Medical devices, molecular degradation

In the extrusion of medical devices, molecular degradation is often a critical issue. This degradation of the MW can be strongly influenced by the geometry of the extruder screw. Unfortunately, little information on this problem is available in the open literature. Paakinaho et al. [127] published results of a study on the MW reduction along the length of a single screw extruder for three polylactic acid (PLA) resins see Fig. 8.111. 

In Chapter 8, a new section on efUcient extrusion of medical devices has been added. It covers good manufacturing practices in medical extrusion and automation. The effect of processing conditions and screw design on molecular degradation is covered in detail. Screws designs that minimize molecular degradation are discussed and explained. 

The hydrolysis of the polymers leads to molecular fragmentation. The hydrolytic degradation of lactic acid based polymers is an undesired phenomenon under certain circumstances, such as during processing or material storage. It is however, beneficial in other applications, for example in medical devices or compostable packages (12). 

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