Date Published: June 01, 2020
Publisher: Mary Ann Liebert, Inc., publishers
Author(s): Cian Vyas, Gokhan Ates, Enes Aslan, Jack Hart, Boyang Huang, Paulo Bartolo.
Complex and hierarchically functionalized scaffolds composed of micro- and nanoscale structures are a key goal in tissue engineering. The combination of three-dimensional (3D) printing and electrospinning enables the fabrication of these multiscale structures. This study presents a polycaprolactone 3D-printed and electrospun scaffold with multiple mesh layers and fiber densities. The results show successful fabrication of a dual-scale scaffold with the 3D-printed scaffold acting as a gap collector with the printed microfibers as the electrodes and the pores a series of insulating gaps resulting in aligned nanofibers. The electrospun fibers are highly aligned perpendicular to the direction of the printed fiber and form aligned meshes within the pores of the scaffold. Mechanical testing showed no significant difference between the number of mesh layers whereas the hydrophobicity of the scaffold increased with increasing fiber density. Biological results indicate that increasing the number of mesh layers improves cell proliferation, migration, and adhesion. The aligned nanofibers within the microscale pores allowed enhanced cell bridging and cell alignment that was not observed in the 3D-printed only scaffold. These results demonstrate a facile method of incorporating low-density and aligned fibers within a 3D-printed scaffold that is a promising development in multiscale hierarchical scaffolds where alignment of cells can be desirable.
Additive manufacturing is enabling the development of complex, multimaterial, functionally graded, and patient-specific structures for tissue engineering applications.1 Extrusion-based three-dimensional (3D) printing is a commonly utilized technique for tissue engineering, allowing the fabrication of structures consisting of both hard and soft materials. These structures or scaffolds allow cell attachment, proliferation, and the generation of new tissues. The precise deposition of biomaterials that can contain biological materials such as cells and growth factors is a promising development within tissue engineering and allows the native structure of tissues and organs to be more accurately mimicked.2
Dual-scale scaffolds were successfully fabricated with a regular printed structure and the 3D-printed fibers having a circular geometry and diameter of 287.2 ± 27.5 μm with a pore size of 299.2 ± 18.3 μm (Fig. 2). The electrospun fibers were spun onto the scaffolds at specific layers and had a fiber diameter of 820 ± 56 nm. Beads can be observed on electrospun fibers on the printed fibers and within the pores. This may be due to the dissipation of charge as the scaffold thickness increases, the poor conductive properties of the 3D-printed PCL scaffold, and the use of acetic acid as a solvent all of which can result in instability in the charged polymer jet. Fiber alignment is observed on meshes spun for 30 s or more within the printed microfiber pores (Fig. 2d).
A dual-scale scaffold composed of 3D-printed and electrospun PCL fibers was successfully fabricated providing both micro- and nanoscale features. Aligned electrospun nanofibers were produced within the porous structure of the 3D-printed scaffold, which is highly relevant in tissue engineering applications to modulate cell behavior. A facile method of incorporating aligned and low-density electrospun meshes into a 3D-printed scaffold was demonstrated as the printed scaffold acted as a combined gap and patterned collector for the charged jet of the polymer solution. Biological assessment demonstrated that cell proliferation increased in the dual-scale scaffolds and aligned cells with an elongated morphology were observed on the mesh in the pores of the printed microfibers. Further investigation is required to understand how the conductivity of the material influences fiber formation and alignment potentially through the incorporation of conductive fillers such as graphene or the use of conductive polymers. The electrical charge distribution can also be altered by changing the printed scaffold geometry (e.g., hexagonal and triangular) and incorporating both conductive and insulating regions within the structure to influence fiber alignment. This study is a promising development in the fabrication of multiscale scaffolds that better reflect the complexity of native tissue and the ability to engineer specific architectures to control cell behavior.