Following the completion and characterisation of the experimental runs, regression analysis was performed for each of the response variables: shell thickness (described as radius, t shell ), monodispersity (described using E n ), and population (% of SPION@SiO 2 NPs compared to all particles formed). Using relevant statistics including the analysis of variance, lack of fit test, and goodness of fit metrics such as the r 2 and root mean squared error (RMSE), the most suitable models for each response were identified. Using the model, a regression equation was generated for each response. A factor was considered active when p ≤ 0.05. Terms greater than this were deemed inactive and were iteratively removed from the model. 3 Results and Discussion