Biomedical Engineering Reference
In-Depth Information
However, there are applications for glass fibers in filtration technolo-
gies within the realm of biotechnology and even as a biocompatible
fiberglass resin for repair in medicine. Optical fibers, such as those used
in endoscopes, tend to be somewhat thicker than the structural fibers
and have a more complex structure involving a high-refractive-index
core that carries the light and a low-refractive-index cladding that con-
fines the light to the core and protects the glass. Glass can be fiberized
whether from the melt (structural fibers) or by heating and stretching
a preform that has the required optical profile (optical fiber). Now
micro- and nanoscale fibers can be generated by electrospinning and
laser spinning techniques (Chapter 3). The fine-scale two-dimensional
meshes and three-dimensional constructs mimic the fine scale of natural
cell matrices and can be manipulated easily to fit into bone defects or
used as membranes to guide tissue growth.
1.5 GLASSES THAT ARE NOT ''MELTED''
High-purity glasses and glasses that would otherwise be difficult to form
from the melt due to the high temperatures required can be made by
other routes. One of the more popular ways is by vapor deposition.
Silicon tetrachloride is a liquid at room temperature, which can be
boiled and reacted with high-purity oxygen to form silica:
SiCl 4 (g)
+
O 2 (g)
SiO 2 (s)
+
2Cl 2 (g)
The resulting highly pure silica deposits on a substrate as a low-density
soot, which can be consolidated into vitreous silica by heat treatment.
It is also possible to make doped silica glasses by this route, either by
adding a component through reaction of a vapor phase with oxygen or by
doping with a solution. Silica is a very important glass in biotechnology
and medicine, as it is possibly the most durable glass and it is relatively
straightforward to carry out surface engineering.
An alternative way of making high-purity and highly refractory glass is
to use the sol-gel process (Chapter 3). Silica can easily be made but there
are also some glasses that cannot be made by melting but can be made
using a sol-gel method, for example, titania and simplified SiO 2 -CaO
compositions (sodium is not needed as there is no melting and therefore
no need to lower the melting point). The sol-gel method is a chemical
reaction method in which an organometallic compound is hydrolyzed
(reacted with water). The resulting species then subsequently undergo a
condensation reaction to form the bridging bonds of the glass network.
Search WWH ::




Custom Search