Microfluidic synthesis of PEG- and folate-conjugated liposomes for one-step formation of targeted stealth nanocarriers

Lab on chip based self-adjustable liposomes for rapid wound healing: An in depth in vitro, in vivo and higher dose toxicity investigation

Thanks to microfluidic technology, different nano-delivery systems are becoming clinically viable. Using a novel and rapid microfluidic hydrodynamic focusing (MHF) method (lipids on chip) we developed self-adaptable liposomes (SLs) containing cefpodoxime proxetil (CP) for the treatment of skin infections caused by Staphylococcus aureus. SLs were optimized using different flow rate ratios in the MHF method and the final formulation CPT3 was found to be the best in terms of particle size (68.27 ± 01.15 nm), % entrapment efficiency (% EE: 82 ± 1.5), polydispersity (PDI: 0.2 ± 0.012), and degree of deformability (DOD: 4.7 ± 0.18 nm). Rats (Sprague Dawley) treated with a self-adaptable CPT3 liposomal formulation recuperate skin injury, exhibited reduced bacterial counts (<106 CFU/mL) in the wounded region, and completely restored (100 %) on day 21. Rat survival, in vivo dermal pharmacokinetics and ex vivo-in vivo relationship were also investigated. Rats treated with an even 10-fold higher dose (100 mg/kg/day) of CP using an equivalent CPT3 formulation did not show any symptoms of toxicity as revealed by hematological, biochemical, and internal organ assessment observations. Finally, the developed CPT3 formulation with special interest in patients with high-risk skin injuries not only delivered CP in a controlled manner but was also clinically effective and safe as it did not produce any serious adverse events even at 10× higher doses in the infected rats.

Microfluidic synthesis of lipid-based nanoparticles for drug delivery: recent advances and opportunities

Microfluidic technologies are revolutionizing the synthesis of nanoscale lipid particles and enabling new opportunities for the production of lipid-based nanomedicines. By harnessing the benefits of microfluidics for controlling diffusive and advective transport within microfabricated flow cells, microfluidic platforms enable unique capabilities for lipid nanoparticle synthesis with precise and tunable control over nanoparticle properties. Here we present an assessment of the current state of microfluidic technologies for lipid-based nanoparticle and nanomedicine production. Microfluidic techniques are discussed in the context of conventional production methods, with an emphasis on the capabilities of microfluidic systems for controlling nanoparticle size and size distribution. Challenges and opportunities associated with the scaling of manufacturing throughput are discussed, together with an overview of emerging microfluidic methods for lipid nanomedicine post-processing. The impact of additive manufacturing on current and future microfluidic platforms is also considered.

Neuroprotective Effect of Curcumin-Loaded RGD Peptide-PEGylated Nanoliposomes

Curcumin is known for its anti-inflammatory, neuroprotective, and antioxidant properties, but its use in biological applications is hindered by its sensitivity to light, oxygen, and temperature. Furthermore, due to its low water solubility, curcumin has a poor pharmacokinetic profile and bioavailability. In this study, we evaluated the potential application of curcumin as a neuroprotective agent encapsulated in RGD peptide-PEGylated nanoliposomes developed from salmon-derived lecithin. Salmon lecithin, rich in polyunsaturated fatty acids, was used to formulate empty or curcumin-loaded nanoliposomes. Transmission electron microscopy, dynamic light scattering, and nanoparticle tracking analysis characterizations indicated that the marine-derived peptide-PEGylated nanoliposomes were spherical in shape, nanometric in size, and with an overall negative charge. Cytotoxicity tests of curcumin-loaded nanoliposomes revealed an improved tolerance of neurons to curcumin as compared to free curcumin. Wild-type SH-SY5Y were treated for 24 h with curcumin-loaded nanoliposomes, followed by 24 h incubation with conditioned media of SH-SY5Y expressing the Swedish mutation of APP containing a high ratio of Aβ40/42 peptides. Our results revealed significantly lower Aβ-induced cell toxicity in cells pre-treated with RGD peptide-PEGylated curcumin-loaded nanoliposomes, as compared to controls. Thus, our data highlight the potential use of salmon lecithin-derived RGD peptide PEGylated nanoliposomes for the efficient drug delivery of curcumin as a neuroprotective agent.

