Hielscher Ultrasound Technology

Ultrasonic Formulation of Nanostructured Lipid Drug Carriers

Nanostructure lipid carriers (NLCs) are an advanced form of nano-sized drug delivery systems featuring a lipid core and a water-soluble shell. NLCs have a high stability, protect the active bio-molecules against degradation and offer sustained drug release. Ultrasonication is a reliable, efficient and simple technique to produce loaded nanostructured lipid carriers.

Ultrasonic Preparation of Nanostructured Lipid Carriers

Nanostructure lipid carriers (NLCs) contain solid lipid, liquid lipid, and surfactant in an aqueous medium, which gives them good solubility and bioavailability characteristics. NLCs are widely used to formulate stable drug carrier systems with a high bioavailability and sustained drug release. NLCs have a broad range of applications ranging from oral to parenteral administration including topical/transdermal, ophthalmic (ocular), and pulmonary administration.
Ultrasonic dispersion and emulsification is a reliable and efficient technique to prepare nanostructured lipid carriers loaded with active compounds. The ultrasonic NLC preparation has the major advantage of not requiring an organic solvent, large amounts of surfactant or additive compounds. Ultrasonic NLC formulation is a relatively simple method as the melting lipid is added to the solution of surfactant and then sonicated.

Exemplary Protocols for Ultrasonically Loaded Nanostructure Lipid Carriers

Dexamethasone-loaded NLCs via Sonication
Ultrasonic extraction with UP200StA non-toxic potential ophthalmic NLC system was prepared under ultrasonication, which resulted in a narrow size distribution, high Dexamethasone entrapment efficacy, and improved penetration. NLC systems were ultrasonically prepared using a Hielscher UP200S ultrasonicator and Compritol 888 ATO, Miglyol 812N, and Cremophor RH60 as components.
The solid lipid, liquid lipid, and surfactant were melted using a heating magnetic stirrer at 85ºC. Then, Dexamethasone was added to the melted lipid mixture and dispersed. The pure water was heated at 85ºC and the two phases were sonicated (at 70% amplitude for 10 min) with the Hielscher UP200S ultrasonic homogenizer. The NLC system was cooled in an ice bath.
The ultrasonically prepared NLCs exhibit a narrow size distribution, high DXM entrapment efficacy, and improved penetration.
The researchers recommend the use of a low surfactant concentration and low lipid concentration (e.g., 2.5% for surfactant and 10% for total lipid) because then the critical stability parameters (Zave, ZP, PDI) and drug loading capacity (EE%) are suitable while the emulsifier concentration can remain at low levels.
(cf. Kiss et al. 2019)

Retinyl Palmitate-loaded NLCs via Sonication
Retinoid is a widely used ingredient in dermatology therapies of wrinkles. Retinol and retinyl palmitate are two compounds from the retinoid group which have an ability to induce the thickness of epidermis and effective as anti-wrinkle agent.
The NLC formulation was prepared using ultrasonication method. The formulation contained 7.2% of cetyl palmitate, 4.8% of oleic acid, 10% of Tween 80, 10% of glycerin, and 2% of retinyl palmitate. The following steps were taken to produce retinyl palmitate-loaded NLCs: The mixture of molten lipids are blended with the surfactant, co-surfactant, glycerin and deionized water at 60-70°C. This mixture is stirred with a high-shear mixer at 9800rpm for 5 min. After the pre-emulsion has formed, this pre-emulsion is immediately sonicated using a probe-type ultrasonic homogenizer for 2 min. Then the obtained NLC was kept at room temperature for 24 h. The emulsion was stored at room temperature for 24 h and the nanoparticle size was measured. The NLC formula showed particle sizes in the range of 200-300nm. the NLC obtained has a pale yellow appearance, a globule size of 258±15.85 nm, and a polydispersity index of 0.31±0.09. The TEM image below shows the ultrasonically prepared retinyl palmitate-loaded NLCs.
(cf. Pamudji et al. 2015)

Ultrasonication is a fast and reliable technique to produce superior nanostructured lipid carriers.

UP400St, a 400 watts powerful ultrasonic homogeniser, for the production of nanostructured lipid carriers (NLCs)

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Spherical nanostructured lipid carriers loaded with retinyl palmitate were prepared under sonication. Ther NLCs have an average size of 200-300nm.

