Significant progress in 3D printing technology over recent decades has allowed for the creation of biomedical products with enhanced properties. The incorporation of composite materials in 3D printing offers innovative solutions to a wide range of real-world challenges in medical applications. The present research focuses on the additively manufactured 3D-printed polymer composites developed through the fused deposition modeling technique. Mechanical characteristics such as tensile, compressive, flexural, and Shore D hardness have been investigated in pure PLA/HDPE and with different 1, 2, 3 wt.% of functionalized nSiO2 reinforced PLA/HDPE. Their results showed that excellent mechanical strength was observed in the 2 wt.% nSiO2/PLA/HDPE composite as 147.3 MPa tensile strength and 4.05 GPa Young's modulus. Subsequently, the material characteristics of the 2 wt.% nSiO2-reinforced composite were investigated with various analytical techniques. FESEM micrographs revealed that the developed composites with a rougher surface promoted cell attachment and proliferation and had no delaminated parts in the printed layer. EDAX analysis confirmed the reinforcement material nSiO2 particles present in the developed composite. The prominent sharp peaks of nSiO2 incorporated in the 3D-printed composite have an excellent crystallinity nature with 84.3%. The presence of nSiO2 reinforcement in the composite matrix was confirmed by FTIR and Raman spectroscopy. TGA/DTG results displayed the 7.36% high thermal stability of the nSiO2-reinforced composite. Thus, the developed composite was found to be a promising material for bone implants in biomedical applications.