Emulgels Containing Propolis and Curcumin: The Effect of Type of Vegetable Oil, Poly(Acrylic Acid) and Bioactive Agent on Physicochemical Stability, Mechanical and Rheological Properties

Abstract

Emulgels are obtained by the entrapment of an organic phase within a three-dimensional network built by hydrophilic molecules. Polymers based on cross-linked poly(acrylic acid) have been utilized as gel matrices, improving adhesiveness, rheological and mechanical performance. Propolis (PRP) produced by Apis mellifera L. bees displays a wide range of biological activities. Together with curcumin (CUR), they may show synergic anti-inflammatory, antioxidant and antimicrobial action on skin disorders. This work investigated the effect of vegetable oils (sweet almond, andiroba, and passion fruit) with regard to the physicochemical properties of emulgels composed of Carbopol 934P®, Carbopol 974P®, or polycarbophil aiming the CUR and PRP delivery. Physicochemical stability enabled the selection of systems containing passion fruit or andiroba oil. Mechanical and rheological characteristics provided rational comprehension of how vegetable oils and bioactive agents affect the structure of emulsion gels. All formulations exhibited high physiochemical stability and properties dependent on the polymer type, oil, and bioactive agent. Formulations displayed pseudoplastic, thixotropic and viscoelastic properties. Emulgels containing andiroba oil were the most stable systems. Carbopol 934P® or polycarbophil presence resulted in formulations with improved smoothness and mechanical properties. Systems containing andiroba oil and one of these two polymers are promising for further investigations as topical delivery systems of CUR and/or PRP on the skin and mucous membranes.

Design and Optimization of a Natural Medicine from Copaifera reticulata Ducke for Skin Wound Care

“…Initially, the mechanical and textural properties of the emulsion-filled gel were evaluated to predict their behavior during the manufacturing process and skin application [ 39 , 51 , 52 ]. The oil phase was incorporated into the three-dimensional crosslinked network of Carbopol ( Figure 1 ) [ 28 , 53 ], with an oil drop interface reinforcement promoted by F127 and natural surfactants from the oil-resin. The presence of active phase droplets (which interact with the interfacial polymer) prevented the coalescence processes during the tests, regardless of the evaluated temperature [ 28 ].…”

“…The oil phase was incorporated into the three-dimensional crosslinked network of Carbopol ( Figure 1 ) [ 28 , 53 ], with an oil drop interface reinforcement promoted by F127 and natural surfactants from the oil-resin. The presence of active phase droplets (which interact with the interfacial polymer) prevented the coalescence processes during the tests, regardless of the evaluated temperature [ 28 ]. The three-dimensional arrangement that led to the stabilizing interfaces (C934P 1.2%, w / w and F127 2.4%, w / w ) of the oil-resin can be visualized in the morphological analysis images ( Figure 1 ).…”

“…Although emulsions are thermodynamically unstable, ECO samples did not display modifications in coloration or evidence of phase separation, even under daily thermal cycles (5 °C and 45 °C, Figure 2 ) [ 56 ]. Additionally, shelf tests showed ECO stability up to 180 days, indicating the polymer blends provided strong interfacial properties that prevented droplet coalescence [ 28 ]. The high stability of the ECO demonstrates that it may go through thermal variations during transportation or storage without changes in its integrity.…”

“…Cohesivity and elasticity are essential parameters for the comprehension of resistance and deformation abilities [ 43 ]. Adhesiveness simulates the work required for the formulation remotion from the original flask, predicting the formulation’s ability to be maintained on the skin for a prolonged period, therefore improving the therapeutic effect [ 28 , 57 ].…”

“…Carbopol 934P, for instance, produces viscous gels, once it has a high crosslinked structure. Moreover, this polymer presents excellent bioadhesive properties, and composes various formulations for dermal and ophthalmologic uses [ 27 , 28 ]. Pluronic ® F127, in turn, is a triblock copolymer of poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) (PEO 106 –PPO 70 –PEO 106 ) units that has been extensively used in pharmaceutical formulations [ 29 ].…”