Wael Mamdouh

Self-assembly of a nanoscale DNA box with a controllable lid

The unique structural motifs and self-recognition properties of DNA can be exploited to generate self-assembling DNA nanostructures of specific shapes using a ‘bottom-up’ approach. Several assembly strategies have been developed for building complex three-dimensional (3D) DNA nanostructures. Recently, the DNA ‘origami’ method was used to build two-dimensional addressable DNA structures of arbitrary shape that can be used as platforms to arrange nanomaterials with high precision and specificity. A long-term goal of this field has been to construct fully addressable 3D DNA nanostructures. Here we extend the DNA origami method into three dimensions by creating an addressable DNA box 42 × 36 × 36 nm3 in size that can be opened in the presence of externally supplied DNA ‘keys’. We thoroughly characterize the structure of this DNA box using cryogenic transmission electron microscopy, small-angle X-ray scattering and atomic force microscopy, and use fluorescence resonance energy transfer to optically monitor the opening of the lid. Controlled access to the interior compartment of this DNA nanocontainer could yield several interesting applications, for example as a logic sensor for multiple-sequence signals or for the controlled release of nanocargos.

Collagen coated tantalum substrate for cell proliferation

The extracellular matrix (ECM) plays a key role in cell culture in various physiological and pathological processes in the field of tissue engineering. Recently, the type I collagen ECM has been widely utilized in vitro model systems for the attachment of many different cell lines since it has multi-functions in human tissues. For example it accounts for 6% of the weight of strong, tendinous muscles. In this paper, we reported a new material by coating tantalum (Ta), one highly biocompatible metal, with type I collagen fibrils. The morphology of the new material was studied by high resolution atomic force microscope. It was shown that the adhesion force between type I collagen fibrils network and Ta was strong enough to overcome surface defects. A possible way to explain the phenomenon is that the longitudinal periodicity of collagen fibrils matches the grain size of the Ta domains, which results in increase of the physical adsorption contact area, thereby inducing the dramatic adhesion enhancement between collagen fibrils and Ta. The obtained material was then employed as a template for cell proliferation. Although the surface of this template is more hydrophobic by comparison with the bare Ta surface, the cells on this material were successfully incubated, indicating that the collagen coated Ta might be used as the buffer layer for proliferating cells in hydrophobic biomaterials.

Effect of ultrasonic treatment on the morphology of casein particles.

In this study, the effect of ultrasonic treatment duration on the morphology of self-assembled casein particles was investigated by atomic force microscopy (AFM), low vacuum scanning electron microscopy (SEM) and transmission electron microscopy (TEM). In the case of AFM images, the particle analysis which was carried out by the SPIP program showed that the self-assembled casein particles after being ultrasonically treated for 2 min got smaller in size compared to the casein particles that have not been exposed to any ultrasonic treatment. Surprisingly, however, increasing the ultrasonic time exposure of the particles resulted in an opposite effect where larger particles or aggregates seemed to be present. We show that by comparing the results obtained by AFM, SEM and TEM, the information extracted from the AFM images and analyzed by SPIP program give more detailed insights into particle sizes and morphology at the molecular level compared to SEM and TEM images, respectively.

Comparative study on radiolabeling and biodistribution of core-shell silver/polymeric nanoparticles-based theranostics for tumor targeting

A simple and rapid method for radiolabeling of three types of Ag NPs has been performed using 125I isotope, with high labeling yields, >90% without disturbing the optical properties. All the factors affecting labeling yield were studied. In order to monitor the in-vivo tissue uptake of radiolabeled Ag NPs using γ-rays, Ag-based radioiodo-NPs with a maximum labeling yield were intravenously injected in normal and solid tumor bearing mice. The preliminary biodistribution study revealed that this new radioiodo-NPs have a high affinity to be localized in the tumor site for a long period of time. The reported highly efficient method provides new radiolabeled Ag-based NPs as tumor-specific agents for both diagnostic and therapeutic applications.

Influence of “Glow Discharge Plasma” as an External Stimulus on the Self-Assembly, Morphology and Binding Affinity of Gold Nanoparticle-Streptavidin Conjugates

In this study, we investigate the influence of glow discharge plasma (GDP) on the self-assembly, morphology and binding affinity of streptavidin coated gold nanoparticles (Au-NP-SV) and biotinylated antibody (bAb) adsorbed on a highly oriented pyrolytic graphite (HOPG) substrate. Atomic force microscope (AFM) was used to image the pre- and post-GDP treated samples. The analysis of the AFM images showed a considerable change in the aggregation and morphology of Au-NP-conjugates after treatment with GDP. To our knowledge, this is the first report on using GDP to enhance and speed-up the aggregation (sintering) of adsorbed NP biomolecular conjugates. These results show a promising route that could be generalized for other NPs and their conjugates. It can also be considered as an alternative and cheap aggregation method for controlling the binding affinity of biomolecular species on different surfaces with interesting applications.

Insights on the use of nanocarriers for acne alleviation

Among the common myths in the cosmetics industry is the perception that acne only happens to teenagers, and specifically to females. However, acne is neither limited to a specific age, nor to a certain gender, it creates a stressful problem for many people. Many chemical treatments for acne were proven to be successful, but when administered as such, they showed many adverse effects, starting from itching to skin dryness and inflammation. Natural remedies have also been explored for acne treatment, and despite their safety, they suffered many stability problems attributed to their physicochemical properties, creating an obstacle for their topical delivery. Therefore, many nanocarriers were used to deliver those chemical and natural remedies topically to maximize their therapeutic potential in acne treatment. The present review discusses the different nanocarriers which were proven successful in improving the acne lesions, focusing on vesicular, lipidic, and polymeric systems.