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Global Health Technologies

Global Health Technologies - Poster Session C & D

P27 - Low-cost measurement of hair mechanics using tensile force and torsion

Friday, October 10, 2025
10:00 AM - 11:00 AM PDT
Location: Exhibit Hall F, G & H

Introduction: : Hair loss, or alopecia, is a prevalent condition impacting over 80 million individuals in the United States alone, with significant psychological and social implications. Although alopecia can be caused by numerous things, including autoimmune diseases, mechanical stress, genetics, and chemical treatments, there is a lack of accessible, low-cost diagnostic tools to assess hair health in clinical settings and underserved communities. Methods currently available to evaluate hair mechanical properties are often expensive, complex, or limited to research laboratories. Hair has viscoelastic properties that exhibit both viscous and elastic responses to mechanical forces. When a hair fiber experiences tension, it elastically deforms, then becomes plastically deformed, and eventually breaks. The mechanical properties of hair, particularly its shear modulus and tensile breaking force, can provide insight into its structural properties and potential underlying health conditions. In this study, we aim to develop a low-cost, reproducible method to measure the shear modulus and breakage force of a single hair strand using a torsion pendulum that can superimpose uniaxial stress and torsion. We further aim to assess how conditioning treatments affect the mechanical strength of hair. We hypothesize that quantifying the viscoelastic properties and breakage force of hair would help differentiate between healthy and damaged hair. This low-cost approach paves the way for the development of accessible diagnostic tools to aid clinics in assessing hair loss conditions and formulating early detection strategies within dermatology.

Materials and

Methods: : We designed a low-cost medical device to measure the shear modulus and breaking force of single human hair strands. A hair strand was firmly held in place by a 3D-printed component, modeled after a mechanical pencil’s lead dispenser. The hair was attached to a torsion pendulum setup supported by a LEGO-based frame. A magnet secured the top end of the hair, while the bottom was connected to a lightweight disk with a red marker indicator and an attached magnet held at the hair’s bottom end. Hair oscillation was induced and recorded using TrackerOnline, a free, open-source motion analysis software. Each trial consisted of 45 seconds of torsional motion, allowing for the calculation of the hair’s shear modulus. After the initial measurement had completed with no force applied, incremental tensile forces (0.005 N per step) were applied to the hair strand. A magnetic pull was applied, exerting a force until the hair exhibited visible plastic deformation and subsequently broke and was recorded on videotape. Measurements were performed on both conditioned and unconditioned hair to examine the effects of treatment on the viscoelastic properties of hair. In each condition, the modulus was calculated after every force increment, allowing for monitoring of changes in stiffness and elasticity leading up to breakage. The elastic-to-plastic transition and breakage were tracked to fully characterize the mechanical properties of the hair samples. This setup enables the conduct of characteristic, precise, and repeatable measurements of hair mechanics inexpensively, using common materials and tools, thereby making diagnostics more accessible.

Results, Conclusions, and Discussions:: According to initial findings, the shear modulus of hair varies with applied tensile force across different strand lengths and conditioning states. As shown in Figure 1, unconditioned hair has a higher shear modulus as compared to conditioned hair, across all measured applied tensile forces and hair strand lengths, suggesting greater resistance to torsional deformation. For example, an unconditioned strand of the length 0.019 m reached a shear modulus of approximately 1.3 × 10¹¹ Pa (shown as a yellow solid line and triangle), while the same hair type that has been conditioned exhibited a modulus of 1.8× 1010 Pa (shown as a dashed purple line) under similar force levels. This pattern suggests that conditioning may soften or plasticize the hair, reducing its torsional stiffness. The results also indicate a general trend of increasing modulus with applied forces, particularly in unconditioned samples. This evidence may reflect strain stiffening behavior, where hair fibers become more rigid under greater tension. In conditioned samples, the modulus values remain relatively low and stable. These findings are based on a single individual’s hair, so the impact of different hair types has yet to be accounted for. Future steps are currently being taken to determine the exact point of breakage of the hair. Ultimately, this low-cost, accessible approach may help inform clinical settings and support early diagnosis and intervention for patients experiencing hair loss, particularly in underserved communities.

Acknowledgements and/or References (Optional): :