In situ elasticity and adhesion measurement of biomembrane by a video enhanced depth-sensing indentation technique

Elasticity and adhesion of a prestressed circular biomembrane to planar graphite surface was investigated by a video enhanced depth-sensing indentation technique. This biomembrane was a combination of human skin cells and biodegradable polymer. Using this kind of membrane as a skeleton facilitated the easy formation of the hybrid sponges into desired shapes that had a high mechanical strength, while the collagen micro sponges nested in the pores, which allowed the cells to interact with the collagen surfaces. A homemade indenter apparatus was constructed to meet force and displacement resolutions of 0.1 μN and 10.0 nm. The indenter possessed the capability of measuring the applied force and resultant displacement simultaneously. By armed with a high magnification side-view system, it could record lateral profile variation of biomembrane, which was essential for observing and analyzing its gradually rupture. A linear theoretical elastic solution was applied to quantitatively interpret the measured central displacement of the membrane under a central point load. Elastic modulus of the biomembrane could be easily determined once the applied force and the central displacement, together with the essential dimensions were known. The biomembrane “jump-into” an adhesion contact when the punch approached the range of the intersurfaces force across the punch-membrane gap. A “pull-off” event was observed at a nonzero contact circle when the tensile load reaching a critical threshold. This technique provided the capability of measuring mechanical behaviors of prestressed ultra thin tissue and thin-walled biocapsules with a residual stress.