Polymers are synthetic and natural macromolecules composed of smaller units called monomers. Many synthetic polymers are produced and utilized because they are resistant to chemical and physical degradation. These polymers resistant to degradation present disposal problems when their usefulness ceases. Research has shown that substitution of natural monomers into synthetic polymers produces polymers that are more easily biodegraded.
A biodegradable polymer is a polymer in which the degradation results from the action of naturally occurring microorganisms such as bacteria, algae or fungi. These biodegradable polymers are largely used in medical application where they undergo degradation by chemical hydrolysis.

Polymers prepared from glycolic acid and lactic acid has found a multitude of uses in the medical industry, beginning with the biodegradable sutures first approved in the 1960s. Since that time, diverse products based on lactic and glycolic acid�and on other materials, including poly(dioxanone), poly(trimethylene carbonate) copolymers, and poly ( -caprolactone) homopolymers and copolymers �have been accepted for use as medical devices. In addition to these approved devices, a great deal of research continues on polyanhydrides, polyorthoesters, polyphosphazenes, and other biodegradable polymers.

Some examples of the biodegradable polymers are shown below.

•  There may be a variety of reasons, but the most basic begins with the physician's simple desire to have a device that can be used as an implant and will not require a second surgical intervention for removal.
•  Besides eliminating the need for a second surgery, the biodegradation may offer other advantages . For example, a fractured bone that has been fixated with a rigid, nonbiodegradable stainless implant has a tendency for refracture upon removal of the implant. Because the stress is borne by the rigid stainless steel, the bone has not been able to carry sufficient load during the healing process. However, an implant prepared from biodegradable polymer can be engineered to degrade at a rate that will slowly transfer load to the healing bone.
•  Another exciting use for which biodegradable polymers offer tremendous potential is as the basis for drug delivery , either as a drug delivery system alone or in conjunction to functioning as a medical device.
•  Biodegradable materials may be the only option for some potential applications. For example, reconstructing functioning blood vessels requires materials that degrade in the body, because nondegradable scaffolds occupy too much volume to allow tissues to regrow completely.
The general criteria for selecting a polymer for use as a biomaterial are to match the mechanical properties and the time of degradation to the needs of the application. The ideal polymer for a particular application would be configured so that:

• It has mechanical properties that match the application, remaining sufficiently strong until the surrounding tissue has healed.
• It does not invoke an inflammatory or toxic response.
• It is metabolized in the body after fulfilling its purpose, leaving no trace.
• It is easily processable into the final product form.
• It demonstrates acceptable shelf life.
• It is easily sterilized.

Significant commercial use of biodegradable polymers:
Sutures.
Of the total medical biodegradable market, this is a mature area expected to grow rapidly in the future. About 125 million synthetic bioabsorbable sutures are sold each year in the United States. They are divided into braided and monofilament categories.
Braided sutures are typically more pliable than monofilament and exhibit better knot security when the same type of knot is used . Monofilament sutures are more wiry and may require a more secure knot. Their major advantage is that they exhibit less tissue drag, a characteristic that is especially important for cardiovascular, ophthalmic, and neurological surgeries.

There are eight objective and three subjective parameters for suture selection based on criteria such as tensile strength, strength retention, knot security, tissue drag, infection potential, and ease of tying. SYNTHETIC degradable sutures have been available commercially since the 1970s. Originally made from polyglycolic acid (PGA), early versions of the products degraded and lost their mechanical strength in just two to four weeks--too fast for some applications. To broaden the range of uses, alternative sutures were made from copolymers of PGA and a more hydrophobic compound, polylactic acid (PLA). PLA's hydrophobicity limits the extent of water uptake in the copolymer, which in turn reduces the rate at which the polymer backbone is hydrolyzed relative to PGA.