Physicochemical characterization of nanotemplate engineered solid lipid nanoparticles

Solid lipid nanoparticles: a versatile approach for controlled release and targeted drug delivery

Solid Lipid Nanoparticles (SLN), the first type of lipid-based solid carrier systems in the nanometer range, were introduced as a replacement for liposomes. SLN are aqueous colloidal dispersions with solid biodegradable lipids as their matrix. SLN is produced using processes like solvent diffusion method and high-pressure homogenization, among others. Major benefits include regulated release, increased bioavailability, preservation of peptides and chemically labile compounds like retinol against degradation, cost-effective excipients, better drug integration, and a broad range of applications. Solid lipid nanoparticles can be administered via different routes, such as oral, parenteral, pulmonary, etc. SLN can be prepared by using high shear mixing as well as low shear mixing. The next generation of solid lipids, nanostructured lipid carriers (NLC), can reduce some of the drawbacks of SLN, such as its restricted capacity for drug loading and drug expulsion during storage. NLC are controlled nanostructured lipid particles that enhance drug loading. This review covers a brief introduction of solid lipid nanoparticles, manufacturing techniques, benefits, limitations, and their characterization tests.

Mesoscopic Structure of Lipid Nanoparticle Formulations for mRNA Drug Delivery: Comirnaty and Drug-Free Dispersions

Lipid nanoparticles (LNPs) produced by antisolvent precipitation (ASP) are used in formulations for mRNA drug delivery. The mesoscopic structure of such complex multicomponent and polydisperse nanoparticulate systems is most relevant for their drug delivery properties, medical efficiency, shelf life, and possible side effects. However, the knowledge on the structural details of such formulations is very limited. Essentially no such information is publicly available for pharmaceutical dispersions approved by numerous medicine agencies for the use in humans and loaded with mRNA encoding a mimic of the spike protein of the severe acute respiratory syndrome coronavirus type 2 (SARS-CoV-2) as, e.g., the Comirnaty formulation (BioNTech/Pfizer). Here, we present a simple preparation method to mimic the Comirnaty drug-free LNPs including a comparison of their structural properties with those of Comirnaty. Strong evidence for the liquid state of the LNPs in both systems is found in contrast to the designation of the LNPs as solid lipid nanoparticles by BioNTech. An exceptionally detailed and reliable structural model for the LNPs i.a. revealing their unexpected narrow size distribution will be presented based on a combined small-angle X-ray scattering and photon correlation spectroscopy (SAXS/PCS) evaluation method. The results from this experimental approach are supported by light microscopy, 1H NMR spectroscopy, Raman spectroscopy, cryogenic electron microscopy (cryoTEM), and simultaneous SAXS/SANS studies. The presented results do not provide direct insights on particle formation or dispersion stability but should contribute significantly to better understanding the LNP drug delivery process, enhancing their medical benefit, and reducing side effects.

Physicochemical characterization of solid lipid nanoparticles comprised of glycerol monostearate and bile salts

Successful applications of solid lipid nanoparticles (SLNs) rely on their physicochemical properties which are mainly governed by their comprising materials (e.g., lipids, emulsifiers) and preparation methods. We have prepared biocompatible solid lipid nanoparticles with glycerol monostearate as lipid and varying combinations of bile salts sodium deoxycholate and sodium cholate (bile salts to lipid ratio 8% w/w) as emulsifiers. The detailed characterization of solid lipid nanoparticles was performed using a combination of light scattering, microscopic, calorimetric, and spectroscopic techniques. It was seen that different compositions of bile salts yield nanoparticles with different sizes. The use of only sodium deoxycholate (8% w/w) produces nanoparticles with average sizes ∼487 nm. The average particle size increases with increasing cholate fraction. A higher average particle size around ∼652 nm is obtained with 8% (w/w) sodium cholate. All the SLNs show good physical stability at room temperature and do not show polymorphic transformation during the storage. In order to study the microenvironments, solid lipid nanoparticles are loaded with an external fluorescent-probe fisetin (probe to lipid ratio 1% w/w). Photophysical properties of fisetin loaded SLNs indicate the micro-heterogenicity inside the nanoparticles.