Morphology of ultrasonically formulated retinyl palmitate NLCs: (A) magnification of 10000x, (B) magnification of 20000x, and (C) magnification of 40000x
source: Pamudji et al. 2016

Zingiber zerumbet-loaded NLCs via Sonication
Nanostructured lipid carriers consist of a mixture of solid-lipid, liquid-lipid and surfactant. The are excellent drug delivery systems to administer bioactive substances with poor water-solubility and to increase their bioavailability significantly.
The following steps were undertaken to formulate Zingiber zerumbet-loaded NLCs. 1% solid lipid, ie. glyceryl monostearate, and 4% liquid lipid, i.e. virgin coconut oil, were mixed and melted at 50°C in order to obtain a homogeneous, clear lipid phase. Subsequently, 1% Zingiber zerumbet oil was added to the lipid phase, whilst the temperature was maintained continuously 10°C above the melting temperature of glyceryl monostearate. For the preparation of the aqueous phase, distilled water, Tween 80 and soy lecithin were mixed together at the correct ratio. The aqueous mixture was immediately added into the lipid mixture to form a pre-emulsion mixture. The pre-emulsion was then homogenized using high-shear homogenizer at 11,000 rpm for 1 min. Afterwards, the pre-emulsion was sonicated using a probe-type ultrasonicator at 50% amplitudes for 20 min, Finally, the NLC dispersion was cooled in ice water bath to room temperature (25±1°C) in order to quench the suspension in the cold bath to prevent particle aggregation. The NLCs were stored at 4°C.
The Zingiber zerumbet-loaded NLCs exhibit a nanometer size of 80.47±1.33, stable polydispersity index of 0.188±2.72 and a zeta potential charge of -38.9±2.11. The encapsulation efficiency shows the ability of lipid carrier to encapsulate Zingiber zerumbet oil more than 80% efficiency.
(cf. Rosli et al. 2015)

Valsaratan-loaded NLCs via Sonication
Valsaratan is an angiotensin II receptor blocker used in antihypertensive drug. Valsartan has a low bioavailability of approx. 23% only due to its poor water-solubility. Using the ultrasonic melt-emulsification method allowed for the preparation of Valsaratan-loaded NLCs featuring a significantly improved bioavailability.
Simply, oily solution of Val was mixed with certain quantity of a melted lipid material at temperature 10°C above the lipid melting point. An aqueous surfactant solution was prepared by dissolving certain weights of Tween 80 and sodium deoxycholate. The surfactant solution was further heated to the same temperature degree and mixed with the oily lipid drug solution by probe-sonication for 3 min. to form an emulsion. Then, the formed emulsion was dispersed in cooled water by magnetic stirring for 10 min. The formed NLC were separated by centrifugation. Samples from the supernatant were taken and analyzed for the concentration of Val using a validated HPLC method.
The ultrasonic melt-emulsification method has a number of advantages including simplicity with minimum stressful condition and deprived of toxic organic solvents. Maximum entrapment efficiency achieved was 75.04%
(cf. Albekery et al. 2017)

Other active compounds such as paclitaxel, clotrimazol, domperidone, puerarin, and meloxicam were also successfully incorporated into solid-lipid nanoparticles and nanostructured lipid carriers using ultrasonic techniques. (cf. Bahari and Hamishehkar 2016)

Ultrasonication as preparation method for the formulation of nano lipid carriers (NLCs) can be used as cold or hot homogenization technique. Ultrasonic homogenization results in a narrow particle size distribution, which improves the NLCs stability and storage properties.

Ultrasonic Cold Homogenisation

When the cold homogenization technique is used to prepare nanostructured lipid carriers, the pharmacologically active molecules, i.e. drug, are dissolved in the lipid melt and then quickly cooled using liquid nitrogen or dry ice. During cooling, the lipids solidify. The solid lipid mass is then ground nanoparticle size. The lipid nanoparticles are dispersed in a cold surfactant solution, yielding a cold pre-suspension. Finally, this suspension is sonicated, often using an ultrasonic flow cell reactor, at room temperature.
Since the substances are only heated once in the first step, ultrasonic cold homogenization is mainly used to formulate heat-sensitive drugs. As many bioactive molecules and pharmaceutical compounds are prone to heat degradation, ultrasonic cold homogenization is a widely used application. A further advantage of the cold homogenisation technique is the avoidance of an aqueous phase, which makes it easier to encapsulate hydrophilic molecules, which might otherwise partition from the liquid lipid phase to the water phase during hot homogenization.

