Extended validation of the mesh integration (MINT) index: a 1-year porcine study

Mesh Integration (MINT) index was previously proposed and validated in the short term as a standardised objective method of evaluating in vivo hernia mesh behaviour. The primary aim was to validate the degradation domain of the mesh integration (MINT) index over a 1-year period using a porcine model, with the secondary aim of determining integration and fibrosis scores after extended implantation.

Six brands of mesh were implanted into three Landrace-White pigs within the retrorectus space. Post-mortems were performed at 1 year. All mesh-tissue samples were subjected to standardised testing specified by MINT. Previous 3-month study conditions were fully replicated.

Mesh was successfully implanted into all pigs, with an unremarkable 1-year natural history. There were no difficulties at post-mortem. Visually, all meshes were highly integrated. The 1-year degradation scores obtained were consistent with changes expected in absorbable meshes. Since study methodology, study conditions and mesh lot numbers were identical, the current study data were combined with the previous 3-month study for statistical analysis. Multi-level regression analysis with maximum likelihood was performed, and model diagnostics were conducted. Non-linear models achieved better fit to data than linear models, namely asymptotic for integration ( $-2LL=76.46,R^2=0.971,RMSE=0.370$ ), biexponential for fibrosis ( $-2LL=127.57,R^2=0.941,RMSE=0.517$ ) and logistic regression for degradation ( $-2LL=199.83,R^2=0.984,RMSE=0.817$ ). Rationale and limitations to interpretation of the study results were extensively discussed.

The degradation domain of the MINT index has been validated at 1 year. The versatility of the MINT index platform could potentially be used to summarise existing literature evidence on in vivo mesh behaviour.