Nano- and Microstructures of Collagen-Nanocellulose Hydrogels as Engineered Extracellular Matrices.

The extracellular matrix (ECM) is the fundamental acellular element of human tissues, providing their mechanical structure while delivering biomechanical and biochemical signals to cells. Three-dimensional (3D) tissue models commonly use hydrogels to recreate the ECM in vitro and support the growth of cells as organoids and spheroids. Collagen-nanocellulose (COL-NC) hydrogels rely on the blending of both polymers to design matrices with tailorable physical properties. Despite the promising application of these biomaterials in 3D tissue models, the architecture and network organization of COL-NC remain unclear. Here, we investigate the structural effects of incorporating NC fibers into COL hydrogels by small-angle neutron scattering (SANS) and ultra-SANS (USANS). The critical hierarchical structure parameters of fiber dimensions, interfiber distance, and coassembled open structures of NC and COL in the absence and presence of cells were determined. We found that NC expanded and increased the homogeneity in the COL network without affecting the inherent fiber properties of both polymers. Cells cultured as spheroids in COL-NC remodeled the hydrogel network without a significant impact on its architecture. Our study reveals the polymer organization of COL-NC hydrogels and demonstrates SANS and USANS as exceptional techniques to reveal nano- and micron-scale details on polymer organization, which leads to a better understanding of the structural properties of hydrogels to engineer novel ECMs.

Composite Hydrogels Based on Bacterial Cellulose and Poly-1-vinyl-1,2,4-triazole/Phosphoric Acid: Supramolecular Structure as Studied by Small Angle Scattering.

New composite hydrogels (CH) based on bacterial cellulose (BC) and poly-1-vinyl-1,2,4-triazole (PVT) doped with orthophosphoric acid (oPA), presenting interpenetrating polymeric networks (IPN), have been synthesized. The mesoscopic study of the supramolecular structure (SMS) of both native cellulose, produced by the strain Komagataeibacter rhaeticus, and the CH based on BC and containing PVT/oPA complex were carried out in a wide range of momentum transfer using ultra- and classical small-angle neutron scattering techniques. The two SMS hierarchical levels were revealed from 1.6 nm to 2.5 µm for the objects under investigation. In addition, it was shown that the native BC had a correlation peak on the small-angle scattering curves at 0.00124 Å-1, with the correlation length ξ being equal to ca. 510 nm. This motive was also retained in the IPN. The data obtained allowed the estimation of the fractal dimensions and ranges of self-similarity and gave new information about the BC mesostructure and its CH. Furthermore, we revealed them to be in coincidence with Brown's BC model, which was earlier supported by Fink's results.

Application of small angle scattering (SAS) in structural characterisation of casein and casein-based products during digestion.

In recent years, small and ultra-small angle scattering techniques, collectively known as small angle scattering (SAS) have been used to study various food structures during the digestion process. These techniques play an important role in structural characterisation due to the non-destructive nature (especially when using neutrons), various in situ capabilities and a large length scale (of 1 nm to ∼20 µm) they cover. The application of these techniques in the structural characterisation of dairy products has expanded significantly in recent years. Casein, a major dairy protein, forms the basis of a wide range of gel structures at different length scales. These gel structures have been extensively researched utilising scattering techniques to obtain structural information at the nano and micron scale that complements electron and confocal microscopy. Especially, neutrons have provided opportunity to study these gels in their natural environment by using various in situ options. One such example is understanding changes in casein gel structures during digestion in the gastrointestinal tract, which is essential for designing personalised food structures for a wide range of food-related diseases and improve health outcomes. In this review, we present an overview of casein gels investigated using small angle and ultra-small angle scattering techniques. We also reviewed their digestion using newly built setups recently employed in various research. To gain a greater understanding of micro and nano-scale structural changes during digestion, such as the effect of digestive juices and mechanical breakdown on structure, new setups for semi-solid food materials are needed to be optimised.

Effect of temperature on the conformation and functionality of poly(N-isopropylacrylamide) (PNIPAM)-grafted nanocellulose hydrogels.

