Physicochemical investigations on the structure of drug-free and drug-loaded solid lipid nanoparticles (SLN) by means of DSC and 1H NMR

A solid lipid nanoparticle (SLN) formulation, based on the lipid Imwitor 900, was developed for the incorporation of the poorly water soluble drug RMEZ98. Physicochemical investigations were undertaken to examine the structure and physical stability of the selected lipid as colloidal dispersion in comparison to the bulk material. Using differential scanning calorimetry (DSC) and proton nuclear magnetic resonance (1H NMR) it could be assessed the influence of the incorporated drug on the structure of the lipid matrix. Investigation of mixtures of Imwitor 900 and RMEZ98 showed an increasing effect on the melting/recrystallization behaviour with increasing drug content (5-30%). DSC and 1H NMR results revealed the formation of a crystalline matrix of SLN when prepared by high pressure homogenization excluding, therefore, the phenomenon of supercooled melt. After preparation of RMEZ98-loaded SLN, the drug remained inside the lipid matrix; however, it exhibited only a small effect on the recrystallization behaviour of Imwitor 900 at the lowest payload required for a therapeutic effect (4% m/m with regard to the lipid matrix). Furthermore, the incorporation of RMEZ98 revealed no distinct influence on the particle size distribution. Imwitor 900 proved to be a suitable lipid for the drug RMEZ98, i.e. possessing a sufficient loading capacity and simultaneously physical stability.     

Polymorphic behaviour of Compritol888 ATO as bulk lipid and as SLN and NLC

CompritolR888 ATO (glycerol behenate) is widely used as a pharmaceutical excipient in the field of solid dosage forms due to its lubricating properties. It is an amphiphilic material with a high melting point (approximately 70 degrees C) and, therefore, it can also be used to prepare aqueous colloidal dispersions. The aim of this paper is to study the suitability of CompritolR888 ATO for the production of solid lipid nanoparticles (SLN) and nanostructured lipid carriers (NLC) for the entrapment of a lipophilic model drug. This study assesses the crystalline structure of the bulk lipid, as well as the changes that occur in its crystal lattice with the addition of 'impurities', such as oil (alpha-tocopherol) and drug (ketoconazole), using DSC and X-ray diffraction analysis before and after thermal stress. Aqueous SLN and NLC dispersions were produced using an appropriate surfactant/co-surfactant system and their physicochemical stability was assessed by PCS, LD, DSC and by WAXS. It was found that the crystalline lattice of CompritolR888 ATO is composed of very small amounts of the unstable alpha polymorphic form characteristic of triacylglycerols, which disappears after thermal stress of bulk lipid. Mixing oils and drug molecules which are soluble in this lipid decreased its lattice organization and, thus, was revealed to be suitable for production of lipid nanoparticles containing ketoconazole. However, particle growth could not be avoided during shelf life.     

Polymorphic behaviour of Compritol®888 ATO as bulk lipid and as SLN and NLC

Compritol®888 ATO (glycerol behenate) is widely used as a pharmaceutical excipient in the field of solid dosage forms due to its lubricating properties. It is an amphiphilic material with a high melting point (～70°C) and, therefore, it can also be used to prepare aqueous colloidal dispersions. The aim of this paper is to study the suitability of Compritol®888 ATO for the production of solid lipid nanoparticles (SLN) and nanostructured lipid carriers (NLC) for the entrapment of a lipophilic model drug. This study assesses the crystalline structure of the bulk lipid, as well as the changes that occur in its crystal lattice with the addition of ‘impurities’, such as oil (α-tocopherol) and drug (ketoconazole), using DSC and X-ray diffraction analysis before and after thermal stress. Aqueous SLN and NLC dispersions were produced using an appropriate surfactant/co-surfactant system and their physicochemical stability was assessed by PCS, LD, DSC and by WAXS. It was found that the crystalline lattice of Compritol®888 ATO is composed of very small amounts of the unstable α polymorphic form characteristic of triacylglycerols, which disappears after thermal stress of bulk lipid. Mixing oils and drug molecules which are soluble in this lipid decreased its lattice organization and, thus, was revealed to be suitable for production of lipid nanoparticles containing ketoconazole. However, particle growth could not be avoided during shelf life.     

