Electric-field-induced displacement of a charged spherical colloid embedded in an elastic Brinkman medium

When an electric field is applied to an electrolyte-saturated polymer gel embedded with charged colloidal particles, the force that must be exerted by the hydrogel on each particle reflects a delicate balance of electrical, hydrodynamic and elastic stresses. This paper examines the displacement of a single charged spherical inclusion embedded in an uncharged hydrogel. We present numerically exact solutions of coupled electrokinetic transport and elastic-deformation equations, where the gel is treated as an incompressible, elastic Brinkman medium. This model problem demonstrates how the displacement depends on the particle size and charge, the electrolyte ionic strength, and Young's modulus of the polymer skeleton. The numerics are verified, in part, with an analytical (boundary-layer) theory valid when the Debye length is much smaller than the particle radius. Further, we identify a close connection between the displacement when a colloid is immobilized in a gel and its velocity when dispersed in a Newtonian electrolyte. Finally, we describe an experiment where nanometer-scale displacements might be accurately measured using back-focal-plane interferometry. The purpose of such an experiment is to probe physicochemical and rheological characteristics of hydrogel composites, possibly during gelation

Sensing viruses by mechanical tension of DNA in responsive hydrogels

The rapid worldwide spread of severe viral infections, often involving novel modifications of viruses, poses major challenges to our health care systems. This means that tools that can efficiently and specifically diagnose viruses are much needed. To be relevant for a broad application in local health care centers, such tools should be relatively cheap and easy to use. Here we discuss the biophysical potential for the macroscopic detection of viruses based on the induction of a mechanical stress in a bundle of pre-stretched DNA molecules upon binding of viruses to the DNA. We show that the affinity of the DNA to the charged virus surface induces a local melting of the double-helix into two single-stranded DNA. This process effects a mechanical stress along the DNA chains leading to an overall contraction of the DNA. Our results suggest that when such DNA bundles are incorporated in a supporting matrix such as a responsive hydrogel, the presence of viruses may indeed lead to a significant, macroscopic mechanical deformation of the matrix. We discuss the biophysical basis for this effect and characterize the physical properties of the associated DNA melting transition. In particular, we reveal several scaling relations between the relevant physical parameters of the system. We promote this DNA-based assay for efficient and specific virus screening.Comment: 11 pages, 7 figures, supplementary material included in the source file

Structure and Dynamics of Solvated Polymers near a Silica Surface: On the Different Roles Played by Solvent

Whereas it is experimentally known that the inclusion of nanoparticles in hydrogels can lead to a mechanical reinforcement, a detailed molecular understanding of the adhesion mechanism is still lacking. Here we use coarse-grained molecular dynamics simulations to investigate the nature of the interface between silica surfaces and solvated polymers. We show how differences in the nature of the polymer and the polymer--solvent interactions can lead to drastically different behavior of the polymer--surface adhesion. Comparing explicit and implicit solvent models, we conclude that this effect cannot be fully described in an implicit solvent. We highlight the crucial role of polymer solvation for the adsorption of the polymer chain on the silica surface, the significant dynamics of polymer chains on the surface, and details of the modifications in the structure solvated polymer close to the interface

