Effects of Pore Structure
Scaffolds for tissue engineering should be porous and permeable to permit the ingress of cells, nutrients and oxygen diffusion, as well as waste removal [45, 46]. In nanofibers/nanotubes-reinforced scaffolds, the incorporated fibers and tubes may
Fig. 5.8 AFM images of poly-acrylonitrile methylacrylate (a-d). Smooth film without (a) and with fibronectin (c). Aligned fibers without (b) and with fibronectin (d). Fluorescence images of ECM organization of glial cells on smooth film (e) and aligned fibers (f). Scale bar indicates 100 nm 
alter the pore structure, which plays vital roles in regulating cell/tissue responses (see Sect. 5.5 for details). In fact, this regulation role by pore structures is realized through protein adsorption. Ma et al.  demonstrated that the pore size of CNT reinforced poly(L-lactide) scaffolds was reduced with the increasing of the CNT incorporation (Fig. 5.9a-d). More importantly, the capacity of protein adsorption was dramatically improved when the percentage of CNT was higher than 1.0 wt% (Fig. 5.9e). Wei et al.  fabricated nano-hydroxyapatite/poly(L-lactic acid) (NHAP/PLLA) composite scaffolds with fibrous pore (Fig. 5.10a,b) and smooth pores (Fig. 5.10c,d) and investigated the effects of pore structures on protein adsorption. It was found that the amount of adsorbed serum proteins on scaffolds with fibrous pores was four times higher than that with smooth pores (Fig. 5.10e). Leong et al.  further fabricated nanopores on poly(DL-lactic acid) (PDLLA) nanofibrous scaffolds by using vapor-induced phase separation method. After incubated in a dilute solution of fetal bovine serum, the nanoporous PDLLA fiber scaffolds were found to have ~ 80% more proteins than the solid fiber scaffolds, though the former demonstrated much weaker mechanical properties. The role of pore structure to protein adsorption is generally attributed to the higher surface area to volume ratio.
Fig. 5.9 (a-d) Micro-morphologies of CNT reinforced poly(L-lactide) scaffolds with different functionalized CNT and loadings (wt%) and corresponding total adsorption proteins (e) 
Fig. 5.10 Micro-micrographs of NHAP/PLLA scaffolds fabricated from pure dioxane (a, b) and dioxane: water = 87: 13 (c, d), and corresponding protein adsorption (e)