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Chapter 9
Biocompatibility
David Williams
Chapter contents 9.1 9.2 9.3 Introduction 256 The evolution of current concepts of biocompatibility 256 The agents of biocompatibility 257
9.4 9.5 9.6 9.7
Tissue engineering scaffolds and matrices 264 General discussion of biocompatibility in tissue engineering 274 Future perspectives 276 Summary 276
Chapter objectives:
●
●
●
Tounderstand the basic concepts of biocompatibility in general To understand the evolution of conventional biomaterials on the basis of their biocompatibility To understand why the mechanisms of biocompatibility of tissue engineering scaffolds differ from those of implantable biomaterials
●
●
To appreciate the differences between scaffolds and matrices on the basis of their biocompatibilitycharacteristics To understand the evolution and potential uses of current scaffold and matrices
Edited by Van Blitterswijk, Lindahl, Thomsen, Williams, Hubbell and Cancedda.
256 Chapter 9 Biocompatibility
9.1 Introduction
One of the most widely discussed factors that controls the overall performance of a tissue engineering product is the biocompatibility of the scaffold or matrix that isused. The main problem with the understanding of this particular subject has been the fact that biocompatibility has, until now, been largely concerned with implantable devices (and the performance of the biomaterials used in their construction) within the human body, where the intention has usually been related to the long term replacement of tissues. Within the context of tissue engineering,however, the specifications of the biomaterials used as scaffolds and matrices are very different to those for long term implantable devices. The precise requirements and characteristics of their biocompatibility will also be substantially different, although this has rarely been discussed. Indeed, it is a matter of concern that the materials used for the majority of tissue engineering scaffolds andmatrices in recent years have been similar to those used for some implantable devices and drug delivery systems, largely on the basis that these materials have had prior regulatory approval with respect to such systems and have, putatively, been demonstrated to display biological safety in these other situations. The most important characteristic that distinguishes a biomaterial from any othermaterial is its ability to exist in contact with the relevant tissues, of the human body, or components of tissues, without causing an unacceptable degree of harm to those tissues or components. It has become clear that there are many ways in which materials and the components of tissues can interact such that this co-existence may be compromized, and the search for biomaterials that are able toprovide for the best performance in devices has been based upon the acquisition of knowledge and understanding about these interactions. These interactions are usually discussed in the broad context of the subject of biocompatibility. Biocompatibility is a word that is used extensively within biomaterials science, but there still exists a great deal of uncertainty about what it actually means andabout the mechanisms that are subsumed within the phenomena that collectively constitute biocompatibility. As biomaterials are being used in increasingly diverse and complex situations, with applications now involving tissue engineering, as well as the longer established implantable medical devices, invasive sensors and drug delivery systems, this uncertainty over the mechanisms of biocompatibilityis becoming a serious impediment to the development of these new techniques.
9.2 The evolution of current concepts of biocompatibility
Biocompatibility has traditionally been concerned with implantable devices that have been intended to remain within an individual for a long time. To those who were developing and using the first generation of implantable devices, during the years between 1940...
Biocompatibility
David Williams
Chapter contents 9.1 9.2 9.3 Introduction 256 The evolution of current concepts of biocompatibility 256 The agents of biocompatibility 257
9.4 9.5 9.6 9.7
Tissue engineering scaffolds and matrices 264 General discussion of biocompatibility in tissue engineering 274 Future perspectives 276 Summary 276
Chapter objectives:
●
●
●
Tounderstand the basic concepts of biocompatibility in general To understand the evolution of conventional biomaterials on the basis of their biocompatibility To understand why the mechanisms of biocompatibility of tissue engineering scaffolds differ from those of implantable biomaterials
●
●
To appreciate the differences between scaffolds and matrices on the basis of their biocompatibilitycharacteristics To understand the evolution and potential uses of current scaffold and matrices
Edited by Van Blitterswijk, Lindahl, Thomsen, Williams, Hubbell and Cancedda.
256 Chapter 9 Biocompatibility
9.1 Introduction
One of the most widely discussed factors that controls the overall performance of a tissue engineering product is the biocompatibility of the scaffold or matrix that isused. The main problem with the understanding of this particular subject has been the fact that biocompatibility has, until now, been largely concerned with implantable devices (and the performance of the biomaterials used in their construction) within the human body, where the intention has usually been related to the long term replacement of tissues. Within the context of tissue engineering,however, the specifications of the biomaterials used as scaffolds and matrices are very different to those for long term implantable devices. The precise requirements and characteristics of their biocompatibility will also be substantially different, although this has rarely been discussed. Indeed, it is a matter of concern that the materials used for the majority of tissue engineering scaffolds andmatrices in recent years have been similar to those used for some implantable devices and drug delivery systems, largely on the basis that these materials have had prior regulatory approval with respect to such systems and have, putatively, been demonstrated to display biological safety in these other situations. The most important characteristic that distinguishes a biomaterial from any othermaterial is its ability to exist in contact with the relevant tissues, of the human body, or components of tissues, without causing an unacceptable degree of harm to those tissues or components. It has become clear that there are many ways in which materials and the components of tissues can interact such that this co-existence may be compromized, and the search for biomaterials that are able toprovide for the best performance in devices has been based upon the acquisition of knowledge and understanding about these interactions. These interactions are usually discussed in the broad context of the subject of biocompatibility. Biocompatibility is a word that is used extensively within biomaterials science, but there still exists a great deal of uncertainty about what it actually means andabout the mechanisms that are subsumed within the phenomena that collectively constitute biocompatibility. As biomaterials are being used in increasingly diverse and complex situations, with applications now involving tissue engineering, as well as the longer established implantable medical devices, invasive sensors and drug delivery systems, this uncertainty over the mechanisms of biocompatibilityis becoming a serious impediment to the development of these new techniques.
9.2 The evolution of current concepts of biocompatibility
Biocompatibility has traditionally been concerned with implantable devices that have been intended to remain within an individual for a long time. To those who were developing and using the first generation of implantable devices, during the years between 1940...
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