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ABM CDT Development of bioinks and bioprinting methods to model the human mammary gland


   EPSRC Centre for Doctoral Training in Advanced Biomedical Materials


About the Project

Mechanical signals within a tissue are required to establish and maintain its function. Consequently, alterations in the properties of the extracellular environment can give rise to perturbed signals, leading to a range of pathological conditions including cancer. High mammographic density (MD) is the second greatest predictor of breast cancer risk after ageing. We have shown that high MD tissue is mechanically stiffer than low MD tissue. However, the mechanism that links high MD to breast cancer is not understood. A major factor limiting current studies of the cell/environment relationship is the lack of model systems that reflect the complexities of real tissues: it is difficult to measure the importance of environmental stiffness, composition and topology without the ability to control these factors independently. Furthermore, an inability to accurately reproduce tissue-like microenvironments limits our capacity to develop high-throughput screening and personalised medicine technologies. Here we propose to develop a three-dimensional cell culture system based on alginate hydrogels that can be functionalised to mimic the native tissue extracellular matrix. These gels will form the basis of bioinks – matrices mixed with cells that can be deposited with spatial resolution using a bioprinter, thus enabling us to reproduce the anatomical features of the breast.

Background:

Changes in the mechanical properties of tissues are correlated with many diseases, including cancer. We are particularly interested in the study of breast cancer, which remains the second highest cause of mortality in women. After ageing, the highest risk predictor for breast cancer is raised mammographic density (MD) - a quantity defined by the opacity of breast tissue in a mammogram. Little is known about how high MD relates to the causes of breast cancer, but we have recently shown that breast tissue with high MD is physically stiffer than corresponding lower density areas. This suggests that breast cancer is in part caused by a fault in mechanical signalling between cells and their surroundings. A major factor limiting current studies of the cell/environment relationship is the lack of model systems that reflect the complexities of real tissues. In vitro culture models are essential tools in the study of breast cancer risk and progression, but have largely been reliant on hydrogels such as Matrigel. However, Matrigel has considerable limitations, including significant batch-to-batch variability, poorly defined composition, mechanical properties unsuited to bioprinting, and reliance on animal-derived products. Here we propose to develop a synthetic replacement for Matrigel that will enable greater control of hydrogel composition, homogeneity, and reproducibility, and compatibility with bioprinting technology. In this project, we will develop applications of new bioinks and three-dimensional bioprinting technologies to replicate features of the human mammary gland, thus allowing high-throughput production of constructs for screening and personalised medicine applications.

Questions to be answered:

This project will seek to deliver a synthetic alternative to mouse-derived Matrigel that can be used to produce bioinks compatible with three-dimensional bioprinting. The hydrogel will be based on an alginate-PEG (polyethylene glycol) scaffold conjugated to an engineered, recombinant human laminin protein, optimised for stability and able to interact with native, cell-synthesised extracellular matrix constituents. The technology will be applied to develop a synthetic model of human breast tissue. The project will address the following questions:

  1. Can the hydrogel be functionalised such that it replicates the mechanical properties and biochemical signatures of the extracellular matrix found in human breast tissue?
  2. Is the hydrogel compatible with human-derived cells, and therefore suitable for the production of a bioink? How does culture within the hydrogel system affect cell viability, morphology and protein expression?
  3. Can the bioink be optimised to work with three-dimensional bioprinting technology, thus allowing the production of constructs that mimic the anatomical features of human breast tissue? Can bioinks be used in combination to replicate more complex features, such as epithelial (rich in laminin proteins) and stromal (rich in type-I collagen proteins) tissue compartments?

References

Wood A, Sun H, Jones M, Percival H, Broadberry E, Zindy E, Lawless C, Streuli C, Swift J, Brennan K, Gilmore AP. Increased microenvironment stiffness leads to altered aldehyde metabolism and DNA damage in mammary epithelial cells through a RhoA-dependent mechanism. BioRxiv.org (2020) https://doi.org/10.1101/2020.10.06.327726
Moxon SR, Cooke ME, Cox SC, Snow M, Jeys L, Jones SW, Smith AM, Grover LM. Suspended manufacture of biological structures. Adv. Mater. (2017) 29, 1605594.
McConnell JC, O’Connell OV, Brennan K, Weiping L, Howe M, Joseph L, et al. Increased peri-ductal collagen micro-organization may contribute to raised mammographic density. Breast Cancer Res. (2016) 18 (1), 5.

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