Deep eutectic systems: An overview of fundamental aspects, current understanding and drug delivery applications

Hydrophobic deep eutectic solvent (HDES) as oil phase in lipid-based drug formulations

There is increasing pharmaceutical interest in deep eutectic solvents not only as a green alternative to organic solvents in drug manufacturing, but also as liquid formulation for drug delivery. The present work introduces a hydrophobic deep eutectic solvent (HDES) to the field of lipid-based formulations (LBF). Phase behavior of a mixture with 2:1 M ratio of decanoic- to dodecanoic acid was studied experimentally and described by thermodynamic modelling. Venetoclax was selected as a hydrophobic model drug and studied by atomistic molecular dynamics simulations of the mixtures. As a result, valuable molecular insights were gained into the interaction networks between the different components. Moreover, experimentally the HDES showed greatly enhanced drug solubilization compared to conventional glyceride-based vehicles, but aqueous dispersion behavior was limited. Hence surfactants were studied for their ability to improve aqueous dispersion and addition of Tween 80 resulted in lowest droplet sizes and high in vitro drug release. In conclusion, the combination of HDES with surfactant(s) provides a novel LBF with high pharmaceutical potential. However, the components must be finely balanced to keep the integrity of the solubilizing HDES, while enabling sufficient dispersion and drug release.

Desosomes and desimicelles - a novel vesicular and micellar system for enhanced oral delivery of poorly soluble drug: Optimization of in vitro characteristics and in vivo performance

This study introduces two innovative nanocarrier systems to improve oral drug delivery. Desosomes and desimicelles combine Deep eutectic solvent (DES) with vesicular or micellar nanosystems, respectively. These novel nanosystems integrate the DES solubilization potency for administering drugs with low aqueous solubility and the vesicular and micellar systems to bypass physiological barriers and improve poor drug bioavailability. Lornoxicam (LRX) is a BCS class II anti-inflammatory with limited aqueous solubility and rapid clearance. Desosomes and desimicelles were prepared and successfully optimized. The optimization depended on particle size, zetapotential, entrapment efficiency, and solubility. The optimized desosomes (LRX-DES-V) and desimicelles (LRX-DES-M) were pictured by transmission electron microscope. Differential scanning calorimetry (DSC) and FTIR analysis indicated the successful inclusion of LRX inside each system. Invitro LRX release profiles revealed controlled release of LRX-DES-V and LRX-DES-M, with more sustained release by the later one. In-vivo study, inflammation was induced using a carrageenan rat model, and the anti-inflammatory effect of LRX-pure, marketed product, traditional niosomes, LRX-DES-V & LRX-DES-M were determined using inhibition %, serum inflammatory cytokines, and histopathology. After 4 h of induction, LRX-DES-M (68.05%) showed a significant inhibition compared to LRX-DES-V (63.57%). LRX-DES-M also showed a better reduction in COX2, PGE2, and TNF-α (1.25-fold, 1.24-fold, and 1.36-fold inhibition), respectively, compared to LRX-DES-V. We can conclude that LRX-DES-V and LRX-DES-M showed better effects than all other groups and that LRX-DES-M might be more effective than LRX-DES-V.

Long-acting transdermal drug delivery formulations: Current developments and innovative pharmaceutical approaches

Transdermal administration remains an active research and development area as an alternative route for long-acting drug delivery. It avoids major drawbacks of conventional oral (gastrointestinal side effects, low drug bioavailability, and need for multiple dosing) or parenteral routes (invasiveness, pain, and psychological stress and bio-hazardous waste generated from needles), thereby increasing patient appeal and compliance. This review focuses on the current state of long-acting transdermal drug delivery, including adhesive patches, microneedles, and molecularly imprinted polymeric systems. Each subsection describes an approach including key considerations in formulation development, design, and process parameters with schematics. An overview of commercially available conventional (adhesive) patches for long-acting drug delivery (longer than 24 h), the reservoir- and matrix-type systems under preclinical evaluation, as well as the advanced transdermal formulations, such as the core-shell, nanoformulations-incorporated and stimuli-responsive microneedles, and 3D-printed and molecularly imprinted polymers that are in development, is also provided. Finally, we elaborated on translational aspects, challenges in patch formulation development, and future directions for the clinical advancement of new long-acting transdermal products.

