Endothelial cell colonization and angiogenic potential of combined nano- and micro-fibrous scaffolds for bone tissue engineering

Abstract

Presently the majority of tissue engineering approaches aimed at regenerating bone relies only on post-implantation vascularization. Strategies that include seeding endothelial cells (ECs) on biomaterials and promoting their adhesion, migration and functionality might be a solution for the formation of vascularized bone. Nano/micro-fiber-combined scaffolds have an innovative structure, inspired by extracellular matrix (ECM) that combines a nano-network, aimed to promote cell adhesion, with a micro-fiber mesh that provides the mechanical support. In this work we addressed the influence of this nano-network on growth pattern, morphology, inflammatory expression profile, expression of structural proteins, homotypic interactions and angiogenic potential of human EC cultured on a scaffold made of a blend of starch and poly(caprolactone). The nano-network allowed cells to span between individual micro-fibers and influenced cell morphology. Furthermore, on nano-fibers as well as on micro-fibers ECs maintained the physiological expression pattern of the structural protein vimentin and PECAM-1 between adjacent cells. In addition, ECs growing on the nano/micro-fiber-combined scaffold were sensitive to pro-inflammatory stimulus. Under pro-angiogenic conditions in vitro, the ECM-like nano-network provided the structural and organizational stability for ECs' migration and organization into capillary-like structures. The architecture of nano/micro-fiber-combined scaffolds elicited and guided the 3D distribution of ECs without compromising the structural requirements for bone regeneration.

Multiscale three-dimensional scaffolds for soft tissue engineering via multimodal electrospinning

“…Encouraging results were obtained. For example, cell motility and spreading could be significantly improved by adding a diluted network of 500 nm nanofibers over a dense substrate scaffold of bulky 160 lm microfibers, where the nanoweb provided cells with a means to bridge across microfibers that were far apart and colonize the entire scaffold [16,17]. Similar observations were confirmed with thinner 5 lm microfibers [19], highlighting that rate and depth of cell infiltration decreased with thickening of the nanofibrous layer.…”

“…These fibers are exceedingly long (km range) compared with their diameters (x), which usually follow a unimodal statistical distribution. The mean and spread of such distributions can be controlled and tweaked via process parameters over a wide range, from a few nanometers to hundreds of microns [10][11][12][13][14][15][16][17][18][19][20][21][22][23]. The fiber diameter x is regarded as the prime controllable design parameter to steer scaffold performance in terms of cell response.…”

“…Reportedly, nanoscale fibers, in the absence of beads, were found to accelerate and improve cell adhesion and proliferation in the presence of growth factors with respect to the microscale counterpart -partly owing to the higher specific surface area providing a kinetic boost [18,21]. Nanofibers also appeared to sustain growth factor-induced stem cell differentiation [14,15,17,22,23]. However, dense nanoscale networks are not optimal, as they tend to block cell migration through the thickness and are outperformed by microscale fibers in terms of cell ingrowth and viability [20].…”

“…Hence, in its simplest form the design problem for a unimodal electrospun scaffold may be reduced to selection of the proper fiber distribution to deliver the optimal trade-off between sufficiently large pores and as small as possible fibers [20,31]. However, for the general case of a 3D complex tissue the design problem is normally more complicated and must account for additional aspects, such as the need to achieve simultaneous vascularization of the engineered tissue [6,7,15,17]. To this end, one single scaffold ought to be capable of accommodating several cell populations seeded at one time, each having specific requirements in terms of fiber width and pore size [22,23].…”

“…This explains the pursuit for more advanced multiscale electrospun scaffolds. While some researchers have focused on unimodal fiber distributions spanning both the nanoscale and the microscale [21], others have begun to look for scaffolds featuring multimodal fiber distributions obtained by the combination of two or more fiber populations [16][17][18][19]. To date, this has typically been achieved by spinning microfibers and nanofibers alternately in a sequential fashion, to fabricate a layered composite that would inherit the advantages of both length scales and show enhanced cell functionality.…”