Reconciliation of high strength and high porosity in pure collagen based structures is a major barrier in collagen’s use in load-bearing applications. The current study developed a CAD/CAM based electrocompaction method to manufacture highly porous patterned scaffolds using pure collagen. Utilization of computerized scaffold design and fabrication allows the integration of mesh-scaffolds with controlled pore size, shape and spacing. 

Figure 1: Process of fabricating individual patterned layer. Patterned electrochemical compaction of monomeric collagen solutions as mechanically robust lattice layers. The layers can be stacked to obtain thicker scaffolds.

Figure 2: Scaffolds with 4 different porosity shapes. A) Diamond-shaped pore; B) Square-shaped pore; C) Rectangle-shaped pore 4) Parallel channel pore. Black color of the scaffolds are due to genipin cross linking.  Black arrow indicates porosity through the thickness of the scaffold and blue arrow indicates spaces between the filaments of the layers of the scaffold.

Three different pore geometries were manufactured to demonstrate the control on pore morphology: i) rectangular ii) square and iii) diamond. The average pore sizes for rectangular, square and diamond-shaped scaffolds are 1.5, 0.8 and 1.2 mm with corresponding porosities of 55%, 43% and 61%, respectively. To assess the effect of pore geometries on the mechanical properties of the scaffold, another pore architecture with parallel pore channels (group iv) with intermittent connections was manufactured. The parallel channel pore scaffold group has 53% porosity which is comparable to rectangular and diamond shape pore scaffold.

Figure 3: DAPI (blue) and F-Actin (green) staining images revealed that cells covered the entire scaffold through thickness. Cells and nucleus became elongated along the length of the collagen filament (bottom enlarged image - horizontal direction).

Mechanical properties of fabricated collagen meshes were investigated as a function of number of patterned layers, and with different pore geometries.  The tensile stiffness, tensile strength and modulus ranges from 10-50 N/cm, 1-6 MPa and 5-40 MPa respectively for all the scaffold groups. These results are within the range of practical usability of different tissue engineering application such as tendon, hernia, stress urinary incontinence or thoracic wall reconstruction. Moreover, 3-fold increase in the layer number resulted in more than 5-fold increases in failure load, toughness and stiffness which suggests that by changing the number of layers and shape of the structure, mechanical properties can be modulated for the aforementioned tissue engineering application.  These patterned scaffolds offer a porosity ranging from 0.8-1.5 mm in size, a range that is commensurate with pore sizes of repair meshes in the market. 

The connected macroporosity of the scaffolds facilitated cell-seeding such that cells populated the entire scaffold at the time of seeding. After 3 days of culture, cell nuclei became elongated. These results indicate that the patterned electrochemical deposition method in this study was able to develop mechanically robust, highly porous collagen scaffolds with controlled porosity which not only tries to solve one of the major tissue engineering problems in a fundamental level but also has a significant potential to be used in different tissue engineering applications.