Deep eutectic solvent self-assembled reverse nanomicelles for transdermal delivery of sparingly soluble drugs

BACKGROUND

Transdermal delivery of sparingly soluble drugs is challenging due to their low solubility and poor permeability. Deep eutectic solvent (DES)/or ionic liquid (IL)-mediated nanocarriers are attracting increasing attention. However, most of them require the addition of auxiliary materials (such as surfactants or organic solvents) to maintain the stability of formulations, which may cause skin irritation and potential toxicity.

RESULTS

We fabricated an amphiphilic DES using natural oxymatrine and lauric acid and constructed a novel self-assembled reverse nanomicelle system (DES-RM) based on the features of this DES. Synthesized DESs showed the broad liquid window and significantly solubilized a series of sparingly soluble drugs, and quantitative structure-activity relationship (QSAR) models with good prediction ability were further built. The experimental and molecular dynamics simulation elucidated that the self-assembly of DES-RM was adjusted by noncovalent intermolecular forces. Choosing triamcinolone acetonide (TA) as a model drug, the skin penetration studies revealed that DES-RM significantly enhanced TA penetration and retention in comparison with their corresponding DES and oil. Furthermore, in vivo animal experiments demonstrated that TA@DES-RM exhibited good anti-psoriasis therapeutic efficacy as well as biocompatibility.

CONCLUSIONS

The present study offers innovative insights into the optimal design of micellar nanodelivery system based on DES combining experiments and computational simulations and provides a promising strategy for developing efficient transdermal delivery systems for sparingly soluble drugs.

Formulation of Ascorbic Acid and Betaine-based Therapeutic Deep Eutectic System for Enhanced Transdermal Delivery of Ascorbic Acid

L-ascorbic acid (AA), a potent antioxidant, is commonly used topically in the pharmaceutical and cosmetic fields. However, the incorporation of AA into topical formulations is difficult because of its highly unstable nature and relatively poor skin permeability. In this study, we propose an alternative strategy for improving the solubility and topical delivery of AA through its conversion to a therapeutic deep eutectic system (THEDES). AA and betaine (Bet)-based THEDESs were prepared at certain molar ratios and characterized using polarized optical microscopy, Fourier transform infrared spectroscopy, and differential scanning calorimetry. Solubility tests showed that AA in the form of THEDES was readily soluble in various polyols (glycerin, 1,3-butylene glycol, dipropylene glycol, and 1,3-propanediol) at a high concentration (approximately 40%). Furthermore, compared to AA alone or the physical mixture of AA and Bet, AA-based THEDES significantly enhanced AA delivery through porcine skin. In an in vivo human study, THEDES-containing serum reduced the markers of aging and induced an even skin tone. These findings indicate the utility of AA and Bet-based THEDES as novel transdermal delivery systems for AA. Furthermore, our approach also showed good extension to developing gluconolactone, a well-known natural antioxidant, and Bet-based THEDES, showing potential application in transdermal delivery systems.

Pharmaceutical applications of therapeutic deep eutectic systems (THEDES) in maximising drug delivery

The issue of poor solubility of active pharmaceutical ingredients (APIs) has been a salient area of investigation and novel drug delivery systems are being developed to improve the solubility of drugs, enhance their permeability and thereby their efficacy. Several techniques for solubilization enhancement of poorly soluble drugs are often employed at various stages of pharmaceutical drug product development. One such delivery system is the therapeutic deep eutectic system (THEDES), which showed great potential in the enhancement of solubility and permeability of drugs and ultimately augmenting their bioavailability. THEDES are made by mixing drugs with deep eutectic solvents (DESs) in a definite molar ratio by the hit and trial method. The DESs are a new class of green solvents which are non-toxic, cheap, easy to prepare, biodegradable and have multiple applications in the pharmaceutical industry. The terminologies such as ionic liquids (ILs), DES, THEDES, and therapeutic liquid eutectic systems (THELES) have been very much in use recently, and it is important to highlight the pharmaceutical applications of these unexplored reservoirs in drug solubilization enhancement, drug delivery routes, and in the management of various diseases. This review is aimed at discussing the components, formulation strategies, and routes of administration of THEDES that are used in developing the formulation. Also, the major pharmaceutical applications of THEDES in the treatment of various metabolic and non-metabolic diseases are reviewed.

