In vitro models of cell-mediated contraction phenomena. Quantitative analyses and applications

Abstract

Cells can pull and contract materials, in particular the extracellular matrices of biological tissues. Besides being the natural mode of operation of our muscles, contraction is indeed a vital part of tissue remodelling, but it can also be exploited in engineered systems. Although beneficial in repair processes such as wound healing, when poorly controlled contraction can lead to pathologies that include fibrosis and scarring. Due to its pivotal role as our body's natural provisional matrix, fibrin has been widely adopted both clinically and for tissue engineering studies. However, a major limitation of fibrin lies in its rapid contraction, particularly when operated by fibroblasts. Therefore, this thesis aims to outline quantitative evaluation of fibroblast-mediated material contraction and strategies to mitigate this contraction. By providing fixed anchor points it was possible to generate cell-mediated modulus-dependent aligned contraction and stiffening of fibrin matrices; which increased upon TGF-beta1 stimulated myofibroblastic differentiation. This process is highly dependent on the mode of seeding with 2D (on the gel surface) and 3D (within the gel) leading to 'wrapping' and 'shrinking' phenomena, respectively; highly relevant for modelling different fibrotic process as well as generating self-organising engineered tissues. To address some of the limitations of fibrin, the incorporation of hyaluronic acid (HA) and heparin into fibrin matrices were explored through their conjugation of specific fibrin-binding peptides. HA-peptide conjugates can modulate nanostructure, mechanical properties and swelling of the resulting matrices which had an inhibitory effect on contraction. Heparin-peptides conjugates, however, introduced dose-dependent defects into the fibrin fibres resulting in: a resistance to degradation; modulation of mechanical properties and cell behaviour; and the enhanced retention and slow release of growth factors indicating their potential utility as cell-instructive scaffolds. An alternative approach employed ROS-scavenging poly(propylene sulfide) nanoparticles (PPS nanoparticles) which demonstrated the capacity to inhibit and even reverse the myofibroblastic differentiation of human dermal fibroblasts leading to reduced fibrin contraction and collagen production; therefore indicating their potential as anti-fibrotic therapies. Overall, the quantitative evaluation of cell-mediated contraction provides insights into the processes underlying this phenomenon and strategies for its prevention. By utilising a range of strategies from cell seeding modality, material composition and biochemical treatments it is possible to influence this contraction for promising anti-fibrotic therapy and tissue engineering applications.

Date of Award	1 Aug 2020
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Nicola Tirelli (Supervisor), Annalisa Tirella (Supervisor) & Giulio Cossu (Supervisor)