Graduation Year

2015

Document Type

Dissertation

Degree

Ph.D.

Degree Name

Doctor of Philosophy (Ph.D.)

Department

Chemical Engineering

Degree Granting Department

Chemical Engineering

Major Professor

Ryan G. Toomey, Ph.D.

Co-Major Professor

Nathan D. Gallant, Ph.D.

Committee Member

John M. Wiencek, Ph.D.

Committee Member

Mark Jaroszeski, Ph.D.

Committee Member

Garrett Matthews, Ph.D.

Keywords

Topography, Electrospun Fibers, PNIPAAm, Biomaterials, Cell Attachment

Abstract

The overall thrust of this dissertation is to gain a fundamental understanding of the synergistic effects between surface topography and chemical functionality of poorly adhesive materials on enhancing the adhesion of mouse embryonic fibroblasts. Cellular response to surface topography and chemical functionality have been extensively studied on their own providing valuable information that helps in the design of new and improved biomaterials for tissue engineering applications. However, there is a lack of understanding of the synergistic effect of microscale and nanoscale topography with chemical functionality and the relative impact and contribution of each in modulating cellular behavior. By understanding the relationship between these cues, in particular using materials that are poorly adhesive, this study will provide new clues as to how cells adapt to their environment and also suggest new dimensions of biomaterial design for fine-tuning cellular control.

A microstructure that combined non adhesive materials with defined surface topography and surface chemistry is presented, to assess and correlate the enhancement of mouse embryonic fibroblasts cell adhesion and spreading. Poly (N-isopropylacrylamide) or PNIPAAm electrospun fibers were overlaid on PNIPAAm thin films (100 nm) at various time points to investigate the role of topography on such coatings by keeping the chemical functionality the same. After doing this, several topographical patterns were developed, spanning from sparse to dense fiber mats, and cell adhesion strongly depended on the relative available areas for attachment on either the fibers or the supporting surface. To gain a better understanding of this finding, two surface chemistries, non-adhesive (self-assembled monolayer of polyethylene glycol (PEGSAM) alkanethiol on gold) or an adhesive coating (3-aminopropyltriethoxysilane (APTES) on glass) with well characterized adhesive properties were included in this study to assess the effect of topographical cues provided by the PNIPAAm electrospun fibers on cellular responses. With the deposition of the PNIPAAm fibers onto a PEGSAM surface, cell adhesion increased to almost 100%, and unlike the PNIPAAm surface, cell spreading was significantly enhanced. With the deposition of PNIPAAm fibers onto APTES, both cell adhesion and spreading were unaffected up to 60% fiber coverage. For both surfaces, PNIPAAm fiber densities above 60% coverage lead to adhesion and spreading independent of the underlying surface. These findings indicate the presence of a sparse topographical feature can stimulate cell adhesion on a typically non-adhesive material, and that a chemical dissimilarity between the topographic features and the background enhances this effect through greater cell-surface interaction.

In addition to the aforementioned studies, cell response was also assessed on PNIPAAm thin films coatings with thicknesses ranging from 100 nm to 7 nm. Cell adhesion and spreading was enhanced as the thickness of the thin film decreased. This change was more noticeable below 30 nm, wherein 7 nm shows the highest cell adhesion and spreading enhancement. The results reported are preliminary results and further experiments will be conducted, to support the data. It is believed that cellular response was enhanced due to a change in surface topography at the nanoscale level.

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