The effect of poly-L-lysine structure on the pH response of polygalacturonic acid-based multilayers

Tunable layer-by-layer films containing hyaluronic acid and their interactions with CD44

We report on the development of layer-by-layer (LbL) constructs whose viscoelastic properties and bioactivity can be finely tuned by using polyanions of different size and/or crosslinking. As a polyanion we used hyaluronic acid (HA) - a multi-signaling biomolecule whose bioactivity depends on its molecular weight. We investigated the interplay between the mechanical properties of the LbL systems built using HA of different sizes and the specific HA-mediated biochemical interactions. We characterized the assembled materials and their interactions with CD44, the main HA receptor, by Quartz Crystal Microbalance with Dissipation (QCM-D), Surface Plasmon Resonance (SPR) and Atomic Force Microscopy (AFM). We observed that the presence of CD44 resulted in the disruption of the non-crosslinked multilayers, while crosslinked films remain stable and bind CD44 in a HA molecular weight and charge specific fashion.

Aptamer-based fiber sensor for thrombin detection

The detection of thrombin based on aptamer binding is studied using two different optical fiber-based configurations: long period gratings coated with a thin layer of titanium dioxide and surface plasmon resonance devices in optical fibers coated with a multilayer of gold and titanium dioxide. These structures are functionalized and the performance to detect thrombin in the range 10 to 100 nM is compared in transmission mode. The sensitivity to the surrounding refractive index (RI) of the plasmonic device is higher than 3100  nm RIU−1 in the RI range 1.335 to 1.355, a factor of 20 greater than the sensitivity of the coated grating. The detection of 10 nM of thrombin was accomplished with a wavelength shift of 3.5 nm and a resolution of 0.54 nM.

Biomimetic Extracellular Environment Based on Natural Origin Polyelectrolyte Multilayers

Surface modification of biomaterials is a well-known approach to enable an adequate biointerface between the implant and the surrounding tissue, dictating the initial acceptance or rejection of the implantable device. Since its discovery in early 1990s layer-by-layer (LbL) approaches have become a popular and attractive technique to functionalize the biomaterials surface and also engineering various types of objects such as capsules, hollow tubes, and freestanding membranes in a controllable and versatile manner. Such versatility enables the incorporation of different nanostructured building blocks, including natural biopolymers, which appear as promising biomimetic multilayered systems due to their similarity to human tissues. In this review, the potential of natural origin polymer-based multilayers is highlighted in hopes of a better understanding of the mechanisms behind its use as building blocks of LbL assembly. A deep overview on the recent progresses achieved in the design, fabrication, and applications of natural origin multilayered films is provided. Such films may lead to novel biomimetic approaches for various biomedical applications, such as tissue engineering, regenerative medicine, implantable devices, cell-based biosensors, diagnostic systems, and basic cell biology.

Nanocoating for biomolecule delivery using layer-by-layer self-assembly

Since its introduction in the early 1990s, layer-by-layer (LbL) self-assembly of films has been widely used in the fields of nanoelectronics, optics, sensors, surface coatings, and controlled drug delivery. The growth of this industry is propelled by the ease of film manufacture, low cost, mild assembly conditions, precise control of coating thickness, and versatility of coating materials. Despite the wealth of research on LbL for biomolecule delivery, clinical translation has been limited and slow. This review provides an overview of methods and mechanisms of loading biomolecules within LbL films and achieving controlled release. In particular, this review highlights recent advances in the development of LbL coatings for the delivery of different types of biomolecules including proteins, polypeptides, DNA, particles and viruses. To address the need for co-delivery of multiple types of biomolecules at different timing, we also review recent advances in incorporating compartmentalization into LbL assembly. Existing obstacles to clinical translation of LbL technologies and enabling technologies for future directions are also discussed.

Size and medium conductivity dependence on dielectrophoretic behaviors of gas core poly-L-lysine shell nanoparticles

Dynamic (dis)assembly of biocompatible nanoparticles into 3D, packed structures would benefit drug delivery, films, and diagnostics. Dielectrophoretic (DEP) microdevices can rapidly assemble and manipulate polarizable particles within nonuniform electric fields. DEP has primarily discerned micrometer particles since nanoparticles experience smaller forces. This work examines conductivity and size DEP dependencies of previously unexplored spherical core-shell nanoparticle (CSnp) into 3D particle assemblies. Poly-L-lysine shell material was custom synthesized around a gas core to form CSnps. DEP frequencies from 1 kHz to 80 MHz at fixed 5 volts peak-to-peak and medium conductivities of 10(-5) and 10(-3) S/m were tested. DEP responses of ∼220 and ∼400 nm poly-L-lysine CSnps were quantified via video intensity densitometry at the microdevice's quadrapole electrode center for negative DEP (nDEP) and adjacent to electrodes for positive DEP. Intensity densitometry was then translated into a relative DEP response curve. An unusual nDEP peak occurred at ∼57 MHz with 25-80 times greater apparent nDEP force. All electrical circuit components were then impedance matched, which changed the observed response to weak positive DEP at low frequencies and consistently weak nDEP from ∼100 kHz to 80 MHz. This impedance-matched behavior agrees with conventional Clausius-Mossotti DEP signatures taking into account the gas core's contributions to the polarization mechanisms. This work describes a potential pitfall when conducting DEP at higher frequencies in microdevices and concurrently demonstrates nDEP behavior for a chemically and structurally distinct particle system. This work provides insight into organic shell material properties in nanostructures and strategies to facilitate dynamic nanoparticle assemblies.

Protein-ligand interactions investigated by thermal shift assays (TSA) and dual polarization interferometry (DPI)

Over the last decades, a wide range of biophysical techniques investigating protein-ligand interactions have become indispensable tools to complement high-resolution crystal structure determinations. Current approaches in solution range from high-throughput-capable methods such as thermal shift assays (TSA) to highly accurate techniques including microscale thermophoresis (MST) and isothermal titration calorimetry (ITC) that can provide a full thermodynamic description of binding events. Surface-based methods such as surface plasmon resonance (SPR) and dual polarization interferometry (DPI) allow real-time measurements and can provide kinetic parameters as well as binding constants. DPI provides additional spatial information about the binding event. Here, an account is presented of new developments and recent applications of TSA and DPI connected to crystallography.