Controlling loading and optical properties of gold nanoparticles on liposome membranes

pH-temperature dual-sensitive nucleolipid-containing stealth liposomes anchored with PEGylated AuNPs for triggering delivery of doxorubicin

Liposomes (Lip) are useful nanocarriers for drug delivery and cancer nanomedicine because of their ability to efficiently encapsulate drugs with different physical and chemical properties. The pH gradient between normal and tumoral tissues, and their rapid metabolism that induces hyperthermia encourage the development of pH- and thermo-sensitive Lip for delivering anticancer drugs. Nucleolipids have been studied as scaffolding material to prepare Lip, mainly for cancer therapy. Herein, we report for the first time the use of 1,2-dipalmitoyl-sn-glycero-3-(cytidine diphosphate) (DG-CDP) to develop pH/thermo-sensitive nucleolipid-containing stealth Lip stabilized by combination with 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and cholesterol, anchored with NH₂-PEGylated gold nanoparticles (PEG-AuNPs, 15 nm) for triggering delivery of doxorubicin (Dox). The optimal composition of DPPC, DG-CDP and cholesterol (94:3:3) was established by Langmuir isotherms. Unloaded and Dox-loaded Lip and AuNPs-Lip exhibited nano-scale sizes (415-650 nm), acceptable polydispersity indexes (<0.33), spherical shapes, and negative Z-potential (-23- -6.6 mV) due to the phosphate groups of DG-CDP, which allowed the anchoring with positively charged AuNPs. High EE% were achieved (>78%) and although efficient control in the Dox release towards different receptor media was observed, the release of Dox from PEG-AuNPs-Lip-Dox was significantly triggered at acidic pH and hyperthermia temperature, demonstrating its responsiveness to both stimuli. Dox-loaded Lip showed high cytotoxic activity against MDA-MB-231 breast cancer cells and SK-OV-3 ovarian cancer cells, suggesting that Dox was released from these nanocarriers over time. Overall, the liposomal formulations showed promising properties as stimuli-responsive nanocarriers for cancer nanomedicine, with prospects for hyperthermia therapy.

Cholesterol Levels Affect the Performance of AuNPs-Decorated Thermo-Sensitive Liposomes as Nanocarriers for Controlled Doxorubicin Delivery

Stimulus-responsive liposomes (L) for triggering drug release to the target site are particularly useful in cancer therapy. This research was focused on the evaluation of the effects of cholesterol levels in the performance of gold nanoparticles (AuNPs)-functionalized L for controlled doxorubicin (D) delivery. Their interfacial and morphological properties, drug release behavior against temperature changes and cytotoxic activity against breast and ovarian cancer cells were studied. Langmuir isotherms were performed to identify the most stable combination of lipid components. Two mole fractions of cholesterol (3.35 mol% and 40 mol%, L1 and L2 series, respectively) were evaluated. Thin-film hydration and transmembrane pH-gradient methods were used for preparing the L and for D loading, respectively. The cationic surface of L allowed the anchoring of negatively charged AuNPs by electrostatic interactions, even inducing a shift in the zeta potential of the L2 series. L exhibited nanometric sizes and spherical shape. The higher the proportion of cholesterol, the higher the drug loading. D was released in a controlled manner by diffusion-controlled mechanisms, and the proportions of cholesterol and temperature of release media influenced its release profiles. D-encapsulated L preserved its antiproliferative activity against cancer cells. The developed liposomal formulations exhibit promising properties for cancer treatment and potential for hyperthermia therapy.

