Microrheological Studies Research Articles

DYNAMIC LIGHT SCATTERING-BASED MICRORHEOLOGY OF THERMOSENSITIVE CHITOSAN HYDROGELS: PRELIMINARY STUDIES

This paper presents a preliminary characterisation of the local mechanical properties of thermosensitive chitosan systems using dynamic light scattering, an endeavour that has not yet been attempted. The tests included solutions of chitosan chloride with the addition of sodium glycerophosphate as well as those without a substance to support the gelation process. There was much better agreement between the data obtained from measurements on the microscopic and macroscopic scales for systems without the addition of glycerophosphate. In most cases, the addition of a pH-neutralising salt resulted in higher values of dynamic moduli than those obtained during microrheological measurements. Therefore, it seems to be possible to use dynamic light scattering to conduct microrheological studies of thermosensitive chitosan systems.

Combatting Antibiotic-Resistant Pathogens: Disrupting Pseudomonas Aeruginosa Biofilm Viscoelasticity Using Carbon Dot Nanoparticles

Bacterial infection is a global burden, killing one in every eight people worldwide, primarily due to antibiotic resistance. Pseudomonas aeruginosa is one of the top five bacteria responsible for around 7.7 million fatalities caused by bacterial infections. P. aeruginosa secretes biofilm, a biological substance with viscoelastic characteristics to avoid antimicrobial treatments particularly, in chronic and serious wound infections. In the bid to create topical treatments, we investigated the mechano-active potentials of cellulase-based carbon dots as a therapeutic agent against P. aeruginosa biofilm where we envisage the retaining of the cellulase hydrolytic activity in the cellulase-based carbon dots. Cellulase is a glycoside hydrolase that has already been shown to be effective in causing biofilm dispersal as well as reduction in biofilm stiffness and elasticity.The cellulase carbon dots were synthesized using the microwave while citric acid carbon dots (CA-CDs) were hydrothermally synthesized to serve as non-protein-based carbon dots and then characterized for surface properties, size, elemental compositions, and fluorescence profile. P. aeruginosa biofilms were grown in a microfluidic environment for 24 hours and then treated with these carbon dots at a range of concentrations. Using microrheology, it was seen that biofilms treated with cellulase-based carbon dots were more viscous and less stiff compared to those treated with citric acid-based carbon dots. This appears to be because the cellulase carbon dots impact PSL within the biofilm based on microrheology studies examining bacteria strains with specific EPS components removed. This is consistent with the impact of molecular cellulase on biofilms. In general, initial studies suggest that the cellulase-based carbon dots have the potential to act as an excellent multi-antibiofilm therapeutic in the future.

Force renormalization for probes immersed in an active bath.

Langevin equations or generalized Langevin equations (GLEs) are popular models for describing the motion of a particle in a fluid medium in an effective manner. Here we examine particles immersed in an inherently nonequilibrium fluid, i.e., an active bath, which are subject to an external force. Specifically, we consider two types of forces that are highly relevant for microrheological studies: A harmonic, trapping force and a constant, "drag" force. We study such systems by molecular simulations and use the simulation data to extract an effective GLE description. We find that within this description, in an active bath, the external force in the GLE is not equal to the physical external force, but rather a renormalized external force, which can be significantly smaller. The effect cannot be attributed to the mere temperature renormalization, which is also observed.

Contact phenomena during water insulation

Microrheological studies of givpan-based gel-forming solutions in micron-sized pores have shown that contact interaction in the fluid–rock formation system leads to structural and mechanical colmatation of the porous medium, blocking of pore channels by elastic-viscous filtrate plugs, which under normal conditions exhibit viscoplastic qualities. It is shown that these processes develop immediately upon contact of the filtrate with the surface, and discontinuities at critical pressures do not worsen the water-insulating properties.

Bedaquiline fumarate microemulsion: formulation optimization, rheological characterizationand in vitro studies.

