Scaffold Fabrication Technologies

3. 3 Scaffold Fabrication Technologies:
A number of scaffold fabrication technologies have been developed or adopted from other disciplines for tissue engineering. There are three basic categories: three-dimensional polymeric scaffold fabrication, fiber and textile fabrication.

1- Three-Dimensional Polymeric Scaffold Fabrication:
These techniques including many methods which proposed and utilized in fabricating three-dimensional scaffolds from polymeric materials.

a) The Stack Method:
The stack method is a very simple way to create a three-dimensional frame structure using small disks with notches, which allows for the stacking of the disks with each other into three-dimensional architectures. This method is similar to the children s building practice using toy bricks. The assembled structure fulfills the tensegrity concept very well and has good mechanical sup-port in the early stages of application. However, the problem with this method is that it requires use of a large amount of polymer in order to form a stable three-dimensional object. The use of too much material with biodegradable polymers is not desirable because it may produce abundant acidic by-products, which may disturb the local environment and affect cell viability and function.

b) Solvent Casting:
Solvent casting is based on the evaporative property of some solvents in order to form scaffolds by one of two routes. One approach is to dip a mold in¬to the polymer solution and allow sufficient time to draw off the solvent, which leads to the formation of a layer of polymeric membrane. The other way is to place the polymer solution in a mold, and allow sufficient time for the solvent to vaporize, which leaves behind a layer of membrane adhering to the mold. This technique is very simple, easy, and inexpensive and there is no need for specialized equipment and no large effects on the degradation behavior. How¬ever, it uses highly toxic solvents which can denature proteins and other incor¬porated molecules. There is also the possibility for retention of toxic solvent within the scaffold, although this can be overcome by allowing the scaffold to fully dry and by using a vacuum process to further remove any solvent. How¬ever, this is a very time consuming and labor intensive fabrication process. Some researchers have combined other techniques with solvent casting to obtain more features in the scaffold and avoid the disadvantages with solvent casting. For example, when combined with particle leaching techniques, scaffolds with 20% — 50% porosity can be obtained. However, this process only works for the construction of very thin scaffolds. Otherwise, it is very difficult to completely dissolve the soluble porogen particles from the core of the scaffolds. If the scaffolds are too thick, particles may remain in the scaffold. One method to overcome this problem may be to use the lamination principle to glue multi¬ple thin porous sheets into a thick three-dimensional architecture. However, this is a very time consuming process.