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 391

on biomaterials surfaces. These tests are used to develop a detailed database of
knowledge about cell/biomaterials microenvironment enabling biomaterials sur-
faces to be screened, characterized, reconstructed, and modified until suitable
for in vivo trials, and (b) contact with simulated blood test solutions (e.g., SBF) to
quickly assess the rate of bonelike apatite formation (traditionally known as bio-
activity testing) on a candidate material surface.

3. In vivo test methods , where fully characterized biomaterials are implanted in whole-
animal models to initially assess cytotoxicity (site is chosen for nonfunctionality
soft-tissue sites such as the peritoneal cavity and subcutaneous “air-pouch” for
screening tests, and cortical and corticocancellous bone (e.g., transcortical-femur,
tibia, and cranium and intramedullary-femur and tibia) for joint replacement or
fracture fixation testing), followed by functional testing in target species/animal
models (e.g., load-bearing sites) [1].

Mechanical Performance

For selecting bioactive glasses for load bearing applications, the following specific materi-
als properties are important: bioactivity, tensile strength, fracture toughness, and elas-
tic modulus. These variables can be combined to produce a qualitative performance ratio
called the quality index ( I q ) (Table 9.6). I q is described by the following equation:

I q = ( k IC I b UTS)/ E (9.4)

where k IC is the fracture toughness, I b is the index of bioactivity, UTS is the ultimate tensile
strength, and E is Young's modulus.
The rate of bonding can be used to rank different bioactive compositions according to
their index of bioactivity ( I b ). I b is the inverse of the time required for more than 50% ( t 0.5bb )
of the materials' interface to be bonded as described by Equation 9.5:

I b = 100/ t 0.5bb (9.5)

TABLE 9.6
Estimated Quality Index ( I q ) for Selected Second-Generation Bioactive Glasses [9]
Material

I q I b

Cortical bone 500 13

Cancellous bone 8 13

HA (hydroxyapatite) 3 13

A/W glass ceramic 20 3

Bioglass (45S5) 9 13

HEPAX
(45% vol. fraction HA, 55% vol. fraction polyethylene)

42 3

Bioglass 0.4% volume fraction/polysulfone composite 103 13