Aim: Bedaquiline fumarate (BQF), an antitubercular drug, shows limited bioavailability due to solubility-limited intestinal absorption. In this research,the authorsformulated aBQF-loaded microemulsion to improve BQF's oral bioavailability. Methods: Microemulsion was prepared by a spontaneous emulsification method and evaluated for thermodynamic stability, size, dispersibility, transmittance, rheology, microrheology, drug release, cytotoxicityand cellular uptake. Results: Microemulsion showed an average globule size of 26.50±6.29nm with spherical geometry and revealed gel-sol-gel behavior in microrheological studies. Cytotoxicity and cell uptake studies in Caco-2 cells showed that BQF microemulsion was cytocompatible at the highest concentration of 500μg/mlwith significantly higher cellular uptake than control. Conclusion: The present study indicates that BQF microemulsion could be explored further for effective treatment of multidrug-resistant tuberculosis.

Amyloid-Like Aggregation in Native Protein and its Suppression in the Bio-Conjugated Counterpart

Prevention of protein aggregation and thus stabilization of proteins has large biological and biotechnological implications. Here we introduce Dynamic Light Scattering (DLS) and DLS-based microrheology to show how native bovine serum albumin (nBSA) forms amyloid fibrils in weakly denaturing conditions as function of time, and how stoichiometric conjugation of BSA with polymer-surfactants (PSpBSA) protects the protein form such aggregation. Employing a combination of Thioflavin-T fluorescence, Fourier transform infrared spectroscopy and other methods, we show that nBSA forms filamentous aggregates with amyloid-like structure, while PSpBSA proteins remain fully dispersed with only minor changes in their folding state, even when continuously heated for up to 5 days in denaturation conditions at 65 °C. Time-resolved DLS-based microrheology studies demonstrate that suspensions of the filamentous nBSA aggregates become viscoelastic for concentrations ≥200 μM. Our results indicate that after 6 days in aggregation conditions, the elastic modulus G′(ω) of nBSA solutions went from zero initially to values of up to 3.6 Pa, indicating that the filaments become long enough to form an entangled, viscoelastic network. Interestingly, heating 200 μM native BSA solutions at 65 °C for 2 days in Eppendorf tubes resulted in self-standing films rather than dispersed filaments. These films exhibited strong ThT-fluorescence intensities and a predominant β-sheet secondary structure in FTIR studies, suggesting that the self-standing microstructure of the film resulted from hierarchical self-assembly of the amyloid fibrils.

The role of glycerol on the thermal gelation of myofibrillar protein from giant squid (Dosidicus gigas) mince

This work studies the effect of glycerol on the chemical physics of the thermal gelatin of protein from giant squid minced meat. The presence of glycerol induced changes in the nano protein particles (NPP) self-assembled structures. These nanoscale events resulted in dramatic changes on the interactions between proteins when forming gels, with the contribution of ionic interactions increasing by 17% upon gelation, that of hydrogen bonds reducing by 50%, that of hydrophobic interactions decreasing by 45%, and that of disulphide bonding increasing by 18%. Glycerol also induced cluster formation in myofibrillar solutions. As a result, incorporation of glycerol increased springiness, resilience, and adhesiveness of the formed gels by 13%, 25%, and 370% respectively. The heating gelation of myofibrillar proteins was monitored at various temperatures via recording the elastic and storage moduli. Rheology and micro-rheology studies revealed that the presence of glycerol increased G′ and G″ of thermally-gelled giant squid meat.

Dynamical heterogeneity in the gelation process of a polymer solution with a lower critical solution temperature.

The gelation of a hydrophobically modified hyaluronic acid aqueous solution which shows a lower critical solution temperature of about 25 °C was investigated by multi-particle tracking microrheology. The linear viscoelasticity of the gelling system is converted from the microrheological data. The critical gelling temperature Tgel = 36.3 °C was determined from the loss tangent by the Winter-Chambon criterion. The critical exponent n = 0.62 was determined from the shift factors of the time-cure superposition. The length scales of the dynamic heterogeneity of the gelling system were analyzed using a proposed framework where single-particle and multi-particle non-Gaussian parameters were compared. The length scale of the dynamic heterogeneous regions monotonically decreases during the gelation process, consistent with the nucleation-and-growth mechanism of phase separation. Distributions of local viscosity in the gelling system were extracted from the observed distributions of particle displacement as a time-dependent fingerprint of the dynamic heterogeneity of the gelling system. The results and analyzing methods proposed in the present work can be applied to other microrheological studies.

