Guaranteeing Larger Pore Sizes and Higher Porosity for a Specific Application
It is well-known that larger pore size and higher porosity are good for nutrients delivery and wastes removal and thus for cell migration and tissue ingrowth [80, 81]. For instance, pore sizes greater than 500 gm are required for rapid vascularization and for the survival of transplanted cells in fibrovascular tissues . Macroporous scaffolds with 150-350 gm pore sizes were seen with optimum osteoblast adhesion, proliferation and bone formation [83, 84]. On the other hand, nanofiber scaffolds, which have been developed to mimic the topographical structure of extracellular matrix, have nanosized interfibrillar pores, which disable efficient ingrowth of cells into deeper layers of the nanofibrillar support . More researches involving the contributions of pore sizes on cell responses have been recently reviewed by Perez and Mestres . Despite the positive contribution of larger pore size and higher porosity, they are commonly accompanied by weakened mechanical properties. Balancing the mechanical properties and pore structures have been being the topic of scaffolds design and fabrication. Nanofibers and nanotubes can reinforce the mechanical properties of the composite scaffolds to a large extent when even added with a small amount [86, 87]. The strong mechanical properties of the reinforced scaffolds provide more possibility to guarantee that the scaffolds meet the mechanical requirement for a specific application even with larger pore sizes and higher porosity. Correspondingly, tissue ingrowth and regeneration may be accelerated. This might be another mechanism for the improved biocompatibility of nanofibers- or nanotubes-reinforced scaffolds by enhanced mechanical properties. More description about the effect of pore structures on cell/tissue responses will be detailed in Sect. 5.5.