Microfluidic approaches for producing lipid-based nanoparticles for drug delivery applications

The importance of drug delivery for disease treatment is supported by a vast literature and increasing ongoing clinical studies. Several categories of nano-based drug delivery systems have been considered in recent years, among which lipid-based nanomedicines, both artificial and cell-derived, remain the most approved. The best artificial systems in terms of biocompatibility and low toxicity are liposomes, as they are composed of phospholipids and cholesterol, the main components of cell membranes. Extracellular vesicles-biological nanoparticles released from cells-while resembling liposomes in size, shape, and structure, have a more complex composition with up to hundreds of different types of lipids, proteins, and carbohydrates in their membranes, as well as an internal cargo. Although nanoparticle technologies have revolutionized drug delivery by enabling passive and active targeting, increased stability, improved solubilization capacity, and reduced dose and adverse effects, the clinical translation remains challenging due to manufacturing limitations such as laborious and time-consuming procedures and high batch-to-batch variability. A sea change occurred when microfluidic strategies were employed, offering advantages in terms of precise particle handling, simplified workflows, higher sensitivity and specificity, and good reproducibility and stability over bulk methods. This review examines scientific advances in the microfluidics-mediated production of lipid-based nanoparticles for therapeutic applications. We will discuss the preparation of liposomes using both hydrodynamic focusing of microfluidic flow and mixing by herringbone and staggered baffle micromixers. Then, an overview on microfluidic approaches for producing extracellular vesicles and extracellular vesicles-mimetics for therapeutic applications will describe microfluidic extrusion, surface engineering, sonication, electroporation, nanoporation, and mixing. Finally, we will outline the challenges, opportunities, and future directions of microfluidic investigation of lipid-based nanoparticles in the clinic.

Microfluidic Generation of Near-Infrared Photothermal Vitexin/ICG Liposome with Amplified Photodynamic Therapy

Glioma, in which a malignant tumor cell occurs in neural mesenchymal cells, has a rapid progression and poor prognosis, which is still far from desirable in clinical treatments. We developed a lab-on-a-chip (LOC) device for the rapid and efficient preparation of vitexin/indocyanine green (ICG) liposomes. Vitexin could be released from liposome to kill cancer cell, which can potentially improve the glioma therapeutic effect and reduce the treatment time through synergistic photodynamic/photothermal therapies (PDT/PTT). The vitexin/ICG liposome was fabricated via LOC and its physicochemical property and release in vitro were evaluated. 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) method and live/dead staining were used to examine the enhanced antitumor effect of vitexin/ICG liposome in cooperation with PDT/PTT, while the related mechanism was explored by flow cytometry and western blot. The results were as follows: (1) The prepared vitexin/ICG liposome was smaller in size, homogenous in particle size distribution with significant low polydispersity index (PDI), and enhanced cumulative release in vitro. (2) We found that the formulated liposome presented strong cancer cell inhibition and suppression of its migration in a dose-dependent manner. (3) Further mechanistic studies showed that liposome combined with near-infrared irradiation could significantly upregulate levels of B cell lymphoma 2-associated X (Bax) protein and decrease B cell lymphoma 2 (Bcl-2) at protein levels. The vitexin/ICG liposomes prepared based on a simple LOC platform can effectively enhance the solubility of insoluble drugs, and the combined effect of PTT/PDT can effectively increase their antitumor effect, which provides a simple and valid method for the clinical translation of liposomes.

An emerging era in manufacturing of drug delivery systems: Nanofabrication techniques

Nanotechnology has the capability of making significant contributions to healthcare. Nanofabrication of multifunctional nano- or micro-character systems is becoming incredibly influential in various sectors like electronics, photonics, energy, and biomedical gadgets worldwide. The invention of such items led to the merger of moderate cost and excellent quality nano or micro-characters into 3D structures. Nanofabrication techniques have many benefits as the primary technology for manipulating cellular surroundings to research signaling processes. The inherent nanoscale mechanisms of cyto-reactions include the existence and death of cells, stem cell segmentation, multiplication, cellular relocation, etc. Nanofabrication is essential in developing various nano-formulations like solid lipid nanoparticles, nanostructured lipid carriers, liposomes, niosomes, nanoemulsions, microemulsions etc. Despite the initial development cost in designing the nanofabrication-based products, it has also reduced the total cost of the healthcare system by considering the added benefits compared to the other standard formulations. Thus, the current review mainly focuses on nanofabrication techniques, advantages, disadvantages, applications in developing various nanocarrier systems, challenges and future perspectives.

