Rheometric Analyses Research Articles

Validation of a Repurposed pH Monitoring Capsule for Cecal Applications Using Novel Synthetic Cecal Contents

Abstract This study presents a novel approach to monitoring pH changes in the cecum, a critical step toward understanding the dynamic interactions between the gut microbiota and probiotics. By repurposing the Bravo® capsule, originally designed for esophageal pH monitoring, we demonstrate its potential for accurate, continuous, and nonobstructive pH detection within a simulated cecal environment. To facilitate this investigation, we introduce the first synthetic cecal content (SCC) formulation. Our formulation closely mimics the mechanical properties of porcine cecal contents, particularly in terms of viscosity and shear response. This SCC recipe addresses a significant gap in the availability of simulated biological fluids for in vitro medical device testing. Rheometric analyses confirm the SCC's consistency with biological cecal contents, providing a cost-effective and efficient platform for preliminary device evaluations. Experimental results show that the Bravo® capsule can accurately detect pH changes within the SCC, closely matching readings from a handheld pH probe. The successful validation of the Bravo® capsule's performance in a simulated cecal environment, along with the development of a reliable SCC formulation, paves the way for future in vivo studies in porcine models. This research represents a significant advancement in the field of gut microbiome monitoring and holds promise for the development of targeted, microbiome-based therapeutics. By enabling real-tim/e, in situ analysis of the cecal microbiota's response to various interventions, this approach has the potential to revolutionize our understanding of the complex interplay between probiotics, diet, and gut health.

Development and optimization of starch-based biomaterial inks and the effect of infill patterns on the mechanical, physicochemical, and biological properties of 3D printed scaffolds for tissue engineering

Plant-based hydrogels have wide application as scaffolds in tissue engineering and regenerative medicine due to their low cost and excellent biocompatibility. Scaffolds act as vehicles for cell-based therapeutics and regenerating diseased tissue. While there is a plethora of methods to generate hydrogels with tunable properties to mimic the tissue of interest, 3D bioprinting is a novel emerging technology with the capability to generate versatile patient-specific scaffolds typically embedded with tissue specific cells. Starch-based hydrogels are garnering attention in extrusion-based 3D printing, however owing to their poor mechanical strength and degradation render this material inefficient in its native form. Additionally, the effect of various printing process parameters on mechanical strength and bioactivity is poorly understood. In the present study, we investigate the use of starch and gelatin as composite biomaterial ink and its effect on mechanical, physical and biological properties. We also investigated printability of composite hydrogels with the aim to understand the correlation between two infill patterns and its effect on mechanical, physicochemical, and biological properties. Our results showed that the composite hydrogels had competent mechanical properties and suitable bioactivity when seeded with H9C2 cardiomyocytes. Rheometric analyses provided a broader insight into the required viscosity for printing and has a direct correlation with the composition of the hydrogel. Thus, the composite materials are found to have tissue-specific mechanical properties and may serve as a better, cheaper and personalized alternative to existing scaffolds for the fabrication of engineered cardiac tissue.

Influence of polymeric molecular chain structure on the rheological-mechanical behavior of asphalt binders and porous asphalt mixes

This manuscript reports on two Styrene-Butadiene-Styrene (SBS) polymeric molecular chains so-called 1101AT and D0243, used to modify a 50/70 pen grade neat asphalt binder sample, generating the matrixes 60/85 E and Highly Modified Asphalt (HiMA), respectively. Some research gaps still exist and need to be investigated further, principally on why and how these distinct molecular chains influence the rheological-mechanical behavior of the asphalt binders and asphalt mixes, even pertaining to the same polymeric group. Dynamic Shear Rheometric (DSR) analyses describe the rheological spectra of the binder samples, considering the dynamic stiffness modulus in the complex plane |G*|. Porous asphalt mixes were evaluated considering the French formulation methodology and the following aspects: compaction ability, deleterious action of water, seepage speed and resistance to rutting. The results obtained indicate that HiMA matrix presented superior long-term rheological and mechanical behavior compared to 60/85 E, due to the more elaborate polymeric chain being associated to a bituminous matrix with rheological spectra providing less thermal and kinetic susceptibility, although its highest dynamic viscosity implies little reduction in the air void content and, consequently, lower seepage speeds to the porous asphalt mixes, but greater rutting resistance.

