Calcium Cations Research Articles

EXPRESSION FEATURES OF CALCIUM-DEPENDENT RECEPTORS IN THE LUNGS IN EXPERIMENTAL COMPENSATED TRAUMATIC BRAIN INJURY

Purpose of the study: to assess the histochemical features of the localization of calciumdependent receptors of the left lung cell membrane on the 8th day of experimental compensated traumatic brain injury. Materials and methods: The object of the study was male albino outbred rats, three months old, weight 270-300 grams. Created two groups of animals: 1 - control: intact rats; 2- experimental: rats with TBI. To create a head injury, a model of a falling weight was used. Animals were withdrawn from the experiment on the 8th day of head injury. We studied paraffin sections of the left lung of rats. Using the Abcam kits (USA), an immunohistochemical study of the localization of endothelin -1 on sections of the left lung was carried out, the histochemical detection of calcium cations was performed using alizarin red C. Results. The morphofunctional characteristics of the lungs of rats with experimental traumatic brain injury were investigated. It was found that when the brain of experimental animals is damaged, lipid-associated lymphoid clusters appear in the root of the left lung of rats, and the content of endothelin-1 in cardiomyocytes of the pulmonary vein and epithelium of terminal bronchioles increases. A change in the histochemical characteristics of the localization of calcium cations in the cells and tissues of the left lung is revealed, which indicates a tendency towards the development of obstruction of terminal bronchioles and migration of macrophages into the parenchyma of the alveoli. Conclusion: Thus, with TBI, the mechanisms of humoral regulation of the respiratory system function significantly change. Histochemical study of endothelin 1 revealed that the expression in the lung tissues is calcium-dependent. receptor and mediator systems of cell membranes. These data are confirmed by staining the lungs with alizarin red C.

Sulfation and Calcium Favor Compact Conformations of Chondroitin in Aqueous Solutions.

The effects of sulfation and calcium cations (Ca2+) on the atomic-resolution conformational properties of chondroitin carbohydrate polymers in aqueous solutions are not well studied owing to experimental challenges. Here, we compare all-atom explicit-solvent molecular dynamics simulations results for pairs of O-type (nonsulfated) and A-type (GlcNAc 4-O-sulfated) chondroitin 20-mers in 140 mM NaCl with and without Ca2+ and find that both sulfation and Ca2+ favor more compact polymer conformations. We also show that subtle differences in force-field parametrization can have dramatic effects on Ca2+ binding to chondroitin carboxylate and sulfate functional groups and thereby determine Ca2+-mediated intra- and interstrand association. In addition to providing an atomic-resolution picture of the interaction of Ca2+ with sulfated and nonsulfated chondroitin polymers, the molecular dynamics data emphasize the importance of careful force-field parametrization to balance ion–water and ion–chondroitin interactions and suggest additional parametrization efforts to tune interactions involving sulfate.

Temperature Induced Physiological Reaction Norms of the Coccolithophore Gephyrocapsa oceanica and Resulting Coccolith Sr/Ca and Mg/Ca Ratios

Coccolithophores are one of the major contributors to the pelagic production of calcium carbonate and their fossilized remains are a key component of the biogeochemical cycles of calcium (Ca), magnesium (Mg), and other divalent cations present in the intracellular precipitated calcitic structures (coccoliths). The geochemical signature of coccoliths (e.g., Sr/Ca and Mg/Ca ratios) is used as paleoproxy to reconstruct past environmental conditions and to understand the underlying physiological precipitation kinetics. Here, we present the elemental fractionation of Sr and Mg in calcite of the coccolithophore Gephyrocapsa oceanica from controlled laboratory experiments applying an extended temperature gradient (12 to 27°C). The physiological reaction norm of G. oceanica, in terms of growth rate, exhibited optimum behavior while the partition coefficient of Sr (DSr) was linearly correlated with temperature and DMg indicated no specific trend. Our results indicate: (1) a presumably secondary physiological control of DSr, and (2) the importance of calibrating coccolithophore-based proxies using experiments that include the full physiological reaction norms (i.e., a possible non-linear response) to environmental drivers (e.g., temperature, salinity, and pH, etc.). The presented results contribute to an improved understanding of the underlying physiological kinetics involved in regulating coccolith elemental fractionation and give additional implications for designing future laboratory experiments to calibrate and apply coccolithophore based paleoproxies on the fossil sediment record.

