Figure 2.

AFM measurements showing increased stiffness of decidua basalis. (A) AFM was used to determine the stiffness of samples by measuring the force between a cantilever and the sample in a feedback mechanism. The reflected laser beam strikes a position-sensitive photo diode consisting of a four segment photo detector, and this is used to determine the angular deflections of the cantilever. The Hertz model can be used to estimate the apparent elastic modulus, E_a. (B) Decidua basalis was stiffer than decidua parietalis in five patient-matched samples (Mann–Whitney; ^****P < 0.0001; ^***P < 0.001; number of measurement points in each sample ranged from n = 10 to 148). Black bars show median for each sample. (C) A comparison of the apparent elastic modulus for decidua basalis, decidua parietalis, nonpregnant endometrium, and placenta villi; values measured for all samples are shown together. Black bars show median for each sample type (Kruskal–Wallis ANOVA with multiple comparison tests between groups; ^****P < 0.001; ns means nonsignificant; N, number of patient samples; n, number of measurements). (D) Map of apparent elastic modulus values for decidua basalis and parietalis in paired samples. Each square has an area of 20 × 20μm, inside which a single measurement was taken; squares colored according to scale bar on right. Crosses represent where a clean measurement could not be taken; these are determined by evaluating the force–displacement curves manually during post-experiment analysis.