Effects of Gradient and Offset Architectures on the Mechanical and Biological Properties of 3-D Melt Electrowritten (MEW) Scaffolds

Abstract

This study describes the fabrication and characterization of three-dimensional (3-D) poly­(ε-caprolactone) (PCL) scaffolds with defined pore architectures prepared using the melt electrowriting (MEW) technique. Three homogeneous pore-sized (250, 500, and 750 μm) scaffolds, two fiber offset (30/70% and 50/50%), and a three-layered (250 μm bottom–500 μm middle–750 μm top) gradient pore-sized scaffolds were designed and printed with ∼10 μm fibers. The mechanical properties (tensile and compression tests), total surface area, porosity of these scaffolds, and their ability to promote the attachment and proliferation of human osteoblasts were then compared. All scaffolds induced good tensile properties; however, they reacted differently during compressive testing. The offset 30/70 scaffold had the highest surface area to volume ratio which enhanced osteoblast attachment after 3 days of cell culture. While the highest initial level of osteoblast attachment at day 1 was found on the 250 μm homogeneous scaffold, the highest degree of cell proliferation and infiltration at day 30 was observed in the three-layered graded porosity scaffold. In terms of physical and biological properties to support bone cell distribution and migration through the entire structure of the scaffold, our results suggest that melt electrowritten offset and gradient scaffolds are good candidate platforms for cell infiltration and growth compared to homogeneous scaffolds.

Role of offset and gradient architectures of 3-D melt electrowritten scaffold on differentiation and mineralization of osteoblasts

“…Although higher porosity increased ALP activity, our results showed the offset scaffolds demonstrated superior matrix mineralization. This may be related to the surface wettability which increases surface free energy resulting in better cell attachment due to greater protein adsorption of ECM-products [44], and the rougher surface of the offset structures after calcium phosphate (CaP) coating modification, which was shown in our previous study by alizarin-red staining and surface area (BET) analysis [22]. It has been displayed the CaP coating on the surface of the fibres within the cells, that the higher level of mineralization was identified on the offset and then 250 μm scaffold structures through alizarin-red staining and micro-CT analysis.…”

“…Our previous studies have shown that, when compared to simpler homogeneous structures, scaffolds with offset and gradient architectures resulted in significantly higher cell proliferation following seeding (Additional file 1) [22]. As a logical extension of this work, this study will investigate the potential effects of heterogeneous porous scaffold architectures, particularly offset and gradient structures on osteogenic gene expression by osteoblasts seeded into these scaffolds and the rate of mineralization throughout the construct.…”

“…A melt electrowriter (MEW) system was used to produce a fibrous scaffold with the fibre diameter in a range of 6-10 μm. The parameters for the components nozzle diameter, voltage, temperature and feeding rate were described in as previously reported [22]. Two different scaffold structures; homogeneous pore size (250 μm, 500 μm, 750 μm) and heterogeneous architecture including a tri-layer scaffolds with different pore sizes from 250 μm on top, 500 μm in the middle, and 750 μm at the bottom of the scaffold and offset scaffolds in which layers were printed with various offset values of 30 and 50% compared to the previous layer ( Fig.…”

“…Human osteoblast cells (hOB) obtaining from alveolar bone of a healthy female were seeded onto the scaffolds (2 × 10 4 in 15 μl) and cultured in either osteogenic or basal medium for 3, 14 and 30 days, according to previously reported protocols [22].…”

“…1 Schematic illustrating the preparation of the scaffolds with different architectures by using MEW method before transferring to 96 well plates and measuring the absorbance at 540 nm in a microplate reader (POLARstar Omega, BMG LABTECH, Germany). The average value of the negative controls (scaffold without cells) [22] was subtracted from the values of the corresponding experimental groups.…”