In medical applications, the choice of material often depends on its biocompatibility and whether it is biodegradable.

Among the options provided:

- Polymethyl methacrylate (PMMA) is a non-biodegradable acrylic polymer commonly used as bone cement and for intraocular lenses. It remains stable and does not degrade in the body.

- Polylactic acid (PLA) is a biodegradable polymer derived from renewable resources such as corn starch. It breaks down into lactic acid, which can be metabolized by the body, making it ideal for applications like sutures, drug delivery systems, and temporary implants.

- Polyethylene terephthalate (PET) is a strong, durable polymer used in applications like vascular grafts and some implantable devices but it is not biodegradable.

- Polyvinyl chloride (PVC), used in tubing and medical bags, is non-biodegradable and often associated with environmental and health concerns related to plasticizers.

Therefore, the correct answer is Polylactic acid (PLA) because it is the most commonly used biodegradable polymer in medical devices, offering safe degradation within the body.

Reference: Biomaterials Science: An Introduction to Materials in Medicine, 3rd Edition, Chapter 7 - Biodegradable Polymers, Page 345-350