Effect of aging time on the viscoelastic properties of amphiphilic polymer-polyacid supramolecular solution

An amphiphilic polymer-based supramolecular system was formulated by exploring the electrostatic interactions between the cationic amphiphilic polymer and polyacid. The effect of aging time on the viscoelastic properties, salt and temperature tolerance, shear resistance, and viscosity recovery of the system was explored by means of rheological measurements. The intrinsic relationship between the viscoelasticity of the system at different aging times and their dynamic growth was studied by macro-rheological and optical micro-rheological methods. The results show that under the influence of various factors, the viscoelastic properties of the supramolecular system increase significantly with aging. Optical micro-rheological studies demonstrated that the viscoelasticity of the system continues to increase over a period of 30 days. After aging, the viscoelastic results indicate the formation of a strong gel. This study clearly demonstrates that the aging time is a key factor that should be considered in the formulation of supramolecular systems formed by the electrostatic interaction between the cationic amphiphilic polymer and polyacid.

Microrheology to probe smectic clusters in bent-core nematic liquid crystals.

Many bent-core nematic liquid crystals exhibit unusual physical properties due to the presence of smectic clusters, known as "cybotactic" clusters, in the nematic phase. Here, we investigate the effect of these clusters on the complex shear modulus (G*(ω)) of two asymmetric bent-core liquid crystals using a microrheological technique. The compound with a shorter hydrocarbon chain (8OCH3) exhibits only a nematic (N) phase whereas the compound with a longer chain (16OCH3) exhibits both nematic (N) and smectic-A (SmA) phases. The rheological results are correlated with the measurements of curvature elastic constants. Our results show that the directional shear modulus of 16OCH3, just above the SmA to N phase transition temperature, is strikingly different than that of 8OCH3, owing to the smectic clusters. An approximate size of the clusters is estimated using a simple model. Therefore, microrheological studies on bent-core nematic liquid crystals are very useful in extracting information about underlying smectic clusters.

Physicochemical and Microbiological Properties of Synbiotic Yogurt Made with Probiotic Yeast Saccharomyces boulardii in Combination with Inulin.

Saccharomyces boulardii is a unique species of yeast previously characterized as a probiotic strain (CNCM I-745) among a few probiotic yeasts reported to date. Inulin is one of the most common prebiotics that exhibit twisted hydrocolloidal properties in dairy products. The present study was designed to develop a synbiotic yogurt by incorporation of S. boulardii and inulin at 1%, 1.5%, and 2% (w/v), comparing with the probiotic and control plain yogurts. Microrheological, microstructural, microbiological, sensory properties, and volatile compounds of the yogurt samples were evaluated. Microrheological analysis showed that addition of inulin to yogurt slightly reduced the values of G′ and G″, while solid–liquid balance (SLB) values confirmed more solid properties of the synbiotic yogurt (0.582~0.595) than the plain yogurt (0.503~0.518). A total of 18 volatile compounds were identified in the synbiotic yogurt, while only five and six compounds were identified in plain and probiotic yogurts, respectively. Physiochemical parameters such as pH, acidity, and protein content were in the normal range (as with the control), while fat content in the synbiotic yogurt decreased significantly. Addition of 1% inulin not only reduced syneresis but also maintained viability of S. boulardii after 28 days of storage. Microstructural and microrheological studies confirmed the dense, compressed, homogeneous structure of the synbiotic yogurt. Thus, addition of inulin improved the textural and sensory properties of the synbiotic yogurt, as well as survival of S. boulardii with viable count above 6.0 log CFU/g in yogurt, as generally required for probiotics. Therefore, novel synbiotic yogurt with desirable quality was developed as an effective carrier for delivery of the probiotic yeast exerting its beneficial health effects.