Enzyme Actuated Bioresponsive Hydrogels

Bioresponsive hydrogels are emerging with technological significance in targeted drug delivery, biosensors and regenerative medicine. Conferred with the ability to respond to specific biologically derived stimuli, the design challenge is in effectively linking the conferred biospecificity with an engineered response tailored to the needs of a particular application. Moreover, the fundamental phenomena governing the response must support an appropriate dynamic range and limit of detection. The design of these systems is inherently complicated due to the high interdependency of the governing phenomena that guide the sensing, transduction, and the actuation response of hydrogels. To investigate the dynamics of these materials, model systems may be used which seek to interrogate the system dynamics by uni-variable experimentation and limit confounding phenomena such as: polymer-solute interactions, polymer swelling dynamics and biomolecular reaction-diffusion concerns. To this end, a model system, α-chymotrypsin (Cht) (a protease) and a cleavable peptide-chromogen (pro-drug) covalently incorporated into a hydrogel, was investigated to understand the mechanisms of covalent loading and release by enzymatic cleavage in bio-responsive delivery systems. Using EDC and Sulfo-NHS, terminal carboxyl groups of N-succinyl-Ala-Ala-Pro-Phe p-nitroanilide, a cleavable chromogen, were conjugated to primary amines of a hydrated poly(HEMA)-based hydrogel. Hydrogel discs were incubated in buffered Cht causing enzyme-mediated cleavage of the peptide and concomitant release of the chromophore for monitoring. To investigate substrate loading and the effects of hydrogel morphology on the system, the concentration of the amino groups (5, 10, 20, and 30 mol%) and the cross-linked density (1, 5, 7, 9 and 12 mol%) were independently varied. Loading-Release Efficiency of the chromogen was shown to exhibit a positive relation to increasing amino groups (AEMA). The release rates demonstrated a negative relation to increasing cross-linked density attributed to decreasing void fractions and increasing tortuosities. The diffusion coefficient of Cht, D0,Cht, was determined to be 6.9 ± 0.5 _ 10-7 cm2 s-1, and the range of Deff of Cht for 1 to 12 mol% TEGDA was determined to 6.9 _10-8 to 0.1 _ 10-8cm2 s-1. We show how these parameters may be optimized and used to achieve programmed release rates in engineered bio-responsive systems. The field of bioresponsive hydrogels is continuing to expand as the need for such materials persists. Future work will enable more control over the loading and release of therapeutic and diagnostic moieties. Continued research regarding in enzymatically actuated hydrogels will involve pre-polymerization loading methodologies; in silico diffusion-reaction multiphysics modeling; enzyme actuated degradation of the polymer; and substation of various mediating enzyme, cleavable peptides, and release molecules

Mechanoelectrical transduction in the hydrogel-based biomimetic sensors

The study addresses the phenomenon of mechanoelectrical transduction in polyelectrolyte hydrogelsand, in particular, the search of the driving force for the change of the electrical potential of a gel underthe applied mechanical stretch. Polyelectrolyte gels of calcium and magnesium salts of polymethacrylicacid were synthesized by the radical polymerization in water solution. Their electrical potential mea-sured by microcapillary electrodes was negative and fall within 100–140 mV range depending on thenature of a counterion and the networking density of a gel. The rectangular samples (∼10 mm in lengthand 2 × 2 mm in cross-section) of gel-based sensors underwent the dynamic axial deformation, and thesimultaneous monitoring of their geometrical dimensions and the electrical potential was performed.Sensor elongation resulted in the overall increase of gel volume, and it was always accompanied by thegel potential change toward the depolarization (diminishing of the negative values). Theoretical modelbased on the assumption of the total electrical charge conservation in the course of the dynamic defor-mation of a filament was proposed to describe the dependence of the electrical potential of a gel on itsvolume. Good agreement between the predictions of the model and the experimental trend was shown.The proposed mechanism of mechanoelectrical transduction based on the stretch-dependant volumechanges in polyelectrolyte hydrogels might be useful to understand the nature of mechanical sensing inmuch more complex biological gels like the cell cytoskeleton.This work has been done under the financial support of theRussian Scientific Fund, project 14-19-00989. One of us (M.T.Lopez-Lopez) has been supported by the Grant FIS2013-41821-R(MINECO, Spain)

Potential Role of Inorganic Confined Environments in Prebiotic Phosphorylation

A concise outlook on the potential role of confinement in phosphorylation and phosphate condensation pertaining to prebiotic chemistry is presented. Inorganic confinement is a relatively uncharted domain in studies concerning prebiotic chemistry, and even more so in terms of experimentation. However, molecular crowding within confined dimensions is central to the functioning of contemporary biology. There are numerous advantages to confined environments and an attempt to highlight this fact, within this article, has been undertaken, keeping in context the limitations of aqueous phase chemistry in phosphorylation and, to a certain extent, traditional approaches in prebiotic chemistry

