Biodegradable polymer materials and their applications in biomedicine
If a material is said to be biodegradable this means it is capable of “being decomposed by biological agents, especially bacteria.”(1) Biodegradable polymers are polymers that break down and lose their initial integrity. Polymers are substances that have a molecular structure made up mainly of a large number of similar units bonded together. Biodegradable polymers are used in medical devices to avoid the need for a second operation to remove them.
There are many different types of polymer degradation. Degradation is a process that deteriorates polymer properties or their external appearance, changing its properties such as tensile strength, colour, shape, etc. Degradation can be cause by a number of factors, such as heat, oxygen, moisture, mechanical stresses and other factors. “Depending on the agent, the following forms of polymer degradation are distinguished: thermal, thermal oxidative, photochemical, hydrolytic, and radiation, among others.”(2) Usually numerous types of degradation processes take place simultaneously in a polymer; for example, making a polymer into a product, it undergoes thermal, thermal oxidation, and mechanical forms of degradation.
Thermal degradation of polymers: thermal degradation of polymers is a molecular weakening as a result of overheating. “At high temperatures the components of the long chain backbone of the polymer can begin to separate (molecular scission) and react with one another to change the properties of the polymer” (3) thermal degradation normally results in changes to the molecular weight of the polymer usual property changes include reduced ductility, colour changes, cracking, general reduction in most other desirable physical properties
UV degradation of polymers: “Common synthetic polymers which may be attacked include polypropylene and LDPE where tertiary carbon bonds in their chain structures are the centres of attack.” (4) The...