Electronic Thesis and Dissertation Repository

Thesis Format

Integrated Article

Degree

Doctor of Philosophy

Program

Biomedical Engineering

Supervisor

Hamilton, Douglas W.

2nd Supervisor

Mittler, Silvia

Co-Supervisor

Abstract

This thesis investigates the impact of mechanical stimuli, specifically substratum topography and elastic modulus, on dermal and gingival fibroblast behaviour associated with scarring and regeneration. Scar formation presents a significant issue for implanted biomaterials often leading to device failure. Even though scar formation is a normal end point to adult human dermal wound healing, gingival wounds are capable of tissue regeneration or scarless wound healing. Understanding how these cells respond to environmental cues, including substratum topography and elastic modulus, is central to the development of novel biomaterials for stimulation of tissue regeneration. It was hypothesized that topographic features, with submicron periodicity, will inhibit increased cell contraction and excessive extracellular matrix deposition on materials with a high stiffness.

The first aim quantifies and compares adhesion behaviors of human dermal and gingival fibroblasts on materials patterned with anisotropic sub-micron topographies. I reveal distinct responses between the two cell types including the necessity of integrin β1 in human dermal fibroblast (HDF) contact guidance. The second aim investigates the impact of varying elastic moduli on fibroblast physiology, highlighting differences in adhesion size and composition, F-actin arrangement, myofibroblast differentiation, and extracellular matrix production. The third aim introduces a novel, combined, elastic modulus-varied, topographic cell culture device, incorporating sub-micron topographies into a tunable elastic modulus material for the first time. This device will facilitate the study of how cells integrate mechanical stimuli, offering insights into their effects in vivo, specifically within soft tissue environments.

This work identifies the tissue of origin as a crucial determinant in fibroblast response to topography and elastic moduli, challenging existing theories on adhesion formation, and providing insights into integrin engagement mechanisms. The interplay between topography and elastic modulus is explored, suggesting a potential strategy for reducing fibrotic events related to implanted biomaterials.

Overall, this thesis enhances our understanding of fibroblast responses to microenvironmental cues, emphasizing the importance of tissue-specific considerations in biomaterial design and paving the way for future research in tissue engineering and wound healing.

Summary for Lay Audience

Currently, a number of bone interfacing biomaterials, including dental and orthopaedic implants, possess varying surface geometries and topographies to optimize tissue repair and integration, implant efficacy and longevity. In contrast, there is less research existing on the effects of surface modifications upon the behaviour of soft-tissue residing cells which is important for implants such as catheters, stents and grafts. Scar formation and fibrosis remain a significant clinical problem in many tissues and organs including skin. Formation of a collagen dense tissue with little cellular presence is the normal response to injury of soft tissues such as skin in adults, but failure of the wound healing process to terminate results in fibrosis, which affects up to 90% of patients and can lead to a significant reduction in physical and psychological quality of life. Scar formation also inhibits the integration of various medical devices including dental and hip implants, leading to device failure. Interestingly, unlike adult skin, fetal and gingival tissues exhibit scarless healing after injury, but the underlying cell and molecular differences in these cells that result in different healing profiles is unknown.

In this thesis, I investigated the molecular behaviours associated with scar formation in dermal and gingival fibroblasts on surfaces incorporating a topography and surfaces with variable stiffness. I determined that human gingival fibroblasts use a different adhesion mechanism when sensing and responding to surface topography compared to human dermal fibroblasts. I also demonstrated that human gingival fibroblasts and human dermal fibroblasts behave differently on surfaces of low stiffness. Finally, I created a means to investigate cell behaviour on a surface of variable, but defined topography and stiffness, combined. The results of this study provided further insight into cell-material interactions and allow optimization of biomaterials to promote regeneration of soft tissues, rather than scar formation and fibrosis.

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