RESUMEN
Stabilizing layers of colloidal dispersions or emulsions to obtain homogeneous films is a real challenge. We describe here a new kind of instability in drying films of emulsions: during evaporation of the internal phase, cracks appear between the droplets that create aggregates according to a regular pattern. We show that this pattern only appears if the emulsion is adhesive, i.e., if droplets stick together. The pattern exhibits a characteristic length which depends on the adhesion strength and film thickness. These experimental results support a model where this instability is due to the gel structure and elastic properties of adhesive emulsions. Understanding this phenomenon will allow us to get a homogeneous film or to control it to get structured materials.
RESUMEN
Here we report the use of natural, chemically-unmodified, microfibrillated cellulose (MFC) as a matrix for hepatocyte culture. We developed an original cell-culture design composed of a thin 3D-microstructured fibrous substrate consisting of a MFC sheet coating a highly O(2)-permeable polydimethylsiloxane (PDMS) membrane. The MFC-coated PDMS membranes were obtained according to a simple process where cellulose fibres were deposited from an aqueous suspension on the PDMS surfaces and the films were dried under mild conditions. To enable oxygen diffusion through the membranes, they were assembled on bottomless frames ('O(2)+' condition). Rat hepatocytes primary-cultured on such MFC-PDMS membranes quickly organized themselves into large hemispherical 3D aggregates which were tightly anchored to the MFC sheets. In contrast, hepatocytes cultured on smooth PDMS membranes in the O(2)+ system (O(2)+, PDMS) organized into unstable 2D monolayers which easily detached from the surfaces. Hepatocyte 3D cultures obtained on MFC-PDMS membranes exhibited higher liver-specific functions over a 2-week culture period, as assessed by both the higher albumin secretion and urea synthesis rate. The MFC-PDMS membranes appear suitable for obtaining stably-attached and functional hepatocyte 3D cultures and appear interesting for drug/chemical screenings in a microplate format, but also for microfluidic applications.
