The interaction of nanomaterials with cells and lipid bilayers is critical in many applications such as phototherapy, imaging, and drug/gene delivery. These applications require a firm control over nanoparticle-cell interactions, which are mainly dictated by surface properties of nanoparticles. This critical Review presents an understanding of how synthetic and natural chemical moieties on the nanoparticle surface (in addition to nanoparticle shape and size) impact their interaction with lipid bilayers and cells. Challenges for undertaking a systematic study to elucidate nanoparticle-cell interactions are also discussed.

Effect of Surface Properties on Nanoparticle–Cell Interactions

https://research-information.bris.ac.uk/files/164059916/Full_text_PDF_final_published_version_.pdf

PAMAM dendrimer - cell membrane interactions.

Nanoscale analysis of supported lipid bilayers using atomic force microscopy.

The energetics, stoichiometry, and structure of poly(amidoamine) (PAMAM) dendrimer-phospholipid interactions were measured with isothermal titration calorimetry (ITC), transmission electron microscopy (TEM), atomic force microscopy (AFM), dynamic light scattering (DLS), and molecular dynamics (MD) simulations. Dendrimers of sixth-generation and smaller interacted with the lipids at an average stoichiometry and enthalpy proportional to the number of primary amines per dendrimers (4.5 ± 0.1 lipids/primary amine and 6.3 ± 0.3 kJ/mol of primary amines, respectively). Larger dendrimers, however, demonstrated a decreased number of bound lipids and heat release per primary amine, presumably due to the steric restriction of dendrimer deformation on the lipid bilayer. For example, eighth-generation PAMAM dendrimers bound to 44% fewer lipids per primary amine and released 63% less heat per primary amine as compared to the smaller dendrimers. These differences in binding stoichiometry support generation-dependent models for dendrimer-lipid complexation, which are consistent with previously observed generation-dependent differences in dendrimer-induced membrane disruption. Dendrimers of seventh-generation and larger bound to lipids with an average stoichiometry consistent with each dendrimer having been wrapped by a bilayer of lipids, whereas smaller dendrimers did not.

/pdf/stoichiometry-and-structure-of-poly-amidoamine-dendrimer-1aigy7id1m.pdf

Stoichiometry and structure of poly(amidoamine) dendrimer-lipid complexes

The unique properties of poly(amido)amine dendrimers such as nano size, multifunctional surface, ability to encapsulate and bind the guest molecules, efficient membrane transport and shelf-life stability have made them a promising carrier in drug delivery. The two key applications of dendrimers include increasing the solubility and sustained release of molecules, and drug targeting by grafting the cell-specific ligands on the surface. Despite their potential in drug delivery, inherent cytotoxicity, reticuloendothelial system uptake and hemolysis limit their use in clinical applications. Research groups have been working on surface modification methods to mitigate these problems. Herein we present a brief discussion on current surface modification approaches to: i) increase targeting efficiency; ii) increase the cellular permeability for enhanced absorption; iii) increase gene transfection efficiency; and iv) decrease the toxicity of the dendrimers, with a few classic examples. As the knowledge of relationship between the dendrimer surface chemistry and its mode of interactions with cell membrane is developed, so do the modifications of dendrimer structure to render them nontoxic, biocompatible, biodegradable and improve their pharmacodynamic and pharmacokinetic properties. Development of multifunctional dendrimers with each functional unit imparting a distinct characteristic feature such as target cell recognition, enhanced cellular transport, reduction in reticuloendothelial system uptake and stability in in vivo environment holds a great potential for future biomedical applications.

Surface modified poly(amido)amine dendrimers as diverse nanomolecules for biomedical applications.

Mechanistic insight into cell growth, internalization, and cytotoxicity of PAMAM dendrimers.

Studies on the interaction of different generation poly (amido amine) (PAMAM) dendrimers (2G, 4G and 6G) and liposomes of different compositions were carried out by a combined turbidity, dynamic light scattering and atomic force microscopic measurements. Liposomes comprising soy lecithin (SLC, negative surface charge), 1, 2-palmitoyl-sn-glycero-3-phosphatidylcholine (DPPC, mildly positive surface charge), 1,2-dipalmitoyl-sn-glycero-3-phospho-(1'-rac-glycerol (DPPG, negatively charged) and a biologically simulated mixture of DPPC + DPPG (7:3, M/M, negatively charged) were used as model bilayers. 30 wt% cholesterol was used in each combination as it is known to control the fluidity of membrane bilayers. Silica was used as a negatively charged hard sphere model with an aim to compare the results. Both the turbidity and hydrodynamic diameter values of all the liposomes, except DPPC, passed through maxima upon the progressive addition of PAMAM; the effect was insignificant in case of DPPC. Formation of dendriosome, a complex formed between dendrimer and liposome, resulted in the charge reversal of the negatively charged liposomes. Interaction between PAMAM and liposome was found to be governed by electrostatic as well as hydrogen bonding. Generation dependent PAMAM activity followed the order: 6G >4G>2G in terms of overall dendrimer concentration. However, interestingly, the order was reverse when PAMAM activity was considered in terms of total end group concentrations. AFM studies reveal the rupture of bilayer structure upon addition of dendrimer.

Physico-chemical studies on the interaction of dendrimers with lipid bilayers. 1. Effect of dendrimer generation and liposome surface charge.

The interaction kinetics of polyamidoamine (PAMAM) dendrimers with supported lipid bilayers of 1,2-sn-glycero-dimyristoylphosphocholine prepared by the vesicle deposition has been probed by optical waveguide lightmode spectroscopy and atomic force microscopy (AFM). In particular, the influence of PAMAM dendrimer generation (G2, G4, and G6) and concentration (1 to 100 nM) on the levels of adsorption and lipid bilayer removal have been determined as a function of time; hence interaction kinetics and mechanisms have been further elucidated. Dendrimer interaction kinetics with the lipid bilayer are concentration dependent in a complex manner, with net bilayer removal at 1 and 100 nM and net adsorption at 10 nM; these effects are irrespective of dendrimer generation. The pseudo first order rate constant for bilayer removal (at 1 and 100 nM) follows the order G6 > G4 > G2. In contrast, the pseudo first order rate constant for adsorption at 10 nM follows the order G2 > G4 > G6. AFM has confirmed expansion of lipid bilayer defects, hole formation, and adsorption to the bilayer or bilayer defects, and their concentration and generation dependence. These findings have implications when designing dendrimers for specific biopharmaceutical activities, e.g., as drugs, drug delivery vehicles, transfection agents, or antimicrobials.

PAMAM Dendrimer Interactions with Supported Lipid Bilayers : A Kinetic and Mechanistic Investigation

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Mechanistic insight into cell growth, internalization, and cytotoxicity of PAMAM dendrimers.

Physico-chemical studies on the interaction of dendrimers with lipid bilayers. 1. Effect of dendrimer generation and liposome surface charge.

PAMAM Dendrimer Interactions with Supported Lipid Bilayers : A Kinetic and Mechanistic Investigation