Response Surface Diagrams Research Articles

Process Control of Injection Molding Based on Multiscale Visualization Methodology - A Case Study

Multiscale visualization approaches are proposed to efficiently assist designers not familiar with statistical mathematics in determining the optimal process parameter schemes for achieving desired part quality in injection molding, based on which the parameters’ relative importance to part quality and their influence on either single quality index or comprehensive part quality can be visually described by the map of the sum of squared deviations, response surface diagram and distribution map of comprehensive part quality. The proposed visualization approaches are universal for analyzing the effects of process parameters on the quality of any injection-molded plastic parts although the mobile phone cover is utilized as an example in the presentation of our work.

Preparation, characterization and relative bioavailability of oral elemene o/w microemulsion

The objective was to develop an elemene oil/water (o/w) microemulsion and evaluate its characteristics and oral relative bioavailability in rats. Elemene was used as the oil phase and drug, polysorbate 80 as a surfactant along with ethanol, propylene glycol, and glycerol as the cosurfactants. The microemulsion was prepared by mixing method, or ultrasonication method in an ultrasonic bath. Its three-dimensional response surface diagram was drawn by Mathcad software. The microemulsion was characterized by visual observation, cross-polarized microscopy, size, zeta potential, acidity, viscosity, and surface tension measurement. The drug content and entrapment efficiency were determined by ultra fast liquid chromatography (UFLC) and liquid surface method. Blood was drawn from rats at different time points after oral administration of an elemene microemulsion or a commercial elemene emulsion for measurement of the drug in plasma by UFLC to establish the pharmacokinetic parameters and relative bioavailability. The elemene microemulsion as a clarified and isotropic system containing 1% elemene (w/v), 5% ethanol (v/v), 15% propylene glycol (v/v), 15% glycerol (v/v), and 5% polysorbate 80 (w/v), was characterized as (57.7 ± 2.8) nm in size, 0.485 ± 0.032 in polydispersity index, (3.2 ± 0.4) mv in zeta potential, (5.19 ± 0.08) in pH, 6 mpa·s in viscosity, (31.8 ± 0.3) mN·m(-1) in surface tension, (8.273 ± 0.018) mg·mL(-1) in content of β-elemene, and (99.81 ± 0.24)% in average entrapment efficiency. The area under the concentration-time curves from 0 h to 24 h (AUC(0→24h)) of the elemene microemulsion and commercial elemene emulsion were integrated to be 3.092 mg·h·L(-1) and 1.896 mg·h·L(-1) respectively, yielding a relative bioavailability of 163.1%. The present study demonstrates the elemene microemulsion as a new formulation with ease of preparation, high entrapment efficiency, excellent clarity, good stability, and improved bioavailability.

Response of MCF-7 human breast cancer cells to some binary mixtures of oestrogenic compounds in-vitro

The effects of simultaneous administration of some binary mixtures of seven natural and synthetic oestrogenic substances (17beta-estradiol, estrone, bisphenol A, butylbenzyl phthalate, endosulfan, methoxychlor and pentachlorophenol) on the cellular proliferation of human breast cancer MCF-7 cells in-vitro (a modified E-screen assay) have been measured. To assess the presence or absence of interactions of the two agents, the data were analysed on the basis of a graphical method in which the types and extents of interactions were described by response-surface diagrams. Of the nine combinations of the agents examined, synergistic interaction was evident for the combination of 17beta-estradiol and bisphenol A, whereas the remaining eight combinations were weakly synergistic, additive and/or weakly antagonistic in the dose-range tested.

High‐throughput screening techniques for rapid PEG‐based precipitation of IgG4 mAb from clarified cell culture supernatant

Locating optimal protein precipitation conditions for complex biological feed materials is problematic. This article describes the application of a series of high-throughput platforms for the rapid identification and selection of conditions for the precipitation of an IgG(4) monoclonal antibody (mAb) from a complex feedstock using only microliter quantities of material. The approach uses 96-microwell filter plates combined with high-throughput analytical methods and a method for well volume determination for product quantification. The low material, time and resource requirements facilitated the use of a full factorial Design of Experiments (DoE) for the rapid investigation into how critical parameters impact the IgG(4) precipitation. To aid the DoE, a set of preliminary range-finding studies were conducted first. Data collected through this approach describing Polyethylene Glycol (PEG) precipitation of the IgG(4) as a function of mAb concentration, precipitant concentration, and pH are presented. Response surface diagrams were used to explore interactions between parameters and to inform selection of the most favorable conditions for maximum yield and purification. PEG concentrations required for maximum yield and purity were dependant on the IgG(4) concentration; however, concentrations of 14 to 20% w/v, pH 6.5, gave optimal levels of yield and purity. Application of the high-throughput approach enabled 1,155 conditions to be examined with less than 1 g of material. The level of insights gained over such a short time frame is indicative of the power of microwell experimentation in allowing the rapid identification of appropriate processing conditions for key bioprocess operations.

