In‐patient versus in vitro degradation of P(L/DL)LA and PLGA

Abstract

To assess and compare degradation rates, poly(70L-lactide-co-30DL-lactide) [P(L/DL)LA] and poly(85L-lactide-co-15-glycolide) (PLGA) copolymer degradation were studied in patients (maxillofacial region) and in vitro. Five patients of a total of 20 with 85:15 PLGA osteosyntheses, and 15 of a total of 60 with 70:30 P(L/DL)LA osteosyntheses, (10 females and 10 males, 26-55 years; mean, 33 years) underwent explantations after 3, 6, 9, 12, 18, and 24 months. Identical resorbables immersed in physiological buffer solution at 37 degrees C were compared at identical intervals. P(L/DL)LA's initial average molecular weight of 45,000 decreased to 25,000 in patients (and to 21,000 in vitro) after 6 months, and to 8000 in patients after 18 months. PLGA's average molecular weight decreased from 44,600 to 22,000 after 3 months in patients and in vitro, and to 11,000 in patients and 1300 in vitro at 6 months. In-patient and in vitro glass-transition temperatures decreased from approximately 60 degrees C to 50 degrees C over 18 months. Crystallinity in explants was < or = 4% in P(L/DL)LA throughout testing, and 16% and 30% in PLGA at 6 and 12 months, respectively. Both copolymers decomposed reliably in patients: 85:15 PLGA within 12 months and 70:30 P(L/DL)LA within 24 months on average (p < 0.005), leaving only extremely small granules that powder upon finger touch. In vitro rates were significantly faster (p < 0.005). Crystallinity associated with foreign-body reactions was minor and did not inhibit decomposition.

Evaluation of the Fatigue Performance and Degradability of Resorbable PLDLLA-TMC Osteofixations

“…[18]. In the present work, however, we were successful by using a modified smaller three-point bending apparatus and explants with a length above 8mm long.…”

“…Yet the stability comes at the price of a large volume. Therefore degradation may be unreliable above all, as in-vitro laboratory, in-vivo animal studies cannot become transferred one-to-one to humans [18,19]. …”

“…Complete disintegration is sought after 3 months of stable fixation and should cause no local irritation of tissues [9,10]. The biodegradation of polymers used in resorbable osteofixations has been demonstrated in many laboratory in-vitro and in-vivo animal studies [11-16], but only few in-situ patient studies have been reported [17,18]. These latter studies have some limitations, such as small number of explants and the results being applicable only to the specific polymer used for fabricating the osteosyntheses.…”

“…In a previous report we showed that in patients, implants fabricated from a 85%mole:15%mole PLGA copolymer degrade considerably faster in-situ , than those fabricated from a 70%mole:30% mole P(L/DL)LA (racemic mix of L and DL lactide) copolymer. Both copolymers degrade reliably in-situ , mainly by hydrolysis, but at a rate that is slower than what occurs in-vitro [18]. The exact moment of total resorption can only be extrapolated from the degradation data of explants and the macroscopic absence of material in patients on surgical revision [18].…”

“…Both copolymers degrade reliably in-situ , mainly by hydrolysis, but at a rate that is slower than what occurs in-vitro [18]. The exact moment of total resorption can only be extrapolated from the degradation data of explants and the macroscopic absence of material in patients on surgical revision [18]. Three point bending test (explants were too small) and scanning electron microscopy were not performed at that time.…”