Surface Dilatational Behavior of Pulmonary Surfactant Components Spread on the Surface of a Pendant Drop. 1. Dipalmitoyl Phosphatidylcholine and Surfactant Protein C

Abstract

Surface rheological characteristics of the components that are part of the film floating on the alveolar lining fluid in mammalian lungs are not well established. We measured the surface dilatational elasticity and viscosity of two of these pulmonary surfactant components, dipalmitoyl phosphatidylcholine (DPPC) and pulmonary surfactant protein C (SP-C). Pure DPPC or DPPC with 2 mol % SP-C was spread on the surface of a pendant phosphate buffered saline drop. Harmonic drop oscillation experiments were carried out below the surface pressure of protein squeeze-out in a frequency range of 0.006-0.25 Hz and at 20, 30, and 40 °C. We found that the dilatational elasticity of DPPC and DPPC/SP-C films increased up to a surface pressure of 40-45 mN/m. The dilatational viscosity of DPPC and DPPC/SP-C films dropped in the frequency range of human respiration (0.4-0.2 Hz). Dilatational elasticity and viscosity decrease with temperature. We conclude that films containing the pulmonary surfactant components DPPC and SP-C are in general viscoelastic but at breathing frequencies spontaneously elastic. SP-C stabilizes DPPC films, forming an alveolar lining layer of low compressibility at surface pressures below the pressure of protein squeeze-out and of high compressibility in the squeeze-out region.

Rheological properties of protein films

“…The area has been reviewed by Ueno [4]. In a series of papers [99][100][101] and a review [102 • ], Wüstneck et al have described the behaviour of spread monolayers of DPPC and the main lung surfactant proteins present at such interfaces. Measurements of the dilatational moduli at different compositions and interfacial pressures suggest that the various proteins work differently to reduce the work of film compression and expansion, whilst adding strength to maintain the film coherence at the limits of expansion and compression.…”

Mixed DPPC/DPPG Monolayers at Very High Film Compression

“…Fluid phospholipids, neutral lipids, and surfactant proteins (SP-A, SP-B, and SP-C) cannot reach high surface pressures but have a significant effect on improving adsorption and respreading. [30][31][32] The presence of anionic phopholipids, e.g., DPPG, in lung surfactant is well established; however, their quantitative contribution to surface activity is less clear. Results presented here suggest that an increased content of DPPG will adversely affect the surface tension lowering ability of DPPC.…”

Powder Particles and Technologies for Medicine Delivery to the Respiratory System: Challenges and Opportunities

“…Langmuir-Wilhelmy balance, oscillating bubble or oscillating drop tensiometers (e.g. Kondej D. and Sosnowski T.R., 2013;Kondej D. and Sosnowski T.R., 2016;Wüstneck R. et al, 2002). These experimental systems allow determination of the dynamic surface tension variations during the breathing-like compression and expansion of the interface with the PS.…”