Djamal Zerrouki

Chiral colloidal clusters

Chirality is an important element of biology, chemistry and physics. Once symmetry is broken and a handedness is established, biochemical pathways are set. In DNA, the double helix arises from the existence of two competing length scales, one set by the distance between monomers in the sugar backbone, and the other set by the stacking of the base pairs. Here we use a colloidal system to explore a simple forcing route to chiral structures. To do so we have designed magnetic colloids that, depending on both their shape and induced magnetization, self-assemble with controlled helicity. We model the two length scales with asymmetric colloidal dumbbells linked by a magnetic belt at their waist. In the presence of a magnetic field the belts assemble into a chain and the steric constraints imposed by the asymmetric spheres force the chain to coil. We show that if the size ratio between the spheres is large enough, a single helicity is adopted, right or left. The realization of chiral colloidal clusters opens up a new link between colloidal science and chemistry. These colloidal clusters may also find use as mesopolymers, as optical and light-activated structures, and as models for enantiomeric separation.

A Novel Thermo‐Induced Self‐Bursting Microcapsule with Magnetic‐Targeting Property

In recent years, considerable efforts have been devoted to the design and fabrication of multifunctional microcapsules due to their potential applications in numerous fields, including controlled release of various substances, 2] protection of active species, 4] and creation of microreactors for confined chemical reaction, 6] etc. In the biomedical field, microcapsules are widely investigated as effective drug delivery carriers for the treatment of deadly diseases such as cancer. Because most anticancer drugs have harmful side effects to the normal tissues, the most ideal delivery carriers should be able to transport and release the anticancer drugs specifically to the targeted tumor site without drug leakage during the transport process. Up to now, numerous studies have been conducted on using external magnetic field for targeted drug delivery by incorporating magnetic nanoparticles into drug delivery carriers. Some stimuli-responsive carriers such as core/shell microparticles and microcapsules functionalized with magnetic nanoparticles have been designed for magnetic-guided drug delivery and subsequent controlled drug release by an external trigger such as temperature, 8] pH, 10] ultrasonic, and high frequency magnetic field. 13] Most of the carriers mentioned above were designed for hydrophilic drugs. However, it is worth noting that, currently available anticancer drugs such as paclitaxel and carmustine are usually lipophilic molecules. Therefore, design of carriers for lipophilic drugs is of great importance and necessity. Here we report on a novel type of monodisperse thermo-induced self-bursting microcapsules with oil cores for encapsulating lipophilic substances. The thermo-responsive polymeric shell embedded with superparamagnetic Fe3O4 nanoparticles enables not only magnetic-guided targeting but also thermoinduced rapid and complete burst-release of encapsulated lipophilic chemicals, and there is no leakage of encapsulated susbtances at all before the thermo-triggering. Figure 1 schematically illustrates the concept of the as-proposed thermo-induced self-bursting microcapsule with magnetic-targeting property and its fabrication procedure. The proposed microcapsules are monodisperse and each of them has a core/shell structure comprising an oil core and a thermo-responsive shell composed of poly(N-isopropylacrylamide) (PNIPAM) and homogeneously embedded superparamagnetic Fe3O4 nanoparticles (Figure 1 a). The expected oil-core/polymer-shell structure and monodispersity can be achieved by using microfluidic fabrication technique. 16] The oil core can be used to encapsulate lipophilic drug molecules. In the shell, the embedded Fe3O4 nanoparticles contribute magnetic-response property to the microcapsule and the PNIPAM network makes the shell thermo-responsive. As a result, the Fe3O4/PNIPAM shell enables the microcapsule to undergo magnetic-guided targeting delivery, have no unintended drug leakage during microcapsule transport, and exhibit thermo-triggered drug release. To better illustrate this design concept, here we present a more detailed description on the transportrelease process of the as-proposed microcapsules. Thermo-responsive behavior of PNIPAM network is characterized by its lower critical solution temperature (LCST). Specifically, PNIPAM shell is in the swollen and hydrophilic state when environmental temperature is lower than the LCST, while it dramatically shrinks when the temperature is higher than the LCST. Because the microcapsules are fabricated at temperatures below the LCST, the as-prepared microcapsules are initially in the swollen and hydrophilic state. Because the encapsulated oil phase and loaded lipophilic chemicals inside the microcapsule are immiscible with or insoluble in aqueous solutions, there is no way for them to pass through the hydrophilic PNIPAM shell via solution/diffusion when the temperature is below the LCST, although the concentration gradient exists between inside and outside of the microcapsule. Therefore, when the microcapsules are stored, transported, or delivered at temperatures below the LCST, there is no leakage of encapsulated lipophilic substances from the microcapsules. After the microcapsules reach the desired site via magnetic guide, burst release of their encapsulated lipophilic substances can be triggered by an external thermal stimulus, for example, local heating. When the environmental temperature is increased from one below the LCST to another one above the LCST, the PNIPAM shell shrinks rapidly. During the shell shrinkage process, internal pressure in the oil core gradually increases because the oil phase is incompressible. When the internal pressure reaches a certain critical value, the PNIPAM shell ruptures due to its limited mechanical strength. Such dramatic shrinkage and final rupture of the PNIPAM shell squeeze the oil core out from the microcapsule with a strong boost to the environment. In such a release process, the loaded lipophilic drug molecules are released together with the burst ejecting of encapsulated oil phase from the microcapsule, which leads to not only rapid release but also complete release. The fabrication procedure of our microcapsules consists of three major steps (see Experimental Section for details). Briefly, [a] W. Wang, L. Liu, Dr. X.-J. Ju, Dr. R. Xie, Dr. L. Yang, Prof. L.-Y. Chu School of Chemical Engineering Sichuan University, Chengdu, Sichuan 610065 (China) Fax: (+ 86) 28-8540-4976 E-mail : chuly@scu.edu.cn [b] Dr. D. Zerrouki Department of Chemical Engineering University of Ouargla, BP 511 Ouargla, 30000 (Algeria) Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/cphc.200900450.

