Morphology and mechanical properties of 3D printed PCL-PLA-ZnO nanocomposite scaffolds

Bone defects are one of the main challenges in universal medicine. When bone tissue is damaged, the cells may be able to regenerate the defect. If the percentage of reconstruction of bone defects is high, using degradable or permanent implants causes inflammation and movement problems for the patient. Today, to solve the problems of implants, it is tried to use bone tissue engineering (BTE). Bone tissue engineering is a science that combines scaffolds, cells and active biomolecules to make a tissue to regenerate or maintain the function and improve the damaged tissue. Recently, several researches have been done to support the extracellular matrix in bone tissue engineering. Polymers like polycaprolactone (PCL), polylactic acid (PLA), polyvinylidene fluoride (PVDF) and poly Lactic co-glycolic acid (PLGA) are used to fabricate bone scaffolds because of their biodegradability, biocompatibility and mechanical properties. Generally, polycaprolactone is one of the well-known biocompatible and bioactive materials for bone scaffolds, but it is hydrophobic and has a low degradation rate. Therefore, other biopolymers, such as polylactic acid are used to increase degradability and hydrophilicity. Also, ceramic nanoparticles such as zinc oxide are used to increase mechanical and biological properties. One of the methods for fabricating scaffolds is 3D printing, which prints a porous scaffold with a uniform morphology. So, in this research, PCL/PLA/ZnO scaffolds were fabricated by 3D printing. For this purpose, PCL or PCL containing 1, 2 and 3 wt% ZnO nanoparticles and PLA were printed layer by layer. 3D porous cube-shaped structures were designed to have 50 % porosity, 0:90° orientation. The printing conditions were considered as follows: rate 40 mm/min for PCL and 700 mm/min for PLA, 0.25 cm layer height, 400 µm Nozzle diameter and Pressure 2-3 bar. The morphology and mechanical properties were studied by SEM images and compression test, respectively. The SEM images showed that the printed scaffolds had a regular structure with a pore size between 300 and 400 micrometers. Also, the diameter of polycaprolactone filaments was almost equal to polylactic acid filaments. Pore size and the 3D structure of the scaffolds play a crucial part in the diffusion of bone cells. The mechanical properties of a perfect bone scaffold should match the mechanical properties of the host bone, and the bone scaffold should be able to tolerate the appropriate load. The stiffness of the samples PCL, PLA, PCL/PLA, PCL/PLA/1%ZnO, PCL/PLA/2%ZnO, PCL/PLA/3%ZnO was 52.39, 762.68, 214.66, 225.64, 233.62, 273.48 MPa, respectively. Adding PLA and ZnO to PCL scaffolds significantly improves mechanical performance. As a result, considering the 50% porosity of the bone composite scaffold (PCL/PLA/ZnO), it has a favorable compressive strength for bone tissue engineering applications.