Bioresorption and Degradation of Biomaterials - Tissue Engineering: Cell-Surface Interactions for Tissue Culture - page 324

body fluid, at a temperature higher than 37 C and lower than the melting tem-
perature for a period of between 2 days and 60 days. This test will lead to sample
degradation, which can be analyzed by sample mass balance and molecular bal-
ance. If the information gathered from the accelerated test is not sufficient to justify
the use of the material, the real-time test will additionally be applied. This test is
designed to mimic the real-time in vivo environment. Therefore, it is conducted at
normal body temperature (37 C) and four different time periods are required. After
these periods, the same mass balance analysis and molecular mass analysis will be
applied and the information on degradation characteristics will be derived from
these data. Both accelerated degradation and normal degradation tests are mainly
designed to stimulate hydrolytic and oxidative degradation.
ISO Degradation Assays for Ceramic Materials
Ceramic materials, which are commonly used in dental and orthopedic applica-
tions, are analyzed differently from polymers. ISO 10993-14 is mainly designed
for testing in vitro degradation of ceramic materials in solutions of different pH.
The test consists of two parts: (1) degradation in an extreme solution, typically
citric acid buffer solution (pH 3) which represents the worst possible environment
in vivo for the material; (2) degradation in a solution that represents the normal in
vivo environment, typically Tris-HCl buffer with a pH of 7.4 ± 0.1. This test is
very easy to conduct and thus is adopted frequently in pre-clinical testing of
ceramic materials.
ISO Degradation Assays for Metals
Since metals or alloys possess high electrical conductivity, the degradation test for
metals or alloys measures not only the possible chemical degradation by immer-
sion testing but also the potentiodynamic and potentiostatic ability of the materials,
trying to predict the in vivo electrochemical behavior. The electrolyte used for
analysis can be an isotonic aqueous solution of 0.9% sodium chloride, artificial
saliva or artificial plasma. The surface of the material, mass balance and elec-
trochemical behavior are measured as parameters to estimate the possible in vivo
degradation.
3.1.2 Degradation Assays for Composite Materials
In recent years, more and more medical devices have been constructed from more
than one class of biomaterials. In this case, therefore, a combination of the above
tests is usually necessary and an assessment is needed of whether each part of the
medical device needs to be analyzed separately or if a combined analysis is
reasonable.