Med-Tech Innovation
degradation. The nature of this degradation in terms of surface erosion can be related to the energy used to deliver the surface specific dose.
As expected, mechanical failure of the sample was found to be dependent on energy and dose of e-beam irradiation with cracks initiating from the irradiated edge and propagating towards the sample centre. Moreover, the extent to which
Figure 1: Calculated O1s/C1s ratios for all sample types
mechanical degradation was observed is synonymous with the energy being delivered by the beam.
XPS analysis of irradiated and non-irradiated PLLA sample surfaces indicated the presence of all expected elements, namely oxygen and carbon. The calculated O1s/C1s ratios are increased for all irradiated polymer samples compared with the non-irradiated controls. Raman data showed all spectral lines characteristic of the polymers studied (Figure 1). Spectral data collected for irradiated PLLA samples showed subtle differences in the size and resolution of peaks associated with νC-COO stretching vibrations indicative of changes in PLLA chain length. Accelerated degradation studies showed increasing mass loss with increased e-beam energy and surface dose. SEM examination of degraded surfaces revealed increased levels of surface cracking for irradiated surfaces compared with the non-irradiated control samples.
Conclusion
E-beam irradiation is a major underpinning technology that can be used to achieve predictable and controlled degradation of bioresorbable polymers. Furthermore, 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. This work has illustrated the potential of e-beam technology in achieving a depth-dependent degradation rate and ultimately improved bioresorbable medical devices.
References
1. A.P. Gupta and V. Kumar, “New Emerging Trends in Synthetic Biodegradable Polymers – Polylactide: A Critique,” European Polymer Journal, 43, 10, 4053–4074 (2007).
2. W. Heidemann et al., “Degradation of Poly(D,L)lactide Implants With or Without Addition of Calciumphosphates In Vivo,” Biomaterials, 22, 2371–2381 (2001).
3. M-L Cairns et al., “Through-Thickness Control of Polymer Bioresoption via Electron Beam Irradiation,” Acta Biomaterialia, 7, 2, 548–557 (2011).
The academic investigators are Dr Marie-Louise Cairns, Professor John Orr and Dr Fraser Buchanan of the School of Mechanical and Aerospace Engineering, Queen’s University Belfast; and
Dr Glen Dickson of School of Medicine, Dentistry and Biomedical Sciences, Queen’s University Belfast, Belfast, UK.
The industry collaborators are David Farrar, Technology Manager Biomaterials at Smith & Nephew, and
Arthur Dumba, UK Quality Manager at Isotron, Moray Road, Elgin Industrial Estate, Swindon SN2 8XS, UK, tel. +44 (0)8456 889 977, e-mail:
arthur.dumba@isotron.com,
www.isotron.com
www.med-techinnovation.com November/December 2011 ¦ 25
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