Spectroscopic photonic force optical coherence elastography.

We demonstrate spectroscopic photonic force optical coherence elastography (PF-OCE). Oscillations of microparticles embedded in viscoelastic hydrogels were induced by harmonically modulated optical radiation pressure and measured by phase-sensitive spectral-domain optical coherence tomography. PF-OCE can detect microparticle displacements with pico- to nano-meter sensitivity and millimeter-scale volumetric coverage. With spectroscopic PF-OCE, we quantified viscoelasticity over a broad frequency range from 1Hz to 7kHz, revealing rich microstructural dynamics of polymer networks across multiple microrheological regimes. Reconstructed frequency-dependent loss moduli of polyacrylamide hydrogels were observed to follow a general power scaling law G''∼ω0.75, consistent with that of semiflexible polymer networks. Spectroscopic PF-OCE provides an all-optical approach to microrheological studies with high sensitivity and high spatiotemporal resolution, and could be especially beneficial for time-lapse and volumetric mechanical characterization of viscoelastic materials.

FILTRATION AND MICRO-RHEOLOGICAL ANOMALIES OF POLYMER DRILLING SOLUTIONS

The article pays attention to the fact that biopolymer drilling solutions without a solid phase acquire viscoelastic properties in a porous medium that are not fixed by means of standard drilling rheometry. Filtration and micro-rheological (pore scale) studies have established that the depth of penetration of the filtrate and the screening of the bottomhole zone in this case are determined by the degree of structural-mechanical colmatation resulting from the contact interaction of the liquid and rock null.

An AFM Dynamic Contact Model with Finite Thickness Correction to Study Micro-Rheology of Biological Cells

One of the major sources of error in Atomic Force Microscopy based Force Spectroscopic studies is bottom substrate effect, which comes due to assumption of infinite sample thickness. In the present work, anew experimentally validated mathematical correction for finite thickness of thesample is incorporated into a dynamic indentation model. This model is an extension of Sneddon’s static indentation contact model developed for conical tip indenters by incorporating the tip geometric effects, correction to hydrodynamic drag, viscoelastic nature of the sample and its finite thickness. The new model is applied to extract the viscoelastic properties of primary mesenchymal stem cells (MSC’s) extracted from human bone marrow and HCT-116 aggressive epithelial colorectal cancer cells. The micro-rheological studies indicated the presence of profound influence of infinite thickness assumption depending upon indentation depth and sample thickness at the point of indentation. The present model nullified this error and provided a better estimate of the rheological properties. The tests were conducted over a wide frequency bandwidth (0.5 to 126 Hz) and frequency dependent material properties were analyzed using power law structural damping model. It was found that MSC’s are stiffer and less viscous in nature compared to cancer cells.

