Direct 3D printing functional surfaces stacked with microstructured filaments

Additive manufacturing based on material extrusion is widely used in industrial production due to low cost, high throughput, and materials compatibility. Surface microstructures endow 3D-printed products with advanced functions, including anti-fouling, anti-corrosion, drag reduction, etc. However, it is challenging to directly achieve surface microstructures during the continuous extrusion of filaments for additive manufacturing. Despite the development of a variety of post- and pre-processing strategies aimed at fabricating microstructured surfaces of 3D printed products, they are unable to online regulate the microscale morphology which often needs additional operations and reduces the manufacturing efficiency. Herein, we propose an online 3D printing strategy based on material extrusion for the direct fabrication of objects stacked with microstructured filaments. It utilizes a microgrooved printing nozzle to extrude microridged filaments. The dimension and geometry of the microridges on surfaces can be controlled by adjusting printing parameters and the microgrooves within the nozzle. The morphology of microridges is influenced by the extrudate swell resulting from the viscoelastic properties of the polymer during extrusion. Triangular, bell-shaped, trapezoidal microridges are fabricated by different cross-sectional profiles. The Bird-Carreau model is applied to describe the flow behavior of melted polymers. Compatibility of the technology with conventional material extrusion-based additive manufacturing is validated by printing a variety of materials and using different diameters of nozzles. The material extrusion additive manufacturing products with anisotropic wetting surfaces are successfully achieved with static contact angles of 155° and 76° in two crossed directions. The technology provides a new paradigm for microstructured 3D printing, leading to potential impacts in the fabrication of smart microfluidic devices, multifunctional tissue engineering scaffolds, and high-performance sensors.