Additive Manufacturing and Surface Modification of Biomaterials using Selfassembled Monolayers - Biointerfaces: Where Material Meets Biology - page 33

has been researched widely in recent years. 20,21 Optimisation methods allow
the prediction of areas of fracture/failure of implants at specific loading
conditions. Thus, implants can be designed to withstand the required load
conditions with less material usage.
Although the mechanical properties of the bulk material, implant design
and manufacturing process are considered to be the major factors deter-
mining implant fracture, corrosion of implants within the biological en-
vironment is also a crucial factor. 3 Corrosion of implants is one of the most
challenging problems after implantation of dental, cardiovascular, maxillo-
facial and load-bearing implants such as hip and knee replacements. 3 Im-
plants corrode within the biological environment due to electrochemical
attack by the electrolytes present in the hostile environment. Leaching of
metal ions from the implant surface due to corrosion will lead to erosion.
The rate of corrosion is accelerated by increased surface area and loss of
protective oxide, later leading to fractures. Also, leaching of metal ions has
been observed to induce acute and chronic effects. Release of nickel was
observed to affect the skin; cobalt was observed to cause anaemia which
inhibits the absorption of iron into the bloodstream; chromium was ob-
served to cause ulcers and disturb the central nervous system; aluminium
was reported to cause epileptic effects and Alzheimer's disease and leaching
of vanadium in its elemental state was observed to be toxic. 22 Hence, cor-
rosion products formed as a result of implant-host interaction have a
significant effect on the long-term stability of

d n 3 r 4 n g | 0

the prosthesis and its

biocompatibility. 23
Biocompatibility, a requirement for all biomedical implants, is the prop-
erty of a material to be compatible with the tissues in the human body by not
producing a toxic, injurious or immunological response. Chronic inflam-
mations, lesions and scarring are some of the adverse reactions that may
take place in the site if the implant is not biocompatible. To achieve better
biocompatibility, two routes are often employed: (1) using biocompatible
materials; and (2) fabrication of implants using off-the-shelf materials with
the application of a suitable biocompatible layer. 6
Contamination of implants by harmful micro-organisms cause severe in-
fections and often forces replacement of the medical device. By entering the
host through contaminated surfaces, bacteria multiply in the host environ-
ment and interfere with the host defence system leading to host tissue
damage and inflammation. 24 Staphylococci species, including Staphylo-
coccus aureus and Staphylococcus epidermidis are the more common cause of
implant-associated infections. 25 Contamination of implants such as stents,
dental, hip and knee implants by harmful microbes has been widely
reported. 26-29

.

2.1.2 Scope of this Chapter
The key to addressing these challenges is to optimise the implant-host
interface. It is envisaged that customised implant designs, due to their