Development of new inhibitor to prevent salt deposition

The inhibitors of inorganic mineral sediments based on orthophosphate acid, monoamid of sulphuric acid (MSA) and carboxymethylcelluloze (CMC) have been developed. Created compositional inhibitors of salt deposition are transparent, fluid water solution with 14.5–22.0 % concentration. To specify the efficiency of developed salt deposition inhibitors, the agent capacity to keep cations of calcium in the volume of artificially prepared mineral waters of carbonate and sulphate types modelling produced water within oil fields has been evaluated. It was defined that adding 20–20 mg/l of developed compositions into the solutions of calcium sulphate provides high protection effect. Inhibitors’ protection capacity using the compositions in the charge of 20 mg/l in sulphate water comprises 89.6–96.8 %, and in the carbonate water - 87.8–92.6 %. Using 25 mg/l of these compositions, protection capacity of the inhibitors in sulphate water reaches up to 94.5–98.7 %, and in carbonate water - 92.5–96.8 %. Protection effect of inhibitors in case of using 30 mg/l of the compositions comprises 98.3–100 % in sulphate water, and 96.8–100 % in carbonated one as well.

Obtaining glucose-based 5-hydroxymethylfurfural on large-pore zeolites

Obtaining such substances-platforms as, in particular, 5-hydroxymethylfurfural is one of the areas most actively investigated at present. They can act as raw materials for the further production of a new generation of biopolymers, fuels, pharmaceuticals, dietary supplements, and other chemicals. This paper reports the catalysts, synthesized by using methods of ion exchange and impregnation, based on the large-pore zeolites X, Y, and M, which contain the cations of rubidium, lanthanum, calcium, and ammonium. It was found that the zeolites' specific surface was 400‒500 m2/g; the selected synthesis conditions did not cause noticeable destruction of the microporous structure. In the presence of the synthesized catalysts, glucose dehydration in the aqueous medium and in dimethyl sulfoxide was carried out at 150–160 °C. The higher efficiency of polycationic forms of zeolites in a non-aqueous medium has been established. In the latter case, a 40 % yield of 5-hydroxymethylfurfural was achieved at an almost complete glucose conversion. Deactivated catalyst samples were investigated using the methods of infrared spectroscopy and differential thermal analysis/thermogravimetry. It was found that the catalyst accumulates fewer oligomerization process by-products when the reaction is implemented in dimethyl sulfoxide. The loss of mass by the samples deactivated in an aqueous medium is 30‒33 %, while in dimethyl sulfoxide – up to 24 %. The obtained results are important for practical application as the only volatile conversion product is 5-hydroxymethylfurfural with a yield of up to 40 %. That is acceptable for the possible implementation of a one-stage process of obtaining 5-hydroxymethylfurfural in the future

Role of Polyuronides in Therapy and Prevention of Lead Intoxication

The capability of beet pectin and kelp thalli extract to accelerate the elimination of lead(II) ions from biological tissues of rats in cases of toxicant introduction to the rats before (medicinal effect) and after (preventive effect) the administration of polyuronides is demonstrated. The preventive effect of pectin and laminaride prior to lead intoxication is manifested by a reduction of the Pb(II) content in bone tissues by 79 – 86 and 79 – 82%, respectively, via liver, kidney, blood, urine, and skin. The content of calcium cations remains almost unchanged. The medicinal effect of pectin and laminaride in animals with lead intoxication is manifested by a reduction of the Pb(II) content in bone tissues by 77 – 82 and 68 – 77%, respectively, also via liver, kidney, blood, urine, and skin. The detoxication properties are not accompanied by undesired side effects for an extract composition with pronounced polyuronides, in contrast to a reference drug.

Characterization of putative salinity-responsive biomarkers in olive (Olea europaea L.)