Smart catalyst deposition by 3D printing for Polymer Electrolyte Membrane Fuel Cell manufacturing

Polymer Electrolyte Membrane Fuel Cells (PEMFC) are arguably the most employed fuel-cell types in various industry sectors, as they operate at low temperature and exhibit short start-up time and high durability. PEMFC manufacturing is currently transitioning from low-volume to mass production. Within this effort, efficient catalyst deposition to produce MEA (Membrane Electrode Assembly) electrodes has become instrumental, since very expensive raw materials are involved. This work focuses on an Additive Manufacturing (AM) technique – a modified 3D printing approach – used to release catalytic inks onto PEMFC electrodes. Some catalyst-free suspensions were designed to resemble a catalytic ink and characterized to assess their printability by microextrusion. Mixtures of distilled water, ethanol and graphite were prepared and tested. Granulometric and rheometric analyses were conducted to optimize the composition towards low viscosity values and short drying time. Repeatability of the released amount and its homogeneousness onto the target surface were evaluated. The most suitable ink formulation was loaded with platinum, a perfluorosulfonic ionomer, a pore former (NH4CO3) and deposited onto Gas Diffusion Layers (GDL). Scanning Electron Microscopy (SEM) measurements were performed on the 3D-printed electrodes to characterize it. Preliminary electrochemical fuel-cell tests were carried out towards a comparison with conventional electrodes: the proposed deposition technique appears able to produce electrodes that align with state-of-the-art performance level.

RHEOMETRIC AND DYNAMIC MECHANICAL ANALYSIS OF COMPLEX NATURAL RUBBER BASED COMPOSITES

This work describes the preparation and characterization of complex natural rubber (NR) based composites containing hybrid nano- and conventional fillers intended for base seismic application. Thorough rheometric and dy-namic mechanical analyses in strain sweep mode at 2 Hz and 10 Hz (two frequencies laying in the range 0 – 15 Hz in which most of the earthquakes have the dominant frequencies) were performed on complex natural rubber (NR) based composites containing hybrid nanofiller (carbon nanotubes, expanded montmorillonite) and different amounts of con-ventional fillers like carbon black (CB) and silica. The rheometric studies showed that the influence of the combina-tion of the different fillers on curing parameters is quite complex, but mainly the introduction of the fillers reduces the scorch and optimum cure time of the compounds. The dynamic mechanical analysis showed a pronounced non-linear strain dependence of the storage modulus and a remarkable increase of the loss factor tanδ for all composites, espe-cially for those containing high CB content, compared to the NR-gum. To describe this strain-dependency of the stor-age modulus the cluster-cluster aggregation (CCA) model was used. The values of the fitting parameters ΔE’0, γc, and E’∞ calculated by this model show that they are affected by the type of the fillers present in the NR matrix and also by the applied frequency.

Perylene as an electron-rich moiety in healable, complementary π–π stacked, supramolecular polymer systems

A two-component, supramolecular polymer blend has been designed using a novel π-electron rich bis-perylene-terminated polyether. This polymer is able to self-assemble through electronically complementary π–π stacking interactions with a π-electron-deficient chain-folding polydiimide to afford thermally healable polymer blends. Model compounds were developed to assess the suitability of the deep green complexes formed between perylene residues and chain-folding bis-diimides for use in polymer blends. The polymer blends thus synthesised were elastomeric in nature and demonstrated healable properties as demonstrated by scanning electron microscopy. Healing was observed to occur rapidly at ca. 75 °C, and excellent healing efficiencies were found by tensometric and rheometric analyses. These tuneable, stimuli-responsive, supramolecular polymer blends are compared to related healable blends featuring pyrene-terminated oligomers.

Time-dependent gel to gel transformation of a peptide based supramolecular gelator.

