Selection of Excipients for the Preparation of Vancomycin-Loaded Poly(D,L-lactide-co-glycolide) Microparticles with Extended Release by Emulsion Spray Drying.

The aim of this study was to relate the composition of the W/O emulsion used as a starting fluid in the spray-drying process to the quality of the dry polymer particles obtained in terms of physical-chemical properties, compatibility and drug release performance. Four W/O emulsions containing vancomycin hydrochloride (VAN), an encapsulating PLGA polymer and Poloxamer® 407, chitosan and/or sorbitan monooleate as stabilisers were spray-dried using an ultrasonic atomising nozzle. The microparticles obtained were micron-sized, with a volume mean diameter between 43.2 ± 0.3 and 64.0 ± 12.6 µm, and spherical with a mostly smooth, non-porous surface and with high drug loading (between 14.5 ± 0.6 and 17.1 ± 1.9% w/w). All formulations showed a prolonged and biphasic VAN release profile, with diffusion being the primary release mechanism. Microparticles prepared from the emulsions with Poloxamer® 407 and sorbitan monooleate released VAN rapidly and completely within one day. The release of VAN from microparticles prepared from the emulsion without additives or with chitosan in the inner aqueous phase was significantly decreased; after four days, a cumulative release of 65% and 61%, respectively, was achieved. Microparticles with encapsulated chitosan had the largest mean particle diameter and the slowest release of VAN.

Use of low-field NMR and rheology to evaluate the microstructure and stability of a poly(d,l-lactide-co-glycolide)-based W/O emulsion to be processed by spray drying.

Drug-loaded emulsions for spray drying should be optimised for their rheological behaviour and stability under operating conditions, as this is essential for achieving the desired physicochemical properties of the final dry product. Our aim was therefore to investigate the structure and stability of a water-in-oil (W/O) emulsion containing vancomycin hydrochloride as the active ingredient in the aqueous phase, poly(d,l-lactide-co-glycolide) as the structural polymer in the dichloromethane-based organic phase, and various stabilisers using low-field nuclear magnetic resonance (LF NMR) and rheological characterisation. Four emulsions were tested, namely-one without stabiliser, one with Poloxamer® 407, one with chitosan and Span™ 80 and one with chitosan only. The theoretical interpretation of the rheological data allowed the determination of the velocity and the shear rate/stress profiles inside the feed path of the W/O emulsion, aspects that are critical for the industrial scale-up of the emulsion drying process. In addition, LF NMR demonstrated that shaking was sufficient to restore the original emulsion structure and that the droplet size of all emulsions was in the range of 1-10 µm, although the emulsion with chitosan had the narrowest droplet size distribution and the higher zero shear viscosity, which accounts for the increased long-term stability due to impeded droplets movement.

Development of fiber optic in vitro release testing method for dexamethasone release from the oil solutions.

For many parenteral drugs, there is still no standardized method for in vitro release (IVR) testing available. This article presents the development of a new IVR method for oil solutions using a dialysis membrane and USP II apparatus coupled to a fiber optic UV-Vis spectrometer. Experiments were performed using dexamethasone formulations containing castor oil as a solvent with the addition of cosolvents, 20 % (v/v) of isopropanol or Capryol® 90. Based on solubility testing results, castor oil was chosen as the best solvent amongst other vegetable oils, while a significant increase in solubility was obtained by adding either of the two cosolvents. Partitioning experiments were performed to ensure these formulations could achieve prolonged drug release. IVR testing was performed with model formulations and critical test parameters were varied in order to examine the method's sensitivity. The developed method was sensitive to temperature and stirring rate, while coupling the USP II apparatus with a fiber optic UV-Vis spectrometer enabled complete automation. Moreover, due to the interference of excipients on fiber optic detection of dexamethasone during the release testing, derivative spectroscopy was successfully introduced for the elimination of the interference. The developed IVR method described herein could be useful in preformulation investigations and the early development of novel formulations.

Evaluation of stability and in vitro wound healing potential of melatonin loaded (lipid enriched) chitosan based microspheres.

