The modification of PLA and PLGA using electron‐beam radiation

Abstract

The degradable polymers polylactide (PLA) and polylactide-co-glycolide (PLGA) have found widespread use in modern medical practice. However, their slow degradation rates and tendency to lose strength before mass have caused problems. The aim of this study was to ascertain whether treatment with e-beam radiation could address these problems. Samples of PLA and PLGA were manufactured and placed in layered stacks, 8.1 mm deep, before exposure to 50 kGy of e-beam radiation from a 1.5 MeV accelerator. Gel permeation chromatography testing showed that the molecular weight of both materials was depth-dependent following irradiation, with samples nearest to the treated surface showing a reduced molecular weight. Samples deeper than 5.4 mm were unaffected. Computer modeling of the transmission of a 1.5 MeV e-beam in these materials corresponded well with these findings. An accelerated mass-loss study of the treated materials found that the samples nearest the irradiated surface initiated mass loss earlier, and at later stages showed an increased percentage mass loss. It was concluded that e-beam radiation could modify the degradation of bioabsorbable polymers to potentially improve their performance in medical devices, specifically for improved orthopedic fixation.

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

“…Previous work has confirmed that e-beam induced chain scission leads to a decrease in molecular weight of PLLA [16,23]. Moreover, Leonard et al [16] also illustrated a depth dependent reduction in PLA molecular weight upon e-beam irradiation which was both predictable and repeatable. The variation in Mn from the sample surface towards the bulk was attributed to differences in the received dose as proportional to sample depth.…”

“…The propagation of these radicals, in particular the peroxyl free radicals, greatly enhances chain scission whereas their recombination can lead to chain branching [27,28]. Previous work has confirmed that e-beam induced chain scission leads to a decrease in molecular weight of PLLA [16,23]. Moreover, Leonard et al [16] also illustrated a depth dependent reduction in PLA molecular weight upon e-beam irradiation which was both predictable and repeatable.…”

“…Previous work has demonstrated the ability to produce a depth-dependent reduction in the molecular weight and associated effects on the degradation of PLA and PLGA [16,23]. This paper investigates further the ability to provide a degree of control over the depth-dependent radiolytic degradation of PLLA through manipulation of process parameters.…”

“…More specifically, e-beam irradiation can cause a decrease in average molecular weight (through chain scission) advancing the process of hydrolytic degradation [15]. Previous work by the authors has illustrated the potential to influence polymer (PLLA/PLGA) properties, such as molecular weight, strength and corresponding degradation, in a depth dependent manner [16]. This can then allow degradation to proceed in a manner occurring from the outside of the device towards the centre engendering early stage mass loss, maintenance of internal mechanical strength and ultimately the provision of optimum conditions for tissue healing.…”

The degradation properties of co-continuous calcium phosphate polyester composites: insights with synchrotron micro-computer tomography

“…Further optimization of the polymer phase is therefore required in order to maintain the porous ceramic S672 Degradation properties of TCP -PDLLA L. M. Ehrenfried et al structure and to serve as a scaffold for bone ingrowth after the degradation of the polymer. A surface-degrading polyester could be obtained by irradiating the composite with an electron beam, which decreases the molecular weight at the surface, resulting in its faster degradation (Leonard et al 2009). Reduced swelling of the polymer phase can be achieved by the use of PLLA with the addition of lauric acid (PLLA-la; Renouf-Glauser et al 2005.…”