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44 January 2016 Tablets & Capsules with an Ultra Aqueous C18 5-micron, 150-by-4.6-mm column (Restek, Bellefonte, PA). A phosphate buffer of 0.02 molarity (M) adjusted to pH 7.5 was used as the mobile phase. The flow rate was 1 ml/min at 25°C, and UV detection was employed at 215 nanometers using a 1200 Series Infinity diode array detector (Agilent). Determining molecular weight. Size exclusion chromatography was performed against polyethylene oxide standards with narrow molecular weight distribution using a solution of 55% of 0.1-M lithium acetate and 45% ethanol in mobile phase at a flow rate of 0.8 ml/min. Two linear TSKgel GMPWxl columns (Tosoh Bioscience, King of Prussia, PA) of 10 microns and measuring 300 by 8 mm were used. Both the column and the differential refractive index detector were main- tained at 40°C. Samples at 2 mg/ml concentration were dissolved in mobile phase and filtered. The injection vol- ume was 150 microliters. Crystallinity determination of the solid dispersions. Absence of crys- tallinity was measured using differential scanning calorimetry (DSC) and pow- der x-ray diffraction (PXRD). DSC was performed using a Q2000 differential scanning calorimeter (TA Instruments) and PXRD was performed with a D8 Focus analyzer using a copper tube ele- ment and a PSD LynxEye detector (Bruker, Madison, WI). Dissolution testing. Dissolution testing of felodipine-HPMCAS (40:60) extrudate powder was carried out using USP Apparatus II in Fasted State Simulated Intestinal Fluid (FASSIF) at 6.5 pH, 37°C, and paddle speed of 200 rpm. Formulation stability. Formu- lations were placed on stability at 25°C/60% relative humidity (RH) and 40°C/75% RH conditions. Felodipine- HPMCAS extrudate powders were removed after 1 month, 3 months, and 6 months and tested for API release rate and presence of crystallinity. HME processing. HME was per- formed using an 18-mm twin-screw extruder (Leistritz, Sommerville, NJ). The collected extrudates were milled through a set of three screens, sizes 6350, 2007, and 1017, using a Comil mill (Quadro, Waterloo, ON Canada) at an impeller speed of 4,000 rpm. The milled extrudates were stored at room temperature for further analysis. The effect of extrusion temperature (between 140°C and 180°C) and shear during HME on the degradation and stability of the polymer and felodipine- polymer formulations was assessed. Physicochemical characterization of the polymer and felodipine-polymer extrudate was performed before and after extrusion. Figure 2 Melt rheology-temperature ramps of HPMCAS and HPMCAS extrudates produced at different temperatures Pure polymers MG extrudates LG extrudates HG extrudates X35009-80A LG X35009-81A MG X35009-82A HG XA1300-145A MG 140°C XA1300-145B MG 160°C XA1300-145C MG 180°C XA1300-146A LG 140°C XA1300-146B LG 160°C XA1300-146C LG 180°C XA1300-144A HG 120°C XA1300-144B HG 140°C XA1300-144C HG 160°C XA1300-144D HG 180°C 150.0 155.0 160.0 165.0 170.0 175.0 180.0 185.0 190.0 195.0 200.0 150.0 155.0 160.0 165.0 170.0 175.0 180.0 185.0 190.0 195.0 200.0 1.00E5 10000 1000 1.00E5 10000 1000 1.00E5 10000 1000 1.00E5 1000 150.0 155.0 160.0 165.0 170.0 175.0 180.0 185.0 190.0 195.0 200.0 150.0 155.0 160.0 165.0 170.0 175.0 180.0 185.0 190.0 195.0 200.0 Temperature (°C) Temperature (°C) Temperature (°C) Temperature (°C) η * (Pa.s) η * (Pa.s) η * (Pa.s) η * (Pa.s)