Thesis or Fecis

It all comes down to this…

Posts Tagged ‘organ_printer

23 – Thesis Title

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It has recently been brought to my attention that the title of my blog is too long. “The Effect of Material Organization on the Structural Properties of Porous Architectures? What does that even mean? Who do you want to read this thing? What are you putting it up for?”

This person was on vicodin.

Right after this conversation she congratulated me for another brilliant post on Stuff White People Like, saying “San Francisco! That’s so funny. You are so white! You’re in grad school and you like The Wire and Eternal Sunshine… and you do crosswords every day. I’m sure that you write that blog, c’mon admit it!”

Drugs aside, it got me thinking why I’m doing this blog: for myself. I don’t care who reads it, I’m not jumping up and down clamoring for people to pore over the inanity of my work from the past seven years, I already abuse twitter heavily enough for that. I’ve got less than 30 days til I defend, I stopped writing in my gurnal over a year ago (So what if I’m not as smart as you!), there needs to be a document of last days…this is it.

But if you do stumble upon this and want to know wtf “The Effect of Material Organization on the Structural Properties of Porous Architectures” means, let’s break it down:

Porosity is a measure of the amount of void space in any unit volume. If you have an empty box and you put something in it, the porosity, which used to be 100% has now been reduced by the volume of material in that box. Bone is around 80 – 90 % porous. It’s on the 90% side if you have osteoporosis where if you fall you shatter like glass, like my mother. It’s on the 80% side if you are a fine shining example of a fit and healthy human like that pitcher guy whose wife took all those steroids for him. The architectures that I work with are ranged in porosity between 50% and 90%. When you change porosity, you change the strength of an architecture: less material, less strength. The exciting part is that if you use the same architecture, you can compare the effects of material arrangement alone:

Von Mises Distribution - Rhombitruncated Cuboctahedron
The porous architecture, Rhombitruncated Cuboctahedron, at five porosities, left to right, 50% through 90%

By “Material Organization” I mean the arrangement of material in any configuration. You have 100 lego bricks and you arrange them into some configuration and then crush them. It’s got a certain strength, say x. Then, you arrange those 100 legos into a completely different arrangement and again, crush it. It has a strength, say y. Unless you know what you’re doing or are extremely lucky, xy. And the difference is the “material organization” not the porosity, since you used the same amount of bricks thus you have the same amount of porosity. Material properties are the characteristics of the construction material: playdoh, steel, clay, plastic. The specific heat, tensile strength, ultimate strength (crushing strength as a friend would understand it), and stiffness. These properties all have to do with the material itself. When you arrange that material into a shape, say a porous architecture, and crush it, you get the structural properties of that architecture.

Structural Properties work the same as Material Properties (stiffness, modulus, ultimate strength, etc. etc.) but they are solely due to the arrangement of the material the architecture is built with. You build a tower out of steel and that steel has its own material properties. The structure that you build then has its own structural properties.

So let’s recap “The Effect of Material Organization on the Structural Properties of Porous Architectures”
I study polyhedra which are “porous architectures”.
There are several polyhedra in the set that I study, each one has a different “material organization”.
Each polyhedra is built with the same material but has a different architecture which means they all have different “structural properties”.
I am looking to create rules which govern how a material organization can result in a tailored structural property.
The application of this is tailored patient implants for spinal repair.

So after all this I’ve decided to change the title to “Thesis or Fecis”

…it all comes down to this.


Written by Matthew Wettergreen

March 24, 2008 at 10:19 am

24 – Chapter 2: Background (Part I)

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The inability of bone to regenerate itself in cases of gross trauma poses a problem still unsolved. The complexity of bone tissue itself is compounded by the requirement that it provide structural support for the patient. Successful treatment should stimulate new bone growth resulting, at the end state, in native bone tissue with no trace of the regenerative device. Bone scaffolds have shown promise in regenerating some critical size defects in non-load bearing anatomic sites but results vary with anatomy and species [1]. Additionally, problems arise in load bearing sites where the scaffold must endure a modicum of mechanical loading. Success requires insight into the mechanisms that dictate bone growth as well as thorough characterization of the intended implanted scaffold. Currently, research has begun to characterize input parameters such as architecture, porosity, permeability and their effect on the resulting tissue ingrowth [2, 3]. The use of techniques such as Computer Aided Tissue Engineering (CATE) may in the future promote the regeneration of a functional bone system where a defect once lay [4]. The following sections will illustrate the importance of structure for function in nature and more specifically in bone. The subsequent architectural discussion will be framed in the effects of specific parameters of architecture and the past work that has attempted to incorporate these concepts into scaffold design.



1. Liebschner, M.A., Biomechanical considerations of animal models used in tissue engineering of bone. Biomaterials, 2004. 25(9): p. 1697-714.

2. Li, S.H., et al., Accurate geometric characterization of macroporous scaffold of tissue engineering. Key Engineering Materials, 2003. 240-242: p. 541-546.

3. Hollister, S.J., et al., Engineering craniofacial scaffolds. Orthod Craniofac Res, 2005. 8(3): p. 162-73.

4. Sun W, D.A., Starly B, Nam J, Computer-Aided Tissue Engineering:Overview, Scope, and Challenges. Biotechnology and Applied Biochemistry, 2004. 39: p. 29-47.




Written by Matthew Wettergreen

March 23, 2008 at 8:00 am

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.

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Written by Matthew Wettergreen

March 22, 2008 at 5:00 am