Office of Technology Transfer – University of Michigan

An Integrated Global Layout and Local Microstructure Topology Optimization for Spinal Cage Design and Fabrication

Technology #2504

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Scott J. Hollister
Managed By
Kristen Wolff
Senior Licensing Specialist, Medical Devices 734-647-5604
Patent Protection
US Patent Pending


Conventional designs of spinal interbody fusion cages have mainly focused on providing immediate strength to maintain disc height and shielding bone grafts within the cage. As such, the geometric features of conventional designs show little distinction from each other and most designs fall into a category consisting of pipe shapes with thick shells as outer walls and a hollow interior space that brackets the fill of grafting materials. While many modifications have been made to reduce the effect of stress shielding, conventional designs do not have the flexibility to meet the multiple design requirements necessary to achieve sufficient rigidity, reduced stress shielding, and large porosity for biofactor delivery.


Researchers at the University of Michigan have developed a new design approach for providing a lumbar spine interbody fusion cage. This approach uses topology optimization algorithms to define the structural layout and the inner microstructures of the cage. The approach addresses the conflicting design issues of providing sufficient stability while at the same time providing appropriate porosity to deliver biofactors like cells, genes, and proteins and impart sufficient mechanical strain to maintain developing tissue. The interior architecture provided by the designed microstructures also reserves channel spaces for substance delivery in potential cell-based therapies and drug delivery. The present design approach allows a design to be modified for different patient types and allows the use of solid free-form fabrication techniques to manufacture the as-designed cage from commonly used biomaterials including but not limited to titanium, hydroxyapatite, tricalcium phosphate, polylactic acid, polyglycolic acid, and Poly (propylene fumarate).

Applications and Advantages


  • Design and fabrication of spine cage


  • Sufficient stability while providing appropriate-nl-porosity for biomolecule delivery
  • Design may be tailored for different-nl-patient types
  • Enables manufacture from commonly-used-nl-biomaterials