Pulmonary surfactant: an engineering marvel

For adequate exchange of oxygen and carbon dioxide with the atmosphere, active animals need lungs with a myriad of small moist alveoli, and surface tension is a serious problem in such microscopic structures. Nature's solution to this problem is pulmonary surfactant, a polymorphic system of phospholipids, neutral lipids and specific surfactant proteins that rapidly forms films at the alveolar surfaces, which stabilize alveoli against collapse. Structure-function relationships of this complex material are still being unraveled. Although knowledge of the system has already had significant clinical impact, many challenging questions remain to be answered.