**12. Conclusion**

Different techniques have been developed for the production of solid lipid particles with the possibility to obtain different size and shape. The size can influence the pharmacological properties of the particles, but it is not the unique parameter considered to compare the various techniques.

Toxicological issues are also very important: the materials used must be biocompatible and biodegradable, while the use of solvents can be a relevant drawback, since they can remain in traces in the final product.

The melted lipid mixture, fed to the sonotrode by a thermostated reservoir through a funnel, is atomised by ultrasound energy into small droplets that fall freely and solidify by cooling at

**Figure 9.** Scheme of the ultrasonic atomiser (not in scale): (A) ultrasound generator; (B) booster; (C) sonotrode; (D)

Another variant of the spray congealing method is to use a rotating disc [59]. With this technique, the melted mixture is dropped onto a high-speed rotating disc. The rotation induces the molten mixture to spread between the disc periphery and the cooled surface on which

Owing to this technique SLM with particle size ranging from 50 to 2000 μm can be produced.

Different techniques have been developed for the production of solid lipid particles with the possibility to obtain different size and shape. The size can influence the pharmacological properties of the particles, but it is not the unique parameter considered to compare the various

inductive coil; (E) supply funnel; (F) cylindrical chamber (collector).

microparticles are collected.

**12. Conclusion**

techniques.

room temperature in a collector.

68 Application of Nanotechnology in Drug Delivery

From a technological point of view, the possibility to scale up the process is very important, but also the feasibility of the method is relevant: in fact the use of expensive and complex machine can hamper the production on lab scale.

Finally the drug entrapment is very important: nowadays more and more complex molecules are entrapped within solid lipid particles. These molecules have different physico-chemical properties (solubility, hydrophobicity, etc.) and stability issues (temperature, pH, etc.). The chosen preparation technique should be the most suitable to enhance drug loading and encapsulation efficiency within the nanoparticles, without hampering the chemical stability of the molecule itself: the working temperatures and operating conditions used to prepare the particles can affect the physico-chemical stability of the drug.

In Table 2 some important parameters, like particle size, solvents used, instrumentation needed, working temperatures and operating conditions, of the various techniques are shown for comparative purposes.



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**Table 2.** Main parameters for the various preparation techniques of solid lipid nano-and microparticles

As it can be noticed, each technique leads to the formulation of particles with different size and shows some limitations and drawbacks: the choice of a preparation technique should be done basing on the desired particle size, on the technology available, on the toxicological issues and on the characteristics of the drug encapsulated within the particles.
