Magnetic polymersomes were prepared by self-assembly of the amphiphilic block copolymer poly(isoprene-b-N-isopropylacrylamide) with monodisperse hydrophobic superparamagnetic iron oxide nanoparticles (SPION). The specifically designed thermoresponsive block copolymer allowed for efficient incorporation of the hydrophobic nanoparticles in the membrane core and encapsulation of the water soluble dye calcein in the lumen of the vesicles. Magnetic heating of the embedded SPIONs led to increased bilayer permeability through dehydration of the thermoresponsive PNIPAM block. The entrapped calcein could therefore be released in controlled doses solely through exposure to pulses of an alternating magnetic field. This hybrid SPION-polymersome system demonstrates a possible direction for release applications that merges rational polymersome design with addressed external magnetic field-triggered release through embedded nanomaterials.

We have created a simple and efficient thermal plasmonic sensor platform by letting a DC current heat plasmonic nanohole arrays. The sensor can be used to determine thermodynamic parameters in addition to monitoring molecular reactions in real-time. As an application example, we use the thermal sensor to determine the kinetics and activation energy for desorption of thiol monolayers on gold. Further, the temperature of the metal can be measured optically by the spectral shift of the bonding surface plasmon mode (0.015 nm/K). We show that this resonance shift is caused by thermal lattice expansion, which reduces the plasma frequency of the metal. The sensor is also used to determine the thin film thermal expansion coefficient through a theoretical model for the expected resonance shift.

Stealth (PEGylated) liposomes have taken a central role in drug formulation and delivery combining efficient transport with low nonspecific interactions. Controlling rapid release at a certain location and time remains a challenge dependent on environmental factors. We demonstrate a highly efficient and scalable way to produce liposomes of any lipid composition containing homogeneously dispersed monodisperse superparamagnetic iron oxide nanoparticles in the membrane interior. We investigate the effect of lipid composition, particle concentration and magnetic field actuation on colloidal stability, magneto-thermally actuated release and passive release rates. We show that the rate and amount of encapsulated hydrophilic compound released by actuation using alternating magnetic fields can be precisely controlled from stealth liposomes with high membrane melting temperature. Extraordinarily low passive release and temperature sensitivity at body temperature makes this a promising encapsulation and external-trigger-on-demand release system. The introduced feature can be used as an add-on to existing stealth liposome drug delivery technology.

Hybrid vesicles of lipid and amphiphilic block copolymer combine the biological and functional versatility of lipid delivery systems with the mechanical stability and robustness of polymersomes. While studies of hybrid systems for ease of characterization have focused on giant vesicles, most encapsulation and release applications require nanoscale (large) unilamellar vesicles. We investigate the structure and physical characteristics important for thermal actuation of vesicle‐forming blends of saturated phospholipid, polybutadiene‐b‐poly(ethylene oxide) and thermoresponsive polyisoprene‐b‐poly(N‐isopropylacryl amide) that are additionally loaded with hydrophobic superparamagnetic nanoparticles in the vesicle membrane and resized to large unilamellar vesicles. Lipid/diblock copolymer hybrid vesicles are shown to be the most efficient option to trigger release of encapsulated compounds by application of an external magnetic field causing local hyperthermia. This superiority is shown to depend on the controlled formation of nanoscale lipid domains in the hybrid vesicle membrane and the efficient loading of hydrophobic nanoparticles into the diblock copolymer membrane that retains its stability.

Liposomes grafted with polymer have long been used in drug delivery applications, and block copolymersomes have emerged as attractive and more robust alternatives for both drug delivery and artificial organelle applications. Hybrid membranes that could combine the respective advantages of fluid lipid and robust polymer bilayers are an attractive and enticing alternative. The properties of membranes in amphiphile vesicles are challenging to study and many applications benefit from surface-based access to the membrane. We therefore explore the self-assembly and mechanical properties of supported hybrid bilayers (SHBs) composed of polybutadiene-block-poly(ethylene oxide) block copolymers and zwitterionic phosphatidylcholine lipids on SiO 2 supports. Quartz crystal microbalance with dissipation monitoring (QCM-D) measurements show that formation of SHB on SiO 2 by vesicle fusion depends on the mass fractions of lipids and block copolymers. Atomic force microscopy was used to study the microscopic mixing of lipids in the SHB to reveal that lipid-phase separation is not observed in SHBs. Force spectroscopy was performed to extract information about thickness and mechanical properties of the hybrid membranes. SHBs are shown to combine the properties of lipid membranes and polymer brushes, and the tip force required to rupture the membrane decreases and the bilayer thickness increases as the block copolymer fraction is increased.

Hybrid vesicles, comprising blends of amphiphilic block copolymers and phospholipids, have attracted significant attention recently because of their unique combination of chemical and physical properties. We report a method to make unilamellar hybrid vesicles with diameters of 100 nm by mixing polybutadiene-block-poly(ethylene oxide) and phosphocholine lipids using a combination of solvent inversion and sonication. We show that homogeneous hybrid vesicles are formed when one component is a minor fraction. At compositions with balanced mass fractions, separate populations of similarly sized pure liposomes and hybrid vesicles are indicated. We investigate the release kinetics of calcein encapsulated in the lumen as hybrid large and giant unilamellar vesicles (LUVs and GUVs) of different compositions are exposed to phospholipase A (PLA). PLA hydrolyzes lipids, which leads to dissolution of lipid domains and provides a trigger for the release of calcein as pores are formed. We demonstrate that depending on the polymer mole fraction, block copolymers can either protect or boost the rate of lipid degradation and thereby the release rate from nanoscale hybrid vesicles. Strong indications of lipid phase separation into nanoscale domains in LUVs are observed. Most importantly, hybrid GUV with lipids in the fluid phase release calcein slowly as lipids in the liquid-disordered phase do not phase-separate, but they show the fastest release of all blends as LUVs. This indicates phase separation on the nanoscale in contrast to on the microscale, but it also indicates retained high mobility of lipids between the nanoscale domains, which is absent for lipids in the gel phase. Our results demonstrate several ways in which nanoscale hybrid vesicles can and should be optimized for PLA-triggered release of water-soluble compounds.

No abstract

No abstract