Biomedical Engineering Reference
In-Depth Information
forming polymer-rich and polymer-poor phases. Polymer solutions
can be dispersed into a non-solvent, and this process will result in
a phase inversion, which causes the polymer to precipitate.
10
Ther-
mally induced phase separation processes are also utilized to fab-
ricate biodegradable 3D polymer scaffolds. By carefully controlling
the thermal gradient and supercooling temperature, different pore
sizesand pore structures can be obtained.
Electrospinning is a highly versatile method for processing solu-
tionsormelts,mainlyofpolymers,intocontinuousfiberswithdiam-
etersrangingfromnanometerstosubmicrometers.Inatypicalelec-
trospinning process, a polymer solution is contained in a syringe
with a metal capillary connected to a high-voltage power supply
as an electrode. The polymer solution is subjected to an electrical
field, and the polymer jet travelling in the electrical field becomes
thin fibers, which are deposited onto a conductive collector.
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The
electrospunmatsconsistofultrafinefibers,whichhavehighsurface-
to-volume ratios and porosity, mimicking the natural ECM of body
tissues.Electrospunfibrousscaffoldshavebeenemployedforregen-
erating various tissues including skin, blood vessel, cartilage, bone,
muscle, ligament, and nerve.
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15
Melt molding and particulate leaching techniques are often com-
bined for scaffold fabrication. A polymer is mixed with a porogen
prior to being loaded into a metal mold. The mold containing the
mixture is then heated under pressure above the glass transition
temperature (or melting temperature) of the polymer, forming a
solid object. The molded product is subsequently immersed in a
solvent for the selective dissolution of the porogen.
16
When the
biodegradable polymers are in the form of microspheres, the term
“microsphere sintering” is used.
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,
18
Extrusion and injection mold-
ingareothermelt-basedprocessingtechniquesinthisscaffoldman-
ufacturing route.
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Some of the non-designed manufacturing techniques can par-
tially control the scaffold architecture by altering certain process-
ing parameters, for example, porogen size, freezing temperature,
organic solvent, and collection method for electrospun fibers.
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22
Althoughthenon-designedmanufacturingtechniqueshaveattained
much improvement and have been widely used in the tissue engi-
neering field over the past two decades, their inherent limitations,
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