Cornelia M. Keck

20 years of lipid nanoparticles (SLN & NLC): present state of development & industrial applications

In 1990, the lipid nanoparticles were invented in the laboratories, the first patent filings took place in 1991. The lipid nanoparticles were developed as alternative to traditional carriers such as polymeric nanoparticles and liposomes. After 20 years of lipid nanoparticles, the present state of development is reviewed - academic progress but also the development state of pharmaceutical products for the benefit of patients. Meanwhile many research groups are active worldwide, their results are reviewed which cover many different administration routes: dermal and mucosal, oral, intravenous/ parenteral, pulmonary but also ocular. The lipid nanoparticles are also used for peptide/protein delivery, in gene therapy and various miscellaneous applications (e.g. vaccines). The questions of large scale production ability, accepted regulatory status of excipients, and - important for the public perception - lack of nanotoxicity are discussed, important pre-requisites for the use of each nanocarrier in products. Identical to the liposomes, the lipid nanoparticles entered first the cosmetic market, product examples are presented. Presently the pharmaceutical product development focuses on products for unmet needs and on niche products with lower development costs (e.g. ocular delivery), which can be realized also by smaller companies. A pharmaceutical perspective for the future is given, but also outlined the opportunities for non-pharmaceutical use, e.g. in nutraceuticals.

Production and characterization of Hesperetin nanosuspensions for dermal delivery

Nanosuspensions of Hesperetin were produced using four different stabilizers, Poloxamer 188, Inutec SP1, Tween 80 and Plantacare 2000, possessing different mechanisms of stabilisation. The nanosuspensions were characterized with regard to size (photon correlation spectroscopy (PCS), laser diffractometry (LD)) and charge (zeta potential measurements). A nanocrystal PCS size of about 300 nm was obtained after 30 homogenization cycles at 1500 bar with the stabilizers Poloxamer, Inutec and Plantacare. Tween was slightly less efficient to preserve the nanocrystal size directly after production (347 nm). The short-term stability was assessed by storage of the nanosuspensions at 4 degrees C, room temperature and 40 degrees C. As predicted from the zeta potential measurements, Inutec and Plantacare stabilized nanosuspensions were stable with no change in PCS diameter and LD diameter 99%. Slight increases in size were found for the Poloxamer and the Tween stabilized nanosuspensions, which is not considered to impair their use in dermal formulations.

Development of an oral rutin nanocrystal formulation

Dried rutin nanocrystals have been prepared by lyophilization and investigated regarding their physicochemical properties with respect to re-dispersability, particle size, morphology and dissolution behavior. Photon correlation spectroscopy (PCS) and laser diffractometry (LD) were employed to determine the particle size. Morphology of the particles was analyzed by light microscopy. Lyophilized rutin nanocrystals were incorporated into tablets and the dissolution behavior of the tablets was evaluated. Very fine particles of lyophilized rutin could be completely re-dispersed in the water. The PCS size average and polydispersity index (PI) of lyophilized rutin were of 721nm and of 0.288 after re-dispersion. The rutin nanocrystal-loaded tablets were produced using direct compression. The dissolution velocity of the rutin nanocrystal-loaded tablet was superior compared to rutin microcrystal-loaded and a marketed tablet. After 30min rutin was released and dissolved completely from the nanocrystal tablets in water. In contrast, only 71% and 55% of the total amount of rutin were dissolved from the microcrystal tablets and the marketed tablet, respectively. The improving dissolution behavior of the rutin nanocrystal-loaded tablet should lead to a better bioavailability of the poorly soluble rutin in the body.

Kinetic solubility and dissolution velocity of rutin nanocrystals.

Lyophilized rutin nanocrystals were intensively evaluated regarding their physicochemical properties with respect to particle size analyses, crystallinity, kinetic solubility and dissolution behavior. The particle size was determined by photon correlation spectroscopy (PCS) and laser diffraction (LD). DSC and X-ray diffraction were used to study the crystalline state of rutin nanocrystals. In a period of 1 week, the kinetic solubility was determined using a shaker at 25 degrees C. DSC and X-ray diffraction analyses showed that lyophilized rutin nanocrystals prepared by high pressure homogenization remained in crystalline state. Lyophilized rutin nanocrystals could be re-dispersed completely in water and the kinetic solubility in water increased to 133 microg/ml.. Lyophilized rutin nanocrystals were almost completely dissolved within 15 min in water, buffer of pH 1.2 and buffer of pH 6.8. In contrast, only 70% of rutin raw material (rutin microcrystals) was dissolved within 15 min. The superior physicochemical properties of rutin nanocrystals should overcome the absorption problem in the gastrointestinal tract and increase the bioavailability.

Size analysis of submicron particles by laser diffractometry--90% of the published measurements are false.

The first part of this paper gives an easy and understandable introduction into modern laser diffractometry (LD). It explains why modern laser diffractometry is not only the simple detection of a diffraction pattern but a combination of two independent technologies, which is done to extend the measuring range down to several nanometers and incorrectly named LD measurement. In the second part the impact of the optical parameters on the result analysed was investigated. The results show, that changes in optical parameters change the particle size and the size distribution tremendously. For a trimodal mixture of latex particles, having a mean particle size of 845nm, mean particle sizes ranging from 284nm to up to 1.005microm were obtained due to the variation of the optical parameters. The obtained particle size distributions varied from monomodal, bimodal over trimodal to even tetramodal distributions. The results prove that the analysis of submicron particles is meaningless, if incorrect optical models are applied. Another hazard was found to be the use of the additional techniques for the extension to the submicron measuring range. Combining this technology with laser diffraction can fail to detect larger particles besides a small sized main population. This can be overcome by analyzing the samples also without the additional technology, i.e. using laser diffraction only. From the results it is concluded that laser diffractometry for submicron particles is only useful if correct optical parameters are applied and if the presence of larger particles is investigated without the enhanced submicron measuring range.

