Standards and biological tests
Biological characteristics, that is the behavior of different tissues and of the
organism vis-à-vis the implant, at a distance or at its contact, can be evaluated by
different tests defined by standards.
A ceramic will be biocompatible if it does not cause inflammatory reactions or
toxicity (no noxious elements brought in: Pb, Cd, As, Hg). This expanded
biocompatibility opens up the notion of this very contemporary concept of
bioactivity, according to which we aim at a material that is no longer inert but
triggers reaction from the living tissue. The standards look essentially to evaluate the
quality of the array of materials used for implants and their innocuousness. There is
at present no standard concerning the measurement of bioactivity.
The specific uses of bioceramics in vivo require their full compatibility with the
living tissues. Taking into account the reliability requirements, implantable
ceramics, whether massive or in the form of coatings, should be subjected to a
number of tests (physical, chemical, mechanical, mineralogical and biological
characterization), for ensuring guaranteed performance without failure in future.
These different types of characterization are presently the subject matter of
important works of standardization in the AFNOR and ISO organizations. We give
below a non-exhaustive overview of tests practiced at present on pieces and ceramic
coatings, with the knowledge that some drafts of ISO, AFNOR or ASTM standards
are under preparation.
Physical and mechanical characterization:
– on massive parts: the basic appraisal consists of dimensional check and static
load test. Other tests can also be done:
- porosity and bulk density (soaking of specimens under vacuum NF EN 623-
2: B41-203),
- micro hardness,
- impact resistance,
- wear resistance;
– on coatings and depositions: the main characteristics required for determining
the quality of deposition on the metallic medium (alloy TA6V) are thickness
(AFNOR S94-069, metallographic sections), porosimetry (ISO/CD 13779), surface
condition (AFNOR S94-071, rugosimetry) and the adherence strength in tension
(AFNOR, S94-072).
Bioceramics 513
Chemical and mineralogical characterization:
– on massive parts: the general techniques of analysis used for ceramics
(fluorescence X and plasma spectrometry) are applicable to bioceramics. For
measurement of low contents (< 100 ppm), the inductive coupled plasma mass
spectrometry (ICP-MS) seems to be the most suited technique. Mineralogical
analysis takes place by x-ray diffraction;
– on coatings and depositions: ceramic depositions for medical applications
essentially consist of hydroxyapatite. Various tests check the purity of the HAP
(AFNOR S94-066, Ca/P determination and AFNOR S94-067, qualitative and
quantitative determination of foreign phases), the crystallinity (AFNOR S94-068)
and the presence of impurities (AFNOR S94-065, As, Hg, Cd, Pb assays).
Biological characterization: mechanical behavior in biological medium can be
studied from tests in Ringer solution [CAL 94] considered as being representative of
the biological environment. These tests apply on cylindrical bars (diameter 5 mm,
length 125 mm) subjected, while immersed in Ringer solution, to a static flexural
stress [LED 95]. The duration of the test is 10 months and the solution is changed
every month. These undergo the tests, including the dimensional check, weighing,
measurement of fracture modulus by three point method and the measureme
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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