Surface Dilatational Behavior of Pulmonary Surfactant Components Spread on the Surface of a Pendant Drop. 2. Dipalmitoyl Phosphatidylcholine and Surfactant Protein B

Abstract

Surface dilatational behavior of spread monolayers of the surfactant protein B (SP-B) and its mixture with dipalmitoyl phosphatidylcholine (DPPC + 0.5 mol % SP-B) were investigated on the surface of a pendant phosphate buffered saline drop. Surface pressure/area isotherms of these pulmonary surfactant components were recorded in a captive bubble device. We found that the dilatational viscosity of SP-B and DPPC/SP-B films strongly decreases in the frequency range of respiration, creating an elastic film. Temperature (20 versus 30 °C) influences surface rheology quantitatively but not qualitatively. DPPC films containing either of the two hydrophobic pulmonary surfactant proteins, SP-B or SP-C, are predominantly elastic at breathing frequencies (0.04-0.2 Hz). We conclude that the hydrophobic surfactant proteins balance the surface rheological behavior of the thin film that covers the alveolar lining layer, by forming an interface of low compressibility at surface pressures below the protein squeeze-out. In the region of the protein squeeze-out, the film compressibility, however, increases. This behavior reduces the mechanical work required for respiration.

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.…”

Interfacial rheology for the assessment of potential health effects of inhaled carbon nanomaterials at variable breathing conditions

“…by determining the apparent surface elasticity and the apparent surface viscosity 31,32 . Several authors studied the surface rheology of air/liquid interfaces with different LS models [33][34][35] , however they did not focus on exact relations to the real breathing conditions (in terms of temperature and surface deformation frequency). In the rheological formalism, the departure from the initial value of the surface tension: Δσ = σ − σ 0 is connected with extensional deformation of the interface, γ:…”

“…Therefore, in the system considered in this work, both surface elasticity and surface viscosity should be considered as not the real (intrinsic) rheological characteristics of the interface but rather as the apparent parameters of the interfacial region. A more comprehensive discussion of these issues may be found elsewhere 31,[33][34][35][36][37] . The phenomenon of surface tension hysteresis has been analyzed and discussed in the relation to the physiological functions of LS 13,26,30,[38][39][40] .…”

Large amplitude oscillatory microrheology

“…Strong flows, e.g., coughing, ideally produce viscous flow. But when the elastic modulus dominates the behavior of airway mucus, serious (sometimes life-threatening) pathology results, for example, in the case of cystic fibrosis [App et al (1998); Banerjee et al (2001); Lai et al (2009);W€ ustneck et al (2002)]. …”