Ethylene vinyl acetate as a binder for additive manufacturing of tricalcium phosphate bio-ceramics

Abstract

Tricalcium phosphate (TCP) ceramic scaffolds were made by the fused filament fabrication (FFF) using different grades of Ethylene vinyl acetate (EVA) as a thermoplastic binder. Stearic acid was studied as a processing aid. A wide range of rheological properties, shaping and debinding behavior could be observed with feedstocks made with different EVA grades. The addition of stearic acid affects flexibility of the solid filaments, the viscosity of feedstocks, and causes a pronounced yield stress behavior. These effects are strongly dependent on the molecular weight of the EVA and influence the printing process and shape stability during the debinding process. EVA binder system works well for thin and small parts, made with nozzle sizes below 0.4 mm, whereas samples made by thicker nozzle size form defects during debinding process. TCP scaffold structures with fin struts of 0.27 mm and partition wall thickness of 0.25 mm and a layer thickness of 0.20 mm could be successfully shaped, debinded and sintered. Excellent fusion between the different layers was achieved, since no defects at the interface could be detected.