Biomedical Engineering Reference
In-Depth Information
10.2 INTRODUCTION MATERIALS FOR HIP IMPLANTS
Some 30 years ago, a revolution in medical care began with the successful replace-
ment of tissues. Two alternatives are possible, transplantation or implantation.
Transplantation belongs to the realm of surgery. Implantation involves the
replacement of tissues by the development or modifi cation of man-made materi-
als to interface with living host tissue, that is, implants made of biomaterials.
Material scientists have investigated metals, polymers, ceramics, as well as com-
posites, as biomaterials for hard and soft tissues. Important issues in the develop-
ment of biomaterials are the interfacial stability with host tissues, appropriate
properties as close as possible to bone, and a minimum of wear debris generation.
Ceramics used for repair, reconstruction, and replacement of human tissue
are called bioceramics. When any artifi cial material is implanted into the body, it
will cause some reaction with the host tissue. Bioceramics exhibit four possible
tissue /implant interactions [Hench and Ethridge, 1982]: toxic, when the tissue
dies due to chemical leaching from the ceramic; biologically inert, when tissues
form a non-adherent fi brous capsule around the implant surface; bioactive, in
case the tissues chemically bond with the implant surface; and dissolution of the
implant, when the implant surface dissolves allowing tissues to refi ll the space
previously occupied by the implant.
Bioceramics have become a diverse class of biomaterials, presently including
three basic types: bioinert high strength ceramics; bioactive ceramics which form
direct chemical bonds with bone or even with soft tissue of a living organism; and
bioresorbable ceramics that actively participate in the metabolic processes of an
organism [Thamaraiselvi and Rajeswari, 2004]. Alumina (Al 2 O 3 ), zirconia (ZrO 2 )
and carbon are bioinert. Bioactive glass and calcium phosphate ceramics such
as hydroxyapatite are bioactive and bioresorbable depending on their composi-
tion and structure. An overview of the applications for bioceramics is given in
Table 10.1 .
TABLE 10.1. Overview of Applications for Bioceramics
Bioceramic
Function
Tissue reaction
Zirconia
Artifi cial total hip, knee, bone screws and
plates, dental crowns and bridges
Bioinert
Alumina
Artifi cial total hip, shoulder, elbow, wrist, bone
screws, porous coatings for femoral stems
Bioinert
Carbon
Coatings on heart valves, blood vessel grafts,
surfaces in dentistry
Bioinert
Calcium phosphates
Drug delivery, bone substitute, coatings for
metal implants, stems, ocular implants
Bioactive,
Bioresorbable
Bioactive glass
Bone cement fi ller, bioactive coating on
implants
Bioactive,
Bioresorbable
TiN
Coating on implants like artifi cial hip, dental
and shoulder implants
Bioactive
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