Biomedical Engineering Reference
In-Depth Information
level of boron in the glass (increased reaction rate) caused cell death due
to significant changes in the micro-environment just above the surface of
the glass where the cells were attached. Using the same conditions except
that the culture is gently disturbed by periodic agitation, the amount of
DNA present in the culture was higher, and only the full borate glass
is statistically lower than the silicate glass [7]. This improvement of cell
sustainability in the dynamic culture over the static culture indicates
that, in a fully dynamic system, such as the body, the expected toxicity
of the borate glass could potentially be non-existent.
The main point from this section is to understand that different types of
materials require different types of testing to get an accurate assessment
of how the material will react when implanted in a mammal. Having
an understanding for the material and how it reacts in an aqueous
environment is valuable information when planning an experiment.
It is important to know that sometimes materials can fail tests, and
sometimes tests can fail materials.
6.4 MULTIFUNCTIONAL BIOACTIVE BORATE
GLASSES
Traditionally, bioactive glasses have been used in orthopedic applications
for the regeneration of bone [10, 11]. Bone is a highly vascular material,
and, in fact, bone cells cannot survive unless they are within 100-200
m
of a blood capillary [12]. Emphasis for most bioactive glass testing is
typically on the ability to form HCA and have osteoblast-like cells
differentiate into osteocytes [8]. These two parameters are important,
but the formation of soft tissues like blood vessels is just as important
in promoting bone growth
in vivo
, especially in full-thickness segmental
defects, where the surrounding vascular network has been severely
damaged [12].
Administration of growth factors such as vascular endothelial growth
factor (VEGF) has been widely studied as a method for inducing vascular
growth in bone implants [13]. Unfortunately, growth factors typically
are expensive (thousands of dollars per dose) and are not likely to be
the long-term solution for this problem. Fortunately, the body uses ions
such as copper to regulate angiogenesis, and copper can easily be added
to bioactive glasses for slow and controlled release to the surrounding
tissues [9, 14]. An added advantage of using bioactive glass is that
the release can occur over the course of weeks to months, which is
preferable to the relatively fast release of a growth factor simply coated
on an implant material [9].
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