JColloids: Image analysis for video-microscopy studies of colloidal suspensions

We present an updated version of JChainsAnalyzer [1], a Java and ImageJ-based software for the analysis of video-microscopy images regarding the aggregation dynamics of super-paramagnetic particles in magneto-rheological fluids [2,3]. This new version of the software has been adapted for a general use in image-based experiments of microprobes in suspension, and, consequently, has been renamed as JColloids. In this new version, the number of available options has been reduced, and the image filtering is virtually automatic, depending only on one numeric factor. JColloids has been recently used in the image analysis for micro-rheological studies using sedimented micro-particles in suspension [4] and for tracking microbeads trapped by optical tweezers. New version program summaryProgram Title: JColloids (JChainsAnalyser v.2.0)Program Files doi:http://dx.doi.org/10.17632/jbw8cdt2s5.1Licensing provisions: GPLv3Programming language: JavaSupplementary material: A new document Help.pdf includes basic running instructions for the new code.Journal reference of previous version: Computer Physics Communications, 80 (2009) 1956–1960Does the new version supersede the previous version?: Yes. This new version provides the same image analysis functionality, but the options available in the graphical user interface (GUI), the number of input parameters and the secondary calculations have been substantially simplified.Nature of problem: The previous version of this software was focused on its application to magneto-rheological fluids or aggregated chains of magnetic particles in colloidal dispersions. However, video-microscopy set-ups capturing objects in the micrometer scale are apt to be used for an extended variety of different video-microscopy experiments regarding colloidal science. Our aim is to modify the JChainsAnalyzer software for it can be used in the detection of colloidal objects by image analysis and the subsequent record of the temporal evolution of their center of masses.Solution method: We modify JChainsAnalyzer to be adapted to the analysis of more general experiments in colloidal science. JColloids is an updated and simplified version of JChainsAnalyzer, which uses the same methodology and image analysis algorithms as the previous version. However, this new software is less complicated for the user and it provides the same general functionalities.Reasons for the new version: The original code needed an update since its publication for its application beyond the aggregation of beads in magnetic colloids. Indeed, the new version, JColloids, can be successfully applied to the image analysis of different but similar video-microscopy experiments in colloidal physics, such as micro-rheology using optical tweezers of the study or the micro-structure of a sedimented suspension of micro-particles, as shown in Fig. 1.Summary of revisions: The external libraries read by the software have been updated to their latest available versions. In this new version of JChainsAnalyzer, the GUI has been notably simplified in comparison with the previous one. The GUI reads the external parameters needed for the image filtering, which have been reduced to only three. Only one of the input parameters is a numeric number, whose modification is not usually needed, with the purpose of multiplying the threshold value calculated from the adaptive algorithms in the image analysis. There are another two external parameters, which may be useful in particular situations: one allows to erode the detected particle’s contour, while the other is used to separate joined particles. Fig. 1 shows several examples of the filtering of images of micro-particles in water in different experimental configurations (see figure’s caption). All the binary images are obtained using the same input parameters, making the process almost automatic. Note that in Fig. 1 (b), the upper-left particle is slightly out of focus compared with its location in Fig. 1 (a), and the adaptative algorithm is still detecting correctly the contour of the particle. The filtering in Fig. 1 (c) corresponds to a different experimental setup [4] and zoom configuration, and the detection is also properly performed.Finally, we have to mention that the code has been notably simplified and it is more readable since we have refined the internal calculations related with technical aspects in the research of the scaling in the aggregation of magnetic fluids [2], assuming that any necessary calculation can be performed afterwards using the output file. In this sense, the output file, which contains the (x,y) positions of the centers of the detected objects, has been designed to be compatible with the input needed with tracking routines in IDL, which are standard in the analysis of micro-rheological experiments [5].Additional comments including Restrictions and Unusual features: The software can be run without GUI, but a long run command indicating all the external libraries is needed (how to do this is indicated in the help file). The software does not perform additional calculations, only the main parameters which characterize the objects are detected from the image analysis.AcknowledgmentsThe authors acknowledge MINECO for its financial support through projects FIS2013-47350-C5-5-R (P.D.G, M.P and M.A.R.) and CTQ-2016-78895-R (F.O.). P.D.G. also acknowledges J. C. Gómez-Sáez for her proofreading of the texts.

PFMCal : Photonic force microscopy calibration extended for its application in high-frequency microrheology