Influence of emulsifiers on the crystallization of solid lipid nanoparticles

The crystallization temperature and polymorphism of tripalmitin nanoparticles in colloidal dispersions prepared by melt-homogenization and stabilized with different pharmaceutical surfactants (sodium glycocholate, sodium oleate, tyloxapol, Solutol HS 15, Cremophor EL) and their combinations with soybean phospholipid (Lipoid S100) were investigated to establish the influence of the emulsifiers on these parameters. There were no major effects on the crystallization temperature but remarkable differences in the time-course of polymorphic transitions after crystallization of the triglyceride particles indicate interaction between the surfactant layer and the triglyceride matrix. The metastable alpha-modification was most stable in dispersions solely stabilized with glycocholate. Upon fast cooling from the melt, these dispersions form an uncommon type of alpha-modification that displays only a very weak small-angle reflection indicating poor ordering between triglyceride layers. Slow crystallization of these glycocholate-stabilized nanoparticles yields the usual alpha-form. Electron microscopic investigations reveal that, in both cases, the particles in the alpha-modification are less anisometric than those of the stable beta-form. These results indicate that major rearrangements still may take place in solid lipid nanoparticles after recrystallization.     

Solid lipid nanoparticles (SLN) for controlled drug delivery II. drug incorporation and physicochemical characterization

Solid lipid nanoparticles (SLN) are a colloidal carrier system for controlled drug delivery. The lipophilic model drugs tetracaine and etomidate were incorporated to study the maximum drug loading, entrapment efficacy, effect of drug incorporation on SLN size, zeta potential (charge) and long-term physical stability. Drug loads of up to 10% could be achieved whilst simultaneously maintaining a physically stable nanoparticle dispersion. Incorporation of drugs showed no or little effect on particle size and zeta potential compared to drug-free SLN. The optimized production parameters previously established for drug-free SLN dispersions can therefore be transferred to drug-loaded systems to facilitate product development.     

Solid lipid nanoparticles (SLN) for controlled drug delivery. II. Drug incorporation and physicochemical characterization

Solid lipid nanoparticles (SLN) are a colloidal carrier system for controlled drug delivery. The lipophilic model drugs tetracaine and etomidate were incorporated to study the maximum drug loading, entrapment efficacy, effect of drug incorporation on SLN size, zeta potential (charge) and long-term physical stability. Drug loads of up to 10% could be achieved whilst simultaneously maintaining a physically stable nanoparticle dispersion. Incorporation of drugs showed no or little effect on particle size and zeta potential compared to drug-free SLN. The optimized production parameters previously established for drug-free SLN dispersions can therefore be transferred to drug-loaded systems to facilitate product development.     

Selection and characterization of suitable lipid excipients for use in the manufacture of didanosine-loaded solid lipid nanoparticles and nanostructured lipid carriers

This research aimed to evaluate the suitability of lipids for the manufacture of solid lipid nanoparticles (SLNs) and nanostructured lipid carriers (NLCs) loaded with the hydrophilic drug, didanosine (DDI). The crystalline state and polymorphism of lipids with the best‐solubulizing potential for DDI was investigated using differential scanning calorimetry (DSC) and wide‐angle X‐ray scattering (WAXS). DSC and WAXS were also used to determine potential interactions between the bulk lipids and DDI. Precirol® ATO 5 and Transcutol® HP showed the best‐solubilizing potential for DDI. Precirol® ATO 5 exists in the β‐modification before heating; however, a mixture of both α‐ and β‐modifications were detected following heating. Addition of Transcutol® HP to Precirol® ATO 5 changes the polymorphism of the latter from the β‐modification to a form that exhibits coexistence of the α‐ and β‐modifications. DDI exists in a crystalline state when dispersed at 5% (w/w) in Precirol® ATO 5 or in a Precirol® ATO 5/Transcutol® HP mixture. DSC and WAXS profiles of DDI/bulk lipids mixture obtained before and after exposure to heat revealed no interactions between DDI and the lipids. Precirol® ATO 5 and a mixture of Precirol® ATO 5 and Transcutol® HP may be used to manufacture DDI‐loaded SLN and NLC, respectively.     

