintained on supportive matrices to preserve their three-dimensional structure and cellular interactions. This method enables the study of localized responses, tissue-specific dynamics, and physiological processes over extended periods. An example is the use of hippocampal slices in neuroscience research to examine long-term cellular and synaptic activity. In some cases, ex vivo electroporation—in which an electric field is applied to cells to facilitate the uptake of genetic material—is used to introduce DNA into cells within tissue slices, allowing researchers to study gene expression in a controlled environment.$^{:241}$
Cell culture involves isolating individual cells from tissues and growing them in a medium enriched with nutrients and growth factors. While these cultures retain some functional characteristics of their tissue of origin, they often exhibit changes in phenotype and gene expression when removed from their native environment. Primary cell cultures, derived directly from tissues, more closely resemble physiological conditions than immortalized cell lines, making them essential for studying cellular behavior, disease mechanisms, and drug effects.

### In electrochemistry

In electrochemical research, ex vivo methods provide a controlled platform for investigating biological analytes with a degree of experimental flexibility not achievable in in vivo studies.$^{:161–164}$ The constraints of living systems limit electrode design and placement in in vivo experiments, where smaller electrodes, such as micro- and nanoelectrodes, are typically preferred to minimize invasiveness.$^{:3–4}$ By contrast, ex vivo techniques allow for the development of custom electrode geometries, enabling precise interfaces with biological tissues under controlled conditions. This adaptability facilitates a detailed examination of analytes and their roles in physiological processes. Ex vivo electrochemical techniques are applied in neuroscience, pharmacology, and biomedical engineering to study neurotransmitter dynamics, metabolic activity, and disease-associated biomarkers.$^{:161–164}$