Page 406 - Biomedical Engineering and Design Handbook Volume 1, Fundamentals

CHAPTER 16

CARDIOVASCULAR

BIOMATERIALS

Roger W. Snyder
Wave CV, Inc., New Braunfels, Texas

Michael N. Helmus
Medical Devices, Drug Delivery, and Nanotechnology, Worcester,
Massachusetts

16.1 INTRODUCTION 383
16.2 MATERIALS 386
16.3 TESTING 389
16.4 MATERIAL PROCESSING AND
DEVICE DESIGN 393
REFERENCES 394

16.1 INTRODUCTION

Numerous definitions for biomaterials have been proposed. One of the more inclusive is “any sub-
stance (other than a drug) or combination of substances synthetic or natural in origin, which can be
used for any period of time, as a whole or part of a system which treats, augments, or replaces tissue,
organ, or function of the body,” proposed by a Biomaterials Consensus Committee meeting at the
1
NIH. This definition must be extended because biomaterials are currently being utilized as drug
delivery coatings and scaffolds for tissue-engineered tissue and organs. Coronary stents are available
that use coatings to release bioactive agents that prevent hyperplastic reactions (excessive tissue
formation). Completely resorbable scaffolds for tissue-engineered devices (hybrids of synthetic or
biologic scaffolds and living cells and tissue for vessels, heart valves, and myocardium) can result in
new organs without a trace of the original biomaterial.
The cardiovascular system consists of the heart and all the blood vessels. Cardiovascular bioma-
terials may contact blood (both arterial and venous), vascular endothelial cells, fibroblasts, and
myocardium, as well as a number of other cells and extracellular matrix that make up all biological
tissue. This chapter will consider a wide range of biomaterials that interact with the heart, blood, and
blood vessels.
Biomaterials used in the cardiovascular system are susceptible to a number of failure modes. Like
all materials, mechanical failure is possible, particularly in implants. Although typical loads are low (as
compared to orthopedic implants, for example), implant times are expected to exceed 10 years. At a
typical heart rate of 90 beats a minute, 10 years of use would require more than 470 million cycles.
Thrombosis is a unique failure mode for cardiovascular biomaterials. The resulting clots may
occlude the device or may occlude small blood vessels resulting in heart attacks, strokes, paralysis,
failures of other organs, etc. On the other hand, devices can also damage blood cells. Hemolysis can

383