Enhanced brain delivery with lower hepatic exposure of lazaroid loaded nanostructured lipid carriers developed using a design of experiment approach

The current study was designed to develop and optimize lazaroid loaded nano-structured lipid carriers (LAZ-NLCs) using design of experiment approach for enhancing lazaroid brain exposure. Response surface plots were used to determine the effects of independent variables (amount of PEGylating agent and liquid lipid) on dependent variables (particle size, zeta potential and encapsulation efficiency), while numerical optimization was used for optimizing LAZ-NLCs composition. The optimal LAZ-NLCs were spherical in shape with measured size of 172.3 ± 3.54 nm, surface charge of -4.54 ± 0.87 mV and encapsulation efficiency of 85.01 ± 2.60%. The optimal LAZ-NLCs were also evaluated for hemolytic potential, storage stability and solid-state properties. The plasma pharmacokinetics along with brain and hepatic distributions of control lazaroid citrate solution and optimal LAZ-NLCs formulation were evaluated in Sprague-Dawley rats after the single bolus intravenous administration. The optimized LAZ-NLCs and the control lazaroid citrate solution had similar plasma pharmacokinetic profiles; however, differential organ bio-distributions were observed. The lazaroid exposure in brain was enhanced by two times with a decreased liver exposure by half for the NLCs group compared to the solution group.

Tailoring of physicochemical properties of nanocarriers for effective anti-cancer applications

Nanotechnology has emerged strongly as a viable option to overcome the challenge of early diagnosis and effective drug delivery, for cancer treatment. Emerging research articles have expounded the advantages of using a specific type of nanomaterial-based system called as "nanocarriers," for anti-cancer therapy. The nanocarrier system is used as a transport unit for targeted drug delivery of the therapeutic drug moiety. In order for the nanocarriers to be effective for anticancer therapy, their physicochemical parameter needs to be tuned so that bio-functionalisation can be achieved to (1) allow drugs being attached to the substrate and for their controlled release, (2) ensure the stability of the nanocarrier up to the point of delivery, and (3) clearance of the nanocarrier after the delivery. It is therefore envisaged that tailoring of the physicochemical properties of nanocarriers can greatly influence their reactivity and interaction in the biological milieu, and this is becoming an important parameter for increasing the efficacy of cancer therapy. This review emphasizes the importance of physicochemical properties of nanocarriers, and how they influence its usage as chemotherapeutic drug carriers. The goal of this review is to present a correlation between the physicochemical properties of the nanocarriers and its intended action, and how their design based on these properties can enhance their cancer combating abilities while minimizing damage to the healthy tissues. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 2906-2928, 2017.

Alendronate Sodium as Enteric Coated Solid Lipid Nanoparticles; Preparation, Optimization, and In Vivo Evaluation to Enhance Its Oral Bioavailability

Treatment of osteoporosis with alendronate sodium has several challenges. The first challenge is the low bioavailability. The second main challenge is side effects, which include oesophageal ulceration. The aim of this research was to reformulate alendronate sodium as enteric coated solid lipid nanoparticles in order to enhance its bioavailability, and preventing the free alendronate sodium from coming into direct contact with the gastrointestinal mucosa, and thereby reducing the possibility of side effects. Enteric coated solid lipid nanoparticles were prepared according to the Box-Behnken design employing Design expert^® software, and characterized for size, morphology, and entrapment efficiency. The optimized formula was coated with an Eudragit S100 and evaluated for drug release in acidic and basic media, stability studies and pharmacokinetic evaluations on rabbits. The results indicated that, using Derringer's desirability functional tool for optimization, the highest entrapment efficiency value of 74.3% and the smallest size value of 98 nm were predicted under optimum conditions with a desirability value of 0.917. The optimized nanoparticles released alendronate sodium only at an alkaline pH. The pharmacokinetic evaluation revealed that alendronate sodium bioavailability was enhanced by more than 7.4-fold in rabbits. In conclusion, enteric coated solid lipid nanoparticles is a promising formula for the delivery of alendronate sodium, eliminating its oesophageal side effects and enhancing its bioavailability.

Targeted solid lipid nanoparticles with peptide ligand for oral delivery of atorvastatin calcium

Designing feasible and effective peptide ligand-modified solid lipid nanoparticles (SLNs) to improve the oral bioavailability of atorvastatin calcium (ATC).

