Defense Date

2009

Document Type

Thesis

Degree Name

Master of Science

Department

Chemical Engineering

First Advisor

Vamsi K Yadavalli

Abstract

Poly (ethylene glycol) (PEG) hydrogel based polymers are among the most widely used synthetic materials for biomedical applications. Because of their biocompatibility, and ease of fabrication, hydrogels are highly suitable for use as constructs to engineer tissues as well as for cell transplantation. A critical parameter of importance for PEG hydrogels is their mechanical properties which are highly dependent on the environmental conditions. Properties of PEG-based hydrogels can be engineered to resemble scaffolds composed of extracellular matrix molecules, which provide structural support, adhesive sites and mechanical as well as biomechanical signals to most cells. The mechanical properties of these synthetic scaffolds can affect the migration, proliferation and differentiation of the cells. Accordingly, it is important to investigate the mechanical properties of these hydrogels and observe their effect on cell behavior as PEG-based scaffolds for example. In this research, the objective is to measure the mechanical properties such as the elastic modulus (Ec) and the stiffness (S) of polyethylene glycol diacrylate (PEGDA) hydrogel matrices at the nanoscale. The effect of varying parameters in the fabrication of PEGDA hydrogels including monomer molecular weight, initiator concentration and rates of hydration were investigated via nanoindentation using an atomic force microscope (AFM). Two different silicon nitride based cantilevers were used to study the effect of varying loading rates on the mechanical properties of these materials. Indentation parameters such as loads applied and indent depths were varied for each hydrogel sample. Different models were used to fit the experimental data to obtain the parameters of interest for the material (Ec and S). In particular, the data was best described using the model of Oliver-Pharr to analyze and fit the nanoindentation curves. Scanning electron microscope was used to image and confirm the geometry of the tip before and after the indentation experiments. Under high load and displacement modes, the indentation analysis was relatively easy and the elastic modulus and stiffness values were obtained for all dry PEGDA hydrogel sample. The variation of the initiator concentration has been analyzed as well. The mechanical properties of the hydrogel increase as the amount of the initiator increase in the precursor. The degree of hydration dramatically affects the mechanical behavior of the PEGDA. The presence of water within the hydrogel network weakens the internal as well the external mechanical properties, leading to smaller values of elastic modulus and stiffness compared with the dry condition. The mechanical properties of the indenter (cantilever tips) have significant impact on the results. It is important to study carefully the indenter properties before and after the indentation experiments. Since little work has been done on investigating the mechanical properties of PEGDA hydrogels at the nanoscale via AFM, the analysis of the mechanical behavior of this type of hydrogel using this strategy is of great importance.

Rights

© The Author

Is Part Of

VCU University Archives

Is Part Of

VCU Theses and Dissertations

Date of Submission

December 2009

Available for download on Saturday, December 14, 2019

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