MODELLING: BIOLOGY ➤
Looking inside the manufacturing process Besides studying what goes on inside the body, models can also help improve those things we put into our bodies. For instance, many soft- tissue medical implants are required only for several months or years before the body’s own tissue regenerates and heals. At this point it’s sometimes desirable to remove them; however, this isn’t always possible. Such implants have traditionally been made of fabrics or biotextiles, but engineers at Continuum Blue are developing soft-tissue implants made of biodegradable hyper-elastic elastomers that, when they’ve served their purpose, dissolve naturally within the body to eliminate the need for revision surgery to remove them. There’s no single elastomeric material up to
this job, so researchers have developed a novel method of injecting two slow-curing polymers into a mould to create a one-piece implant with the desired anisotropic hyper-elastic properties. Continuum Blue was contracted by a manufacturer of implants to refine the modelling process. The first prototypes, explains R&D director Dr Mark Yeoman, involved two
A fabric-based LARS (ligament replacement and augmentation system) implant shown in a shoulder joint. Note
the two screws in the bone that anchor the fixation holes at one end of the implant. Using modelling software from Comsol, Continuum Blue is working on a multi-elastomeric version of this implant that biodegrades once the joint has been healed
elastomers that flow into the mould in the right concentration, at the right sequence, at the right speed, and under the right conditions. Each end of the moulded product consists of 100 per cent of one of the elastomers, and the regions in between have a continuous mix of the two. Engineers must control the point of injection as well as the temperatures of the injected polymers, the overall mould, and the faces of the mould. Other aspects that must be controlled are when the polymer enters the mould and their combined volumes. Determining the proper parameters for
all of these variables is far from easy. In fact, when developing the first implant of this type, Continuum Blue’s engineers encountered a
manufacturing problem, but couldn’t identify the cause in the moulding process. Then they turned to simulation software, Comsol Multiphysics, to provide more insight into the process. The model, consisting of about 50,000 finite elements and almost 300,000 degrees of freedom, solves in 18 hours on a 2.8GHz Intel Core 2 quad processor with 8GB of memory.
‘It’s now possible for them to investigate multiple mould variations in a reasonable time and cost’
With the model, it’s now possible for them
to investigate multiple mould variations in a reasonable time and cost. They estimate that a single mould redesign and trial run with the model takes roughly 1.5 days and costs approximately £850. In contrast, to do a physical sample run, where a specialised silicone mould costs approximately £3,000, the estimated total costs are almost £9,000, and the time to get the redesigned silicone mould is around three to four weeks.
ILABORATORY
NFORMATICS GUIDE 2011
ILABORATORY
NFORMATICS GUIDE 2011
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