Spray drying is a very fast drying method due to its very large product particle specific surface area and extremely high heat exchange coefficient. The large product particle specific surface area also allows drying to be carried out in moderate to low temperature environments. The fast drying and moderate temperature allow spray drying to be used for heat sensitive materials. Rapid drying and the accompanying rapid stability of the materials make spray drying ideal for embedding and producing dry emulsions or amorphous materials. The possibility of particle engineering also includes powder performance characteristics such as the aerodynamic size of the particles, the geometry of the particles, the particle size distribution and the powder flow characteristics.
Spray drying of the nanoparticles involves drying the nanoparticles suspended in a suitable liquid such as water. After spray drying, the original granules are protected and at the same time new, desirable powder properties are obtained. That is, the powder has good flow properties and reduces the tendency to generate dust or has good powder flow properties and a small aerodynamic particle size.
Microencapsulation can be achieved by using a spray drying and spray coagulation process. The material used for spray drying microembedding is a liquid in which the drug is present in the package in a suspended or dissolved form. Suitable solvents can be water, alcohol, acetone, and the like. Another alternative is spray coagulation, in which case the coating solution is replaced with a melt of the packaging material. By spray drying or spray coagulation, the particle size can be very easily changed to a controlled release form suitable for commissioning and to obtain other desirable powder properties.
Dry emulsions are a variation of microencapsulation technology. In the dry emulsion, it is required to embed the microdroplets, that is, the oil solution containing the oil-soluble drug. A material which requires spray drying to produce a dry emulsion is an emulsion comprising a dissolved solid carrier. The dry emulsion after spray drying can be recombined to maintain the original droplet size to increase the bioavailability of the drug while achieving other desirable powder characteristics.
The solid amorphous dispersant/solution can be achieved by using spray drying. The material used to produce the solid amorphous dispersant consists of the drug and a suitable solvent containing a stabilizing material. Suitable solvents include alcohol, acetone, dichloromethane, and the like. The spray-dried solid amorphous dispersant can improve the bioavailability of the drug and enhance the stability of the drug, while obtaining other desirable powder characteristics such as flow properties of the powder and direct tableting properties.
Drying When the drug exhibits thermoplastic properties and has a high affinity for the solvent, it will result in the product being difficult to dry. For drugs with high solvent affinity, a higher drying temperature or a lower solvent vapor content in the exhaust gas may be required for a given solvent level in a given product, especially for products that have both thermoplastic properties. It is a considerable challenge. For those drugs that exhibit thermoplastic properties and have lower switching temperatures, the effective temperature range for drying is quite limited. Two contradictory factors determine the limited temperature range: The product temperature must be low enough to ensure product stability and no bonding; at the same time, the drying temperature must be high enough to allow the material droplets/particles to collide with the drying tower wall Dry the material within the effective time. Even worse, the solvent in the material behaves like a plasticizer, reducing the allowable temperature of the product. Incorrect drying conditions can result in very low acquisition rates due to accumulation of tower walls, too low and too high drying temperatures can cause this result.
For spray drying, it is important to distinguish between dryer inlet temperature, product temperature, drying temperature, and dryer outlet temperature. In a well-designed co-flow spray dryer, the drying temperature and dryer outlet temperature are the same. Due to evaporation of the solvent in the product, the product temperature will be below the dryer outlet temperature, typically 5-20 °C.
The drying of the granules is first determined by the outlet temperature of the spray dryer and the solvent vapor content of the spray dryer vent. Higher spray dryer outlet temperatures or lower solvent vapor content of the spray dryer vent will affect product drying. For a fixed spray dryer outlet temperature and dry gas flow rate, lowering the dryer inlet temperature will result in a decrease in the feed rate, a decrease in the amount of evaporation, and a decrease in the solvent vapor content of the spray dryer vent. Therefore, the parameters of the spray drying must be balanced very carefully, and the answer can usually be found in a window of opportunity.
The spray drying window may allow drying to occur at a high rate of availability, but may also result in the final product failing to meet the residual solvent level. For many products, effective drying time is even more important. When the residual solvent diffusion in the product is constrained, the single-stage dryer cannot be effectively dried, and in many cases additional drying sections must be added.
The thermoplasticity exhibited by some drugs will make them unsuitable for drying in conventional spray dryers. Thus, low pressure spray drying can be an option. Spray dryers operating at 0.5 to 0.7 bar allow for a significant reduction in drying temperature.
Dryer Forms Recently, Nitro has introduced a series of dryers that can be used to accomplish these tasks. PHARMASD® (PSD) (Figures 1, 2) and other necessary components can be combined to produce cGMP-compliant production at the pharmaceutical company.
The principle of PSD is to design a series of equipment with similar performance and different output, batches can range from a few grams to a few tons of powder. The PSD equipment with consistent performance enables the scale-up process from early development to final scale production to be successfully implemented. PSD devices are a combination of modules designed to meet specific requirements regardless of operating temperature, operating pressure, solvent, throughput, or other factors. Therefore, dryers of the same throughput may be completely different in design, configuration, and physical dimensions. PSD dryers are designed to use hot air or when drying non-water based materials with nitrogen as a drying gas (eliminating the risk of combustion). They can be used to dry a wide variety of acetone, methylene chloride, alcohol and other organic solvents. When using organic solvents and nitrogen, the dryer is typically operated in a closed loop system to minimize nitrogen loss and avoid organic solvent volatilization (Figure 3).
Summary By carefully selecting the operating parameters, drugs that exhibit thermoplastic and solvent affinity can be produced by spray drying. Spray drying has unparalleled advantages for the production of embedded, dry emulsions or amorphous materials with controlled release properties and/or bioavailable drugs.