Scalable Liposome Synthesis by High Aspect Ratio Microfluidic Flow Focusing

Microfluidic flow focusing provides an efficient approach to the generation of nanoscale lipid vesicles of tunable size and low size variance. Scalable nanoliposome synthesis over a wide range of production rates can be readily achieved using a high aspect ratio flow focusing device fabricated by widely available additive manufacturing methods. Here we detail methods for the manufacture and operation of a 3D-printed microfluidic flow focusing technology enabling the synthesis of liposomes with modal diameters ranging from ca. 50-200 nm at production rates up to several hundred milligrams lipid per hour.

One-Step Formation of Targeted Liposomes in a Versatile Microfluidic Mixing Device

Targeted liposomes, as a promising carrier, have received tremendous attention in COVID-19 vaccines, molecular imaging, and cancer treatment, due to their enhanced cellular uptake and payload accumulation at target sites. However, the conventional methods for preparing targeted liposomes still suffer from limitations, including complex operation, time-consuming, and poor reproducibility. Herein, a facile and scalable strategy is developed for one-step construction of targeted liposomes using a versatile microfluidic mixing device (MMD). The engineered MMD provides an advanced synthesis platform for multifunctional liposome with high production rate and controllability. To validate the method, a programmed death-ligand 1 (PD-L1)-targeting aptamer modified indocyanine green (ICG)-liposome (Apt-ICG@Lip) is successfully constructed via the MMD. ICG and the PD-L1-targeting aptamer are used as model drug and targeting moiety, respectively. The Apt-ICG@Lip has high encapsulation efficiency (89.9 ± 1.4%) and small mean diameter (129.16 ± 5.48 nm). In vivo studies (PD-L1-expressing tumor models) show that Apt-ICG@Lip can realize PD-L1 targeted photoacoustic imaging, fluorescence imaging, and photothermal therapy. To verify the versatility of this approach, various targeted liposomes with different functions are further prepared and investigated. These experimental results demonstrate that this method is concise, efficient, and scalable to prepare multifunctional targeted liposomal nanoplatforms for molecular imaging and disease theranostics.

Nanoliposome based biosensors for probing mycotoxins and their applications for food: A review

Mycotoxins are the most common feed and food contaminants affecting animals and humans, respectively; continuous exposure causes tremendous health problems such as kidney disorders, infertility, immune suppression, liver inflammation, and cancer. Consequently, their control and quantification in food materials is crucial. Biosensors are potential tools for the rapid detection and quantification of mycotoxins with high sensitivity and selectivity. Nanoliposomes (NLs) are vesicular carriers formed by self-assembling phospholipids that surround the aqueous cores. Utilizing their biocompatibility, biodegradability, and high carrying capacity, researchers have employed NLs in biosensors for monitoring various targets in biological and food samples. The NLs are used for surface modification, signal marker delivery, and detection of toxins, bacteria, pesticides, and diseases. Here, we review marker-entrapped NLs used in the development of NL-based biosensors for mycotoxins. These biosensors are sensitive, selective, portable, and cost-effective analytical tools, and the resulting signal can be produced and/or amplified with or without destroying the NLs. In addition, this review emphasizes the benefits of the immunoliposome method in comparison with traditional detection approaches. We expect this review to serve as a valuable reference for researchers in this rapidly growing field. The insights provided may facilitate the rational design of next-generation NL-based biosensors.

Microfluidic vortex focusing for high throughput synthesis of size-tunable liposomes

Control over vesicle size during nanoscale liposome synthesis is critical for defining the pharmaceutical properties of liposomal nanomedicines. Microfluidic technologies capable of size-tunable liposome generation have been widely explored, but scaling these microfluidic platforms for high production throughput without sacrificing size control has proven challenging. Here we describe a microfluidic-enabled process in which highly vortical flow is established around an axisymmetric stream of solvated lipids, simultaneously focusing the lipids while inducing rapid convective and diffusive mixing through application of the vortical flow field. By adjusting the individual buffer and lipid flow rates within the system, the microfluidic vortex focusing technique is capable of generating liposomes with precisely controlled size and low size variance, and may be operated up to the laminar flow limit for high throughput vesicle production. The reliable formation of liposomes as small as 27 nm and mass production rates over 20 g/h is demonstrated, offering a path toward production-scale liposome synthesis using a single continuous-flow vortex focusing device.