AbstractLow-quality water and soil salinization are increasingly becoming limiting factors for food production, including olive – a major fruit crop in several parts of the world. Identifying putative salinity-stress tolerance in olive would be helpful in the future development of new tolerant varieties. In this study, novel salinity-responsive biomarkers (SRBs) were characterized in the species, namely, monooxygenase 1 (OeMO1), cation calcium exchanger 1 (OeCCX1), salt tolerance protein (OeSTO), proteolipid membrane potential modulator (OePMP3), universal stress protein (OeUSP2), adaptor protein complex 4 medium mu4 subunit (OeAP-4), WRKY1 transcription factor (OeWRKY1) and potassium transporter 2 (OeKT2). Unique structural features were highlighted for encoded proteins as compared with other plant homologues. The expression of olive SRBs was investigated in leaves of young plantlets of two cultivars, ‘Nabali’ (moderately tolerant) and ‘Picual’ (tolerant). At 60 mM NaCl stress level, OeMO1, OeSTO, OePMP3, OeUSP2, OeAP-4 and OeWRKY1 were up-regulated in ‘Nabali’ as compared with ‘Picual’. On the other hand, OeCCX1 and OeKT2 were up-regulated at three stress levels (30, 60 and 90 mM NaCl) in ‘Picual’ as compared to ‘Nabali’. Salinity tolerance in olive presumably engages multiple sets of responsive genes triggered by different stress levels.

Physiochemical characterization of agricultural waste biochars for partial cement replacement

PurposeThe purpose of this study is to explore the feasibility of utilizing agricultural (almond shell, rice husk and wood) waste biochars for partial cement replacement by evaluating the relationships between the physiochemical properties of biochars and the early-age characteristics of cement pastes.Design/methodology/approachBiochars are prepared through the thermal decomposition of biomass in an inert atmosphere. Using varying percentages, biochars are used to replace ordinary Portland cement (OPC) in cement pastes at a water/binder ratio of 0.35. Characterization methods include XPS, FTIR, SEM, TGA, BET, Raman, loss-on-ignition, setting, compression and water absorption tests.FindingsAccelerated setting in biochar-modified cement pastes is attributed to chemical interactions between surface functional groups of biochars and calcium cations from OPC, leading to the early development of metal carboxylate and alkyne salts, alongside the typical calcium-silicate-hydrate (C-S-H). Also, metal chlorides such as calcium chlorides in biochars contribute to the accelerate setting in pastes. Lower compression strength and higher water absorption result from weakened microstructure due to poor C-S-H development as the high carbon content in biochars reduces water available for optimum C-S-H hydration. Amorphous silica contributes to strength development in pastes through pozzolanic interactions. With its optimal physiochemical properties, rice-husk biochars are best suited for cement replacement.Research limitations/implicationsWhile biochar parent material properties have an impact on biochar properties, these are not investigated in this study. Additional investigations will be conducted in the future.Practical implicationsCarbon/silicon ratio, oxygen/carbon ratio, alkali and alkaline metal content, chlorine content, carboxylic and alkyne surface functional groups and surface areas of biochars may be used to estimate biochar suitability for cement replacement. Biochars with chlorides and reactive functional groups such as C=C and COOH demonstrate potential for concrete accelerator applications. Such applications will speed up the construction of concrete structures and reduce overall construction time and related costs.Social implicationsReductions in OPC production and agricultural waste deterioration will slow down the progression of negative environmental and human health impacts. Also, agricultural, manufacturing and construction employment opportunities will improve the quality of life in agricultural communities.Originality/valueEmpirical findings advance research and practice toward optimum utilization of biomass in cement-based materials.