Off-state viscosity and yield stress optimization of magneto-rheological fluids: A mixture design of experiments approach

The purpose of this paper was to optimize the blend ratio of ternary mixtures of carbonyl iron powders with different modes to get the minimum "off-state" viscosity as well as to maximize the yield stress under field in MRF. The Mixture Design of Experiments methodology was here employed considering the powders 'A' (coarse); 'B' (medium); and 'C' (fine) as mixture components and the viscosity and yield stress as mixture responses. The minimum viscosity was found over the A-C triangle edge of a response surface diagram. On the other hand, the maximum yield stress was found on the C corner (no blend). The results show the power and robustness of DOE methodology to optimize and to tailor MRF performance, according to the desired application.

LC-UV/MS characterization and DOE optimization of the iodinated peptide obestatin

The aim of this study was to investigate the direct iodination of the recently discovered peptide obestatin by LC-UV/ESI ion trap MS analysis. The influence of selected reaction parameters on obestatin iodination by chloramine-T, Iodo-Gen ® and lactoperoxidase was investigated by experimental design. Different responses, i.e. species percentage and yield, peptide recovery and iodination yield were evaluated. Mono-up till tetra-iodinated species are possible depending on the reaction conditions with electrophilic substitutions occurring at Tyr 16 and His 19 as confirmed by LC/MS/MS. The two possible mono-iodinated obestatin isomers, i.e. [I 1-Tyr 16]-obestatin and [I 1-His 19]-obestatin, could be chromatographically separated. Several significant main and quadratic effects, and interaction of factors were observed from which optimum conditions for a specific response could be derived. The highest impact on the response surface diagrams was overall attributed to the amount of iodide added. Synthesis methods were compared relative to the different response factors: lactoperoxidase was found to be the overall most robust iodination technique, and also gave the highest mono-iodinated species yield. The applicability of our research was demonstrated by non-carrier-added 125I-radioiodination. To our knowledge, this is the first time an LC separation of mono-iodinated peptide isomers has been reported.

Micronization of Insulin by High Pressure Homogenization

The aim of this study was to establish the high pressure homogenization of proteins in non-aqueous suspension as an alternative method for classical micronization strategies and to investigate the effect of high pressure on protein stability and bioactivity. The influence of drug loading, homogenization pressure and cycles on particle size reduction was investigated by experimental design using a Box Behnken matrix with insulin as a model compound. Particle size measurements were performed by laser light scattering. Protein stability was investigated by HPLC and HPLC-MS analysis and the bioactivity of insulin was tested in a chondrocyte proliferation assay. For investigations into the effect of temperature on protein stability, insulin was micronized in molten lipid at 75 degrees C in one cycle at 1,000 bar. Within one homogenization cycle at 1,500 bar, the particle size of insulin could be reduced from 15.8 to 7.3 microm, six cycles resulted in a particle size of 3.7 microm d(0.5) (50% of the particles are smaller than the indicated value). Evaluation of the response surface diagram revealed that the homogenization pressure had the highest impact on micronization efficiency, followed by the number of homogenization cycles. Protein stability was maintained during the micronization process as well as bioactivity. Micronization at elevated temperature (75 degrees C) had no effect on protein stability. High pressure homogenization of protein suspensions can be used as an alternative method for the micronization of proteins without affecting protein stability or bioactivity.

Chemometric Optimization of a RP‐HPLC Method for the Simultaneous Analysis of Abacavir, Lamivudine, and Zidovudine in Tablets

A method has been developed and validated for the separation of abacavir, lamivudine, and zidovudine by high‐performance liquid chromatography (HPLC) on a C18 column with uv detection at 270 nm. The optimal conditions for separation were determined with the aid of a “critical resolution map” technique using the program DryLab®. The effect of simultaneously varying the pH and proportion of methanol in the mobile phase was studied to optimize the separation. A response surface diagram was used to study the interaction between factors determining the separation. The mobile phase composition that provides an optimal resolution of components in an acceptable elution time is water:methanol (60:40 v/v) + 0.2% TEA and pH = 3.20 (pH adjusted with H3PO4). A method is applied for the analysis of Trizivir® tablets (Glaxo Wellcome, UK). The powdered tablets were extracted with methanol:water (50:50 v/v) mixture and after addition of stavudine as an internal standard subjected to HPLC analysis and assayed by comparison of analyte to internal standard peak areas to concentration ratios.