Microfluidic Manufacture of Lipid-Based Nanomedicines

Nanoparticulate technologies have revolutionized drug delivery allowing for passive and active targeting, altered biodistribution, controlled drug release (temporospatial or triggered), enhanced stability, improved solubilization capacity, and a reduction in dose and adverse effects. However, their manufacture remains immature, and challenges exist on an industrial scale due to high batch-to-batch variability hindering their clinical translation. Lipid-based nanomedicines remain the most widely approved nanomedicines, and their current manufacturing methods remain discontinuous and face several problems such as high batch-to-batch variability affecting the critical quality attributes (CQAs) of the product, laborious multistep processes, need for an expert workforce, and not being easily amenable to industrial scale-up involving typically a complex process control. Several techniques have emerged in recent years for nanomedicine manufacture, but a paradigm shift occurred when microfluidic strategies able to mix fluids in channels with dimensions of tens of micrometers and small volumes of liquid reagents in a highly controlled manner to form nanoparticles with tunable and reproducible structure were employed. In this review, we summarize the recent advancements in the manufacturing of lipid-based nanomedicines using microfluidics with particular emphasis on the parameters that govern the control of CQAs of final nanomedicines. The impact of microfluidic environments on formation dynamics of nanomaterials, and the application of microdevices as platforms for nanomaterial screening are also discussed.

Microfluidic Nanoparticles for Drug Delivery

Nanoparticles (NPs) have attracted tremendous interest in drug delivery in the past decades. Microfluidics offers a promising strategy for making NPs for drug delivery due to its capability in precisely controlling NP properties. The recent success of mRNA vaccines using microfluidics represents a big milestone for microfluidic NPs for pharmaceutical applications, and its rapid scaling up demonstrates the feasibility of using microfluidics for industrial-scale manufacturing. This article provides a critical review of recent progress in microfluidic NPs for drug delivery. First, the synthesis of organic NPs using microfluidics focusing on typical microfluidic methods and their applications in making popular and clinically relevant NPs, such as liposomes, lipid NPs, and polymer NPs, as well as their synthesis mechanisms are summarized. Then, the microfluidic synthesis of several representative inorganic NPs (e.g., silica, metal, metal oxide, and quantum dots), and hybrid NPs is discussed. Lastly, the applications of microfluidic NPs for various drug delivery applications are presented.

Microfluidic Applications in Drug Development: Fabrication of Drug Carriers and Drug Toxicity Screening

Microfluidic technology has been highly useful in nanovolume sample preparation, separation, synthesis, purification, detection and assay, which are advantageous in drug development. This review highlights the recent developments and trends in microfluidic applications in two areas of drug development. First, we focus on how microfluidics has been developed as a facile tool for the fabrication of drug carriers including microparticles and nanoparticles. Second, we discuss how microfluidic chips could be used as an independent platform or integrated with other technologies in drug toxicity screening. Challenges and future perspectives of microfluidic applications in drug development have also been provided considering the present technological limitations.

Formulation Strategies for Folate-Targeted Liposomes and Their Biomedical Applications

The folate receptor (FR) is a tumor-associated antigen that can bind with folic acid (FA) and its conjugates with high affinity and ingests the bound molecules inside the cell via the endocytic mechanism. A wide variety of payloads can be delivered to FR-overexpressed cells using folate as the ligand, ranging from small drug molecules to large DNA-containing macromolecules. A broad range of folate attached liposomes have been proven to be highly effective as the targeted delivery system. For the rational design of folate-targeted liposomes, an intense conceptual understanding combining chemical and biomedical points of view is necessary because of the interdisciplinary nature of the field. The fabrication of the folate-conjugated liposomes basically involves the attachment of FA with phospholipids, cholesterol or peptides before liposomal formulation. The present review aims to provide detailed information about the design and fabrication of folate-conjugated liposomes using FA attached uncleavable/cleavable phospholipids, cholesterol or peptides. Advances in the area of folate-targeted liposomes and their biomedical applications have also been discussed.