The aim of this study was to evaluate long-term stability and assess the wound healing potential of the innovative melatonin-loaded lipid-enriched hybrid system compared to conventional melatonin-loaded chitosan microspheres. The hybrid system contained nanostructured lipid carrier incorporated in the chitosan matrix, in order to modify melatonin release and alter physicochemical characteristics of the delivery system. Stability testing was performed during a six-month period under two conditions: refrigerated (5 ± 3 °C) and at room temperature (25 ± 2 °C/60 ± 5 % RH). Samples stored at both conditions were analyzed in terms of particle size, zeta potential, moisture content and thermal properties. At the end of testing, drug content was determined in all samples. Dressings wound healing potential was assessed by in vitro scratch test using human skin fibroblast cell line. Although both systems showed good stability characteristics, the addition of lipids in the system has improved its wound healing potential.

Preparation of in situ hydrogels loaded with azelaic acid nanocrystals and their dermal application performance study.

Azelaic acid (AZA) is a dicarboxylic acid that is topically used in the treatment of acne and rosacea since it possesses antibacterial and keratolytic activity. The primary objective of this study was to develop an AZA nanocrystal suspension. It is expected that improved solubility and dissolution rate will result in advanced biopharmaceutical properties, primarily the dermal bioavailability. Furthermore, a topical nanocrystal AZA-loaded hydrogels composed of Pluronic® F127 and hyaluronic acid mixture that are able to deliver AZA into the stratum corneum and deeper skin layers were considered. This study was conducted in order to: 1) determine the effect of non-ionic Polysorbate 60 on the stabilization and particle size of the AZA nanocrystals, as well as the effect of Pluronic® F127, used as an in situ gelation agent, and hyaluronic acid on the viscoelastic properties and the drug release of composed hydrogels, 2) determine the relationship between the rheological properties of the gels and the penetration of AZA into the stratum corneum. The composed hydrogels revealed pseudoplastic flow behaviour. The increase in Pluronic® F127 concentration induced a domination of elastic over viscous behaviour of the gels. The gel containing 15% of Pluronic® F127, 1% of hyaluronic acid and lyophilised 10% nanocrystal AZA suspension was considered to be an optimal formulation, since it possessed the rheological and drug delivery properties desirable for an in situ gelling platform for dermal application.

Single-Dose Pharmacokinetic Properties and Relative Bioavailability of Different Formulations of Posaconazole Oral Suspension in Healthy Volunteers.

The rate and extent of absorption of drugs belonging to Biopharmaceutics Classification System class II are rate-limited by dissolution and highly dependent on the performance of the formulated product. The purpose of the present study was to investigate the potential impact of a surfactant and the particle size of the active substance on the in vitro drug dissolution profiles and in vivo pharmacokinetics of the poorly soluble drug posaconazole. A comparative physicochemical evaluation was conducted, and 3 formulations of posaconazole oral suspension were tested in various dissolution media compared with the reference product. In addition, a comparative bioavailability study was conducted in healthy volunteers under high-fat fed conditions. Bioequivalence was assessed based on plasma concentrations of the parent drug (posaconazole) measured by a validated high-pressure liquid chromatography-tandem mass spectrometry method. The 90% confidence intervals for Cmax and AUC0-72 least-squares mean T/R ratios of all 3 posaconazole formulations were within the bioequivalence acceptance range of 80.00% to 125.00%. The study was useful in the formulation development process and demonstrated that neither surfactant type nor particle size of the active substance within the studied range affected the extent or rate of absorption of posaconazole under the tested fed conditions.

Development of a Clinically Relevant Dissolution Method for Metaxalone Immediate Release Formulations Based on an IVIVC Model.

PURPOSE: The aim of the present work was to classify metaxalone according to the Biopharmaceutics Classification System (BCS), to develop a clinically relevant dissolution method that can be used to predict the oral absorption of metaxalone and to establish an in vitro-in vivo correlation (IVIVC). METHODS: Solubility of the drug was studied in different pH media and permeability studies were performed using a Caco-2 cell model. The in vitro dissolution and in vivo disposition of metaxalone from 3 different immediate release (IR) tablet formulations were investigated using USP 2 apparatus and a single dose, four-way, crossover bioequivalence study in healthy humans along with an oral solution of the drug, respectively. An IVIVC was established by using a direct, differential based method. RESULTS: Metaxalone has been confirmed as a Class II drug according to BCS. Bioavailability studies performed in humans demonstrated that dissolution was the rate limiting step for bioavailability of the drug and one of the test products had significantly improved bioavailability compared to the marketed product Skelaxin®. An IVIVC model was developed that demonstrated an acceptable internal predictability. CONCLUSION: The IVIVC demonstrated that formulation factors play a significant role in dissolution and absorption of metaxalone. A pH 4.5 dissolution medium containing 0.5% NaCl with 0.2% SLS (USP apparatus 2 at 50 rpm) is clinically relevant to predict bioavailability of the drug and is superior to the USP method in terms of the Quality by Design (QbD) concept.

