Optimized Tripeptide-3-loaded Nanoemulsions compared with Microemulsions for dermal delivery

Abstract

This study aimed to develop a submicron colloidal formulation for delivering of Tripeptide-3 to inhibit sebaceous gland activity, thereby reducing the oiliness of facial skin and acne. The experimental design used pseudoternary phase diagram plots to determine the factors influencing microemulsions formation. These factors include HLB values of the surfactant mixture, co-surfactants, whether single or double tails, types and ratios of co-solvents, and the content of caprylic/capric triglyceride (CCT oil) in formulations. Notably, the combination of Cremophor® RH 40 and a double-tailed co-surfactant, Lameform® TGI (referred to as Smix), at a hydrophilic-hydrophobic balance (HLB) of 13, in conjunction with water and a co-solvent (Propylene Glycol, PG) at a 1:1 ratio, yielded the largest microemulsion area (57%) compared with those from other Smix and co-solvent combinations. Further refinement was achieved through the optimization employing a Design Expert® program with a two-level full factorial experimental design (two-level FFD). The three independent variables include HLB value (11 or 13), polypropylene glycol (PG) content (20% or 40%), and oil content (5% or 10% CCT oil), while ensuring a limited Smix content at 10%. The. dependent variables were observed, including physical appearance, particle size (nm) and percent transmittance (%T). The optimal formulation is achieved by heating the oil and water phases to 70±2 °C then pouring the water phase into the oil phase with vigorous stirring until the formulation cooldown to approximately 40 °C. Among the eight formulations tested, the optimal formulation consisted of 10% Smix with an HLB of 13, 20% PG, and 5% oil content. This combination yielded submicron emulsions with droplet sizes of 25.7±1.2 nm, a PDI of 0.237±0.1, and %T of 70.6±0.5%. The formulation demonstrated stability under various stress tests, including centrifugation at 10,000 rpm for 30 minutes, six heating-cooling cycles, and three freeze-thaw cycles. Furthermore, the results indicated stable Tripeptide-3 when the pH was adjusted to 4.5. Considering the method of preparation and characteristics of the optimized Tripeptide-3 formulation, this nano-colloidal dispersion was conclusively identified as stable and translucent nanoemulsions. The Tripeptide-3 in the optimized nanoemulsion exhibited a significantly enhanced permeation through the Strat-M® artificial skin membrane in Franz diffusion cells when compared to three microemulsions (o/w, bicontinuous, and w/o microemulsions), and a coarse emulsion. Consequently, the nanoemulsions displayed significantly elevated levels of both skin flux and skin retention of Tripeptide-3 within the membrane. Further clinical evaluation was performed in 23 healthy volunteers with oily facial skin. The formulation displayed no signs of skin irritation and efficacy of facial oil reductions by 21.61±4.76%, 19.92±4.76%, and 15.54±7.83% on the forehead, nose, and chin, respectively, while concomitantly augmenting skin moisture levels on the forehead, cheek, and chin by 12.65±6.98%, 3.58±3.29%, and 9.88±6.54%, respectively, after 28 days of intervention. In conclusion, the study has optimized a low-surfactant nanoemulsion formulation for hydrophilic peptide delivery into facial skin to reduce oiliness. The optimized nanoemulsion exhibited thermodynamic stability and significantly higher skin permeation compared to microemulsions and an emulsion used for comparison. Through evaluation in volunteers, this formulation was efficacious in reducing facial oiliness and non-irritated when used as a cosmetic product, demonstrating potential as a therapeutic intervention in managing sebum levels in individuals with oily skin conditions.