Sterically stabilized liposomes production using staggered herringbone micromixer: Effect of lipid composition and PEG-lipid content

Preparation of lipid-based drug delivery systems by microfluidics has been increasingly popular, due to the reproducible, continuous and scalable nature of the microfluidic process. Despite exciting development in the field, versatility and superiority of microfluidics over conventional methods still need further evidence, since preparing clinically-relevant sterically stabilised liposomes has been lacking. The present study describes the optimisation of PEGylated liposomal formulations of various rigidity using staggered herringbone micromixer (SHM). The effect of both processing parameters (total flow rate (TFR) and aqueous-to-ethanol flow rate ratio (FRR)) and formulation parameters (lipid components and composition, initial lipid concentration and aqueous media) was investigated and discussed. Liposomal formulations consist of 1,2-dioleoyl-sn-glycero-3-phosphatidylcholine (DOPC), 1,2-dipalmitoyl-sn-glycero-3-phosphatidylcholine (DPPC) or 1,2-distearoyl-sn-glycero-3-phosphatidylcholine (DSPC), with cholesterol and PEGylated lipid (DSPE-PEG₂₀₀₀) were successfully prepared with the desired size (∼100 nm) and dispersity (<0.2). Doxorubicin was successfully encapsulated in these liposomes at high (>80%) encapsulation efficiency using the pH-gradient remote loading method, illustrating their bilayer integrity and capability as drug delivery systems. We demonstrated that clinically-relevant PEGylated liposomal formulations could be prepared with properties comparable to conventional techniques. Limitations and recommendations on the microfluidic production of PEGylated liposomes were also discussed.

Synthesis of Biomaterials Utilizing Microfluidic Technology

Recently, microfluidic technologies have attracted an enormous amount of interest as potential new tools for a large range of applications including materials synthesis, chemical and biological detection, drug delivery and screening, point-of-care diagnostics, and in-the-field analysis. Their ability to handle extremely small volumes of fluids is accompanied by additional benefits, most notably, rapid and efficient mass and heat transfer. In addition, reactions performed within microfluidic systems are highly controlled, meaning that many advanced materials, with uniform and bespoke properties, can be synthesized in a direct and rapid manner. In this review, we discuss the utility of microfluidic systems in the synthesis of materials for a variety of biological applications. Such materials include microparticles or microcapsules for drug delivery, nanoscale materials for medicine or cellular assays, and micro- or nanofibers for tissue engineering.

The importance of microfluidics for the preparation of nanoparticles as advanced drug delivery systems

INTRODUCTION

Nanoparticles are anticipated to overcome persistent challenges in efficient drug delivery, but the limitations associated with conventional methods of preparation are resulting in slow translation from research to clinical applications. Due to their enormous potential, microfluidic technologies have emerged as an advanced approach for the development of drug delivery systems with well-defined physicochemical characteristics and in a reproducible manner.

AREAS COVERED

This review provides an overview of microfluidic devices and materials used for their manufacturing, together with the flow patterns and regimes commonly used for nanoparticle preparation. Additionally, the different geometries used in droplet microfluidics are reviewed, with particular attention to the co-flow geometry used for the production of nanoparticles. Finally, this review summarizes the main and most recent nanoparticulate systems prepared using microfluidics, including drug nanosuspensions, polymeric, lipid, structured, and theranostic nanoparticles.

EXPERT OPINION

The production of nanoparticles at industrial scale is still a challenge, but the microfluidic technologies bring exciting opportunities to develop drug delivery systems that can be engineered in an easy, cost-effective and reproducible manner. As a highly interdisciplinary research field, more efforts and general acceptance are needed to allow for the translation of nanoparticulate drug delivery systems from academic research to the clinical practice.

Continuous-Flow Production of Injectable Liposomes via a Microfluidic Approach

Injectable liposomes are characterized by a suitable size and unique lipid mixtures, which require time-consuming and nonstraightforward production processes. The complexity of the manufacturing methods may affect liposome solubility, the phase transition temperatures of the membranes, the average particle size, and the associated particle size distribution, with a possible impact on the drug encapsulation and release. By leveraging the precise steady-state control over the mixing of miscible liquids and a highly efficient heat transfer, microfluidic technology has proved to be an effective and direct methodology to produce liposomes. This approach results particularly efficient in reducing the number of the sizing steps, when compared to standard industrial methods. Here, Microfluidic Hydrodynamic Focusing chips were produced and used to form liposomes upon tuning experimental parameters such as lipids concentration and Flow-Rate-Ratios (FRRs). Although modelling evidenced the dependence of the laminar flow on the geometric constraints and the FRR conditions, for the specific formulation investigated in this study, the lipids concentration was identified as the primary factor influencing the size of the liposomes and their polydispersity index. This was attributed to a predominance of the bending elasticity modulus over the vesiculation index in the lipid mixture used. Eventually, liposomes of injectable size were produced using microfluidic one-pot synthesis in continuous flow.