Didodecyldimethylammonium Bromide Role in Anchoring Gold Nanoparticles onto Liposome Surface for Triggering the Drug Release

Liposomes with their capacity to anchor gold nanoparticles (AuNPs) onto their surface are used in the treatment of several pathologies such as cancer. The objective of this work was the optimization of the vesicle composition by using cationic agents in order to reinforce the anchoring process of AuNPs, and for the study of the influence of local temperature and vesicle size on drug release. A Plackett-Burman design was conducted to determine the optimal composition for the anchoring of AuNPs. A comprehensive study of the influence of lipid bilayer composition on the surface charge, size, and polydispersity index (PdI) of liposomes was carried out. Afterwards, in vitro release studies by dialysis were performed and several release parameters were evaluated as a function of temperature. Cholesterol was fixed as the rigid agent and Didodecyldimethylammonium bromide (DDAB) was selected as the cationic lipid into the liposome bilayer. Photomicrographs revealed that DDAB facilitated the anchoring of AuNPs onto the liposomal surface. The anchoring of AuNPs also enhanced the amount and rate of calcein released, especially in extruded samples, at several incubating temperatures. In addition, it was observed that both the anchoring of AuNPs and the calcein release were improved by increasing the surface of the vesicles. The contributions of liposome composition (DDAB inclusion, incubation temperature, anchoring of AuNPs) and size and surface availability of the vesicles on calcein release could be used to design improved lipid nanostructures for the controlled release of anticancer drugs.

A Concise Review of Gold Nanoparticles-Based Photo-Responsive Liposomes for Controlled Drug Delivery

The focus of drug delivery is shifting toward smart drug carriers that release the cargo in response to a change in the microenvironment due to an internal or external trigger. As the most clinically successful nanosystem, liposomes naturally come under the spotlight of this trend. This review summarizes the latest development about the design and construction of photo-responsive liposomes with gold nanoparticles for the controlled drug release. Alongside, we overview the mechanism involved in this process and the representative applications.

Electrochemical extraction of gold from wastes as nanoparticles stabilized by phospholipids

A simple one-step method for the extraction of gold from wastes as nanoparticles stabilized by phospholipids is demonstrated. This is achieved by applying an AC voltage for 5s to the gold-containing wastes, which act as the electrodes in a buffer solution containing a dispersed phospholipid (1,2-dioleoyl-sn-glycero-3-phosphocholine, DOPC). This is an environmentally friendly and rapid method for recovering gold from wastes. The extracted gold nanoparticles have significant potential as a catalyst or biomedical material.

Multifunctional Magnetoliposomes for Sequential Controlled Release

The simultaneous or sequential delivery of multiple therapeutic active principles to a specific target is one of the main challenges of nanomedicine. This goal requires the construction of complex devices often extremely time and cost consuming. Supramolecular self-assemblies, with building blocks of different nature, each providing a specific function to the final construct, can combine a facile synthetic route with a high tunability and structural control. In this study we provide the proof-of-principle of a drug delivery system, DDS, constituted of (i) liposomes, providing a fully biocompatible lipid scaffold suitable to host both hydrophobic and hydrophilic drugs; (ii) a double-stranded DNA conjugated with a cholesteryl unit that spontaneously inserts into the lipid membrane; and (iii) hydrophobic and hydrophilic superparamagnetic iron oxide nanoparticles (SPIONs) embedded inside the lipid membrane of liposomes or connected to the DNA, respectively. Upon application of an alternating magnetic field, the SPIONs can trigger, through thermal activation, the release of a DNA strand or of the liposomal payload, depending on the frequency and the application time of the field, as proved by both steady-state and time-resolved fluorescence studies. This feature is due to the different localization of the two kinds of SPIONS within the construct and demonstrates the feasibility of a multifunctional DDS, built up from self-assembly of biocompatible building blocks.

Gold nanoparticles covalently assembled onto vesicle structures as possible biosensing platform

In this contribution a strategy is shown to covalently immobilize gold nanoparticles (AuNPs) onto vesicle bilayers with the aim of using this nanomaterial as platform for the future design of immunosensors. A novel methodology for the self-assembly of AuNPs onto large unilamellar vesicle structures is described. The vesicles were formed with 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) and 1-undecanethiol (SH). After, the AuNPs photochemically synthesized in pure glycerol were mixed and anchored onto SH-DOPC vesicles. The data provided by voltammetry, spectrometry and microscopy techniques indicated that the AuNPs were successfully covalently anchored onto the vesicle bilayer and decorated vesicles exhibit a spherical shape with a size of 190 ± 10 nm. The developed procedure is easy, rapid and reproducible to start designing a possible immunosensor by using environmentally friendly procedures.

