The adhesion capability of S. aureus cells is heterogeneously distributed over the cell envelope

Understanding and controlling microbial adhesion is an important biomedical problem. However, many properties of the adhesion process of bacteria are still unknown, for example the distribution of adhesive strength over the cell wall. While a patchy colloid model for adhesion has been developed recently for Gram-negative Escherichia coli cells, a comparable model for Gram-positive cells is not known. Here, we use single-cell force spectroscopy to measure the adhesion of Staphylococcus aureus at different positions on tailored surfaces. We find a heterogenous distribution of the adhesion forces with varying degrees of intensity. By comparing these results to simulations, we obtain the distribution of adhesive strength on the cell wall: The cells have several distinct spots of high adhesion capability, similar to the patchy colloid model. We discuss implications of our results for the development of new materials and the design and analysis of future studies.

Influence of Tailored Surfaces and Superimposed-Oscillation on Sheet-Bulk Metal Forming Operations

Producing complex sheet metal components in fewer process steps motivated the development of the innovative forming process called sheet-bulk metal forming (SBMF). In this process, sheet metal forming and bulk-metal forming are combined to create a unique forming process in which a component with external and internal gearing is produced in three production steps. However, the high degrees of deformation that occur using high-strength steels and the number of different process steps result in high process forces, strongly limiting the service life of tools. To reduce the forming force during SBMF processes, tool and process modifications were investigated. Therefore, plane-strain compression tests were conducted to examine the influence of a CrAlN PVD coating and tailored surfaces produced by high-feed milling (HF) of tool-active elements on the material flow of the specimens. In addition to the tool-sided modifications, the influence of an oscillation overlay during the forming process was investigated. Based on the results of the compression tests, the surfaces of the active tool elements of the SBMF process were modified in order to transfer the basic experimental results to the production of a functional component. The friction is thus adapted locally in the SBMF process.

Extension of the forming limits of extrusion processes in sheet-bulk metal forming for production of minute functional elements

Increasing demands in modern production pose new challenges to established forming processes. One approach to meet these challenges is the combined use of established process classes such as sheet and bulk forming. This innovative process class, also called sheet-bulk metal forming (SBMF), facilitates the forming of minute functional elements such as lock toothing and gear toothing on sheet-metal bodies. High tool loads and a complex material flow that is hard to control are characteristic of SBMF. Due to these challenging process conditions, the forming of functional elements is often insufficient and necessitates rework. This negatively affects economic efficiency. In order to make use of SBMF in industrial contexts, it is necessary to develop measures for improving the forming of functional elements and thereby push existing forming boundaries. This paper describes the design and numerical replication of both a forward and a lateral extrusion process so as to create involute gearing in combination with carrier teeth. In a combined numerical-experimental approach, measures for extending the die filling in sheet-metal extrusion processes are identified and investigated. Here, the focus is on approaches such as process parameters, component design and locally adjusted tribological conditions; so-called ‘tailored surfaces’. Based on the findings, fundamental mechanisms of action are identified, and measures are assessed with regard to their potential for application. The examined approaches show their potential for improving the forming of functional elements and, consequently, the improvement of geometrical accuracies in functional areas of the workpieces.