Biomedical Engineering Reference
In-Depth Information
differentiation and thus promote tissue regeneration. In scaffold-
based tissue engineering, although ideal scaffolds have not yet been
achieved (or actually, there are no such ideal scaffolds and each
scaffold should be designed according to specific tissue regenera-
tion requirements), certain minimum criteria, namely, biocompat-
ibility, mechanical properties similar to those of the target tissue,
biodegradability at a degradation rate commensurate with the tis-
sue formation rate, etc., shouldbe metfor the scaffolds.
There are many methods for scaffold fabrication, including non-
designed manufacturing techniques and designed manufacturing
techniques. Using polymer solutions and sometimes with high pres-
sure or high temperature, non-designed manufacturing techniques
include solvent casting/particulate leaching, phase separation, gas
foaming/high-pressure processing, melt molding, electrospinning,
and combinations of these techniques (e.g., gas foaming plus par-
ticulate leaching, etc.). Designed manufacturing techniques, usually
referred to as SFF or RP technologies in the general manufacturing
sector of the industry, have attracted much attention recently and
are investigated and developed for scaffold fabrication in the tissue
engineering field.
6
Solvent casting/particulate leaching is a simple and the most
commonlyusedmethodforproducingporousbonetissueengineer-
ing scaffolds.
7
This method involves dispersing granules of a water-
soluble salt such as sodium chloride, sodium citrate, or sucrose in
a polymer solution. The polymer solution with dispersed salt parti-
clesisthenprocessedviaeithersolventcastingorfreezedryingina
moldofdesiredshape.Afterthesolventisremoved,thesaltparticles
are leached out, forming a highly porous structure.
8
The pore size
of the scaffold can be controlled by selecting different sizes of the
porogenandbychangingtheporogen/polymerratioofthepolymer
solution. However, the porous scaffolds produced through solvent
casting/particulate leaching are usually thin pieces and sometimes
lack pore interconnectivity.
Phaseseparationoccurswhen,undercertainconditions(usually
induced by the change of solvent or temperature), a homogeneous
multicomponent system becomes thermodynamically unstable and
separates into more than one phase in order to lower the system
freeenergy.
9
Thereareseveralmethodstoinducephaseseparation,
Search WWH ::
Custom Search