Assessment of surface heterogeneity of lime treated kaolinites: Probed by low-pressure argon and nitrogen gas adsorption

It is a common practice to alter the undesirable behavior of clayey soils (i.e. swelling-shrinkage and high plasticity) with lime addition. However, the reaction mechanism involved in the early stage (first minute up to 24 h after mixing) of lime treatment is still not well explored. In the present work, the surface chemistry of lime ([Ca] = 22 mmol/l and pH = 12.63) treated kaolinites (Kaol) was studied using argon and nitrogen gas adsorption. The effect of pH ([Ca] = 22 mmol/l and. pH = 12.63 vs. [Ca] = 22 mmol/l and pH = 7) was also examined. The derivative low-pressure adsorption isotherms were analyzed using derivative isotherm summation (DIS), focusing on the analysis of surface heterogeneity. After the treatment with lime, the specific surface area and adsorption energy distribution of Kaol were modified. The adsorption of the calcium cation at both investigated pH (i.e. pH 7 and pH 12.63) takes place on the basal and lateral face of Kaol, however, the species of adsorbed calcium cation appeared to be different. The treatment also leads to a decrease in basal surface area due to basal face-basal face particle aggregation. The basal surface of Kaol treated with lime exhibited polar sites when probed with nitrogen molecule. These sites may have promoted linkage and flocculation of Kaol particles, which in turn play a role in the short-term modification of the macroscopic behavior of lime treated kaolins.

Heavy metals bioaccumulation in marine cultured fish and its probabilistic health hazard.

In aquacultures, heavy metals could be accumulated in fish tissues from natural and human-related sources depending on different factors. This study aims to estimate the level of bioaccumulation of heavy metals in cultured Gilt-head sea bream Sparusaurata. In this regard, heavy metals concentrations were measured in both water and fish musculature that were collected from a private fish farm in Kafr ElSheikh, Egypt. Regarding the water samples, heavy metals were within the permissible limits with exception of Cd, Cu, and Zn. In fish musculature, all heavy metals were within the WHO/FAO permissible limits. The bioaccumulation factor (BAF) indicated that mostly all heavy metals accumulation in the Gilt-head sea bream musculature decreased with time which may be correlated with the increase in water pH, calcium, and other cations concentrations. The hazard index (HI) calculations indicate no adverse health effects of heavy metals on humans through daily fish consumption so far. However, health risks are not negligible making the regular monitoring of metal contaminants in the studied area a necessity.

Changes in Soil Chemistry and Foliar Metabolism of Himalayan Cedar (Cedrus deodara) and Himalayan Spruce (Picea smithiana) along an Elevational Gradient at Kufri, HP, India: The Potential Roles of Regional Pollution and Localized Grazing

We investigated changes in soil chemistry and foliar metabolism of Himalayan cedar [Cedrus deodara (Roxb. Ex Lamb.) G.Don] and Himalayan spruce [Picea smithiana (Wall.) Boiss] trees along a steep elevational gradient in the lower Himalayan Mountains at Kufri, Himachal Pradesh (HP), India. The foliar and soil samples were collected from four locations along a 300 m elevational gradient at ridge, high-, mid-, and low-elevation sites within the forested Shimla Water Catchment Wildlife Sanctuary that provides water for the city of Shimla, HP,. Observations at the time of sampling revealed that the high-elevation site was being heavily grazed. Soils collected at the four sites showed differences in soil chemistry along the gradient. Surface soils (top 10 cm) at the high-elevation site had the highest concentrations of carbon, nitrogen, calcium, magnesium, phosphorus, organic matter, and effective cation exchange capacity, possibly caused by grazing. Mineral soils were slightly acidic at all sites except the mid-elevation site, which was extremely acidic in the upper mineral soil. Similar to surface soil chemistry, foliar metabolism was also comparatively unique for high elevation. In Himalayan cedar foliage, higher concentrations of soluble proteins, polyamines, amino acids, and potassium were observed at the high-elevation site as compared to the ridge, mid and low elevations. No major differences were observed in the metabolic profiles of cedar between the ridge and low elevation ranges. Spruce foliage was sampled only from the ridge and low elevations and its metabolic profiles suggested healthier conditions at the low elevation. The results of the study demonstrate the impact of the interplay between local and regional drivers of forest health on cedar and spruce trees in a forested catchment that acts as a water source for downstream communities.