HYPOTHESIS: Poly(N-isopropylacrylamide) [PNIPAM]-grafted cellulose nanofibers (CNFs) are new thermo-responsive hydrogels which can be used for a wide range of applications. Currently, there is no clear understanding of the precise mechanism by which CNFs and PNIPAM interact together. Here, we hypothesize that the physical crosslinking of grafted PNIPAM on CNF inhibits the free movement of individual CNF, which increases the gel strength while sustaining its thermo-responsive properties. EXPERIMENTS: The thermo-responsive behaviour of PNIPAM-grafted CNFs (PNIPAM-g-CNFs), synthesized via silver-catalyzed decarboxylative radical polymerization, and PNIPAM-blended CNFs (PNIPAM-b-CNFs) was studied. Small angle neutron scattering (SANS) combined with Ultra-SANS (USANS) revealed the nano to microscale conformation changes of these polymer hybrids as a function of temperature. The effect of temperature on the optical and viscoelastic properties of hydrogels was also investigated. FINDINGS: Grafting PNIPAM from CNFs shifted the lower critical solution temperature (LCST) from 32 °C to 36 °C. Below LCST, the PNIPAM chains in PNIPAM-g-CNF sustain an open conformation and poor interaction with CNF, and exhibit water-like behaviour. At and above LCST, the PNIPAM chains change conformation to entangle and aggregate nearby CNFs. Large voids are formed in solution between the aggregated PNIPAM-CNF walls. In comparison, PNIPAM-b-CNF sustains liquid-like behaviour below LCST. At and above LCST, the blended PNIPAM phase separates from CNF to form large aggregates which do not affect CNF network and thus PNIPAM-b-CNF demonstrates low viscosity. Understanding of temperature-dependent conformation of PNIPAM-g-CNFs engineer thermo-responsive hydrogels for biomedical and functional applications.

Shear influence on colloidal cluster growth: a SANS and USANS study.

This study examines the time evolution of silica/water clusters where the formation of a gel network from unitary silica particles is interrupted by a simple Couette shear field. The aim is to enable the general understanding of this simple system by examining the microscopic basis for the changes in viscosity by providing structural inputs from small-angle scattering for a simple theoretical model. The experimental system is an 8.3 nm particle silica solution (Ludox) where the gelation has been initiated by lowering the pH in a Couette cell providing a constant shear rate of 250 s-1. A unified small-angle neutron scattering (SANS) and ultra-small-angle neutron scattering (USANS) procedure is described to measure the scattered intensity in a wavevector range of 3 × 10-4 ≤ q (nm-1) ≤ 3.1 × 10-1, probing structural changes over a broad range of length scales from the nanometre to the micrometre. Scattering data provide a new means of better understanding the behaviour of colloidal clusters when subjected to an external applied shear over a continuous time sequence after gel initiation; a fit of the time-dependent scattered intensity leads to an estimation of the cluster's effective volume fraction and size as a function of time. A reductionist theoretical basis is described to predict the time-dependent viscosity behaviour of the sheared colloidal suspension gel-initiated cluster growth from the volume fraction of the clusters.

Ordered Mesoporous Silica Prepared in Different Solvent Conditions: Application for Cu(II) and Pb(II) Adsorption.

In this work, the synthesis of ordered mesoporous silica of MCM-41 type was investigated aimed at improving its morphology by varying the synthesis conditions in a one-pot process, employing different temperatures and solvent conditions. 2-methoxyethanol was used as co-solvent to ethanol. The co-solvent ratio and the synthesis temperature were varied. The pore morphology of the materials was characterized by nitrogen porosimetry and small angle neutron scattering (SANS), and the particle morphology by transmission electron microscopy (TEM) and ultra-small angle neutron scattering (USANS). The thermal behavior was investigated by simultaneous thermogravimetry-differential scanning calorimetry (TG-DSC) measurements. The SANS and N2 sorption results demonstrated that a well-ordered mesoporous structure was obtained at all conditions in the synthesis at room temperature. Addition of methoxyethanol led to an increase of the pore wall thickness. Simultaneously, an increase of methoxyethanol content led to lowering of the mean particle size from 300 to 230 nm, according to the ultra-small angle scattering data. The ordered porosity and high specific surfaces make these materials suitable for applications such as adsorbents in environmental remediation. Batch adsorption measurements of metal ion removal from aqueous solutions of Cu(II) and Pb(II) showed that the materials exhibit dominantly monolayer surface adsorption characteristics. The adsorption capacities were 9.7 mg/g for Cu(II) and 18.8 mg/g for Pb(II) at pH 5, making these materials competitive in performance to various composite materials.

Recent advances in small-angle scattering and its expanding impact in structural biology.

