HPD Research Day | February 16, 2018

30 Atrium – Poster 3 12:15-1:15 p.m. Effect of Crosslink Density and Concentration on Rheological Properties of Crosslinked Acrylic Acid Homopolymers Rand H. Ahmad, Ph.D. in Pharmacy Student, College of Pharmacy, Nova Southeastern University Samaneh Alaei, Ph.D. in Pharmacy Student, College of Pharmacy, Nova Southeastern University Hamid Omidian, Ph.D., Professor, College of Pharmacy, Nova Southeastern University Objective. In this study, using gel strength analysis we measured the effect of polymer crosslink density and its concentration on rheological behavior of poly(acrylic acid) gelling agents in aqueous solutions. Background. Crosslinked acrylic acid homopolymers are commercially available in different types and grades suitable for wide range of pharmaceutical applications, in particular in semi-solid dosage forms. At pH 5-8, these polymers thicken, forming viscous gels in aqueous or hydroalcoholic solutions. Although the effect of structural and environmental factors have widely been reported in terms of solution viscosity, the gel strength analysis was found to be very informative in characterizing flow behavior of such formulations. Methods. Different polymer (lightly and highly crosslinked) solutions were prepared in water at 0.1%, 0.3%, 0.5%, 0.7%, and 1.0%w/w concentrations. The pH of the solutions was adjusted to 5-6, and the gel strength was measured using a Texture Analyzer before and after neutralization. Results. The gel strength of the neutralized lightly and highly crosslinked polymer solutions at 0.1- 1.0% w/w concentrations ranged from 28-56 mN, and 18-196 mN, respectively. Conclusion. Degree of crosslinking affected the rigidity and uncoiling behavior of the polymer in solutions. Lightly crosslinked structures are less rigid and become easily uncoiled in solutions, resulting in greater interaction with the solvent and thus higher gel strength at low concentrations. On the other hand, highly crosslinked structures, despite their lower uncoiling and solvent interaction, provide higher gel strengths when used at higher polymer concentrations. Grants. This study was supported by NSU Grant 335081. Atrium – Poster 4 12:15-1:15 p.m. Herschel-Bulkley Model Describing the Rheology of Polyacrylates Superabsorbent Homopolymers Samaneh Alaei, Ph.D. in Pharmacy Student, College of Pharmacy, Nova Southeastern University Rand Ahmad, Ph.D. in Pharmacy Student, College of Pharmacy, Nova Southeastern University Hamid Omidian, Ph.D., Professor, College of Pharmacy, Nova Southeastern University Objective. The objective was to investigate the fitness of Newtonian and non-Newtonian rheological models in characterizing the rheological behavior of two grades of polyacrylic acid homopolymers commonly used in the preparation of semi-solid pharmaceutical dosage forms. Background. Bingham model is relevant to Newtonian flow. Herschel-Bulkley and Casson are relevant to non-Newtonian behavior, with the latter being pertinent to suspension systems. All the three models are used to describe materials with yield stress. In this study, we examined the rheological behavior of two polyacrylate homopolymers differing in their degrees of crosslinking. Methods. The samples were prepared in water at 0.1-1.0%w/w concentration range and neutralized by NaOH (pH 5.0-6.0). Cone and plate rheometer (spindle 2.4cm, 0.5mL sample) was used to generate the shear stress/shear rate and viscosity/shear rate rheograms. The confidence of fit (COF) to the three models was determined using Rheolac V3.3 software. Results. Herschel-Bulkley model fitted all concentrations of carbomer samples with COF exceeding 99%. Confidence of fit for Bingham and Casson models did not exceed 88% and 97%, respectively. Viscosity/shear rate profiles demonstrated shear thinning behavior and shear stress/shear rate profiles showed yield stress values ranging from 36-1703 D/cm 2 and 188-947 D/cm 2 for the highly crosslinked and lightly-crosslinked carbomers, respectively. Conclusion. Hydrophilic non-Newtonian polyacrylate homopolymers, possessing yield stress are best described by Herschel-Bulkley model, where the material is in solution, exhibiting shear thinning flow after the yield value is surpassed. Grants. This study was supported by NSU Grant 335081.