Several other sustained ocular drug delivery systems composed of either nonbiodegradable or biodegradable polymers have been reported in the literature.
18 Polymeric systems have been used widely as implantable devices for controlled release of drugs in various organs.
19,20 In ophthalmic use, PLGA copolymers are used more commonly, for example, incorporating timolol for intraocular pressure control,
21 all-trans retinoic acid to reduce muscle adhesion in strabismus surgery,
22 cyclosporin for treatment of uveitis,
23 or 5-fluorouracil for antifibrotic effects.
24 In our study, we used PLC copolymers instead. PLC is a relatively new copolymer that is made of poly(L-lactide) and poly(caprolactone), each of which has been approved by the Food and Drug Administration (FDA) in implantable products. Even though to our knowledge it has not been used previously in ophthalmology, its use has been reported in neurologic, orthopedic, and cardiovascular research.
25–27 In comparison with PLGA, PLC is quite hydrophobic as the caprolactone ester bonds of the copolymer are not easily hydrolyzed. Because of this slower hydrolysis rate, PLC microfilms degrade more slowly and, therefore, achieve a longer release.
28,29 Polymeric structural difference in crystallinity also affects degradation rates. PLGA is an amorphous copolymer and is easier to be degraded than a PLC copolymer, which has semicrystalline structure. Our previous studies have confirmed that PLC microfilms degrade slower than PLGA microfilms in vitro and in vivo,
30 which enables PLC to be a better candidate for a sustained ocular drug delivery system. Furthermore, PLGA copolymers have a higher glass transition temperature than PLC copolymers, which makes PLGA copolymers physically hard, while PLC copolymers appear to be soft and elastic.
31,32 Hence, we chose the softer material for the microfilm fabrication as it minimizes the possibility of surgical trauma during the implantation procedure as well as of extrusion after the implantation.