Chemical and structural investigation of lipid nanoparticles: drug-lipid interaction and molecular distribution

Effect of Functional Groups in Lipid Molecules on the Stability of Nanostructured Lipid Carriers: Experimental and Computational Investigations

Lipid nanoparticles have been used as drug carriers for decades. Many lipid types have been screened for both solid lipid nanoparticles and nanostructured lipid carriers (NLCs). Specifically, for NLCs that are composed of lipids in the solid form mixed with lipids in the liquid form, compatibility of lipid combination and phase behavior play a significant role in the NLC quality. In this study, stearic acid (STA) and cetyl palmitate (CTP) were used as solid lipids, and oleic acid (OLA), isopropyl palmitate (IPP), and caprylic/capric triglycerides were used as liquid lipids. NLCs were prepared at solid:liquid ratios of 50:50, 70:30, and 90:10, respectively. The characteristics and stability of the prepared NLCs were investigated. Laboratory results showed that the solid lipid had a greater influence on the particle size than the liquid lipid. Meanwhile, cetyl palmitate, an ester compound, provides higher NLC stability compared to stearic acid, a carboxylic acid compound. A MARTINI-based coarse-grained molecular dynamics simulation was used to simulate the lipid droplet in water. The distribution of lipid molecules in the droplet was characterized by the polar group density distribution. Different spatial arrangements of the lipid headgroup and lipid molecules, when CTP or STA was used as solid lipids, might contribute to the different stabilities of prepared NLCs. The understanding of mixed lipid systems via simulations will be a significant tool for screening the type of lipids for drug carriers and other pharmaceutical applications.

Natural-Origin Betaine Surfactants as Promising Components for the Stabilization of Lipid Carriers

In the present work, we demonstrate studies involving the influence of the formulation composition on the physicochemical properties of nanocarriers: solid lipid nanoparticles (SLNs) and nanostructured lipid carriers (NLCs). Novel lipid-origin platforms were prepared using two "green" betaine-based surfactants, cocamidopropyl betaine (ROKAmina K30) and coco betaine (ROKAmina K30B), in combination with three different solid lipids, cetyl palmitate (CRODAMOL CP), trimyristin (Dynasan 114), and tristearin (Dynasan 118). Extensive optimization studies included the selection of the most appropriate lipid and surfactant concentration for effective SLN and NLC stabilization. The control parameters involving the hydrodynamic diameters of the obtained nanocarriers along with the size distribution (polydispersity index) were determined by dynamic light scattering (DLS), while shape and morphology were evaluated by atomic force microscopy (AFM) and transmission electron microscopy (TEM). Electrophoretic light scattering (ELS) and turbidimetric method (backscattering profiles) were used to assess colloidal stability. The studied results revealed that both betaine-stabilized SLN and NLC formulations containing CRODAMOL CP as lipid matrix are the most monodisperse and colloidally stable regardless of the other components and their concentrations used, indicating them as the most promising candidates for drug delivery nanosystems with a diverse range of potential uses.

When it is too much: Identifying butamben excess on the surface of pharmaceutical preformulation samples by Raman mapping

Butamben is a topical local anesthetic which formulation in lipid-based drug delivery systems (DDS) is challenging due to its affinity for hydrophilic excipients. This means that a medium polarity excipient is preferred for the development of a stable nanostructured lipid carrier (NLC) formulation. In turn, in NLC, the type and number of excipients will determine the active pharmaceutical ingredient (API) solubility and the maximum drug upload. To solve this dilemma and get the best formulation, a throughout screening study to evaluate API solubilization in different excipients was carried out. Subsequently, excipients with different solubilization capacities were selected for microscopic evaluation by Raman mapping, and in turn analysis of the distributional homogeneity index (DHI) and standard deviation of the histograms allowed solving the posed question. Design of experiments (DoE) was employed to understand better the interactions between the excipients; linear and higher-order models were obtained with R2 above of 0.8824. Even though DHI is a good parameter to be used as response, an API concentration higher than 30% (w/w) provided a homogeneous surface in case of good miscibility and, in this case, this parameter needs to be employed with an inspection and/or evaluation of other parameters. A curve of concentration vs. mean scores of images proved to be an alternative to identify the saturation/limit of linear range.

