Buffer Components Research Articles

Improving Stability of Spiroplasma citri MreB5 Through Purification Optimization and Structural Insights.

MreB is a prokaryotic actin homolog. It is essential for cell shape in the majority of rod-shaped cell-walled bacteria. Structural and functional characterization of MreB protein is important to understand the mechanism of ATP-dependent filament dynamics and membrane interaction. In vitro studies on MreBs have been limited due to the difficulty in purifying the homogenous monomeric protein. We have purified MreB from the cell-wall-less bacteria Spiroplasma citri, ScMreB5, using heterologous expression in Escherichia coli. This protocol provides a detailed description of purification condition optimization that led us to obtain high concentrations of stable ScMreB5. Additionally, we have provided a protocol for detecting the presence of monovalent ions in the ScMreB5 AMP-PNP-bound crystal structure. This protocol can be used to obtain a high yield of ScMreB5 for carrying out biochemical and reconstitution studies. The strategies used for ScMreB5 show how optimizing buffer components can enhance the yield and stability of purified protein. Key features • The protocol is a useful approach to standardize purification of nucleotide-dependent cytoskeletal filaments and other nucleotide-binding proteins. • The mechanistic basis of how different ions could stabilize a protein, and hence improve yield in purification, has been demonstrated. • The change in buffer conditions/salt enabled us to get sufficient yield for biochemical and structural characterization.

Optimisation of bronchoalveolar lavage technique for isolating alveolar macrophages in mice

Bronchoalveolar lavage (BAL) is a widely used technique to collect immune cells from the lungs, with alveolar macrophages (AMs) being the most prevalent cells in BAL fluid. AMs are vital for maintaining lung homeostasis and providing immune defence against airborne pathogens. However, in murine models, BAL procedures usually yield low numbers of AMs, thus limiting experimental design, especially when high cell counts are needed. Objective — to optimise the BAL technique in mice to maximise the collection of AMs. Materials and methods. Young and older BALB/c mice were used in the study. Bronchoalveolar lavage was performed following the method of Luckow and Lehmann (2021) with modifications. Statistical analysis was done using the Mann‑Whitney U test, with a significance level set at p<0.05. Results. Female BALB/c mice of different ages were chosen due to the frequency of their use as models of pulmonary diseases. A simplified method described by Luckow and Lehmann (2021), which avoids tracheotomy by using peroral cannula insertion, was employed. The protocol was modified by securing the cannula with a ligature to prevent BAL fluid leakage in older mice. To reduce mechanical stress on alveoli, a buffer volume of 0.6 mL was used, and the study compared two buffer variants: one at room temperature without EDTA, and another heated to 37°C with EDTA. The pre‑heated buffer with EDTA significantly increased BAL cell yields in all mice groups, confirming the importance of these optimisations for higher cell recovery. Conclusions. Our modified bronchoalveolar lavage protocol includes securing the trachea with a ligature to prevent BAL fluid leakage, reducing lavage volume to 0.6 mL to minimise lung damage, and using a 37°C solution with EDTA for improved AM recovery rates. Further studies are needed to explore the significance of other buffer components for BAL protocol optimisation, the possible age‑related differences in AM isolation in male BALB/c mice, and the strain‑specific features of the BAL technique.

Alternative buffer systems in biopharmaceutical formulations and their effect on protein stability.