Some excursions in the world of stimuli-responsive polymeric gels

Stimuli-responsive polymeric gels are attracting increasing attention due to their great potential as smart materials. Some of the recent work in the area of science and applications of these materials, including from our own school at NCL, is described. The quantitative basis for volume transltion in the gels is first presented. Our recent findlugs on deformation-dependent swelling as well as certain aspects of microdynamics in gels studied through NMR have been highlighted. Specific appilcatlons based on this fundamental understandmg have been described. These include the development of a macromolecular separation technique based on swelling/collaping gels. The basis for diffusion modulation of gels to switch from Fickian to non-Fickian dlifusion has been presented. A practical application of such diffusion modulation in sustained-release ystrms is described. Diverse applications exploiting the stimuli-responsive ability of gels in areas such as sensors, soft actuators, artificial muscles, intelligent sponges, etc., are finally presented

Design and development of specific nanostructured systems based on biocompatible materials

Las diferentes aplicaciones y usos de las proteínas han crecido durante los últimos 50 años de forma continua. Sin embargo, en los últimos años hemos sido testigos de una irrefrenable aparición de aplicaciones más vanguardistas: materiales biomiméticos, ingeniería para tejidos, liberación de fármacos, bioelectrónica o modelos para nanopartículas. En este sentido, las interacciones entre moléculas pequeñas en solución de proteínas afectan su respectiva función bilógica y determina la estabilidad de las soluciones con respecto a la agregación, licuefacción, y otras transformaciones de fases. Además, la agregación de proteínas, formación de cristales, plegamiento o desnaturalización, están definidas en gran parte por las fuerzas que actúan sobre las moléculas

Gelatin-Hyaluronic Acid Hydrogels with Tuned Stiffness to Counterbalance Cellular Forces and Promote Cell Differentiation

[EN] Cells interact mechanically with their environment, exerting mechanical forces that probe the extracellular matrix (ECM). The mechanical properties of the ECM determine cell behavior and control cell differentiation both in 2D and 3D environments. Gelatin (Gel) is a soft hydrogel into which cells can be embedded. This study shows significant 3D Gel shrinking due to the high traction cellular forces exerted by the cells on the matrix, which prevents cell differentiation. To modulate this process, Gel with hyaluronic acid (HA) has been combined in an injectable crosslinked hydrogel with controlled Gel-HA ratio. HA increases matrix stiffness. The addition of small amounts of HA leads to a significant reduction in hydrogel shrinking after cell encapsulation (C2C12 myoblasts). We show that hydrogel stiffness counterbalanced traction forces of cells and this was decisive in promoting cell differentiation and myotube formation of C2C12 encapsulated in the hybrid hydrogels.The authors are grateful for the financial support received from the Spanish Ministry through the MAT2013-46467-C4-1-R project (including the FEDER financial support), the BES-2011-046144, and the EEBB-I-14-08725 grants. CIBER-BBN is an initiative funded by the VI National R&D&I Plan 2008-2011, Iniciativa Ingenio 2010, Consolider Program. CIBER actions are financed by the Instituto de Salud Carlos III with assistance from the European Regional Development Fund. M.S.S. acknowledges ERC through HealInSynergy 306990.Poveda Reyes, S.; Moulisova, V.; Sanmartín Masiá, EDR.; Quintanilla-Sierra, L.; Salmerón Sánchez, M.; Gallego Ferrer, G. (2016). Gelatin-Hyaluronic Acid Hydrogels with Tuned Stiffness to Counterbalance Cellular Forces and Promote Cell Differentiation. Macromolecular Bioscience. 16(9):1311-1324. https://doi.org/10.1002/mabi.201500469S1311132416