Self-healable and reversible liposome leakage by citrate-capped gold nanoparticles: probing the initial adsorption/desorption induced lipid phase transition

We herein report that the adsorption/desorption of citrate-capped gold nanoparticles (AuNPs) transiently causes leakage in fluid phase DOPC liposomes, while the liposomes do not leak with AuNPs capped with mercaptopropionic acid (MPA). Leakage also fails to occur for gel phase DPPC liposomes. Citrate-capped (but not MPA-capped) AuNPs raise the phase transition temperature of DPPC. We conclude that citrate-capped AuNPs interact with the PC liposomes very strongly, inducing a local fluid-to-gel lipid phase transition for DOPC. Leakage takes place during this transition, and the membrane integrity is resumed after the transition. Citrate-capped AuNPs allow stronger van der Waals forces than MPA-capped AuNPs with PC liposomes, since the latter are separated from the liposome surface by the ∼0.3 nm MPA layer.

Formation of lipid and polymer based gold nanohybrids using a nanoreactor approach

Nanocarriers encapsulating gold nanoparticles hold tremendous promise for biomedical applications. The nanoreactor approach offers a versatile, efficient, and highly reproducible preparation technology.

A new class of pegylated plasmonic liposomes: synthesis and characterization

The multifunctional nanoobjects that can be controlled, manipulated and triggered using external stimuli represent very promising candidates for nanoscale therapeutic and diagnostic applications. In this study we report the successful synthesis and characterization of a new class of very stable multifunctional nanoobjects, containing cationic liposomes decorated with PEGylated gold nanoparticles (PEGAuNPs). The multifunctional hybrid nanoobjects (mHyNp) were prepared by taking advantage of the electrostatic interactions between small unilamelar cationic liposomes and negatively charged gold nanoparticles. The mHyNps have been investigated by UV-VIS absorption spectroscopy, Dynamic Light Scattering (DLS), Zeta Potential Measurements and Transmission Electron Microscopy (TEM). The TEM images clearly revealed the attachment of individual gold nanoparticles onto the spherical outer surface of the cationic liposomes which was also confirmed by DLS and UV-VIS data. Furthermore, the plasmonic properties of the hybrid complexes have been evaluated by using the Surface Enhanced Raman Spectroscopy (SERS) technique. It is shown that PEG mediated interaction between the liposomes and the gold nanoparticles enabled the recording of the SER spectra of the liposomes in aqueous environment, thus demonstrating the plasmonic properties of the hybrids.

Softening of phospholipid membranes by the adhesion of silica nanoparticles--as seen by neutron spin-echo (NSE)

The interactions between nanoparticles and vesicles are of significant interest both from a fundamental as well as from a practical point of view, as vesicles can serve as a model system for cell membranes. Accordingly the effect of nanoparticles that bind to the vesicle bilayer is very important with respect to understanding their biological impact and also may shed some light on the mechanisms behind the effect of nanotoxicity. In this study we have investigated the influence of small adsorbed silica nanoparticles (SiNPs) on the structure of zwitterionic DOPC vesicles. By a combination of SANS, cryo-TEM, and DLS, we observed that the SiNPs are bound to the outer vesicle surface without significantly affecting the vesicle structure. Most interestingly, by means of neutron spin-echo (NSE) local bilayer fluctuations were studied and one finds a small but marked decrease of the membrane rigidity upon binding of the nanoparticles. This surprising finding may be a relevant aspect for the further understanding of the effects that nanoparticles have on phospholipid bilayers.

Construction of thermal- and light-responsive liposomes noncovalently decorated with gold nanoparticles

GNP–DPPC, a gold nanoparticle-decorated DPPC liposome complex, can release encapsulated dyes upon heating or illumination. GNP–DPPC also has a faster thermal response and higher critical leakage temperature than liposomes.

