Page 362 - Biomedical Engineering and Design Handbook Volume 1, Fundamentals

CHAPTER 14

BIOMEDICAL COMPOSITES

Arif Iftekhar
University of Minnesota, Minneapolis

14.1 INTRODUCTION 339 14.6 FRACTURE AND FATIGUE
14.2 CLASSIFICATION 341 FAILURE 348
14.3 CONSTITUENTS 341 14.7 BIOLOGIC RESPONSE 350
14.4 PROCESSING 345 14.8 BIOMEDICAL APPLICATIONS 351
14.5 PHYSICAL PROPERTIES 345 REFERENCES 354

14.1 INTRODUCTION

A common debate about the definition of composite materials among composite engineers and
materials scientists continues to this day. More recently, biomedical engineers have used the term
composite prolifically for newly developed biomaterials, and it might be argued that not every usage
of the term composite for a biomaterial would satisfy the traditional composite engineer, who is used
to thinking in terms of fibers, matrices, and laminates. That said, defining composites a certain way
in this chapter is not meant to preclude its use outside this definition.
The difficulty lies, on the one hand, in the depth of the material to which the definition refers.
Practically everything is a composite material in some sense, except for pure elements. For example,
a common piece of metal is a composite (polycrystal) of many grains (or single crystals). Thus
alloys, ceramics, steels, etc., would be considered composites if the definition refers to the microstruc-
ture. However, if it is the macrostructure that concerns us, then we get the traditional treatment of
composites as a materials system of different macroconstituents. 1
On the other hand, there is also a question in this definition regarding how these macrocon-
stituents are brought together and for what purpose. For instance, thin coatings on a material do not
make it a typical composite, and the same could be said about adding resin-extending fillers to
plastics, although the constituents exist at the macrostructure. Furthermore, a structure that is
assembled with components made of different materials does not qualify it to be a composite. Thus
a pacemaker lead that has a metallic core and a polymeric sheath would not be considered a composite
in the strict sense, whereas a catheter tube polymer reinforced with embedded braided metal wires
would. In addition, foams and porous coatings on materials will not be considered composites in
this discussion.
The following is an operational definition for the purpose of this chapter:
A composite material consists of two or more physically and/or chemically distinct, suitably
arranged or distributed materials with an interface separating them. It has characteristics that are
not depicted by any of the components in isolation, these specific characteristics being the purpose
of combining the materials.

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