**1. Introduction**

Reactive oxygen species (ROS) are directly associated with a variety of degenerative and age-related diseases, and other pathologies, including di fferent types of cancers. ROS are generated as by-products of cellular metabolism and their excessive production can damage lipids, proteins, and DNA, different cells, and tissues [1].

Resveratrol (RSV) (trans-3,4,5-trihydroxystilbene) is a natural antioxidant commonly found in grapes, berries, and nuts that has shown promising results in the treatment of a variety of degenerative and age-related diseases. It blocks the activation of nuclear factor κB (NF-κB), reducing the generation of ROS and pro-inflammatory cytokines (interleukin IL-1 β and IL-6), which results in the inhibition of chondrocyte apoptosis, inflammation, and the progression of several diseases [2,3]. It is also a direct inhibitor of cyclooxygenase 2 (COX-2) which produces pro-inflammatory lipid mediators (leukotrienes and prostaglandins) responsible for pain sensation [4].

In recent years, RSV has also shown beneficial results in modulation of tissue regeneration, microcirculation, the function of peripheral nerves, production of anti-inflammatory cytokines, and insulin [5–9]. However, RSV shows low long-term stability, rapid metabolism, and release; low aqueous solubility (0.05 mg/mL) and bioavailability. RSV is also unstable under the influence of light, certain pH levels, and temperature, which causes isomerization or degradation of RSV, making it difficult to apply in the medical–pharmaceutical area [10–13]. To overcome these limitations, RSV has been employed in pharmaceutical formulations in different drug delivery systems (DDS), including microparticulate system [14,15], micro/nanocapsules [16], cyclodextrin complexes [17,18], solid lipid nanoparticles (SLN) [19–22], nanosuspensions [23], vesicular systems liposomes [24], niosomes [25], nanosponges [18,26], microspheres [27], transfersomes and ethosomes [14,15,28], and nanostructured lipid carriers (NLC) [19,20]. The DDS are employed to improve the physicochemical stability of loaded drugs, provide a sustained-release profile, increase plasma half-life, decrease the risk of immunogenicity, improve the drug solubility and thereby its bioavailability and therapeutic activity, enhance antioxidant activity, and improve the permeation and targeted delivery [14,15].

NLC consists of a mixture of solid and liquid lipids, which creates an imperfect crystalline structure, providing more space between the lipid chains and the matrix [29,30]. The main advantages of the use of NLC are high encapsulation efficiency and storage stability, the possibility of controlling the release of several drugs, low toxicity due to the absence of solvents in the production process, and the possibility of production in an industrial scale [31,32]. Moreover, Gokce et al. [14] observed that RSV-loaded NLC penetrated deeper into the skin [19]. Jose et al. showed a negligible release of resveratrol over several hours, corroborating the high stability of RSV-loaded NLC [20].

Experimental designs have been the most used tools to simultaneously analyze the influence of different variables on the properties of NLC, aiming to ensure the high product quality, the economy of production, and reduction of production time, allowing the scale-up of the process [33].

To evaluate the optimum experimental conditions for NLC production, several authors have assessed the influence of different factors which can affect the final properties of formulations, including type, ratio, and concentration of lipids and stabilizers, cycle numbers, time and intensity of homogenization, and pressure [34–36]. Thus, this work reports the effects of the production process parameters, shear intensity, and homogenization time of RSV-loaded NLC by means of a 22 factorial design with triplicate of the central point, measuring the mean particle size (PS) and polydispersity index (PDI) as the dependent variables.

#### **2. Materials and Methods**