A dipeptide with a long fatty acid chain at its N-terminus gives hydrogels in phosphate buffer in the pH range 7.0-8.5. The hydrogel with a gelator concentration of 0.45% (w/v) at pH 7.46 (physiological pH) provides a very good platform to study dynamic changes within a supramolecular framework as it exhibits remarkable change in its appearance with time. Interestingly, the first formed transparent hydrogel gradually transforms into a turbid gel within 2 days. These two forms of the hydrogel have been thoroughly investigated by using small angle X-ray scattering (SAXS), powder X-ray diffraction (PXRD), field emission scanning electron microscopic (FE-SEM) and high-resolution transmission electron microscopic (HR-TEM) imaging, FT-IR and rheometric analyses. The SAXS and low angle PXRD studies substantiate different packing arrangements for the gelator molecules for these two different gel states (the freshly prepared and the aged hydrogel). Moreover, rheological studies of these two gels reveal that the aged gel is stiffer than the freshly prepared gel.

Assembly of an Injectable Noncytotoxic Peptide-Based Hydrogelator for Sustained Release of Drugs

A new synthetic tripeptide-based hydrogel has been discovered at physiological pH and temperature. This hydrogel has been thoroughly characterized using different techniques including field emission scanning electron microscopic (FE-SEM) and high-resolution transmission electron microscopic (HR-TEM) imaging, small- and wide-angle X-ray diffraction analyses, FT-IR, circular dichroism, and rheometric analyses. Moreover, this gel exhibits thixotropy and injectability. This hydrogel has been used for entrapment and sustained release of an antibiotic vancomycin and vitamin B12 at physiological pH and temperature for about 2 days. Interestingly, MTT assay of these gelator molecules shows almost 100% cell viability of this peptide gelator, indicating its noncytotoxicity.

Processability of Biobased Thermoset Resins and Flax Fibres Reinforcements Using Vacuum Assisted Resin Transfer Moulding

Biocomposite panels consisting of biobased thermoset resins (EP, PU, UP, and tannin) and flax fibre reinforcements were produced using the vacuum assisted resin transfer moulding process. Panels based on a conventional chemical-based resin matrix were also produced, and investigated comparatively. Rheometric analyses were performed to evaluate the suitability of these resins for liquid composite moulding. Tensile, shear, and impactbending tests have been carried out to assess the quality and mechanical performance of manufactured laminates. The impregnation quality was assessed by means of ultrasonic-C-scanning and microscopy. It turned out that the properties of the biobased composite panels made of biobased epoxy resin and a biobased UP-resin from the company Nuplex in New Zealand were onlay slightly inferior to those produced with a conventional epoxy resin. A biobased PU-resin from the company USSC in the USA developed voids during curing. A tannin-based resin containing of formaldehyde was not processable.

Viscosity measurement of gelcasting slurry during in-situ gelation by a micro X-ray CT scan system

Abstract This paper reports the use of a micro X-ray CT scan system to measure the viscosity increase during in-situ gelation of a gelcasting slurry. Three small steel balls were dropped in the slurry at a desired time interval after the addition of the gelling agent, while being monitored by the CT scan system. It was determined that the plot of the logarithm of the calculated viscosities based on the settling velocity of the falling ball versus the gelation time can be classified into three regions with increasing slopes. The first region is designated as the idle time during which the gelcasting slurry can be further processed and cast into a mold. The second region is the onset of gelation during which the polymer networks start to form with a gradual increase in the viscosity, whereas the third region is attributed to the increased concentration of the polymerized networks as typified by the significant increase in the slurry viscosity. Moreover, the falling ball method was found to be more sensitive to detecting the onset of gel formation in the gelcasting slurry than stress-controlled rheometric analyses.

