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 384

Bioceramics

For example polycrystalline materials, glasses, glass ceramics, glass composites

Bioinert

Bioactive

Minimal level immunological
response at the implant surface
resulting in the implant being
covered in a thin, nonadherent,
fibrous layer

Elicits a specific biological response
at the implant surface facilitating
biological bonding and tissue ingrowth

Resorbable Nonresorbable

For example, alumina, zirconia ceramics

Material interface is
gradually replaced with
host tissue

For example, hydroxyapatite;
Tricalcium phosphate;
calcium phosphate
ceramics

For example, bioactive glass,
bioactive glass-ceramics

FIGURE 9.3
Classification of bioceramics and bioactive glasses [11].

No first-generation bioactive glasses exist. By definition, bioactivity is a second-genera-
tion material property.

Bioactive Glasses

The discovery in the late 1960s that certain compositions of glass could elicit a bioactive
response (host tissue responds biologically to implant facilitating tissue growth—osteo-
production—across surface and in some instances tissue growth into the implant surface)
initiated a revolutionary paradigm shift. They have been incorporated into implant devices
in the form of monoliths, coatings, powders, and composites. Introduction of bioactivity
prolongs the lifetime of the device via encouragement of hard tissue (e.g., bone) into and
onto the device, forming a mechanically strong and biologically stable interface. Materials
compositional changes allow bioactive glasses to bond to soft tissues as well. Another
advance of bioactive glasses is their ability to resorb (network degradation facilitating the
release of ionic species into the host tissue, allowing biomaterial to be replaced with new
host tissue).

45S5 Composition (Bioglass®)

In the late 1960s, Hench demonstrated that interfacial bonding to bone could be achieved
with a certain compositional range of glasses that contained SiO 2 , Na 2 O, CaO, and P 2 O 5
in specific proportions. These bioactive glasses differ from traditional SiO 2 -Na 2 O-CaO
glasses in that their SiO 2 content is much lower than 60 mol% and they have a high Na 2 O
and CaO content and a high CaO/P 2 O 5 ratio. These compositional factors directly account
for their high surface reaction kinetics and subsequent interfacial bond with bone.
Many melt-derived bioactive glass compositions are based on the 45S5 formula (45 wt.%
SiO 2 , S as the network former, and a 5:1 molar ratio of Ca to P in the form of CaO and