[Memory effect of resorbable polymers]

The present study analyzed the memory effect of resorbable polymers. Depending on temperature, this effect describes the ability of different materials to "remember" their original form after mechanical deformation. Resorbable polymers serve as materials to stabilize and fix bone fractures. Compared to metal transplants, resorbable polymers are able to undergo thermoplastic deformation. The precise adaptation of the transplant to the surrounding bone guarantees an exact anatomical reconstruction. However, during normal applications, it was observed that these biodegradable plastic materials tend to revert to their original form at body temperature. This "memory effect" could result in negative consequences for the medical treatment.

By the process of compression molding, geometrically formed specimens (lattice, rod, plate) consisting of different polyglycolides and polylactides were prepared. After warming up the specimens to 50 degrees C (water bath) they were deformed into definite angles. Following this procedure, the specimens were put in a water bath at 37 degrees C to mimic the adaptation of the transplant at body temperature. The retroflexion of the material (memory effect) was measured using an XY-measuring desk.

The present study clearly reveals that highly deformed specimens react with stronger retroflexions. In addition, the results indicate that the memory effect depends on geometrical design as well as on chemical composition. All tested polymers showed a strong initial memory effect that decreased with time.