Bioactive Glass-Based Coatings and Modified Surfaces: Strategies for the Manufacture, Testing, and Clinical Applications for Regenerative Medicine - Biological and Biomedical Coatings: Processing and Characterization - page 394

TABLE 9.8
NAMSA Four-Phase Approach for Safety Evaluation of Medical Devices

Phase
1

Characterization of material
• Chemical characterization
• Physical characterization
• Biological characterization

2 Biocompatibility of material

3 Product and process validation

• Environment control
• Manufacturing process control
• Sterility
Finished product quality

4 Release and animal testing

• Release testing
• Periodic audit testing
Product release

formation of bonelike apatite on its surface when implanted in the living body. This in
vivo apatite formation can be reproduced in an SBF with ion concentrations nearly equal
to those of human blood plasma [17].
A bioactive material is a material on which bonelike hydroxyapatite (apatite) will form
selectively after its immersion in a body fluid-like solution, where the rate of bioactivity
( I b ) infers the candidates suitability for clinical application.
Typical testing procedures include the following steps:

1. Immersion of candidate material(s) using a defined surface area to volume ratio in
an SBF.

2. Soaking is performed at 37ºC for 24 h to 4 weeks under either static (no agitation of
the SBF solution) conditions or dynamic conditions (agitation of the SBF solution
via an orbital shaker).

3. The glass surface after being soaked in the SBF is studied by FT-IR (see Figure 9.8
for an example of a typical profile), thin film x-ray diffraction spectrometry
(TF-XRD) and SEM-XPS to assess apatite formation.

Studies by Vallet-Regi and coworkers showed that dynamic conditions can postpone
apatite formation [18]. In addition, immersion of smaller particles leads to increase surface
area to volume ratios facilitating faster changes in SBF local solution chemistry, resulting
in faster apatite formation [21].
FT-IR is the most commonly used tool to assess surface chemistries and has been exten-
sively used to characterize surface reaction kinetics (Figure 9.7). For a detailed review of
FT-IR technique, the reader should refer to Hench and Wilson [9].
Soaking times to identify hydroxyapatite precipitation on the surface of the bioactive
glasses in SBF solutions is often measured by TF-XRD. Based on the analysis of bioactivity
of the glass and the soaking time, a new index to evaluate the bioactivity of materials can
be proposed.