Nanostructured lipid carriers: effect of solid phase fraction and distribution on the release of encapsulated materials

Emulsions, solid lipid nanoparticles (SLN), and nanostructured lipid carriers (NLC) containing a mix of liquid and solid domains are of interest as encapsulation vehicles for hydrophobic compounds. Studies of the release rate from these particles yield contradictory results: Some find that increasing the fraction of solid phase increases the rate of release and others the opposite. In this paper we study the release of encapsulated materials from lipid-based nanoparticles using Monte Carlo simulations. We find that, quite surprisingly, the release rate is largely insensitive to the size of solid domains or the fraction of solid phase. However, the distribution of the domains significantly affects the rate of release: Solid domains located at the interface with the surrounding solution inhibit transport, while nanoparticles where the solid domains are concentrated in the center enhance it. The latter can lead to release rates in NLCs that are faster than in the equivalent emulsions. We conclude that controlling the release rate from NLCs requires the ability to determine the location and distribution of the solid phase, which may be achieved through choice of the surfactants stabilizing the particles, incorporation of nucleation sites, and/or the cooling rates and temperatures.

Progress in the characterization of bio-functionalized nanoparticles using NMR methods and their applications as MRI contrast agents

Significant progress has been made over the last three decades in the field of NMR, a technique which has proven to have a variety of applications in many scientific disciplines, including nanotechnology. Herein we describe how NMR enables the characterization of nanosystems at different stages of their formation and modification (raw materials, bare or functionalized nanosystems), even making it possible to study in vivo nanoparticle interactions, thereby importantly contributing to nanoparticle design and subsequent optimization. Furthermore, the unique characteristics of nanosystems can open up new prospects for site-targeted, more specific contrast agents, contributing to the development of certain nuclear magnetic resonance applications such as MRI.

Nanocarriers of solid lipid from micelles of amino acids surfactants coated with polymer nanoparticles

Polymer nanoparticle coated micelle assemblies of lauryl ester of tyrosine (LET) act as potential nanocarriers for the model solid lipid stearyl alcohol. The coating is afforded by a simple methodology of heterophase polymerization reaction of styrene or the mixture of styrene and butyl acrylate at a mole ratio of 0.8:0.2 in the presence of 200 mM LET in water. On the contrary, the polymer nanoparticles produced under similar conditions in the presence of a structurally similar surfactant, lauryl ester of phenyl alanine (LEP), failed to act as nanocarrier. The micelle templates of LET and LEP favored polymerization under controlled conditions as observed from the near monodisperse distribution of molecular weight and size of the polymers. The particle size distribution of poly(styrene) (PS) and poly(styrene-co-butyl acryalte) (PS-co-PBA) nanoparticles from LET was smaller at 24 and 20 nm in comparison to those from LEP. The encapsulation efficiency of polymer nanoparticles from LET surfactant is explained on the basis of difference in the coating of micelle assemblies, which we believe must be arising due to difference in the solubilization site of the monomers in the surfactant micelles before polymerization reaction. The solubilization of the model monomer, benzene at different regions, varying between shell and core of LET and LEP micelles is established from (1)H nuclear magnetic resonance spectra. The evidence for the coating of micelle assemblies from surface tension measurements and the encapsulation of stearyl alcohol in the polymer nanoparticle dispersions from LET drawn from transmission electron microscopy, differential scanning calorimetry, and thermogravimetric analysis is discussed.

Carboxylesterase-triggered hydrolysis of nanoparticle PEGylating agents

Despite the importance of PEGylation in achieving long nanoparticle circulation times, many nanoparticles are coated with PEGylating agents susceptible to enzymatic degradation. In this study, solid lipid nanoparticles (SLNs) prepared with ester-containing compounds were evaluated for their stability in the presence of carboxylesterase. SLN suspensions became turbid within 30 min of enzymatic exposure, indicating possible disassociation of a portion of the nanoparticles. The particle size of SLNs incubated with the enzyme was smaller than the size of controls, although their morphologies appeared similar in transmission electron microscopy images. Although SLNs offered some protection over micelles, PEG6000 monostearate was rapidly degraded within 15 min. Hydrolysis of polysorbate 60 was much slower, reaching only 36% in 2 h. These studies reveal the importance of confirming the stability of PEG surface coatings prior to undertaking in vivo experiments in small animal models, which can have considerably higher plasma esterase activity than humans.