Particle size, particle morphology, and particle density are important factors that determine lung deposition.\u00a0Particles of different aerodynamic diameters (Dae) collide, settle and diffuse inertially when entering the lungs.\u00a0Dae is an imaginary particle size that describes the movement of particles.\u00a0It is defined as:\u00a0to make the unit density sphere moving at low Reynolds number in still air, and the actual diameter reached the same final particle sedimentation rate, which is the actual particle size in terms of equivalent aerodynamic characteristics of the same diameter, that is,\u00a0the actual particle size The diameter is converted into an equivalent diameter with the same aerodynamic characteristics.<\/p>\n There are three main mechanisms for the deposition of drugs with different aerodynamic diameters in the lungs: 1.\u00a0Inertial embedding.\u00a0Particles with Dae greater than 5\u03bcm have a higher weight and velocity.\u00a0They are deposited in the oropharynx and upper respiratory tract due to inertial collisions, and there is not much deposition in the lungs;\u00a02.\u00a0Sedimentation, due to inertial collision and sedimentation, smaller particles with a Dae of 0.5-5\u03bcm easily reach the deep part of the respiratory tract and deposit on the surface of the trachea, bronchi and alveoli;\u00a03.\u00a0Brownian diffusion, most of the particles smaller than 0.5\u03bcm are due to Brownian motion Suspended in the air and diffused, it is exhaled out of the body, usually 80% is expelled, basically can not be deposited in the respiratory tract, so the best Dae for depositing particles in the alveolar area is 0.5-5\u03bcm.<\/p>\n Particles with smaller aerodynamic particle size will also be deposited in the lower respiratory tract, such as large porous particles (LPP) with a particle size of 5\u03bcm or more and a density of less than 0.4g\/cm3.\u00a0LPP overcomes the traditional atomization of micropowder (ball) drug delivery system Shortcomings such as low efficiency, easy adhesion and easy aggregation, LPP is not easy to be cleared by the alveoli, easy to deposit in the lower respiratory tract, and can make the drug slow release in the lungs.\u00a0Using para-acetamidosalicylic acid as the model drug, DPPC as the carrier material, spray drying method to prepare the macroporous microsphere lung inhalation drug delivery system, Dae is 7.0~7.5\u03bcm, the proportion of inhalable particles (FPF) is 31%~39 %, the drug load is 95%.\u00a0Animal experiments have shown that the blood drug concentration reaches its peak after 15 minutes of administration, and the effective lung drug concentration is maintained for more than 3 hours.<\/p>\n Single photon emission computed tomography was used to study the pulmonary deposition of mannitol powders with three different particle sizes (Dae: 2.7\u03bcm, 3.6\u03bcm and .5.4\u03bcm) labeled with radiolabel Tc-DTPA.\u00a0The lung deposition of 2.7\u03bcm and 3.6 \u03bcm particles is twice that of 5.4 \u03bcm particles.\u00a0The deposition of smaller particles is negligible.\u00a075.9% of 5.4\u03bcm particles are deposited in the upper respiratory tract and have no therapeutic effect.\u00a0The smaller the particle size, the less the upper respiratory tract deposition (42.4% for 3.6\u03bcm and 36% for 2.7\u03bcm).\u00a0This result confirms that lung deposition depends on Particle size, especially aerodynamic particle size.<\/p>\n Carriers and <\/b><\/strong>D<\/b><\/strong>rugs<\/b><\/strong><\/p>\n The drug in dry powder inhalation needs to be micronized to reach the appropriate particle size. Micronization methods mainly include grinding and spray drying. The grinding method cannot well control the particle size and particle morphology. Spray drying is the use of an atomizer to disperse the drug solution into fine droplets, and quickly evaporate the solvent in a thermal drying medium (such as hot air) to form dry powder or particles, with high cleanliness, narrow particle size distribution, and easy industrial production.<\/p>\n![\"\"](\"\/wp-content\/uploads\/sites\/2\/2021\/07\/Pulmonary-deposition-of-inhaled-particles-and-their-way-of-separation-in-healthy-847x1024.png\")