Open-source three-dimensional printing of biodegradable polymer scaffolds for tissue engineering

Abstract

The fabrication of scaffolds for tissue engineering requires elements of customization depending on the application and is often limited due to the flexibility of the processing technique. This investigation seeks to address this obstacle by utilizing an open-source three-dimensional printing (3DP) system that allows vast customizability and facilitates reproduction of experiments. The effects of processing parameters on printed poly(ε-caprolactone) scaffolds with uniform and gradient pore architectures have been characterized with respect to fiber and pore morphology and mechanical properties. The results demonstrate the ability to tailor the fiber diameter, pore size, and porosity through modification of pressure, printing speed, and programmed fiber spacing. A model was also used to predict the compressive mechanical properties of uniform and gradient scaffolds, and it was found that modulus and yield strength declined with increasing porosity. The use of open-source 3DP technologies for printing tissue-engineering scaffolds provides a flexible system that can be readily modified at a low cost and is supported by community documentation. In this manner, the 3DP system is more accessible to the scientific community, which further facilitates the translation of these technologies toward successful tissue-engineering strategies.

Figure 1

Photograph of BariCUDA extruder with schematic representations of heating and PCL components superimposed. Nitrogen gas is used to pneumatically control extrusion through a syringe-based extruder. Nichrome wire acts as a heating element around the entire surface of the syringe and melts the PCL pellets for facilitated extrusion. No solvents are needed for polymer extrusion in this system.

Figure 2

Programmed fiber spacing (s, mm), printing speed (F, mm/min), and operating pressure (P, psi) are specified in the Python code to print 0° and 90° PCL layers. One 0° and one 90° layer are considered to be a complete grid with square pores. Pore size (d_p, mm) and fiber diameter (d_f, mm) can be measured using optical microscopy and later used to calculate the experimental fiber spacing to compare to its corresponding programmed value (s).

Figure 3

Representative optical micrograph (0.9× magnification) of a top view of a 3DP PCL scaffold with (A) s = 1.8mm, (B) s = 2.0mm, (C) s = 2.5mm.

Figure 4

Comparison of the porosities of 3DP scaffolds printed at a) F = 300mm/min and b) 400mm/min measured using gravimetry. The data represent means of four samples with the error bars representing the standard deviations. One-way ANOVA was used to determine significant differences within each F/s combination (p < 0.05). Significance in (#) s = 1.8 group, (*) s = 2.0 group, (†) s = 2.5 group. A–B Values marked with same letter do not differ. Note: It was not possible to print all F/s combinations at P = 8, 10, 12, 16, 18, 20psi (where bars are absent).

Figure 5

Comparison of the a), b) fiber diameters and c), d) pore sizes of 3DP scaffolds printed at a), c) F = 300mm/min and b), d) 400mm/min measured using optical microscopy. The data represent means of four samples with the error bars representing the standard deviations. One-way ANOVA was used to determine significant differences within each F/s combination (p < 0.05). Significance in (#) s = 1.8 group, (*) s = 2.0 group, (†) s = 2.5 group. A–C Values marked with same letter do not differ. Note: It was not possible to print all F/s combinations at P = 8, 10, 12, 16, 18, 20psi (where bars are absent).

Figure 5

Comparison of the a), b) fiber diameters and c), d) pore sizes of 3DP scaffolds printed at a), c) F = 300mm/min and b), d) 400mm/min measured using optical microscopy. The data represent means of four samples with the error bars representing the standard deviations. One-way ANOVA was used to determine significant differences within each F/s combination (p < 0.05). Significance in (#) s = 1.8 group, (*) s = 2.0 group, (†) s = 2.5 group. A–C Values marked with same letter do not differ. Note: It was not possible to print all F/s combinations at P = 8, 10, 12, 16, 18, 20psi (where bars are absent).

Figure 6

Comparison of the fiber spacings of 3DP scaffolds printed at a) F = 300mm/min and b) 400mm/min. The data represent means of four samples with the error bars representing the standard deviations. One-way ANOVA was used to determine significant differences within each F/s combination (p < 0.05). Significance in (#) s = 1.8 group, (*) s = 2.0 group, (†) s = 2.5 group. A–B Values marked with same letter do not differ. Note: It was not possible to print all F/s combinations at P = 8, 10, 12, 16, 18, 20psi (where bars are absent).

Figure 7

Comparison of the porosities of uniform and gradient 3DP scaffolds printed at F = 400mm/min, P = 16psi. (solid) indicates a fiber spacing that produces 0% theoretical porosity at the given F and p values. Groups with dashed lines are printed in the same manner as their solid counterpart. (Pa) Scaffold was tested with smaller pore size on bottom. (Pb) Scaffold was tested with smaller pore size on top. The data represent means of three samples with the error bars representing the standard deviations. One-way ANOVA was used to determine significant differences among groups (p < 0.05). A–E Values marked with the same letter do not differ.

Figure 8

Compressive testing a) yield strength, b) modulus, of porous 3DP scaffolds (uniform and gradient) printed at F = 400mm/min, P = 16psi. (solid) indicates a fiber spacing that produces 0% theoretical porosity at the given F and p values. Groups with dashed lines are printed in the same manner as their solid counterpart. (Pa) Scaffold was tested with smaller pore size on bottom. (Pb) Scaffold was tested with smaller pore size on top. † and # indicate statistical significance (p < 0.05, n = 3) within compressive yield strength and modulus values, respectively.

Figure 9

Mechanical properties of both uniform and gradient scaffolds. a) Scaffold compressive yield strength and b) compressive modulus as a function of volume fraction, where ε = porosity and both axes are on a logarithmic scale (base 10). Predicted values for dotted line (Theory) a) slope = 1.5 and b) = 2, follow a power law relationship of an isotropic cubic cell. Experimental values follow a best fit power law relationship as stated in Table 4.