Fabrication method proves value for bone scaffold design

Researchers at the University of Illinois have developed a new method for the fabrication of artificial bone scaffolds that can assess important pore design factors such as porosity and their role in new bone formation. Their method’s capabilities for in vivo control of different scale porosities could lead to more flexible, efficient design of bone scaffolds used for regeneration of bone tissue lost to disease or injury.

Manufacturing result for designs 1 and 2. Design 1 has a completely walled off quadrant interface preventing fluid transport, while design 2 has open channels between quadrants.

“We believe that completely flexible manufacturing systems such as the one developed here are well suited to replicate natural bone function with high-fidelity,” explained Amy Wagoner Johnson, an assistant professor of mechanical science and engineering (MechSE) and co-author of the paper, “Design and Manufacture of Cobinatorial Calcium Phosphate Bone Scaffolds”, which appeared in in the Journal of Biomechanical Engineering.

Using a fabrication method of robotic deposition developed by Jennifer Lewis, a professor materials science and engineering at Illinois, the researchers modified it to precisely control ink flow, enabling the fabrication of scaffolds with multiple materials in a single scaffold and with multiple length scales of porosity. This method, they wrote, could play an important role in the drive to create artificial bone replacements that can serve to seed new tissue growth and obviate the need for bone harvesting.

“The method is relevant for both scientific and clinical applications,” said Wagoner Johnson, who also holds faculty and research appointments in the Department of Bioengineering (BioE), the Institute for Genomic Biology, and the Beckman Institute. “For basic science, it will allow us to understand how neighboring domains with different structural and material characteristics might influence each other. For clinical applications, this manufacturing approach will allow us to really tailor scaffold characteristics to a specific defect and specific person because we can precisely tune and manipulate the spatial characteristics of the scaffolds.”

The researchers focused on pore design in scaffolds because, they wrote, “pore design is an important determinant of both the quantity and distribution of regenerated bone in artificial bone tissue scaffolds” and that it “is well known that mechanical properties and porosity are important considerations for scaffold design in tissue engineering.”

They added that the effects of features such as porosity and mechanical properties at the microscale are not well-understood. Their paper reported on the manufacture and characterization of a new scaffold method using combinatorial calcium phosphate that can test micro- and macroporosity designs within a single scaffold.

In order to create the scaffolds, the researchers used a nozzle-based solid freeform fabrication (SFF) system as the manufacturing platform because the method enables strict control of the macrostructure, while at the same time integrating multiple materials with different microstructures or chemistries.

“Scaffolds such as this,” they wrote, “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.”

Wagoner Johnson said there are several advantages to this method.

“Other methods either cannot create pores of different sizes in distinct domains or cannot incorporate more than one material or microstructure in a single scaffold,” she said. “The manufacturing approach described in this paper is the only one that can accomplish both: distinct domains with different pore sizes and multiple materials and/or microstructures in one scaffold.”

Using three representative scaffolds, they were able to demonstrate the feasibility of the method for scaffold fabrication and a range of porosities, and as a platform with manufacturing capabilities. Wagoner Johnson said the calcium phosphate ceramics used in the method are already used as fillers for small defects and coatings for dental and orthopedic implants, but “to our knowledge, there is nothing on the market that allows for such flexibility in scaffold characteristics as what we have shown here.”

More work and testing needs to be done toward future clinical applications, but the researchers wrote that the first step in that direction has been taken.

“Three unique scaffolds are produced from a single training routine, displaying that the designed manufacturing workflow is efficient and flexible. Importantly, the capabilities displayed here can be applied to even more complex scaffolds. With the ability to strictly control the placement of dissimilar materials comes the ability to functionalize bone scaffolds.”

Former PhD student David Hoelzle was lead author for the article. Co-authors include Wagnoner Johnson, MechSE professor Andrew Alleyne, and BioE undergraduate researcher Shelby Svientek.
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Contact: Amy J. Wagoner Johnson, Department of Mechanical Science and Engineering, 217/265-5581.

Writer: Steve McGaughey, Beckman Institute

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