Biomedical Engineering Reference
In-Depth Information
introduced for biomedical applications. With recent advancements in
human healthcare systems and with the availability of improved diagnostic
tools, biomedical implants have found applications in almost all body
functions. It is expected that virtually every individual will have contact with
biomaterials and/or biomedical implants at some point of time during his or
her life. This contact may occur in several ways including (1) permanent
implantation (such as heart valves and total joint replacement); (2) long-term
applications (such as contact lenses, dental prostheses and fracture fixation
devices); and (3) transient applications (including needles for vaccination,
wound healing dressings/sutures and cardiac assist systems).
Biomedical implants range from simple wires and screws for fracture plate
fixation to joint prostheses for hips, knees, shoulders and so on. Depending
on the requirement and load conditions, implants are made of natural and/
or synthetic materials such as polymers, metals, ceramics or composites. For
example, metals are generally preferred for load-bearing implants and in-
ternal fixation devices whereas ceramics are preferred for skeletal and hard
tissue repair.
4
Polymers are preferred in applications where elasticity of the
material would be an advantage.
Biomedical implants have significantly improved the quality of life for
countless people; however, they still impose significant challenges on cur-
rent manufacturing processes due to their need to function within a rela-
tively harsh biological environment.
2
Customisation, fabrication of complex
geometries and the reduction of post-implant complications including im-
plant migration, fracture and poor biocompatibility are major challenges to
overcome.
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2.1.1 Issues with Current Biomedical Implants
2.1.1.1 Customisation and Fabrication of Complex Geometries
Most off-the-shelf implants are available in a selection of dimensions to
meet the patient requirement; however, they are not customised. Customi-
sation is key in conditions such as where the patient's anatomy deviates
from the standard sizes or is affected by individual defects. The primary
objective of customisation is to fit the unique anatomy of a particular pa-
tient, especially where the implant is not fixed. Personalised hearing aid
shells for 'in-the-ear' and 'in-the-canal' devices are one example of a cus-
tomised implant that has achieved superior fit compared to conventionally
manufactured aids, increasing both comfort and device functionality.
5
Orthopaedic implants usually perform better when they match exactly the
anatomy of the patient, through the distribution and normalisation of the
stresses incurred in the remaining skeletal system and reduction of stress
shielding, migration and failure.
6
Migration of an implant is the movement of the implant from the actual or
surgically positioned area and is a mechanically triggered rather than a
biological process.
7
Forces higher than expected may deteriorate fixation
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