Solid lipid nanoparticles incorporated in dextran hydrogels: a new drug delivery system for oral formulations

Solid lipid nanoparticles (SLN) containing or not (S)-(+)-2-(4-isobutylphenyl)propionic acid (ibuprofen) were prepared with Preciol ATO 5 as lipid phase by the hot homogenization technique and characterized through particle size analyses and zeta potential measurements. DSC experiments carried out on the freeze-dried samples of loaded SLN showed a shift of the melting endotherm of the lipid phase, with the maximum at a temperature value higher then that of the "empty" SLN. (1)H NMR of the nanosuspension allowed to calculate the encapsulation efficiency of the particles that was 52+/-3%. By adding dextran methacrylate (DEX-MA) to the aqueous phase and submitting the mixture to UV irradiation, systems of SLN (drug-loaded and unloaded) incorporated into a dextran hydrogel were prepared. Finally, dissolution studies of ibuprofen from the freeze-dried samples were performed. The comparison among the release profiles of ibuprofen from SLN, DEX-MA hydrogel and SLN/DEX-MA-hydrogel allows to affirm that this last system, retaining about 60% of the drug after 2h in acid medium and releasing it slowly in neutral solution, is suitable for modified delivery oral formulations.     

Solid Lipid Nanoparticles (SLN) and Oil-Loaded SLN Studied by Spectrofluorometry and Raman Spectroscopy

Purpose Recently, colloidal dispersions made of mixtures from solid and liquid lipids have been described to overcome the poor drug loading capacity of solid lipid nanoparticles (SLN). It has been proposed that these nanostructured lipid carriers (NLC) are composed of oily droplets, which are embedded in a solid lipid matrix. High loading capacities and controlled release characteristics have been claimed. It is the objective of the present paper to investigate these new NLC particles in more detail to obtain insights into their structure. Methods Colloidal lipid dispersions were produced by high-pressure homogenization. Particle sizes were estimated by laser diffraction and photon correlation spectroscopy. The hydrophobic fluorescent marker nile red (NR) was used as model drug, and by fluorometric spectroscopy, the molecular environment (polarity) was elucidated because of solvatochromism of NR. The packaging of the lipid nanoparticles was investigated by Raman spectroscopy and by densimetry. The light propagation in lipid nanodispersions was examined by refractometry to obtain further insights into the nanostructural compositions of the carriers. Results Fluorometric spectroscopy clearly demonstrates that NLC nanoparticles offer two nanocompartments of different polarity to accommodate NR. Nevertheless, in both compartments, NR experiences less protection from the outer water phase than in a nanoemulsion. In conventional SLN, lipid crystallization leads to the expulsion of the lipophilic NR from the solid lipid. Measurements performed by densimetry and Raman spectroscopy confirm the idea of intact glyceryl behenate lattices in spite of oil loading. The lipid crystals are not disturbed in their structure as it could be suggested in case of oil incorporation. Refractometric data reveal the idea of light protection because of incorporation of sensitive drug molecules in NLC. Conclusion Neither SLN nor NLC lipid nanoparticles did show any advantage with respect to incorporation rate compared to conventional nanoemulsions. The experimental data let us conclude that NLC lipid nanoparticles are not spherical solid lipid particles with embedded liquid droplets, but they are rather solid platelets with oil present between the solid platelet and the surfactant layer.     