Topical caffeine-loaded nanostructured lipid carriers for enhanced treatment of cellulite: A 32 full factorial design optimization and in vivo evaluation in rats

The goal of this study was the development and evaluation of semisolid caffeine (CAF) loaded nanostructured lipid carriers (NLCs) for topical treatment of cellulite. CAF-loaded NLC formulations were prepared via high-speed homogenization followed by ultrasonication. A 32 full factorial design was employed for formulation optimization. The total lipid content (%) and the liquid lipid content per total lipids (%) were chosen as factors, whereas particle size (PS), polydispersity index (PDI), zeta potential (|ZP|) and viscosity (VIS) were selected as responses. The design suggested CAF-NLC3 as the optimum formulation consisting of a total lipid content of 15% w/w (palmitic acid and soft paraffin/isopropyl myristate, 7:3 w/w) and a surfactant content of 10% w/w (Tween 80/lecithin, 8:1.2 w/w). CAF-NLC3 revealed PS, PDI, ZP, VIS and CAF content values of 318.8 nm, 0.253, -41.1 mV, 18.0 Pa.s and 97.57%, respectively. It showed a pseudoplastic rheological behavior, acceptable pH value (5.25), good spreadability (1.12 mm2/g) and spherical shape employing transmission electron microscopy. Differential scanning calorimetry and X-ray diffraction demonstrated the amorphization of CAF in CAF-NLC3. CAF-NLC3 remained stable for 3 months at room and refrigeration conditions. A single topical application of CAF-NLC3 on shaved abdominal skins of Wistar rats revealed enhanced skin retention of CAF by 2-fold and 1.4-fold after 4 h when compared with plain CAF gel (CAF-P) and marketed CAF gel (CAF-M), respectively. Furthermore, CAF-NLC3 exhibited a superior anti-cellulite activity in comparison with CAF-P and CAF-M through elevating extracellular matrix components (collagen 1, elastin and hyaluronic acid) and stimulating the brown adipose tissue thermogenesis via up-regulating UCP1 and PPAR-γ expression. In addition, CAF-NLC3 prominently increased lipolysis through HSL activity and decreased pro-inflammatory cytokines such as ICAM-1 and VCAM-1 after 30 days of treatment on a high fat diet-induced cellulite rat model. These findings were further confirmed by histopathological examination supported by morphometric analysis. Therefore, incorporation of CAF in a semisolid NLC formulation would be a promising cosmetic approach for the topical treatment of cellulite.

Formulation design, production and characterisation of solid lipid nanoparticles (SLN) and nanostructured lipid carriers (NLC) for the encapsulation of a model hydrophobic active

•

Lipid materials were chosen based on theoretical and experimental lipid screening.

•

SLNs and NLCs with high curcumin loading were produced using the selected lipids.

•

Nano-sized lipid particles fabricated by tuning the processing parameters.

•

Lipid matrix component compatibility affects thermal properties as shown by DSC.

•

Formation of distinct lipid structures in liquid lipid concentration-dependent manner.

Lipid nanoparticles have been widely investigated for their use as either carriers for poorly water soluble actives or as (Pickering) emulsion stabilisers. Recent studies have suggested that the fabrication of lipid nanostructures that can display both these performances concurrently, can enable the development of liquid formulations for multi-active encapsulation and release. Understanding the effects of different formulation variables on the microstructural attributes that underline both these functionalities is crucial in developing such lipid nanostructures. In this study, two types of lipid-based nanoparticles, solid lipid nanoparticles and nanostructured lipid carriers, were fabricated using varying formulation parameters, namely type of solid lipid, concentration of liquid lipid and type/concentration of surface active species. The impact of these formulation parameters on the size, thermal properties, encapsulation efficiency, loading capacity and long-term storage stability of the developed lipid systems, was studied. Preliminary lipid screening and processing conditions studies, focused on creating a suitable lipid host matrix of appropriate dimensions that could enable the high loading of a model hydrophobic active (curcumin). Informed by this, selected lipid nanostructures were then produced. These were characterised by encapsulation efficiency and loading capacity values as high as 99% and 5%, respectively, and particle dimensions within the desirable size range (100-200 nm) required to enable Pickering functionality. Compatibility between the lipid matrix components, and liquid lipid/active addition were shown to greatly influence the polymorphism/crystallinity of the fabricated particles, with the latter demonstrating a liquid lipid concentration-dependent behaviour. Successful long-term storage stability of up to 28 weeks was confirmed for certain formulations.