Biopharmaceutical evaluation of surface active ophthalmic excipients using in vitro and ex vivo corneal models.

The objective of this study was to systematically investigate the effects of surface active ophthalmic excipients on the corneal permeation of ophthalmic drugs using in vitro (HCE-T cell-based model) and ex vivo (freshly excised porcine cornea) models. The permeation of four ophthalmic drugs (i.e., timolol maleate, chloramphenicol, diclofenac sodium and dexamethasone) across in vitro and ex vivo corneal models was evaluated in the absence and presence of four commonly used surface active ophthalmic excipients (i.e., Polysorbate 80, Tyloxapol, Cremophor® EL and Pluronic® F68). The concentration and self-aggregation-dependent effects of surface active ophthalmic excipients on ophthalmic drug permeability were studied from the concentration region where only dissolved monomer molecules of surface active ophthalmic excipients exist, as well as the concentration region in which aggregates of variable size and dispersion are spontaneously formed. Neither the surface active ophthalmic excipients nor the ophthalmic drugs at all concentrations that were tested significantly affected the barrier properties of both corneal models, as assessed by transepithelial electrical resistance (TEER) monitoring during the permeability experiments. The lowest concentration of all investigated surface active ophthalmic excipients did not significantly affect the ophthalmic drug permeability across both of the corneal models that were used. For three ophthalmic drugs (i.e., chloramphenicol, diclofenac sodium and dexamethasone), depressed in vitro and ex vivo permeability were observed in the concentration range of either Polysorbate 80, Tyloxapol, Cremophor® EL or Pluronic® F68, at which self-aggregation is detected. The effect was the most pronounced for Cremophor® EL (1 and 2%, w/V) and was the least pronounced for Pluronic® F68 (1%, w/V). However, all surface active ophthalmic excipients over the entire concentration range that was tested did not significantly affect the in vitro and ex vivo permeability of timolol maleate, which is the most hydrophilic ophthalmic drug that was investigated. The results of the dynamic light scattering measurements point to the association of ophthalmic drugs with self-aggregates of surface active ophthalmic excipients as the potential mechanism of the observed permeability-depressing effect of surface active ophthalmic excipients. A strong and statistically significant correlation was observed between in vitro and ex vivo permeability of ophthalmic drugs in the presence of surface active ophthalmic excipients, which indicates that the observed permeability-altering effects of surface active ophthalmic excipients were comparable and were mediated by the same mechanism in both corneal models.

D-Optimal Design in the Development of Rheologically Improved In Situ Forming Ophthalmic Gel.

In situ forming ophthalmic gels need to be fine tuned considering all the biopharmaceutical challenges of the front of the eye in order to increase drug residence time at the application site resulting in its improved bioavailability and efficacy. The aim of this study was to develop in situ forming ophthalmic poloxamer P407/poloxamer P188/chitosan gel fine tuned in terms of polymer content, temperature of gelation, and viscosity. Minimizing the total polymer content while retaining the advantageous rheological properties has been achieved by means of D-optimal statistical design. The optimal in situ forming gel was selected based on minimal polymer content (P407, P188, and chitosan concentration of 14.2%, 1.7%, and 0.25% w/w, respectively), favorable rheological characteristics, and in vitro resistance to tear dilution. The optimal in situ forming gel was proved to be robust against entrapment of active pharmaceutical ingredients making it a suitable platform for ophthalmic delivery of active pharmaceutical ingredients with diverse physicochemical properties.

An overview of in vitro dissolution/release methods for novel mucosal drug delivery systems.

In vitro dissolution/release tests are an important tool in the drug product development phase as well as in its quality control and the regulatory approval process. Mucosal drug delivery systems are aimed to provide both local and systemic drug action via mucosal surfaces of the body and exhibit significant differences in formulation design, as well as in their physicochemical and release characteristics. Therefore it is not possible to devise a single test system which would be suitable for release testing of such complex dosage forms. This article is aimed to provide a comprehensive review of both compendial and noncompendial methods used for in vitro dissolution/release testing of novel mucosal drug delivery systems aimed for ocular, nasal, oromucosal, vaginal and rectal administration.

