Modelling breast-to-bone metastatic mechanisms via microfluidic biofabrication

Bone is a frequent homing site for breast cancer metastasis. Unfortunately, the majority of patients diagnosed with primary breast cancer is often affected by bone metastasis from where cancer can reach other vital organs such as the lungs. Thus, it is vital that the process of metastatic attraction and homing is modeled in vitro, harnessing tissue engineering technology, generating viable models that would be able to closely mimic the in vivo homing mechanism. We engineered a three-dimensional breast-to-bone model using a novel microfluidic biofabrication approach by depositing human bone marrow stromal cells (hBMSCs) and a highly aggressive, invasive and poorly differentiated triple-negative breast cancer cell line (MDA-MB-231). Initially, the co-culture conditions have been optimised in order to preserve the viability of both cell types over 21-days of culture. Material inks were designed to grant the robust differentiation of HBMSCs and aid MDA-MB- 231 migration in 3D. A novel nanoclay-based material, comprising a variable ratio of alginate and gelatin, was used to encapsulate HBMSCs and investigate viability and functionality, while MDA-MB-231 were included in an RGD-based material to support cell migration and proliferation in 3D. A metastasis-colonisation model was 3D printed and investigated for ultimate functionality. HBMSC- laden nanoclay-based ink was deposited in 3D following a lattice architecture with porosity augmented over a single planar direction, followed by the inclusion of MDA-MB-231- laden matrix on the most- top model surface, allowing the penetration and colonisation of the bone tissue. In conclusion, we demonstrate the functionality of a 3D printed breast-to-bone model able to recapitulate the complex skeletal secondary site, illustrating the potential as a testing platform for novel therapeutic agents for metastatic process studies.