Biomedical Engineering Reference
In-Depth Information
9
Soft Tissue Replacements
9.1 Blood-Interfacing Implants .............................................................
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Introduction • Heart Valve Prostheses • TAHs or Ventricular
Assist Devices • Vascular Prostheses • Conclusions
Defining Terms ...........................................................................................
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References ....................................................................................................
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9.2 Nonblood-Interfacing Implants for Soft Tissues .......................
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Sutures and Allied Augmentation Devices • Percutaneous
and Skin Implants • Maxillofacial Implants • Ear and
Eye Implants • Space-Filling Implants • Fluid Transfer
Implants • Technologies of Emerging Interest
References ....................................................................................................
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Further Information ...................................................................................
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K.B. Chandran
University of Iowa
K.J.L. Burg
Clemson University
S.W. Shalaby
*
Poly-Med, Inc.
9.1 Blood-Interfacing Implants
9.1.1 Introduction
Blood comes in contact with foreign materials for a short term in extracorporeal devices such as
dialys-
ers
,
blood oxygenators
, ventricular assist devices, and
catheters
. Long-term vascular implants include
heart valve prostheses,
vascular grafts.
, and
cardiac pacemakers
among others. In this section, we will
be concerned with the development of biomaterials for long-term implants, specifically for heart valve
prostheses, total artificial heart (TAH), and vascular grafts. The primary requirements for biomateri-
als for long-term implants are biocompatibility, nontoxicity, and durability. Furthermore, the material
should be nonirritating to the tissue, be resistant to
platelet
and
thrombus
deposition, be nondegrad-
able in the physiological environment, and neither absorb blood constituents nor release foreign sub-
stances into the bloodstream (Shim and Lenker, 1988). In addition, design considerations include that
the implant should mimic the function of the organ that it replaces without interfering with the sur-
rounding anatomical structures and must be of suitable size and weight. The biomaterials chosen must
be easily available, inexpensive, easily machinable, sterilizable, and have a long storage life. The selec-
tion of material will also be dictated by the strength requirement for the implant being made. As an
example, an artificial heart valve prosthesis is required to open and close on an average once every sec-
ond. The biomaterial chosen must be such that the valve is durable and will not fail under
fatigue stress
after implantation in a patient. As sophisticated measurement techniques and detailed computational
analyses become available with the advent of supercomputers, knowledge on the complex dynamics of
the functioning of the implants is increasing. Improvements in design based on such knowledge and
improvements in selection and manufacture of biomaterials will minimize problems associated with
*
This chapter is dedicated to the memory of Dr. Shalaby W. Shalaby.
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