Applications of small-angle scattering (SAS) in structural biology have benefited from continuing developments in instrumentation, tools for data analysis, modeling capabilities, standards for data and model presentation, and data archiving. The interplay of these capabilities has enabled SAS to contribute to advances in structural biology as the field pushes the boundaries in studies of biomolecular complexes and assemblies as large as whole cells, membrane proteins in lipid environments, and dynamic systems on time scales ranging from femtoseconds to hours. This review covers some of the important advances in biomolecular SAS capabilities for structural biology focused on over the last 5 years and presents highlights of recent applications that demonstrate how the technique is exploring new territories.

Effects of Silicon, Chromium, and Copper on Kinetic Parameters of Precipitation during Tempering of Medium Carbon Steels.

Understanding the tempering behavior of medium carbon steels is mandatory if their mechanical properties are to be improved. For an optimal technology to be developed for this purpose, a substantial experimental basis is needed to extract quantitative information on the microstructure of the tempered material. This paper reports on the characterization of microstructural changes induced by tempering in medium-carbon steels alloyed with Si, Cr, Cu, and Mn using state-of-the-art experimental techniques. Complementarities among these techniques are highlighted. The evolution of transition carbides, cementite, and copper precipitates is described using data from X-ray diffraction, small and ultra-small angle neutron diffraction, transmission electron microscopy, and dilatometry observation. The effects of silicon, chromium, and copper on the mechanism of carbide and copper precipitation are discussed. The considerable changes found in the size and volume of copper precipitates correlate well with the difference in the yield stress between tempered steels with and without copper.

Effect of amyloglucosidase hydrolysis on the multi-scale supramolecular structure of corn starch.

The effects of amyloglucosidase digestion on the multi-scale supramolecular structural changes of native corn starch were examined by ultra-small angle neutron scattering (USANS), small angle X-ray scattering (SAXS), particle sizing, and scanning electron microscopy (SEM). Well-defined and spherical pores were formed upon amyloglucosidase digestion as revealed by SEM. The pore polydispersity was determined using USANS by assuming spherical pore morphology with log-normal distribution. Both USANS and SEM measurements demonstrated that the pores become larger and more polydisperse as the digestion time increased. Moreover, SAXS revealed that the lamellar peak area decreased gradually for both thermally and enzymatically treated starches, indicating partial loss of lamellar organisation. Overall, the results demonstrate structural changes occur on multiple length scales upon enzymatic digestion from granular to lamellar with small-angle scattering demonstrated to provide detailed characterization of the resultant microporous structures.

Hierarchical assembly in PLA-PEO-PLA hydrogels with crystalline domains and effect of block stereochemistry.

Understanding the development of microstructure (e.g., structures with length scales roughly 0.5-500 µm) in hydrogels is crucial for their use in several biomedical applications. We utilize ultra-small-angle neutron scattering (USANS) and confocal microscopy to explore microstructure of poly(lactide)-poly(ethylene oxide)-poly(lactide) (PLA-PEO-PLA) triblock copolymer hydrogels with varying l/d-lactide ratio. We have previously found that these polymers self-assemble on the nanoscale into micelles. Here, we observe large-scale structures with diverse morphologies, including highly porous self-similar networks with characteristic sizes spanning approximately 120 nm-200 µm. These structural features give rise to power-law scattering indicative of fractal structures in USANS. Mass fractal and surface fractal structures are found for gels with l/d ratios of 80/20 and 50/50, respectively. Confocal microscopy shows microscale water-filled channels and pores that are more clearly evident in gels with a higher fraction of l-lactide in the PLA block as compared to the 50/50 hydrogels. Tuning block stereochemistry may provide a means of controlling the self-assembly and structural evolution at both the nanoscale and microscale, impacting application of these materials in tissue engineering and drug delivery.

Multi-scale assembly of hydrogels formed by highly branched arabinoxylans from Plantago ovata seed mucilage studied by USANS/SANS and rheology.