A Low Transition Temperature Mixture-based viscosupplementation complemented with celecoxib for osteoarthritis treatment

Viscosupplementation consists of hyaluronic acid (HA) intra-articular injections, commonly applied for osteoarthritis treatment while non-steroidal anti-inflammatory drugs (NSAIDs) are widely administered for pain relief. Here, HA and a NSAID (celecoxib) were combined in a formulation based on a low transition temperature mixture (LTTM) of glycerol:sorbitol, reported to increase celecoxib's solubility, thus rendering a potential alternative viscosupplement envisioning enhanced therapeutic efficiency. The inclusion of glucosamine, a cartilage precursor, was also studied. The developed formulations were assessed in terms of rheological properties, crucial for viscosupplementation: the parameters of crossover frequency, storage (G') and loss (G'') moduli, zero-shear-rate viscosity, stable viscosity across temperatures, and shear thinning behaviour, support viscoelastic properties suitable for viscosupplementation. Additionally, the gels biocompatibility was confirmed in chondrogenic cells (ATDC5). Regarding drug release studies, high and low clearance scenarios demonstrated an increased celecoxib (CEX) release from the gel (6 to 73-fold), compared to dissolution in PBS. The low clearance setup presented the highest and most sustained CEX release, highlighting the importance of the gel structure in CEX delivery. NMR stability studies over time demonstrated the LTTM+HA+CEX (GHA+CEX) gel as viable candidate for further in vivo evaluation. In sum, the features of GHA+CEX support its potential use as alternative viscosupplement.

Deep Eutectic Solvents: An Eco-friendly Design for Drug Engineering

In the spirit of circular economy and sustainable chemistry, the use of environmentally friendly chemical products in pharmacy has become a hot topic. In recent years, organic solvents have been the subject of a great range of restriction policies due to their harmful effects on the environment and toxicity to human health. In parallel, deep eutectic solvents (DESs) have emerged as suitable greener solvents with beneficial environmental impacts and a rich palette of physicochemical advantages related to their low cost and biocompatibility. Additionally, DESs can enable remarkable solubilizing effect for several active pharmaceutical ingredients (APIs), thus forming therapeutic DESs (TheDESs). In this work, special attention is paid to DESs, presenting a precise definition, classification, methods of preparation, and characterization. A description of natural DESs (NaDESs), i. e., eutectic solvents present in natural sources, is also reported. Moreover, the present review article is the first one to detail the different approaches for judiciously selecting the constituents of DESs in order to minimize the number of experiments. The role of DESs in the biomedical and pharmaceutical sectors and their impact on the development of successful therapies are also discussed.

Saquinavir-Piperine Eutectic Mixture: Preparation, Characterization, and Dissolution Profile

The dissolution rate of the anti-HIV drug saquinavir base (SQV), a poorly water-soluble and extremely low absolute bioavailability drug, was improved through a eutectic mixture formation approach. A screening based on a liquid-assisted grinding technique was performed using a 1:1 molar ratio of the drug and the coformers sodium saccharinate, theobromine, nicotinic acid, nicotinamide, vanillin, vanillic acid, and piperine (PIP), followed by differential scanning calorimetry (DSC). Given that SQV-PIP was the only resulting eutectic system from the screening, both the binary phase and the Tammann diagrams were adapted to this system using DSC data of mixtures prepared from 0.1 to 1.0 molar ratios in order to determine the exact eutectic composition. The SQV-PIP system formed a eutectic at a composition of 0.6 and 0.40, respectively. Then, a solid-state characterization through DSC, powder X-ray diffraction (PXRD), including small-angle X-ray scattering (SAXS) measurements to explore the small-angle region in detail, Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), and a powder dissolution test were performed. The conventional PXRD analyses suggested that the eutectic mixture did not exhibit structural changes; however, the small-angle region explored through the SAXS instrument revealed a change in the crystal structure of one of their components. FT-IR spectra showed no molecular interaction in the solid state. Finally, the dissolution profile of SQV in the eutectic mixture was different from the dissolution of pure SQV. After 45 min, approximately 55% of the drug in the eutectic mixture was dissolved, while, for pure SQV, 42% dissolved within this time. Hence, this study concludes that the dissolution rate of SQV can be effectively improved through the approach of using PIP as a coformer.

