Biomedical Engineering Reference
In-Depth Information
• analytical calculations, for example, to calculate the likely stress or deflection in
the implant.
A number of techniques, such as brainstorming and TRIZ (theory of inventive
problem solving) exist to help with the development of design concepts. The
developed range of concepts for a joint replacement implant can then be rated by
the design team to determine the most suitable concept to develop into a final
design. This may involve rating each concept against known criteria, such as cost
or ease of manufacture, or against a known ''gold standard'' joint replacement
implant [58]. During the decision process to determine which concept to develop
into the final design, it is important to not just rely on the opinion of the engineers.
It is vital that orthopedic surgeons and sales personnel are involved. Surgeons have
to implant the joint replacement devices, while the sales people have to actually sell
them.
Once the concept to be developed has been decided, the process moves on to the
detail of the design stage where the concept design is worked up into a full design
for a joint replacement implant. This stage will include
•
producing models using computer-aided design software - this helps to visualize
the implants and to see how the instruments will interact with it;
•
specification of appropriate materials;
•
drafting engineering drawings - this helps to determine if any parts of the design
can be simplified;
•
consultation with manufacturers - this helps to determine if the device can
be manufactured at a reasonable cost and whether any special manufacturing
processes are likely to be required.
8.5.4
Verification
During the design stage, it is essential to verify that the proposed design of joint
replacement implant meets the design requirements. Verification is essentially
asking the question: ''are we building the thing right?'' [59]. Verification of designs
of joint replacement implants can include
•
finite element analysis
•
rapid prototyping
•
risk analysis.
Finite element analysis is a computational technique that can be used to simulate
the loading conditions in the human body to verify if a joint replacement implant
has sufficient strength and stiffness to withstand the expected loading conditions
[60]. The technique can also be used to predict the wear of joint replacement
implants [61]. However, finite element analysis must not be used on its own;
the models must be validated against known results, whether they be analytical
solutions or mechanical testing.
