Polymeric hydrogel-based creams and oil-based organogels were formulated to develop a topical preparation containing carbonized and triturated powder of pine cone (CPC). Microscopic observation showed homogenous dispersion of CPC throughout the oil phase. Under centrifugal stress (1000-20000×g, 10 min, 20 oC), the physical stability of the hydrogel-based formulation was greater than those of organogels. Hydrogel-based ultra-moisturizing cream2 (HUMC2) and lauric acid/Vaseline-based gel2 (LV2) were selected as representative aqueous and organogel formulations, respectively, and both showed shear-thinning behavior in rheograms. A simulated pinch strength test was established to evaluate flow properties of the formulations for practical application. In human sensory evaluation, HUMC2 showed a higher score than LV2 regarding spreadability, moistness, and removal capacity, whereas the shininess score of LV2 was higher than that of HUMC2. In conclusion, HUMC2 was superior to LV2 in most evaluations, but had limited CPC-loading capacity (< 10% w/w), compared to the high loading capacity of LV2 (approximately 40% w/w).

미분화된 솔방울 탄화물(CPC)을 함유한 외용제로서 고분자 하이드로젤 기반 크림과 오일 기반 유기젤을 개발하였다. 현미경 관찰을 통해 유상 전반에 걸쳐서 CPC가 균질하게 분산되었다. 원심분리 조건(1000-20000×g, 10분, 20도) 하에서, 유기젤에 비하여 수화젤 기반 제제의 물리적 안정성이 더 컸다. 수화젤 기반 고보습 크림2(HUMC2)와 라우르산/바셀린 기반 젤2(LV2)는 각각 수성 및 유기젤의 대표 제제로 선택되었으며, 두 제제 모두 전단박화의 유동학적 거동특성을 나타내었다. 별도로, ‘가상 집기력 시험법’을 설정하여 제제의 실질적 적용 시 흐름특성을 평가하였다. 사람을 대상으로 한 관능 평가에서 HUMC2가 퍼짐성, 보습성, 수세성 측면에서 LV2보다 높은 점수를 나타내었으나, 광택성 점수는 LV2가 HUMC2보다 높았다. 결론적으로 대부분의 평가에서 HUMC2가 LV2보다 우수했다, 그러나 HUMC2가 제한적인 CPC 탑재능력(10% w/w 미만)을 보인 반면 LV2는 높은 CPC 탑재능력(약 40% w/w)을 나타내었다.

Keywords: carbonized pine cones, o/w cream, organogel, physical stability, pinch strength test, sensory evaluation

Pine cones are the seed-producing cones of the pine tree, Pinus densiflora Siebold et Zuccarini. Pine cones have been used in folk medicine owing to their antimicrobial effects, which are caused by active oxygen production via their constituent lignin-carbohydrate complexes.¹ They also exert antiviral effects, inhibiting virus multiplication.^2,3 Carbonized pine cones (CPC) have been prepared by complete combustion of pine cones at extremely high temperatures of 100-300 ℃, followed by pulverization using a 50-200 mesh sieve. A CPCcontaining semisolid formulation has been patented in Korea to treat burns,⁴ in which several excipients such as sesame oil, purified lanolin, white petrolatum, and selective organic acids form a cream or ointment base. However, with a high CPC content, such conventional formulations revealed imperfec-tions in either the physical stability of the homogenous dispersion or consumer acceptance for dermal application. We therefore needed to develop an advanced topical preparation to overcome the above limitations as well as enhance skin hydration.
Various types of topical formulations, including creams, hydrogels, and organogels, are currently in use.⁵ Creams are the most common preparation, wherein oil and water are balanced in the presence of surfactant to make a homogenous dispersion, which can be of either an oil-in-water (o/w) or a water-in-oil (w/o) type. Recently, we developed a hydrogelbased ultra-moisturizing cream (HUMC) that efficiently hydrates the skin and increases the dermal delivery of both hydrophilic and lipophilic molecules.⁶ As HUMC contains Carbopol 934P, an acrylic acid polymer crosslinked with polyalkenyl polyethers or divinyl glycol, it offers a stabilized, networked gel structure, resulting in advantages such as relatively high viscosity, compatibility with various active ingredients, bioadhesive properties, and thermal stability.^7,8 However, creams and hydrogels have limitations on their capacities to hold high levels of water-insoluble solid particles. Oil-based formulations, including organogels, might be a preferable alternative, as insoluble particles can easily be dispersed throughout the oil component. Upon dermal application, organogels, oils, or oleaginous fatty acids contained in organogels form a thin occlusive film on the skin surface, preventing transepidermal water loss, thereby potentially enhancing skin hydration.
Achieving pharmaceutical elegance in topical formulations generally requires not only the physical stability of the homogenous dispersion, but also patient acceptance of dermal application. To predict physical stability, products are subjected to accelerated conditions such as centrifugal force,⁹ temperature stress,¹⁰ and light exposure.¹¹ Meanwhile, to compare the organoleptic properties of products, such as odor, moistness, shininess, and spreadability, sensory evaluations via a panel test are generally recommended.¹² The descriptive analysis method, using a trained panel of skin-feel evaluators, can provide instructive information for research.¹³
The present study was performed to develop a novel CPCcontaining topical preparation with excellent dispersion stability and in vivo performance upon dermal application. Based on the dispersion compatibility of CPC, different types of aqueous creams and oil-based organogels were formulated and subjected to stability assessment at 25 ℃ under accelerated gravitational force. Flow properties of selected formulations were further characterized by a pinch strength squeezing test and rheological observation. Finally, panel sensory evaluations were employed to compare the organoleptic properties of the products.