Graduation Year

2015

Document Type

Dissertation

Degree

Ph.D.

Degree Name

Doctor of Philosophy (Ph.D.)

Degree Granting Department

Chemical and Biomedical Engineering

Major Professor

Nathan Gallant, Ph.D.

Committee Member

Robert Frisina, Jr., Ph.D.

Committee Member

Piyush Koria, Ph.D.

Committee Member

Ryan Toomey, Ph.D.

Committee Member

Marzenna Wiranowska, Ph.D.

Keywords

fibronectin, hydrophobicity, mechanotransduction, polydimethyl siloxane (PDMS), stiffness, surface chemistry

Abstract

Biomaterials have evolved over the years from the passive role of mere biocompatibility to an increasingly active role of presenting instructive cues to elicit precise responses at the molecular and cellular levels. Various characteristics common to synthetic biomaterials in vitro and extracellular matrices in vivo, such as immobilized functional or peptide groups, mechanical stiffness, bulk physical properties and topographical features, are key players that regulate cell response. The dynamics in the cell microenvironment and at the cell adhesive interface trigger a web of cell-material and cell-cell information exchanges that have a profound impact in directing the ultimate cell fate decision. Therefore, comprehension of cell substrate interactions is crucial to propel forward the evolution of new instructive biomaterials. Combinatorial biomaterials that encompass a wide range of properties can help to recapitulate the complexity of a cell microenvironment. The objective of this research was to fabricate combinatorial biomaterials with properties that span wide ranges in both surface chemistries and mechanical moduli. These materials were based on polydimethyl siloxane (PDMS), an elastomeric silicone biomaterial with physiologically relevant stiffness. After developing these mechano-chemical gradient biomaterials, we conducted high throughput screening of cell responses on them to elucidate cell substrate interactions and material directed behaviors.

Our central hypothesis was that materials encompassing monotonic gradients in mechanical elastic modulus and orthogonal surface chemistry gradients could be engineered using the soft biomaterial, polydimethyl siloxane (PDMS) and that these gradient biomaterials would evoke a varied cell response. Furthermore, we expected high throughput screening of cell-material interactions using these materials would elucidate patterns and thresholds of synergy or antagonism in the overall cell response to the increased complexity presented by combinatorial materials. First, reproducible gradients in surface chemistry were generated on PDMS through surface modification techniques. Cell response to PDMS surface chemistry gradients was then screened in a rapid high throughput manner. Additionally, characteristics of the adhesive interface were probed to understand its role in cell response. Finally, a 2D combinatorial gradient with a gradient in mechanical elastic modulus and an orthogonal gradient in surface chemistry was fabricated with PDMS. High throughput screening of the synergistic influence of the varied mechanical and biochemical extracellular signals presented by the combinatorial biomaterial on cell response was conducted in a systematic manner. This research demonstrates the fabrication of combinatorial biomaterials with a wide range of mechanochemical properties for rapid screening of cell response; a technique that will facilitate the development of biomaterial design criteria for numerous biomedical engineering applications including in vitro cell culture platforms and tissue engineering.

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