An experimental study of heat adaptation of bioabsorbable craniofacial meshes and plates

Intraoperative heating of bioabsorbable plates and mesh panels to above the glass transition temperature is commonly performed to assist their adaptation to bone. Some studies suggest that once heat-adapted, such implants under certain conditions tend to partially revert to their preadapted shape, termed a "memory effect." We investigated this phenomenon by using heat-adapted 82:18 poly-L-lactic acid:polyglycolic acid copolymer mesh panel and plate specimens with a glass transition temperature of 57 degrees C. The specimens retained limited malleability even at temperatures as low as 45 degrees C, substantially below the nominal glass transition temperature, as measured by shape relaxation experiments. At 40 degrees C to 42 degrees C, however, shape relaxation was not observed. A three-dimensional synthetic bone construct was also fixated using 90 degrees C heat-adapted plates, then incubated in a 37 degrees C buffer bath for 4 weeks, with periodic measurement of the shape of the construct. No changes in shape were recorded over this interval, suggesting that heat-adapted bioabsorbable implants forming a three-dimensional fixation network with multiple bone fragments cannot independently shape relax with the overall interconnectedness of the network ensuring its stability over time.