Harnessing plant power: Plant-based 3D tissue models to study disease

Creating a plant-based scaffold on which human cells can grow

When cells grow, they need a support scaffold. To create this, Professor Vassalli successfully ‘decellularized’ (removed cells from) spinach leaves, celery and tobacco, essentially leaving an empty scaffold, on which cells can grow. He tested different methods of removing the plant cells using different strength chemicals, including mild detergent and bleach. The latter was more successful in removing plant cells whilst also maintaining the structure of the plant (shown in the image below). Professor Vassalli determined that it’s critical to find the most suitable method for decellularization for each particular plant and then to optimise it, rather than using a ‘one size fits all’ approach.

Spinach leaves and celery which have been decellularized (plant cells removed) using bleach, shown by their decolouration.

Professor Vassalli evidenced that the plant structure was still intact by injecting a stain into the plant, enabling its intact vasculature (its water and food transport systems) to be seen.

The next stage was to use these empty scaffolds to grow human cells. The cells that were grown or ‘seeded’ were human skin fibroblasts which, through physical and chemical cues, can be cleverly re-programmed into forming smooth muscle-like cells. Furthermore, to produce a completely animal-free model, Professor Vassalli replaced the more commonly used cell growth medium, foetal bovine serum (derived from the foetal blood of pregnant cows during the slaughter process), with animal-free growth supplements.

Growing human cells on empty plant scaffolds

Collagen from animals (mainly rats) is normally used to help newly introduced cells stick to scaffolds. To create an entirely animal-free model, Professor Vassalli followed a genetic engineering method, aimed at instructing the plants (tobacco) to produce their own human-like collagen. He found however, that the bleach which was needed for the decellularization of spinach, celery and tobacco (detergent was too weak), also damaged proteins, including any in-house collagen.

Professor Vassalli therefore opted to use purified human genetically engineered collagen instead as a scaffold adhesive. This way, he was able to successfully re-populate the empty scaffolds with human cells. He used specialised microscopes to visualise successful adhesion and cell growth, proving that human collagen works just as well as animal-derived biomaterials as an adhesive.

“This project is about connecting two kingdoms, the vegetal and animal ones. Plant leaves are decellularized and used as a scaffold to harbour human stem cells and grow a functional 3D microtissue. But the project is also about connecting scientists with relevant backgrounds, in plant science, tissue engineering and biophysics, and leveraging their diverse expertise to foster innovation in an interdisciplinary field. This research could be used in the future to produce scalable and sustainable drug discovery” – Professor Massimo Vassalli

Next steps

This work lays the foundation for an optimised 3D tissue model made from plants which can be used to study diseases and to test drugs.

Research is currently being undertaken by a PhD student (from Oct 22) to optimise the methods piloted in this study. The student is using the model to investigate a disease called visceral myopathy and plans to subsequently publish the findings in a scientific journal.

Visceral myopathy (VM), is a gastrointestinal motility disorder, is caused by a smooth muscle weakness and can lead to Chronic Intestinal Pseudo Obstruction, whereby it’s difficult or impossible for people to move food, fluids, and air through their digestive systems.

People who are affected by VM, frequently undergo surgery to remove parts of the bowel and may need parenteral nutrition (nutrition delivered through veins) for the rest of their lives. Misdiagnosis and inadequate treatment can lead to life threatening intestinal attacks and severely affected babies often do not survive their early years of life. There’s an urgent need to find new ways to diagnose and treat VM. The wide array of natural scaffolds offered by plant-based scaffolds hold great potential for a variety of lab engineered tissues to study diseases and to test drugs.