Spray drying is a technique widely used in the manufacturing industry for making a very fine dry powder from a solution, slurry, or emulsion that contains one or more components of the final product. The atomization of a liquid to transform it into a powder is widely used in the food and pharmaceutical industries. Many of the foods we eat and medicines we take are actually manufactured via spray drying techniques.
In a typical spray dryer, an atomizer is used to disperse the liquid as a mist of fine droplets. At this point, the heated gas atmosphere facilitates the process and dried particles fall through the drying chamber. Finally, different methods are used to collect and process the dried particles.
While the concept of spray drying sounds pretty innovative, it has its benefits and drawbacks when it comes to the use of the equipment and the collection or processing of dried substances. To help you better understand why spray dryers are used and how they work, below are 10 advantages and disadvantages of spray drying.
Advantages of Spray Drying
There are numerous reasons why manufacturers choose spray drying techniques to create and process pharmaceuticals, dried dairy products, colorings, spices, and many more. And this is all thanks to the benefits spray dryers offer.
The advantages of spray drying include improved bioavailability of APIs, enhanced dissolution rates, being useful for aseptic manufacturing, the ability to produce very fine powders for inhaled medicines, stabilization of biopharmaceuticals, and taste-masking powers.
Here are the pros of spray drying:
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Spray Drying Improves the Bioavailability of Active Pharmaceutical Ingredients by Enhancing Dissolution Rates
Bioavailability is a term that describes the rate at which active drugs or metabolites enter systematic circulation and reach the site of action. Along with a bunch of other factors, the bioavailability of drugs depends on aqueous solubility and dissolution rate. According to Pharma Manufacturing, at least 40% and up to 90% of new chemical entities (NCEs) are characterized by low solubility, meaning that their bioavailability and efficacy are also low.
While different methods can be used to increase the bioavailability of active pharmaceutical ingredients (APIs), spray drying is considered one of the most optimal technologies. As spray dryers allow manufacturers to control the size and morphology of particles, it enables the production of drugs with enhanced solubility and enhanced bioavailability. This is mainly achieved by creating stable crystalline structures during the spray drying process.
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Spray Drying Can Be Used for the Production of Aseptic Products
Aseptic processing refers to a method of manufacturing that produces products free from bacteria without using any harsh or terminal techniques of sterilization. This method is widely used for products that may degrade and become ineffective when processed through harsh conditions of terminal sterilization. Therefore, aseptic processing allows manufacturers to create products that are both safe and effective.
While spray drying is widely used in the manufacture of biopharmaceutical injectables, it is also quite effective for the aseptic processing of these products. When converting a liquid formulation into a dry powder by means of aseptic spray drying, there is no need for further terminal sterilization. Still, spray drying systems that operate under cGMP standards, sterile conditions, and a robust manufacturing facility are absolutely crucial for the production of aseptic products.
While lyophilization is currently more widely used than aseptic spray drying technology, experts believe that the use of the latter approach will increase in the following years.
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Spray Drying Is Among the Most Optimal Methods for Manufacturing Inhaled Drugs
Inhaled drugs are widely used for the treatment of pulmonary and systemic diseases. There are three primary types of inhaled medicines available on the market: dry-powder inhalers, pressurized metered-dose inhalers, and nebulizers. When inhaling different medicines, it is crucial for the particles to be tiny enough to stay airborne until they reach the lungs.
While there are different methods for producing inhaled drugs, spray drying is among the best techniques. By creating very fine powders, spray drying allows manufacturers to produce suitable medicines for inhalation. One of the major benefits of using spray drying to manufacture inhaled drugs is that this technique can easily transform different biotherapeutics, such as hormones and peptides, into a very fine powdery form.
Read more about preparing powders for inhalation using the spray drying process in this scientific review. The article also discusses the advantages of spray-dried powders for pulmonary drug delivery.
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Spray Drying Can Be Used for Stabilizing Biopharmaceuticals
Biopharmaceuticals, also known as biologics, are drugs that are produced by isolating them from natural sources, including humans, animals, and microorganisms. Along with being larger and more complex molecules than medicines synthesized through chemical reactions, biologics are inherently unstable. Therefore, biopharmaceuticals are formulated in a way that reduces or slows down the process of aggregation.
As protein-based pharmaceuticals are sensitive to temperature, moisture, denaturants, organic solvents, oxygen, and changes in pH, protein aggregation is one of the primary challenges in the production of pharmaceuticals. And this is when spray drying comes into play.
By producing biologics with unique particle characteristics, spray drying allows manufacturers to achieve improved stability, especially for shipping and storage of such medicines.
This review article discusses various mechanisms of spray drying and formulation strategies that can be used to reduce or even minimize factors that affect the stability of biomolecules.
