Biofouling, the accumulation of unwanted biological matter on surfaces, is a serious problem in many sectors of human society. The colonization of bacteria on the surfaces of pipelines and ship hulls leads to severe efficiency loss and thus higher operating cost. The problem is especially severe for medical implants, as their surfaces are preferred sites for the adhesion of bacteria from wound, operating room, or equipment contaminations, and post-operatively via contact with bloodborne bacteria. The conventional approach to minimize the risk of such infections typically involves coating the surface of the implants with a layer of slowly releasing antibiotics or biocides. However, the sustained release of antibiotics can lead to drug resistance and toxic side effects. The goal of this project is to develop a novel antimicrobial coating to overcome these limitations. The project’s design is inspired by the bactericidal (bacteria killing) nanopillar arrays identified on cicada and dragonfly wings, which are believed to be crucial for their survival in humid and bacteria-rich environments. Such nanopillar arrays have the unique capability to kill a wide spectrum of attached bacteria through purely physical (e.g. membrane rupture causing) interactions, without releasing any harmful chemicals. Despite their attractive antimicrobial properties, the nanopillar arrays on cicada and dragonfly wings are quite challenging to mimic due to their nanometer-scale dimensions and their high length to width ratios. To date, fabrication obstacles have limited the capability to fully reveal the bactericidal mechanism or to produce large-area nontoxic antimicrobial coatings for practical applications. This project will overcome these obstacles by developing a cost-effective approach to prepare such nanopillar arrays, with independently adjustable pillar height, radius, and spacing, on various polymer substrates with a wide range of elastic properties. A combination of experiments and computer simulations will be used to provide insight into the bactericidal mechanism. This insight, combined with fundamental engineering-design principles, will be used to design bioinspired antimicrobial films that can outperform their natural counterparts in terms of bactericidal efficacy and the number of bacteria species affected. The educational goal is to prepare a sustainable, adaptable, and globally competitive STEM workforce by exploiting the outreach opportunities and knowledge generated in the project. Efforts include a summer research project (involving training in microscopic techniques for measuring the surface topology of collected cicada wings) for local high-school students from underrepresented groups as part of the PhYSics Young Scholars program and by developing a multidisciplinary module on electronic devices for biomedical applications that will be incorporated into an undergraduate-level course on biomaterials.
The overarching objective of this project is to significantly advance the prospect of bioinspired non-toxic and high-efficiently bactericidal thin-film coatings for biomedical implant applications. The work is inspired by surfaces formed in nature, such as cicada and dragonfly wings, that have nano pillared structures that can kill attached bacteria through rupturing their cell membranes in a purely mechanical stretching process, and thus offer an attractive “chemical-free†and wide-spectrum strategy to fight against bacteria-related infections and fouling. The objective will be achieved by fulfilling two specific goals. The FIRST Goal is to develop a cost-effective and large-area applicable approach to fabricate nanopillar arrays (with sub-100 nm critical dimensions) with precisely adjustable pillar height, radius, and spacing on various polymer substrates with a wide range of Young’s moduli. The process starts from the fabrication of nanowell arrays on a Si substrate as the master, using low cost and large-area-applicable nanosphere lithography together with the anisotropic deep Si reactive-ion etching. Precursors of polymers with different mechanical properties are then casted against the master to yield the complementary replicas. Pillar height, radius, spacing, and the Young’s modulus are controlled independently by adjusting the nanosphere size, the etching time, and the choice of prepolymers. The fabricated films will be used to elucidate the detailed correlation between the film topology, mechanical properties and bactericidal efficacy through a combination of experiment and simulation, which will provide critical insight into their bactericidal mechanism. The SECOND Goal is to engineer nanostructured bactericidal films, as guided by modeling, to outperform their natural counterparts in terms of higher bactericidal efficacy against a broader bacterial spectrum. The films can be combined with multiple bactericidal approaches and functionalities. The nanostructured physical bactericidal coats can be made electrically conductive to demonstrate the potential for the films to be used as electrodes for biosensors. The films can be further integrated with flexible electronic components, e.g. a Wheatstone bridge with strain-sensing capabilities, as “smart†coatings on orthopedic implants to provide both long-term antibacterial and structure-health monitoring capabilities.
This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
