Christina McDonald
BioE Ph.D. Proposal Presentation
1:30 PM on Tuesday, March 4, 2025
Location: 2229 Ford ES&T
Advisor: M. Saad Bhamla, Ph.D. (ChBE, Georgia Institute of Technology)
Committee:
Marianne Alleyne, Ph.D. (Integrative Biology, University of Illinois Urbana-Champaign)
David Hu, Ph.D. (ME, Georgia Institute of Technology)
Yuhang Hu, Ph.D. (ME & ChBE, Georgia Institute of Technology)
Todd Sulchek, Ph.D. (ME, Georgia Institute of Technology)
Wax “Tails” and Fairy Knots:
Dynamic Functions of Passive Adornments in Planthoppers and Humans
The striking appearance of wax “tails” – posterior wax projections produced by planthopper nymphs (immature form) – has captivated entomologists and naturalists alike. Despite their common presence, the functional roles of these projections are not fully understood. During their powerful jumps, nymphs experience an airborne phase, making aerial stabilization strategies an important component of their locomotion. Other wingless insects generate stabilizing aerodynamic torques from appendage movements. Similarly, we hypothesize that wax-bearing nymphs leverage their wax structures for aerial stability and subsequent successful landings. In Aim 1, we analyze rotational stability and landing success rates from high-speed videos of nymph jumps with wax intact and wax removed. For Aim 2, we assess the role of stabilizing drag forces and develop a computational model of nymph jumps. These findings will provide insight into the adaptive significance of wax structures, revealing the relationship between wax morphology and aerial maneuverability.
The second research topic shifts the study of passive adornments from insect wax to human scalp hair. Fairy knots, also known as single-strand knots, are a common occurrence in coily-curly hair. The name evokes the knots' seemingly spontaneous and precise formation on a single strand of hair, indicating that only a small fairy could tie the tiny, meticulous knot unnoticed. Once formed, fairy knots are difficult to detangle and remove leading to breakage, hindered growth, and increased surface roughness. Despite their common occurrence in coily-curly hair, the mechanisms behind fairy knot formation, although having speculated causes, have not been formally investigated. This research aims to identify the biomechanical mechanisms behind fairy knot formation. In Aim 1, we characterize fairy knot form, frequency, and location as well as use new and established hair classification methods to characterize fairy knot prone hair. Aim 2 and Aim 3 examine how hair recoil, induced through mechanical manipulation (e.g., pulling and releasing, smoothing, and combing) or hydromechanical forces (e.g., wetting and drying), contributes to knotting. Additionally, measure relevant mechanical and physical properties of hair to link quantifiable parameters with knot formation. This research has broader implications for understanding hair behavior and can inform the development of hair care products and technologies (e.g., hairstyles) designed to prevent knot formation.