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Spray Drying Offers Excellent Taste-Masking Ability
Taste masking refers to the reduction of a bitter or unpleasant taste of active pharmaceutical ingredients (APIs). While some people do not have any issues taking medicines that taste really bad, this is often a barrier for pediatric and geriatric patients. When it comes to the production of orally disintegrating and chewable tablets or inhaled drugs, taste masking is an efficient method for successfully treating kids and elderly patients.
While organoleptic methods, polymer coating, hot-melt extrusion, microencapsulation, and complexation are widely used for taste masking, spray drying is an excellent alternative to these approaches. As a result of spray drying, dried granules or beads containing taste-masking encapsulated medicine are produced.
As spray drying can be performed as a single-step process, it offers less processing time compared to other taste-masking techniques. Besides, spray drying allows manufacturers to choose from a variety of solvents and polymers. Still, the process requires sufficient research, careful process design, and deliberate polymer selection to achieve the goal.
Disadvantages of Spray Drying
Although spray drying offers some exceptional benefits, there are some drawbacks one should consider before investing in a spray dryer or deciding to process powdered products using this method.
The disadvantages of spray drying include high initial costs and expensive equipment, the need for plenty of time and attention to maintain the equipment, the lack of spray drying facilities, the need for proper expertise, low thermal efficiency, and high heat consumption.
Here are the cons of spray drying:
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Spray Drying Equipment Is Quite Expensive
While spray drying is an excellent technique for producing different types of powdered products, it comes with a few disadvantages. Whether you have decided to add spray drying equipment to your manufacturing facility or you are willing to build a spray drying facility from scratch, you will need to invest thousands if not hundreds of thousands of dollars.
While the equipment itself is pretty expensive, spray dryers are large and, therefore, require a large area, meaning that you will need sufficient space in your facility for the machine to operate properly. In addition, you will need to hire professionals to set up the machine, which is also linked to finances.
Last but not least, owning a spray drying facility will also include overhead costs, such as the expenses associated with running the facility or manufacturing products using the equipment.
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Spray Drying Equipment Pieces Are High-Maintenance
Obviously, a spray dryer is not a low-maintenance plant you can purchase for your living room and take minimal care of. These machines require plenty of attention and time so that they operate properly and produce high-quality powdered products.
Regular maintenance is an absolute must when it comes to owning and running a spray drying facility. Otherwise, you may end up getting material aggregates, especially in spray granulation dryers.
Besides, it is recommended to thoroughly inspect the spray dryer after approximately 600 hours of operation. This is because some parts of the spray drying equipment are prone to damage. Ideally, you should regularly check nozzles that may be clogged or rotary disk atomizers that may become corroded.
As a spray drying facility owner, you should consider outsourcing your spray dryer to an experienced CDMO to keep your equipment maintained at all times.
Read more about some basic safety and maintenance tips for a spray dryer in this article by Hawach Scientific.
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Spray Drying Facilities Are Not Widely Available
Another disadvantage of spray drying is that you may not always be able to find a spray drying facility near your area. This is mainly because knowledge of spray drying is pretty limited in the food and pharmaceutical manufacturing industries. Therefore, there are not many facilities that specialize in product and process development through spray drying.
As the spray drying technique is becoming increasingly popular, we should expect to see more spray drying facilities in the future. At this moment, you may have to produce your powdered goods using the spray drying process outside of your city or even the country.
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Spray Drying Requires Proper Expertise
Just like any other manufacturing technique, spray drying requires proper expertise for the equipment to function properly. Without sufficient knowledge in the field, it is hardly possible to produce high-quality products that are both effective and safe for consumption.
This is especially true when it comes to the manufacture of pharmaceuticals. If you fail to hire professionals to design, create, and process spray-dried medicines, the resulting drugs may cause severe health issues in patients. The same applies to powdered products manufactured in the food industry.
Keep in mind that hiring a professional specializing in spray drying will also increase the expenses associated with running a spray drying facility.
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Spray Dryers Are Characterized by Low Thermal Efficiency and High Heat Consumption
Last but not least, spray dryers are characterized by low thermal efficiency. According to this research article, the heat efficiency of a spray dryer ranges from 25% to 60%, and in some cases, thermal efficiency is below 20%.
Based on these results, we can conclude that spray dryers consume plenty of heat. As highlighted in the research paper mentioned earlier, the heat consumption of spray dryers accounts for roughly 60% of the total cost. And the worst part is that about ⅔ of the energy of hot air cannot even be used, meaning that there is a huge energy waste during the spray drying process.
While there are several ways to reduce the energy consumption of spray dryers, low thermal efficiency still remains one of the major disadvantages of spray drying.