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Brittany Coats, McKenna MARIE Drysdale, Hee-Kyoung Lee, Barbara M Wirostko; Mechanical Properties of Four Carboxymethylated Hyaluronic Acid Hydrogel Polymer Formulations. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):4167.
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Bioerodable hydrogel polymers are a promising topical drug delivery system because they are biocompatible, diffuse drug easily, and improve retention time. Toward this end, Jade Therapeutics is developing a proprietary biodegradable cross-linked, thiolated carboxymethylated hyaluronic acid (CMHA)-based hydrogel film for topical ocular applications. To assess the structural integrity of the film and establish baselines for future degradation studies, four different cross-linked CMHA formulations were evaluated in uniaxial stress relaxation and pull-to-failure tests before and after ethylene oxide sterilization.
Films were fabricated by varying the HA-based polymers (thiolated CMHA with or without gelatin) and cross-linkers (Poly(ethyleneglycol) diacrylate (PEGDA) or glutathione disulfide (GSSG)). The polymerized gel was dried at room temperature overnight. Dried strips (6 x 10 mm) were hydrated in phosphate buffered saline (PBS) for 24 hrs and dimensioned using an optical stereomicroscope. Hydrated specimens were mounted in custom clamps located in a PBS chamber attached to a material test system (Model 5943, Instron) and a 500 gram submersible load cell (LSB210, Futek). The stress relaxation protocol was applied at a rate of 1.0 in/min up to 9% strain in increments of 0.5% strain (Fig. 1). Pull-to-failure tests were performed at 1.0 in/min. All measured load and displacement data were converted to stress and strain. Elastic modulus, relaxation modulus, and ultimate stress were extracted.
All four films exhibited non-linear stress-strain behavior. The CMHA-PEGDA film had the largest hydrated thickness (0.281±0.092 mm), the lowest relaxation modulus (35.4±3.2 kPa, Fig. 2) and lowest ultimate stress (26.2±19.9 kPa). Sterilization significantly increased the relaxation modulus and ultimate stress in all formulations, but following sterilization CMHA-PEGDA was the only formulation that remained comparable to standard soft contact lens properties.
CMHA-PEGDA was the most promising formulation in terms of both its comfort as a topical ocular film (i.e., low relaxation modulus) and structural integrity.
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