Electrohydrodynamic jet printing of gelatin-GPTMS-PEO hybrid biomaterial inks for high-resolution fibre patterning

Electrohydrodynamic jet printing (EHD jet printing) enables high-resolution direct writing of fibrous biomaterial architectures, which are of interest for future biointerface, scaffold-mimetic, and sensing-oriented platforms. Yet EHD jet printing of aqueous gelatin systems remains challenging because of temperature-dependent viscosity increase, capillary instability, and narrow cone-jet stability windows. Here, we adapt an aqueous gelatin-GPTMS-PEO hybrid biomaterial ink for near-field EHD jet printing using acetic acid as a process-modifying additive. Acidification improved precursor clarity and extended the low-viscosity processing window during cooling, the printable formulation had an apparent viscosity of 49.6 mPa $\cdot$ s at 40 °C, electrical conductivity of approximately 102 mS ${\text{m}}^{-1}$ , and surface tension of 47.2 mN ${\text{m}}^{-1}$ . Jetting behaviour was mapped across applied voltage, working distance, and flow rate, identifying dripping, pulsating, stable cone-jet, and unstable regimes. Stable fibre deposition was achieved within a process window defined by $B{o}_E$ = 0.26-0.74, $d/h\le 0.50$ , and $Ca$ = 0.025-0.050. FTIR-ATR and Raman spectroscopy supported retention of the principal gelatin and PEO vibrational signatures after acidification and printing, with no major spectroscopically detectable degradation. Under optimised conditions, continuous fibres with a mean diameter of 1.19 $\pm$ 0.49 µm were obtained, and programmed parallel patterns were deposited with a mean absolute spacing error of 3.3% relative to a nominal 1 mm spacing. These results establish a process-structure platform for EHD printing of aqueous gelatin-based hybrid biomaterial inks and provide a foundation for patterned fibrous architectures in nanobiotechnology.