Ultrasonic Hot Homogenisation

When sonication is used as hot homogenization technique, the molten lipids and the active compound (i.e. pharmacologically active ingredient) are dispersed in a hot surfactant under intense stirring to obtain a pre-emulsion. For the hot homogenization process it is important that both solutions, the lipid/drug suspension and the surfactant have been heated to same temperature (approx. 5–10°C above the melting point of the solid lipid). In the second step, the pre-emulsion is then treated with high-performance sonication whilst maintaining the temperature.

High-Performance Ultrasonicators for Nanostructured Lipid Carriers

UIP2000hdT - a 2000W high performance ultrasonicator for industrial milling of nano particles.Hielscher Ultrasonics’ powerful ultrasonic systems are used worldwide in pharmaceutical R&D and production to produce high-quality nano drug carriers such as solid lipid nanoparticles (SLNs), nanostructured lipid carriers (NLCs), nanoemulsions and nanocapsules. To meet its customers’ demands, Hielscher supplies ultrasonicators from the compact, yet powerful hand-held lab homogeniser and bench-top ultrasonicators to fully industrial ultrasonic systems for the production of high-volumes of pharmaceutical formulations. A broad range of ultrasonic sonotrodes and reactors are available to ensure an optimal setup for your production of nanostructured lipid carriers (NLCs). The robustness of Hielscher’s ultrasonic equipment allows for 24/7 operation at heavy duty and in demanding environments.
In order to enable our customers to fulfil Good Manufacturing Practices (GMP) and to establish standardised processes, all digital ultrasonicators are equipped with intelligent software for precise setting of the sonication parameter, continuous process control and automatic recording of all important process parameters on a built-in SD-card. High product quality depends on process control and continuously high processing standards. Hielscher ultrasonicators help you to monitor and standardise your process!

Hielscher Ultrasonics’ industrial ultrasonic processors can deliver very high amplitudes. Amplitudes of up to 200µm can be easily continuously run in 24/7 operation. For even higher amplitudes, customized ultrasonic sonotrodes are available. The robustness of Hielscher’s ultrasonic equipment allows for 24/7 operation at heavy duty and in demanding environments.
The table below gives you an indication of the approximate processing capacity of our ultrasonicators:

Batch Volume Flow Rate Recommended Devices
1 to 500mL 10 to 200mL/min UP100H
10 to 2000mL 20 to 400mL/min UP200Ht, UP400St
0.1 to 20L 0.2 to 4L/min UIP2000hdT
10 to 100L 2 to 10L/min UIP4000hdT
n.a. 10 to 100L/min UIP16000
n.a. larger cluster of UIP16000

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Hielscher Ultrasonics manufactures high-performance ultrasonic homogenizers for dispersion, emulsification and cell extraction.

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Facts Worth Knowing

Advanced Nano-Sized Drug Carriers

Nanoemulsions, liposomes, niosomes, polymeric nano-particles, solid-lipid nanoparticles, and nanostructured lipid nanoparticles are used as advanced drug delivery systems to improve bioavailability, reduce cytotoxicity and to achieve sustained drug release.

The difference of solid lipid nanoparticles and nanostructured lipid carriers is the composition of the lipid matrix.

The schematic structure of a) solid lipid nanoparticle b) nanostructured lipid carrier
Source: Bahari and Hamishehkar 2016

The term solid-lipid-based nanoparticles (SLBNs) comprises the two types of nano-sized drug carriers, solid lipid nanoparticles (SLNs) and nanostructured lipid carriers (NLCs). SLNs and NLCs are distinguished by the composition of solid particle matrix:
Solid-lipid nanoparticles (SLNs), also known as lipospheres or solid lipid nanospheres, are submicron particles with an average size between 50 and 100nm. SLNs are made from lipids that remain solid at room and body temperature. The solid lipid is used as a matrix material, in which drugs are encapsulated. Lipids for the preparation of SLNs can be selected from a variety of lipids, including mono-, di-, or triglycerides; glyceride mixtures; and lipid acids. The lipid matrix is then stabilized by biocompatible surfactants.
Nanostructured lipid carriers (NLCs) are lipid-based nanoparticles made of a solid lipid matrix, which is combined with liquid lipids or oil. The solid lipid provide a stable matrix, which immobilizes the bioactive molecules, i.e. drug, and prevents the particles from aggregating. The liquid lipid or oil droplets within the solid lipid matrix enhance the drug loading capacity of the particles.