A Mechanistic Study on Cellular Uptake of Nanoparticles for Enhanced Drug Delivery

Open Access
Author:
Huang, Changjin
Graduate Program:
Engineering Science and Mechanics
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
February 28, 2014
Committee Members:
  • Sulin Zhang, Dissertation Advisor
  • Sulin Zhang, Committee Chair
  • Bernhard R Tittmann, Committee Member
  • Melik C Demirel, Committee Member
  • Jian Xu, Committee Member
  • Peter J Butler, Committee Member
  • Cheng Dong, Committee Member
Keywords:
  • Nanoparticle
  • cellular uptake
  • substrate stiffness
  • topography
  • thermodynamics
  • molecular dynamics
  • drug delivery
  • cancer
Abstract:
Inspired by the high specificity and efficiency of the invasion of viruses into mammalian cells, extensive effort has been devoted to develop biomimetic nanoparticle (NP)-based therapeutics. Driven by the specific binding of ligands on the NP with the complementary receptors overexpressed on cancer cells, NPs enter cells through receptor-mediated endocytosis. As drugs are loaded either on or inside NPs, the efficacy of such systems is largely controlled by the amount of NPs that enter cells, i.e. cellular uptake. Despite considerable progress in the optimization of the NP design for enhanced cellular uptake, a comprehensive design map that presents the optimal combination of various variables is still missing. In addition, due to the active responses of cells to physical stimuli via mechanotransduction, the cellular uptake may also be regulated by the physical environments of cells. Especially, whether and how substrate stiffness and surface topography modulate cellular uptake of NPs requires further investigation. To understand the endocytosis process, we developed a thermodynamics model for receptor-mediated endocytosis of spherical NPs. This model allowed us to interpret the endocytosis process from a general energy-balance framework of NP-membrane adhesion and membrane deformation. The model foresaw the interrelated effects of particle size and ligand density on endocytosis. The phase diagrams of the endocytic time of a single NP, cellular uptake of multiple NPs and the phenomenal cellular uptake rate in the space of particle size and ligand density provide a clear design map for spherical NP-based bioagents. To study the endocytosis of nonspherical NPs, which is inaccessible by theoretical approaches, we extended our coarse-grained molecular dynamics (CGMD) membrane model to simulate receptor-mediated endocytosis of NPs of various sizes and shapes. Our simulations demonstrated that NP shape modulates the kinetics of endocytosis via rotation mediated by the membrane deformation. For a spherocylindrical NP with the initial upright docking position on the membrane plane, endocytosis proceeds through a laying-down-then-standing-up sequence. A free energy analysis revealed that NP size encodes the maximal membrane curvature energy that primarily determines the completion of endocytosis, while NP shape breaks the symmetry of curvature energy landscape and hence dictates the endocytic pathway and the angle of entry. By performing cellular uptake assay on polyacrylamide (PA) gel of various stiffnesses and substrates of various topographies, we confirmed the direct regulations on cellular uptake of NPs by the physical environments of cells. Our experiments indicated that physical stimuli modulate cellular uptake via mechanotransduction by dictating cellular spreading and membrane mechanics. Our results not only provide fundamental guidelines, but also open up new avenues for engineering NP-based drug delivery system for more sensitive disease diagnosis and more effective anticancer drug delivery.