Degradation of poly-L-lactide. Part 1: in vitro and in vivo physiological temperature degradation

Abstract

Poly-L-lactide (PLLA) is one of the most significant members of a group of polymers regarded as bioresorbable. The degradation of PLLA proceeds through hydrolysis of the ester linkage in the polymer's backbone and is influenced by the polymer's initial molecular weight and degree of crystallinity. To evaluate its degradation PLLA pellets were processed by compression moulding into tensile test specimens and by extrusion into 2 mm diameter lengths of rod, prior to being sterilized by ethylene oxide gas (EtO) and degraded in both in vitro and in vivo environments. On retrieval at predetermined time intervals, procedures were used to evaluate the material's molecular weight, crystallinity, mechanical strength, and thermal properties. Additionally, the in vivo host tissue's biological response was analysed. The results from this study suggest that in both the in vitro and in vivo environments, degradation proceeded at the same rate and followed the general sequence of aliphatic polyester degradation, ruling out enzymes contributing and accelerating the degradation rate in vivo. Additionally, the absence of cells marking an inflammatory response suggests that the PLLA rods investigated in vivo were biocompatible throughout the 44 weeks duration of the study, before any mass loss was observed.

Additive manufactured biodegradable poly(glycerol sebacate methacrylate) nerve guidance conduits

“…Compression results on PGSm conduits showed an average Young's modulus of 3.2 MPa, similar to that of the native nerve (0.45 MPa) [44]. This similarity is further understood when compared with polycaprolactone (PCL), poly-L-lactide (PLLA) and poly(3-hydroxybutyrate) (P3HB), materials widely researched for peripheral nerve repair, with reported modulus values of 400 MPa, 668.4 MPa, 1160 MPa, respectively, far stiffer than that of the native nerve [25,[45][46][47][48]. Suture retention mechanical tests found PGSm conduits to have an average suture retention strength of 12.3 MPa, similar to the value reported for clinically used poly(tetrafluoroethylene) (as Gore-Tex vascular grafts), 23 MPa [49][50][51].…”

Bioresorbable Scaffold

“…Assuming that the concentrations of ester bonds and water are approximately constant throughout the degradation process and that the concentration of carboxylic acid end groups is inversely proportional to the number-average molecular weight (Mn) of the polymer (ie, [COOH]ϭ1/Mn), Weir and coworkers 57,58 showed that…”

Electron-beam treatment of poly(lactic acid) to control degradation profiles

“…In accordance with ISO15814, samples were placed in glass vials containing 15 ml of phosphate buffered saline (PBS, pH 7.4). For accelerated degradation, a higher temperature of 70 C was used [18,19]. At defined time points, samples were removed from the PBS, filtered through Grade 1 filter paper and rinsed with distilled water.…”