Influence of different parameters on reconstitution of lyophilized SLN

Drug-loaded solid lipid nanoparticles (SLN) suitable for parenteral administration were freeze-dried. The lipid matrix Imwitor 900 (concentration, 2.5%) was stabilized with Lipoid E 80 and sodium glycocholate. The influence of different parameters of lyophilization like the protective effect of cryoprotectants, freezing velocity, and thermal treatment was investigated. The results of this study demonstrate that, by optimizing critical process parameters, i.v.-injectable SLN-dispersions can be freeze-dried, preserving their small particle size.     

Key production parameters for the development of solid lipid nanoparticles by high shear homogenization

In this work, we report the development and optimization of solid lipid nanoparticles (SLN) production by a simple, fast, and cost-effective high shear homogenization process. A screening of several solid lipids (Compritol 888 ATO, Precirol ATO 5, Cetyl Palmitate, Dynasan 118, Imwitor 900K, Stearic acid) has been carried out in combination with Poloxamer 188 as the selected surfactant, based on the mean particle size and polydispersity index. The improvement of the physical stability of the SLN dispersions was achieved by the use of a cationic lipid (cetyl trimethylammonium bromide) reaching zeta potential values above +60 mV. Combining the optimized speed and time of shear, monodispersed SLN (PdI < 0.25) under the nanometer range could be produced.     

Comparison of wax and glyceride solid lipid nanoparticles (SLN)

The present study compares solid lipid nanoparticles (SLN) formulated with either wax or glyceride bulk material. While most published data deal with glyceride SLN, little knowledge is reported on wax carriers. The two types were compared with respect to drug encapsulation efficacy, particle size distribution after production and storage, and crystal packing. The inclusion of retinol as a model drug was investigated. Retinol is chemically unstable in water and rather stable in lipid phases. Thus, rapid degradation of retinol indicates rapid drug expulsion from the carrier. Good stability indicates an effective drug encapsulation in the lipid phase of the nanoparticles. Particle size distribution was measured by laser diffractometry. Subcell packing and assignment of polymorphic forms was investigated by WAXS measurements. Glyceride SLN showed good drug encapsulation, while physical stability was poor. In contrast, wax SLN possessed good physical stability but lacked sufficient drug encapsulation in the solidified state. These differences were attributed in part to different crystal packing. Less ordered crystal lattices favour successful drug inclusion, as in the case of glyceryl monosterate and glyceryl behenate SLN. The highly ordered crystal packing of wax SLN comprised of beeswax or cetyl palmitate, for instance, leads to drug expulsion, but also to superior physical stability.     

Investigation of the factors influencing the incorporation of clotrimazole in SLN and NLC prepared by hot high-pressure homogenization

Clotrimazole, a fungicidal effective for the local treatment of cutaneous and mucosal infections, was incorporated into solid lipid nanoparticles (SLN) and nanostructured lipid carriers (NLC). The aim was to increase its dermal bioavailability and to control drug release, thereby potentially reducing its side effects. Prior to the release studies, the carrier was optimized and characterized by using different techniques. Laser diffractometry (LD), photon correlation spectroscopy (PCS) and scanning electron microscopy (SEM) indicated that SLN were spherical in shape with a mean size of approximately 400 nm. Some aggregation phenomena occurred during preparation of SEM samples due to the lipid character of the carriers. No physico-chemical instability of the drug-loaded lipid nanoparticles was detected during 2 years of storage at different temperatures. X-ray and DSC results suggested that during storage time the drug remained molecularly dispersed in the lipid matrix. Drug associated to SLN and NLC in its crystal form could be excluded.     

Evaluation of the physical stability of SLN and NLC before and after incorporation into hydrogel formulations.