Effectiveness of fresh cement kiln dust as a soil stabilizer and stabilization mechanism of high swelling clays

The expansive clay soils, which cover most of the new urbanized areas in Egypt, create major damages in most of the engineering structures and infrastructures such as buildings, roads, bridges, pipelines and others due to bad human activities, e.g. lack of maintenance for sewage and drinking lines, and flood irrigation of golf areas which causes fluctuation of water content through the foundation clay layers associated with shrink-swell behavior. These geotechnical challenges and their treatment solutions consume most of the urbanized project budget and delay the development plan. Therefore, in this study the high plasticity and soft to firm clay soils were stabilized using various dosages of fresh cement kiln dust (CKD) as an economical alternative to the other expensive stabilizing agents (stabilizers or binders) such as lime, cement and other chemical stabilizers. The effectiveness of this type of CKD as a stabilizing agent, soil stabilization mechanism, and changes in mineralogical and microstructural characteristics of stabilized soils due to this stabilization process were evaluated through Atterberg limits, unconfined compressive strength (UCS), stiffness (stress–strain behavior, Es), pH, electrical conductivity (EC), total dissolved solids (TDS), X-Ray diffraction (XRD) and scanning electron microscope (SEM) investigations. The present study revealed that by adding CKD, the workability of the treated clays was increased by decreasing the liquid limit and plasticity index as well as increasing the bearing capacity and decreasing the settlement by increasing UCS and Es. This study also showed that by adding CKD, the initial pH, EC, and TDS of CKD-clay system increased, creating favorable conditions for dissolution of edges and surfaces of clay flakes. The active montmorillonite clay flakes adsorbed the soluble calcium cation and sulfate anion on their surfaces that are rich in soluble silica and alumina and then the cation exchange and flocculation–agglomeration processes began. With curing, the pozzolanic products grew on the surfaces and edges of clay flakes and extended into the voids of the agglomerated inter-clay particles resulting in the filling of these micro-voids. The present investigation also found that, the progressive decreasing in pH, EC, and TDS values of CKD-clay systems through different curing periods is a good indicator for pozzolanic activity.

Self-healing and self-strengthening dual-function polyelectrolytes coating for corrosion protection of titanium sheet

A polyelectrolytes coating with self-healing and self-strengthening dual-function was fabricated on the titanium sheet for anticorrosion studies in fluorine-containing artificial saliva. The coating contains a polydopamine bottom film and 2-hydroxypropyltrimethyl ammonium chloride chitosan and sodium alginate multilayers. The incorporated polydopamine bottom film was modified to assure the adhesion of the polyelectrolytes coating on the titanium sheet. Based on the scratch assay, there are two stages for the scratched coating immersed in fluorine-containing artificial saliva: healing and strengthening. Results exhibited that the coating possesses a remarkable self-healing property in the early-stage immersion due to the swollen polyelectrolytes migrating to the scratched region and the calcium cations of the corrosive medium as an ionic crosslinker intercalated in the swollen polyelectrolytes forming calcium alginate and filling the micro-scale scratch. During the later-stage immersion, the self-healing coating showed excellent self-strengthening performance originating from the formation of the more and more compact film with calcium cations intercalated. This research provides an effective strategy to prolong the service life and improve corrosion performance for the implants in the human body environments.

INVESTIGATION OF METHODS FOR REMOVAL OF PHOSPHATES FROM HOUSEHOLD WASTE WATER

A study of the reagent removal of phosphates from domestic wastewater is presented. The research involved works, the authors of which describe methods for extracting phosphorus compounds from water. The article compares the removal of phosphates from wastewater by various methods in comparison with reagent methods. The analysis of existing technologies for regenerative dephosphorization of wastewater has shown that a promising direction is the search for new reagents for extracting phosphates from wastewater. Preference is given to such reagents as calcium oxide and hydroxide, iron chloride and sulfate, aluminum sulfate. The most eff ective for binding phosphates is the calcium cation, since a greater amount of hardly soluble compounds are formed with it.

