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Molecular and macromolecular architecture of organized fluids and interfaces

Keywords : polymersomes, liquid crystals, artificial molecular motors, artificial muscles, actuators, surface, nanoparticle

Group Leader : Patrick KELLER

Molecular and macromolecular architecture of organized fluids and interfaces

 

Read the scientific activity report. (pdf 880Ko, last update 26th, march 2010)


Our group is involved in different aspects of the interface between material chemistry and physical chemistry from fundamental to applied research. We create bio-related materials using mainly organic and polymer chemistry. These materials are either biomimetic, inspired by Nature (artificial muscles, biomimetic surface, polymersomes),  or designed to interact with life sciences for biotechnological and medical applications  (polymer nanoparticles, gold nanorods, antiadhesive surfaces).

1. Artificial Muscles and Biomimetic Responsive Surfaces

Artificial muscles are man-made soft materials that try to reproduce the two main characteristics of real muscle fibers, namely, elasticity and contractility. They respond to various external stimulations (ion concentration, electric field, temperature, light etc.) by a significant shape or size change. Our group has developed a bottom-up strategy to make artificial muscles using nematic liquid crystal polymers as building blocks. The overall material response in these artificial muscles reflects the individual macromolecular response: the contraction/elongation of the material results from the individual macromolecular chain shape change, from stretched to spherical, at the nematic to isotropic phase transition triggered by external stimuli (light and temperature changes). This approach is particularly interesting for the development of micro- and nano-sized actuators.
Macro-, Micro- and Nano-Actuators based on liquid crystal artificial muscles have been achieved using this bottom-up molecular design. Our goal is to further develop biomimetic systems, such as responsive micro-structured surfaces on which living cells can move, and responsive polymer vesicles that can be used as artificial drug vectors or biomimetic organelles.

Figure 1

Figure 1.  Thermal responsive micro-structured surface : schematic presentation and SEM images. The pillars contract reversibly up to 400%. Left: room temperature, Right: high temperature (JACS 2009).

 

[1] Adv. Mater., 2003, 15, 1922-1925. 

[2] Adv. Mater., 2004, 16, 1922-1925.

[3] J. Am. Chem. Soc., 2006, 128, 1088-1089. 

[4] J. Am. Chem. Soc., 2009, 131, 15000-15004 

 

 

2. Nanomaterials for Cancer Imaging and Therapy

Polymersomes
The stability, the robustness and the chemical design flexibility of polymersomes make polymersomes excellent potential candidates as drug or imaging agent carriers. The introduction of actuator in polymersomes and the engineering of their targeted cell adhesion/internalisation are two critical issues for the applications of disease imaging and therapy, which we aim to address. We are focusing on the development of stimuli-responsive and functionalized polymersomes, polymer micelles, polymer nanofibers and polymer nanotubes. We want also to incorporate inorganic nanoparticles (gold and magnetic nanoparticles, quantum dots) in these polymer nanomaterials for the purpose of theranostics.

We designed amphiphilic polymers and constructed via self-assembly smart polymersomes that respond, by bursting or by changing permeability, towards external physical and chemical stimuli. Our first strategy was to use physical stimuli, such as light, leading to a fast modification of physical or chemical structure at the molecular level. We developed different systems of photo-responsive polymersomes. The first system made use of a nano-actuator based on liquid crystal artificial muscles. The polymersome had an enclosed spherical nano-bimorph composed of an asymmetrical bilayer membrane with only one photo-responsive layer. The photo-actuation created a spontaneous curvature in the membrane and resulted in instantaneous polymersome bursting (see Figure 2). The second photo-responsive polymersome was based on a linear-dendritic block copolymer with an azobenzene-containing hydrophobic dendrimer. Wrinkles and rupture of membrane were observed in the polymersomes upon UV illumination. The third photo-responsive polymersome used a composite system, where a PDT (photodynamic treatment) photosensitizer was introduced into the membrane composed of a photo-inert and unsaturated polymer. Drastic polymersome shape and size changes with a release stage were obtained upon exposure to UV or visible light.

Figure2

Figure 2. Asymmetrical  polymersomes and their bursting upon UV illumination during hundreds of micro-seconds. Scale bar = 5 µm (PNAS 2009).

 

[5] Chem. Commun., 2005, 4345 – 4347. 

[6] Proc. Natl. Acad. Sci. U. S. A., 2009, 106, 7294-7298.

[7] J. Am. Chem. Soc., 2010, 132, 3762-3769.

[8] Soft Matter, 2010, 6, 4863-4875.

 

 

Gold nanorods

Gold nanorods (GNRs) exhibit transverse and longitudinal surface plasmon resonances that correspond to electron oscillations perpendicular and parallel to the rod length direction, respectively. Their longitudinal surface plasmon wavelengths (LSPWs) are tunable from the visible to infrared regions by controlling the aspect ratio of GNRs. Owing to their easily tunable optical properties, gold nanorods are attractive nanoparticles for a wide range of applications in the field of biological and biomedical sciences such as drug delivery, molecular imaging, and photothermal therapy. We are currently developing GNRs functionalized by different ligands to target tumors allowing photothermal therapy.

Figure 3

Figure 3. (A) Transmission electron microscopy of gold nanorods (B) Surface modification of gold nanorods 

 

[9] Journal of Colloid and Interface Science, 2011, 357, 75-81

 

 

3. Anti-adhesive Surfaces – A Translational Research

Surfaces play a critical role in biology and medicine, promoting biological interactions such as protein and cell adhesion, and particularly, when biomedical devices are implanted, mediating a variety of adverse reactions: inflammation, thrombosis, occlusion, bacterial infection, fibrosis leading to severe complications, most of the time, difficult to handle particularly with immunocompromised patients. The infection, thrombosis and internal occlusion of catheters are the most frequent complications with the use of central venous catheters (CVC) with implantable access port throughout the cancer therapy (chemotherapy mainly, nutrition, antibiotherapy, transfusions and treatment of pain). These devices have contributed to the improved comfort and safety of patients and greatly contributed to the expansion of treatment and outpatient treatment at home.

Silicone elastomers  (polydimethylsiloxane (PDMS)) widely used in medical implants like CVC have many attributes that make them excellent materials  for biomedical applications but their hydrophobicity is particularly prompt to generate a strong bioadhesion.
In this context, we have developed a strategy to create nanoassemblies of polysaccharide on surfaces that, by mimicking the non-adhesive properties of the glycocalyx, allow the bioadhesion control. These nanoassemblies consist of a methylcellulose layer grafted in one single step, in water, on unmodified commercial surfaces via an orthogonal click reaction using unreacted SiH groups. The resulting antiadhesive biomimetic surfaces are effective in suppressing protein adsorption, bacterial and mammalian adhesion. This first example of a new class of biologically inspired surfaces should have great potential in the design of various devices aimed to easily trigger and modulate the bioadhesion in the field of implantable biomedical devices as well as microfluidic devices.

 

[10] Angew. Chem. Int. Ed., 2011, 50, 10871–10874