Chitosan modified squalene nanostructured lipid carriers as a promising adjuvant for freeze-dried ovalbumin vaccine

As immune adjuvants assisting vaccines, nanoparticle delivery systems have been widely exploited. Squalene, the major ingredient of approved adjuvant MF59, has great potential in activating immune responses. In the current study, model antigen ovalbumin (OVA) was encapsulated into squalene-based nanostructured lipid carriers (NLCs), and the chitosan, a cationic polysaccharide, was used for modifying nanoparticles to develop a functionalized and cationic nanoparticle delivery system (OVA-csNLCs). Firstly, the optimal formulation of csNLCs was successfully screened out, and had hydrodynamic diameter of 235.80 ± 5.99 nm and zeta potential of 34.90 ± 6.95 mV. Then, the generated OVA-csNLCs had no significant difference in hydrodynamic diameter and exhibited lower zeta potential of 19.03 ± 0.31 mV and high encapsulation efficiency of 83.4%. Sucrose (10%, w/w) was selected as optimal lyoprotectant, exhibiting good stability of OVA-csNLCs in the form of freeze-dried powder. More importantly, the OVA-csNLCs effectively promoted OVA antigen uptake by macrophage, significantly enhanced the level of OVA-specific IgG, and induced a Th2-based immune response in vivo. Furthermore, mice immunization experiment demonstrated that OVA-csNLCs had well biocompatibility and facilitated spleen lymphocytes proliferation. Above findings indicate that chitosan modified squalene nanostructured lipid carriers show promise as antigen delivery system and an open adjuvant platform.

Lipid nanoparticles with improved biopharmaceutical attributes for tuberculosis treatment

Tuberculosis is a topic of relevance worldwide because of the social and biological factors that triggered the disease and the economic burden on the health-care systems that imply its therapeutic treatment. Challenges to handle these issues include, among others, research on technological breakthroughs modifying the drug regimens to facilitate therapy adherence, avoid mycobacterium drug resistance, and minimize toxic side-effects. Lipid nanoparticles arise as a promising strategy in this respect as deduced from the reported scientific data. They are prepared from biodegradable and biocompatible starting materials and compared to the use of the free drugs, the entrapment of active molecules into the carriers might lead to both dose reduction and controlled delivery. Moreover, the target to the lung, the organ mainly affected by the disease, could be possible if the particle surface is modified. Although conclusive statements cannot be made considering the limited number of available research works, looking into what has been achieved up to now definitively encourages to continue investigations in this regard.

Analytical tools and evaluation strategies for nanostructured lipid carrier-based topical delivery systems

INTRODUCTION

The inception of nanostructured lipid carriers (NLCs) proved to be a revolutionary step toward the treatment of dermatological disorders. To uncover its true potential, it is imperative that the system be characterized and evaluated comprehensively.

AREAS COVERED

The present review has been written to furnish an in-depth account of analytical tools and evaluation procedures under one roof. Besides discussing the challenges of topical delivery and benefits of NLCs, the paper elaborates on their physicochemical characterization. Further, in vitro evaluation of NLCs for dermatological benefits, followed by their evaluation in a hydrogel/cream base is covered. Lastly, disease-specific evaluation of NLC-based formulations is presented.

EXPERT OPINION

The research endeavors for NLCs have largely focused on the fabrication of NLCs for different bioactives. However, scientific efforts should be aimed toward the lesser explored realm of NLCs, i.e. exploitation of analytical techniques, such as Parelectric spectroscopy, Electron Spin Resonance, and Nuclear Magnetic Resonance spectroscopy. NLCs have been proven for their potential to foster the therapeutic modalities applicable to cutaneous disorders. More attention needs to be devoted to their evaluation for disease-specific parameters. The futuristic steps must involve clinical studies, to lay the path for their commercialization.

