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(96 L/4D-lactide) (PLA96) implants and to evaluate their suitability for r epair 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 pro duced 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 unde r a static load corresponding to a retrobulbar pressure of 13 mm Hg as well as unloaded. Both implant types were able to counteract the appl ied static load without fracturing or excessive sagging. The type A im plants 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 woul d not have resulted in positional changes of the eyeball. it is conclu ded that with respect to the mechanical properties, both types of PLA9 6 implants tested are suitable for repair of large orbital floor defec ts.