The formulation of biopharmaceutical drugs is designed to eliminate chemical instabilities, increase conformational and colloidal stability of proteins, and optimize interfacial stability. Among the various excipients involved, buffer composition plays a pivotal role. However, conventional buffers like histidine and phosphate buffers may not always be the optimal choice for all monoclonal antibodies (mAbs). In this study, we investigated the effects of several alternative buffer systems on seven different mAbs, exploring various combinations of ionic strengths, concentrations of the main buffer component, mAb concentrations, and stress conditions. Protein stability was assessed by analyzing soluble aggregate formation through size exclusion chromatography. At low protein concentrations, protein instability after temperature stress was exclusively observed in the bis-TRIS/ glucuronate buffer. Conversely, freeze-thaw stress led to a significant increase in aggregate formation in tested formulations, highlighting the efficacy of several alternative buffers, particularly arginine/ citrate, in preserving protein stability. Under temperature stress, the introduction of arginine to histidine buffer systems provided additional stabilization, while the addition of lysine resulted in protein destabilization. Similarly, the incorporation of arginine into histi-dine/HCl buffer further enhanced protein stability during freeze--thaw cycles. At high protein concentrations, the histidine/citrate buffer emerged as one of the most optimal choices for addressing temperature and light-induced stress. The efficacy of histidine buffers in combating light stress might be attributed to the light-absorbing properties of histidine molecules. Our findings demonstrate that the development of biopharmaceutical formulations should not be confined to conventional buffer systems, as numerous alternative options exhibit comparable or even superior performance.

A Mathematical Model for Conical Hopper Mass Efficiency

Almost every branch of industry, at a certain point, utilizes omnifarous materials in their granular form. A key constituent in many bulk material logistic systems is the hopper, which usually acts as a buffering component. In order to achieve the desired throughput, the geometry of the particular hopper must be carefully determined. Considering the geometric properties of the given hopper, the inclination of the walls and the outlet orifice characteristics are the pivotal determinants of hopper functionality. In this paper, the authors have developed an analytical model of the conical hopper’s mass efficiency and compared the model with the experimental results for two distinctive granular materials. The model inputs were: the density of the bulk material, critical angle of material repose, generatrix inclination angle of the cone, and diameter of the circular outlet. The experiment was conducted according to a 32 full factorial design. The repeatability of the results was examined according to Cochran’s theorem and the adequacy of the data was evaluated via Fisher’s criterion, which confirmed the quality of the mathematical model. The error of the developed model does not exceed 4.5%.

Enhanced Recognition of a Herbal Compound Epiberberine by a DNA Quadruplex-Duplex Structure.

The small molecule epiberberine (EPI) is a natural alkaloid with versatile bioactivities against several diseases including cancer and bacterial infection. EPI can induce the formation of a unique binding pocket at the 5' side of a human telomeric G-quadruplex (HTG) sequence with four telomeric repeats (Q4), resulting in a nanomolar binding affinity (KD approximately 26 nM) with significant fluorescence enhancement upon binding. It is important to understand (1) how EPI binding affects HTG structural stability and (2) how enhanced EPI binding may be achieved through the engineering of the DNA binding pocket. In this work, the EPI-binding-induced HTG structure stabilization effect was probed by a peptide nucleic acid (PNA) invasion assay in combination with a series of biophysical techniques. We show that the PNA invasion-based method may be useful for the characterization of compounds binding to DNA (and RNA) structures under physiological conditions without the need to vary the solution temperature or buffer components, which are typically needed for structural stability characterization. Importantly, the combination of theoretical modeling and experimental quantification allows us to successfully engineer Q4 derivative Q4-ds-A by a simple extension of a duplex structure to Q4 at the 5' end. Q4-ds-A is an excellent EPI binder with a KD of 8 nM, with the binding enhancement achieved through the preformation of a binding pocket and a reduced dissociation rate. The tight binding of Q4 and Q4-ds-A with EPI allows us to develop a novel magnetic bead-based affinity purification system to effectively extract EPI from Rhizoma coptidis (Huang Lian) extracts.

Enhancement of growth media for extreme iron limitation in Escherichia coli.

