The electrostatic spray drying technology uses an atomizing nozzle where a charge is applied to the feedstock during atomization.

Spray drying technology dates back to the late 19th century, but there has been little true innovation since its introduction. Similarly, aside from perforated tablet coaters and the Wurster fluid bed in the 1950s, solid dosage technology in the pharmaceutical industry has remained largely unchanged for well over a century.

During this same era, the pharmaceutical industry has exploded with innovation — from the science of formulation, to advancements in testing and beyond. It’s time for a spray dry transformation that meets the needs of modern pharmaceutical research and development.

Enter a true industry-changer: The incorporation of electrostatic technology.

Not only does electrostatic spray dry technology enable solid dosage powder production that is more energy efficient, cost-effective, emission reducing and sustainable, it also significantly improves the quality, stability and shelf life of the final product.

Fluid Air’s PolarDry patent pending electrostatic spray dry technology is poised to open up whole new branches of Active Pharmaceutical Ingredients (APIs) that previously could not withstand the thermal abuse of traditional spray drying, and nanoparticle technology where complete microencapsulation is critical. Electrostatic Spray Dry technology promises to empower pharmaceutical R&D professionals to do formulation work never before possible.

The implications and advantages for pharmaceutical R&D and, ultimately, manufacturing are game changing.

Traditional Spray Dry Versus Electrostatic Spray Dry

In the traditional spray dry process, a slurry is fed into a spray chamber where it is exposed to heated air and converted into a powder. This requires very high heat (+200°C), which contributes to active ingredient loss, degradation, or denaturalization. Conversely, electrostatic spray dry systems use significantly lower evaporation temperatures (ambient to 80°C) which protect active ingredients.

Spray drying is used to microencapsulate active or other components where, ideally, the carrier surrounds the active entirely as the solvent is dried off with the heated drying gas. The carrier acts as a protective layer around the active, protecting it from the outside environment, particularly oxygen, which keeps it from oxidizing. Traditionally, atomization in the spray dryer is achieved using a nozzle or rotary atomizer. The electrostatic spray drying technology uses an atomizing nozzle where a charge is applied to the feedstock during atomization.

A major barrier to achieving perfect microencapsulation using traditional spray drying is the intense heat that can dry the particle too quickly with no mechanism to draw the active into the particle. This results in a dried particle that has active trapped both inside and on the surface of the particle, partially defeating the intention of microencapsulation.

The use of electrostatic technology in spray drying virtually eliminates this disadvantage, especially if the component of the feedstock component has differing electrical properties with the solvent having the highest ability to polarize. As an example, consider the spray dry process that uses an emulsion made up of several components or ingredients.

A solvent (water or organic solvent), a carrier (starch) and an active (API, oil, vitamin, etc.). If the solvent has the highest ability to polarize, which is usually the case, it will pick up the most electrons from the applied charge. The carrier, being less conductive than the solvent, will pick up fewer electrons, and the active being least conductive, picks up the fewest.

The solvent molecules having the greatest charge density will repel each other as they try to return to a neutral state. This effect forces the solvent and carrier to migrate to the outer sphere of the droplet, while the active remains at the center, virtually eliminating surface active. The aggressive movement of the solvent to the outer surface through the carrier creates the ideal drying condition, leading to a near perfect encapsulation of the active without the use of high evaporation temperatures.

In fact, electrostatic spray drying allows water evaporation at significantly lower processing temperatures (from ambient to 80°C) compared to traditional spray drying. In testing, this improved microencapsulation extended the shelf life of the tested product from six months to two years, a factor of four.

Granulation/Agglomeration

Traditional spray drying requires separate equipment to achieve granulation or agglomeration. Not so with electrostatic spray drying. Fluid Air’s PolarDry™ patent pending technology, for example, offers a streamlined, one-step process.

One standard agglomeration method for traditional spray dried products is the use of a fluidized bed spray granulator. Inside this machinery, spray-dried particles are fluidized with a circulated heated air stream followed by the addition of a binding solution. A liquid “bridge” is formed that allows the particles to stick together. The agglomerated particles are formed when the liquid is evaporated. This additional process is time consuming, increases costs and potentially causes further active ingredient loss or degradation from exposure to even more heat.

By controlling the electrostatic charge applied to the feed on an intermittent basis, electrostatic technology enables the agglomeration of particulates, as they are being spray dried. In the PolarDry Technology, a patent pending feature, PWM (Pulse Width Modulation), precludes the need for secondary granulation machinery and operations and eliminates further detrimental heating.

By controlling the voltage applied to the spray droplet as it is being atomized, some particles form an outer shell readily, while others develop their shell gradually resulting in a wet or tacky particle. As these two types of particles collide, they bond forming an agglomerated particle. This results in a finished product with larger particles, higher bulk density, excellent flowability, and exceptional hydration. Large particles with a small percentage of fines greatly reduces dusting and dust containment issues commonly seen with smaller particles made using a traditional spray drying system.

Potential New Formulations

APIs, proteins and molecules that cannot withstand traditional spray drying temperatures can be effectively produced using the electrostatic spray drying technology in a solid dosage form, where previously, they could only be produced in a pallid powder or liquid form. Logistical advantages of powders over liquids include deliverability, longer shelf-life, and less shipping costs.

Due to the intense heat required in traditional spray drying, APIs are lost, degraded or denaturalized. To compensate, more of the API must be used in the formulation. For example, to formulate vitamin tablets, more of the raw ingredient—such as Vitamin B or Vitamin D—must be used at the start in order to retain potency for the final product to be effective.

Because of the lower heat factor in electrostatic spray drying, more of the API is retained. In testing involving volatile components, approximately 20 percent of the active ingredient was lost during traditional spray drying. With electrostatic technology,  processing of the same formula, a 98 percent active ingredient retention rate could be achieved. Requiring less raw materials, which results in considerable cost savings.

Cleanup and Changeover

As with all industries, the concepts of “six-sigma” and “lean operations” are a factor in the pharmaceutical field. They are seen as a means to contain costs. When processing multiple products, whether in the R&D phase or in manufacturing, equipment downtime for cleaning and changeover is a crucial issue. The PolarDry™ Patent Pending electrostatic spray dryers offers quick set up from one run to the next by integrating a disposable inner chamber liner that can be changed in a matter of minutes and the entire system can be washed in place.

Energy & Emissions

Beyond the obvious energy-saving factor resulting from highly reduced operating temperatures, a low-energy recirculating process minimizes emissions with safe non-reactive processing; nitrogen inertion. In traditional spray drying, the solvent becomes a vapor that cannot be released into the atmosphere without violating regulatory regulations designed to protect the environment.

The vapor exhaust must be properly handled and is often burned off using a thermal oxidizer that requires a great deal of natural gas, not to mention the capital, operational, regulatory and maintenance expense that is associated with this type of solvent handling equipment.

In electrostatic systems with a closed loop exhaust system, the vapor is sent to a condensing coil or heat exchanger where it is condensed into a liquid form and collected. Not only is this process much more energy efficient, it enables a much easier disposal process or in some industries, the recovered condensate can be recycled, repurposed or reused.

Conclusion

The use of electrostatic spray drying promises to make available, in solid dose form, pharmaceuticals, nutraceuticals, vitamins, proteins and other heat sensitive products more efficiently than ever before, opening up new areas of formulation and new novel drug delivery methods, in hopes of creating new and more effective cures.

This article originally appeared in the March 23 edition of the 2017 INTERPHEX Show Daily.

Follow us on Twitter and Facebook for updates on the latest pharmaceutical and biopharmaceutical manufacturing news!