The terminology ìbiodegradable polymersî covers many polymers based on organic acids and derivatives of polylactides and polyglycolides.

Under normal physiological conditions, polylactides/polyglycolides are hydrolytically degraded into non-toxic (lactic and/or glycolic acid) easily metabolized and eliminated by the body under CO2 and H2O.

Several properties depend on the initial composition of monomers :
- polymer with amorphous or crystalline structure : polymers with a high degree of L-Lactide or glycolide are highly crystalline, the mixtures of D and L-Lactides are amorphous.
- mechanical properties
- polymer degradation rate : polymers with a high degree of L-Lactide are degrading more slowly than mixtures D,L. Polyglycolides are degrading faster than polylactides.

Molded parts made from polymers show mechanical properties that are similar to those of other plastics. Tensile strength, bending strength and modulus of elasticity can be influenced to a great extent by the following factors :
- Composition : the strength of highly crystalline types is higher than that of low-crystalline or amorphous products.
- Molecular weight : the strength increases with higher molecular weight.

Physiological compatibility

The various polymers types are non-toxic and are well-tolerated by the organism. This has been verified by numerous animal tests and clinical trials with polyesters based on lactic and glycolic acid. The degradation of polymers in the organism into lactic or glycolic acid takes place by non-specific hydrolysis.

Degradation by hydrolysis

Under environmental as well as physiological conditions, polymers are hydrolytically degraded into glycolic acid or lactic acid, naturally present in the human body and easily metabolised.

The degradation rate depends on the molecular weight, the surface quality, the composition of the polymers crystalinity, manufacturing parameters and, shape, size and site of the implant:

The degradation rate depend on the different polymer properties :
Type L-Lactide : degradation time in: Months/years
Type D,L-Lactide and glycolide: degradation time in : Months
Mix : degradation time in : Weeks/Months

The hydrolytic degradation of the polymers leads first to a decrease in molecular weight. Only at the end of the degradation time can a loss in mass be observed, which leads to the complete decomposition of the polymer in water and carbonic gas.

BOEHRINGER INGELHEIM (Germany).