HCE-T cell-based permeability model: A well-maintained or a highly variable barrier phenotype?

The most extensively characterized human-derived cell line used in transcorneal permeability studies, in terms of passive transcellular and paracellular transport, transporter expression and metabolic enzymes, is the immortalized human corneal epithelial cell line (HCE-T). The purpose of this study is to describe the changes in the HCE-T barrier phenotype in vitro when valid cultivation conditions, in accordance with the standardized HCE-T cell-based model protocol, were employed. Evaluation of the structural and functional barrier properties revealed two different HCE-T barrier phenotypes, depending on the polycarbonate membrane pore size. Model I (pore size 0.4µm) was characterized by a multilayered HCE-T epithelium at the apical side and a weak barrier function (70-115Ω×cm2), whereas Model II (pore size 3µm) consisted of an apical lipophilic HCE-T monolayer and a basolateral lipophilic monolayer of migrated HCE-T cells that showed improved barrier properties (1700-2600Ω×cm2) compared with Model I. Considering the permeation of ophthalmic compounds and in vitro/ex vivo correlation, Model II was better able to predict transcorneal drug permeation. This study highlights the important aspects of HCE-T barrier phenotype variability that should be continuously monitored in the routine application of HCE-T cell-based models across both academic and pharmaceutical industry research laboratories.

Melatonin-loaded chitosan/Pluronic® F127 microspheres as in situ forming hydrogel: An innovative antimicrobial wound dressing.

The aim of this study was to develop melatonin-loaded chitosan based microspheres as dry powder formulation suitable for wound dressing, rapidly forming hydrogel in contact with wound exudate. Microspheres were produced by spray-drying method. Fractional factorial design was employed to elucidate the effect of formulation and process parameters (feed flow rate, inlet air temperature, chitosan concentration, chitosan/melatonin ratio and chitosan/Pluronic® F127 ratio) on the product characteristics related to process applicability (production yield, entrapment efficiency and product moisture content) and microsphere performance in biological environment (microsphere mean diameter and surface charge). Appropriate formulation and process parameters for the establishment of efficient drying process resulting in fine-tuned chitosan and chitosan/Pluronic® F127 microspheres (efficient melatonin encapsulation, small diameter positive surface charge and low moisture content) were identified. Microspheres were characterized by appropriate flowability and high rate and extent of fluid uptake. Incorporation of Pluronic® F127 in microsphere matrix resulted in high melatonin amorphization and consequent higher melatonin release rate. Entrapment of melatonin in chitosan/Pluronic® F127 microspheres has potentiated chitosan antimicrobial activity against Staphylococcus aureus and five clinical isolates S. aureus MRSA strains. Microspheres were shown to be biocompatible with skin keratinocytes and fibroblasts at concentrations relevant for antimicrobial activity against planktonic bacteria.

Evaluation of cationic nanosystems with melatonin using an eye-related bioavailability prediction model.

In this study, two types of nanosystems, namely lecithin/chitosan nanoparticles and Pluronic® F127/chitosan micelles, have been prepared and evaluated for their potential for the ocular delivery of melatonin, which is known to exert an ocular hypotensive effect. The melatonin content, particle size, zeta potential and in vitro drug release properties were studied as a function of the presence of chitosan in the nanosystem. Lecithin/chitosan nanoparticles were evaluated in terms of the mucoadhesive properties by a newly established method based on HCE-T cells, also used in in vitro biocompatibility and permeability studies. Lecithin/chitosan nanoparticles were significantly larger than the corresponding F127/chitosan micelles (mean diameter of 241.8 vs. 20.7nm, respectively) and characterised by a higher surface charge (22.7 vs. 4.3mV, respectively). The HCE-T cell viability assay did not show significant toxic effects of nanosystems investigated at the (relevant) chitosan concentration tested. The permeability study results confirmed the permeation enhancing effect of F127, which was hindered in the presence of chitosan. Lecithin/chitosan nanoparticles were characterised by prominent mucoadhesive properties and prolonged melatonin release, which was shown to control melatonin permeation across an in vitro corneal epithelial model. Such properties demonstrate the potential for nanoparticles to provide an extended pre-corneal residence time of melatonin, ensuring higher eye-related bioavailability and extended intraocular pressure reduction compared to melatonin in both aqueous and micelle solutions.