Hydrogel-Based Microactuators with Remote-Controlled Locomotion and Fast Pb2+-Response for Micromanipulation

Hydrogel-based microactuators that enable remote-controlled locomotion and fast Pb(2+)-response for micromanipulation in Pb(2+)-polluted microenvironment have been fabricated from quadruple-component double emulsions. The microactuators are Pb(2+)-responsive poly(N-isopropylacrylamide-co-benzo-18-crown-6-acrylamide) microgels, each with an eccentric magnetic core for magnetic manipulation and a hollow cavity for fast Pb(2+)-response. Micromanipulation of the microactuators is demonstrated by using them for preventing Pb(2+)-leakage from microchannel. The microactuators can be remotely and precisely transported to the Pb(2+)-leaking site under magnetic guide, and then clog the microchannel with Pb(2+)-responsive volume swelling to prevent flowing out of Pb(2+)-contaminated solution. The proposed microactuator structure provides a potential and novel model for developing multifunctional actuators and sensors, biomimetic soft microrobots, microelectro-mechanical systems and drug delivery systems.

Control of Cement Slurry Formulation for an Oil Well in a Critical Geological Layer

In this study we were interested in the cementing of 9″ 5/8 casing corresponding to 12″ ¼ drilling section from an oil well drilled in the field of Hassi Messaoud in southern Algeria. This section is located in a very critical geological layer called LD2 (Horizon B), which is characterized by the production of calcic chloride waters that are very aggressive and virulent. Therefore the complexity of the geological formation encountered when drilling implies the need for a very precise pumping process to check pore pressure and the venus. This constraint has been imposed in high density work to avoid the dilution of cement slurry by chloride calcic waters. As a consequence, particular attention must be given to the proper control of the properties of cement slurry such as adequate rheology in order to achieve the target of obtaining a sustainable cement sheath. The cement type is of great importance in performance. Here we used a mixture of salt-saturated water with some basic additives and a combination of three materials: Dyckerhoof cement class G blended with the silica flour and hematite powder as a powerful additive to maintain the density of the slurry.