Abstract
The burden of breast cancer incidence is increasing with the growing and aging population, yet despite interdisciplinary research effort towards improving therapeutic options, there still remains a number of unmet clinical challenges necessary for enhancing patient quality of life. Recent advances in the bioengineering field provide promise for the development of physiologically-relevant preclinical models for studying the pathology of breast cancer in vitro, as well as the opportunity to improve the structural capacity of autologous-based breast reconstruction approaches. This thesis focussed on exploiting extracellular matrix (ECM) interactions to engineer adipose tissue-derived analogues as translational tools for confronting breast cancer burden at both a physiological and therapeutic level. To obtain enhanced control over the mechanical and structural properties of the developed analogues, a visible light-mediated crosslinking approach was adopted through incorporation of ruthenium and sodium persulfate photoinitiators into adipose tissue-derived materials of increasing complexity.
At a physiological level, ECM remodelling and increased ECM stiffness is characteristic of native breast tumours during the metastatic cascade, but current in vitro models do not replicate the temporal biomechanical cues and scale of this process. To address this limitation, a smart composite biomaterial was developed by photocrosslinking adipose-derived decellularised ECM (AdECM) and silk fibroin, to provide tissue-specific cues as well as dynamic matrix stiffening cues, respectively. The biomaterial could be programmed to progressively stiffen over 21 days without the use of external stimuli, and represented a dynamic scale range equivalent to those of solid breast tumours. Breast cancer cells (MCF-7) grown as large spheroids within the material, underwent growth arrest upon matrix stiffening and formed mature organoid-like structures which mimicked the organisation and heterogeneity of physiological breast tissue. The preclinical model described here, provides a novel strategy to uncouple ECM biomechanical properties from the cellular complexities of the tumour microenvironment, and through incorporation of other tissue-specific biomaterials (decellularised ECM), provides an invaluable platform for modelling a range of other pathologies in vitro.
At a therapeutic level, for those patients who require surgical resection of breast tumour tissue, autologous fat grafting is the ideal strategy for repairing contour deformities. However, the utility of autologous fat grafting as a breast reconstruction strategy is currently limited due to a number of clinical complications which are proportionate to graft size, including unpredictable graft resorption. A critical review of the clinical challenges associated with fat grafting, revealed a distinct need for enhanced structural control within grafts, while using an autologous, minimally-invasive, single-surgery approach. To meet this clinical need, patient-derived lipoaspirate was photocrosslinked, and the mechanistic and clinical applicability of the technique for improving the structure of fat grafts was comprehensively assessed. Through dityrosine bonding within ECM molecules, the structure of lipoaspirate could be controlled to achieve grafts with enhanced height retention and tissue retention in vitro. The enhanced structure permitted ex vivo culture of patient-derived lipoaspirate and supported cell infiltration and neovascularisation when implanted in vivo. Local structural changes brought about significant reductions in fibre diameter which is particularly important for increasing the graft-to-recipient interface in layered, large volume grafts. To investigate patient variability in response to this technology, the ECM was comprehensively profiled using quantitative mass spectrometry, providing an optimised experimental pipeline for understanding the adipose tissue-specific ECM in related pathologies.
This thesis has contributed both to enhancing in vitro model systems of breast cancer and improving the clinical outcomes of breast reconstruction techniques. By exploiting ECM interactions, adipose tissue-derived analogues of different hierarchical levels were engineered, to provide physiologically- and clinically-relevant tools for future breast cancer research. A focus on simplicity and clinical relevance from the outset, means that these tools can be easily adapted to a range of model systems or for clinical translation and commercialisation.