(T1530-07-43) Effect of Gelling Agents on the Rheological Properties of Organogels Designed for Intramammary Administration

Purpose: Bovine mastitis is a prevalent inflammatory disease caused by various pathogens, affecting dairy cows, leading to reduced milk production, increased veterinary costs, and significant economic losses worldwide. Conventional antibiotic therapies often require repeated systemic administration, raising concerns about drug residues in milk and the development of antimicrobial resistance. The efficiency of mastitis prevention during the dry period of cattle has been accepted as a clinical strategy. The inner surface of teat canal has a hydrophobic, non-mucous producing keratin lining. Thus, it is proposed that organogels, which are hydrophobic, have potentially greater wettability/spreading within the canal than aqueous gel systems, and, if formulated to offer optimum rheological properties, may also be better retained within the canal. This study aimed to systematically evaluate the effects of different gelling agents on the rheological properties of organogel formulations developed for the intramammary administration for the prevention of bovine mastitis.

Methods: Arachis oil (AO) obtained from a local store was employed as oil phases, Stearic acid (SA), aluminium monostearate (AmS) and aluminium distearate (AdS), all obtained from Sigma-aldrich and aluminium tristearate (AtS) from Thermo Scientific Chemicals were utilised as gelators. By combining AO with four different gelators (SA, AmS, AdS, and AtS), four distinct component combinations were generated. For each combination, a range of gelator concentrations was tested to systematically study their effect on gel formation and stability. These gels by heating and mixing oil phase and gelling agents at specific temperatures before cooling to room temperature. To protect the light-sensitive Miglyol during preparation and storage, manufacture and storage were prepared and stored using foil covered vessels/containers. The prepared gels were rheologically analyzed at 25 deg C using a HAAKE MARS 40 rheometer equipped with a 35mm parallel plate. This analysis involved oscillation amplitude to establish the linear viscoelastic region (LVR) and frequency sweeps for each formulation. All experiments were performed in at least triplicate. This rheological characterization was crucial to ascertain the viscoelastic properties of the gels under controlled conditions. Polarised light microscopy (PLM) was employed to examine the presence of crystalline structures within the gel samples. Samples were spread into thin layers on glass slides and covered with cover slips. Observations were conducted using a IXplore IX85 Evident polarised microscope under crossed polarisers at room temperature.

Results: This study demonstrates that the selection and concentration of gelling agents play a critical role in determining the rheological behaviour and gel structure of organogels. Among all formulations AOSA formulations uniquely had a crystalline structure (apparent from PLM), absent from the other formulations (which displayed a micellar network structure). The viscosity of all formulations increased progressively when gelator concentration increased from 5% to 7.5% and 10% w/w. At the same gelator weight concentrations, AmS formulations showed the highest viscosity, followed by AdS and AtS. In oscillation frequency sweep of all gel samples, viscosity (|η*|) decreased while frequency increased and showed shear-thinning. Increasing the concentration of SA in AOSA formulations increased, |η*|, G’ and G’’, whilst tan δ decreased, and were less than 1, evidence of gel formation. This phenomenon can be explained by network density in organogel. At the same concentration of stearate, the rheological parameters of AOAdS were lower than AOSA, resulting from differences in the nature of the organogel network.

Conclusion: All gel formulations showed shear thinning in oscillation frequency sweep, which is advantageous for product administration. The elastic nature of the organogels offer promise as platforms that will resist product removal following administration. The mechanism of gelation of stearic acid organogels differed from that associated with the aluminium stearates. Gelation of stearic acid organogels was due to the formation of a crystalline network whereas for the other gelators, a 3-D network micellar structure was apparent.

References: K. Nakano, S. Akita, and M. Yamanaka, ‘Fabrication of superhydrophobic surfaces from mixtures of aluminium distearate and fatty acids via intermediate organogel formation’, Colloid Polym. Sci., vol. 292, no. 6, pp. 1475–1478, Jun. 2014

Acknowledgements: This project was funded by the China Scholarship Council/Queen’s University Belfast (CSC-QUB) scholarship (NO. 202308060337).


The effect of gelator type on the Storage Modulus (solid lines) and Loss Tangent of arachis oil organogels.  Black line/symbol refer to Aluminium monostearate, green line/symbol refer to Aluminium distearate and blue line/symbol refer to Aluminium tristearate