3D-Printed Metamaterials Mimic Natural Bone-Tendon Interface

Musculoskeletal disorders are among the leading causes of disability worldwide, explains associate professor Mohammad J. Mirzaali, noting that improved methods for connecting hard and soft tissues could help advance future implants and tissue engineering strategies.

Researchers at Delft University of Technology published a study in Nature Communications detailing a new algorithm that uses 3D-printed metamaterials to recreate the compact connection between bone and tendon. While bone is hard and rigid and tendon is soft and flexible, the human body connects them through a strong interface over a very short distance that scientists have long struggled to recreate.

Engineering the Metamaterial Transition

Engineers work with two major classes of metamaterials: sheet-based metamaterials, which consist of continuous surfaces suited for stiff structures and bone cell integration, and strut-based metamaterials, which use interconnected beams to mimic softer tissues.

Combining these two types of metamaterials has been a true challenge for engineers. Directly connecting the two often creates weak zones where failure can occur. The first engineering instinct is to gradually transition from one architecture to the other, but that causes the transition region to become far too long and too far away from the compact bone-tendon interface found in nature, explains first author Dr. Jianxing Yang.

To solve this, the TU Delft team developed an algorithm that identifies compatible sheet-based and strut-based lattices, aligning their geometries and introducing a transition cell that shares characteristics of both.

Rather than creating an abrupt boundary, the transition cell enables a short, gradual change from one structure to the other, much like the natural bone-tendon interface, explains Dr. Vahid Moosabeiki.

The team validated their approach by 3D-printing several of the designs and subjecting them to mechanical tests, confirming that the computationally designed transitions can create strong connections between the two metamaterial families.

In follow-up research, the team is investigating how living cells respond to these hybrid structures by culturing cells on the newly developed designs to understand how geometry influences cell attachment, growth and differentiation, according to professor Amir A. Zadpoor.