The use of a response surface methodology on HPLC analysis of methyldopa, amiloride and hydrochlorothiazide in tablets.

A multifactor optimisation technique is successfully applied to develop a new HPLC method in which methyldopa, hydrochlorothiazide and amiloride were analysed and determined on a C18 column with detection at 286 nm. The optimal conditions of HPLC separation were determined with the aid of the response surface diagram -- 'window diagram'. The effect of simultaneously varying the pH, proportion aqueous acetic acidum and methanol in the mobile phase were studied to optimise the separation. The mobile phase composition that provides an acceptable resolution methyldopa, hydrochlorothiazide and amiloride in a short elution time is water--methanol (75:25) and pH 3.60. The k' values for methyldopa, hydrochlorothiazide and amiloride after optimisation were 1.40, 2.50 and 5.33, respectively. Relative retention (alpha) for ratio hydrochlorothiazide/methyldopa and amiloride/hydrochlorothiazide were 1.767 and 2.159, respectively. Correlation coefficients of the calibration curves for all analytes were greater than 0.995 and the R.S.D. values for the slope and the intercept with respect to the linearity were less than 2%. A method is applied for the quantitative analysis of Alatan tablets (Lek-Ljubljana). The powdered tablets are extracted with methanol, containing caffeine as the internal standard and assayed by comparison of peak areas after liquid chromatography. The high recovery (for all analytes about 100%) and the low R.S.D. (<2%) confirm good precision and reproducibility of the chromatographic method.

Statistical optimization of a reversed-phase liquid chromatographic method for the analysis of amiloride and hydrochlorothiazide in tablets

A method has been developed for the separation of hydrochlorothiazide and amiloride by high-performance liquid chromatographic (HPLC) method on a C 18 column with detection at 280 nm. The optimal conditions of separation were determined with the aid of ‘window diagram’ technique of Laub and Purnell. The effect of simultaneously varying the pH, proportion aqueous acetic acid and methanol in the mobile phase were studied to optimize the separation. A response surface diagram was used to optimize the experimental conditions for the separation. The mobile phase composition that provides an acceptable resolution hydrochlorothiazide and amiloride in a short elution time is water:methanol (60:40) and pH 3.2 (pH adjusted to 3.2 with CH 3COOH). A method is applied for the quantitative analysis of Moduretic® tablets (Merck Sharp & Dokme International). The powdered tablets are extracted with methanol, containing caffeine as the internal standard, and assayed by comparison of peak areas after liquid chromatography.

Deriving and Applying Response Surface Diagrams for Evaluating Climate Change Impacts on Crop Production

This paper presents the method to develop response surface diagrams (RSD) suitable to evaluate the impacts of climate change on potential crop production and crop area. The diagrams depict the response of different agricultural crops to average long-term changes in ambient temperature and precipitation on a country basis. They take into account the spatial and seasonal variability of climate, and differences in the climate response of important crops. RSDs for Germany and the Democratic Republic of Congo illustrate that countries and crop types differ greatly in their sensitivity to unit changes in long-term average climate. In comparing the area-weighted RSDs for Germany and Democratic Republic of Congo, it was found that the potential production in Germany of a weighted aggregation of crops is mainly sensitive to changes in temperature, whereas the potential crop production in the Democratic Republic of Congo mainly responds to changes in precipitation (over the specified ranges of climate variables). The RSDs can provide a visual overview of these varying sensitivities, and are a convenient and simple-to-understand method to summarize crop responses to climate change in a particular country.

Development of extruded snacks using jatobá ( Hymenaea stigonocarpa Mart) flour and cassava starch blends

The use of the jatoba trees (Hymenaea stigonocarpa Mart) by the timber industry poses an ecological problem in Brazil. The objective of this research was to investigate the use of jatoba flour for the production of snacks by the thermoplastic extrusion of a composite flour consisting of jatoba and cassava starch. Chemical analysis showed that the jatoba fruit provides high-fibre flour (486 g kg−1) with 66 g kg−1 protein, and 398 and 88 g kg−1 of insoluble and soluble fibre, respectively. Such flour is of potential use for the production of high-fibre snacks, allowing for the economical exploitation of the jatoba while preserving the tree. Composite flours with jatoba flour and cassava starch mixtures (150: 850, 300: 700, 450: 550), conditioned to moisture levels of 170, 200 and 230 g kg−1 were processed in a Brabender single-screw extruder. The extrusion conditions were 150 rpm screw speed, 4 mm die diameter and 125, 150 and 175°C of barrel temperatures. The snacks produced were evaluated as to their sensory characteristics and response surface methodology was used to optimise the extrusion process. Response surface and contour diagrams revealed that all mixtures conditioned to 170 g kg−1 moisture and extruded at 150°C produced snacks of acceptable quality, higher levels of jatoba flour leading to significant quality losses with respect to sensory characteristics. © 1998 Society of Chemical Industry.

