Spray Drying Technology for Microspheres Preparation

Microsphere Preparation Steps

The preparation of microspheres by spray drying method is a method of spraying the liquid raw excipients into the hot drying medium to convert the raw excipients into dry powder in the spray dryer. The specific preparation process can be divided into three steps: the atomizer atomizes the original excipient solution into small droplets; the drying gas cures and dries the small droplets; and the dry particles are separated from the drying medium.

Advantages of Spray Drying Technology

Applicable to a variety of drugs, especially protein and peptide drugs with biological activity, small activity loss in the preparation process by controlling the equipment; no external water phase is used in the preparation process to reduce drug loss and higher encapsulation rate; when preparing thermal temperature sensitive peptide drugs, it can be achieved by adjusting the type or temperature of drying gas.

Spray Drying Process Investigation and Analysis

In order to obtain high quality and homogeneous microspheres, in addition to adjusting the raw materials required for preparation, the spray drying process needs to be examined and analyzed.

Inlet and outlet air temperature regulation

Because whether the inlet air temperature can achieve continued drying depends mainly on the boiling point of the selected solvent, the inlet air temperature will usually be controlled around the boiling point of the solvent used.

Atomizer inspection

As the core component of spray drying, the parameters of the atomizer are one of the important scope of investigation. The solution passes through the feed pump and the first thing that reaches the nebulizer is the nebulizer, and the strength of the nebulizer capacity determines the effect of the nebulization.

Pump speed adjustment

The feed rate is easily neglected in spray drying, and its speed also affects the droplet forming form. When the frequency of the nebulizer is certain, the amount of solution that the nebulizer can handle per unit time is certain. A slower pump speed of the suspension means a longer time in the pipe, and the long slow movement will allow solid-liquid separation to occur with the deposition of the suspension in the pipe. As time advances, the solids that form deposits are driven by the liquid to accumulate at the front of the feed pipe until they block the pipe.

Solid content adjustment

Solids content is a concept commonly used in spray drying and refers to the mass ratio of solids to the solvent used. Different solids have different solubilities in different solvents and also produce different viscosities.

Reference

1. Gavini, E., et al. (2004) PLGA microspheres for the ocular delivery of a peptide drug, vancomycin using emulsification/spray-drying as the preparation method: in vitro/in vivo studies. European journal of pharmaceutics and biopharmaceutics, 57(2), 207-212.