The present document is an update of the previously published MatLab code for the calibration of optical tweezers in the high-resolution detection of the Brownian motion of non-spherical probes [1]. In this instance, an alternative version of the original code, based on the same physical theory [2], but focused on the automation of the calibration of measurements using spherical probes, is outlined. The new added code is useful for high-frequency microrheology studies, where the probe radius is known but the viscosity of the surrounding fluid maybe not. This extended calibration methodology is automatic, without the need of a user’s interface. A code for calibration by means of thermal noise analysis [3] is also included; this is a method that can be applied when using viscoelastic fluids if the trap stiffness is previously estimated [4]. The new code can be executed in MatLab and using GNU Octave. New version program summaryProgram Title: PFMCalProgram Files doi:http://dx.doi.org/10.17632/s59f3gz729.1Licensing provisions: GPLv3Programming language: MatLab 2016a (MathWorks Inc.) and GNU Octave 4.0Operating system: Linux and Windows.Supplementary material: A new document README.pdf includes basic running instructions for the new code.Journal reference of previous version: Computer Physics Communications, 196 (2015) 599Does the new version supersede the previous version?: No. It adds alternative but compatible code while providing similar calibration factors.Nature of problem (approx. 50–250 words): The original code uses a MatLab-provided user’s interface, which is not available in GNU Octave, and cannot be used outside of a proprietary software as MatLab. Besides, the process of calibration when using spherical probes needs an automatic method when calibrating big amounts of different data focused to microrheology.Solution method (approx. 50–250 words): The new code can be executed in the latest version of MatLab and using GNU Octave, a free and open-source alternative to MatLab. This code generates an automatic calibration process which requires only to write the input data in the main script. Additionally, we include a calibration method based on thermal noise statistics, which can be used with viscoelastic fluids if the trap stiffness is previously estimated.Reasons for the new version: This version extends the functionality of PFMCal for the particular case of spherical probes and unknown fluid viscosities. The extended code is automatic, works in different operating systems and it is compatible with GNU Octave.Summary of revisions: The original MatLab program in the previous version, which is executed by PFMCal.m, is not changed. Here, we have added two additional main archives named PFMCal_auto.m and PFMCal_histo.m, which implement automatic calculations of the calibration process and calibration through Boltzmann statistics, respectively. The process of calibration using this code for spherical beads is described in the README.pdf file provided in the new code submission. Here, we obtain different calibration factors, β (given in μm/V), according to [2], related to two statistical quantities: the mean-squared displacement (MSD), βMSD, and the velocity autocorrelation function (VAF), βVAF. Using that methodology, the trap stiffness, k, and the zero-shear viscosity of the fluid, η, can be calculated if the value of the particle’s radius, a, is previously known. For comparison, we include in the extended code the method of calibration using the corner frequency of the power-spectral density (PSD) [5], providing a calibration factor βPSD.Besides, with the prior estimation of the trap stiffness, along with the known value of the particle’s radius, we can use thermal noise statistics to obtain calibration factors, β, according to the quadratic form of the optical potential, βE, and related to the Gaussian distribution of the bead’s positions, βσ2. This method has been demonstrated to be applicable to the calibration of optical tweezers when using non-Newtonian viscoelastic polymeric liquids [4].An example of the results using this calibration process is summarized in Table 1. Using the data provided in the new code submission, for water and acetone fluids, we calculate all the calibration factors by using the original PFMCal.m and by the new non-GUI code PFMCal_auto.m and PFMCal_histo.m. Regarding the new code, PFMCal_auto.m returns η, k, βMSD, βVAF and βPSD, while PFMCal_histo.m provides βσ2 and βE. Table 1 shows how we obtain the expected viscosity of the two fluids at this temperature and how the different methods provide good agreement between trap stiffnesses and calibration factors.Additional comments including Restrictions and Unusual features (approx. 50–250 words): The original code, PFMCal.m, runs under MatLab using the Statistics Toolbox. The extended code, PFMCal_auto.m and PFMCal_histo.m, can be executed without modification using MatLab or GNU Octave. The code has been tested in Linux and Windows operating systems.

