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 392

TABLE 9.7
Five-feature Characterization Approach as Proposed by Hench

Feature CharacterizationofInterest MethodofCharacterizationTechnique

1 Chemical composition SEM-x-ray photoelectron spectroscopy (XPS), Auger

electron spectroscopy (AES), Fourier transform
spectroscopy (FT-IR), x-ray diffraction (XRD), SIMS.

2 Size, shape, and morphological

features of particulate solids and
monoliths

Scanning electron microscopy (SEM), wettability, atomic
force microscopy (AFM) (incl. Maple technique).

3 Phase state and structure Thin-film XRD and FT-IR reflection spectra are usually

obtained after soaking in SBF solutions.

4 Microstructure Usually used to determine quality control and assurance.

Quantitative microscopy, using either optical or scanning
electron microscopy (SEM).

5 Surface behavior

(bioactivity testing)

The candidate material is soaked in simulated body fluid
(SBF) solutions and degree of apatite formation is
investigated.

I q can be used to select appropriate biomaterials for load-bearing applications that avoid,
as much as possible, stress-shielding* of bone.

Standards for Biocompatibility Testing

Biocompatibility is defined as the ability of a material to perform an appropriate host
response for a specific application [15]. Biocompatibility testing of materials is based on
their potential interactions with cells, muscles and ligaments, bones, fat, and/or organs.
Where chemical, mechanical, pharmacological, and surface reaction layer responses are
assessed to determine the local toxicity, surface degradation, and mechanical stability.
In the early 1990s, Hench et al. introduced a five-feature approach (see Table 9.7) for the
characterization of bioactive glasses that has been widely accepted by the research com-
munity as the minimum common denomination for biomaterials characterization [16].
Since bioactive glass surface reaction layer formation is time-dependent, it is useful to
use a range of characterization methods (mentioned in Table 9.9) to characterize reaction
layer formation with time and depth (see Figure 9.6).
In addition to the above-mentioned methods, contact angle analysis can be performed to
estimate surface energies. Sampling depth is very small at 0.3 to 2 nm.
SEM-x-ray photoelectron spectroscopy (SEM-XRD) has proved to be an invaluable tool
in characterizing surface coatings. Although it is destructive, its sampling depth is deep
enough (greater than 80 μm) to obtain chemical composition profiles spanning from the
outer reaction layers through to the silica-gel layers and into the unreacted bulk material.

* Stress-shielding is the redistribution of load (and consequently stress on the bone) that occurs when the host
bone tissue is replaced by a corresponding implant component (e.g., replacement of a femoral head by the
femoral component of a total hip replacement).