Filament Extrusion-Based Conductive TPU Composite Scaffolds Enable Superior Neuronal Growth and Synaptic Maturation...

Fused filament fabrication (FFF) three-dimensional (3D) printing technologies offer new opportunities for fabricating customizable, low-cost platforms for tissue engineering applications. Here, we developed and characterized 3D-printed scaffolds using conductive thermoplastic polyurethane (cTPU) filaments and evaluated their mechanical, electrical, and biological performance in vitro. Dynamic mechanical analysis (DMA) across a range of temperatures and frequencies revealed that both TPU and cTPU exhibit temperature- and rate-dependent elastic moduli, with cTPU showing enhanced mechanical stiffness due to the incorporation of conductive fillers. Electrical testing confirmed that cTPU exhibited a stable conductivity (∼1-2 mS/cm) resembling physiological conditions. Surface characterization showed that cTPU was significantly more hydrophilic and exhibited higher nanoscale roughness, both of which are favorable for cell-material interactions. Mouse embryonic fibroblasts (MEFs) cultured on both scaffolds showed high viability (>85%) and significant proliferation. Notably, immunofluorescence analysis of cultured hippocampal neurons revealed significantly higher density of neuronal networks represented by higher microtubule-associated protein 2 (MAP-2)-positive cell density, greater MAP-2 area coverage, larger average MAP-2 cell area, and enhanced postsynaptic density protein 95 (PSD-95) expression on cTPU scaffolds. Together, these results demonstrate that FFF 3D-printed cTPU platforms can support long-term neuronal growth and synaptic maturation, offering promising applications in neural tissue modeling and bioelectronic interfaces. Practical Application: Characterizing soft viscoelastic materials whose properties strongly depend on temperature and strain rate is challenging and typically requires extensive testing across multiple conditions. Using a single-specimen Dynamic Mechanical Analysis-based mechanical testing method and a viscoelastic-elastic transformation that converts frequency-domain viscoelastic measurements into elastic constants over a broad range of test conditions, validated by tensile tests, we efficiently generated reliable modulus data across a range of conditions, enhancing testing throughput without sacrificing accuracy. As a case study, we demonstrate the successful fabrication and comprehensive characterization of FDM 3D-printed conductive TPU (cTPU) scaffolds for potential applications in neural tissue modeling and bioelectronic interfaces, with the results positioning cTPU composites as cost-effective, tunable, cytocompatible, and electrically active platforms capable of supporting neuronal growth and function.