Nanotechnology. 2017 Jan 10;28(6):064004. doi: 10.1088/1361-6528/aa536f.

Hybrid 3D-2D printing for bone scaffolds fabrication.

Seleznev VA, Prinz VY.
Rzhanov Institute of Semiconductor Physics, Siberian Branch of the Russian Academy of Sciences (ISP SB RAS), pr. Lavrentieva 13, Novosibirsk, 630090, Russia.

Abstract

It is a well-known fact that bone scaffold topography on micro- and nanometer scale influences the cellular behavior. Nano-scale surface modification of scaffolds allows the modulation of biological activity for enhanced cell differentiation. To date, there has been only a limited success in printing scaffolds with micro- and nano-scale features exposed on the surface. To improve on the currently available imperfect technologies, in our paper we introduce new hybrid technologies based on a combination of 2D (nano imprint) and 3D printing methods. The first method is based on using light projection 3D printing and simultaneous 2D nanostructuring of each of the layers during the formation of the 3D structure. The second method is based on the sequential integration of preliminarily created 2D nanostructured films into a 3D printed structure. The capabilities of the developed hybrid technologies are demonstrated with the example of forming 3D bone scaffolds. The proposed technologies can be used to fabricate complex 3D micro- and nanostructured products for various fields.

PMID: 28071595

 

Supplement:

Inexpensive and low time-consuming methods for fabrication of 3D structures which would ensure surface micro- and nanostructuring in strictly defined regions are required. Successive stereolithography methods intended for point-by-point creation of 3D objects with a high resolution of 100 nm are known; however, such methods are too time-consuming. For instance, two-photon stereolithography facilities permit fabrication of 3D nanoobjects sized smaller than 100 nm; however, such facilities still remain expensive and extremely slow [1]. Nanoimprint lithography permits mass and inexpensive production of 2D micro- and nanostructured surfaces. Projection stereolithography permits rapid production of 3D structures of prescribed shape; however, it fails to ensure controllable nanostructuring at prescribed places. It is known that the combining of microstructuring and nanostructuring methods in a hybrid method permits solving some problems [2].
In the present work, we have proposed and demonstrated new possibilities in the implementation of new hybrid technologies based on a combination of 2D (nano imprint) and 3D printing methods (fig.1). The first method implies using 3D printing and simultaneous 2D nanostructuring of each of the layers during the formation of the 3D structure (fig.1.b). The second method is based on the sequential integration of preliminarily created 2D nanostructured films into a 3D printed structure (fig.1.c). Note that the proposed methods (see fig.1.b, c) permit reaching full automation and extended functionality. Unlike known methods, the proposed methods feature a high production capacity and a possibility of rapid production of variously shaped 3D nanostructures.

 

 

Fig. 1. Schematic illustrating the standard projection stereolithography method (a) and the hybrid projection stereolithography and nanoimprint lithography methods (b), (c). (a) The elevator platform is elevated in steps to a certain height, the DMD projector is used to photopolymerize the material in certain regions of the layer in between the elevator platform and the vat window. Repetition of the procedures leads to the formation of a 3D object. (b) A hybrid method using a transparent nanostructured stamp built into the vat bottom of the projection stereolithography facility. The stamp provides for structuring of each of the photopolymerizable layers during the 3D object printing process. (с) A hybrid method using the integration of transparent nanostructured polymer films into the scaffold structure the 3D object printing process. The structured polymer film is placed on a given curing layer of the 3D object; then, a next curing layer is to be formed.

 

 

For demonstrating the possibilities offered by method illustrated in fig.1.b, we have prepared a pyramid in which sizes of each subsequent layer were made decreasing in value. Figure 2.a, b shows SEM images of one rib in the pyramid. It is clearly seen that, here, there formed steps whose surface had a stamp-printed micrometer relief (fig.2.b). We have not noticed any substantial difference in the quality of the micrometer-sized imprints made on the top and bottom layers. A comparison between the qualities of the imprints made with stamps prepared from various PDMS materials have showed that the stamps prepared from UV-PDMS were capable of withstanding more than 104 stamping processes without any substantial deterioration of imprint quality.

Figure 2.c shows SEM image 3D structure with embedded nanostructured polymer films by method illustrated in fig.1.c. The 3D structure contains four structured films clamped at their edges by clamp bars and suspended on supporting pillars to span a distance of 400 Î¼m. Such a configuration ensures rigid fixation of the films and complete removal of non-polymerized resin.

The capabilities of the developed hybrid technologies are demonstrated with the example of forming 3D bone scaffolds (fig.3) [3]. We have successfully fabricated examples of 3D micro- and nanostructured polymer bone scaffolds. The application area of the proposed hybrid technologies extends far beyond biology and medicine. These technologies can be used for fabrication of devices and materials, for which the surface micro- or nanostructuring is crucial. First of all it is necessary to mention superhydrophobic surfaces, gecko-inspired adhesives, optical metasurfaces and metamaterials, antireflective coatings, and micro- and nanofluidic systems.

 

 

Fig. 2. (a, b) SEM images rib in the pyramid formed using the hybrid stereolithography method (fig.1b). (a) Top view of 20 steps, the height of each step being 50 μm. (b) An enlarged image of the microstructured surfaces on three steps of the pyramid. Each of the layers was made structured using a stamp with a microgroove array. The depth and width of the microgrooves were 0.5 and 4 Î¼m, and the array pitch was 6 Î¼m. The sizes of each of the pyramiding layers were made decreasing in magnitude; as a result, steps with microstructured surface were formed. (d) SEM image of an end-face fragment of the 3D sample formed using the hybrid stereolithography method (fig.1c); the nanostructured polymer films are built-in with their edges into a formed bar.

 

 

Fig. 3. Bone scaffold with suspended nanostructured perforated membranes fabricated using the hybrid stereolithography method (Fig.1b). (a) Optical photo; (b) AFM image of the nanostructured membrane surface.

 

References

[1] M. Emons, et al, Opt. Mater. Express 2, 942-47 (2012).

[2] W.-S. Chu et al, Int. J. Prec. Eng. Manuf.-Green Technol. 1, 75-92 (2014).

[3] V.A. Seleznev and V.Ya. Prinz, Nanotechnology, 28, 064004 (2017)