Gram for gram, human bone can be several times stronger than steel in certain measures of strength, combining a lightweight structure with remarkable resistance to compression and bending.
Overview
Bone is a composite material made of a mineral phase (mostly hydroxyapatite) and an organic matrix (primarily collagen). This combination produces a material that is both stiff and tough: the mineral gives hardness and compressive strength while the collagen provides flexibility and resistance to fracture. Because bone is much less dense than steel, comparisons by weight often show bone outperforming steel in specific strength metrics.
Mechanical properties
Strength can be measured in different ways. In compression and specific strength (strength per unit mass), cortical bone rivals or exceeds some steels. In bending or impact resistance, the organised microstructure of bone helps absorb energy and prevent catastrophic failure. However, steel typically has higher absolute tensile strength and is less variable than biological materials.
Example: the femur
The femur is the longest and one of the strongest bones in the human body. Its cylindrical shape, dense cortical shell and spongy interior distribute loads efficiently, allowing it to support many times a person’s body weight during everyday activities. Under controlled tests and depending on how loads are applied, individual bones like the femur can bear extraordinarily large forces relative to their mass.
Limitations and context
Comparing bone and steel requires context: bones are living tissues that remodel and repair, but they are anisotropic and variable between individuals, ages and health conditions. Steel is uniform, manufactured to specification and generally outperforms bone in absolute tensile strength, fatigue life and predictable behaviour under engineered loads.
Significance
Bone’s combination of lightness, toughness and adaptive design has inspired engineers and materials scientists in fields such as biomimetics and implant design. Understanding how bone achieves high strength with low mass helps inform safer, lighter structures and better biomedical materials.
Quick related facts
- Composition: mineral (hydroxyapatite) and collagen matrix
- Strength type: high specific strength and compression resistance
- Femur capability: designed to carry many times body weight in normal use
- Comparison note: steel has higher absolute tensile strength; bone excels for weight-sensitive, adaptive biological roles