SPIN: rapid synthesis, purification, and concentration of small drug-loaded liposomes

Liposomes are one of the most studied nano-delivery systems. However, only a handful of formulations have received FDA approval. Existing liposome synthesis techniques are complex and specialized, posing a major impediment in design, implementation, and mass production of liposome delivery systems as therapeutic agents. Here, we demonstrate a unique 'synthesis and purification of injectable nanocarriers' (SPIN) technology for rapid and efficient production of small drug-loaded liposomes using common benchtop equipment. Unilamellar liposomes with mean diameter of 80 nm and polydispersity of 0.13 were synthesized without any secondary post-processing techniques. Encapsulation of dextrans (300-20,000 Da) representing small and large molecular drug formulations was demonstrated without affecting the liposome characteristics. 99.9% of the non-encapsulated molecules were removed using a novel filter centrifugation technique, largely eliminating the need for tedious ultracentrifugation protocols. Finally, the functional efficacy of loaded liposomes as drug delivery vehicles was validated by encapsulating a fluorescent cell tracker (CMFDA) and observing the liposomal release and subsequent uptake of dye by metastatic breast cancer cells (MDA-MB-231) in vitro. The proposed simplified technique addresses the existing challenges associated with liposome preparation in resource limited settings and offers significant potential for advances in translational pharmaceutical development.

Deformable Nanovesicles Synthesized through an Adaptable Microfluidic Platform for Enhanced Localized Transdermal Drug Delivery

Phospholipid-based deformable nanovesicles (DNVs) that have flexibility in shape offer an adaptable and facile method to encapsulate diverse classes of therapeutics and facilitate localized transdermal delivery while minimizing systemic exposure. Here we report the use of a microfluidic reactor for the synthesis of DNVs and show that alteration of input parameters such as flow speeds as well as molar and flow rate ratios increases entrapment efficiency of drugs and allows fine-tuning of DNV size, elasticity, and surface charge. To determine the ability of DNV-encapsulated drug to be delivered transdermally to a local site, we synthesized, characterized, and tested DNVs carrying the fluorescently labeled hydrophilic bisphosphonate drug AF-647 zoledronate (AF647-Zol). AF647-Zol DNVs were lyophilized, resuspended, and applied topically as a paste to the calvarial skin of mice. High-resolution fluorescent imaging and confocal microscopy revealed significant increase of encapsulated payload delivery to the target tissue-cranial bone-by DNVs as compared to nondeformable nanovesicles (NVs) or aqueous drug solutions. Interestingly, NV delivery was not superior to aqueous drug solution. Our studies show that microfluidic reactor-synthesized DNVs can be produced in good yield, with high encapsulation efficiency, reproducibility, and stability after storage, and represent a useful vehicle for localized transdermal drug delivery.

Scalable preparation of poly(ethylene glycol)-grafted siRNA-loaded lipid nanoparticles using a commercially available fluidic device and tangential flow filtration

While a number of siRNA delivery systems have been developed, the methods used in their preparation are not suitable for large-scale production. We herein report on methodology for the large-scale preparation of liposomal siRNA using a fluidic device and tangential flow filtration (TFF). A number of studies have appeared on the use of fluidic devices for preparing and purifying liposomes, but no systematic information regarding appropriate membrane type of commercially available apparatus is available. The findings reported herein indicate that, under optimized conditions, a microfluidic device and TFF can be used to produce siRNA lipid nanoparticles with the same characteristics as traditional ones'. The in vivo silencing efficiency of these lipid nanoparticles in the liver was comparable to laboratory-produced nanoparticles. In addition, con-focal laser scanning microscopy analyses revealed that they accumulated in the liver accumulation at the same levels as particles produced by batch-type and continuous-type procedures. This methodology has the potential to contribute to the advancement of this process from basic research to clinical studies of liposomal DDS.

Controllable synthesis of functional nanoparticles by microfluidic platforms for biomedical applications - a review

Nanoparticles have drawn significant attention in biomedicine due to their unique optical, thermal, magnetic and electrical properties which are highly related to their size and morphologies. Recently, microfluidic systems have shown promising potential to modulate critical stages in nanosynthesis, such as nucleation, growth and reaction conditions so that the size, size distribution, morphology, and reproducibility of nanoparticles are optimized in a high throughput manner. In this review, we put an emphasis on a decade of developments of microfluidic systems for engineering nanoparticles in various applications including imaging, biosensing, drug delivery, and theranostic applications.

