Biomedical Engineering Reference
In-Depth Information
3.1
Chapter 3.1
Properties of materials
Buddy D. Ratner, Allan Hoffman, Frederick J. Schoen,
and Jack E. Lemons
have been determined. The content of the various
sections is intended to be relatively basic.
3.1.1 Introduction
Jack E. Lemons
3.1.2 Bulk properties
of materials
The bulk and surface properties of biomaterials used for
medical implants have been shown to directly influence, and
in some cases, control the dynamic interactions that take
place at the tissue-implant interface. These interactions are
included in the concept of compatibility, which should be
viewed as a two-way process between the implanted mate-
rials and the host environment that is ongoing throughout
the
in vivo
lifetime of the device.
It is critical to recognize that synthetic materials have
specific bulk and surface properties or characteristics.
These characteristics must be known prior to any medical
application, but alsomust be known in terms of changes that
may take place over time
in vivo
. That is, changes with time
must be anticipated at the outset and accounted for through
selection of biomaterials and/or design of the device.
Information related to basic properties is available
fromnational and international standards, plus handbooks
and professional journals of various types. However, this
information must be evaluated within the context of the
intended biomedical use, since applications and host
tissue responses are quite specific for given areas, e.g., car-
diovascular (flowing blood contact), orthopedic (functional
load bearing), and dental (percutaneous).
In the following, we discuss basic information about
bulk and surface properties of biomaterials based on
metallic, polymeric, and ceramic substrates, the finite
element (FE) modeling and analyses, and the role(s) of
water and surface interaction with biomaterials. Also in-
cluded are details about how some of these characteristics
Francis W. Cooke
Introduction: the solid state
Solids are distinguished from the other states of matter
(liquids and gases) by the fact that their constituent
atoms are held together by strong interatomic forces
(
Pauling, 1960
). The electronic and atomic structures,
and almost all the physical properties, of solids depend
on the nature and strength of the interatomic bonds. For
a full account of the nature of these bonds one would
have to resort to the modern theory of quantum me-
chanics. However, the mathematical complexities of this
theory are much beyond the scope of this chapter and we
will instead content ourselves with the earlier, classical
model, which is still very adequate. According to the
classical theory there are three different types of strong
or primary interatomic bonds:
ionic, covalent, and
metallic.
Ionic bonding
In the ionic bond, electron donor (metallic) atoms transfer
one or more electrons to an electron acceptor (non-
metallic) atom. The two atoms then become a cation (e.g.,