Iron is an essential nutrient for microbial growth and bacteria have evolved numerous routes to solubilize and scavenge this biometal, which is often present at very low concentrations in host tissue. We recently used a MOPS-based medium to induce iron limitation in Escherichia coli K-12 during the characterization of novel siderophore-conjugated antibiotics. In this study we confirm that growth media derived from commercially available M9 salts are unsuitable for studies of iron-limited growth, probably through the contamination of the sodium phosphate buffer components with over 100 µM iron. In contrast, MOPS-based media that are treated with metal-binding Chelex resin allow the free iron concentration to be reduced to growth-limiting levels. Despite these measures a small amount of E. coli growth is still observed in these iron-depleted media. By growing E. coli in conditions that theoretically increase the demand for iron-dependent enzymes, namely by replacing the glucose carbon source for acetate and by switching to a microaerobic atmosphere, we can reduce background growth even further. Finally, we demonstrate that by adding an exogeneous siderophore to the growth media which is poorly used by E. coli, we can completely prevent growth, perhaps mimicking the situation in host tissue. In conclusion, this short study provides practical experimental insight into low iron media and how to augment the growth conditions of E. coli for extreme iron-limited growth.

Research on adaptive penetration characteristics of space harpoon based on aluminum honeycomb buffer

To address the issues of high impact and limited adaptability in capturing space debris with space harpoons, a novel harpoon capture device based on aluminum honeycomb buffering was proposed. The issue of excessive impact force for harpoons could be effectively addressed by the excellent energy-absorbing characteristics of aluminum honeycomb. A simulation model was established to analyze the penetration of space harpoons into aluminum alloy target plates using Johnson-Cook’s dynamic constitutive model and fracture failure criteria. Ground experiments were conducted to validate the correctness of the simulation model. The impact of aluminum honeycomb was investigated by analyzing the simulation results of harpoons with and without aluminum honeycomb. With the introduction of aluminum honeycomb as a buffering component, the rebound velocity of the harpoon decreased by 76.2 %, and the impact force reduced by 78.6 %. Then the model was used to study the influence of different launching angles and different targets on the penetration characteristics of the space harpoon. The research findings indicate that space harpoons could successfully penetrate and capture aluminum alloy targets at a launch velocity of 53.1 m/s to 58.5 m/s, as determined through ground experiments and simulation analysis. The error in the crushing height of the aluminum honeycomb was found to be 2.19 %, while the error in the harpoon penetration depth was 9.02 %. Moreover, within a launch angle error of 10°, space harpoons also demonstrate the capability for adaptive capture of both aluminum alloy plates and aluminum honeycomb sandwich panels, with average correction capabilities of 92.5 % and 95.5 %. In conclusion, the analysis of the adaptive penetration characteristics of space harpoons provides a solid theoretical foundation and technical support for the design of harpoon capture systems.

Reducing Cathodic Drift during Isoelectric Focusing Using Microscale Immobilized pH Gradient Gels.

Microfluidic analytical tools play an important role in miniaturizing targeted proteomic assays for improved detection sensitivity, throughput, and automation. Microfluidic isoelectric focusing (IEF) can resolve proteoforms in lysate from low-to-single cell numbers. However, IEF assays often use carrier ampholytes (CAs) to establish a pH gradient for protein separation, presenting limitations like pH instability in the form of cathodic drift (migration of focused proteins toward the cathode). Immobilized pH gradient (IPG) gels reduce cathodic drift by covalently immobilizing the pH buffering components to a matrix. To our knowledge, efforts to implement IPG gels at the microscale have been limited to glass microdevices. To adapt IEF using IPGs to widely used microfluidic device materials, we introduce a polydimethylsiloxane (PDMS)-based microfluidic device and compare the microscale pH gradient stability of IEF established with IPGs, CAs, and a hybrid formulation of IPG gels and CAs (mixed-bed IEF). The PDMS-based IPG microfluidic device (μIPG) resolved analytes differing by 0.1 isoelectric point within a 3.5 mm separation lane over a 20 min focusing duration. During the 20 min duration, we observed markedly different cathodic drift velocities among the three formulations: 60.1 μm/min in CA-IEF, 2.5 μm/min in IPG-IEF (∼24-fold reduction versus CA-IEF), and 1.4 μm/min in mixed-bed IEF (∼43-fold reduction versus CA-IEF). Lastly, mixed-bed IEF in a PDMS device resolved green fluorescent protein (GFP) proteoforms from GFP-expressing human breast cancer cell lysate, thus establishing stability in lysate from complex biospecimens. μIPG is a promising and stable technique for studying proteoforms from small volumes.

