Quantification of Adhesion Force of Bacteria on the Surface of Biomaterials: Techniques and Assays

Biomaterials associated infection (BAI) has been identified as one of the leading causes of failure of bioimplants. A failed implant requires revision surgery, which is about 20 times costlier and more painful than primary surgery. Infection starts from initial attachment of bacteria onto the surface of biomaterials followed by colonization and biofilm formation. Once a biofilm is developed the bacteria become resistant toward antibiotics. On account of microbial cell development, their metabolic activity and viability are strongly affected by the adhesion. Hence a thorough investigation warrants an in-depth understanding of the interfacial adhesion. Several methods such as plate-and-wash assay, spinning-disc assay, centrifugation assay, step-pressure technique, optical tweezers, atomic force microscopy (AFM) and nanoindentation are used for the measurement of the bacterial adhesion. Most of the aforementioned techniques are nonquantitative and provide only approximate values of adhesion forces. Techniques such as AFM and nanoindentation can quantify a wide range of force 10 pN to 1 μN and 1 nN to 10 μN respectively, and hence they are particularly useful for exact quantification of the adhesion force as well as adhesion strength of bacterial cells on various surfaces of biomaterials. In this review, we present a comparative study of the techniques available to measure the bacterial adhesion force and strength, discuss the use of AFM in adhesion force quantification in detail and conclude by hypothesizing that the AFM technique has an edge over other techniques for quantification of bacterial adhesion force.