Effect of Deep Eutectic System (DES) on Oral Bioavailability of Celecoxib: In Silico, In Vitro, and In Vivo Study

Different deep eutectic systems (DES) of choline chloride (CC)-urea (UA) (1:2), CC-glycerol (GLY) (1:2), CC-malonic acid (MA) (1:1), and CC-ascorbic acid (AA) (2:1) were generated and characterized by polarized light microscope (PLM) and Fourier transform infrared spectroscope (FTIR). The equilibrium solubility of celecoxib (CLX) in DES was compared to that in deionized water. The CC-MA (1:1) system provided ~10,000 times improvement in the solubility of CLX (13,114.75 µg/g) and was used for the generation of the CLX-DES system. The latter was characterized by PLM and FTIR to study the microstructure and intermolecular interaction between the CLX and CC-MA (1:1) DES. FTIR demonstrated the retention of the chemical structure of CLX. In vitro drug release studies in FaSSIF initially demonstrated high supersaturation, which decreased by ~2 fold after 2 h. Density functional theory (DFT)-based calculations provided a molecular-level understanding of enhanced solubility. Gibbs free energy calculations established the role of the strongest binding of CLX with CC and MA. A phase solubility study highlighted the role of hydrotropy-induced solubilization of the CLX-DES system. Animal pharmacokinetic studies established 2.76 times improvement in Cmax, 1.52 times reduction in tmax, and 1.81 times improvement in AUC0-∞. The overall results demonstrated the potential of developing a DES-based supersaturating drug-delivery system for pharmaceutical loading of drugs having solubility and dissolution rate-limited oral bioavailability.

Leveraging the use of in vitro and computational methods to support the development of enabling oral drug products: An InPharma commentary

Due to the strong tendency towards poorly soluble drugs in modern development pipelines, enabling drug formulations such as amorphous solid dispersions, cyclodextrins, co-crystals and lipid-based formulations are frequently applied to solubilize or generate supersaturation in gastrointestinal fluids, thus enhancing oral drug absorption. Although many innovative in vitro and in silico tools have been introduced in recent years to aid development of enabling formulations, significant knowledge gaps still exist with respect to how best to implement them. As a result, the development strategy for enabling formulations varies considerably within the industry and many elements of empiricism remain. The InPharma network aims to advance a mechanistic, animal-free approach to the assessment of drug developability. This commentary focuses current status and next steps that will be taken in InPharma to identify and fully utilize 'best practice' in vitro and in silico tools for use in physiologically based biopharmaceutic models.

Polymer-embedded deep eutectic solvents (PEDES) as a novel bio-enabling formulation approach

There is a growing interest in using deep eutectic solvents (DES) as a pharmaceutical delivery system for poorly water-soluble compounds. To reduce the risk of drug precipitation following oral administration, this study addresses the hypothesis that directly including a polymeric precipitation inhibitor (PI) in a DES mixture could obtain a polymer-embedded deep eutectic system (PEDES) as a novel bio-enabling formulation principle. Following broad formulation screening, a PEDES embedding 15 % w/w of polyvinyl pyrrolidone K30 (PVP) in L-carnitine:ethylene glycol (1:4, molar ratio) DES was successfully formulated as a supersaturating formulation using indomethacin as model drug. The solubility of 175.6 mg/mL obtained in DES was remarkably high, and upon release (phosphate buffer, pH 6.5) a maximum supersaturation factor of 9.8 was recorded, whereby the release kinetics displayed a suitable "parachute effect". The formulation was further characterized to include a molecular dynamics simulation. It can be concluded that PEDES appears to be a viable novel formulation approach, setting solid grounds for further research to assess the full potential of this novel type of supersaturating drug delivery system.

Are all poorly soluble drugs dissolved in deep eutectic solvents true solutions?

