The Role of Endogenous Proteins on the Emulsification of Silicone Oils Used in Vitreoretinal Surgery

Abstract

The present work is aimed at investigating the chemicophysical properties of the interface between silicone oils (SOs) used in vitreoretinal surgery and aqueous solutions, in the presence of surfactant biomolecules. Such molecules are thought to play an important role in the formation of SO emulsions in vitrectomised eyes, in which the natural vitreous body has been replaced with a SO. In particular, we have measured the interfacial tension (IT) and the interfacial dilational viscoelasticity (DV) of the interface between SO (Siluron 1000) and serum proteins (albumin and γ-globulins) at various concentrations in a Dulbecco alkaline buffer. The equilibrium IT value is relevant for the onset of emulsification, and the DV influences the stability of an emulsion, once formed. The study is complemented by preliminary emulsification tests. The experimental results show that, when proteins are dissolved in the aqueous solution, the rheological properties of the interface change. The IT decreases significantly for physiological protein concentrations, and the DV modulus achieves high values, even for small protein concentrations. The emulsification tests confirm that, in the presence of proteins, emulsions are stable on the time scale of months. We conclude that the measured values of IT in the presence of serum proteins are compatible with the promotion of droplet formation, which, in addition, are expected to be stable against coalescence. Adsorption of biomolecules at the interface with the SO is, therefore, likely to play an important role in the generation of an emulsion in eyes subjected to vitrectomy. These findings are relevant to identify strategies to avoid or control the formation of emulsions in eyes.

Figure 1

Time evolution of the dynamic IT of the SO-DPBS (black) and SO-water (blue) interfaces (left y-axis). For the first 1800 s, the interfacial area is kept fixed. From there on, oscillations of the interfacial area with an amplitude of 2% are imposed, for a range of different frequencies. The green line represents the interfacial area variation in time (right y-axis).

Figure 2

Time evolution of the dynamic IT between SO and buffer solutions containing γ-globulins or albumin. The curves refer to different concentrations, in which values are normalised with the corresponding value in the blood. 0.1 light blue, 1.0 red, 0.14 blue, and 1.0 green.

Figure 3

Equilibrium IT as a function of protein concentration. Concentration is normalised with the value corresponding to the concentration in blood.

Figure 4

DV modulus as a function of protein concentration for different perturbation frequencies.

Figure 5

1 : 1 volume ratio emulsions between SO and aqueous phases, 1 hour after formation. (a) DBPS; (b) albumin 0.1 normalised concentration in DBPS; (c) γ-globulins 0.1 normalised concentration in DBPS; (d) albumin+γ-globulins 0.1 normalised concentration in DBPS.