Acute Toxicity Assays with the Artemia salina Model: Assessment of Variables.

The use of the brine shrimp Artemia salina (Leach) in acute toxicity assays has great potential due to its simplicity, low cost and reproducibility. In the current study, some of the variables that can influence the reliability of the assay in terms of test organism survival, were evaluated as part of its implementation in our laboratory. The quality and type of water used, the buffer components and other parameters (salinity, pH and dissolved oxygen level), were all evaluated for optimisation purposes. DMSO (dimethyl sulphoxide) was used as the test substance in the toxicity assay, to evaluate the concentration limits as a solvent in sample preparation. Regarding the buffer salinity, pH and dissolved oxygen level, we found that a 25% to 30% deviation from the standard values did not affect the survival of the nauplii (the first-instar larval stage) under assay conditions. In summary, we corroborate the potential use of this model for the prediction of the toxic potential of substances, to inform future testing strategies.

Retention behavior of nucleosides and nucleobases on a 3 μm undecylenic acid-functionalized silica column in per aqueous liquid chromatography and hydrophilic interaction liquid chromatography separation modes

A 3 μm undecylenic acid-functionalized stationary phase (UAS) was prepared for the separation of nucleosides and nucleobases using per aqueous liquid chromatography (PALC) and hydrophilic interaction liquid chromatography (HILIC). The retention behaviors of nucleosides and nucleobases in PALC and HILIC modes were explored by adjusting parameters such as water content, buffer concentration, pH of the mobile phase and column temperature. The experimental data and separation chromatogram demonstrated that PALC could provide retention comparable to that of HILIC for nucleosides and nucleobases. Comparative studies using diluted adenosine solutions evaluated theoretical plates and peak shape for the same retention factors (between 0.25 and 5.0) in PALC and HILIC. There was no buffer component in the mobile phases used to operate the comparisons. HILIC mode is more efficient for adenosine than PALC mode at low retention factors. It's the exact opposite phenomenon for high retention factors. It is proposed that the mass transfer of adenosine between the UAS, the water-rich layer and the ACN-rich mobile phase in HILIC is relatively slow. Given the significant use of toxic ACN in HILIC, PALC emerges as a safer and more effective alternative for separating nucleosides and nucleobases.

Microscale Thermophoresis Analysis of Membrane Proteins

Microscale Thermophoresis Analysis of Membrane Proteins

Optimized Refolding Buffers Oriented Humoral Immune Responses Versus PfGCS1 Self-Assembled Peptide Nanoparticle.

Developing a novel class of vaccine is pivotal for eliminating and eradicating malaria. Preceding investigations demonstrated partial blocking activity in malaria transmission against recombinant vaccine PfHAP2-GCS1 and conserved region of the cd loop. The effectiveness of immune response varies with the size and shape of the self-assembly of peptide nanoparticles (SAPNs) displaying antigen, affected by different components in refolding buffers. Plasmodium falciparum Generative Cell Specific 1 (PfGCS1), a promising malaria transmission-blocking vaccine (TBV) candidate, was expressed, purified, and followed by a four-step refolding process to form nanoparticles (PfGCS1-SAPNs). The influence of buffer components on the size and shape of SAPNs was investigated by DLS and FESEM. Furthermore, the immunogenicity of nanostructures was assessed in different mouse groups. The results showed that PfGCS1-SAPN was immunogenic and its administration with Poly (I:C), stimulated humoral and cellular responses in the mouse model. In the immunized mice groups, the level of IgG antibodies against PfGCS1-SAPN was significantly increased in different time points (second and third boost) and heterogeneous boosters. The various IgG-subclasses profile shifted to Th1, Th2, or Th1/Th2 mix responses in mice immunized with PfGCS1-SAPN refolded in different buffers, indicating a prerequisite for further investigations to optimize vaccine formulation to enhance and modulate Th1/cellular responses. Such studies pave the way to improve biophysical features related to the nanoparticles' size, shape, and conformational epitopes of candidate antigens and T- and B-cells presented on the superficial structure to elicit robust immune responses.