Intranasal Nanoparticulate Systems as Alternative Route of Drug Delivery

There is always a need for alternative and efficient methods of drug delivery. The nasal cavity can be considered as a non-invasive and efficient route of administration. It has been used for local, systemic, brain targeting, and vaccination delivery. Although many intranasal products are currently available on the market, the majority is used for local delivery with fewer products available for the other targets. As nanotechnology utilization in drug delivery has rapidly spread out, the nasal delivery has become attractive as a promising approach. Nanoparticulate systems facilitate drug transportation across the mucosal barrier, protect the drug from nasal enzyme degradation, enhance the delivery of vaccines to the lymphoid tissue of the nasal cavity with an adjuvant activity, and offer a way for peptide delivery into the brain and the systemic circulation, in addition to their potential for brain tumor treatment. This review article aims at discussing the potential benefit of the intranasal nanoparticulate systems, including nanosuspensions, lipid and surfactant, and polymer-based nanoparticles as regards productive intranasal delivery. The aim of this review is to focus on the topicalities of nanotechnology applications for intranasal delivery of local, systemic, brain, and vaccination purposes during the last decade, referring to the factors affecting delivery, regulatory aspects, and patient expectations. This review further identifies the benefits of applying the Quality by Design approaches (QbD) in product development. According to the reported studies on nanotechnology-based intranasal delivery, potential attention has been focused on brain targeting and vaccine delivery with promising outcomes. Despite the significant research effort in this field, nanoparticle-based products for intranasal delivery are not available. Thus, further efforts are required to promote the introduction of intranasal nanoparticulate products that can meet the requirements of regulatory affairs with high patient acceptance.

Comparison of different chemometric methods to extract chemical and physical information from Raman images of homogeneous and heterogeneous semi-solid pharmaceutical formulations

In formulations of nanostructured lipid carriers, lipid solid dispersions and self-emulsifying drug delivery systems, it is common that a solid or semi-solid lipid excipient is mixed with a liquid solvent or liquid lipid. Even when the excipients are visually miscible upon melting, they might have microscopic non-homogeneities which could lead to instability over time and future phase separation. Raman mapping associated with chemometric methods can be useful to evaluate spatial distribution of compounds, however it has not been extensively applied to the formulations mentioned above. The aim of this work was to compare the outcomes of three different chemometric methods - principal components analysis (PCA), multivariate curve resolution with alternating least squares (MCR-ALS) and independent components analysis (ICA) - to study two systems of very different degrees of microscopic miscibility: cetyl palmitate + Transcutol^© (heterogeneous) and polyethylene glycol 6000 (PEG 6000) + Tween 80^© (homogeneous). These two samples were chosen due to large differences in spatial distribution of the compounds over the pixels which could require different approaches for data treatment. The three methods were compared regarding recovered concentrations (or scores), signals (or loadings) and the need for matrix augmentation to obtain reliable results. Results showed that PCA loadings were the mathematical differences of the spectra of pure compounds for both samples, and therefore only 'contrast images' could be generated. MCR and ICA provided signals that could be related to the chemical components, however MCR presented rotational ambiguities even for the very heterogeneous sample, a situation in which ICA performed better as a blind search method. For the homogeneous sample, both methods showed rank deficiency and therefore the use of a matrix augmentation was necessary. ICA and PCA allowed identifying physical modifications in the homogeneous semi-solid PEG 6000/Tween 80^® sample over the time, probably due to the folding/unfolding of the crystalline chains of PEG 6000. Therefore, this work discusses the ability of the three chemometrics methods to extract information from Raman spectra in order to characterize the chemical, spatial and even physical aspects of semi-solid pharmaceutical formulations, which could be of much use for stability studies of different drug delivery systems.

Silver nanoparticle functionalized CS-g-(CA-MA-PZA) carrier for sustainable anti-tuberculosis drug delivery

Recently, drug functionalized biodegradable polymers have been appreciated to be imperative to fabricate multi-drug delivery nanosystems for sustainable drug release. In this work, amphiphilic chitosan-grafted-(cetyl alcohol-maleic anhydride-pyrazinamide) (CS-g-(CA-MA-PZA)) was synthesized by multi-step reactions. The incorporation of rifampicin (RF) and entrapment of silver nanoparticles (Ag NPs) on CS-g-(CA-MA-PZA) polymer was carried out by dialysis technique. From the FT-IR experiment, the polymer modification, incorporation of drugs and the entrapment of Ag NPs on micelles were confirmed. The surface morphology of Ag NPs, polymeric system and drug loaded micelles was described by SEM, TEM and AFM techniques. In addition, the controlled release behaviour of CS-g-(CA-MA-PZA) micelles was studied by UV-Vis spectroscopy. In vitro cell viability, cell apoptosis and cellular uptake experiments shows that multi-drug delivery system could enhance the biocompatibility and higher the cytotoxicity effect on the cells. Since the prepared amphiphilic polymeric micelles exhibit spotty features and the system is a promising strategy for a novel candidate for immediate therapeutically effects for alveolar macrophages.

