ABSTRACT
Three-dimensional (3D) and Four-dimensional (4D) printing emerged as the next generation of fabrication techniques, spanning across various research areas, such as engineering, chemistry, biology, computer science, and materials science. Three-dimensional printing enables the fabrication of complex forms with high precision, through a layer-by-layer addition of different materials. Use of intelligent materials which change shape or color, produce an electrical current, become bioactive, or perform an intended function in response to an external stimulus, paves the way for the production of dynamic 3D structures, which is now called 4D printing. 3D and 4D printing techniques have great potential in the production of scaffolds to be applied in tissue engineering, especially in constructing patient specific scaffolds. Furthermore, physical and chemical guidance cues can be printed with these methods to improve the extent and rate of targeted tissue regeneration. This review presents a comprehensive survey of 3D and 4D printing methods, and the advantage of their use in tissue regeneration over other scaffold production approaches.
ABSTRACT
A bone tissue replacement with relevant anatomical size requires the production of 3D scaffolds, which in turn limits the mass transport of nutrients and oxygen to sustain cell survival. A viable vascular network is required to overcome this problem. However, this cannot be established immediately after the implantation of a scaffold. The aim of this study was to develop a 3D wet-spun bone tissue engineering scaffold, coated with an elastin-like recombinamer (ELR) peptide with an endothelial cell-attracting REDV sequence to promote early vascularization. Scaffolds were produced using biodegradable poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), and an ELR was immobilized onto it after oxygen plasma treatment (PHBV-O2-ELR-REDV). O2 plasma treatment and ELR modification of the PHBV changed the wettability, topography, and composition of the surface. A moderately hydrophilic surface was obtained after oxygen plasma treatment and ELR-REDV coating with a contact angle of 66.63 ± 0.77°. The surface roughness decreased after plasma treatment from 343.4 to 160.0 nm and increased to 280.3 nm after ELR-REDV coating. FTIR-ATR showed amide I and amide II bonds after ELR-REDV coating showing that the coating was successful. Scaffolds were tested in vitro with rabbit bone marrow mesenchymal cells. ELR modification did not cause a significant difference in adhesion or proliferation compared to unmodified controls. On the other hand, ELR-modified scaffolds attracted a higher number of human umbilical vein endothelial cells (HUVECs) due to the REDV sequence. The Alamar Blue test and confocal laser scanning microscopy micrographs showed that HUVEC migration and attachment on PHBV-O2-ELR-REDV scaffolds was around 2.5-fold higher than untreated PHBV scaffolds after 14 d. Plasma-treated scaffolds (PHBV-O2) showed an increase in the number of adhered HUVECs due to increased surface wettability. It can, therefore, be suggested that PHBV-O2-ELR-REDV scaffolds have significant potential to induce early vascularization due to increased attractiveness for endothelial cells. This could alleviate the vascularization problem of 3D implants for bone tissue engineering.