Inter-penetrating hydrogels (IPHs) as a new class of injectable polysaccharide hydrogels with thixotropic nature and interesting mechanical and biological properties

Hydrogels are important and very promising materials for biomedical applications, such as cell scaffolds and drug delivery systems. A new class of injectable materials was obtained by mixing polysaccharide chemically crosslinked hydrogels. The mixing was performed by exploiting the thixotropic behaviour of the polysaccharide hydrogels: in other words they were passed through a syringe to subject them to shear stress and render them fluid, then they were mixed together in the fluid state. Once the material regained its consistency, a new hydrogel was obtained, called an inter-penetrating hydrogel (IPH), containing both the native hydrogels. This new class of materials showed different physical-chemical, mechanical and biological properties from the native hydrogels utilized for the mixing. The hydrogels taken into consideration were: negatively charged carboxy methyl cellulose (CMC) and hyaluronic acid (Hyal), uncharged guar gum (GG), and chitosan (CHT), which bore positive charges at physiological pH. The IPHs obtained – i.e. CMC-CHT, CMC-GG and CMC-Hyal – were characterized by means of Fourier transform infrared spectroscopy (FT-IR) and swelling measurements. The mechanical properties of the IPHs were investigated by rheometric analyses, while their morphology was studied by scanning electronic microscopy (SEM). The biological performance of the IPHs was evaluated using fibroblasts (NIH 3T3 cell line) and compared with that of the native hydrogels.

Synthesis and characterization of PEO–PCL–PEO triblock copolymers: Effects of the PCL chain length on the physical property of W 1/O/W 2 multiple emulsions

A series of poly(ethylene glycol)- block-poly( ɛ-caprolactone)- block-poly(ethylene glycol) (PEO–PCL–PEO) triblock copolymers were prepared and then used for the investigation of the effects of the ratio of ɛ-caprolactone to poly(ethylene glycol) (i.e., [CL]/[EO]) on the physical properties of water-in-oil-in-water (W 1/O/W 2) multiple emulsions containing a model reagent, ascorbic acid-2-glucoside (AA2G). In the synthesis, the [CL]/[EO] was varied from 0.11 to 0.31. The molecular weights and compositions of PEO–PCL–PEO were determined by GPC and 1H NMR analyses. Thermal behavior and crystal formation were studied by DSC, XRD, FT-IR, and polarized optical microscopy (POM). Aggregate behavior of PEO–PCL–PEO was confirmed by DLS, UV, and 1H NMR. Morphology and relative stiffness of the W 1/O/W 2 multiple emulsions in the presence of PEO–PCL–PEO were studied by confocal laser scanning microscopy (CLSM) and rheometer. Variation in the [CL]/[EO] significantly affects the crystalline temperature and spherulite morphology of PEO–PCL–PEO. As the [CL]/[EO] increases, the CMCs of PEO–PCL–PEO decreases and the slope of aggregate size reduction against the copolymer concentration becomes steeper except for the lowest [CL]/[EO] value of PEO–PCL–PEO (i.e., P-222). P-222 significantly increases the viscosity of continuous (W 2) phase, which implies the copolymer would exist in the W 2 phase. On the other hand, the triblock copolymers with relatively high [CL]/[EO] ratios mainly contribute to the size reduction of multiple emulsions and the formation of a firm wall structure. The particle size of the multiple emulsion decreases and the elastic modulus increased as [CL]/[EO] increases, confirmed by microscopic and rheometric analyses.

Dual Polymer Conditioning of Water Treatment Residuals

Conditioning of either wastewater biosolids or water treatment residuals conventionally utilizes a single polymer to improve subsequent dewatering. The sequential addition of two polymers has been reported to enhance biosolids dewaterability, but comparable benefits have not been demonstrated for water treatment residuals. This paper evaluated the use of cationic and nonionic polymers, singly and in combination (dual), to investigate whether dual polymer conditioning of residuals offers any advantages, and to determine whether the results could be accommodated by current mechanistic understandings. For this purpose, lab-scale tests used capillary suction time (CST), supernatant viscosity, zeta potential, streaming current, turbidity, floc size, and rheometric analyses. Comparisons of CST and viscosity results for single and dual polymer additions indicated that dual polymer use gave moderately improved dewaterability, possibly due to the increased mixing utilized for dual polymer addition. Using a cationic polymer produced a less turbid supernatant. Zeta potential and streaming current were not good indicators of conditioning efficacy when a nonionic polymer was used. Rheometric analyses were only meaningful in one selected method for treatment of the data: the area under the rheogram up to a shear rate of 30inverses. Overall, implementation of dual polymer use does not appear warranted.