Med-Tech Innovation Materials
Table I: Guidance on materials factors for designers and failure investigation of medical devices Polymer materials history
Batch-to-batch and other variations leading to problems/ failures
Molecular weight variation
Composition variation for copolymers
Supplied materials characterisation, including raw materials made from polymerisation, post compounding process to make pellets to be used for medical device manufacturers
Crystal structures, including short and long range crystals and crystallinity for semi-crystalline polymers
Viscoelastic property variation
Spherulite crystal phase variation
Nano/micro structure variation
Process ability variation
Changes in production and process, equipment (maintenance schedule, inspection, adjustment), manufacturing material and personnel
Product failure investigation: here product means any products from start to the end of a process. This is because a medical device can fail at any stage of the manufacturing process; each stage can potentially cause polymer structure changes and therefore potentially lead to a defect(s) causing finished device failure before shipping and afterwards.
Material changes during manufacturing: Variation can lead to changes in nano/microstructure and mechanical properties and therefore affect the performance of the medical device
Tests/methods for materials characterisation
Gel permeation chromatography
Fourier transform infrared spectroscopy (FTIR)
Wide/small angle X-ray scattering (WAXS/SAXS)
Differential scanning calorimeter (DSC)
Dynamic mechanical thermal analysis (DMTA)
Cross polarisation optical microscope
Scanning electron microscopy/ Transmission electron microscopy (SEM/TEM)
Rheology: Cone plate or capillary rheometer
Update SOPs, equipment inspection, measuring and test, training record
Surface analysis
Important parameters/factors to know
Number average (Mn); weight average (Mw)
Chemical finger print
Nano crystal cell dimension; long range lamellae
Glass transition temperature (Tg) Melting and crystallisation temperatures (Tm/Tc)
Viscoelastic properties and dynamic modulus as a function of temperatures and Tg
Spherulite crystal structure
Different nano/micro structure/ phases arrangement within polymer matrix
Process ability: Viscosity variation as function of shear rates and/or temperature
What, why, when changes are made: Calibrations, calibration standards, calibration records
X-ray photoelectron spectroscopy (XPS): Quantitative chemical mapping of materials
Secondary ion mass spectrometry (SIMS) and Time-of-flight surface mass spectrometry (ToFSIMS)
Surface topography: 3D non-contact profiling
Bulk mechanical property analysis, including films and fibres and other geometries
SEM and 3D SEM analysis Mechanical test such as tensile deformation to failure to evaluate basic mechanical properties
Fracture mechanics to evaluate fracture toughness
Viscoelastic properties: Creep/stress relaxation variation as function of time and temperature
Internal nano and microstructure analysis
WAXS/SAXS to evaluate crystallinity and long range changes
SEM/TEM: Nano/micro structure/ phases changes caused by variation of manufacturing
Thermal analysis
DSC for evaluation of manufacturing caused variation, including glass transition temperature and melting temperature for semi-crystalline polymers
DMTA for evaluation of manufacturing caused variation of viscoelastic and mechanical properties as function of temperature
Continued...
www.med-techinnovation.com November/December 2011 ¦ 31
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54