Page 380 - Biomedical Engineering and Design Handbook Volume 1, Fundamentals

CHAPTER 15

BIOCERAMICS

David H. Kohn
University of Michigan, Ann Arbor, Michigan

15.1 INTRODUCTION 357 15.5 SUMMARY 377
15.2 BIOINERT CERAMICS 359 ACKNOWLEDGMENTS 377
15.3 BIOACTIVE CERAMICS 363 REFERENCES 377
15.4 CERAMICS FOR TISSUE ENGINEERING
AND BIOLOGICAL THERAPIES 370

15.1 INTRODUCTION

The clinical goal when using ceramic biomaterials, as is the case with any biomaterial, is to replace
lost tissue or organ structure and/or function. The rationale for using ceramics in medicine and den-
tistry was initially based upon the relative biological inertness of ceramic materials compared to
metals. However, in the past 25 years, this emphasis has shifted more toward the use of bioactive
ceramics, materials that elicit normal tissue formation and also form an intimate bond with bone tis-
sue through partial dissolution of the material surface. In the last decade, bioceramics have also been
utilized in conjunction with more biological therapies. In other words, the ceramic, usually resorbable,
facilitates the delivery and function of a biological agent (i.e., cells, proteins, and/or genes), with an
end-goal of eventually regenerating a full volume of functional tissue.
Ceramic biomaterials are processed to yield one of four types of surfaces and associated
mechanisms of tissue attachment (Kohn and Ducheyne, 1992): (1) fully dense, relatively inert
crystalline ceramics that attach to tissue by either a press fit, tissue growth onto a roughened sur-
face, or via a grouting agent; (2) porous, relatively inert ceramics, where tissue grows into the
pores, creating a mechanical attachment between the implant and tissue; (3) fully dense, surface
reactive ceramics, which attach to tissue via a chemical bond; and (4) resorbable ceramics that
integrate with tissue and eventually are replaced by new or existing host tissue. Ceramics may
therefore be classified by their macroscopic surface characteristics (smooth, fully dense, rough-
ened, or porous) or their chemical stability (inert, surface reactive, or bulk reactive/resorbable). The
integration of biological (i.e., inductive) agents with ceramics further expands the clinical potential
of these materials.
Relatively inert ceramics elicit minimal tissue response and lead to a thin layer of fibrous tissue
adjacent to the ceramic surface. Surface-active ceramics are partially soluble, resulting in ion
exchange and the potential to lead a direct chemical bond with tissue. Bulk bioactive ceramics are
fully resorbable, have greater solubility than surface-active ceramics, and may ultimately be
replaced by an equivalent volume of regenerated tissue. The relative level of bioactivity mediates
the thickness of the interfacial zone between the biomaterial surface and host tissue (Fig. 15.1).

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