Biomedical Engineering Reference
In-Depth Information
2.3 Surface Modification
Material selection is crucial for any application since the performance of a
manufactured part will reflect the properties of the selected material.
Finding a material with optimum bulk as well as optimum surface prop-
erties for any given application is rare and biomaterials are no exception.
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Bulk alteration of a material is not generally preferred since it is expensive,
time consuming and will impose limitations for the use of the material.
Surface modification of a solid material at either atomic or molecular level is
therefore performed to achieve the required surface properties without
altering the key bulk properties of the material. Surface modification has
wide applications including adhesive bonding enhancement, modifying
wetting and non-wetting characteristics, creating micro-porous structures,
altering the grain size and distribution, generating uniform 3D structures on
the surface and optimisation of surface chemistries of an engineered part.
Although surface modification is carried out in a number of engineering
disciplines, its application in the biomedical field is unique since it directly
affects the quality of life of the patient.
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2.3.1 Issues with Current Surface Modification Techniques
Morphological, physico-chemical and biological modifications are the
common types of surface modifications generally performed to improve the
quality and properties of implants. However, they all have limitations. In
most cases, a single surface modification technique is not enough to achieve
the desired surface property and hence two or more surface modifications
are performed to achieve better biological properties. For example, Kim et al.
reported good adherence and spreading of human osteoblast cells for
sand-blasted and acid-etched surfaces.
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Though the use of two techniques
provided improved results in terms of cellular attachments, the use of two
or more techniques to modify the surface can be time consuming and
expensive.
In recent years, surface modifications have been performed not just to
improve the surface finish but also to make the implant biocompatible and a
drug carrier. Bacterial infections due to implants are one of the main risk
factors in orthopaedic surgery leading to surgical removal of implants.
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Treatment measures available for bacterial infections include systemic,
antibiotic-loaded cements and antimicrobial coatings.
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However, the re-
lease of drugs in a systemic therapy prevails as one of the major problems
when conventional coating techniques are used. Slower release of antibiotics
for a longer period of time is a potential cause of antibiotic resistance in the
human body.
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For example, in drug eluting stents (DES), to reduce the
restenosis rate, the stents are coated with polymers containing a drug using
simple techniques including dip/spray/spin coating or solvent casting.
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After implantation, the DES is expanded to conform to the vessel wall.
During this expansion, fractures, peeling of the polymeric coating and
.
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