Date of Award

Spring 2008

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biomedical Engineering

First Advisor

Steven A. Jones

Abstract

There is an ever-increasing awareness that the field of tissue engineering offers many potential solutions to clinical problems. While advances along these lines have been made, the design and implementation of an "off the shelf" tissue is yet to be realized. Thus, the objectives of this work were largely aimed at the design and fabrication of biocompatible, bioactive structures which could be integrated into existing biomaterial products.

The electrostatic layer-by-layer (LbL) self-assembly technique was used to incorporate biologically relevant molecules within controlled release systems, cell culture platforms, and 3-D cellular capsules. Two delivery systems were investigated to determine the release of a model drug, dexamethasone (DEX). In the first system, nanothin polyelectrolyte (PE) layers were applied to the micronized drug crystals as a diffusion barrier. In the second system, DEX was physically entrapped within calcium alginate microspheres which were further modified with PE layers. The fabrication of cell culture platforms functionalized with nanothin layers of PEs, TiO2 nanoparticles, and the growth factor TGFβ1 was achieved through ultrasonic nebulization. Finally, individual cellular capsules were fabricated by elaborating the LbL process on mesenchymal stem cell and human dermal fibroblast templates.

Materials characterization and cell culture testing were performed as preliminary indicators of potential cytotoxicity. Release of the drug DEX was enhanced when directly templated with polyelectrolyte layers while DEX entrapment within polyelectrolyte-modified alginate microspheres reduced drug release by a factor of three. An encouraging result of in vitro cell culture assessment was the distinct change in fibrochondrocyte morphology when compared with positive and negative controls. An ultrasonic nebulizer produced 14-layered cell culture substrates containing DEX, TiO2 nanoparticles, and the growth factor TGFβ1. In comparison with traditionally dipped substrates, layer fabrication was expedited six-fold. Moreover, the positioning of TGFβ1 within the layer architecture modulated cell behavior. For example, incorporation of the growth factor as a terminal layer produced visible cellular extensions associated with enhanced adhesion of human dermal fibroblasts (HDFs) to the substrates. The final application of LbL was for production of nanothin cellular capsules. Layer fabrication onto both HDFs and mouse mesenchymal stem cells (MSCs) was demonstrated with acceptable cell tolerances although cell viability is likely affected by layer composition and encapsulation time.

The major findings of this work not only demonstrated the feasibility of the technologies, but also their ability to influence cellular behavior by exposure to specific layer chemistries and architectures. The results are extremely promising for both further fundamental research, as well as translation into products. A major obstacle is determining optimal parameters necessary to yield a given cell response. Moreover, cost effectiveness must be addressed before clinical implementation of these systems is realized. Undoubtedly, the work here provides an underpinning for the development of additional capsules, microspheres, and substrates which could ultimately be integrated to create novel, biocompatible, heterogeneous assemblies.

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