A study assessing the viability of using Fused Filament Fabrication (FFF) Additive Manufacturing (AM) technology to manufacture customised Class I medical devices

Parry, Elen J. (2023) A study assessing the viability of using Fused Filament Fabrication (FFF) Additive Manufacturing (AM) technology to manufacture customised Class I medical devices. Doctoral thesis (PhD), Manchester Metropolitan University.

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Abstract

Additive manufacturing (AM) is becoming an increasingly common manufacturing method for medical devices due to the benefits of advanced customisation, improved fit and opportunities for innovation. However, many AM medical devices remain inaccessible due to high costs of hardware and consumables, and the large infrastructural requirements required for operation. Fused filament fabrication (FFF) is a highly accessible AM technique due to its open-source nature, which has led to an extensive market of affordable desktop 3D printers. In this work FFF has been demonstrated as a potentially viable technique to fabricate low-risk medical devices in two case studies presented in this thesis: a customised daily living aid and a range of medical devices in response to the COVID-19 pandemic. Although the potential of the technology has been demonstrated, research around the practical suitability of FFF for medical applications remained limited, with much of the research in the field focussing on proof-of-concept applications, which did not explore the necessary requirements for the integration of the technology into daily clinical practices. This thesis investigates the fundamental requirements of the FFF AM technique for it to be used for Class I medical device applications in three identified use cases: non-specialist, research and industrial use. In keeping with the ambition for FFF to provide accessible solutions, mid-range hardware aimed at professional printing applications was selected to carry out this work, which encompasses the activities present in each of the three identified use cases. A methodology was presented to determine the repeatability and reproducibility of FFF across three potential use cases, which revealed varying process capability between the X-, Y- and Z- printing directions for individual machines, and significant variation between multiple machines of the same make and model. The repeatability and reproducibility of the FFF technique was identified as a key limitation for the widespread adoption of FFF technology for specialist and industrial use. The smallest tolerance achieved from a professional desktop FFF printer was 0.3mm in both the X- and Y- directions, and 0.4mm in the Z-direction. Additional variable factors were studied, including the condition of filament with respect to its storage environment and duration of storage, the influence of different colours and pigments present in filament and the use of an air management add-on unit intended to enhance the hardware. The glass transition temperature of Tough PLA remained largely unaffected from variable storage conditions, which when submerged in water decreased by around 1.4ºC from that of ambiently stored filament. The mechanical properties of printed parts were influenced by filament colour, with white filament producing parts with increased elongation and tensile strength than other colours studied. Dimensional accuracy in the Z-printing direction was affected by air management, where samples produced with air management were measured higher than the nominal value, and without air management lower than the nominal value. This thesis is the first known work to explore the suitability of FFF technology for Class I medical devices, from the perspective of both specialist and non-specialist users. The key barriers to widespread adoption were identified as the repeatability and reproducibility of the technique, and the influence of variable factors on the process and part performance. The exploration of these continually referenced medical device regulations, whilst consideration was given to how the experimental work can be applied to real-world Class I medical device manufacturing applications.