Draft:Flash nanoparticle precipitation

• Comment: This article is not close to appropriate. Currently it is not neutral (WP:NPOV), has a lot of merging of different topics (WP:SYNTH), a lot of bragging (WP:PEACOCK), incorrectly formatted references, is largely a how-to guide. This is not everything. A major rewrite. Ldm1954 (talk) 17:59, 19 May 2025 (UTC)

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Flash Nanoparticle Precipitation (FNP)

Flash nanoprecipitation (FNP) is a widely used method for synthesizing nanoparticles. FNP produced nanoparticles are being used and studied for drug delivery methods. In addition to clinical applications, FNP is being used in other industries, such as agriculture, for pesticide delivery.

One desirable trait of FNP, and a reason for its use in these industries, is its scalability. This technique works by using rapid, turbulent mixing to achieve supersaturation of solvent in a polymer-containing solution. These conditions result in precipitation of the solvent, which is then encapsulated in polymer, forming the nanoparticle product. These resulting particles have a high degree of drug loading. Essentially, FNP works because of the highly turbulent environments (low Reynold’s number) it occurs in. Besides this, the polymer used also plays a significant role in size and stability of the particles that are formed. With these being the key dependent variables, the process can be easily scaled to accommodate larger, or smaller if needed, batches.

Another hallmark of FNP is the ability to encapsulate hydrophilic, or poorly water soluble, molecules. It is estimated around 30-40% of new drugs with clinical promise are hydrophobic, despite efforts to avoid this in formulation. In order to take advantage of their therapeutic potential, such drugs need to be delivered in a way that they will not be hydrophobic, so they will have better bioavailability. FNP is one method of achieving that.

Background History

FNP was originally developed in 2003 by Johnson and Prud’homme to develop nanoparticles.The process is based on the principles of nucleation and growth. It involves combining a hydrophobic molecule and amphiphilic polymer in a water-miscible organic solvent while rapidly mixing with an aqueous anti-solvent. Originally handheld syringes were used to push the streams of the solvent and anti-solvents together, this mixing method is not referred to as confined impinging jet (CIJ) mixing.

Confined impinging fluid for mixing was previously used as early as 1923 by Hartridge and Roughton for studying oxygen uptake via blood. Hartridge and Roughton conducted their studies using two opposing fluid streams, similar to the original CIJ mixing, but also proposed the possibility of a four inlet mixing device. While their work never included designing the devices made and used by Prud'homme and others, it serves as a foundation by establishing mixing using multiple fluid streams.

In order to surpass limitations of CIJ devices, Liui and Prud'homme designed a four channel device production of nanoparticles. Four inlet devices are now called multi-inlet vortex mixers (MIVM), and are able to overcome CIJ limitations by relying on the momentum from each inlet to drive the mixing.

The MIVM device has been redesigned to improve various weaknesses. A 2018 design addressed current volume limitations. In collaboration with Prud’homme, Markwalter reengineered the device to decrease the volume of reagents required per batch. This design allows for volumes on the microliter scale to be used, which is especially useful for nanoparticle research development.

Advantages of FNP

There are currently other methods that are used to synthesize nanoparticles but compared to FNP these pose many disadvantages. Generally there are two approaches to synthesising nanoparticles, top-down and bottom-up. Top-down methods refer to bulk material being physically broken down. Common methods to break down initial bulk material include milling, laser and spark ablation. These methods are often simpler compared to bottom-up approaches. However top down approach methods often result in significant defects in surface structure. The semiconductor industry uses these approaches in the development of metal oxide semiconductor field effect transistors, the most common approaches being ball milling and plastic deformation. Many of the wires and other products produced from these methods have surface contaminants and defects. While top-down methods are currently common in manufacturing, especially  for semiconductors, bottom-up approaches have become increasingly explored.

Bottom up approaches utilize small scale components and self assembly to form the desired nanoparticles. Often these approaches will build the material from molecules, atoms, or clusters of either, resulting in less material wasted. Additionally these approaches are reported to produce smaller particles, on the nanometer scale, compared to the micron scale made from the top down approach.  These approaches allow for development of uniform shapes and sizes. Broadly there are two methods for bottom up synthesis of nanoparticles, chemical and biological. Chemical synthesis include emulsions, chemical vapor, and FNP techniques. Biological synthesis comes from employing various microorganisms or other biological compounds.

While bottom up approaches generally result in more controlled sized nanoparticles with fewer surface defects, FNP holds advantages over other methods. FNP is relatively easy to increase scale, allowing for large scale manufacturing, which is not true of other bottom up methods. Additionally FNP allows for controlled size and surface properties of the produced nanoparticles.

Protocol Overview

FNP generates nanoparticles through rapid mixing and precipitation. This technique is considered a bottom-up approach to formulate nanoparticles.

First, the solution containing the solute to be encapsulated is rapidly mixed with an anti-solvent. These should be miscible fluids. This creates conditions with a high level of supersaturation of the solute in solution. These supersaturation conditions cause nucleation of the solute to begin. This means that a crystalline structure of solute will begin to form. These small aggregates are stable.

These aggregates will undergo growth once they form, continuing to add more solute to each cluster. This will become the hydrophobic core of the resulting nanoparticle. At the same time, precipitation of the encapsulating compound occurs. This stabilizes the aggregates, and results in the formation of the hydrophilic coating that makes us the outside of the particle. The precipitation of the encapsulating compound also inhibits continued aggregation of solute. This allows for precise control of the size of the particles; if conditions are such that the aggregation of that particles occurs for a longer period, larger particles can be formed, and the reverse is true for smaller particles.