Nanotoxicological classification system (NCS) – A guide for the risk-benefit assessment of nanoparticulate drug delivery systems

There is an increasing discussion about potential toxicity of nanoparticles (nanotoxicity). A classification system is proposed classifying the nanoparticles in four classes (I to IV) from low/no risk to high risk. It is based on the nanoparticle size (>/<100 nm) and size-related differences in interaction with human cells, and on biodegradability/non-biodegradability in the body. This classification is superimposed by biocompatibility (B) and non-biocompatibility (NB) of the nanoparticle surface, resulting in a total of eight classes from I-B (best tolerated) to IV-NB (highest potential risk). The classification should help as a guideline in pharmaceutical formulation development, but also as a guide for risk assessment in other product areas and environmental exposure.

Twenty years of drug nanocrystals: Where are we, and where do we go?

Drug nanocrystals were invented at the start of the 1990s, based on the dates of the first patent filings by Nanosystems (now Élan) [1], RTP Canada (now SkyePharma Canada) [2] and DDS Drug Delivery Services GmbH (IP now owned by SkyePharma) [3]. Pioneering work was performed by Liversidge et al. at Nanosystems [4–6]. Initially, companies were reluctant to use nanocrystal technology to formulate poorly soluble drugs. Pharmacists have attempted to conservatively solve this problem using available, proven technologies instead.

Development of curcumin nanocrystal: Physical aspects

Curcumin, a naturally occuring polyphenolic phytoconstituent, is isolated from the rhizomes of Curcuma longa Linn. (Zingiberaceae). It is water insoluble under acidic or neutral conditions but dissolves in alkaline environment. In neutral or alkaline conditions, curcumin is highly unstable undergoing rapid hydrolytic degradation to feruloyl methane and ferulic acid. Thus, the use of curcumin is limited by its poor aqueous solubility in acidic or neutral conditions and instability in alkaline pH. In the present study, curcumin nanocrystals were prepared using high-pressure homogenization, to improve its solubility. Five different stabilizers [polyvinyl alcohol (PVA), polyvinyl pyrrolidone (PVP), d-α-tocopherol polyethylene glycol 1000 succinate (TPGS), sodium dodecyl sulfate (SDS), carboxymethylcellulose sodium salt] possessing different stabilization mechanism were investigated. The nanoparticles were characterized with regard to size, surface charge, shape and morphology, thermal property, and crystallinity. A short-term stability study was performed storing the differently stabilized nanoparticles at 4°C and room temperature. PVA, PVP, TPGS, and SDS successfully produced curcumin nanoparticle with the particle size in the range of 500-700 nm. PVA, PVP, and TPGS showed similar performance in preserving the curcumin nanosuspension stability. However, PVP is the most efficient polymer to stabilize curcumin nanoparticle. This study illustrates that the developed curcumin nanoparticle held great potential as a possible approach to improve the curcumin solubility then enhancing bioavailability.

Skin photoprotection improvement: synergistic interaction between lipid nanoparticles and organic UV filters.

A photoprotective formulation was developed with an increased sunprotection factor (SPF), compared to a conventional nanoemulsion, but having the same concentration of three molecular sunscreens, namely ethylhexyl triazone, bis-ethylhexyloxyphenol methoxyphenyl triazine, and ethylhexyl methoxycinnamate. The sunscreen mixture was incorporated into nanostructured lipid carriers (NLCs). The ability of nine different solid lipids to yield stable aqueous NLC suspensions was assessed. After the production by hot high pressure homogenization, the NLC were analyzed in terms of particle size, physical state, particle shape, ultraviolet absorbance and stability. The particle size for all NLC was around 200 nm after production. The NLC suspension with carnauba wax had superior UV absorbance, NLC from bees wax showed similar efficiency as the reference emulsion. The NLC formulations were incorporated into hydrogel formulations and the in vitro SPF was measured. This study demonstrated that approximately 45% higher SPF values could be obtained when the organic UV filters were incorporated into carnauba wax NLC, in comparison to the reference nanoemulsion and bees wax NLC. The data showed that the synergistic effect of NLC and incorporated sunscreens depends not only on the solid state of the lipid but also on its type.

Ultra-small NLC for improved dermal delivery of coenyzme Q10

Coenzyme Q10 (CoQ10) acts as an antioxidant in the skin and is frequently contained in anti-aging products. In previous studies, it could be shown that nano-structured lipid carriers (NLC) with a size of about 230 nm are beneficial for the dermal delivery of CoQ10. They increased Q10 skin penetration when compared to equally sized nanoemulsion. In this study, ultra-small NLC were prepared with even smaller mean particles sizes of around 80 nm. The influence of this decrease of particle size was investigated in terms of skin permeation and penetration as well as physicochemical stability of the NLC. Improved dermal delivery of CoQ10 by ultra-small NLC could be achieved.