Hitchhiker plants proliferate by adhering relatively stiff seeds to relatively soft fur and fabrics through a series of hooks, a bi-material attachment problem that is notoriously difficult to overcome in engineering and surgery. In Harpagonella palmeri, these long and slender hooks are arranged in a linear pattern with varied spacing and graded lengths. Here, we analyzed how these distributions and gradations optimize the distribution of the forces over the hooks and applied this optimization scheme to improve the strength of surgical attachment of hard to soft tissues. Results indicated that Harpagonella palmeri thorns are spaced and functionally graded to minimize the concentrations of stress that arise at a bi-material interface. By tailoring the spacings and stiffnesses of sutures using an analogous scheme in an in vitro model of rotator cuff repair, we showed that the forces could be balanced over sutures in a way that increased repair strength by a factor of 2.5. Results suggest a pathway for optimizing the material and structural aspects of a surgical repair to increase repair strength, and more broadly to design material systems for bi-material attachment.

A Hitchhiker's Guide to Orthopedic Repair: The Mechanics of how Harpagonella Palmeri Fruit Hitches onto Fabric, with Application to Suture Spacing

The Virtual Technical Meeting of the Society of Engineering Science 2020 is the first fully virtual meeting of the SES community to envision and connect during the hiatus created by Covid-19, providing a platform for the exchange of ideas, and to showcase the latest research in the field of engineering science.

[Visit the Programme](https://drive.google.com/file/d/1BoCPBzrr1IQFANuzQI8a-paXCJoOcCkB/view?usp=sharing) | [Visit the Prerecorded Video/Poster List](https://drive.google.com/file/d/1XHLeEXJxEFjCSsNScuLDfMwy1X7oy7oJ/view?usp=sharing) | [View the Session Grid](https://drive.google.com/file/d/1VeDOC-Ev5m_ymYjXnjaXSZHR3_DARiLt/view?usp=sharing)