Definition

Solid lipid nanoparticles are particles with a mean average size in the nanometer range, which means approximately 50-1000 nm, being composed of a lipid matrix material that is solid at room temperature, but also at body temperature. Originally, the term "solid lipid nanoparticles" and the abbreviation "SLNs" were introduced by Müller and Lucks, the inventors of the patent describing the production of SLNs by high-pressure homogenization [3]. Then this name was also transferred to lipid nanoparticles with a solid matrix, but being produced by using microemulsions, a technique developed by Gasco in Turin [4]. Meanwhile, the term SLNs is used for all lipid nanoparticles with a solid matrix, independent of the method of production. This includes particles being produced by solvent evaporation, precipitation, or phase inversion methods.

Strictly speaking, by definition, nanoparticles are particles with a mean diameter in the nanometer range, that is, below 1000 nm. Microparticles are defined to be in the micrometer range, that is, having a minimum size of 1 /m, and going up to a few hundred micrometers. The upper size limit of microparticles is not unanimously defined. Based on the word "micro"particle, one could define an upper size limit of 1000 /m, that is, 1 mm. However, such large particles might be better described as pellets, and so on. Based on this, larger lipid particles were introduced to the literature as solid lipid microparticles (SLMs) [10]. There is a range of different techniques to produce SLMs, ranging from highspeed stirring techniques to static blenders, and recently, the so-called micromixers [11].

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