No abstract

We have developed a reproducible and facile one step strategy for the synthesis of doxorubicin loaded magnetoliposomes by using a thin-layer evaporation method. Liposomes of around 200 nm were made of 1,2-Dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and iron oxide nanoparticles (NP) with negative, positive and hydrophobic surfaces that were incorporated outside, inside or between the lipid bilayers, respectively. To characterize how NP are incorporated in liposomes, advanced cryoTEM and atomic force microscope (AFM) techniques have been used. It was observed that only when the NP are attached outside the liposomes, the membrane integrity is preserved (lipid melt transition shifts to 38.7 ºC with high enthalpy 34.8 J/g) avoiding the leakage of encapsulated drug while having good colloidal properties and the best heating efficiency under an alternating magnetic field (AMF). These magnetoliposomes were tested with two cancer cell lines, MDA-MB-231 and HeLa cells. First, 100 % of cellular uptake was achieved with a high cell survival (above 80 %), which is preserved (83 %) for doxorubicin loaded magnetoliposomes. Then, we demonstrate that doxorubicin release can be triggered by remote control, using a noninvasive external AMF for 1 hour, leading to a cell survival reduction of 20 %. Magnetic field conditions of 202 kHz and 30 mT seem to be enough to produce an effective heating avoiding drug degradation. In conclusion, these drug loaded magnetoliposomes prepared in one step could be used for drug release on demand at a specific time and place efficiently using an external AMF reducing or even eliminating side effects.

High-speed AFM enabled the imaging of protein interactions with millisecond time resolutions (10 fps). However, the acquisition of nanomechanical maps of proteins is about 100 times slower. Here, we developed a high-speed bimodal AFM that provided high-spatial resolution maps of the elastic modulus, the loss tangent and the topography at imaging rates of 5.7 fps. The new microscope was applied to identify the initial stages of the self-assembly of the collagen structures. By following the changes in the physical properties we identified four stages, nucleation and growth of collagen precursors, formation of tropocollagen molecules, assembly of tropocollagens into microfibrils, and alignment of microfibrils to generate microribbons. Some emerging collagen structures never matured and, after an existence of several seconds, they disappeared into the solution. The elastic modulus of a microfibril (~4 MPa) implied very small stiffness (~3x10 -6 N/m). Those values amplified the amplitude of the collagen thermal fluctuations on the mica plane which facilitated microribbon built-up.

The nanoscale determination of the mechanical properties of interfaces is of paramount relevance in materials science and cell biology. Bimodal atomic force microscopy (AFM) is arguably the most advanced nanoscale method for mapping the elastic modulus of interfaces. Simulations, theory, and experiments have validated bimodal AFM measurements on thick samples (from micrometer to millimeter). However, the bottom-effect artifact, this is, the influence of the rigid support on the determination of the Young’s modulus, questions its accuracy for ultrathin materials and interfaces (1–15 nm). Here we develop a bottom-effect correction method that yields the intrinsic Young’s modulus value of a material independent of its thickness. Experiments and numerical simulations validate the accuracy of the method for a wide range of materials (1 MPa to 100 GPa). Otherwise, the Young’s modulus of an ultrathin material might be overestimated by a 10-fold factor.