Additive Manufacturing and Surface Modification of Biomaterials using Selfassembled Monolayers - Biointerfaces: Where Material Meets Biology - page 32

and cause implant migration. Migration of an implant to a more harmful
anatomical space can sometimes be life threatening. Implant migration has
been reported for a number of devices including total hip and knee re-
placement, dental, maxillo-facial and vascular implants. 8-12 Some of the
factors that determine the rate of migration other than mechanical forces
are implant design and fixation methods. 7 Cementing, screw retention of the
implant, expanding the implant to conform to the walls and press fitting of
the implant to the diseased/damaged area are some of the common fixation
methods. The advantages, complications and limitations of these methods
are reported extensively in literature. 13-16
Fixation of implants may sometimes be dicult depending on the site
and anatomy of the diseased/damaged part. In such cases, customisation
may render improved fixation with the patient's anatomy and may nor-
malise stresses, thus preventing implant migration. For example, cus-
tomised hip implants can be more durable, in particular for younger
patients, by improving the stability of the femoral stem, allowing load
transfer to the proximal part of the femur and restoration of normal
geometry of the hip joint. 6 However, the ability to achieve customised and
complex geometries of biomedical implants using traditional manu-
facturing methods (such as moulding, die casting and subtractive pro-
cesses) are limited and are often time consuming. 17 This is because
traditional methods have limitations in the geometries that they can pro-
duce. Moulding and die casting methods require dies or moulds to fabri-
cate the part. Hence, extra time for the manufacturing process is required
in addition to fabricating the actual part.Inaddition,itisexpensiveto
make a die or mould for a one-off design.

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2.1.1.2 Post-implant Complications
There are many reasons for the failure of an implant within the biological
environment including manufacturing, chemical, mechanical, tribological
and surgical failures. 3 The patient's health condition and the physician's
experience could also be contributing factors. A variety of biomaterials
(polymers, metals, ceramics and composites), fabrication techniques (such
as compression moulding, die casting, bar stock milling and laser cutting)
and surface modification techniques (biocompatible material coating, sur-
face polishing, drug loading etc.) have been employed to improve the
mechanical and biological properties of the implant; however, there are still
constraints in achieving this.
Even when using a biomaterial with the most superior material and bio-
logical properties, there are possibilities for the failure of an implant due to
faulty mechanical design or inappropriate application of the implant. In-
adequate mechanical properties (e.g., elastic modulus, yield strength, tensile
strength) can result in fracture leading to implant failure. 8,18,19 Fracture of
an implant mainly occurs when the implant is not capable of bearing the
load exerted on it. Optimisation of the implant designs to bear specific loads