Lorena Ruiz-Pérez

Mechanical actuation by responsive polyelectrolyte brushes and triblock gels

Progress in the development of actuating molecular devices based on responsive polymers is reviewed. The synthesis and characterization of “grafted from” brushes and triblock copolymers is reported. The responsive nature of polyelectrolyte brushes, grown by surface initiated atomic transfer radical polymerization (ATRP), has been characterized by scanning force microscopy, neutron reflectometry, and single molecule force measurements. The molecular response is measured directly for the brushes in terms of both the brush height and composition and the force generated by a single molecule. Triblock copolymers, based on hydrophobic end blocks and polyacid mid‐block, have been used to produce polymer gels where the deformation of the molecules can be followed directly by small angle X‐ray scattering (SAXS), and a correlation between molecular shape change and macroscopic deformation has been established. A Landolt pH‐oscillator, based on bromate/sulfite/ferrocyanide, with a room temperature period of 20 min and a range of 3.1<pH<7.0, was used to drive periodic oscillations in volume in this pH responsive hydrogel. The triblock copolymers demonstrate that the individual response of the polyelectrolyte molecules scale affinely to produce the macroscopic response of the system in an oscillating chemical reaction. Dedicated to Professor John L. Stanford on the occasion of his 60th birthday.

Chemotactic synthetic vesicles: Design and applications in blood-brain barrier crossing

Brain homing nanoswimmers: Glucose-fueled propulsion combined with blood-brain barrier crossing enhances brain delivery. In recent years, scientists have created artificial microscopic and nanoscopic self-propelling particles, often referred to as nano- or microswimmers, capable of mimicking biological locomotion and taxis. This active diffusion enables the engineering of complex operations that so far have not been possible at the micro- and nanoscale. One of the most promising tasks is the ability to engineer nanocarriers that can autonomously navigate within tissues and organs, accessing nearly every site of the human body guided by endogenous chemical gradients. We report a fully synthetic, organic, nanoscopic system that exhibits attractive chemotaxis driven by enzymatic conversion of glucose. We achieve this by encapsulating glucose oxidase alone or in combination with catalase into nanoscopic and biocompatible asymmetric polymer vesicles (known as polymersomes). We show that these vesicles self-propel in response to an external gradient of glucose by inducing a slip velocity on their surface, which makes them move in an extremely sensitive way toward higher-concentration regions. We finally demonstrate that the chemotactic behavior of these nanoswimmers, in combination with LRP-1 (low-density lipoprotein receptor–related protein 1) targeting, enables a fourfold increase in penetration to the brain compared to nonchemotactic systems.

Nanoscale detection of metal-labeled copolymers in patchy polymersomes

We report the synthesis of polymersome-forming block copolymers using two different synthetic routes based on Atom Transfer Radical Polymerization (ATRP) and Reversible Addition Fragmentation chain Transfer (RAFT) polymerization, respectively. Functionalization with 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) allowed the block copolymer chains to be labelled with electron-dense metal ions (e.g. indium). The resulting metal-conjugated copolymers can be visualized by transmission electron microscopy with single chain resolution, hence enabling the study of polymer/polymer immiscibility and phase separation on the nano-scale.

Molecular engineering of polymersome surface topology

Self-assembling vesicles made of copolymer mimics biological systems. Biological systems exploit self-assembly to create complex structures whose arrangements are finely controlled from the molecular to mesoscopic level. We report an example of using fully synthetic systems that mimic two levels of self-assembly. We show the formation of vesicles using amphiphilic copolymers whose chemical nature is chosen to control both membrane formation and membrane-confined interactions. We report polymersomes with patterns that emerge by engineering interfacial tension within the polymersome surface. This allows the formation of domains whose topology is tailored by chemical synthesis, paving the avenue to complex supramolecular designs functionally similar to those found in viruses and trafficking vesicles.Biological systems exploit self-assembly to create complex structures whose arrangements are finely controlled from molecular to mesoscopic level. Herein we report an example of using fully synthetic systems that mimic two levels of self-assembly. We show the formation of vesicles using amphiphilic copolymers whose chemical nature is chosen to control both membrane formation and membrane-confined interactions. We report polymersomes with patterns that emerge by engineering interfacial tension within the polymersome surface. This allows the formation of domains whose topology is tailored by the chemical synthesis paving the avenue to complex supramolecular designs functionally similar to those found in viruses and trafficking vesicles. Living systems are the result of a very precise and balanced hierarchical organisation of molecules and macromolecules. These are constructed with specific chemical signatures that direct supramolecular interaction between themselves and/or with water. Such interactions, typically low in energy (i.e. tens of kTs), allow the formation of mesoscale architectures with exquisite spatial and temporal control. This process known as self-assembly is very much ubiquitous in Nature and is at the core of any biological transformation [1]. Alongside such a positional control of molecules, Nature creates specific energy pools by enclosing chemicals into aqueous volumes using gated compartments [2]. Both compartmentalisation and positional self-assembly create structures whose surfaces express several chemistries performing their function holistically according to specific topological interactions. Biological surfaces are far from homogenous systems and organise their components according to specific (quasi)regular patterns. It is now well-established that any cell membrane has a mosaic-like structure made of dynamic nanoscale assemblies of lipids, sterols, glycols, and proteins collectively known as rafts and that these rafts control membrane signalling and trafficking [3]. Such a topological control is also conserved in smaller biological structures such as viruses, synaptic vesicles, lipoproteins and bacteria. In these, key ligands are combined into topologies with super-symmetric arrangements such as in most nonenveloped viruses[4], or have semi-ordered topologies such as in lipoproteins[5] or even into Turing-like patterns such as in most enveloped viruses [6] and endogenous trafficking vesicles [7]. Surface topology is not stochastic and is the result of an evolutionary drive often associated with a specific function. Viruses, for example, change their surface topology during maturation from a noninfectious, almost inert assembly, to an infectious cell-active structure capable of entering cells

