by Müller and Lucks possess a particle (solid) content of 0.1 to a maximum of 30%. The lower concentrated dispersions in particular show good diffusibility of the particles and potential random collision. However, SLN and NLC dispersions can be produced with a solid content above 30% up to 95%. The high particle concentration leads to a dense packing of the particles; depending on the concentration, they form a pearl-like network or an even denser hexagonal packing. The pearl-like network can be compared to the structure of gels formed by Aerosil or Bentonit (Montmorillonit). In such a network, particle diffusion is minimized, the particles are fixed in a certain structure, and aggregation does not occur or is less pronounced. Physical stability studies were performed by producing lipid nanoparticle dispersions with increasing lipid content. When diluting the highly concentrated particle dispersion after storage, finely dispersed lower concentrated suspensions were obtained. This means that such highly concentrated lipid particle dispersions can be produced that are optimal for storage. Producing the lipid particle dispersions, for example, in oils or PEG 600 instead of water, such dispersions can be directly filled into soft gelatine capsules. In the stomach, the capsule dissolves, the concentrated lipid particle dispersion is diluted, and releases finely dispersed particles for drug delivery.

Physical stabilization of the dispersitivity of particles can also be achieved by spray drying (Fig. 3, upper part) or lyophilization (Fig. 3, lower part). There are no basic differences between SLNs and NLCs in these processes; we refer to the publications regarding spray drying [44, 45] and lyophilization of SLNs [46, 47].

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