## 1 Introduction  
There is a growing interest in ready-to-use nonsolid emulsions for the topical application of active compounds to treat inflamed skin and painful conditions caused by different mechanisms [1, 2]. Our interest is focused on patients with osteoarthritis (OA) characterized by low-grade chronic inflammation. In the initial phases of OA, pain and inflammation are treated using several strategies, such as anti-inflammatory drugs, painkillers, and physical therapies [3, 4, 5]. The use of pharmacological treatments with analgesics or anti-inflammatory agents, administered orally or topically, is debated [6]. Topical application of nonsteroidal anti-inflammatory drugs (NSAIDs), such as ibuprofen, diclofenac, and acetylsalicylic acid, is considered particularly useful in the management of OA [7, 8]. However, although the efficacy of NSAIDs in relieving pain remains debatable for hand and knee osteoarthritis, topical application of diclofenac and ketoprofen can help reduce pain in a modest number of patients [9]. Currently, the use of topical gels/creams containing analgesic and anti-inflammatory drugs, as well as natural compounds, to treat skin conditions in patients with OA is being studied [10, 11, 12, 13]. Aimed at increasing the pharmacological potency and penetration of drugs and, simultaneously, controlling pain and itch, natural molecules are added to creams or gels containing anti-inflammatory and antinociceptive drugs [14, 15]. The exploitation of natural herbal extracts or purified compounds is considered a green method, and these substances are generally better tolerated by patients, especially those who make chronic use of them. _Glycyrrhiza glabra, Nerium indicum_, and other herb extracts have been shown to stimulate epithelization [16]. The use of natural anti-inflammatory compounds has been observed to decrease the expression of inflammatory cytokines on keratinocytes [17]. Moreover, natural compounds shown to have anti-inflammatory properties also exhibit painkilling activity. Among compounds with multiple effects, _Salix alba_, rich in salicylic acid, is one of the oldest herbal remedies for pain and inflammation, dating back to ancient Egyptian, Roman, Greek, and Indian civilizations, as an analgesic and antipyretic agent [18]. Scar management and wound healing are also important for osteoarthritis patients, especially for those who have received implants and experience complications in skin healing [19; 20]. Following the implantation of a prosthesis joint, in about 10% of patients, the skin develops a form of dermatitis. Consequently, the skin undergoes an inflammatory process that manifests as pain [21]. Therefore, considering that joint and skin problems coexist in patients with OA, it is useful to explore natural anti-inflammatory and analgesic agents that can be used to treat both joint pain prior to prosthetic surgery and wounds [22]. Over the past few years, we have studied the effects of pure N-acetylglucosamine in nanoparticle form (nNAG) on inflammation and pain, as well as its influence on extracellular matrix synthesis, showing that nNAG is 10-fold more active than in bulk form [23]. We have also studied the effects of some _Harpagophytum proclumbens_ root extracts (HPEs) on pain relief, obtaining results of great interest. However, because it has not been possible to identify a single HPE phytocative compound responsible for the painkiller activity, we decided to focus our attention on nNAG, a pure molecule [24]. In the present manuscript, we describe the preparation of creams and gels containing HPE, NAG, and nNAG. Moreover, we compare the flow properties of different types of creams (hydrophilic and lipophilic) to test their apparent viscosity as a function of the different base ingredients and shear rates. Considering that the availability of drugs or other active substances to permeate the skin depends on the release of these substances from the vehicles, studies on the properties of vehicles, such as rheological behavior, are very desirable in the pharmaceutical field.