This Small Business Innovation Research (SBIR) Phase I project will enable the manufacture of Sharklet patterns on metallic surfaces. A Sharklet pattern is an engineered micro-surface texture that mimics the texture of shark skin and inhibits bacterial biofilm growth without the use of anti-microbial agents. The Sharklet surface texture technology has been successfully produced in soft materials using photolithographic methods but its extension to metals-based applications has been inhibited by the absence of a suitable manufacturing process. This project will demonstrate feasibility of a micro-grooving process. The efficacy of the micro-grooving process will be proved by machining the Sharklet pattern in steel dies, thereby facilitating the transfer of the Sharklet pattern to metal surfaces for testing.
The commercial potential of this project is a significant reduction in hospital-borne infections, the 4th leading cause of death in United States. The estimated market size of such patterned metallic surfaces in the healthcare sector alone is $8.6 billion. Additional markets benefiting from this technology include energy, marine (exceeding $450 million/year), and space exploration. In addition, the presence of a micro-grooving process capability at the micron size scale will enable high-performance cooling solutions for defense and electronics industries that are experiencing a strong need for making smaller and more tightly spaced channels in their cooling devices to significantly enhance their thermal performance. Additionally, many micro-machining centers are machining 3D channels with 50-100 micron channel widths for micro-fluidics research. The ability to make channels and grooves below or near 1 micron in width will enable cutting-edge micro-fluidics researchers to explore additional fundamental fluidics phenomena at 3D micro-/nano-scales at a reduced cost footprint, compared to using conventional (2D geometry-limited) and expensive MEMS-based etching processes.
The objective of this research effort was to develop a novel micro-grooving process which can be leveraged in commercial applications. The application that was targeted for this effort is manufacturing a bacterial-biofilm-inhibiting surface texture designed by Sharklet Technologies, Inc. This surface texture has multiple applications in the biomedical and defense industries. Previously, the Sharklet surface texture technology had been successfully manufactured in soft materials using micro-replication manufacturing methods but its extension to metals-based applications, particularly in hard metals and over large surface areas, had been inhibited by the absence of a suitable manufacturing process. There are many different industries where this technology could be utilized, including Healthcare (medical implants and joints), Naval (ship hulls and marine sensor systems), and Energy (intake valves for hydro- or nuclear power plants). The overarching objective of the research and development program for Phase I was to clearly demonstrate the feasibility of using the micro-scale grooving process developed at the University of Illinois to machine the Sharklet pattern in metals for the purpose of inhibiting the growth of bacterial biofilms. The micro-grooving process was developed to address these four (4) scientific and technological challenges: 1. The process is capable of machining of the Sharklet pattern in metals; 2. The process has the speed necessary to be viable; 3. The process can facilitate the transfer of the Sharklet pattern to large surfaces; 4. The anti-fouling property of Sharklet pattern is effective when applied to metals by the process. Microlution, through its partnership with The University of Illinois Urbana-Champaign (UIUC) and Sharklet Technologies, was able to demonstrate the technical feasibility of creating the Sharklet pattern in metal using a micro-grooving process. The ability to transfer the pattern from a steel die to metal foil was also demonstrated, which makes large scale production of the pattern a very promising opportunity. This technology has a wide range of applications, including biomedical and defense-related industries, and has already proven to be quite successful in soft materials such as plastics and other non-metals. In order to satisfy the process attributes required, parallel paths were executed by Microlution and UIUC that would work to the strengths of each party, and allow the evaluation of multiple approaches. At UIUC, a cantilevered beam force regulation approach was pursued based on an Atomic Force Microscopy (AFM) probe. The force was regulated by controlling the deflection of the beam, which was determined using a laser probe or strain gage feedback. UIUC also continued efforts on researching and developing the tool geometry to meet groove definition requirements. Tools were fabricated through FIB machining and imaged/evaluated using a Scanning Electron Microscope (SEM). Microlution pursued a non-cantilevered approach, utilizing near-frictionless air bearings and varying tilt angle to regulate the force. Gravity provides the cutting force, which is regulated by varying the tilt angle of the rotating trunnion of the Microlution 5100 5-axis Micro-Machining center. The Microlution 5100 is a micro-milling machine with a positional accuracy of +/- 1 micron. The system has the accuracy and repeatability to provide the motions necessary to create the Sharklet pattern. Through the combined efforts of Microlution and UIUC, the goals of Phase 1 were met. Through the combination of the work completed at UIUC and Microlution, it was demonstrated that: The technology developed at UIUC is capable of production tools that can produce 2 micron wide grooves that have a depth of 2-3 microns in stainless steel with a high degree of repeatability; The Microlution micro-grooving test-bed completed an 8mm x 8mm pattern in 6.5 hours, demonstrating the speed necessary to create larger dies for the large scale production of metallic foils with the Sharklet pattern; Both the Microlution and UIUC micro-grooving test-beds can accurately, and with a high degree of repeatability, create the curvilinear lines necessary for the completion of the Sharklet pattern; The pattern created was transferred from the steel die to a metallic foil in a repeatable manner for over 20 samples; After evaluating the results of the two design approaches, we have been able to identify areas where significant improvement can be achieved. By integrating the tool technology developed at UIUC, which was successful in meeting the tool development goals, into the gravity-based test-bed developed at Microlution, which was successful in meeting the motion profile and pattern transfer goals, we are confident that a pattern which meets the bacterial inhibiting requirements can be produced quickly and effectively. With these completed tasks, and the lessons learned, Microlution is confident that this process presents a viable solution for the creation of the Sharklet pattern in steel, and its transfer to other materials where previous processes have been lacking.
