Experimental Optimization of Polymer Jetting Additive Manufacturing Process Using Taguchi Design

Polymer jet printing (PJP) is a direct-write additive manufacturing process, emerging as a rapid high-resolution method particularly in the medical field for the fabrication of a wide spectrum of products, e.g., anatomical models, tissue scaffolds, implants, and prosthetics. PJP allows for non-contact multi-material deposition of functional polymer inks. The PJP process centers on simultaneous deposition of build and support photopolymer materials on a free surface, which are immediately cured in situ using a UV light source, allowing for solid-freeform fabrication. The PJP process is inherently complex, governed by a multitude of parameters as well as material-machine-process interactions, which collectively affect the functional properties of a fabricated structure. Consequently, physics-based characterization and optimization of the PJP process would be inevitable. In this study, a new test standard was forwarded for the characterization of the mechanical properties of PJP-fabricated bone structures; the standard was designed on the basis of an X-ray p-CT scan of a femur bone in addition to the ASTM D638-14 standard. Furthermore, the Taguchi L8 orthogonal array design was utilized to investigate the effects of influential PJP process parameters on the mechanical properties of the bone structures, including Young’s modulus of elasticity, tensile strength, breaking strength, and ductility. The selected process parameters (each at two levels) were: (i) print direction, (ii) resolution factor, (iii) UV light intensity, and (iv) deposition head temperature. The mechanical properties of the femur bone structures were measured using a tensile testing machine. The UV light intensity appeared as the most significant factor, influencing all the aforementioned mechanical properties, while the resolution factor was identified as an inconsequential factor. In addition, it was observed that the print direction and the head temperature significantly affected the breaking strength and the ductility, respectively. Overall, the results of this study pave the way for further investigation of the effects of the PJP parameters toward optimal fabrication of complex bone tissue scaffolds and implants with long-lasting functional characteristics.

Direct Enantiomeric Separation and Determination of Hexythiazox Enantiomers in Environment and Vegetable by Reverse-Phase High-Performance Liquid Chromatography

In the present study, the direct enantiomeric separation of hexythiazox enantiomers on Lux cellulose-1, Lux cellulose-2, Lux cellulose-3, Lux cellulose-4, Lux amylose-1 and Chirapak IC chiral columns were carefully investigated by reverse-phase high-performance liquid chromatography (RP-HPLC). Acetonitrile/water and methanol/water were used as mobile phase at a flow rate of 0.8 mL·min−1. The effects of chiral stationary phase, temperature, thermodynamic parameters, mobile phase component and mobile phase ratio on hexythiazox enantiomers separation were fully evaluated. Hexythiazox enantiomers received a baseline separation on the Lux cellulose-3 column with a maximum resolution of Rs = 2.09 (methanol/water) and Rs = 2.74 (acetonitrile/water), respectively. Partial separations were achieved on other five chiral columns. Furthermore, Lux amylose-1 and Chirapak IC had no separation ability for hexythiazox enantiomers when methanol/water was used as mobile phase. Temperature study indicated that the capacity factor (k) and resolution factor (Rs) decreased with column temperature increasing from 10 °C to 40 °C. The enthalpy (ΔH) and entropy (ΔS) involved in hexythiazox separation were also calculated and demonstrated the lower temperature contributed to better separation resolution. Moreover, the residue analytical method for hexythiazox enantiomers in the environment (soil and water) and vegetable (cucumber, cabbage and tomato) were also established with reliable accuracy and precision under reverse-phase HPLC condition. Such results provided a baseline separation method for hexythiazox enantiomers under reverse-phase conditions and contributed to an environmental and health risk assessment of hexythiazox at enantiomer level.

The application of Box-Behnken-Design in the optimization of HPLC separation of fluoroquinolones

Box-Behnken Design is a useful tool for the optimization of the chromatographic analysis. The goal of this study was to select the most significant factors that influenced the following parameters of the chromatographic separation: retention time, relative retention time, symmetry of the peaks, tailing factor, a number of theoretical plates, Foley – Dorsey parameter, resolution factor, peak width at half height. The results underwent the ANOVA test to find the statistically significant variables and interactions between them. The level of significance was for p < 0.05. The polynomial equations described quantitatively the statistically significant parameters and the interactions between them. The statistical analysis indicated both the best conditions for the separation of the compounds and the variables that were most influential for peaks’ parameters. The four-factor analysis performed for LEVO and MOXI indicated that ACN, TEA and pH are the most significant factors that influence the separation. The analysis for the pair CIPRO and LEVO required six factors. The statistical analysis proved that the most significant factors are ACN, MeOH and TEA. In the separation of these two compounds on the HPLC column, the interaction ACN × MeOH was also significant.