Supercapacitor Implementation To Prototype Energy Storage System Optimizer in PV System

This research aims to create a prototype of an energy storage optimizer in a PV system using a supercapacitor in combination with batteries. The purpose of adding supercapacitors in this prototype is to maintain battery usage when there is a change in irradiation with a loading source that refers to the amount of electrical current and voltage as a supply of energy. A sudden increase in load without an energy buffer component can affect battery endurance. This can result in a decrease in electrical energy supply. Based on experimental results, it has been found that the battery and supercapacitor complement each other. The battery works more statically while the supercapacitor works more dynamically. Thus, the power output to the load is more stable, and the battery can be more durable because when there are extreme changes in irradiation and load, they can be overcome by supercapacitors.

Lyoprotectant Constituents Suited for Lyophilization and Reconstitution of Stem-Cell-Derived Extracellular Vesicles.

Stem-cell-derived extracellular vesicles (EVs) are emerging as an alternative approach to stem cell therapy. Successful lyophilization of EVs could enable convenient storage and distribution of EV medicinal products at room temperature for long periods, thus considerably increasing the accessibility of EV therapeutics to patients. In this study, we aimed to identify an appropriate lyoprotectant composition for the lyophilization and reconstitution of stem-cell-derived EVs. MSC-derived EVs were lyophilized using different lyoprotectants, such as dimethyl sulfoxide, mannitol, trehalose, and sucrose, at varying concentrations. Our results revealed that a mixture of trehalose and sucrose at high concentrations could support the formation of amorphous ice by enriching the amorphous phase of the solution, which successfully inhibited the acceleration of buffer component crystallization during lyophilization. Lyophilized and reconstituted EVs were thoroughly evaluated for concentration and size, morphology, and protein and RNA content. The therapeutic effects of the reconstituted EVs were examined using a tube formation assay with human umbilical vein endothelial cells. After rehydration of the lyophilized EVs, most of their generic characteristics were well-maintained, and their therapeutic capacity recovered to levels similar to those of freshly collected EVs. The concentrations and morphologies of the lyophilized EVs were similar to the initial features of the fresh EV group until day 30 at room temperature, although their therapeutic capacity appeared to decrease after 7 days. Our study suggests an appropriate composition of lyoprotectants, particularly for EV lyophilization, which could encourage the applications of stem-cell-derived EV therapeutics in the health industry.

PH dependent physicochemical signatures of amino acids in aqueous buffers: Thermodynamic analysis

The physicochemical signatures such as apparent molar volume (V2,Φ), isoentropic compressibilities (KS,2,φ), and dilution enthalpies of a series of amino acids (AAs) glycine (Gly), L-alanine (Ala), DL-α-amino-n-butyric acid (ABA), L-valine (Val) and L-leucine (Leu) have been measured at various pH values (pH = 2, 5 7 and 9) at a buffer molality of 0.1 mol kg−1 of water at 298.15 K. The data obtained from high sensitivity densimeter and sound analyser along with ultrasensitive isothermal titration calorimetry has been analyzed to evaluate the values of standard partial molar quantities such as for volume at infinite dilution (V2,m0), compressibility KS, 2,m0 and dilution enthalpy (ΔdilH0) of the AAs together with standard partial molar quantities of transfer of these solutes from water to aqueous buffer systems at these pH values. The linear correlation of V2,m0 for this series of AAs against number of carbon atoms in their alkyl chain has been used to evaluate the contribution of zwitterionic end groups (NH3+, COO–), the CH2 group, and other parts of alkyl chains of the AAs to the overall value of V2,m0. The results of standard partial molar transfer properties on volumes, compressibilities and enthalpies of dilution from water to aqueous buffer systems at various pH values have been connected and explained in terms of ion-polar, ion-hydrophilic, hydrophobic-hydrophobic and ion-hydrophobic interactions of the participating groups. These thermodynamic signatures when compared at different pH values suggest that at electrostriction of water dominates at pH 2. Such physicochemical properties of constituents of proteins such as amino acids have not been reported earlier. Thus, the results demonstrate that the interaction of individual amino acid residues with the buffer components does not lead to significant change in their physicochemical properties thereby permitting their use in obtaining mechanistic insights into systems of biological interest consisting of these constituents.

