Ex vivo

Ex vivo brainstem: A. coronal view displaying the anterior portion of the tissue sample; B. sagittal view displaying the left-hand side of the tissue sample

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 and in vivo studies. They provide a balance between experimental control and physiological relevance, allowing for investigations that may be ethically or technically impractical in living subjects.

Advantages and limitations

Ex vivo, meaning 'out of the living' in Latin, refers to biological studies involving tissues, organs, or cells maintained outside their native organism under controlled laboratory conditions. These studies preserve the extracted materials' functional viability and structural integrity for limited periods by precisely managing the conditions, which typically include oxygenation, temperature, nutrient delivery, and humidity. The conditions are often facilitated through cell culture media or specialized perfusion chambers. As an intermediate approach between in vitro studies, which traditionally use isolated cells in artificial environments, and in vivo research, conducted within living organisms, ex vivo models preserve more of the native tissue architecture than traditional cell cultures, while offering greater experimental control than whole-organism studies. By maintaining natural tissue organization, ex vivo models address some limitations of in vitro work, such as oversimplified cellular interactions, and mitigate the variability and systemic influences inherent to in vivo approaches. Ex vivo models may offer ethical benefits by reducing reliance on animal testing, allowing researchers to conduct physiologically relevant experiments without using entire living systems.

In dermatological research, human skin organ culture (hSOC)—a technique where excised human skin is maintained in an artificial medium while preserving its native structure—is used to investigate wound healing, drug penetration, and toxicology. These models retain architectural features of the skin, enabling the study of conditions unique to humans, such as keloids, which are not replicated in animal models. Skin explants from surgical procedures allow researchers to observe early-stage physiological responses to laser treatments in ways that closely resemble in vivo conditions, though processes like re-epithelialization occur more slowly than in living tissue. In intervertebral disc research, ex vivo models that retain vertebral bone allow for testing potential drugs and investigating loading effects on disc degeneration and repair. In biosensing and electroanalytical applications, ex vivo methods offer experimental flexibility unavailable in living systems. While many in vivo experiments favor micro- and nanoelectrodes to minimize invasiveness, larger electrodes are routinely used for specific purposes. Ex vivo approaches, by contrast, permit custom electrode geometries that interface precisely with biological tissues under controlled conditions, without the same constraints on size and invasiveness. This adaptability enables detailed examination of biological analytes and their physiological roles. Ex vivo electroanalytical methods are applied in neuroscience, pharmacology, and biomedical engineering to study neurotransmitter dynamics, metabolic activity, and disease-associated biomarkers.

However, ex vivo models have inherent limitations, including significant changes in biophysical properties of tissues after the organism's death, tissue degradation that increases with time, restricted viability duration, as well as absence of whole-body physiological responses, such as lack of blood circulation and nerve innervation. These constraints prevent the models from replicating long-term or systemic effects. The comparison between in vivo and ex vivo models can be complex due to these changes in tissue properties. For instance, studies have found large changes in electric fields between in vivo and ex vivo measurements that increased with postmortem time.

History

Carl Ludwig

Max von Gruber

Ex vivo models have been a longstanding methodology in biomedical research. The earliest known studies on isolated and artificially perfused kidneys were conducted by German physiologist Carl Eduard Loebell, who presented his findings in a doctoral dissertation titled De conditionibus quibus secretiones in glandulis at the University of Marburg in 1849. German physiologist Carl Ludwig and his students conducted experiments on isolated animal organs in the mid-19th century, including the perfusion of excised kidneys and hearts with oxygenated fluids, as well as the development of manometric devices to record pressure changes within blood vessels. These approaches enabled the study of organ function independently of systemic variables present in vivo and established foundational techniques for organ perfusion. In 1876, Gustav von Bunge and Oswald Schmiedeberg demonstrated the synthesis of hippuric acid in the isolated dog kidney. In 1885, Maximilian von Frey and Max von Gruber, working at the Physiological Institute of Leipzig University, constructed an apparatus combining a mechanical pump with an early oxygenator that substituted the function of the heart and lungs in experiments on dogs. This device oxygenated blood outside the body and served as a precursor to the heart-lung machine, expanding the experimental possibilities of ex vivo perfusion systems.

In the 1880s, British physiologist Sydney Ringer developed a salt solution that sustained rhythmic contractions in the isolated frog heart. Later named Ringer's solution, it enabled extended observation of cardiac activity and supported controlled experimental studies on cardiac physiology in isolated preparations. In 1895, German physiologist Oskar Langendorff introduced a method for isolated heart perfusion involving retrograde flow through the aorta to supply the coronary circulation. The Langendorff preparation allowed for direct measurement of cardiac function and precise control of perfusion parameters while minimizing systemic confounders inherent to in vivo models. It became a widely used technique in the study of cardiac physiology and remains a standard method in cardiovascular research.

A heart–lung machine (upper right) in a coronary artery bypass surgery

Throughout the 20th century, ex vivo techniques were adapted for a range of animal models. A significant refinement was the development of the working heart model, in which perfusate enters the left atrium and exits through the aorta, more closely replicating physiological flow conditions. Advances in instrumentation enabled detailed assessments of cardiac function, including pressure–volume relationships, oxygen consumption, and myocardial contractility. In 1953, American surgeon John Heysham Gibbon successfully employed a heart-lung machine during open-heart surgery on a human patient.

Techniques

Further information: Ex vivo lung perfusion and Machine perfusion

Demonstration of isolation of choroid from the mouse eye

In situ lung function evaluation, and assessment of total lung capacity (TLC) and basal elastance after performing a recruitment maneuver

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. By contrast, organ culture traditionally 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.

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.

See also

• List of medical roots, suffixes and prefixes
• Neoclassical compound – Compound words composed from Latin or ancient Greek