Fabrication of meso/macroporous TiO₂/PCL composite scaffolds by direct ink writing: The effects of porogen content on the compressive modulus and in vitro behavior

In this paper, TiO₂/PCL composite scaffolds with different pore sizes were fabricated by a combination of sol-gel, porogen leaching, and direct ink writing techniques. The effects of porogen content and leaching time on the compressive modulus and porosity percentage were investigated. The central composite design was employed for statistical modeling and prediction of the compressive modulus and porosity percentage for deferent porogen contents and leaching time. The results showed that with increasing the porogen content (in the printing ink) from 30 to 70 wt%, the compressive modulus decreased from 20.03 to 4.96 MPa and the porosity percentage increased from 74.56% to 80.02%. The optimum leaching time for porogen removal was around 7 days in deionized water. In vitro degradability of the scaffolds was enhanced by increasing the NaCl content in the printing ink and reached 15% for the samples containing 70 wt% NaCl. Furthermore, the hydrophilicity of the samples was also increased and the water contact angle decreased from 74.80 to 58.48 º. The suitability of the scaffolds for bone tissue engineering applications was proved by in vitro cytotoxicity (MTS) and Alkaline Phosphatase activity assays (performed on Human Bone Marrow Stromal cells). DAPI/Phalloidin cell staining was also employed to monitor the cell morphology on the scaffolds. The results indicated the existence of multiscale porosity in 3D-printed TiO₂/PCL scaffolds which supplies a suitable structure for cell nesting, tissue regeneration, and potential drug delivery applications.