The 3Rs – Replacement

Replacement refers to methods that avoid or replace the use of live animals in scientific procedures, while still achieving the same research objectives. At the University of Dundee, we use full and partial replacement methods to answer our scientific questions.  

Modelling bacterial infection

Dr Daniel Neill's research group studies how bacteria infect human airways, including pneumonia and the chronic infections that affect people with impaired airway defences, such as those with cystic fibrosis or bronchiectasis.  

Animal models have long been used in respiratory infection research to assess bacterial virulence (disease-causing potential) or to trial new antibacterial drugs. However, several major drawbacks to vertebrate airway infection models have encouraged us to adopt or develop novel replacement technologies.  

Mice are the most widely used vertebrate system for studying respiratory disease, but they do not naturally develop chronic bacterial airway infections. Studies have shown that the available mouse models don’t accurately copy how microbes behave and function in the human airway. Recent years have seen rapid proliferation of and validation of alternative non-vertebrate models for study of airway disease and we have increasingly been adopting these, as well as developing new models in-house. 

We use three complementary non-vertebrate systems to study airway infection. First, we use a special liquid that contains all the nutrients and chemicals bacteria would normally find in the human airways — but without any cells in it. This lab-made liquid closely mimics the environment inside the lungs and airways. When bacteria that commonly infect the airways are grown in this liquid, they behave much like they do during a real infection in the human body.

Secondly, we use simple invertebrate infection models, where larval forms of insects (Wax Moth, Melonella Galleria) are infected with bacteria. These offer a higher throughput and more ethical alternative to using mice for infection research. The larvae have an immune system that works in a similar basic way to the early (“innate”) immune response in mammals, including humans. This means we can use them to study how the bacteria and the body interact in ways that are relevant to human disease.

Lastly, we use three-dimensional (3D) cell culture models, developed in partnership with the University of Dundee’s National Phenotypic Screening Centre, to study bacterial interactions with human airway cells grown between air and a liquid.

We use these models to better understand how microbes work at a basic level and to help us find and test new drugs that can kill or control harmful bacteria. Although our focus is on human pathogens (bacteria that cause diseases in people), these systems are also suitable for the study of infectious agents affecting animals. To date, we estimate that adopting these approaches has replaced the use of more than 500 mice in our research.

iPlacenta: transforming pregnancy drug study

The iPlacenta project has transformed how we study maternal health by creating a “placenta‑on‑a‑chip” – a tiny lab‑grown model of the human placenta that replicates the organ’s function in 3D.  

Each chip, roughly the size of a mobile phone SIM card, is made using human stem cells – these cells can turn into different types, including skin or nerve cells. These are in contact with tiny channels that let small amounts of fluid flow through, mimicking how the body works (microfluidic technology). This allows researchers to safely and efficiently test how medicines interact with the placenta during pregnancy, helping fill a major gap in understanding how drugs affect the placenta, how they are processed there, and what doses are, or aren’t, safe in pregnancy. 

The project is led by Dr Colin Murdoch at the University of Dundee’s Faculty of Health and funded by a €3.9 million EU Horizon grant. It brings together international experts to move beyond older research methods that rely on cancer‑derived cells or animal models, which often don’t accurately mimic how a real human placenta works. iPlacenta offers a more ethical model that behaves more like a placenta and gives answers to the scientific questions more quickly. 

To create the model, researchers grow placenta‑like cells (stem cell derived trophoblasts) inside the OrganoPlate® — a 3D “lab‑on‑a‑chip” platform developed by Dutch biotech company Mimetas. These chips produce small, functional placenta models that allow scientists to study how drugs pass between mother and foetus and to investigate placental diseases, without needing to use animal tissue. 

The model has already been published in the journal iScience and has proven valuable for studying preeclampsia and checking the safety of medicines during pregnancy. The project has received significant attention, including a front‑page feature in The Herald, an interview on the Making Sense of Pregnancy podcast, and winning the Research Project Award 2024 at The Herald Higher Education Awards. These achievements highlight its impact on science, society, the move toward replacing animals in research, and the future of maternal healthcare. 

Using human endothelial cells to simulate the structure of blood vessels

The brain uses a large amount of energy and relies almost entirely on glucose for fuel. This glucose is delivered through the bloodstream, and a constant, well-regulated blood supply is essential for normal brain function. The blood vessels in the brain form the blood-brain barrier (BBB). This barrier works like a filter: it lets in oxygen and nutrients the brain needs but blocks harmful substances such as toxins and bacteria. 

In many neurodegenerative conditions – including Alzheimer’s disease, Parkinson’s disease, and potentially diabetes – this barrier can weaken or become “leaky”, making the brain more vulnerable to damage. Most research into the BBB still relies on animal models. However, the research group led by Dr Alison McNeilly, in collaboration with scientists in Edinburgh, is developing a non‑animal, cell‑based model of the BBB. 

In this model, human endothelial cells (the cells that line blood vessels) are grown on a thin membrane to mimic the structure of real blood vessels. Researchers then measure the electrical resistance across this cell layer — a method called transepithelial electrical resistance (TEER) — to determine the integrity of the barrier. 

The system can be made even more realistic by adding other key brain cell types, such as astrocytes and pericytes. Researchers can then change the conditions the cells are exposed to — for example, growing them in consistently high glucose or subjecting them to glucose ups and downs, similar to what people with insulin‑treated diabetes experience. This allows scientists to study how these changes affect the BBB without the need for animal models.