POLY(96L/4D-LACTIDE) IMPLANTS FOR REPAIR OF ORBITAL FLOOR DEFECTS - AN IN-VITRO STUDY OF THE MATERIAL PROPERTIES IN A SIMULATION OF THE HUMAN ORBIT

To test the mechanical and physical properties of two types of poly(96L/4D-lactide) (PLA96) implants and to evaluate their suitability for repair of large orbital floor defects, a study using an in vitro set-up was performed. Implants, 0.2 mm thick and 28 mm in diameter, were produced by either an extrusion process (type A) or by direct machining (type B) and had a molecular weight (($) over bar M(w))) of 64 x 10(3) and 146 x 10(3) g/mole, respectively, after gamma-sterilization with a dose of 25 kGy. The implants were tested over 8 weeks in an apparatus simulating the human orbit with a 3.1 cm(2) orbital floor defect under a static load corresponding to a retrobulbar pressure of 13 mm Hg as well as unloaded. Both implant types were able to counteract the applied static load without fracturing or excessive sagging. The type A implants sagged more than the type B implants (2.3 +/- 0.1 mm versus 1.0 +/- 0.0 mm, p < 0.01) but retained and even increased their strength during the study whereas the type B implants showed a gradual strength-loss. In the clinical setting the observed sagging in both types would not have resulted in positional changes of the eyeball. it is concluded that with respect to the mechanical properties, both types of PLA96 implants tested are suitable for repair of large orbital floor defects.