Solvent

Typically, polar organic solvents are chosen, either to be used alone as the sole solvent or to be combined with other organic solvents. The solvent that is selected should be one that is best able to dissolve the chosen drug or other compound to be encapsulated. Solvent can be removed by a variety of methods, including dialysis and evaporation, depending on the physical properties.

Anti-Solvent

Anti-solvents are generally some water-based buffer solution, or water itself. It needs to be a fluid that will be miscible with the solvent. The solvent to anti-solvent ratio is important. A lower ratio will result in a higher level of supersaturation, while a higher ration will result in a lower level.

Drug

When selecting drugs, evaluating solubility is important to ensure that the chosen drug is a viable candidate for use with FNP. Hydrophobicity must be determined, which is usually determined with the calculated log P (Clog P). Based on studies, a Clog P value above 12 is ideal to ensure stability of the nanoparticle product produced.

Drug concentration is also something to consider when aiming to formulate nanoparticles via FNP. The higher the drug concentration, the higher the supersaturation level achieved. This is correlated to a smaller resulting particle.

Confined Impinging Jet (CIJ) Mixers

The confined impinging jet (CIJ) mixer or confined impinging jet reactor is a common mixer type used to synthesize nanoparticles via FNP. The CIJ mixer was first used by Prud’homme and Johnson for FNP in 2003 and has been widely used to synthesize nanoparticles since. Two opposing streams collide, rapidly mixing, in the main chamber of the device. This area where the streams combine is referred to as the impingement zone. These streams have the same momentum due to the precise geometry of the device, and syringe pumps are often used to ensure they have the same velocity.

Confined impinging jet mixer with all notable features defined.

The properties of a specific CIJ mixer depend on the geometry of the device. The chambers, jets, and the ratio of the relative size of the chambers to the jets all affect the resulting particles that are formed. A t-junction geometry is fairly standard, but other variants can be found too. Because the geometry is essential to the approach, as long as it is maintained, these mixers can be easily scaled allowing for the creation of larger and smaller batches of nanoparticles synthesized via FNP. CIJ mixers have been used to create a variety of nanoscale drug products, including polymeric nanoparticles, polymer-based drug micelles, and lipid nanoparticles.  

One key limitation of the use of CIJ mixer is as there are two streams and an essentially equal flow rate is required of each in order to achieve FNP, there is a prescribed solvent to anti-solvent ratio of 1:1 that generally must be upheld when using a CIJ mixer for FNP. As mentioned previously, the ratio of solvent to antisolvent can be tuned to control supersaturation conditions. With this being pre-determined for a CIJ mixer, this is a major limitation of FNP using this device.

Multi-Inlet Vortex Mixer (MIVM)

Diagram of a multi-inlet vortex mixer. All inlets are labeled.

The multi inlet vortex mixer (MIVM) is commonly used to synthesize nanoparticles via FNP. Instead of two jets, as the CIJ mixer has, the MIVM consists of four, allowing for more complex formulations and different ratios of solvent to anti-solvent to be used. The MIVM was developed to achieve this while maintaining the “rapid micromixing, scalability, and ease of operation” of the CIJ mixer according to its creators. This group includes members who developed the CIJ mixer. Novelly compared to the CIJ mixer, the MIVM allows for control over the stream velocities.

Pre-Clinical Applications

Currently there are many clinical applications of FNP being explored, ranging from cancer treatments to targeting the blood brain barrier. Pre-clinical studies in a research setting have shown promising results in various in vivo and in vitro models. Given that many cancers are still a leading cause of death worldwide, there are major efforts to combat the disease. A recent publication used functionalized nanoparticles loaded with a current cancer drug for the treatment of non-small cell lung cancer. These nanoparticles were synthesized using FNP, and achieved high drug loading efficiency. Additionally the surface functionalization allowed for increased specificity, validated by increased uptake in non-small cell lung cancer cells, along with increased cytotoxicity compared to free drug delivery. These studies were then applied to in vivo models, where selective delivery was shown along with enhanced tumor inhibition relative to free drug administration.

In addition to cancer therapies FNP particles are being used for surpassing the blood brain barrier. Nanoparticles are  a prime candidate for surpassing the blood brain barrier given that their size increases bioavailability. A study uses curcumin, a drug that is used to prevent the aggregation of a protein that is often collected in Alzheimer's patients. However the drug has poor aqueous solubility, and bioavailability. This study aimed to increase these factors by formulating curcumin in nanoparticles using FNP. They were able to achieve higher plasma concentrations of curcumin in mice with an Alzheimer’s disease model. This study indicates success with targeting the blood brain barrier for therapeutic effects.

Clinical Applications

Given that FNP is relatively new, there are not many applications that are currently clinically approved. FNP-synthesized nanoparticles are used for delivering therapeutics. Currently COVID-19 vaccines have been manufactured using the FNP technology to package mRNA vaccines. These vaccines indicate the safety and efficacy of the FNP technology for therapeutic use. Additionally the vaccines are being produced at an industrial scale, indicating the technology can be scaled up for mass manufacturing.

Agricultural Applications

There are also possible applications of FNP within the agricultural industry. Agrochemicals can be difficult to deliver to plants. The method used is known as foliar delivery, in which drugs, suspended in a water-based solution, are directly sprayed on the leaves of the plants. The difficulty with delivery is partially due to the hydrophilic drugs having difficulty entering the leaf, however, the drugs that are able to enter the leaf are still not reaching the right places. Systemic distribution is suboptimal, and the drugs do not always reach all of the organs they are intended to reach. Based on this, one study used FNP to create nanoparticles and assessed their ability to enter and be dispersed within plants after foliar administration. They found that their particles were able to penetrate the leaves and that they were able to disperse within the plant as predicted.

See Also

Nanoparticle

Nanomedicine

Characterization of nanoparticles

Nanoparticle drug delivery