Exponent lite

A universal testing device (Testometric M-500, Rochdale, Lancashire, UK) was used to measure tensile strength at the breakpoint using 3 samples cut from each film of 1.5 × 4 cm to fit into the equipment. Tensile strength was determined at 24 °C in the tension state. The instrument consisted of two tensile grips, the lower one fixed and the upper one movable. The insert formulations were positioned between two clamps. The upper arm pulled the polymeric films at a 1 mm/s rate until they broke. Tensile strength (mPa) was determined by using Exponent Lite version 6.1.4.0 (Stable Micro-System Ltd., Surrey, UK) [29 (link)].

Blends of light mineral oil and white petroleum were made by adding one, two, three, four, or five parts light mineral oil (0.84 g/mL at 25 °C; Sigma-Aldrich) to 10 parts white petroleum blends (Vaseline; Sigma-Aldrich). The light mineral oil was mixed into the white petroleum on a black pill tile and sheered together using two 30 cm spatulas until an even consistency was obtained. To compare these to commercially available ophthalmic ointments, 1% (w/w) chloramphenicol ophthalmic ointment (GoldenEye, Typharm Limited) was used. Texture analysis of semi-solid samples used 10 ml wide-necked glass vials placed on a Stable Microsystems TA.XTplus Texture Analyser testing stage and clamped into position. The probe tested the sample twice, automatically, before the sample was removed, the surface flattened, and tested again. Each sample was thus tested five times. Stable Microsystems Exponent Lite (version 6.1.4.0) software was used to obtain data and to combine each of the five replicates into representative plots.

Textural analysis was used only in CCM and PP, as their texture allowed this type of analysis. Samples were measured in the original packaging by penetration test utilising the TA.XTplus texture analyser (Stable Micro Systems Ltd., Godalming, UK) with a plate aluminium probe (20 mm diameter). A software Exponent Lite (version 4.0.13.0; Stable Micro Systems Ltd., Godalming, UK) was used for data collection and expression as force–time curves. The following parameters were set up: 50% strain, trigger force 5 g, deformation rate 2 mm/s and temperature 25 ± 1 °C. The hardness values were calculated as the maximum force (N) observed during the penetration.