Interfacial stress transfer and nanoparticle size as key factors in the strength of hydroxyapatite-polymer dental nanocomposites

Objectives: Existing models for estimating the strength of polymer/hydroxyapatite (HA) dental nanocomposites neglect important parameters, restricting the production and optimization of such nanocomposites. Hence, an advanced model is proposed to estimate the tensile strength of dental nanocomposites, considering the key properties of the rod-like HA nanoparticles and the adjoining interphase. Methods: The proposed model incorporates the interfacial bonding parameter (B), interfacial stress parameter (S), nanoparticle radius (R), nanoparticle length (l), interphase strength (σ_i), and interphase thickness (t), with S being defined by the properties of the HA nanoparticles and the interphase. Results: The strength and thickness of the interphase directly influence the nanocomposite strength, while the nanoparticle length and radius exhibit a direct and inverse relationship with composite strength, respectively. The model is validated against extensive experimental data from diverse systems. At σ_i = 80 MPa and t = 20 nm, S increases to 100 MPa, with the sample strength growing by 550 %; however, at σ_i = 30 MPa and t = 5 nm, S < 0, with no observable reinforcement. Moreover, the nanocomposite strength increases by 350 % at R = 20 nm and l = 150 nm. Significance: The significant influence of the considered parameters on the mechanical properties of the samples validates the proposed model. Thus, the model is a useful tool for estimating the strength of HA-filled dental nanocomposites.