Guitars and their immediate family are constructed quite a bit like the violins. They have a similar wood body and a sound hole in front, not to mention the bridge that carries the sound of the strings into the wood. Guitar bodies can also be made of composites like carbon fiber.
Then there are electric guitars with small solid bodies made from wood like maple. These don't have a normal bridge, but electrical contacts that carry the sounds of the strings out to an amplifier and speakers.
Most guitar strings are made of steel. They are made a lot like piano strings. Some are wire while the lower strings have a wire core with another wire wrapped around it. They even make low guitar strings that are wound with flat steel, nickel or silver "ribbon" like violin strings. These metal strings are not polymers. but there is a type of guitar that uses polymer strings.
The classical guitar is different than the steel string acoustic guitar used for pop, folk or country music. You can see the difference in the pictures of both types of guitar. The classical guitar - in the front - looks almost the same but it has nylon strings and the player uses his fingernails rather than a pick to play it. This gives it a much softer harp-like sound. Also because there is no need for a pick, the classical guitar has no polystyrene pickguard like a steel string guitar. By the way, guitar pics are made from nitrous cellulose - one of the earliest synthetic polymers, and fingernails are a type of protein.
The mandolin and lute are instruments similar to guitars but with different body shapes, so - of course - they sound different from guitars.
These instruments have all been around for a long time. In fact J.S. Bach (1685-1750) played the lute and wrote quite a few pieces to be performed on it during the Baroque period. It has a soft sound like a classical guitar because the strings are made of nylon plated with a metal like silver. The mandolin, a "descendant" of the lute, has a more "metallic" sound because it has metal strings wrapped in bronze. The distinct sound it makes is very popular in American folk and Bluegrass music, though traditionally it is used in Italian music. Though the lute and mandolin are made of wood, they - most of all the stringed instruments - keep their ancient gourd-shaped bodies. Lutes, and even some mandolins, are rounded in the back. That's because a long time ago these types of stringed instruments were made out of large gourds which were cut in half and hollowed out and covered with the front wood piece. And - like wood - gourds, being plant material, are a form of cellulose.
