Researchers at Ohio State University (OSU; Columbus, USA) and the University of Illinois (Chicago, USA) used a computational technique called topological optimization (TO) to design an experimental 3D structure that can withstand the forces of chewing, facilitate speaking and swallowing, and replace large portions of the facial skeleton. The technique combines a series of algorithms with advanced 3D imaging to produce a structure that can accommodate specific spatial boundaries and mechanical loads, taking into account both spaces that need to be filled and space that must remain unoccupied.

The work is focused on the center of the face, home to the most complicated bony structures in the human head, as well hollow sections such as nasal sinuses, passages, and auditory canals. Eventually, the researchers plan to use tissue engineering techniques to grow bone around these and other lightweight structures, and implant the new bone during facial reconstruction surgeries; the researchers predict that fully functional bone replacements based on these structural designs could be in use in operating rooms within 10 years.

The technology is based a sample magnetic resonance image (MRI) of a damaged face to establish the outer boundaries of a rectangular space in which a replacement structure would be placed surgically. The designers specify spaces that must be left void, and then apply a number of mathematical equations that account for how strong the structure must be and how it should be shaped to support the skull and accommodate the loads of chewing and blunt pressure on the face. Another important detail is determining the vascular needs for the tissue-engineered bone that would be grown around these model structures. After adding several more variables to the design process, the researchers plan to conduct feasibility tests of the structures. The study was published early online on July 13, 2010, in the Proceedings of the National Academy of Sciences (PNAS).

"The difference between what is done now and our design is that we take into account all of the loads on the structure. And this is not a generic shape; for each person, we could create a patient-specific design,” said lead author Alok Sutradhar, Ph.D., a postdoctoral researcher in plastic surgery at OSU. "The purpose is to find the most optimized macrostructure to replace the missing bone. It would contain the minimum amount of tissue positioned in three-dimensional space and supported upon remaining uninjured portions of the facial skeleton.”

Topology optimization is distinct from shape optimization, since typically shape optimization methods work in a defined subset of allowable shapes that already have fixed topological properties, such as a set number of holes allowed in the shape. A discriminating definition is that topology optimization is used to generate concepts, and shape optimization is used to fine-tune a chosen design topology.

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