The structures of two hydrogels formed by purified brush-like polysaccharides from Plantago ovata seed mucilage have been characterised from the nanometre to micrometre scale by using a combination of SANS and USANS techniques. These two hydrogels have distinctly different melting and rheological properties, but the structure of their gel networks bears striking similarity as revealed by USANS/SANS experiments. Surprisingly, we find that the dramatic changes in the rheological properties induced by temperature or change in the solvent quality are accompanied by a small alteration of the network structure as inferred from scattering curves recorded above melting or in a chaotropic solvent (0.7 M KOD). These results suggest that, in contrast to most gel-forming polysaccharides for which gelation depends on a structural transition, the rheological properties of Plantago ovata mucilage gels are dependent on variations in intermolecular hydrogen bonding. By enzymatically cleaving off terminal arabinose residues from the side chains, we have demonstrated that composition of side-chains has a strong effect on intermolecular interactions, which, in turn, has a profound effect on rheological and structural properties of these unique polysaccharides.

Micron-scale restructuring of gelling silica subjected to shear.

HYPOTHESIS/OBJECTIVE: We examine the time dependent viscometric behavior of a well-defined system of gelling colloidal silica and how this behavior may be understood from a simple theoretical model which incorporates the microstructure of the gel. The ultra-small angle neutron scattering (USANS) technique is used to interrogate structure during the gelation process. EXPERIMENTS: The investigations focused on a system where both particles and interactions are well-defined: 7 nm silica particle acid-treated aqueous solution subjected to a constant applied shear in Couette geometry. Ultra-small angle neutron scattering (USANS) time-dependent scattering intensities were measured at wave vectors, q, in the range, 1.0 × 10-3 ≤ q/nm ≤ 7.3 × 10-2 coupled with viscosity data recorded simultaneously. The interpretation of the USANS scattering data is reliant on an isotropic sample. This assumption has been investigated, over a limited range of scattering vectors, using more suitable small angle neutron scattering (SANS) instrumentation with a restricted q-range. FINDINGS: The first recorded direct kinetic measurements of the micron-scale structure in a gelling system. A critical micro-structural feature of the intensity-viscosity time behavior of a gelling colloid subjected to a shear is the cluster size. A viscosity/intensity coupling observed at the time of a viscosity maximum that corresponds to a time-dependent critical stress and speculated to be independent of the wave vector over a wide q-range.

Shear Thickening Electrolyte Built from Sterically Stabilized Colloidal Particles.

We present a method to prepare shear thickening electrolytes consisting of silica nanoparticles in conventional liquid electrolytes with limited flocculation. These electrolytes rapidly and reversibly stiffen to solidlike behaviors in the presence of external shear or high impact, which is promising for improved lithium ion battery safety, especially in electric vehicles. However, in initial chemistries the silica nanoparticles aggregate and/or sediment in solution over time. Here, we demonstrate steric stabilization of silica colloids in conventional liquid electrolyte via surface-tethered PMMA brushes, synthesized via surface-initiated atom transfer radical polymerization. The PMMA increases the magnitude of the shear thickening response, compared to the uncoated particles, from 0.311 to 2.25 Pa s. Ultrasmall-angle neutron scattering revealed a reduction in aggregation of PMMA-coated silica nanoparticles compared to bare silica nanoparticles in solution under shear and at rest, suggesting good stabilization. Conductivity tests of shear thickening electrolytes (30 wt % solids in electrolyte) at rest were performed with interdigitated electrodes positioned near the meniscus of electrolytes over the course of 24 h to track supernatant formation. Conductivity of electrolytes with bare silica increased from 10.1 to 11.6 mS cm-1 over 24 h due to flocculation. In contrast, conductivity of electrolytes with PMMA-coated silica remained stable at 6.1 mS cm-1 over the same time period, suggesting good colloid stability.

SUSANS With Polarized Neutrons.

Super Ultra-Small Angle Neutron Scattering (SUSANS) studies over wave vector transfers of 10(-4) nm(-1) to 10(-3) nm(-1) afford information on micrometer-size agglomerates in samples. Using a right-angled magnetic air prism, we have achieved a separation of ≈10 arcsec between ≈2 arcsec wide up- and down-spin peaks of 0.54 nm neutrons. The SUSANS instrument has thus been equipped with the polarized neutron option. The samples are placed in a uniform vertical field of 8.8 × 10(4) A/m (1.1 kOe). Several magnetic alloy ribbon samples broaden the up-spin neutron peak significantly over the ±1.3 × 10(-3) nm(-1) range, while leaving the down-spin peak essentially unaltered. Fourier transforms of these SUSANS spectra corrected for the instrument resolution, yield micrometer-range pair distribution functions for up- and down-spin neutrons as well as the nuclear and magnetic scattering length density distributions in the samples.