MOLECULAR MECHANISM OF RELAXATION ABSORPTION OF ULTRASONIC WAVES IN AN AQUEOUS SOLUTION OF CALCIUM ACETATE

The absorption of ultrasonic waves in the frequency range from 6 to 146 MHz in aqueous solutions of sodium acetate, sodium chloride and calcium has been studied. It was found that only in solutions of calcium cations and acetate anion present simultaneously, relaxation absorption of ultrasonic waves is observed. The experimental data obtained indicate that the observed relaxation absorption of ultrasound in the studied frequency range by an aqueous solution of calcium acetate is associated with the interaction of the acetate anion with the calcium cation in the solution.

Differing Phosphorus Crop Availability of Aluminium and Calcium Precipitated Dairy Processing Sludge Potential Recycled Alternatives to Mineral Phosphorus Fertiliser

The European dairy industry generates large volumes of wastewater from milk and dairy food processing. Removal of phosphorus (P) by complexing with metal (e.g., aluminium, calcium) cations in P rich sludge is a potential P source for agricultural reuse and P recycling. However, there is a significant knowledge gap concerning the plant availability of this complexed P in comparison to conventional mineral P fertiliser. The current absence of information on plant P bioavailability of dairy processing sludge (DPS) limits the ability of farmers and nutrient management advisors to incorporate it correctly into fertiliser programmes. The present study examined the most common types of dairy sludge—(1) aluminium-precipitated sludge (“Al-DPS”) and (2) calcium-precipitated lime-stabilised sludge (“Ca-DPS”) at field scale to assess P availability in grassland versus mineral P fertiliser over a growing season. The experimental design was a randomised complete block with five replications. Crop yield and P uptake were assessed for 4 harvests. The initial soil test P was at a low level and the experimental treatments were super phosphate at 15, 30, 40, 50 and 60 kg P ha−1, two dairy sludge applied at 40 kg P ha−1 (comparison was made with mineral P at same application rate) and a zero P control applied in a single application at the beginning of the growing season. Results showed a significant positive slope in the relationship between P uptake response and mineral P application rate indicating the suitability of the experimental site for P availability assessment. The P bioavailability of Al- and Ca-DPS varied greatly between treatments. The P fertiliser replacement value based on the 1st harvest was 50 and 16% increased to 109 and 31% cumulatively over the four harvests for Al- and Ca-DPS, respectively. The Al concentration in Al-DPS did not limit P bioavailability, but low P bioavailability from Ca-DPS can be associated with its high Ca content that can lead to formation of low soluble Ca-P compounds at alkaline pH conditions with a high Ca/P ratio. These findings show that P availability from dairy sludge can be quite different depending on treatment process. Consequently, it is critical to have P availability information as well as total P content available to ensure the application rate meets crop requirements without creating environmental risk by over application.

Impact of basic tillage systems and fertilization on agrochemical indices of soil fertility in the right bank of the Forest-Steppe of Ukraine

The paper presents the results of stationary multifactor field experiment on study of the mutual impact of various systems of soil deep and surface tillage in combination with various levels of organic and mineral fertilizers application on crop rotation performance, as well as on a number of agrochemical indicators of black soil fertility. Researches were carried out as a stationary field experiment on the experimental field of Bila Tserkva National Agrarian University in 2013-2018. During the crop rotation in all the studied tillage methods, especially mouldboardless and disking tillage, the hydrolytic acidity of the arable layer increased with increase in fertilizer rates, and the amount of bases absorbed, saturation degree, level of exchangeable calcium and magnesium cations decreased, but in most cases these changes were not significant. Systematic mouldboardless and disking tillage enhance the topsoil heterogeneity in relation to agrochemical indicators of its fertility. Heterogeneity increases with increase in the level of applied fertilizers. With the mouldboard tillage during the crop rotation period at unfertilized areas, the largest part of humus loss in the arable layer is observed in the top, and the smallest - in its bottom parts; the opposite pattern was observed on fertilized areas at the highest rate. With mouldboardless and disking tillage, directly opposite patterns were observed in comparison with mouldboard tillage. An annual application of 8 t/ha of manure + N76P64K57 stabilizes the humus state of the arable soil layer when carrying out differentiated and disking tillage in crop rotation. Fertilization rate of 12 t/ha of manure + N95P82K75 for these tillage options a significant increase in humus and total nitrogen reserves is provided.