Development and validation of an in vitro release method for topical particulate delivery systems.

The aim of this study was to develop an in vitro release method for topical particulate delivery systems using the immersion cell in combination with paddle dissolution apparatus. Chitosan- and methacrylate-based microparticles with mupirocin were prepared and used as model topical delivery systems for method development. Diffusion of the drug occurred across a mixed cellulose ester membrane, which demonstrated low drug adsorption and low diffusional resistance. After an initial lag phase the amount of drug released became proportional to the square root of time. The method was discriminative toward differences in formulation, as well as toward differences in drug concentration inside the sample compartment. The method was further used to confirm sameness between batches of the same composition prepared by the same process. Variations in paddle rotation speed (25 rpm, 50 rpm, 100 rpm), paddle height (1cm, 2.5 cm) and volume of release medium (100ml, 200 ml) did not significantly alter the release rates. The method of analysis was validated according to ICH guidelines. Currently there are no compendial or standard methods and apparatuses for in vitro release testing of topical microparticles. The developed method can be a useful guide in formulation development of such delivery systems.

Toward the practical implementation of eye-related bioavailability prediction models.

The development and registration of reformulated ophthalmic products (OPs) requires eye-related bioavailability (BA) assessments. Common BA algorithms associated with other routes of application, such as the oral route, cannot be easily applied to eye-related BA testing. Here, we provide an analysis of the current literature and suggestions for further directions in the development of high-capacity, cost-effective, and highly predictive nonclinical models of eye-related drug BA. One, or a combination of these models, has the potential for routine use in research laboratories and/or the pharmaceutical industry to overcome various obstacles in reformulated OP development and registration.

In vitro vs. canine data for assessing early exposure of doxazosin base and its mesylate salt.

In this study, we evaluated the usefulness of biorelevant in vitro data and of canine data in forecasting early exposure after the administration of two phases of a BCS Class II compound, i.e., doxazosin base (DB) and its mesylate salt (DM). DB, DM, and doxazosin hydrochloride (DH) were prepared and characterized. In vitro data were collected in various media, including human aspirates. Solubilities of DB and DM in human gastric fluid were forecasted by data in fasted state simulating gastric fluid containing physiological components (FaSSGF-V2) but not by data in HCl(pH 1.8). Unlike data in FaSSGF-V2, dissolution of DB and DM tablets in HCl(pH 1.6) is rapid. Dissolution of DB tablet in FaSSGF-V2 is incomplete and conversion to DH seems to occur. Differences between DB and DM in dissolution in the small intestine are overestimated in the absence of physiological solubilizers. Using the in vitro data and previously described modeling procedures, the cumulative doxazosin profile in plasma was simulated and the 0-2h profile was used for evaluating early exposure. Individual cumulative doxazosin profiles in plasma, after single DM tablet administrations to 24 adults, were constructed from corresponding actual plasma profiles. Compared with in vitro DM data in pure aqueous buffers, DM data in biorelevant media led to better prediction of early exposure. Based on intersubject variability in early exposure after DM administration and simulated profiles, the administered phase, DB or DM, does not have a significant impact on early exposure. Partial AUCs were used for evaluating early exposure after DB and DM administration in 4 dogs. Early exposure was significantly higher after administration of DM to dogs. Dogs are not appropriate for evaluating differences in early exposure after DB and DM administrations.

Spray dried microparticles for controlled delivery of mupirocin calcium: process-tailored modulation of drug release.

Spray dried microparticles containing mupirocin calcium were designed as acrylic matrix carriers with modulated drug release for efficient local drug delivery at minimum daily dose. Particle generation in spray drying and its effect on release performance were assessed by varying drug : polymer ratios with consequently altered initial saturations. Narrow-sized microparticles with mean diameters of 1.7-2.5 µm were obtained. Properties of the generated solid dispersions were examined by X-ray, thermal (thermogravimetric analysis, modulated differential scanning calorimetry) and spectroscopic (Fourier transformed infrared, Fourier transformed Raman) methods and correlated with drug loading and in vitro release. The best control over mupirocin release was achieved for 2 : 1 (w/w) drug : polymer ratio and found to be strongly process-dependent. For a particular ratio, increased feed concentration (>4%) boosted while increased inlet temperature (≥ 100 °C) reduced drug release. Antimicrobial activity testing confirmed that encapsulated drug preserved its antibacterial effectiveness. Conclusively, spray drying was proven as a suitable method for preparing structured microparticles which can control drug release even at exceptionally high drug loadings.

