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 390

Morphological (e.g., powder size) and textural characteristics (e.g., porosity) impact on
Si degradation rates and eventual bioactivity. For 58S, there is a direct increase in dissolu-
tion rate with increasing porosity and pore volume (Table 9.5). Rate constants ( k ) can be
significantly increased when pore sizes are greater than 2 nm. Precipitation of HA is likely
to occur first within the pores due to the following:
1. Increase in surface area/volume ratio increases the surface area exposed to media
thus enhancing degree of ion exchange
2. Greater release of soluble silica and rapid formation of silica-rich layer
3. Increased ionic concentration (Ca 2+ , HPO 4- ) in pores until supersaturation
4. Precipitation of HCA in pores where rate is controlled by diffusion of ions into the
pores
Ca 2+ and HPO 4− concentration in the pores increases due to increasing pore size (due to
glass network degradation), which results in rapid formation of the silica-gel layer on the
surface and precipitation of HCA on the gel-layer surface.
For gel glasses, particle sizes can be used as an efficient way to control ionic dissolution
rates and hence bioactivity.
The introduction of pores and precise control of materials composition to tailor both bio-
active and resorbability offers new applications for regenerative medicine. Tailoring bioac-
tive and resorbability with tissue type and tissue growth rates is an ideal scenario/design
requirement for bone tissue regenerative materials. Sol-gel bioactive glasses, in-part, ful-
fill these requirements but more is being done to improve resorption rates, bioactivity, and
even combining with other entities (e.g., macromolecules) to create new novel composite
materials that address issues in regenerative medicine and drug delivery.
DevelopmentandSelectionofBioactiveGlasses
(InVivoandInVitroTesting)
The human body is a complex biological, chemical, and mechanical system. Bioactivity
of a biomaterial is defined as the interaction between the materials and their operational,
biological, and cellular microenvironment.
The aim of testing is to identify and minimize the risk of failure in clinical applica-
tion. Strategies for determining the mechanical, surface chemistry properties (traditional
bioactivity testing), and cellular bioactivity of bioactive glasses to assess the suitability of
candidate biomaterials for osteogenic tissue regeneration can be tested using the following
methods:
1. Mechanical performance test methods are screening methods where a detailed
database of knowledge of bulk material properties, phase, state, and structure,
micro- and nanostructure, surface topology, and coating surface attachment is
created [14].
2. In vitro test methods are screening methods where the bioactive surface is exposed
to (a) cell, tissue, or organ culture to assess the maintenance viable cellular function