As I lay down, leg up and staring at the ceiling, after my leg injury, a flurry of thoughts enter me.. What is the need to keep lying down.. Why cannot I treat my ligament tear like a simple injury and move about. I cannot, since it hurts, but even then I 
would have preferred to walk about independently than being bed-bound. I have unleashed my creativity by doodling on the plaster but then as I do it, I wonder what is the need?
Plasters and casts have been used widely for a while to immobilize areas which are injured and could do with some rest to aid its recovery.
The purpose of such an immobilization is to ensure that the area affected due to a fracture, ligament, muscular or soft tissue injury is not stressed by load-bearing, which can accelerate the healing process.
Wonder what the cast is made of? PLASTER OF PARIS…Yes, you read it right.. the same building material used for making sculptures and also protective/ decorative coatings of walls in some buildings.
So what is this Plaster of Paris? (I shall refer to it as POP for the rest of the article).
The name originated due to the abundance of gypsum (one of the primary materials used to make POP) near Paris. POP does not crack when dry thereby making it a good substance to cast molds with.
POP is made of a fast setting chemical called calcium sulphate hemihydrate. It is in a powdery form which when moistened would harden into the shape it is molded into as it dries. This makes it an ideal material for making cast bandages to suit the shape of the body part needing the support be it leg, finger, elbow or so.
The powdery form of the Calcium sulphate hemihydrate when mixed with water converts into a crystalline form of gypsum. This process releases heat during the crystallization and the hydrated chemical begins to harden. Crystals have a very highly organized arrangement of atoms in it making it stronger mechanically. The interlocking of the crystals thus formed in the plaster gives strength and rigidity to the cast. All of us know that crystals are very strong – Kryptonite crystal can weaken even Superman!!!
The cast dries by the process of evaporation of the surplus water which are not required for crystallization and this increases the strength of the cast. The mechanical strength of the cast makes it ideal for immobilizing injured parts of the body which needs to be at rest to facilitate healing.
Other than plaster, which is generally not water-proof, fiberglass casts have also been used recently. The advantages of these over the conventional POP casts are the light weightedness, water-resistance, and a better aesthetic appeal (One could sport casts of one’s favorite color if that would confer comfort to the wounded mind). However, there remain concerns about its strength, mouldability, and irritability to skin surfaces.
Other than fractures and injured ligaments, casts are also used in medicine to facilitate healing and to provide relief from pain, to improve functionality, and to prevent or correct deformities.
All, that said and done, knowing the chemistry may have ‘POP’PED the mystery behind casts. Of course, one may make the casts prettier and more acceptable by doodling over it. After all love and care of loved ones is a good healer too.
For those who wish to read more:
https://musculoskeletalkey.com/cast-and-bandaging-techniques/
https://www.healthline.com/health/types-of-casts
https://en.wikipedia.org/wiki/Orthopedic_cast
