Orthogonal self-assembly of surfactants and hydrogelators:towards new nanostructures

Self-assembly of small molecular components holds great promises as a bottom-up approach for nano-objects, but functionality of the resulting nanostructures can by far not compete with the sophisticated systems provided by nature. Surfactants, for instance, can lead to a great diversity of aggregates and mesophases (micelles, vesicles, cubic phases...), but with a level of complexity and functionality that still remains limited. Just like in nature, to increase the level of complexity in self-assembling systems, a straightforward approach consists in making use of multiple components that can display orthogonal self-assembly –i.e. the independent formation of two supramolecular structures each with their own characteristic within a single system. More precisely, we have associated surfactants with low-molecular weight hydrogelators: these molecules, based on cyclohexyl-tris-amino acid, can also self- assemble in one direction through the establishment of H-bonds, leading to the formation of a fiber network and consequently macroscopic gels. Work on mixing behavior of surfactants and various gelators have shown the independent formation of a fibrillar network with encapsulated spherical micelles, Figure 1. In order to produce even more complex nanostructures, this approach has been extended to worm-like micelles that can lead to viscoelastic gels, due to their entanglement. Interestingly, the formation of interpenetrating networks, with original and tuneable rheological properties, has been evidenced by cryo-TEM [1]. Screening of various gelators with vesicle-forming surfactants also revealed that most combinations display orthogonal self assembly, Figure 1. Vesicles were indeed successfully incorporated in a highly responsive network of fibers, without any significant disturbance of these two supramolecular structures. By mean of fluorescent spectroscopy, the stability of these encapsulated vesicles with respect to fusion and leakage has also been investigated. This last example has been exploited to successfully develop liposomes with an encapsulated self-assembling hydrogel (“gellosomes”) [1]. The high responsive character of the gelator makes it very interesting as a mimic of cytoskeleton and it is expected that this new type of nanostructure might be of great interest in drug delivery.1. A. M. A. Brizard, M. C. A. Stuart, K. J. C. van Bommel, A. Friggeri, M. R. de Jong, J. H. van Esch. Angewandte Chemie int. ed. 47, (2008), 2063.<br/

Orthogonal self-assembly of surfactants and hydrogelators: towards new nanostructures

Self-assembly of small molecular components holds great promises as a bottom-up approach for nano-objects, but functionality of the resulting nanostructures can by far not compete with the sophisticated systems provided by nature. Surfactants, for instance, can lead to a great diversity of aggregates and mesophases (micelles, vesicles, cubic phases...), but with a level of complexity and functionality that still remains limited. Just like in nature, to increase the level of complexity in self-assembling systems, a straightforward approach consists in making use of multiple components that can display orthogonal self-assembly –i.e. the independent formation of two supramolecular structures each with their own characteristic within a single system. More precisely, we have associated surfactants with low-molecular weight hydrogelators: these molecules, based on cyclohexyl-tris-amino acid, can also self- assemble in one direction through the establishment of H-bonds, leading to the formation of a fiber network and consequently macroscopic gels. Work on mixing behavior of surfactants and various gelators have shown the independent formation of a fibrillar network with encapsulated spherical micelles, Figure 1. In order to produce even more complex nanostructures, this approach has been extended to worm-like micelles that can lead to viscoelastic gels, due to their entanglement. Interestingly, the formation of interpenetrating networks, with original and tuneable rheological properties, has been evidenced by cryo-TEM [1]. Screening of various gelators with vesicle-forming surfactants also revealed that most combinations display orthogonal self assembly, Figure 1. Vesicles were indeed successfully incorporated in a highly responsive network of fibers, without any significant disturbance of these two supramolecular structures. By mean of fluorescent spectroscopy, the stability of these encapsulated vesicles with respect to fusion and leakage has also been investigated. This last example has been exploited to successfully develop liposomes with an encapsulated self-assembling hydrogel (“gellosomes”) [1]. The high responsive character of the gelator makes it very interesting as a mimic of cytoskeleton and it is expected that this new type of nanostructure might be of great interest in drug delivery. 1. A. M. A. Brizard, M. C. A. Stuart, K. J. C. van Bommel, A. Friggeri, M. R. de Jong, J. H. van Esch. Angewandte Chemie int. ed. 47, (2008), 2063

Spin-echo small-angle neutron scattering (SESANS) measurements of needle-like crystallites of gelator compounds

From dibenzoyl cystine, a low molecular weight gelator, we have prepared needle shaped crystals at relatively high concentrations. For the first time SESANS measurements are performed on objects with this geometry. From the measurements the average diameter can be seen directly. From a more careful analysis the width distribution is determined. The gel phase itself prepared at lower concentrations did not show any signal, in contrast to what one observes with conventional SANS. This shows the complementarity of SESANS and SANSRadiation, Radionuclides & ReactorsApplied Science

Imaging the In Vivo Degradation of Tissue Engineering Implants by Use of Supramolecular Radiopaque Biomaterials

For in situ tissue engineering (TE) applications it is important that implant degradation proceeds in concord with neo-tissue formation to avoid graft failure. It will therefore be valuable to have an imaging contrast agent (CA) available that can report on the degrading implant. For this purpose, a biodegradable radiopaque biomaterial is presented, modularly composed of a bisurea chain-extended polycaprolactone (PCL2000-U4U) elastomer and a novel iodinated bisurea-modified CA additive (I-U4U). Supramolecular hydrogen bonding interactions between the components ensure their intimate mixing. Porous implant TE-grafts are prepared by simply electrospinning a solution containing PCL2000-U4U and I-U4U. Rats receive an aortic interposition graft, either composed of only PCL2000-U4U (control) or of PCL2000-U4U and I-U4U (test). The grafts are explanted for analysis at three time points over a 1-month period. Computed tomography imaging of the test group implants prior to explantation shows a decrease in iodide volume and density over time. Explant analysis also indicates scaffold degradation. (Immuno)histochemistry shows comparable cellular contents and a similar neo-tissue formation process for test and control group, demonstrating that the CA does not have apparent adverse effects. A supramolecular approach to create solid radiopaque biomaterials can therefore be used to noninvasively monitor the biodegradation of synthetic implants