An Organometallic Ir(III) Molecular Probe for Imaging Microtubules in Fluorescence and Electron Microscopy

We report a versatile cyclometalated Iridium (III) complex probe that achieves synchronous fluorescence-electron microscopy correlation to reveal microtubule ultrastructure in cells. The selective insertion of probe between repeated α and β units of microtubule triggers remarkable fluorescent enhancement, and high TEM contrast due to the presence of heavy Ir ions. The highly photostable probe allows live cell imaging of tubulin localization and motion during cell division with an resolution of 20 nm, and under TEM imaging reveals the αβ unit interspace of 45Å of microtubule in cells.Microtubules are a critical component of the cell cytoskeleton and an important actor in cell mitosis and adhesion. Yet their imaging has been limited by the lack of effective probes. Fluorescent imaging can be performed using either taxol derivates, immunoglobins, or genetically encoded fluorescent proteins. These approaches however tend to hinder microtubulin functionality and they do not bestow any contrast in electron microscopy. Here we present a cyclometalated Iridium(III) complex that bind to microtubulin and allow both fluorescent and electron microscopy imaging. The complex displays a light switch phenomena coupled with strong luminescence intensity upon tubulin protein binding without interfering into cell proliferation. Furthermore, the application of super resolution imaging of microtubule ultrastructure within brain neuron network under stimulated emission depletion (STED) microscopy was successfully demonstrated. More importantly, the Ir-Tub showed its capability to display microtubule structure under protein monomeric level by means of energy-filtered transmission electron microscopy (EF-TEM). This innovative complex sheds light on the visualization and modeling of precise microtubule structure, aiding a much better understanding of correlated cellular mechanisms and ultimately associated diseases.

Active delivery to the brain by chemotaxis

One of the most promising tasks is the ability to engineer nanocarriers that can autonomously navigate within tissues and organs, accessing nearly every site of the human body guided by endogenous chemical gradients. Here we report a fully synthetic, organic, nanoscopic system that exhibits attractive chemotaxis driven by enzymatic conversion of glucose. We achieve this by encapsulating glucose oxidase, alone or in combination with catalase, into nanoscopic and biocompatible asymmetric polymer vesicles (known as polymersomes). We show that these vesicles self-propel in response to an external gradient of glucose by inducing a slip velocity on their surface, which makes them move in an extremely sensitive way towards higher concentration regions. We finally demonstrate that the chemotactic behaviour of these nanoswimmers enables a four-fold increase in penetration to the brain compared to non-chemotactic systems.In recent years, scientists have created artificial microscopic and nanoscopic self-propelling particles, often referred to as nano- or micro-swimmers, capable of mimicking biological locomotion and taxis. This active diffusion enables the engineering of complex operations that so far have not been possible at the micro- and nanoscale. One of the most promising task is the ability to engineer nanocarriers that can autonomously navigate within tissues and organs, accessing nearly every site of the human body guided by endogenous chemical gradients. Here we report a fully synthetic, organic, nanoscopic system that exhibits attractive chemotaxis driven by enzymatic conversion of glucose. We achieve this by encapsulating glucose oxidase — alone or in combination with catalase — into nanoscopic and biocompatible asymmetric polymer vesicles (known as polymersomes). We show that these vesicles self-propel in response to an external gradient of glucose by inducing a slip velocity on their surface, which makes them move in an extremely sensitive way towards higher concentration regions. We finally demonstrate that the chemotactic behaviour of these nanoswimmers enables a four-fold increase in penetration to the brain compared to non-chemotactic systems.