(T1030-04-20) Impact of Freeze-Thaw Cycles on Kolliphor P407's Thermogelling and Mucoadhesion

Purpose: The poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) triblock copolymers, known as poloxamer (Pluronic®), are unique thermoresponsive amphiphilic polymers with many pharmaceutical and biomedical applications such as the development of drug delivery systems[1]. Though widely exploited in the healthcare sector, their use in clinical settings has been limited because they may either gel above or below the body temperature or possess poor mechanical properties [2]. Freeze-thaw cycle experiments with poloxamer solutions are vital in the fields of pharmaceuticals, biomaterials, and biotechnology. These experiments subject poloxamer solutions to repeated freezing and thawing, replicating conditions faced during the transportation, storage, and administration of biotechnological products, pharmaceuticals, or during cryopreservation.

Methods: Different concentrations of Kolliphor P 407 Geismer were prepared using the cold method with deionized water and stored overnight in a refrigerator. Each 30 mL concentration was gently heated in a water bath with a magnetic stirrer, and the temperature at which the magnetic stirrer stopped was recorded as the gelation temperature. The gels were then refrigerated until they turned liquid, reheated through multiple cycles, and their gelation temperatures were investigated. Additionally, the 17.5% gels were examined for their mechanical properties using a Brookfield CT3-1000 Texture Analyzer equipped with an acrylic probe, a 1 Kg loading cell, and a TA-RT Kit.

Results: For 20% Kolliphor solutions, the initial gelation temperature was 30.3 ± 0.1°C, which slightly decreased to 29.4 ± 0.1°C by the 5th cycle and to 29.0 ± 0.1°C by the 10th cycle. For 17.5% Kolliphor P 407 solutions, the gelation temperature started at 31.8 ± 0.1°C, decreasing to 31.0 ± 0.1°C for the 5th cycle and 29.6 ± 0.1°C for the 10th cycle. The 15% Kolliphor P 407 solutions had an initial gelation temperature of 33.2 ± 0.1°C, which decreased to 32.4 ± 0.1°C by the 5th cycle and to 31.9 ± 0.1°C by the 10th cycle. For 12.5% Kolliphor P 407 solutions, the gelation temperature began at 33.7 ± 0.1°C and decreased to 33.0 ± 0.1°C by the 5th cycle and to 32.7 ± 0.1°C by the 10th cycle. Regarding the hardness of the 17.5% Kolliphor solutions, the initial hardness recorded was 1.052 ± 0.002 N, increasing to 1.167 ± 0.002 N and 1.206 ± 0.002 N for the first and second hardness cycles of the 5th cycle, respectively, and to 1.323 ± 0.002 N and 1.342 ± 0.002 N for the first and second hardness cycles of the 10th cycle, respectively. The force of adhesion and adhesiveness for the 17.5% Kolliphor solutions were initially 0.812 ± 0.02 N and 4.30 ± 0.01 mJ, respectively. These values increased to 0.941 ± 0.01 N and 4.37 ± 0.02 mJ for the 5th cycle and to 1.072 ± 0.02 N and 4.53 ± 0.01 mJ for the 10th cycle. The resilience remained constant at 0.04 ± 0.00 for all cycles. The method employed in this study involved preparing various concentrations of Kolliphor P 407 Geismer solutions using the cold method, followed by repeated sol-gel cycling to investigate gelation temperatures and mechanical properties. The results demonstrated a consistent decrease in gelation temperature across all concentrations with increased cycling, indicating changes in the polymer network that affect its thermogelation properties. Notably, higher concentrations exhibited a more pronounced decrease in gelation temperature, reflecting a stronger impact of sol-gel transitions on these formulations. Additionally, the mechanical properties of the 17.5% Kolliphor solutions showed a significant increase in hardness with repeated cycles, suggesting that the gel matrix undergoes structural changes leading to enhanced rigidity. The adhesive properties also improved, with both the adhesive force and adhesiveness showing incremental increases across cycles, while resilience remained constant. These observations suggest that repeated sol-gel transitions enhance the mechanical strength and adhesive capabilities of Kolliphor P 407 solutions, which is essential for applications requiring robust and consistent gel performance.

Conclusion: The data indicates that the gelation temperature of poloxamer solutions decreases with the number of sol-gel cycles, with this effect being more pronounced in higher-concentration formulations. This suggests that the polymer network undergoes changes that affect its thermogelation properties. Understanding these changes is crucial for optimizing formulations for applications where repeated sol-gel transitions are expected, ensuring consistent performance and stability. The hardness data demonstrates that the mechanical properties of poloxamer solutions become progressively harder with repeated sol-gel cycles, indicating structural changes in the gel matrix that lead to increased rigidity and resistance to deformation. The mucoadhesiveness data shows an increase in the adhesive force of poloxamer solutions with repeated sol-gel cycles, while adhesiveness shows a slight increase and resilience remains constant. These findings suggest that repeated cycling enhances the gel's adhesive properties without compromising its structural integrity.

References: 1. Mfoafo, K., et al., Contemporary Applications of thermogelling PEO-PPO-PEO triblock copolymers. Journal of Drug Delivery Science and Technology, 2022: p. 103182.
2. Sosnik, A., et al., Crosslinkable PEO-PPO-PEO-based reverse thermo-responsive gels as potentially injectable materials. Journal of Biomaterials Science, Polymer Edition, 2003. 14(3): p. 227-239.

Acknowledgements: Acknowledge BASF for supplying Kolliphor P 407 for the research

A graph showing the mean ± SD gelation temperatures of different concentrations of Kolliphor ® P 407 that have undergone different freeze-heat cycles.



A graph showing the mean ± SD hardness of 17.5% Kolliphor P407 that have undergone different freeze-heat cycles.



A graph showing mean ± SD mucoadhesion of Kolliphor P407 solutions that have undergone different
freeze-heat cycles.