Magnetoliposomes: opportunities and challenges

Abstract

Combining liposomes with magnetic nanoparticles is an intriguing approach to create multifunctional vesicles for medical applications, which range from controlled drug delivery vehicles to diagnostic imaging enhancers. Over the past decade, significant effort has been invested in developing such hybrids -widely known as magnetoliposomes -and has led to numerous new concepts. This review provides an overview on of the current state of the art in this field. The concept of magnetic fluid hyperthermia and stimuli-responsive nanoparticles for drug delivery is briefly recapitulated. The materials needed for these hybrids are addressed as well. The three typically followed approaches to associate magnetic nanoparticles to the liposomes are described and discussed more in detail. The final chapters are dedicated to the analytical methods used to characterize these hybrids and to theoretical considerations relevant for bilayer-embedded nanoparticles.

Easy Formation of Functional Liposomes in Water Using a pH‐Responsive Microbial Glycolipid: Encapsulation of Magnetic and Upconverting Nanoparticles

“…The sonication‐assisted phase change method developed in the previous section for bare iron oxide NPs could be an interesting alternative to more classical encapsulation approaches, which would require surface engineering steps to make UCNP water‐dispersible. Furthermore, as shown in many magnetoliposome systems, stable NPs bearing a hydrophobic coating classically partition in the lipid bilayer of the vesicles, and in general only the employment of surfactants, which guarantee oil‐water phase transfer, forces them to aggregates in the lumen . Otherwise, standard hydrophilic stabilizers (e. g., citric acid, polymers) are used to surface stabilizers that help them aggregate in the lumen .…”

“…Furthermore, as shown in many magnetoliposome systems, stable NPs bearing a hydrophobic coating classically partition in the lipid bilayer of the vesicles, and in general only the employment of surfactants, which guarantee oil‐water phase transfer, forces them to aggregates in the lumen . Otherwise, standard hydrophilic stabilizers (e. g., citric acid, polymers) are used to surface stabilizers that help them aggregate in the lumen . In this section, we make the hypothesis that the sonication‐assisted phase‐change method employing the pH‐responsive GL can also be used to encapsulate hydrophobic colloids under the same conditions employed to form magnetoliposomes.…”

“…The case of magnetoliposomes, an idea being at least three decades old, is particularly interesting. Magnetoliposomes refer to liposomes that contain magnetic NPs (mainly Fe 3 O 4 and γ‐Fe 2 O 3 ) in their lumen, lipid bilayer or at the vesicle surface, and which are particularly interesting for the well‐known applications in hyperthermia or as contrast agent in magnetic resonance imaging . Either alone or in combination with drug loading, liposomal protection increases the blood circulating time, bioavailability and delivery .…”

“…Most, if not all, of these methods require the use of stable colloids in general. In most cases, many nanoparticle systems are passivated by a hydrophobic layer, which easily guarantees encapsulation in the vesicle bilayers . However, ligand exchange, commonly regarded at as a tedious unavoidable step, use of surfactants or hydrophilic coatings, become then necessary for encapsulation in the lumen in water‐based media .…”

“…In most cases, many nanoparticle systems are passivated by a hydrophobic layer, which easily guarantees encapsulation in the vesicle bilayers . However, ligand exchange, commonly regarded at as a tedious unavoidable step, use of surfactants or hydrophilic coatings, become then necessary for encapsulation in the lumen in water‐based media . Moreover, the interaction between the (coated or uncoated) NPs with the phosphate groups of phospholipids may destabilize the bilayer membrane, thereby affecting the vesicle formation mechanism and reducing their stability .…”