Quaternized poly(ethyleneimine) in PMMA bone cement: Impact on polymerization reaction and mechanical behavior

Poly(methyl methacrylate) (PMMA) bone cements are widely used in orthopedic applications but lack intrinsic antimicrobial activity, making them susceptible to implant-associated infections. While antibiotics are commonly incorporated, their limitations have motivated the exploration of alternative polymeric modifiers, including quaternized poly(ethyleneimine) (PEI-QA), for use in bone cement formulations. In this study, PEI-QA was evaluated as an additive in PMMA bone cement, focusing on its effects on polymerization behavior and material properties. PEI-QA was synthesized via alkylation of branched PEI and incorporated at 1.25 wt%. Its presence significantly disrupted the curing process, leading to a reduced exothermic peak (T_max 29.0 ± 1.4 °C), lower glass transition temperature, and increased apparent density. Despite a seemingly more compact microstructure, the compressive strength decreased markedly from ∼92.45 MPa to ∼40 MPa. EDS analysis revealed residual bromide and iodide species from the quaternization process, suggesting that halide counter-ions interfere with free-radical polymerization, hindering chain propagation. These findings demonstrate that residual halides critically impair MMA polymerization kinetics, limiting the direct application of PEI-QA in PMMA bone cements. Overall, this work highlights the need for improved purification protocols or alternative functionalization strategies to ensure compatibility between cationic polymers and PMMA polymerization systems.