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26 – Chapter 1: Introduction and Objectives

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Chapter 1: Introduction and Objectives

1.1 Introduction

The overall goal of this research is to determine relationships that govern the apparent properties of architectures evaluated solely from a material arrangement standpoint. This work specifically evaluates the structural and material properties of regular architectures that exhibit symmetry, homogeneity, and order. Additionally, this work will evaluate the apparent properties of architectures composed of random pore distributions. These properties and their relationships will be determined through modulation of the solid material and manipulation of the void space. Characterization of these structures will be used in the application of computer aided tissue engineering for the design of novel implants and tailored solutions to clinical problems stemming from tissue defects. Applied focus will be on the design of implants for bone regenerative scaffolds or other mechanically modulated systems. Numerous studies have demonstrated effects of specific scaffold architecture on tissue ingrowth [1-15]. As of yet, no rules have been generated to explain the exact structure’s exact effect nor has any quantifiable difference ever been demonstrated for given architectures as a result of their material organization [16]. Therefore, the global hypothesis of this research is that organization of material affects the structural and material properties of that architecture [17] and ultimately, the success of the implant. Furthermore, the use of design principles to create structures and scaffolds with specific architectures may be used to characterize mechanisms that dictate tissue regeneration in therapeutic scaffolds.

The architectural components (examination of the solid phase, examination of the void phase) of these studies have been chosen for two reasons. First, the simplicity of a general shape exhibiting symmetry and homogeneity will allow construction of relationships between material organization and resulting structural properties. Architectures of this type have previously been explored as constructs for tissue regeneration scaffolds [18-21]. Utilizing a randomized system of pore architectures, while a less general case than the ordered one, should follow similar rules. Random architectures such as these are the simplest to generate and have been used repeatedly as constructs to facilitate tissue ingrowth and regeneration [10, 14, 15, 22-28]. The expected benefit of this research is that it will determine which architecture, if any plays a role in the modulation of tissue regeneration for bone tissue engineering.

1.2 Overall Objective

The engineering goals of this research include the construction of relationships that relate the arrangement of material to structural and material properties of the global architecture. These architectures may then be used in vitro and in vivo to evaluate the effect of design on selection by biological systems for tissue regeneration. The following goals are proposed:

1.3 Specific Aims and Hypotheses

1.3.1 Specific Aim #1(Chapter 3)

To determine the effect of material organization (strut length, strut diameter, connectivity, material volume) on the architectural properties (structural stiffness, strength, structural modulus, ultimate stress) of solids based on regular, porous architectures.

Hypotheses

· A deliberate arrangement of architecture can be used to usurp density as the dominant controlling factor of strength

· For a constant density, tailored mechanical properties can be obtained through reorganization of architecture.

· Rapid Prototyped models can be used as accurate representations of modeled cellular solids and can replicate finite element modeling results of the structural and material properties of the porous architectures.

1.3.2 Specific Aim #2 (Chapter 4)

To determine the effects of void phase organization (pore size, surface to volume ratio, pore architecture, total void volume) on the architectural properties properties (structural stiffness, strength, structural modulus, ultimate stress) and flow properties of solids based on particulate leached systems with defined pore architectures.

Hypotheses

· A derived relationship exists between surface to volume ratio of a void architecture and its resulting permeability.

· A derived relationship exists between surface to volume ratio of void architecture on the structural properties of a random porous architecture.

· A derived relationship exists between porosity and permeability for defined architectural parameters and porosity values.

1.3.3 Specific Aim #3 (Chapter 5)

To apply the derived relationships in Specific Aim 1 and 2 through material rearrangement towards the design of tissue regenerative scaffolds employing the steps of Computer Aided Tissue Engineering

Engineering Objectives

· Utilize architectures characterized in Specific Aim 1 in the design of tissue regenerative scaffolds for a load-bearing system to determine the dominant design principles governing the success of such an implant.

· Utilize derived relationships from Specific Aim 2 in the design of implants which will require fluid transport and determine the dominant design principles governing the success of these implants.

· Determination of the dominant design principles governing tissue invasion into porous scaffolds for the architectures examined and the important characteristics of those scaffolds.

 

 

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Written by Matthew Wettergreen

March 22, 2008 at 5:00 am

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