HYPOTHESIS

The ability of deep eutectic solvents (DES) to enhance solubility of poorly soluble drugs has attracted increasing attention. Researchers have shown that drugs could be dissolved well in DES. In this study, we propose a new existence state of drugs in DES: a quasi-two-phase colloidal system.

EXPERIMENTS

Six poorly soluble drugs were used as the models. The formation of colloidal systems was observed visually by the Tyndall effect and DLS. TEM and SAXS were performed to obtain their structure information. The intermolecular interactions between components were probed via DSC and ¹H¹H-ROESY. In addition, the properties of colloidal systems were further studied.

FINDINGS

Our key finding is that several drugs like lurasidone hydrochloride (LH) could form stable colloids in [Th (thymol)] - [Da (decanoic acid)] DES, resulting from weak interactions between drugs and DES, which is different from the true solution of drugs like ibuprofen where strong interactions were formed. In this LH-DES colloidal system, DES solvation layer was directly observed on the surface of drug particles. In addition, the colloidal system with polydispersity shows superior physical and chemical stability. Different to the prevailing view that substances are fully dissolved in DES, this study discovers another existence state as stable colloidal particles in DES.

Development and optimization of natural deep eutectic solvent-based dispersive liquid-liquid microextraction coupled with UPLC-UV for simultaneous determination of parabens in personal care products: evaluation of the eco-friendliness level of the developed method

Dispersive liquid-liquid microextraction (DLLME) combined with ultra-high performance liquid chromatography-diode array detector (UHPLC-DAD) method has been developed and validated for the determination of parabens in personal care products. In this study, a natural deep eutectic solvent (NADES) composed of menthol and formic acid at a molar ratio of 1 : 2 was prepared and used as an extraction solvent. The influencing variables on the extraction efficiency such as extraction solvent type and volume, composition of NADES, salt addition, vortex and centrifugation time were investigated. The proposed method exhibited good linearity with determination coefficients of ≥0.9992. The relative recoveries for the studied analytes ranged from 82.19 to 102.45%. Limits of detection and limits of quantification were in the range of 0.17-0.33 ng mL^-1 and 0.51-0.99 ng mL^-1, respectively. To evaluate the applicability of the developed method, it was successfully applied to determine four parabens in personal care products. Additionally, the eco-friendliness level of the presented method was evaluated using Eco-Scale Assessment, Green Analytical Procedure Index and Analytical GREEnness metric. The developed method is simple, environmentally friendly and cost effective and it could be employed for determination of parabens in personal care products without harming the environment.

Therapeutic Deep Eutectic Solvents: A Comprehensive Review of Their Thermodynamics, Microstructure and Drug Delivery Applications

Deep eutectic solvents (DES) are multicomponent liquids that are usually formed by coupling a hydrogen bond donor and acceptor leading to strong non-covalent (NC) intermolecular networking and profound depression in the melting point of the system. Pharmaceutically, this phenomenon has been exploited to improve drugs' physicochemical properties, with an established DES therapeutic subcategory, therapeutic deep eutectic solvents (THEDES). THEDES preparation is usually via straightforward synthetic processes with little involvement of sophisticated techniques, which, in addition to its thermodynamic stability, make these multi-component molecular adducts a very attractive alternative for drug enabling purposes. Other NC bonded binary systems (e.g., co-crystals and ionic liquids) are utilized in the pharmaceutical field for enhancing drug's behaviours. However, a clear distinction between these systems and THEDES is scarcely discussed in the current literature. Accordingly, this review provides a structure-based categorization for DES formers, a discussion of its thermodynamic properties and phase behaviour, and it clarifies the physicochemical and microstructure boundaries between DES and other NC systems. Additionally, a summary of its preparation techniques and their experimental conditions preparation is supplied. Instrumental analysis techniques can be used to characterize and differentiate DES from other NC mixtures, hence this review draws a road map to for this purpose. Since this work mainly focuses on pharmaceutical applications of DES, all types of THEDES including the highly discussed types (conventional, drugs dissolved in DES and polymer based) in addition to the less discussed categories are covered. Finally, the regulatory status of THEDES was investigated despite the current unclear situation.

