Design Better Implants: Is Bone Material Stronger than Steel?

Bone typically has an elastic modulus that is like concrete but it’s 10 times stronger in compression.

As for the stainless-steel comparison, bone has a similar compressive strength but is three times lighter.

So, what happens when a bone becomes so compromised that human engineers need to step in? It turns out that Nature’s genius is even more apparent when we try to replace its work.
 

Why is Bone Material so Strong?

Though implants are a necessity for many people, their performance over time cannot compare with the longevity of the average bone. For example, it could take 60 to 80 years for a knee joint to wear out. However, a knee replacement is lucky to last a quarter of that time.

A typical knee could last 60 to 80 years while an artificial one could last 15 to 20 years. 

Engineers need to design their implants to handle a large load. During everyday activities, like walking or jumping, a typical skeletal framework could experience loads that are four to 20 times a person’s body weight. These loads can be in the form of:

• Compression
• Torsion
• Shear
• Tension

How does bone survive these forces? It’s because of its composite microstructure. Bone is made up of collagen fibres that are stiffened by a dense filling and surrounding minerals. It also contains:

• Blood vessels
• Living cells
• Protein
• Water

Similarly, composites have become an important part of material design and selection. However, the fact that bone can adapt and change to its environment is a hard characteristic for engineers to mimic. As a result, they are using both material selection and design to iterate their implants until they meet expectations.
 

Engineers Continue the Search for Bone Material Substitutes

Joint replacements have their own challenges. In this case, engineers will need to find a material that matches the performance of the surrounding bone. These material properties will vary based on the patient’s age, gender, weight, lifestyle and more. The engineers will also need to ensure the material has the right corrosion resistance and biocompatibility properties.

Using a material selection tool, engineers can match the proper material to a patient and their medical condition. Alternatively, engineers will use materials intelligence software to help design new materials to perform better than what’s currently on the market.

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