Shape-Dependent Entropic Forces Govern Synergistic Bystander Nanoparticle Uptake

Area of Science:

• Nanomedicine
• Biophysics
• Materials Science

Background:

• Designing multicomponent nanocarriers for synergistic drug delivery is crucial in nanomedicine.
• Understanding the biophysical principles governing nanoparticle-cell interactions is often incomplete.
• Bystander uptake, where active uptake of functionalized nanoparticles (F-NPs) promotes co-internalization of nonfunctionalized bystander nanoparticles (B-NPs), is a key process.

Purpose of the Study:

• To investigate the role of nanoparticle shape in bystander uptake.
• To determine the optimal nanoparticle geometry for enhanced co-internalization.
• To elucidate the underlying biophysical mechanisms driving shape-dependent uptake.

Main Methods:

• Combined experimental studies, molecular dynamics simulations, and theoretical modeling.
• Investigated nanoparticle uptake across various shapes including spheres, triangles, plates, and nanorods.
• Analyzed the influence of nanoparticle aspect ratio (AR) on uptake efficiency and underlying forces.

Main Results:

• Demonstrated a nonmonotonic dependence of bystander uptake on nanoparticle geometry.
• Identified nanorods with an aspect ratio (AR) of approximately 3 as exhibiting markedly superior uptake compared to other shapes.
• Revealed that enhanced uptake is driven by shape-dependent entropic forces promoting rapid particle reorientation, not binding affinity, linked to a staircase free energy landscape.

Conclusions:

• Established shape selectivity as a critical principle for designing multicomponent nanocarriers.
• The optimal AR ≈ 3 balances entropic benefits with rotational constraints, a phenomenon predictable by a theoretical framework incorporating collective F-NP action.
• Shifts focus from enthalpy-modulated affinity to engineering entropy-driven state transitions for improved drug delivery systems.