Research on the characteristics and similarity relationships of impact load reduction of a vehicle entering water

The strong, transient, and high-peak impact load caused by a vehicle entering water at high speed is the primary factor threatening its structural strength and equipment safety. One of the effective methods for water entry protection is to use head-mounted buffer components. To this end, based on the arbitrary Lagrangian-Eulerian method, a numerical model of impact load reduction of water entry was established in this study. The results showed that the impact load could be characterised by a narrow pulse width and a high peak value, which gradually stabilises in a fluctuating manner. Five typical stages in the failure process of the cushion foam and four typical stages in that of the nose cap were observed. The prediction accuracy decreased as the scaling ratio decreased. Furthermore, the buffer components increased the occurrence of an error in the prediction results of the scaling model. The primary causes are the strain-rate sensitivity of the foam and dissimilarity in the failure criteria, which lead to dissimilarities in the foam failure process after scaling. This research will be useful for the designing of water load reduction structures and scaled model experimental schemes.

Pitfalls in RNA Modification Quantification Using Nucleoside Mass Spectrometry.

In recent years, there has been a high interest in researching RNA modifications, as they are involved in many cellular processes and in human diseases. A substantial set of enzymes within the cell, called RNA writers, place RNA modifications selectively and site-specifically. Another set of enzymes, called readers, recognize these modifications which guide the fate of the modified RNA. Although RNA is a transient molecule and RNA modification could be removed by RNA degradation, a subclass of enzymes, called RNA erasers, remove RNA modifications selectively and site-specifically to alter the characteristics of the RNA. The detection of RNA modifications can be done by various methods including second and next generation sequencing but also mass spectrometry. An approach capable of both qualitative and quantitative RNA modification analysis is liquid chromatography coupled to mass spectrometry of enzymatic hydrolysates of RNA into nucleosides. However, for successful detection and quantification, various factors must be considered to avoid biased identification and inaccurate quantification. In this Account, we identify three classes of errors that may distort the analysis. These classes comprise (I) errors related to chemical instabilities, (II) errors revolving around enzymatic hydrolysis to nucleosides, and (III) errors arising from issues with chromatographic separation and/or subsequent mass spectrometric analysis.A prominent example for class 1 is Dimroth rearrangement of m1A to m6A, but class 1 also comprises hydrolytic reactions and reactions with buffer components. Here, we also present the conversion of m3C to m3U under mild alkaline conditions and propose a practical solution to overcome these instabilities. Class 2 errors-such as contaminations in hydrolysis reagents or nuclease specificities-have led to erroneous discoveries of nucleosides in the past and possess the potential for misquantification of nucleosides. Impurities in the samples may also lead to class 3 errors: For instance, issues with chromatographic separation may arise from residual organic solvents, and salt adducts may hamper mass spectrometric quantification. This Account aims to highlight various errors connected to mass spectrometry analysis of nucleosides and presents solutions for how to overcome or circumnavigate those issues. Therefore, the authors anticipate that many scientists, but especially those who plan on doing nucleoside mass spectrometry, will benefit from the collection of data presented in this Account as a raised awareness, toward the variety of potential pitfalls, may further enhance the quality of data.

