This study investigates the impact of PEG immunogenicity on the efficacy of PEG hydrogel-mediated tissue engineering, specifically in bone regeneration. PEG hydrogels are widely used in medical devices and tissue engineering due to their biocompatibility and tunable properties. However, concerns over PEG immunogenicity have emerged, with a high prevalence of anti-PEG antibodies detected in the general population. The study immunizes mice against PEG to induce anti-PEG antibody production and evaluates bone defect regeneration using bone morphogenetic protein-2 (BMP-2)-loaded PEG hydrogels. Results show that PEG sensitization increases bone formation compared to naive controls, but histological analysis reveals abnormally porous bone morphology, particularly in males. Immune cell recruitment is higher in PEG-sensitized mice treated with PEG-based treatment compared to naive controls. Additionally, naive controls that received PEG-based treatment also developed anti-PEG antibodies. Sex differences in bone formation and immune cell recruitment are observed, highlighting the need for further investigation into the implications of anti-PEG immune responses in tissue engineering applications.This study investigates the impact of PEG immunogenicity on the efficacy of PEG hydrogel-mediated tissue engineering, specifically in bone regeneration. PEG hydrogels are widely used in medical devices and tissue engineering due to their biocompatibility and tunable properties. However, concerns over PEG immunogenicity have emerged, with a high prevalence of anti-PEG antibodies detected in the general population. The study immunizes mice against PEG to induce anti-PEG antibody production and evaluates bone defect regeneration using bone morphogenetic protein-2 (BMP-2)-loaded PEG hydrogels. Results show that PEG sensitization increases bone formation compared to naive controls, but histological analysis reveals abnormally porous bone morphology, particularly in males. Immune cell recruitment is higher in PEG-sensitized mice treated with PEG-based treatment compared to naive controls. Additionally, naive controls that received PEG-based treatment also developed anti-PEG antibodies. Sex differences in bone formation and immune cell recruitment are observed, highlighting the need for further investigation into the implications of anti-PEG immune responses in tissue engineering applications.