As we have seen to this point, identifying a material for a biomedical
As we have seen to this point, identifying a material for a biomedical
application requires more than verifying adequate mechanical properties. We must also be concerned about the material’s resistance to mechanical and chemical degradation (wear and corrosion). Beyond those traditional engineering issues, however, applications in biomedicine have the additional requirement of biocompatibility, i.e., long term physiologic compatibility (Martin 1996a).
Ordinarily, an implant is expected to function for many years. Changes which occur in and around the implant must not be physiologically harmful. The biomaterial should either release no toxic ions or release them gradually, or those ions should not accumulate to the point that they would produce an immunological response. From a biomechanical perspective, an implant should not perturb the stress distribution in adjacent tissues to the extent that normal tissue remodeling is prevented.
To appreciate the challenges of biocompatibility, one must recall that living organisms have evolved with the one over-riding principle of survival. As a result, all organisms seek to prevent the invasion of foreign matter. The organism will generally attempt to destroy the invader at the molecular level or to encapsulate with an impenetrable, cellular wall. Overcoming the body’s resistance by destroying the body’s defenses (the immune system) is a dangerous strategy. More practical is to choose an implant material which is “invisible” to the body’s chemical sensors. Better yet is to find a material that is “attractive” to the physiology of the body. The recent success of hydroxyapatite implant materials is due to its similarity to bone mineral and the resulting integration with bone when implanted in the skeleton.
Related Biological Materials
Certain natural, biological materials have a significant relationship to engineered ceramics used in biomedicine. In this Chapter, these will be described in terms of either their inherent similarity to ceramics or their relationship to an implanted bioceramic.
4.1
HYDROXYAPATITE
Hydroxyapatite, Ca10(PO4)6(OH)2, is the primary mineral content of bone and calcified cartilage, representing 43% by weight of bone (Martin, 1996b). It has the desirable physiochemical attributes of stability, inertness, and biocompatibility. The elastic modulus of hydroxyapatite is two orders of magnitude greater than that of collagen, the primary polymeric component of bone to be described in the next section of this chapter. It should also be noted that the mineralization of vertebrat
application requires more than verifying adequate mechanical properties. We must also be concerned about the material’s resistance to mechanical and chemical degradation (wear and corrosion). Beyond those traditional engineering issues, however, applications in biomedicine have the additional requirement of biocompatibility, i.e., long term physiologic compatibility (Martin 1996a).
Ordinarily, an implant is expected to function for many years. Changes which occur in and around the implant must not be physiologically harmful. The biomaterial should either release no toxic ions or release them gradually, or those ions should not accumulate to the point that they would produce an immunological response. From a biomechanical perspective, an implant should not perturb the stress distribution in adjacent tissues to the extent that normal tissue remodeling is prevented.
To appreciate the challenges of biocompatibility, one must recall that living organisms have evolved with the one over-riding principle of survival. As a result, all organisms seek to prevent the invasion of foreign matter. The organism will generally attempt to destroy the invader at the molecular level or to encapsulate with an impenetrable, cellular wall. Overcoming the body’s resistance by destroying the body’s defenses (the immune system) is a dangerous strategy. More practical is to choose an implant material which is “invisible” to the body’s chemical sensors. Better yet is to find a material that is “attractive” to the physiology of the body. The recent success of hydroxyapatite implant materials is due to its similarity to bone mineral and the resulting integration with bone when implanted in the skeleton.
Related Biological Materials
Certain natural, biological materials have a significant relationship to engineered ceramics used in biomedicine. In this Chapter, these will be described in terms of either their inherent similarity to ceramics
المادة المعروضة اعلاه هي مدخل الى المحاضرة المرفوعة بواسطة استاذ(ة) المادة . وقد تبدو لك غير متكاملة . حيث يضع استاذ المادة في بعض الاحيان فقط الجزء الاول من المحاضرة من اجل الاطلاع على ما ستقوم بتحميله لاحقا . في نظام التعليم الالكتروني نوفر هذه الخدمة لكي نبقيك على اطلاع حول محتوى الملف الذي ستقوم بتحميله .
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