Bioadhesive eutectogels supporting drug nanocrystals for long-acting delivery to mucosal tissues

Eutectogels (Egels) are an emerging class of soft ionic materials outperforming traditional temperature-intolerant hydrogels and costly ionogels. Due to their excellent elasticity, non-volatile nature, and adhesion properties, Egels are attracting a great deal of interest in the biomedical space. Herein, we report the first example of adhesive Egels loading drug nanocrystals (Egel-NCs) for controlled delivery to mucosal tissues. These soft materials were prepared using gelatin, glycerine, a deep eutectic solvent (DES) based on choline hydrochloride and glycerol, and nanocrystallised curcumin, a model drug with potent antimicrobial and anti-inflammatory activities. We first explored the impact of the biopolymer concentration on the viscoelastic and mechanical properties of the networks. Thanks to the dynamic interactions between gelatin and the DES, the Egel showed excellent stretchability and elasticity (up to ≈160%), reversible gel-sol phase transition at mild temperature (≈50 ​°C), 3D-printing ability, and good adhesion to mucin protein (stickiness ≈40 ​kPa). In vitro release profiles demonstrated the ability of the NCs-based Egel to deliver curcumin for up to four weeks and deposit significantly higher drug amounts in excised porcine mucosa compared to the control cohort. All in all, this study opens new prospects in designing soft adhesive materials for long-acting drug delivery and paves the way to explore novel eutectic systems with multiple therapeutic applications.

Deep eutectic solvents: Recent advances in fabrication approaches and pharmaceutical applications

Deep eutectic solvents (DESs) have received increasing attention in the past decade owing to their distinguished properties including biocompatibility, tunability, thermal and chemical stability. Particularly, DESs have joined forces in pharmaceutical industry, not only to efficiently separate actives from natural products, but also to dramatically increase solubility and permeability of drugs, both are critical for the drug absorption and efficacy. As a result, lately DESs have been extensively and practically adopted as versatile drug delivery systems for different routes such as nasal, transdermal and oral administration with enhanced bioavailability. This review summarizes the emerging progress of DESs by introducing applied fabrication approaches with advantages and limitations thereof, and by highlighting the pharmaceutical applications of DESs.

Deep Eutectic Solvent as Green Solvent in Extraction of Biological Macromolecules: A Review

Greater awareness of environmental sustainability has driven many industries to transition from using synthetic organic solvents to greener solvents in their manufacturing. Deep eutectic solvents (DESs) have emerged as a highly promising category of green solvents with well-demonstrated and wide-ranging applications, including their use as a solvent in extraction of small-molecule bioactive compounds for food and pharmaceutical applications. The use of DES as an extraction solvent of biological macromolecules, on the other hand, has not been as extensively studied. Thereby, the feasibility of employing DES for biomacromolecule extraction has not been well elucidated. To bridge this gap, this review provides an overview of DES with an emphasis on its unique physicochemical properties that make it an attractive green solvent (e.g., non-toxicity, biodegradability, ease of preparation, renewable, tailorable properties). Recent advances in DES extraction of three classes of biomacromolecules—i.e., proteins, carbohydrates, and lipids—were discussed and future research needs were identified. The importance of DES’s properties—particularly its viscosity, polarity, molar ratio of DES components, and water addition—on the DES extraction’s performance were discussed. Not unlike the findings from DES extraction of bioactive small molecules, DES extraction of biomacromolecules was concluded to be generally superior to extraction using synthetic organic solvents.

Computer Simulations of Deep Eutectic Solvents: Challenges, Solutions, and Perspectives

Deep eutectic solvents (DESs) are one of the most rapidly evolving types of solvents, appearing in a broad range of applications, such as nanotechnology, electrochemistry, biomass transformation, pharmaceuticals, membrane technology, biocomposite development, modern 3D-printing, and many others. The range of their applicability continues to expand, which demands the development of new DESs with improved properties. To do so requires an understanding of the fundamental relationship between the structure and properties of DESs. Computer simulation and machine learning techniques provide a fruitful approach as they can predict and reveal physical mechanisms and readily be linked to experiments. This review is devoted to the computational research of DESs and describes technical features of DES simulations and the corresponding perspectives on various DES applications. The aim is to demonstrate the current frontiers of computational research of DESs and discuss future perspectives.