Structural and Mechanical Evaluation of Polycaprolactone Scaffold with the Gradient Porous Microstructure for Bone Tissue Engineering

In gradient scaffolds, changes in porosity, pore size or chemical composition occur gradually. Recently, different methods have been applied to create gradient in the scaffolds, but they have some disadvantages such as high cost and control. The main purpose of this research was to fabricate porous gradient scaffolds by a novel, functional, simple, and low-cost method. Two homogenous scaffolds (Homog 1 and Homog 2) and two gradient scaffolds (Grad 1 and Grad 2) were fabricated and compared. Polycaprolactone scaffolds with the pore size gradient along the radial direction were fabricated by combining layer-by-layer assembly and porogen leaching techniques. Paraffin micro particles were used as porogen in two size ranges: 250 to 420 µm and 420 to 600 µm. The average pore size of Homog 1 and Homog 2 was 278.48 ± 11.23 µm and 417.79 ± 14.62, which were suitable for bone tissue engineering. The porosity of the samples was: Homog 1: 77.5 ± 1.25 %, Homog 2: 61.3 ± 3.5 %, Grad 1: 74 ± 0.5 % and Grad 2: 79.8 ± 4 %. It should be stated that the required porosity for cell survival and growth was above 70 %. Compressive strength at 80% strain and compressive modulus for Homog 1, Homog 2, Grad 1 and Grad 2 were 0.16 ± 0.16 MPa and 0.25 ± 0.11 MPa, 0.26 ± 0.20 MPa and 0.53 ± 0.34 MPa, 0.19 ± 0.34 MPa and 0.33 ± 0.43 MPa, 0.12 ± 0.28 MPa and 0.16 ± 0.51 MPa, respectively. The results showed that pore size gradient had a negligible effect on the mechanical properties of the scaffolds and using polycaprolactone (PCL) as the only material of scaffold was not appropriate. The structure of gradient scaffolds showed the radial pore size gradient with a good adhesion between layers without any detectable interface; the result of the compression test also confirmed it.