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Research Papers

# Design and Manufacture of Combinatorial Calcium Phosphate Bone Scaffolds

[+] Author and Article Information
David J. Hoelzle1

Department of Mechanical Science and Engineering,  University of Illinois at Urbana-Champaign, Urbana, IL 61801hoelzle2@illinois.edu

Shelby R. Svientek

Department of Bioengineering,  University of Illinois at Urbana-Champaign, Urbana, IL 61801sviente1@illinois.edu

Andrew G. Alleyne

Department of Mechanical Science and Engineering,  University of Illinois at Urbana-Champaign, Urbana, IL 61801alleyne@illinois.edu

Amy J. Wagoner Johnson

Department of Mechanical Science and Engineering,  University of Illinois at Urbana-Champaign, Urbana, IL 61801ajwj@illinois.edu

1

Corresponding author.

J Biomech Eng 133(10), 101001 (Oct 27, 2011) (8 pages) doi:10.1115/1.4005173 History: Received May 21, 2011; Accepted September 09, 2011; Revised September 09, 2011; Published October 27, 2011; Online October 27, 2011

## Abstract

It is well known that pore design is an important determinant of both the quantity and distribution of regenerated bone in artificial bone tissue scaffolds. A requisite feature is that scaffolds must contain pore interconnections on the order of 100–1000 $μm$ (termed macroporosity). Within this range, there is not a definitive optimal interconnection size. Recent results suggest that pore interconnections permeating the scaffold build material on the order of 2–20 $μm$ (termed microporosity) drive bone growth into the macropore space at a faster rate and also provide a new space for bone growth, proliferating throughout the interconnected microporous network. The effects of microstructural features on bone growth has yet to be fully understood. This work presents the manufacture and characterization of novel combinatorial test scaffolds, scaffolds that test multiple microporosity and macroporosity designs within a single scaffold. Scaffolds such as this can efficiently evaluate multiple mechanical designs, with the advantage of having the designs colocated within a single defect site and therefore less susceptible to experimental variation. This paper provides the manufacturing platform, manufacturing control method, and demonstrates the manufacturing capabilities with three representative scaffolds.

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Topics: Manufacturing , Bone , Design

## Figures

Figure 1

Monolithic scaffold design demonstrating the macropore and micropore space. This example was fabricated by a nozzle-based solid freeform fabrication (SFF) method. For scaffolds built by SFF methods, macroporosity is a function of material placement and microporosity is a function of material composition.

Figure 2

Representation of the span of design options demonstrated. The reachable set of macroporosities and microporosities are a continuous distribution, whereas quadrant communication is binary (represented by connected and disconnected sets, respectively).

Figure 3

Combinatorial test scaffold designs. (a) Diagram of the designs fabricated in this study. Specifications are given for each quadrant and interface. (b) Top view displays specific features in Design 2. Cross-section views display the quadrant interfaces for Design 1 (non-communicating) and Design 2 (communicating). The quadrant interface is completely walled off in Design 1, whereas there exist open channels for fluid transport across the quadrant interfaces in Design 2.

Figure 4

Deposition system displaying the array of four extrusion systems. Rotational system indexes between extrusion systems and, therefore, materials. Build material is extruded (output) by the displacement of a plunger (input). A machine vision system measures extruded material volumetric flow rate.

Figure 5

μRD hardware displaying the positioning system, extrusion system, and material flow rate measurement system which uses machine vision

Figure 6

Schematic of the BTILC method. Individual basis tasks are learned in a training routine then applied during scaffold manufacture. The objective for the training routine is to fabricate a thin cylinder of material as best as possible. The information gained in training can be extrapolated to fabricate more complex structures.

Figure 7

Workflow for the manufacture of combinatorial test scaffolds

Figure 8

Representative μCT image displaying the macropore measurements taken with each design. This particular image is taken from Design 2, quadrant m1M2. Axes orientation is shown on the figure, where the Y axis is orthogonal to the X-Z plane.

Figure 9

Manufacturing results for Designs 1-3. Columns 1 and 2 are optical images of the designs. Column 3 displays orthogonal slices through the set of μCT data at the quadrant interfaces. Design 1 has a completely walled off quadrant interface preventing fluid transport. Designs 2 and 3 have open channels between quadrants. Design 3 incorporates multiple filament sizes within a single scaffold.

Figure 10

Boxplot representation of the set of measured interconnection sizes for each scaffold quadrant. Box horizontal lines represent the 25%, 50%, and 75% quartiles of data. Circles represent outliers. The nominal designed interconnection sizes are given for comparison. Specific labels for each quadrant are omitted for clarity. Data display a distinct difference between the macroporosity design levels.

Figure 11

SEM data displaying the microstructural differences at the interface between distinct material compositions

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