Physical gelation of supramolecular hydrogels cross-linked by metal-ligand interactions: Dynamic light scattering and microrheological studies

Microrheology based on diffusing-wave spectroscopy, dynamic light scattering (DLS), and macrorheology were performed on solutions of polyacrylamide-derivative associating polymer containing imidazole groups. By adding Ni ion, the physical gel is formed by metal-ligand bond. The physical gel point, where the percolation of a transient network is supposed to occur, was microrheologically determined. In the DLS measurement showing ergodicity at all the conditions studied, we observed three modes in the autocorrelation functions: fast, intermediate, and slow modes. The fast mode is the collective diffusion (gel mode), while the slow mode is attributed to the diffusion of clusters. For the intermediate mode, with increase in Ni ion concentration, the transition from diffusive mode to relaxation mode was observed near the microrheologically determined physical gel point. In postgel regime, intermediate mode can be attributed to the macroscopic relaxation since the activation energies are comparable with the relaxation energy estimated by macrorheology.

Passive microrheology of soft materials with atomic force microscopy: A wavelet-based spectral analysis

Compared to active microrheology where a known force or modulation is periodically imposed to a soft material, passive microrheology relies on the spectral analysis of the spontaneous motion of tracers inherent or external to the material. Passive microrheology studies of soft or living materials with atomic force microscopy (AFM) cantilever tips are rather rare because, in the spectral densities, the rheological response of the materials is hardly distinguishable from other sources of random or periodic perturbations. To circumvent this difficulty, we propose here a wavelet-based decomposition of AFM cantilever tip fluctuations and we show that when applying this multi-scale method to soft polymer layers and to living myoblasts, the structural damping exponents of these soft materials can be retrieved.

Hybrid polymeric hydrogels via peptide nucleic acid (PNA)/DNA complexation

This work presents a new concept in hybrid hydrogel design. Synthetic water-soluble N-(2-hydroxypropyl)methacrylamide (HPMA) polymers grafted with multiple peptide nucleic acids (PNAs) are crosslinked upon addition of the linker DNA. The self-assembly is mediated by the PNA–DNA complexation, which results in the formation of hydrophilic polymer networks. We show that the hydrogels can be produced through two different types of complexations. Type I hydrogel is formed via the PNA/DNA double-helix hybridization. Type II hydrogel utilizes a unique “P-form” oligonucleotide triple-helix that comprises two PNA sequences and one DNA. Microrheology studies confirm the respective gelation processes and disclose a higher critical gelation concentration for the type I gel when compared to the type II design. Scanning electron microscopy reveals the interconnected microporous structure of both types of hydrogels. Type I double-helix hydrogel exhibits larger pore sizes than type II triple-helix gel. The latter apparently contains denser structure and displays greater elasticity as well. The designed hybrid hydrogels have potential as novel biomaterials for pharmaceutical and biomedical applications.

A review of mixing and propulsion of chyme in the small intestine: fresh insights from new methods.

The small intestine is a convoluted flexible tube of inconstant form and capacity through which chyme is propelled and mixed by varying patterns of contraction. These inconstancies have prevented quantitative comparisons of the manner in which contractile activity engenders mixing of contained chyme. Recent quantitative work based on spatiotemporal mapping of intestinal contractions, macro- and micro-rheology, particle image velocimetry and real-time modelling has provided new insights into this process. Evidence indicates that the speeds and patterns of the various types of small intestinal contraction are insufficient to secure optimal mixing and enzymatic digestion over a minimal length of intestine. Hence particulate substrates and soluble nutrients become dispersed along the length of the lumen. Mixing within the lumen is not turbulent but results from localised folding and kneading of the contents by contractions but is augmented by the inconstant spatial disposition of the contractions and their component contractile processes. The latter include inconstancies in the sites of commencement and the directions of propagation of contraction in component groups of smooth muscle cells and in the coordination of the radial and circular components of smooth muscle contraction. Evidence suggests there is ongoing augmentation of mixing at the periphery of the lumen, during both the post-prandial and inter-meal periods, to promote flow around and between adjacent villi. This results largely from folding of the relatively inelastic mucosa during repeated radial and longitudinal muscular contraction, causing chyme to be displaced by periodic crowding and separation of the tips of the relatively rigid villi. Further, micro-rheological studies indicate that such peripheral mixing may extend to the apices of enterocytes owing to discontinuities in the mobile mucus layer that covers the ileal mucosa.