Biomimetic Nanofi brous Scaffolds for Bone Tissue Engineering Applications - Biomimetics: Advancing Nanobiomaterials and Tissue Engineering - page 80

( a ) ( b )

Figure 4.3 Phase-separated nanofi brous PLLA scaffold with macropores
produced by a sacrifi cial porogen. At the microscale a highly interconnected
open cell foam with uniform surface texture is visible (a), a magnifi ed view of the
same scaffold shows a interconnected web of PLLA nanofi bers (b). Adapted from
Wei & Ma, 2006 [98], Copyright © 2006 John Wiley and Sons.

By itself, the TIPS method suffers from the same drawbacks of other
means of fabricating materials with nanoscale features, namely extremely
small pore spaces that do not allow for cellular infi ltration and tissue regen-
eration within the material. However the starting polymer solution is easily
cast into a mold before phase separation, and through a sacrifi cial porogen
approach it is possible to produce a scaffold with highly interconnected
macropores that still exhibits a nanofi brous texture [96, 97] (Figure 4.3a).
This method has several advantages—the size of the pores can be controlled
precisely, and the level of interconnection can be controlled by partially
melting the porogen particles prior to casting. In a PLLA-THF/Dioxane
system, both paraffi n [97] and fructose [98] microspheres have been suc-
cessfully utilized to produce interconnected pore spaces, and other materi-
als are likely compatible provided their solubility in the chosen solvent is
not high. Solid freeform fabrication techniques (SFF) can be utilized to fab-
ricate the sacrifi cial porogen mold [99], allowing for the design of scaffolds
for specifi c anatomical sites in individual patients, or allowing for complex
spatial variation in pore size and interconnectivity across a scaffold.
The compressive modulus of nanofi brous materials with 2-10% PLLA
by mass ranges from 3-20 MPa, and scaffolds with included micropores
can achieve a modulus of 300 kPA [100]. While not comparable to native
bone tissue, a stiffness of 300 kPa is far higher then the expected moduli
for macroporous electrospun materials, or of peptide amphiphile gels
(1-10 kPa) [101].

4.4.2 Biological Behavior of TIPS Scaffolds

When soaked in bovine serum, nanofi brous PLLA scaffolds absorb over
4X more protein than comparable solid-walled scaffolds. Western blot