Mathematicians are helping to design a new generation of bone implants that are structurally more like human bone and could reduce surgery and rehabilitation time, plus give patients for whom the current orthopaedic implants are not suitable, some new options.
Dr Vivien Challis from the School of Mathematics and Physics at The University of Queensland, Australia, and colleagues, have designed a prototype for a porous bone implant scaffold that can be customized to match the properties of human bone as needed by patients. A paper on their work was published in the journal Advanced Engineering Materials in November 2010.
The prototype is an example of what can be achieved by linking computational design with precision fabrication to produce tissue scaffolds with customizable properties as the building blocks for a new generation of bone implants.
By tweaking the physical variables available, such scaffolds can be tailored to make bone implants that match patients’ needs.
Current implants are made of fully dense and non-porous titanium which can be too stiff for the surrounding bone, a major cause of implant loosening. Also, these may be unsuitable for patients who have suffered major trauma, infection, tumors or deformities.
Challis told the press that:
“Customised, porous implants may be able to alleviate these issues by matching both the geometry and the properties of the surrounding bone.”
In their paper the researchers described how they used a new mathematical method called “topology optimization” to optimize the layout of a material in a particular space, and thus produce a three-dimensional scaffold with stiffness similar to human bone, while at the same time having a porous structure for transporting essential nutrients through the implant.
They matched the scaffold stiffness to that of human bone by choosing a suitable scaffold porosity, and showed that the templates can be scaled to give desired pore sizes without losing their elastic or diffusive properties.
They saw two major benefits in the structures they designed. One was they don’t have “directions of low stiffness”, which can be a problem with conventional “layered-grid designs” whose stiffness is variable depending on which way the load on them is aligned.
The other benefit was that the material of the scaffold is distributed efficiently through the structure rather than forming “clumps” in non load-bearing regions.
The researchers tested these theoretical models by using selective laser melting to make physical prototypes and then testing their elasticity.
Selective laser melting uses a high-powered laser to melt metal powder into the required scaffold shape, layer by layer.
The “excellent agreement between theory and experiment” confirmed that this method of designing and fabricating a new generation of bone implants was viable, concluded the authors.
Challis said that:
“Our project is a great example of the way in which mathematics can drive interdisciplinary, cutting-edge research.”
“A feature of our research is the constant interaction between theory, experiment and numerical simulation,” she added.
She and her multi-disciplinary team hope their research will help developers design and make better orthopaedic implants for Australia’s aging population.
They have been working on the project, which is funded by the Australian Research Council (ARC), since 2008. It is set to continue under a new ARC fund to cover 2011-2013.
“Prototypes for Bone Implant Scaffolds Designed via Topology Optimization and Manufactured by Solid Freeform Fabrication.”
Vivien J. Challis, Anthony P. Roberts, Joseph F. Grotowski, Lai-Chang Zhang, Timothy B. Sercombe.
Article first published online: 13 SEP 2010; DOI: 10.1002/adem.201000154
Additional source: University of Queensland (press release, 3 Feb 2011).
Written by: Catharine Paddock, PhD