STABILITY INDICATING RP-HPLC METHOD FOR ESTIMATION OF REPAGLINIDE IN RABBIT PLASMA

Objective: A simple, selective and sensitive reverse-phase high-performance liquid chromatography (RP-HPLC) method to estimate repaglinide (REP) in rabbit plasma using rabeprazole (RAB) as an internal standard was developed and validated for various qualifications. Methods: The chromatographic separation was performed on C18 (2) analytical column (5 μ, 250×4.6 mm) using acetonitrile: 0.05% trifluoroacetic acid in water (55:45, v/v) as mobile phase at the flow rate of 1 ml/min. Validation of the analytical method was performed as per ICH guidelines. Results: The retention times of REP and RAB were found at ~4.3 and 5.1 min respectively, with adequate system suitability parameters (theoretical plates ≥3619, tailing factor ≤1.38, resolution factor 2.37). The method has linearity over a concentration range of 10 to 1000 ng/ml (r2=0.9987). The results of accuracy (≥98.17%), intra-, inter-day precision (≤2.9%), recovery (101.21±2.09%) and process efficiency (99.77±3.74%) found satisfactory with no matrix effect. The analyte in samples were found stable up to 6 h, 3 freeze-thaw cycles and not more than 2 mo corresponding to bench-top, short and long term stability studies respectively. Conclusion: The developed RP-HPLC method for estimation of REP in rabbit plasma was developed. The method was found to be rapid, cost-effective and accurate to estimate the REP from the sample matrix. The method can be a most useful tool for in vivo study of REP in the rabbit.

Methodology for Porphyrin Isolation by High-Performance Countercurrent Chromatography

Countercurrent chromatography is a versatile technique for the isolation of a wide variety of plant substances. However, little attention has been devoted to the application of this technique for the isolation of porphyrins. This class of compounds are of great importance in the medical area and in photocatalysis due to their heterocyclic structure, composed of four modified pyrrol subunits interconnected on their α carbon atoms by methinic bridges. The methanol extract of Gallesia integrifolia was partitioned using different solvents; the dichloromethane fraction was then submitted to countercurrent chromatography. The solvent system composed of n-hexane, ethyl acetate, methanol, and water (1:2.5:2.5:1) was chosen to perform the chromatographic analysis due to the enhanced solubility and the best distribution coefficients of the target compounds. Two porphyrins were isolated by this method and identified as 132-hydroxypheophorbide a methyl ester and pheophorbide a, methyl ester. The solvent system proposed provided good distribution coefficients for both substances (1.27 and 1.87, respectively), and a high resolution factor.

Microemulsion Liquid Chromatographic Method for Simultaneous Determination of Simvastatin and Ezetimibe in Their Combined Dosage Forms

A rapid HPLC procedure using a microemulsion as an eluent was developed and validated for analytical quality control of antihyperlipidemic mixture containing simvastatin (SIM) and ezetimibe (EZT) in their pharmaceutical preparations. The separation was performed on a column packed with cyano bonded stationary phase adopting UV detection at 238 nm using a flow rate of 1 mL/min. The optimized microemulsion mobile phase consisted of 0.2 M sodium dodecyl sulphate, 1% octanol, 10% n-propanol, and 0.3% triethylamine in 0.02 M phosphoric acid at pH 5.0. The developed method was validated in terms of specificity, linearity, lower limit of quantification (LOQ), lower limit of detection (LOD), precision, and accuracy. The proposed method is rapid (8.5 min), reproducible (RSD < 2.0%) and achieves satisfactory resolution between SIM and EZT (resolution factor = 2.57). The mean recoveries of the analytes in pharmaceutical preparations were in agreement with those obtained from a reference method, as revealed by statistical analysis of the obtained results using Student’st-test and the variance ratioF-test.

Determination Of Curcumin In Capsule Containing Curcuma xanthorrhiza Roxb. Extracts By High Performance Liquid Chromatography

Curcumin, the major yellow pigment of Curcuma sp. has several interesting biological activities, such as anticarcinogenecity, antiinflamatory, and antioxidant. Curcumin naturally occurs as major compound in Curcuminoid substance beside its derivatives, i.e. Bisdemethoxycurcumin (BDC) and Demethoxycurcumin (DC). Quantitative analysis of Curcumin is difficult to carry out unless prior to completely resolved Curcumin from BDC and DC. A good resolution, reproducible, and accurate method for determination Curcumin in pharmaceutical product (capsule formed) by HPLC has been carry out. Using C18 colurnn and mixture of Acetonitrile: Acetic Acid glacial 1% (45:55 v/v) as eluent, BDC, DC, and Curcumin were retained with retention time of 10.79, 12.29, and 13.91 minutes, respectively. Curcumin was simultaneously separated from BDC or DC. The resolution factor (Rs) between Curcumin and DC was 1.73. Good linear relationship (r = 0.9997, Vxo = 0.99%) between peak area and concentrations was found at range of the Curcumin concentration used, i.e. 23.56-62.83 µg/mL. Curcumin recoveries were (93.60-118.17)% with the coefficient of variation (CV) 6.99%. Curcumin content in each capsule sample was found to be (8.89±0.06) mg. It showed that samples contained higher amount of Curcumin than that claimed on its label, 5 mg.