Structural and dynamical consistency in lipid vesicles across all-atom, MARTINI, and dissipative particle dynamics

We develop and validate a mesoscale dissipative particle dynamics (DPD)-4 lipid model, parameterized from an established MARTINI force field. We benchmark this DPD model and a MARTINI model for coarse-grained (CG) lipid vesicles against All-Atom simulations to evaluate their ability to capture structural properties across their respective scales. Dynamical properties are evaluated through comparison between the CG models themselves and against experimental trends. We find that the CG models can capture multiscale spatio-temporal properties of ultrasmall unilamellar vesicles (USUVs) and small unilamellar vesicles (SUVs) with diameters under and over 50 nm, respectively. Specifically, MARTINI and mesoscale DPD lipid models are in agreement in capturing local structural changes of USUVs, such as curvature-dependent lipid packing. For this particular system, structural consistency has been validated using all-atom simulations. At shorter times, dynamical consistency has been validated through agreement between the MARTINI and DPD models. The CG dynamics (with short timescales matched to all-atom simulations) of 60 nm SUVs have been seen to follow the same stretched-exponential relaxation behavior observed in corresponding experiments. This near multi-scale validation highlights a stronger requirement for assessing CG models across length and time. In so doing, we have also demonstrated the potential for using both MARTINI and DPD models to extend vesicle simulations and provide dynamical information in mesoscale regimes with significant computational savings.