Final answer:
Artificial joints for small joints are typically made of metals like stainless steel or titanium, while large joints use plastic materials such as polyethylene for enhanced movement and reduced friction.
Step-by-step explanation:
Artificial joints are built of metals (stainless steel or titanium) for small joints and plastic (polyethylene) for large joints. For example, metal and plastic are used in artificial hip joint replacements, where the metal acts as the ball and the plastic as the socket. This creates an artificial ball-and-socket joint that mimics the natural joint, with a very small coefficient of friction, allowing for smooth movement and reduced wear.