Cationic gel-phase liposomes with "decorated" anionic SPIO nanoparticles: morphology, colloidal, and bilayer properties

The assembly and complexation of oppositely charged colloids are important phenomena in many natural and synthetic processes. Liposome-nanoparticle assemblies (LNAs) represent an interesting hybrid system that combines "soft" and "hard" colloidal materials. This work describes the formation and characterization of gel-phase LNAs formed by the binding of anionic superparamagnetic iron oxide (SPIO) nanoparticles to cationic dipalmitoylphosphatidylcholine (DPPC)/dipalmitoyltrimethylammonium propane (DPTAP) liposomes. Particles were examined with hydrodynamic diameters below (16 nm) and above (30 nm) the cutoff reported for supported lipid bilayer formation. LNA formation with 16 nm particles was entropically driven and particles bound individually to yield "decorated" structures. In this case, increasing nanoparticle concentration yielded colloidal LNA aggregates and eventual charge inversion. In contrast, LNA formation with 30 nm particles was enthalpically driven, and the nanoparticles aggregated at the bilayer interface. These aggregates led to significant LNA aggregation and large bilayer sheets due to liposome rupture despite minimal charge screening of the liposome surface. In this case SLBs were present, but these structures were not dominant. Differences in LNA structure were also revealed through the lipid phase transition behavior. This work infers size-dependent nanoparticle binding and LNA formation mechanisms that can be used to tailor colloidal and bilayer properties. Analogies are made to polyelectrolyte patch charge heterogeneities and DNA complexation with cationic liposomes.

Stimuli-responsive liposome-nanoparticle assemblies

INTRODUCTION

Nanoscale assemblies are needed that achieve multiple therapeutic objectives, including cellular targeting, imaging, diagnostics and drug delivery. These must exhibit high stability, bioavailability and biocompatibility, while maintaining or enhancing the inherent activity of the therapeutic cargo. Liposome-nanoparticle assemblies (LNAs) combine the demonstrated potential of liposome-based therapies, with functional nanoparticles. Specifically, LNAs can be used to concentrate and shield the nanoparticles and, in turn, stimuli-responsive nanoparticles that respond to external fields can be used to control liposomal release. The ability to design LNAs via nanoparticle encapsulation, decoration or bilayer-embedment offers a range of configurations with different structures and functions.

AREAS COVERED

This paper reviews the current state of research and understanding of the design, characterization and performance of LNAs. A brief overview is provided on liposomes and nanoparticles for therapeutic applications, followed by a discussion of the opportunities and challenges associated with combining the two in a single assembly to achieve controlled release via light or radiofrequency stimuli.

EXPERT OPINION

LNAs offer a unique opportunity to combine the therapeutic properties of liposomes and nanoparticles. Liposomes act to concentrate small nanoparticles and shield nanoparticles from the immune system, while the nanoparticle can be used to initiate and control drug release when exposed to external stimuli. These properties provide a platform to achieve nanoparticle-controlled liposomal release. LNA design and application are still in infancy. Research concentrating on the relationships among LNA structure, function and performance is essential for the future clinical use of LNAs.

Controlled release from bilayer-decorated magnetoliposomes via electromagnetic heating

Nanoscale assemblies that can be activated and controlled through external stimuli represent a next stage in multifunctional therapeutics. We report the formation, characterization, and release properties of bilayer-decorated magnetoliposomes (dMLs) that were prepared by embedding small hydrophobic SPIO nanoparticles at different lipid molecule to nanoparticle ratios within dipalmitoylphosphatidylcholine (DPPC) bilayers. The dML structure was examined by cryogenic transmission electron microscopy and differential scanning calorimetry, and release was examined by carboxyfluorescein leakage. Nanoparticle heating using alternating current electromagnetic fields (EMFs) operating at radio frequencies provided selective release of the encapsulated molecule at low nanoparticle concentrations and under physiologically acceptable EMF conditions. Without radio frequency heating, spontaneous leakage from the dMLs decreased with increasing nanoparticle loading, consistent with greater bilayer stability and a decrease in the effective dML surface area due to aggregation. With radio frequency heating, the initial rate and extent of leakage increased significantly as a function of nanoparticle loading and electromagnetic field strength. The mechanism of release is attributed to a combination of bilayer permeabilization and partial dML rupture.