A LC-MS-MS method for determination of low doxazosin concentrations in plasma after oral administration to dogs.

A rapid and sensitive reversed phase liquid chromatography- tandem mass spectrometry (LC-MS-MS) method is developed for the determination of doxazosin in canine plasma. The samples are prepared by precipitation of proteins using a mixture of methanol and acetonitrile, followed by freezing and evaporation of the organic solvent. The remaining dry residue is redissolved in mobile phase and analyzed by LC-MS-MS with positive electrospray ionization using the selected reactions monitoring mode. An XTerra MS C(18) column, a mobile phase composed of acetonitrile and 2mM ammonium acetate with gradient elution, and a flow rate of 400 microL/min are employed. The elution times for prazosin (internal standard) and doxazosin are approximately 8 and 10 min, respectively. Calibration curves are linear in the 1-20 ng/mL concentration range. Limits of detection and quantification are 0.4 ng/mL and 1.2 ng/mL, respectively. Recovery is higher than 94%. Intra- and inter-day relative standard deviations are below 7% and 8%, respectively. The method is applied for the determination of doxazosin plasma levels following a single administration of doxazosin base and doxazosin mesylate tablets (2 mg dose) to dogs in the fed state. The results indicate possible superiority of the mesylate salt on the plasma input rates of doxazosin.

Intestinal permeability and excretion into bile control the arrival of amlodipine into the systemic circulation after oral administration.

The objective of this study was to identify the factors controlling the arrival of amlodipine into the systemic circulation after oral administration in the fasting state. Dissolution data were collected with the rotating paddle and the flow-through apparatus. Caco-2 cell lines were used to assess the intestinal permeability characteristics. Actual in-vivo data were collected in 24 fasted healthy subjects after single-dose administration of the same amlodipine besylate tablet formulation used in the in-vitro dissolution studies. Regardless of the hydrodynamics, dissolution of amlodipine besylate tablets was rapid and complete in media simulating the contents of the upper gastrointestinal tract in the fasting state. Permeability of amlodipine through Caco-2 cell lines was lower than propranolol's and higher than ranitidine's, indicating that transport through the intestinal mucosa may be one process that limits the arrival into the systemic circulation. Indeed, the de-convoluted profile indicated that arrival into portal blood occurs at rates much slower than gastric emptying or dissolution rates. However, prediction of amlodipine's mean plasma profile after oral administration became possible only after additionally assuming excretion of amlodipine into the bile and a reasonable gastrointestinal residence time. Interestingly, in-vitro permeability data collected in this or in previous studies were inappropriate for simulating the mean actual plasma profile.

Influence of cyclodextrin complexation on piroxicam gel formulations.

The aim of this work was to evaluate the role of cyclodextrins in topical drug formulations. Solid piroxicam (PX) complexes with beta-cyclodextrin (beta-CD) and randomly methylated beta-cyclodextrin (RAMEB) were prepared by freeze-drying and characterized using differential scanning calorimetry (DSC), X-ray powder diffractometry (XRPD), Fourier transform infrared spectroscopy (FTIR) and near infrared spectroscopy (NIR). A physical mixture of PX and cyclodextrins was characterized by enhanced dissolution properties compared to the dissolution profile of the pure drug due to in situ complex formation. Formation of the PX-cyclodextrin inclusion complex additionally improved the drug dissolution properties. Influence of CDs on drug permeation from the water dispersion and the prepared hydroxypropyl methylcellulose (HPMC) gels was investigated. Permeation of the drug involved three consecutive processes: dissolution of the solid phase, diffusion across the swollen polymer matrix and drug permeation through the membrane. Complexation increased PX diffusion by increasing the amount of diffusible species in the donor phase. Slower drug diffusion through the HPMC matrix was the rate limiting step in the overall diffusion process. Possible interaction between the hydrophilic polymer and cyclodextrin may result in physicochemical changes, especially in a change of rheological parameters.