Experimental Evaluation of Flow Formability of Sheet Metals for Armament Applications

Flow forming is a promising process for the manufacture of certain critical armament components. This paper deals with the statistical design of an experiment carried out by the authors while flow forming different sheet metals employing various combinations of controlling variables in order to arrive at a functional relationship between flow formability (R/sub f/} and controlling variables. The relationship, established has been tested for its adequacy by proper analysis of variance (ANOVA). Response surface diagrams for a given R/sub f/ in the case of three specific materials are presented.

Optimized preparation of poly d,l (lactic-glycolic) microspheres and nanoparticles for oral administration

A rotatable central composite design (RCCD) was applied to optimize the preparation of cyclosporine-loaded poly D,L (lactide-glycolide) (PLAGA) nanoparticles (NP) and microspheres (MS) by solvent displacement and solvent evaporation techniques, respectively. The joint influence of needle gauge, polymer amount and the injection rates on the mean particle size, relative standard deviation (RSD), yield and drug encapsulation percentage in NP were evaluated. With regards to MS, the polymer amount and the stirring rate were evaluated. Scan electron microscopy of MS and NP showed spherical particles with a dense polymeric network in the first case. From the statistical analysis of data polynomial equations were generated. The mean particle size ranged from 50 to 150 nm for NP and from 1.5 to 30/pm for MS. Smallest nanoparticles (46 nm) were obtained by using the lowest polymer amounts, the highest injection rates and the lowest needle gauges ( r 2 = 0.9443). Under these conditions the drug entrapment percentage was maximum (85.2%), suggesting the drug might be entrapped and adsorbed on the nanoparticle surface. The relative standard deviation was only affected by the polymer amount ( r 2 = 0.8034) and the yield rose with the amount of PLAGA ( r 2= 0.9016). A very important increase in particle size ( r 2 = 0.9855), relative standard deviation ( r 2 = 0.9353) and encapsulation percentage ( r 2 = 0.9669 ) were observed for MS by decreasing emulsification stirring rates and increasing polymer amounts, the stirring rate being the most significant independent variable ( α < 0.0001) in all cases. The highest experimental encapsulation value (97.69 ± 0.78%) correspond to samples prepared from 150 mg of polymer and a global stirring rate of 2000 rpm. By using response surface diagrams and the mathematical models proposed, it is possible to easily deduce experimental conditions to prepare NP and MS with the desired properties.

Experimental design applied to a spectrophotometric study of a diclofenac sodium–copper(II) complex

An extraction method with spectrophotometric detection for the determination of diclofenac sodium, using copper(II) acetate as the analytical reagent has been established, with the aid of two statistical optimization procedures. A three-variable, two-level full factorial design was used to estimate the effects of varying the pH, ionic strength (I) and concentration of copper(II) acetate in the reaction mixture, in addition to the interaction between them. A response surface diagram was used to optimize the experimental conditions for the complex formation and extraction. It was found that diclofenac sodium reacts with copper(II) acetate, in the pH range 4.4–6.4, to form a green chloroform-extractable complex with a molar ratio of diclofenac sodium to CuII of 2:1 and with a maximum absorbance at 480 nm. The relative stability constant of the complex, at the optimum pH of 6.0 and I of 0.18 mol dm–3, was found to be 106.8. Good agreement with Beer's law was found for diclofenac sodium concentrations of up to 6.29 mmol dm–3, calculated for the final solution, with a detection limit of 72 µg ml–1. The nominal recovery of diclofenac sodium was 98.5%(n= 10).

Joint effects of monomer and stabilizer concentrations on physico-chemical characteristics of poly(butyl 2-cyanoacrylate) nanoparticles

A rotatable central composite design was applied to the formulation of poly(butyl 2-cyanoacrylate) nanoparticles with the aim of modifying some physico-chemical properties of these carriers in a controlled way. The joint effect of stabilizer concentration and monomer concentration on the mean particle size, on the electrophoretic mobility and on the polymer molecular weight has been investigated. The results demonstrate that the particle size is only dependent on the stabilizer concentration, nevertheless the electrophoretic mobility and the molecular weight distribution were affected simultaneously by the monomer and the stabilizer concentrations. Moreover, using the response surface diagrams it is possible to deduce the experimental conditions to design particles with the desired properties. Finally, the degradation rates for two different molecular weight formulations were compared, showing the relevance of this property.