Electron-beam surface modification of bioresorbable polymers for enhanced release of silver nano-particles: an anti-bacterial strategy

摘要

Introduction: Interest is developing in manipulating bioresorbable polymers with regards to biofitm prevention which can help alleviate major implant complications such as infection and implant removal. Previous work has shown that near-surface modification of bioresorbable polymers can be achieved via low energy electron beam (e-beam) irradiationFl which enhances the release of bioactive additives.An additive which has previously shown potential as an antimicrobial is silver nano-particles.It is hypothesized that the e-beam treatment will reduce biofilm formation via controlled release of silver nano-particles. The aim of this study was to utilise low energy e-beam irradiation to initiate preferential surface degradation of a clinically relevant bioresorbable polymer, focusing on mechanisms for biofilm prevention. Materials and Methods: Poly(lactide-co-glycolide) (PLG) sheets (Purac PURASORB PLG 8531), loaded with 0,1 and 2 wt% silver nano-particles (SNP), particle size: 20-40nm (QuantumSphere, USA) were produced by melt-extrusion compounding followed by compression moulding. Samples of 010 × 1mm were cut from these sheets. Two sets of samples were irradiated at Rise HDRL, Technical University of Denmark, at an energy of 125keV and doses of 150kGy and 450kGy. Following e-beam treatment, irradiated and non-irradiated samples were subjected to a 28 day static degradation study. Samples were placed in Phosphate Buffered Saline (PBS) solution (pH of 7.4) and held at 47°C (to accelerate degradation kinetics). During the study silver release was monitored using inductively coupled plasma spectroscopy (ICP) at time points of 3,7,17 and 28 days. Using gram positive bacteria, Staphylococcus aureus, static biofilm adherence testing was carried out on non-degraded and pre-degraded samples in order to ascertain the degree of biofilm inhibition. Results and Discussion: Figure 1 shows the silver release during degradation testing (1 and 2% wt SNP loading). Significantly higher levels of silver release (approximately ten times) were observed for electron beam irradiated specimens compared to non-irradiated (Nl) controls at 17 and 28 days. Figure 2 shows that samples with a 2% wt SNP loading, irradiated at 450kGy and statically pre-degraded for 7 days, did show a viable reduction in Staphylococcus aureus attachment compared to samples subjected to the same irradiation treatment and pre-degradation but with 0% wt SNP loading. This corresponded to an approximate reduction in colony forming units of 90%. No viable reduction In attachment was evident for non-irradiated samples (Nl) or samples irradiated at 150kGy. Figure 3 shows corresponding images of bacterial colony growth for 7 days pre-degraded specimens (0% and 2% SNP, 450 kGy). The results suggest that bacterial inhibition is influenced positively by SNP release but negatively by the physical condition of the degraded polymer. It would seem that one factor may nullify the other. Conclusion: This work has shown that low energy e-beam treatment can modify bioactive release by up to one order of magnitude. Furthermore irradiated SNP loaded PLG exhibited microbial inhibition when compared to irradiated, non-SNP loaded PLG. It is proposed that the use of an antimicrobial in conjunction with irradiation treatment has potential benefits for applications where antimicrobial efficacy is required.