Preparation and in vivo safety evaluations of antileukemic homoharringtonine-loaded PEGylated liposomes

In order to improve the in vivo safety and specific delivery efficiency of the antileukemic homoharringtonine (HHT) at the targets, the long-circulating PEGylated liposomes loaded with HHT (LCLipo-HHT) were prepared. Their physical characteristics, in vitro drug release, in vivo pharmacokinetic properties and elementary toxicity were evaluated. The mean diameter of the prepared LCLipo-HHT is 75.6 ± 3.2 nm and the zeta potential is -16.9 ± 2.5 mV. The entrapment efficiency of HHT in the liposomes is 69.5 ± 1.7%. In pharmacokinetic experiments, an increased plasma concentration as well as blood circulation time was obtained when distearoyl phosphoethanolamine-PEG 2000 lipid was added in the formulation, which results in enhancing drug delivery efficiency. Hemolysis test, vascular irritation test and acute toxicity test were used to demonstrate toxicity of LCLipo-HHT. Compared with clinical HHT injection dosage, LCLipo-HHT indicated no vascular irritation, good hemocompatibility, as well as much better safety. Therefore, the prepared LCLipo-HHT can be used as a promising anticancer formulation for antileukemic therapy in the future.

Droplet-microfluidics towards the assembly of advanced building blocks in cell mimicry

Therapeutic cell mimicry is an approach in nanomedicine aiming at substituting for missing or lost cellular functions employing nature-inspired concepts. Pioneered decades ago, only now is this technology empowered with the arsenal of nanotechnological tools and ready to provide radically new solutions such as assembling synthetic organelles and artificial cells. One of these tools is droplet microfluidics (D-μF), which provides the flexibility to generate cargo-loaded particles with tunable size and shape in a fast and reliable manner, an essential requirement in cell mimicry. This minireview aims at outlining the developments in D-μF from the past four years focusing on the assembly of nanoparticles, Janus-shaped and other non-spherical particles as well as their loading with biological payloads.

Microfluidic synthesis of multifunctional liposomes for tumour targeting

Nanotechnology has started a new era in engineering multifunctional nanoparticles for diagnosis and therapeutics by incorporating therapeutic drugs, targeting ligands, stimuli-responsive release and imaging molecules. However, more functionality requires more complex synthesis processes, resulting in poor reproducibility, low yield and high production cost, hence difficulties in clinical translation. Herein we report a one-step microfluidic method for making multifunctional liposomes. Three formulations were prepared using this simple method, including plain liposomes, PEGylated liposomes and folic acid functionalised liposomes, all with a fluorescence dye encapsulated for imaging. The size and surface properties of these liposomes can be precisely controlled by simply tuning the flow rate ratio and the ratio of the lipids to PEGylated lipid (DSPE-PEG₂₀₀₀) and to the DSPE-PEG₂₀₀₀-Folate, respectively. The synthesised liposomes remained stable under mimic serum conditions. Compared to the plain liposomes and PEGylated liposomes, the targeted folic acid functionalised liposomes exhibited enhanced cellular uptake by the FA receptor positive SKOV3 cells, but not the negative MCF7 cells, and this enhanced uptake could be inhibited by adding excess free folic acid, indicating high specificity of FA ligand-receptor endocytosis. Further evaluation using the 3D tumour spheroid model also showed higher internalisation of the targeted liposome formulation in comparison with the PEGylated one. To the best of our knowledge, this work demonstrates for the first time the versatility of this microfluidic method for making different liposome formulations in a single step, their superior physicochemical properties as well as the enhanced cellular uptake and tumour spheroid uptake of the targeted liposomes.

Liposome production by microfluidics: potential and limiting factors

This paper provides an analysis of microfluidic techniques for the production of nanoscale lipid-based vesicular systems. In particular we focus on the key issues associated with the microfluidic production of liposomes. These include, but are not limited to, the role of lipid formulation, lipid concentration, residual amount of solvent, production method (including microchannel architecture), and drug loading in determining liposome characteristics. Furthermore, we propose microfluidic architectures for the mass production of liposomes with a view to potential industrial translation of this technology.

