Spheroids
Spheroids are cell aggregates that form 3D spheroidal structures to mimic the organisation of cells in human tissues. They are typically made from cell lines, but can also incorporate primary cells. Spheroids don’t require scaffolding to form 3D cultures; they do so by simply sticking to each other. Cells will adhere to each other when in the presence of a surface not compatible for cell attachment. They can however also be formed using scaffolds that mimic ECM, providing a structure for the cells to attach and grow. These scaffolds are typically made from biological materials like collagen or synthetic polymers like polyethylene glycol (PEG), and are becoming more complex with tailored synthetic scaffolds that more closely mimic tissue ECM, as well as being combined with cell printing technologies.
Courtesy of Concept Life Sciences
Spheroid Applications
- Basic research and early drug discovery: Suitable for investigating cellular biology, interaction and crosstalk, drug mechanisms, and drug responses.
- Disease modelling: Valuable for studying disease mechanisms and identifying potential therapeutic targets in areas such as cancer, liver disease, neurodegenerative disease, and cardiovascular disease.
- Drug screening: Provide a system for testing drug efficacy and toxicity, and predictions of drug metabolism and clearance (ADME).
- Drug carrier analysis: Offer a 3D environment to evaluate the delivery and efficacy of carriers for targeted therapies. (e.g. nanoparticles, liposomes, and micelles).
Spheroid Advantages
- Improved biomimicry: Replicate the physiological behaviours, cellular heterogeneity, gene expression, and structural organisation of human tissues better than 2D cultures, making them more predictive for studying cellular behaviours, disease mechanisms, and drug responses.
- Cellular interactions: Allow the study of complex cell-cell and cell-ECM interactions, improving predictions regarding drug efficacy and toxicity.
- Diverse cell types: Support the inclusion of different cell types, such as fibroblasts, immune cells, and endothelial cells, which are essential for studying tissue microenvironments.
- Higher reproducibility: Generally considered more consistent and reproducible across studies than other 3D culture models (e.g. organoids).
- High-throughput capabilities: Depending on cell-source, can be used in high-throughput studies and screening applications.
Spheroid Limitations
- Diffusion challenges: Although an improvement over 2D models, due to the lack of media flow, oxygen and nutrient diffusion to the spheroid core can be limited, creating gradients that may not reflect real in vivo conditions. However, spheroids with a necrotic core can represent a good tumour model.
- Accumulation of waste: Biological waste may accumulate in the core, affecting cell viability and leading to quick senescence in differentiated cells.
- Lack of mechanical stimulation: Lack external mechanical forces like fluid shear stress or hydrostatic pressure, which are crucial for regulating certain cell behaviours in vivo.
- Scalability issues: Spheroids derived from primary patient cells are often not scalable due to limited cell availability.
- Imaging difficulties: Imaging the interior of spheroids typically requires sectioning, which is labour-intensive, but scaffolds can help with lots of small spheres in a well.
- Limited ability to reproduce the tissue architecture: Cells in a spheroid do not organise in the same manner that they would in a tissue.