POLY(L-LACTIC)ACID IMPLANTS IN REPAIR OF DEFECTS OF THE ORBITAL FLOOR - A 5-YEAR ANIMAL STUDY

Biodegradable as-polymerized poly(l-lactic)acid (PLLA) implants were used for the repair of artificially created orbital floor defects in goats. The results of a five year histological follow-up of one animal per period are reported in this study. After 3 years of implantation the PLLA material had degraded but had not fully disintegrated into small particles. After 5 years of implantation, the PLLA was still not fully absorbed. In all sections, the implants were fully encapsulated by a fibrous tissue layer. This capsule was fully covered by newly formed bone at both the orbital and antral side. Ultrastructural investigation showed that lamellar or needlelike PLLA particles were situated between bundles of collagen and in various cells. These results are compared to our findings of an earlier study in humans

Creating the international tax order : transfer pricing and the search for coordination in international tax policy

Digitised version produced by the EUI Library and made available online in 2020

IN-VIVO DEGRADATION AND BIOCOMPATIBILITY STUDY OF IN-VITRO PRE-DEGRADED AS-POLYMERIZED POLYLACTIDE PARTICLES

The degradation of high molecular weight as-polymerized poly(L-lactide) (PLLA) is very slow; it takes more than 5.6 yr for total resorption. Moreover, the degradation products of as-polymerized PLLA bone plates, consisting of numerous stable particles of high crystallinity, are related with a subcutaneous swelling in patients 3 yr postoperatively. In order to avoid these complications, polymers were developed that are anticipated to have comparable mechanical properties but a higher degradation rate and do not degrade into highly stable particles that can induce a subcutaneous swelling. On chemical grounds it can be expected that copolymerization of PLLA with 4% D-lactide (PLA96) or by modifying PLLA through cross-linking (CL-PLLA) will lead to less stable particles and a higher degradation rate. To evaluate the long-term suitability of these as-polymerized polymers, the biocompatibility of the degradation products should be studied. Considering the very slow degradation rate of as-polymerized PLLA, in vitro pre-degradation at elevated temperatures was used to shorten the in vivo follow-up periods. In this study, the biocompatibility and degradation of as-polymerized PLLA, PLA96 and CL-PLLA were investigated by implanting pre-degraded particulate materials subcutaneously in rats. Animals were killed after a postoperative period varying from 3 to 80 wk. Light and electron microscopical analysis and quantitative measurements were performed. The histological response of all three pre-degraded materials showed a good similarity with in vivo implanted material. Pre-degraded PLLA induced a mild foreign body reaction and showed a slow degradation rate. PLA96 and CL-PLLA had a substantially lower crystallinity, a smaller mean particle size and an enhanced degradation rate compared to PLLA. Based on the chemical and quantitative analysis, the degradation of PLA96 and CL-PLLA was much more enhanced and thus more favourable than the degradation of PLLA

Maritime Museum Reports

The degradation of high molecular weight as-polymerized poly(l-lactide) (PLLA) is very slow; it takes more than 5.6 yr for total resorption. Moreover, the degradation products of as-polymerized PLLA bone plates, consisting of numerous stable particles of high crystallinity, are related with a subcutaneous swelling in patients 3 yr postoperatively. In order to avoid these complications, polymers were developed that are anticipated to have comparable mechanical properties but a higher degradation rate and do not degrade into highly stable particles that can induce a subcutaneous swelling. On chemical grounds it can be expected that copolymerization of PLLA with 4% d-lactide (PLA96) or by modifying PLLA through cross-linking (CL-PLLA) will lead to less stable particles and a higher degradation rate. To evaluate the long-term suitability of these as-polymerized polymers, the biocompatibility of the degradation products should be studied. Considering the very slow degradation rate of as-polymerized PLLA, in vitro pre-degradation at elevated temperatures was used to shorten the in vivo follow-up periods. In this study, the biocompatibility and degradation of as-polymerized PLLA, PLA96 and CL-PLLA were investigated by implanting pre-degraded particulate materials subcutaneously in rats. Animals were killed after a postoperative period varying from 3 to 80 wk. Light and electron microscopical analysis and quantitative measurements were performed. The histological response of all three pre-degraded materials showed a good similarity with in vivo implanted material. Pre-degraded PLLA induced a mild foreign body reaction and showed a slow degradation rate. PLA96 and CL-PLLA had a substantially lower crystallinity, a smaller mean particle size and an enhanced degradation rate compared to PLLA. Based on the chemical and quantitative analysis, the degradation of PLA96 and CL-PLLA was much more enhanced and thus more favourable than the degradation of PLLA

BIOCOMPATIBILITY STUDY OF AS-POLYMERIZED POLY(L-LACTIDE) IN RATS USING A CAGE IMPLANT SYSTEM

To evaluate the biocompatibility of in vitro predegraded as polymerized poly(L-lactide) (PLLA), a cage implant system was used to investigate white cell and enzyme concentrations with time. The use of a cage permits in a serial fashion a quantitative and qualitative measurement of exudate components formed around an implant. Subcutaneously in rats, caped cages manufactured from stainless-steel mesh were implanted with in vitro predegraded, as-polymerized PLLA, as-polymerized PLLA cylinders, and empty cages serving as controls. In vitro predegradation was used to simulate the degradation products of long-term in vitro degradation. Predegraded PLLA particles were obtained by in vitro hydrolysis at elevated temperatures. The first 7 days of implantation were characterized by an acute inflammatory reaction; the exudate extracted from the cages showed predominantly neutrophils for all types of implants. After day 7, there was a more chronic inflammatory reaction with predominantly macrophages and lymphocytes. There were no significant differences in the total leukocyte concentration or macrophage concentration for any of the cages in the period from 10-21 days. Extracellular enzyme activity also did not show any significant differences among the three types of cages. A possible explanation for the absence of any significant differences could be that the in vitro predegraded particles were sieved before implantation, thus eliminating all small particles (<70 mu m) that are probably mandatory to provoke an increased cellular reaction. (C) 1995 John Wiley and Sons, Inc