Aqueous dispersions of lipid nanoparticles are being investigated as drug delivery systems for different therapeutic purposes. One of their interesting features is the possibility of topical use, for which these systems have to be incorporated into commonly used dermal carriers, such as creams or hydrogels, in order to have a proper semisolid consistency. For the present investigation four different gel-forming agents (xanthan gum, hydroxyethylcellulose 4000, Carbopol943 and chitosan) were selected for hydrogel preparation. Aqueous dispersions of lipid nanoparticles--solid lipid nanoparticles (SLN) and nanostructured lipid carriers (NLC)--made from tripalmitin were prepared by hot high pressure homogenization and then incorporated into the freshly prepared hydrogels. NLC differ from SLN due to the presence of a liquid lipid (Miglyol812) in the lipid matrix. Lipid nanoparticles were physically characterized before and after their incorporation into hydrogels. By means of rheological investigations it could be demonstrated that physical properties of the dispersed lipid phase have a great impact on the rheological properties of the prepared semisolid formulations. By employing an oscillation frequency sweep test, significant differences in elastic response of SLN and NLC aqueous dispersions could be observed.     

Lipid-Drug-Conjugate (LDC) Nanoparticles as Novel Carrier System for the Hydrophilic Antitrypanosomal Drug Diminazenediaceturate

The objective of the present study was to incorporate the hydrophilic drug diminazenediaceturate at a high loading into lipid nanoparticles by creating nanoparticles from lipid-drug conjugates (LDC). IR and DSC data showed that the antitrypanosomal drug diminazene is able to react with fatty acids to form water-insoluble salts like diminazenedistearate and -dioleate. The salts could be transformed into nanoparticles using high-pressure homogenization technique, established for solid lipid nanoparticles (SLN). By using polysorbate 80 as surfactant, physically stable LDC nanoparticle dispersions of both salts could be obtained. The mean PCS diameters and polydispersity indices were 364 nm and 0.233 for diminazenedistearate and 442 nm and 0.268 for diminazenedioleate, respectively. Due to the composition of the LDC bulk materials, nanoparticles with a high drug load of 33% (w/w) were obtained even for this highly water-soluble drug diminazenediaceturate. The new carrier system of LDC nanoparticles overcomes one limitation of SLN, i.e. the limited loading capacity for hydrophilic drugs. Transforming water-soluble hydrophilic drugs into LDC and formation of nanoparticles allows prolonged drug release and targeting to specific sites by i.v. injection. These results provide a first basis of using LDC-polysorbate 80 nanoparticles for brain delivery of diminazene to treat second stage human African trypanosomiasis (HAT).     

A novel lipid nanocarrier for insulin delivery: production,characterization and toxicity testing

A novel nanocarrier based on solid lipid nanoparticles (SLNs) was developed for insulin delivery using a novel double emulsion method. Physical stability of particles was assessed by size analysis using dynamic light scattering (DLS), matrix crystallinity by differential scanning calorimetry (DSC) and toxicity analysis by Drosophila melanogaster testing. Insulin-SLNs were composed of Softisan®100 1.25% wt, Lutrol®F68 1% wt, soybean lecithin 0.125% wt, and loaded with 0.73–0.58?mg/mL peptide. Placebo-SLNs (insulin-free) also contained 0.025% wt Tween®80. Mean particle sizes of placebo-SLN and insulin-SLN were 958?±?9.5 and 978?±?8.3?nm, respectively. The polydispersity index (PI) was 0.28?±?0.018 and 0.29?±?0.013, respectively. Polarized light microscopy analysis depicted no aggregation of developed particles. DSC analysis allowed characterizing SLN with 43–51% matrix crystallinity. Using Drosophila melanogaster test, no toxicity was reported for SLN and for the bulk lipid. This study shows that SLNs are promising and helpful to overcome conventional insulin therapy, in particular for their lack of toxicity for oral delivery.     