Development of cholate conjugated hybrid polymeric micelles for FXR receptor mediated effective site-specific delivery of paclitaxel

The aim of the present study was to explore the tumor targeting potential of a cholic acid (CA) conjugated polymeric micelle system for the effective delivery of paclitaxel (PTX).

Optimised NLC: a nanotechnological approach to improve the anaesthetic effect of bupivacaine

The short time of action and systemic toxicity of local anaesthetics limit their clinical application. Bupivacaine is the most frequently used local anaesthetic in surgical procedures worldwide. The discovery that its S(-) enantiomeric form is less toxic than the R(+) form led to the introduction of products with enantiomeric excess (S75:R25 bupivacaine) in the market. Nevertheless, the time of action of bupivacaine is still short; to overcome that, bupivacaine S75:R25 (BVC_S75) was encapsulated in nanostructured lipid carriers (NLC). In this work, we present the development of the formulation using chemometric tools of experimental design to study the formulation factors and Raman mapping associated with Classical Least Squares (CLS) to study the miscibility of the solid and the liquid lipids. The selected formulation of the nanostructured lipid carrier containing bupivacaine S75:R25 (NLC_BVC) was observed to be stable for 12 months under room conditions regarding particle size, polydispersion, Zeta potential and encapsulation efficiency. The characterisation by DSC, XDR and TEM confirmed the encapsulation of BVC_S75 in the lipid matrix, with no changes in the structure of the nanoparticles. The in vivo analgesic effect elicited by NLC_BVC was twice that of free BVC_S75. Besides improving the time of action_, no statistical difference in the blockage of the sciatic nerve of rats was found between 0.125% NLC_BVC and 0.5% free BVC_S75. Therefore, the formulation allows a reduction in the required anaesthesia dose, decreasing the systemic toxicity of bupivacaine, and opening up new possibilities for different clinical applications.

Structure of solid lipid nanoparticles produced by a microwave-assisted microemulsion technique

The current study investigates the structure of solid lipid nanoparticles, prepared using a recently reported microwave-assisted microemulsion technique, by multi-angle static and dynamic light scattering and small angle X-ray scattering techniques.

Transport of stearic acid-based solid lipid nanoparticles (SLNs) into human epithelial cells

Development of drug delivery systems, as much as the drug molecule itself, is an important consideration for improving drug absorption and bioavailability. The mechanisms by which drug carriers enter target cells can differ depending on their size, surface properties and components. Solid lipid nanoparticles (SLNs) have gained an increased attention in recent years and are the drug carriers of interest in this paper. They are known to breach the cell-membrane barrier and have been actively sought to transport biomolecules. Previous studies by our group, and also other groups, provided an extensive characterization of SLNs. However, few studies have investigated the uptake of SLNs and these have had limited mechanistic focus. The aim of this work was to investigate the pathway of uptake of SLNs by human epithelial cells i.e., lung A549 and cervical HeLa cells. To the best of our knowledge, this is first study that investigates the cellular uptake of SLNs by human epithelial cells. The mechanism of cellular uptake was deciphered using pharmacologic inhibitors (sucrose, potassium-free buffer, filipin and cytochalasin B). Imaging techniques and flow assisted cell sorting (FACS) were used to assess the cellular uptake of SLNs loaded with rhodamine 123 as a fluorescent probe. This study provided evidence that the cellular uptake of SLNs was energy-dependent, and the endocytosis of SLNs was mainly dependent on clathrin-mediated mechanisms. The establishment of entry mechanism of SLNs is of fundamental importance for future facilitation of SLNs as biological or drug carriers.

