Biomaterials Tutorial

Porous Scaffolds

Elizabeth Donaldson
University of Washington Engineered Biomaterials

Tissue engineering aims to create functional tissue using cells seeded onto 3-D scaffolds, providing an alternative to traditional transplants.  Tissue engineering techniques in general require the use of porous scaffolds, which serve as a 3-D template for initial cell attachment and growth leading to tissue formation.  The architecture of the scaffold used defines the ultimate shape of the newly grown tissue.  An ideal tissue scaffold must meet several requirements: the scaffold must comprise an interconnected, open pore network allowing nutrients and cells to pass into the scaffold while ensuring waste products can get out.  Also the scaffold must have mechanical properties closely matching those of the tissues at the site of implantation.   For example, the human heart is always beating, the muscle of the heart is constantly stretching and contracting so any tissue scaffold used in the heart must be able to withstand this constant motion (a brittle material would crack while a soft material might deform like silly putty).  In addition to structure and mechanics, the scaffold chemistry will be very important.  The scaffold must have a surface chemistry suitable for cell attachment and growth.  There are thousands of patients that could benefit from tissue engineered products.  To be successful, a scaffold material must be easily processed into a variety of shapes and sizes, and its production must be inexpensive and reproducible on a large scale.

A wide variety of techniques can be used to design and fabricate porous tissue scaffolds.  One such technique is called salt leaching where salt crystals such as NaCl (common table salt) are put into a mold and polymer is poured over the salt, penetrating into all the small spaces left between the salt crystals.  The polymer is hardened and then the salt is removed by dissolving it in a solvent (such as water or alcohol) which washes/leaches the salt out.  Upon removal of the salt crystals all that remains is the hardened polymer with open holes/pores where the salt once was (see Fig. 1).  A new fabrication technique under development at UWEB uses polymer foams called aphrons to create porous scaffolds.  A polymer is first stirred rapidly to create a foam and then hardened, creating a solid sponge-like material where the foam’s air bubbles form the pores of the final scaffold.   To learn more about these and other techniques used to create porous tissue scaffolds, check out Chapter 8 of Biomaterials Science: An Introduction to Materials in Medicine.

Figure 1. Poly(l-lactic acid) scaffold prepared by salt leaching.  (Scaffold and image reproduced with permission from Steve Gingrich)

References

Biomaterials Science: An Introduction to Materials in Medicine, 2nd ed. Ratner BD, Hoffman AS, Schoen FJ, Lemons JE,Eds.Elsevier Academic Press: New York, 2004.