Small molecule therapeutic-loaded liposomes as therapeutic carriers: from development to clinical applications

In this review, various methods and mechanisms for encapsulation of small therapeutic molecules in liposomes for targeted delivery and triggered release, as well as their potential in the clinical uses, are discussed.

High-Throughput Continuous Flow Production of Nanoscale Liposomes by Microfluidic Vertical Flow Focusing

Liposomes represent a leading class of nanoparticles for drug delivery. While a variety of techniques for liposome synthesis have been reported that take advantage of microfluidic flow elements to achieve precise control over the size and polydispersity of nanoscale liposomes, with important implications for nanomedicine applications, these methods suffer from extremely limited throughput, making them impractical for large-scale nanoparticle synthesis. High aspect ratio microfluidic vertical flow focusing is investigated here as a new approach to overcoming the throughput limits of established microfluidic nanoparticle synthesis techniques. Here the vertical flow focusing technique is utilized to generate populations of small, unilamellar, and nearly monodisperse liposomal nanoparticles with exceptionally high production rates and remarkable sample homogeneity. By leveraging this platform, liposomes with modal diameters ranging from 80 to 200 nm are prepared at production rates as high as 1.6 mg min(-1) in a simple flow-through process.

Continuous flow generation of magnetoliposomes in a low-cost portable microfluidic platform

We present a low-cost, portable microfluidic platform that uses laminated polymethylmethacrylate chips, peristaltic micropumps and LEGO® Mindstorms components for the generation of magnetoliposomes that does not require extrusion steps. Mixtures of lipids reconstituted in ethanol and an aqueous phase were injected independently in order to generate a combination of laminar flows in such a way that we could effectively achieve four hydrodynamic focused nanovesicle generation streams. Monodisperse magnetoliposomes with characteristics comparable to those obtained by traditional methods have been obtained. The magnetoliposomes are responsive to external magnetic field gradients, a result that suggests that the nanovesicles can be used in research and applications in nanomedicine.

Microfluidic remote loading for rapid single-step liposomal drug preparation

Microfluidic-directed formation of liposomes is combined with in-line sample purification and remote drug loading for single step, continuous-flow synthesis of nanoscale vesicles containing high concentrations of stably loaded drug compounds. Using an on-chip microdialysis element, the system enables rapid formation of large transmembrane pH and ion gradients, followed by immediate introduction of amphipathic drug for real-time remote loading into the liposomes. The microfluidic process enables in-line formation of drug-laden liposomes with drug : lipid molar ratios of up to 1.3, and a total on-chip residence time of approximately 3 min, representing a significant improvement over conventional bulk-scale methods which require hours to days for combined liposome synthesis and remote drug loading. The microfluidic platform may be further optimized to support real-time generation of purified liposomal drug formulations with high concentrations of drugs and minimal reagent waste for effective liposomal drug preparation at or near the point of care.

Microfluidic-enabled liposomes elucidate size-dependent transdermal transport

Microfluidic synthesis of small and nearly-monodisperse liposomes is used to investigate the size-dependent passive transdermal transport of nanoscale lipid vesicles. While large liposomes with diameters above 105 nm are found to be excluded from deeper skin layers past the stratum corneum, the primary barrier to nanoparticle transport, liposomes with mean diameters between 31-41 nm exhibit significantly enhanced penetration. Furthermore, multicolor fluorescence imaging reveals that the smaller liposomes pass rapidly through the stratum corneum without vesicle rupture. These findings reveal that nanoscale liposomes with well-controlled size and minimal size variance are excellent vehicles for transdermal delivery of functional nanoparticle drugs.

Liposomal delivery and polyethylene glycol-liposomal oxaliplatin for the treatment of colorectal cancer (Review)

Oxaliplatin is effective for the treatment of advanced colorectal cancer; however, its application is restricted due to its dose-limiting toxicity. Liposomes are sphere-shaped vesicles consisting of one or more phospholipid bilayers. Liposomes as drug carriers are characterized by delayed release, lesion targeting and may be used as a drug-delivery system to decrease the side effects of cytotoxic drugs. Active targeting modification of liposomes may change the biological distribution of the anticancer agents, reduce or reverse multidrug resistance of tumor cells and enhance the effects of anticancer therapy. Based on the characteristics mentioned above, the aim of the present review was to demonstrate that polyethylene glycol-liposomes containing oxaliplatin may offer advantages for the treatment of colorectal cancer in clinical practice.