High-performance reverse osmosis CNT/polyamide nanocomposite membrane by controlled interfacial interactions

Polyamide reverse osmosis (RO) membranes with carbon nanotubes (CNTs) are prepared by interfacial polymerization using trimesoyl chloride (TMC) solutions in n-hexane and aqueous solutions of m-phenylenediamine (MPD) containing functionalized CNTs. The functionalized CNTs are prepared by the reactions of pristine CNTs with acid mixture (sulfuric acid and nitric acid of 3:1 volume ratio) by varying amounts of acid, reaction temperature, and reaction time. CNTs prepared by an optimized reaction condition are found to be well-dispersed in the polyamide layer, which is confirmed from atomic force microscopy, scanning electron microscopy, and Raman spectroscopy studies. The polyamide RO membranes containing well-dispersed CNTs exhibit larger water flux values than polyamide membrane prepared without any CNTs, although the salt rejection values of these membranes are close. Furthermore, the durability and chemical resistance against NaCl solutions of the membranes containing CNTs are found to be improved compared with those of the membrane without CNTs. The high membrane performance (high water flux and salt rejection) and the improved stability of the polyamide membranes containing CNTs are ascribed to the hydrophobic nanochannels of CNTs and well-dispersed states in the polyamide layers formed through the interactions between CNTs and polyamide in the active layers.

Fourier transform infrared spectroscopy and Raman spectroscopy as tools for identification of steryl ferulates

Steryl ferulates are a mixture of minor bioactive compounds, possessing well-established health benefits. However, individual steryl ferulate species show structural differences, which seem to substantially influence their health-promoting potential. In this study, we tested Fourier transform infrared (FTIR) spectroscopy and Raman spectroscopy, as potential tools in the identification of steryl ferulates. On the basis of our spectral data obtained from various individual steryl ferulates and steryl ferulate mixtures extracted from rice (γ-oryzanol), corn bran, and wheat bran, we provide comprehensive peak assignment tables for both FTIR and Raman. With the help of FTIR spectroscopy, structural differences between individual steryl ferulates were possible to identify, such as the presence of the cyclopropane ring and additional differences in the side chain of the sterane skeleton. Data obtained with Raman spectroscopy provided us with a control for FTIR peak assignment and also with some additional information on the samples. However, detecting structural differences between steryl ferulates was not possible with this method. We consider that FTIR spectroscopy alone or combined with Raman provides detailed data on the structures of steryl ferulates. Moreover, thorough peak assignment tables presented in this study could prove to be helpful tools when identifying steryl ferulates, especially as a group, in future studies.

Lipid nanoparticles based on butyl-methoxydibenzoylmethane: in vitro UVA blocking effect

The aim of the present study was to obtain efficient lipid nanoparticles loaded with butyl-methoxydibenzoylmethane (BMDBM) in order to develop cosmetic formulations with enhanced UVA blocking effect. For this purpose, two adequate liquid lipids (medium chain triglycerides and squalene) have been used in combination with two solid lipids (cetyl palmitate and glyceryl stearate) in order to create appropriate nanostructured carriers with a disordered lipid network able to accommodate up to 1.5% BMDBM. The lipid nanoparticles (LNs) were characterized in terms of particle size, zeta potential, entrapment efficiency, loading capacity and in vitro UVA blocking effect. The efficiency of lipid nanoparticles in developing some cosmetic formulations has been evaluated by determining the in vitro erythemal UVA protection factor. In order to quantify the photoprotective effect, some selected cream formulations based on BMDBM-LNs and a conventional emulsion were exposed to photochemical UV irradiation at a low energy to simulate the solar energy during the midday. The results obtained demonstrated the high ability of cream formulations based on BMDBM-LNs to absorb more than 96% of UVA radiation. Moreover, the developed cosmetic formulations manifest an enhanced UVA blocking effect, the erythemal UVA protection factor being four times higher than those specific to conventional emulsions.

Effect of Surfactant on Characteristics of Solid Lipid Nanoparticles (SLN)

SLN have shown a great promise as an alternative drug carrier for intravenous and dermal applications. This work focuses on the basic properties of drug-free Compritol® ATO 888 based SLN systems by using cationic surfactant (CPC) and nonionic surfactant (Tween 80). Effects of surfactant on the physical properties of SLNs were investigated in the absence of model drug to avoid the interaction between drug and surfactant. These SLN samples have different particle size, zeta potential and morphology. DSC was used to quantify the crystallinity of SLN systems. It was found that %RI of both SLNs was similar, indicating that types of surfactant did not affect on crystallization of solid lipid. Spherical-like particle was observed with SLN-C, while rod-like particle was found with SLN-T. The results demonstrated that surfactant plays an important role on SLN physical characteristics.