Minimise thermo-mechanical batch variations when processing medical grade lactide based copolymers in additive manufacturing. (November 2020)

• Record Type: Journal Article
• Authors: Ahlinder, Astrid; Charlon, Sebastien; Fuoco, Tiziana; Soulestin, Jérémie; Finne-Wistrand, Anna
• Is Part Of: Polymer degradation and stability. Volume 181(2020)
• Publication Date: 2020-11
• Subjects: Additive manufacturing -- polyester -- L-lactide -- e-caprolactone -- trimethylene carbonate -- medical device -- Freeforming -- polymer degradation; Polymers -- Deterioration -- Periodicals; Stabilizing agents -- Periodicals; Polymères -- Dégradation -- Périodiques; Stabilisants -- Périodiques; 668.9
• DOI: 10.1016/j.polymdegradstab.2020.109372
• Languages: English
• ISSNs: 0141-3910

Abstract

Highlights: Degradation and variations in polymer properties within one batch cycle using Arburg Plastic Freeforming was elucidated for two medical grade aliphatic copolyesters, the poly(L-lactide-co-ε−caprolactone) and the poly(L-lactide-co-trimethylene carbonate). The variation of the mechanical properties during one batch cycle increased drastically when poly(L-lactide-co-trimethylene carbonate) was processed at or above 220°C, whilst the properties of poly(L-lactide-co-ε−caprolactone) were more stable. The viscoelastic properties, rheological fingerprint, in combination with the understanding of degradation and variation in mechanical properties were used to identify a stable processing window to minimise the variations. Abstract: Additive manufacturing is suitable for producing complex geometries; however, variation in thermo-mechanical properties is observed during one batch cycle when degradable aliphatic polyesters are used in melt extrusion-based methods. This is one important reason for why additive manufacturing has not yet been fully utilised to produce degradable medical implants. Herein, the internal variation has been minimised during one batch cycle by assessing the effect of different processing parameters when using commercially available medical grade copolymers. To minimise the molar mass, thermal and mechanical variation within one batch cycle, the rheological fingerprint of the commercially available medical grade poly(L-lactide-co-ε- caprolactone) and poly(L-lactide-co-trimethylene carbonate) has been correlated to the process parameters of the ARBURG Plastic Freeforming. An increase in the temperature up to 220°C and the associated increase in pressure are beneficial for the viscoelastic and thermally stable poly(L-lactide-co-ε-caprolactone). In contrast, a temperature below 220°C should be used for the poly(L-lactide-co-trimethylene carbonate) to reduce the variation in strain at break during one batch cycle. The residence time is decreased through the increase of the discharge parameter. An increase in temperature is however required to reduce the viscosity of the polymer and allow the pressure to stay within the machine limitations at higher discharge parameters. The results are highly relevant to the development of additive manufacturing for the production of degradable medical devices with identical properties. In fact, Food and Drug Administration guidelines for additive manufacturing of medical implants specify the need to control changes in for example material properties during the process.