Biomedical Engineering Reference
In-Depth Information
The design of implants and prostheses is a challenging process
since the targeted materials must imitate the structure and properties
of biological tissues and respond to specific requirements. These
requirements are categorized into three classes [LON 98, NAG 12]:
- compatibility: the biomaterial must be non-toxic, non-allergenic,
non-thrombogenic, non-antigenic and non-carcinogenic. The
biomaterial can be inert or tissue activating, but it must not lead to
local deleterious changes and cause little or no foreign-body reaction.
Debris generation has to be minimized;
- mechanical and physical properties: the biomaterial should
possess optimized properties depending on the application, such as
elasticity, yield stress, ductility, toughness, ultimate strength, fatigue
strength, hardness, wear resistance and porosity. Moreover, the
biomaterial must resist to mechanical, biochemical and chemical
constraints induced by the human body;
- manufacturing: the medical device should be relatively easy to
fabricate with a high reproducibility and at reduced production costs.
The fabrication process must keep the quality of the raw materials and
give an excellent surface finishing or texture. The final material must
be safely and efficiently sterilized.
Above all, the selection of the material itself is the main factor to
form the medical device. All materials are constituted of atoms that
are bonded together by interactions and all material properties may be
attributed to the structural features on the atomic/molecular level
[PAR 07]. In metals, metallic atoms are closely packed in a crystal
structure and atoms are held together through a non-directional strong
metallic bond which is produced by the electrostatic interactions
between free electrons and metallic cations. This property provides the
ability of metals to easily transmit electricity and undergo plastic
deformation [DAV 03]. Ceramics are divided into two different
groups based on the interactions between atoms. In ceramics like
diamond and graphite, atoms are arranged in a crystal structure and
share their valence electrons to form a covalent bond which is
directional and strong. In ceramics containing metallic and non-
metallic atoms like oxide, the solid structure is maintained by strong
directional ionic bonds. This bond is produced by electron exchanges