The ionic composition of distilled beverages and its effect on their stability during storage

During prolonged storage of distilled beverages, turbidity may form in them, which leads to the loss of their presentation, so one of the main problems of the distillery is the increased stability of a finished product during storage and increasing shelf life of products. Identifying the causes of turbidity and precipitation is one of the most important and urgent tasks in the control of alcoholic beverages. In this work, industrial samples of alcoholic beverages containing inclusions, turbidity and precipitation were investigated using the method of ion chromatography. The ionic composition of the studied samples is represented mainly by cations of sodium, potassium, calcium and magnesium and anions of fluorides, chlorides, nitrates, phosphates and sulfates. Mass concentrations of the ions represented fluctuate over a wide range, which is explained by the rich microelement composition of plant components, the specifics of the formulations and the peculiarity of water treatment from different manufacturers. The analysis of results showed that one of the main reasons for the appearance of turbidity and precipitation in distilled beverages is the increased content of calcium and magnesium ions.

Dynamic Mechanical Control of Alginate-Fibronectin Hydrogels with Dual Crosslinking: Covalent and Ionic.

Alginate is a polysaccharide used extensively in biomedical applications due to its biocompatibility and suitability for hydrogel fabrication using mild reaction chemistries. Though alginate has commonly been crosslinked using divalent cations, covalent crosslinking chemistries have also been developed. Hydrogels with tuneable mechanical properties are required for many biomedical applications to mimic the stiffness of different tissues. Here, we present a strategy to engineer alginate hydrogels with tuneable mechanical properties by covalent crosslinking of a norbornene-modified alginate using ultraviolet (UV)-initiated thiol-ene chemistry. We also demonstrate that the system can be functionalised with cues such as full-length fibronectin and protease-degradable sequences. Finally, we take advantage of alginate’s ability to be crosslinked covalently and ionically to design dual crosslinked constructs enabling dynamic control of mechanical properties, with gels that undergo cycles of stiffening–softening by adding and quenching calcium cations. Overall, we present a versatile hydrogel with tuneable and dynamic mechanical properties, and incorporate cell-interactive features such as cell-mediated protease-induced degradability and full-length proteins, which may find applications in a variety of biomedical contexts.

Phase diagrams and microstructures of aqueous short alkyl chain polyethylene glycol ether carboxylate and carboxylic acid triblock surfactant solutions

HypothesisThe surfactant C8EO8CH2COOH (Akypo LF2) and its salts have a small hydrophobic and a significantly longer hydrophilic part. As a consequence, there must be a significant steric constraint, once these surfactant molecules form micelles. In addition, the partially charged headgroups should bring some additional fine-tuning via electrostatic interactions to this “essentially non-ionic” surfactant. ExperimentsPhase diagrams of binary mixtures of water and C8EO8CH2COOH are established over large concentration and temperature ranges, also at different pHs and in the presence of sodium and calcium ions. Surface tensions and osmotic pressures are measured to understand the systems. To evaluate the microstructures, also Dynamic Light Scattering and Small-Angle X-ray Scattering are performed. FindingsApart from the formation of coacervates at very low surfactant concentrations, spherical micelles persist over the whole concentration and temperature range and do not change in size and shape. At very high surfactant concentrations, above 60% by weight, where the headgroups are no longer fully hydrated, the standard core-shell structure of micelles vanishes and highly stabilized aggregates of 8–26 octyl chains are suspended in interdigitated polyoxyethylene layers and form an “osmotic brush”. When the acid is partially transformed to a sodium salt, the repulsion between the micelles increases, whereas bridging between micelles prevails, when the counterions are calcium cations. Remarkably, the negative charges of the headgroups are randomly distributed in the hydrophilic ethylene oxide shell. Altogether, a phase diagram without lyotropic liquid crystalline phases and an extreme shift of the cloud-point in temperature and composition is found, similar to the phase diagram of C8EO8OH already known in literature. The phase properties can be explained by the curvature and packing constraints together with the Lindemann rule applied to short hydrocarbon chains.