Collaborative Research: Mechanical Phase Transitions Organizing Cartilage Function

This award supports a collaborative research project to advance understanding of articular cartilage, the soft tissue covering the ends of bones in joints. The project will examine how cartilage responds to physical forces relevant to daily activities like walking and jumping. While much is known about how cartilage resists compression, less is understood about how it responds to shear forces, during twisting and sliding. Recent findings suggest the collagen fiber network, which provides structural support, is close to a mechanical phase transition, where small structural changes can significantly impact mechanical properties. By integrating theoretical modeling, simulations, and experiments, the researchers will study how osmotic pressure and different types of mechanical stress influence cartilage structure and function. Understanding these processes could lead to better osteoarthritis treatments, improved tissue engineering and repair strategies, and bio-inspired materials for various other applications. This project will support education and workforce development by training students in biomechanics equipping them with valuable research skills. Additionally, the project will provide mentorship opportunities through workshops and outreach programs and facilitate public outreach activities. This award supports a collaborative research project to advance our understanding of articular cartilage, a living load-bearing tissue that can endure decades of mechanical stress. While its compressive behavior is well understood, the mechanisms governing shear resistance and its interaction with compression remain unclear. Recent findings suggest that collagen fibers form a percolating network near a mechanical phase transition, where small structural changes significantly alter mechanics. Prior studies examined small strains, but cartilage undergoes large deformations, reaching strains up to 40 percent under normal and extreme conditions. This project looks to develop next-generation rigidity percolation models to investigate cartilage mechanics under physiologic and super-physiologic loading. It plans to integrate experiments, theory, and simulations in an interactive feedback loop to examine how osmotic stress, mechanical loading, and collagen network reorganization shape tissue function. Rigidity percolation models intend to capture large deformations and multi-directional loading, providing a predictive framework for mechanical phase transitions. Experimental tests seek to validate and refine these models, while imaging looks to track fiber alignment and network adaptation. This research intends to reveal how mechanical phase transitions regulate cartilage response under extreme condition, informing cartilage repair and tissue engineering. The project will train students in biomechanics, and modeling while facilitating science communication and public outreach. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.