The dynamic effects of surface topography and chemistry on cell attachment, alignment, and motility on smart, polyelectrolyte materials

Date of Award

August 2017

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biomedical and Chemical Engineering

Advisor(s)

Patrick T. Mather

Second Advisor

James H. Henderson

Keywords

cell behavior, layer by layer, polyelectrolyte multi-layers, shape memory polymer, wrinkling

Subject Categories

Engineering

Abstract

An ideal biomaterial should provide a structure to support cell attachment, proliferation, differentiation, and extracellular matrix (ECM) deposition. The biomaterial surface wettability, microstructure, and mechanical properties have been shown to significantly influence these cell behaviors and adverse reactions leading to implant failure. By studying the effects of these variables in a controlled environment, we can optimize the biomaterial interface to elicit the necessary and desired cell interactions. In this thesis, we focused on the effects of wettability on cell attachment, alignment, and motility. Both surface chemistry and topography have been shown to greatly effect surface wettability. Thereby, we designed a novel, smart cell culture platform to distinguish between the competing effects of both factors on cell behavior. This cell culture platform consists of a shape memory polymer (SMP) coated with polyelectrolyte multi-layers (PEMs). Previously, SMPs have been used to dynamically form gold wrinkles and align adipose stem cells in vitro upon the presence of a temperature stimulus while PEMs have been used to improve cell attachment on flat and topographical surfaces. However, the extent to which PEM topography effects cell attachment, alignment, and motility remains poorly understood. Here, these polymers are uniquely combined such that SMPs intrinsically buckle PEM coatings when triggered at physiological temperature, resulting in a chemically charged, nano-topographical surface.

To fully characterize and study the effects of this surface, there are two categories of objectives that in total create a hierarchy of five objectives. The first category of objectives is materials development and characterization. In this category, objective 1 is to create and characterize the SMP-PEM cell culture platform. Objective 2 is to create and characterize reversible PEM wrinkles. For objective 3, gradient PEM wrinkles were created and characterized. The second category of objectives is cell behavior evaluation. In this category, objective 4 is to study cell study cell attachment and alignment on static PEM wrinkles. Objective 5 is to study cell motility on “active” PEM wrinkles. The term active is used to describe topographical changes triggered in vitro. The question that this work seeks to answer is to determine if surface chemistry or topography is more important for cell attachment, alignment, and motility. Based on previous work and preliminary data, we hypothesized that the positive terminated PEM wrinkles would promote attachment and alignment of cells more than negative terminated PEM wrinkles and that cell alignment and velocity would increase on positive PEM wrinkles with higher PEM wrinkle amplitudes.

The molecular mechanisms for cell responses to charge and topography as well as the current cell culture platforms available used to study these processes are discussed in Chapter 1. The development, characterization, and use of a novel cell culture platform to study the effects of surface chemistry and topography on cell attachment, alignment, and motility are discussed in Chapters 2, 5, and 6. The effects of pre-strain, recovery time, recovery temperature, media, and polyelectrolyte coating variables on wrinkle amplitude and wavelength were characterized for Chapter 2. The effects of pre-strain and multiple recoveries on the final topography on reversible wrinkles were determined for Chapter 3. The material presented in this chapter has the potential to be used as for anti-fouling, anti-reflection, sensing, and smart adhesion applications. In Chapter 4, the effects of fabrication temperature and recovery temperature on the formation gradient wrinkles on functionally graded SMPs were studied. Given the optical properties of this material, it can be used for temperature sensing applications. Furthermore, it has the potential to determine the effects of charge, modulus, and dynamic topographical changes on a single, smart cell culture platform in vitro.

In Chapter 5, mouse embryonic fibroblasts are seeded on the substrate developed in Chapter 2 to study cell attachment and alignment. The effects of charge and topography were studied. In Chapter 6, the effects of chemistry and topography on mouse embryonic fibroblast motility on PEM active wrinkles were determined. An automated, contour-based tracking and analysis software program was used to determine nuclei density, nuclei alignment angle, and nuclei angular standard deviation, cell velocity, cell diffusion, and mean squared displacement.

Overall, a novel shape memory cell culture platform was developed, characterized, and used to study cell behavior. Future work recommendations for all chapters are discussed in Chapter 7. The unique contributions of this thesis to the field are the development of a reversible and repeatable topographical coating on a smart, cell culture platform. The work in this thesis will demonstrate that surface chemistry is more important than topography for cell alignment and motility. However, cells attach well on topographical surfaces more than flat surfaces despite charge.

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