Impact of Solution Chemistry on the Biotechnological Synthesis and Properties of Palladium Nanoparticles

The biosynthesis of palladium nanoparticles supported on microbial cells (bio-Pd) has attracted much recent interest, but the effect of solution chemistry on the process remains poorly understood. Biological buffers can be used to maintain physiological pH during the bioreduction of Pd(II) to Pd(0) by microbial cells, however, buffer components have the potential to complex Pd(II), and this may affect the subsequent microbe-metal interaction. In this study, a range of Pd(II) salts and biological buffers were selected to assess the impact of the solution chemistry on the rate of bioreduction of Pd(II) by Geobacter sulfurreducens, and the resulting biogenic palladium nanoparticles. The different buffer and Pd(II) combinations resulted in changes in the dominant Pd(II) species in solution, and this affected the amount of palladium recovered from solution by the microbial cells. The physical properties of the bio-Pd nanoparticles were altered under different solution chemistries; only slight variations were observed in the mean particle size (<6 nm), but significant variations in particle agglomeration, the extent of Pd(II) bioreduction and subsequent catalytic activity for the reduction of 4-nitrophenol (4-NP) were observed. The combination of sodium tetrachloropalladate and bicarbonate buffer resulted in bio-Pd with the smallest mean particle size, and the fastest initial rate of reaction for 4-NP reduction (0.33 min–1). Other solution chemistries appeared to damage the cells and result in bio-Pd with relatively poor catalytic performance. This work emphasises that future studies into bio-Pd synthesis should consider the importance of solution chemistry in controlling the speciation of Pd(II) and its impact on both the bioreduction process and the resulting properties of the nanoparticles produced, in order to maximise Pd(II) biorecovery and optimise catalytic properties.

A hydromechanical material model for compacted bentonite

This paper presents a new hydromechanical model, developed with the intention to be used for predicting the mechanical evolution of compacted bentonite components in repositories for spent nuclear fuel. The model is based on a thermodynamic relation for the chemical potential of the clay water, and uses empirical functions which are parametrized and calibrated with data on water retention properties at free swelling conditions, swelling pressure, and shear strength; the latter two are central for defining technical requirements for the bentonite buffer components. This results in a model which at its core incorporates all these properties, as well as the hysteresis behaviour. The validity of the model was investigated by analysing nine experimental test conditions, using COMSOL Multiphysics®, with a single set of parameter values. Model results were compared with experimental data for both saturated conditions (free swelling retention test; oedometer tests and triaxial compression tests) and for unsaturated conditions (swelling pressure build-up; swelling or shrinkage at constant load; compression at constant water or constant suction and unconfined compression tests). These comparisons gave a broad demonstration of the predictive capabilities of the model. Some limitation of the model regarding the representation of shrinkage, the shear strength at lower water contents, and the path dependence can nevertheless be noted.

Realizing zero-order controlled transdermal drug permeation through competing doubly ionic H-bond in patch

Transdermal drug delivery system (TDDS) was an effective way to realize controlled drug delivery. However, realizing zero-order controlled drug skin delivery was still challenging in the drug-in-adhesive patch. This study provided a strategy to accomplish this delivery form by stabilizing the drug concentration in adhesive through concentration-dependent competitive interaction. Clonidine (CLO) and Granisetron (GRA) were chosen as the model drugs which were of high skin permeability, and polydimethylaminoethyl acrylate (EA) as an excipient to interact with hydroxyphenyl adhesive (HP). Drug release, permeation and pharmacokinetic study were conducted to evaluate the controlled effect of HP-EA. The molecular interaction was characterized by FT-IR, 1H NMR and XPS. Dynamic simulation and molecular docking further clarified the competitive interaction involved in the release process. Both the drug skin permeation study of CLO and GRA patch based on the HP-EA adhesive showed good zero-order fitting with r of 0.994 and 0.998, compared with non-functional adhesive (0-PSA). Furthermore, the pharmacokinetic study of the CLO patch showed a plateau phase for around 52 h without influencing the area under concentration–time curve (AUC), indicating that the HP-EA could realize zero-order drug skin delivery. The mechanism study revealed that EA serving as a ‘buffer component’ promoted the conversion of the ionic CLO to the neutrals the as the neutrals released, which stabilized ‘1% neutrals CLO concentration’. In conclusion, the drug delivery system based on the concentration-dependent competitive interaction broadened our understanding of the molecular mechanisms involved in zero-order controlled release in transdermal patches which would promote the development of zero-order drug delivery in TDDS.