The effects of molecular weight and porosity on the degradation and drug release from polyglycolide.

This paper explores the influence of initial molecular weight and porosity on the release of the drug, theophylline, from polyglycolide (PGA). PGA was made by a variety of processes to vary the molecular weight and was blended with NaCl with different crystal sizes and in different proportions to vary the pore size and volume. Overall, results showed that decreasing the molecular weight and increasing the pore size and volume increased the rate of drug release. The exact variation of these trends agreed well with the previously established four-stage degradation mechanism for PGA, but was more complex than a simple linear behaviour. Because both the molecular weight and the porosity of PGA have a substantial influence on the polymer degradation, and can be varied in a controlled manner, these parameters can play an important role in developing PGA as a controlled drug delivery material with tailored drug release.

The distribution of water in degrading polyglycolide. Part I: sample size and drug release.

The effect of sample thickness on the degradation of polyglycolide (PGA) disks and on their drug release profiles is explored in this paper, and conclusions drawn about the distribution of water across a sample during degradation. The degradation process was monitored by measuring changes in the long period calculated from small angle X-ray scattering profiles, and by following changes in the pH of the buffer solutions. Drug release profiles were obtained using UV-spectrophotometry. The measurements suggest that reaction-erosion fronts form at the surface of all samples after around 7 days of degradation, and that these fronts progress through the sample at a constant rate of 0.032 mm/day. The data are consistent with a model in which drug is released quickly from the porous, hydrated regions behind the front, and reaches 100% release when the fronts meet.

The distribution of water in degrading polyglycolide. Part II: magnetic resonance imaging and drug release.

This paper reports the use of magnetic resonance imaging (MRI) on polyglycolide disks to monitor the change in water ingress with degradation time. Very little response was measured before 13 days, but after this time, water began to penetrate the disks as fronts, starting from the sample surface and moving inwards towards the centre. These results provide more direct evidence in support of the four-stage degradation model for PGA outlined in previous literature, and in particular, that fairly sharp reaction-erosion fronts move in from the sample surface to the centre when the polymer is undergoing significant mass loss and water gain. A combination of MRI and drug release data suggest that fronts originate at the surface at about 7 (+/-2) days, and proceed at a rate of 0.033 (+/-0.002) mm/day. These results agree with results obtained from cumulative drug release profiles for different sample thicknesses presented in Part I. They support the hypothesis that drug releases quickly from the swollen regions behind the fronts where the polymer is open and porous, and that release finishes when the fronts meet in the centre of the sample.