RESOURCES

Abstract
Electrostimulation and electroactive scaffolds can positively influence and guide cellular behaviour and thus has been garnering interest as a key tissue engineering strategy. The development of conducting polymers such as polyaniline enables the fabrication of conductive polymeric composite scaffolds. In this study, we report on the initial development of a polycaprolactone scaffold incorporating different weight loadings of a polyaniline microparticle filler. The scaffolds are fabricated using screw-assisted extrusion-based 3D printing and are characterised for their morphological, mechanical, conductivity, and preliminary biological properties. The conductivity of the polycaprolactone scaffolds increases with the inclusion of polyaniline. The in vitro cytocompatibility of the scaffolds was assessed using human adipose-derived stem cells to determine cell viability and proliferation up to 21 days. A cytotoxicity threshold was reached at 1% wt. polyaniline loading. Scaffolds with 0.1% wt. polyaniline showed suitable compressive strength (6.45 ± 0.16 MPa) and conductivity (2.46 ± 0.65 × 10(-4) S/cm) for bone tissue engineering applications and demonstrated the highest cell viability at day 1 (88%) with cytocompatibility for up to 21 days in cell culture.

Abstract
Conductive polymers have been used for various biomedical applications including biosensors{,} tissue engineering and regenerative medicine. However{,} the poor processability and brittleness of these polymers hinder the fabrication of three-dimensional structures with desirable geometries. Moreover{,} their application in tissue engineering and regenerative medicine has been so far limited to excitable cells such as neurons and muscle cells. To enable their wider adoption in tissue engineering and regenerative medicine{,} new materials and formulations that overcome current limitations are required. Herein{,} a biodegradable conductive block copolymer{,} tetraaniline-b-polycaprolactone-b-tetraaniline (TPT){,} is synthesised and 3D printed for the first time into porous scaffolds with defined geometries. Inks are formulated by combining TPT with PCL in solutions which are then directly 3D printed to generate porous scaffolds. TPT and PCL are both biodegradable. The combination of TPT with PCL increases the flexibility of the hybrid material compared to pure TPT{,} which is critical for applications that need mechanical robustness of the scaffolds. The highest TPT content shows the lowest tensile failure strain. Moreover{,} the absorption of a cell adhesion-promoting protein (fibronectin) and chondrogenic differentiation of chondroprogenitor cells are found to be dependent on the amount of TPT in the blends. Higher content of TPT in the blends increases both fibronectin adsorption and chondrogenic differentiation{,} though the highest concentration of TPT in the blends is limited by its solubility in the ink. Despite the contradicting effects of TPT concentration on flexibility and chondrogenic differentiation{,} a concentration that strikes a balance between the two factors is still available. It is worth noting that the effect on chondrogenic differentiation is found in scaffolds without external electric stimulation. Our work demonstrates the possibility of 3D printing flexible conductive and biodegradable scaffolds and their potential use in cartilage tissue regeneration{,} and opens up future opportunities in using electric stimulation to control chondrogenesis in these scaffolds.