# Nanomechanical Properties of Rib Bones in Diabetic vs. Healthy Rat Models

## TL;DR

This study shows that diabetes makes rat bones stiffer and more brittle at the nanoscale, while aging affects how bones absorb energy, which could explain why bones break more easily in older or diabetic individuals.

## Contribution

The study introduces a combined static–dynamic nanoindentation protocol to distinguish diabetes- and age-related bone degradation at the tissue level.

## Key findings

- Diabetic rat bones showed significantly higher hardness and elastic modulus compared to healthy controls.
- Aging significantly altered the storage and loss moduli, indicating changes in viscoelastic damping capacity.
- Diabetes reduced the modulus-to-hardness ratio, suggesting increased brittleness despite higher stiffness.

## Abstract

This study examines how diabetes mellitus and physiological aging influence the nanomechanical behavior of rat rib cortical bone using combined static and dynamic nanoindentation. Ribs from young control, old, and streptozotocin-induced diabetic rats were analyzed to quantify both intrinsic and frequency-dependent mechanical properties. Static nanoindentation revealed markedly higher hardness and elastic modulus in the diabetic group (0.47 ± 0.22 GPa and 9.53 ± 3.03 GPa, respectively) compared to controls (0.11 ± 0.03 GPa and 3.21 ± 0.51 GPa; p < 0.001). The modulus-to-hardness ratio, an indicator of fracture toughness, was reduced from 30.34 in controls to 20.45 in diabetics, suggesting increased stiffness but greater brittleness. Dynamic nanoindentation (0–4.5 Hz) demonstrated significant aging-related changes in the storage and loss moduli (p < 0.001), while the loss factor (tan δ < 1) and viscosity remained similar across groups, indicating predominantly solid-like behavior. These results show that diabetes stiffens bone tissue through matrix-level alterations, whereas aging primarily affects its viscoelastic damping capacity. The combined static–dynamic nanoindentation protocol provides a robust framework for distinguishing disease- and age-related bone degradation at the tissue scale. Translationally, the findings help explain why bones in diabetic or elderly individuals may fracture despite normal mineral density, underscoring the need to assess bone quality beyond conventional densitometry.