Materials Science and Biomaterials for Prosthetics
Scope
The exam tests selection of metals, polymers, composites, foams and adhesives by mechanical properties, durability, manufacturability and skin contact.
Materials
- Metals: 316L stainless (E ≈ 193 GPa, density 8.0), Ti-6Al-4V (E ≈ 114 GPa, density 4.43), aluminium 6061 (E ≈ 69 GPa, density 2.70). Specific stiffness is similar, so choose on strength, fatigue, corrosion and cost.
- Thermoplastics: PP and PE for flexible sockets and liners; acrylic and PETG for check sockets; PVA bags and laminating resin for definitive sockets.
- Composites: carbon fibre gives high stiffness at low weight but is brittle and anisotropic; glass fibre is cheaper and tougher; aramid absorbs impact.
- Foams: Pelite and Plastazote for padding; silicone and gel liners reduce shear.
- Biocompatibility follows ISO 10993; lower-limb structural testing follows ISO 10328, with general device requirements in ISO 22523.
Worked example
Compare equal-length tubes of the same cross-section in aluminium 6061, Ti-6Al-4V and 316L. Mass ratio follows density (2.70 : 4.43 : 8.0). Stiffness follows E (69 : 114 : 193), but normalised by mass the values are 25.6, 25.7 and 24.1 - almost equal. So all three give similar stiffness per kilogram; choose aluminium for a light pylon, titanium for corrosion-resistant fatigue duty, and steel for cost.
Traps
Confusing strength with stiffness; assuming a composite is isotropic; ignoring creep of thermoplastics under sustained load; mixing resin and hardener by eye; using a material without skin-contact data against the residual limb.