Lipid-drug-conjugate (LDC) nanoparticles as novel carrier system for the hydrophilic antitrypanosomal drug diminazenediaceturate

The objective of the present study was to incorporate the hydrophilic drug diminazenediaceturate at a high loading into lipid nanoparticles by creating nanoparticles from lipid-drug conjugates (LDC). IR and DSC data showed that the antitrypanosomal drug diminazene is able to react with fatty acids to form water-insoluble salts like diminazenedistearate and -dioleate. The salts could be transformed into nanoparticles using high-pressure homogenization technique, established for solid lipid nanoparticles (SLN). By using polysorbate 80 as surfactant, physically stable LDC nanoparticle dispersions of both salts could be obtained. The mean PCS diameters and polydispersity indices were 364 nm and 0.233 for diminazenedistearate and 442 nm and 0.268 for diminazenedioleate, respectively. Due to the composition of the LDC bulk materials, nanoparticles with a high drug load of 33% (w/w) were obtained even for this highly water-soluble drug diminazenediaceturate. The new carrier system of LDC nanoparticles overcomes one limitation of SLN, i.e. the limited loading capacity for hydrophilic drugs. Transforming water-soluble hydrophilic drugs into LDC and formation of nanoparticles allows prolonged drug release and targeting to specific sites by i.v. injection. These results provide a first basis of using LDC-polysorbate 80 nanoparticles for brain delivery of diminazene to treat second stage human African trypanosomiasis (HAT).     

Solid lipid nanoparticles (SLN) for topical drug delivery: incorporation of the lipophilic drugs N,N-diethyl-m-toluamide and vitamin K

Solid lipid nanoparticles (SLN) for topical delivery were prepared by high pressure homogenization using solid lipids. The lipophilic agents DEET (N,N-diethyl-m-toluamide) and vitamin K were used as model drugs. These topical agents were incorporated into SLN which were characterized. Differential scanning calorimetry studies were performed in order to detect probable interactions in the SLN dispersions. Physical stability of SLN in aqueous dispersions and the effect of drug incorporation into SLN were investigated by photon correlation spectroscopy and zeta potential measurements. Characterization and short-term stability studies showedthat DEET and vitamin K are good candidates for topical SLN formulations.     

Characterization of indomethacin-loaded lipid nanoparticles by differential scanning calorimetry

Solid lipid nanoparticles (SLN) and nanostructured lipid carriers (NLC) are interesting nanoparticulate delivery systems produced from solid lipids. Both carrier types are submicron size particles but they can be distinguished by their inner structure. In the present paper, indomethacin (IND)-loaded SLN and NLC were prepared and the organization and distribution of the different ingredients originating each type of nanoparticle system were studied by differential scanning calorimetry (DSC) technique. Furthermore, mean particle size and percentage of drug encapsulation were also determined. From the results obtained, NLC lipid organization guaranteed an increased indomethacin encapsulation in comparison with SLN. DSC static and dynamic measurements performed on SLN and NLC showed that oil nanocompartments incorporated into NLC solid matrix drastically influenced drug distribution inside the nanoparticle system. Controlled release from NLC system could be explained considering both drug partition between oil nanocompartments and solid lipid and a successive partition between solid lipid and water.     

全反式维甲酸固体脂质纳米粒的制备及体内外评价

目的以山嵛酸甘油酯(Compritol 888 ATO)为脂质材料，采用超声分散法制备维甲酸固体脂质纳米粒，并考察其体内外性质。方法选用脂溶性较高的维甲酸作为模型药物，采用超声分散法制备固体脂质纳米粒，并对其各种理化性质进行研究。考察了纳米粒的体外释放，以维甲酸溶液剂为对照，测定了两种纳米粒在大鼠体内的药代动力学参数。结果采用超声分散法可以简便、快速制备得到两种维甲酸固体脂质纳米粒，透射电镜测得纳米粒为圆球状，大小均匀。动态光散射法测得平均粒径分别为(158±9) nm和(89±11) nm。于4 ℃放置1年粒径无明显变化，载药量为3.3%，包封率大于95%。药物体外释放符合Weibull方程。与对照组相比，两种维甲酸固体脂质纳米粒静脉注射后药物在血液中的滞留时间显著延长。结论超声分散法适用于固体脂质纳米粒的制备。