Superselective Targeting Using Multivalent Polymers

Despite their importance for material and life sciences, multivalent interactions between polymers and surfaces remain poorly understood. Combining recent achievements of synthetic chemistry and surface characterization, we have developed a well-defined and highly specific model system based on host/guest interactions. We use this model to study the binding of hyaluronic acid functionalized with host molecules to tunable surfaces displaying different densities of guest molecules. Remarkably, we find that the surface density of bound polymer increases faster than linearly with the surface density of binding sites. Based on predictions from a simple analytical model, we propose that this superselective behavior arises from a combination of enthalpic and entropic effects upon binding of nanoobjects to surfaces, accentuated by the ability of polymer chains to interpenetrat

Volume and porosity thermal regulation in lipid mesophases by coupling mobile ligands to soft membranes

Short DNA linkers are increasingly being exploited for driving specific self-assembly of Brownian objects. DNA-functionalised colloids can assemble into ordered or amorphous materials with tailored morphology. Recently, the same approach has been applied to compliant units, including emulsion droplets and lipid vesicles. The liquid structure of these substrates introduces new degrees of freedom: the tethers can diffuse and rearrange, radically changing the physics of the interactions. Unlike droplets, vesicles are extremely deformable and DNA-mediated adhesion causes significant shape adjustments. We investigate experimentally the thermal response of pairs and networks of DNA-tethered liposomes and observe two intriguing and possibly useful collective properties: negative thermal expansion and tuneable porosity of the liposome networks. A model providing a thorough understanding of this unexpected phenomenon is developed, explaining the emergent properties out of the interplay between the temperature-dependent deformability of the vesicles and the DNA-mediated adhesive forces.Funding was provided by the Ernest Oppenheimer Fund and Emmanuel College Cambridge (L.D.M.), EPSRC Programme Grant CAPITALS number EP/J017566/1 (L.P., J.K., P.C. and L.D.M.) and the Winton Fund for Physics of Sustainability (E.E.).This article was originally published in Nature Communications (L Parolini, BM Mognetti, J Kotar, E Eiser, P Cicuta, L Di Michele, Nature Communications 2015, 6, 5948

Adaptable DNA interactions regulate surface triggered self assembly

DNA-mediated multivalent interactions between colloidal particles have been extensively applied for their ability to program bulk phase behaviour and dynamic processes. Exploiting the competition between different types of DNA–DNA bonds, here we experimentally demonstrate the selective triggering of colloidal self-assembly in the presence of a functionalised surface, which induces changes in particle–particle interactions. Besides its relevance to the manufacturing of layered materials with controlled thickness, the intrinsic signal-amplification features of the proposed interaction scheme make it valuable for biosensing applications

Self-similarity of contact line depinning from textured surfaces

The mobility of drops on surfaces is important in many biological and industrial processes, but the phenomena governing their adhesion, which is dictated by the morphology of the three-phase contact line, remain unclear. Here we describe a technique for measuring the dynamic behaviour of the three-phase contact line at micron length scales using environmental scanning electron microscopy. We examine a superhydrophobic surface on which a drop’s adhesion is governed by capillary bridges at the receding contact line. We measure the microscale receding contact angle of each bridge and show that the Gibbs criterion is satisfied at the microscale. We reveal a hitherto unknown self-similar depinning mechanism that shows how some hierarchical textures such as lotus leaves lead to reduced pinning, and counter-intuitively, how some lead to increased pinning. We develop a model to predict adhesion force and experimentally verify the model’s broad applicability on both synthetic and natural textured surfaces.National Science Foundation (U.S.) (CAREER Award 0952564)DuPont MIT AllianceNational Science Foundation (U.S.). Graduate Research Fellowship ProgramNational Science Foundation (U.S.) (Award ECS-0335765

The role of peptides in bone healing and regeneration: A systematic review

Background: Bone tissue engineering and the research surrounding peptides has expanded significantly over the last few decades. Several peptides have been shown to support and stimulate the bone healing response and have been proposed as therapeutic vehicles for clinical use. The aim of this comprehensive review is to present the clinical and experimental studies analysing the potential role of peptides for bone healing and bone regeneration. Methods: A systematic review according to PRISMA guidelines was conducted. Articles presenting peptides capable of exerting an upregulatory effect on osteoprogenitor cells and bone healing were included in the study. Results: Based on the available literature, a significant amount of experimental in vitro and in vivo evidence exists. Several peptides were found to upregulate the bone healing response in experimental models and could act as potential candidates for future clinical applications. However, from the available peptides that reached the level of clinical trials, the presented results are limited. Conclusion: Further research is desirable to shed more light into the processes governing the osteoprogenitor cellular responses. With further advances in the field of biomimetic materials and scaffolds, new treatment modalities for bone repair will emerge

Using electrowetting to control interface motion in patterned microchannels

info:eu-repo/semantics/publishe

Partial-post Laplace barriers for virtual confinement, stable displacement, and >5 cm s(-1) electrowetting transport.

Laplace barriers composed of full-posts or ridges have been previously reported as a mechanism for virtual fluid confinement, but with unstable displacement (capillary fingering or fluid trapping, respectively). A new platform of 'partial-posts' eliminates the disadvantages of full-posts or ridges, while providing ~60-80% open channel area for rapid electrowetting fluid transport (>5 cm s(-1)). The fluid mechanics of partial-post Laplace barriers are far more complex than previous Laplace barriers as it involves two mechanisms: fluid can first begin to propagate either between, or under, the partial-posts. Careful design of channel and partial-post geometries is required, else one mechanism will dominate over the other. The physics and performance of partial-post Laplace barriers are verified using theoretical equations, experimental results, and dynamic numerical modeling

Research Data: Membrane Adhesion through Bridging by Multimeric Ligands

File formatt is .tiff, with each .tiff file representing a single frame of video or slice of stack. Individual vesicles are organised into .zip files corresponding to their SA/DNA concentration ratios and experiment type: Z-Stack, Flickering or FRAP. In the Z-stacks .zip files, two channels were recorded, using a 488nm and 633nm laser respectively. For each vesicle folder, there is a separate subfolder for each of these channels channel. Each frame of the Z-stacks represents a 0.1um slice. In Flickering videos, each .tiff file is a frame of a 1000 frame video, with a framerate of 97ms/frame, taken at the equator of the vesicle. In FRAP experiments, each vesicle subfolder contains subfolders at different frame rates. These are: StagePre (10fps), StagePost1 (10fps), StagePost2 (0.5fps) and StagePost3 (0.1fps). These correspond to stages of the pre- and post-bleaching process

Communication: a simple analytical formula for the free energy of ligand-receptor-mediated interactions

Recently [P. Varilly, S. Angioletti-Uberti, B. M. Mognetti, and D. Frenkel, “A general theory of DNA-mediated and other valence-limited colloidal interactions,” J. Chem. Phys. 137, 094108 (2012)], we presented a general theory for calculating the strength and properties of colloidal interactions mediated by ligand–receptor bonds (such as those that bind DNA-coated colloids). In this Communication, we derive a surprisingly simple analytical form for the interaction free energy, which was previously obtainable only via a costly numerical thermodynamic integration. As a result, the computational effort to obtain potentials of interaction is significantly reduced. Moreover, we can gain insight from this analytic expression for the free energy in limiting cases. In particular, the connection of our general theory to other previous specialised approaches is now made transparent. This important simplification will significantly broaden the scope of our theory