{"id":175,"date":"2018-10-25T17:43:32","date_gmt":"2018-10-25T17:43:32","guid":{"rendered":"https:\/\/commons.mtholyoke.edu\/aidalalab\/?page_id=175"},"modified":"2019-06-10T04:29:55","modified_gmt":"2019-06-10T04:29:55","slug":"earlier-work","status":"publish","type":"page","link":"https:\/\/commons.mtholyoke.edu\/aidalalab\/earlier-work\/","title":{"rendered":"Earlier Work – Biofilms"},"content":{"rendered":"

Mechanical Properties of Soft Materials – Bacterial Biofilms<\/strong><\/h2>\n

The Atomic Force Microscope can measure mechanical properties of materials, including adhesion and stiffness.\u00a0 This is most often accomplished by what is known as a “force curve” which plots force on the tip vs. distance (Figure 1).\u00a0 \u00a0As the tip approaches the surface, it is in its neutral position.\u00a0 Just before it touches the surface, it may deflect downwards to the surface, due to attractive forces.\u00a0 As the tip continues to be lowered, the amount it deflects and how far into the surface it depresses depends on the stiffness of the material.\u00a0 (Imagine pushing a meter stick down into a pillow compared to a table top; for the pillow, it pushes down and may bend slightly while for the table it bends a lot and may push in slightly.)\u00a0 The slope of the force curve indicates the stiffness of the material – careful models are required to to extract parameters like young’s modulus.\u00a0 As the tip is retracted, it may stick to the surface if there are adhesive forces, causing the tip to bend down before often “popping” off, a sudden change in the deflection as adhesive forces are overcome.\u00a0 Force curves on homogeneous materials are more straightforward to interpret, and can yield information about viscoelasticity and poroelasticity in the case of a material like a hydrogel.\u00a0 For a heterogeneous sample like a bacterial biofilm, there is a wealth of information contained within the force curve.\u00a0 Our lab has studied a few different biofilm-forming bacteria along with the predator bacteria Bedellovibrio bacteriovorus<\/em> in collaboration with Megan Nunez<\/a>, Eileen Spain<\/a>, and Megan Ferguson<\/a>.<\/p>\n

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Figure 1:\u00a0 Schematic of a typical force curve.\u00a0 As the tip is lowered towards the surface (left to right on the graph, red curve), there is no interaction and zero force.\u00a0 As it encounters the surface, the force increases, and the tip depresses into the surface.\u00a0 When the tip reverses direction (blue curve), there may be hysteresis (not shown).\u00a0 The tip often adheres to the surface, creating a negative force.\u00a0 When the force is high enough, the tip may “snap” off the surface, allowing us to measure the strength of adhesion.\u00a0\u00a0<\/em><\/p>\n

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Microorganisms, such as bacteria, can form communities on surfaces called biofilms.\u00a0 \u00a0As certain kinds of these films play a role to spreading infectious diseases, there is a need for a greater understanding in their behaviour in order to preserve the public health.\u00a0 In particular, if we can understand how the biofilms adhere early in their formation, it might be possible to inhibit or prevent adhesion.<\/p>\n

One challenge in working with bacteria is simply imaging them.\u00a0 A range of methods exist to artificially fix bacteria to the surface, in fluid.\u00a0 Some of these methods may change the properties of the bacteria.\u00a0 Once fixed, it can still be challenging to image the bacteria because imaging in fluid is generally more finicky and sticky surfaces create additional complications – imaging trying to tap your finger a long a sticky note; as you stick to the surface for a moment, you alter your image. Figure 2 shows height images of bacteria natively adhered to a surface.<\/p>\n

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Figure 2:\u00a0 Images of bacteria natively adhered to the surface in fluid.\u00a0 \u00a0 (A) B. subtilis. The height (Z-axis) scale is 800 nm. (B) M. luteus. The height scale is 600 nm. (C) E. coli ZK1056. The height scale is 400 nm. (D) P. putida. The height scale is 600 nm. (E) E. coli ML35. The height scale is 800 nm.\u00a0 \u00a0 From Volle, et al., Colloids and Surfaces B, 67<\/b> (2008)<\/em><\/p>\n

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Figure 3:\u00a0\u00a0Cellular spring constants for natively adhered bacterial biofilm cells and chemically fixed planktonic cells. The spring constant is calculated from the linear region of the extension curve. The error bars represent the standard error for each data set. The number of force curves averaged is n.<\/em><\/p>\n

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Generally, adhesion forces are measured with a regular silicon tip or a spherical bead with a chemical coating.\u00a0 We instead grew a biofilm of E. coli<\/em> directly onto a tipless cantilever (Figure 4), before bringing it into contact with different chemical coatings on a silicon wafer (Figure 5).<\/p>\n

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Figure 4:\u00a0 To directly measure adhesion of E. coli to different surfaces, we grow a biofilm of E. coli onto a tipless cantilever.\u00a0 We bring the tip into contact with surfaces that have different coating to measure the adhesion between the tip and the surface.\u00a0\u00a0<\/em><\/p>\n

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Figure 5:\u00a0 The maximum adhesion force is largest for fluorosilane and smallest for the PEG coated silicon wafer.\u00a0 See Hu et al., Langmuir, 29<\/b>, 2000-2011 (2013) for more information.\u00a0\u00a0<\/em><\/p>\n

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<\/h6>\n","protected":false},"excerpt":{"rendered":"

Mechanical Properties of Soft Materials – Bacterial Biofilms The Atomic Force Microscope can measure mechanical properties of materials, including adhesion and stiffness.\u00a0 This is most often accomplished by what is known as a “force curve” which plots force on the tip vs. distance (Figure 1).\u00a0 \u00a0As the tip approaches the surface, it is in its…<\/p>\n","protected":false},"author":1030,"featured_media":674,"parent":0,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","meta":{"_monsterinsights_skip_tracking":false,"footnotes":""},"class_list":["post-175","page","type-page","status-publish","has-post-thumbnail","hentry"],"_links":{"self":[{"href":"https:\/\/commons.mtholyoke.edu\/aidalalab\/wp-json\/wp\/v2\/pages\/175","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/commons.mtholyoke.edu\/aidalalab\/wp-json\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/commons.mtholyoke.edu\/aidalalab\/wp-json\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/commons.mtholyoke.edu\/aidalalab\/wp-json\/wp\/v2\/users\/1030"}],"replies":[{"embeddable":true,"href":"https:\/\/commons.mtholyoke.edu\/aidalalab\/wp-json\/wp\/v2\/comments?post=175"}],"version-history":[{"count":22,"href":"https:\/\/commons.mtholyoke.edu\/aidalalab\/wp-json\/wp\/v2\/pages\/175\/revisions"}],"predecessor-version":[{"id":786,"href":"https:\/\/commons.mtholyoke.edu\/aidalalab\/wp-json\/wp\/v2\/pages\/175\/revisions\/786"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/commons.mtholyoke.edu\/aidalalab\/wp-json\/wp\/v2\/media\/674"}],"wp:attachment":[{"href":"https:\/\/commons.mtholyoke.edu\/aidalalab\/wp-json\/wp\/v2\/media?parent=175"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}