Prevention and characterization of thin film defects induced by contaminant aggregates in initiated chemical vapor deposition.

As initiated Chemical Vapor Deposition (iCVD) finds increasing application in precision industries like electronics and optics, defect prevention will become critical. While studies of non-ideal morphology exist in the iCVD literature, no studies investigate the role of defects. To address this knowledge gap, we show that the buildup of short-chain polymers or oligomers during normal operation of an iCVD reactor can lead to defects that compromise film integrity. We used atomic force microscopy to show that oligomer aggregates selectively prevented film growth, causing these hole-like defects. X-ray diffraction and optical microscopy demonstrated the crystallinity of the aggregates, pointing to a flat-on lamellar or mono-lamellar structure. To understand the origin of the aggregates, spectroscopic ellipsometry showed that samples exposed to the reactor consistently accrued low-volatility contaminants. X-ray photoelectron spectroscopy revealed material derived from polymerization in the contamination, while scanning electron microscopy showed the presence of defect-causing aggregates. We directly linked oligomeric/polymeric contamination with defect formation by showing an increased defect rate when a contaminant polymer was heated alongside the sample. Most importantly, we showed that starting a deposition at a high sample temperature (e.g., 50 °C) before reducing it to the desired setpoint (e.g., 9 °C) unilaterally prevented defects, providing a simple method to prevent defects with minimal impact on operations.

Mechano-Bactericidal Surfaces: Mechanisms, Nanofabrication, and Prospects for Food Applications.

Mechano-bactericidal (MB) nanopatterns have the ability to inactivate bacterial cells by rupturing cellular envelopes. Such biocide-free, physicomechanical mechanisms may confer lasting biofilm mitigation capability to various materials encountered in food processing, packaging, and food preparation environments. In this review, we first discuss recent progress on elucidating MB mechanisms, unraveling property-activity relationships, and developing cost-effective and scalable nanofabrication technologies. Next, we evaluate the potential challenges that MB surfaces may face in food-related applications and provide our perspective on the critical research needs and opportunities to facilitate their adoption in the food industry.

Reduced Biofilm Formation at the Air-Liquid-Solid Interface via Introduction of Surfactants.

Reduced biofilm formation is highly desirable in applications ranging from transportation to separations and healthcare. Biofilms often form at the three-phase interface where air, liquid, and solid coexist due to the close proximity to nutrients and oxygen. Reducing biofilm formation at the triple interface presents challenges because of the conflicting requirements for hydrophobicity at the air-solid interface (for self-cleaning properties) and for hydrophilicity at the liquid-solid interface (for reduced foulant adhesion). Meeting those needs simultaneously likely entails a dynamic surface, capable of shifting the surface energy landscape in response to wetting conditions and thus enabling hydrophobicity in air and hydrophilicity in water. Here, we designed a facile approach to render existing surfaces resistant to biofilm formation at the triple interface. By adding trace amounts (∼0.1 mM) of surfactants, biofilm formation of Pseudomonas aeruginosa (known to form biofilm at the triple interface) was reduced on all surfaces tested, ranging from hydrophilic to hydrophobic, polar to nonpolar. That reduced fouling was not a result of the known antimicrobial effects. Instead, it was attributed to the surface-adsorbed surfactants that dynamically control surface energy at the triple interface. To further understand the effect of surfactant-surface interactions on biofilm reduction, we systematically varied the surfactant charge type and surface properties (surface energy and charge). Electrostatic interactions between surfactants and surfaces were identified as an influential factor when predicting the relative fouling reduction upon introduction of surfactants. Nevertheless, biofilm formation was reduced even on the charge-neutral, fluorinated surface made of poly(1H, 1H, 2H, 2H-perfluorodecyl acrylate) by more than 2-fold simply via adding 0.2 mM dodecyl trimethylammonium chloride or 0.3 mM sodium dodecyl sulfate. Given its robustness, this strategy is broadly applicable for reducing fouling on existing surfaces, which in turn improves the cost-effectiveness of membrane separations and mitigates contaminations and nosocomial infections in healthcare.

On-Demand Synthesis of Antiseptics at the Site of Infection for Treatment of Otitis Media.

Otitis media (OM) is the main reason for pediatric antibiotic prescriptions. The current treatment mandates a rigorous regimen of multidose antibiotics over 5-10 days. The systemic antibiotic exposure and often prematurely terminated treatment due to the challenge of drug administration to young patients are believed to breed antibiotic resistance. To address these challenges, we designed a local treatment that converted a metabolic product (H2O2) of an OM pathogen (Streptococcus pneumoniae) into a potent antiseptic (HOBr), a reaction catalyzed by locally administered vanadium pentoxide nanowires. The therapeutic, HOBr, was only synthesized in the presence of the pathogen, enabling on-demand generation of therapeutics for OM treatment. Hypohalous acids are broad-spectrum and have a long history in general disinfection applications without breeding substantial drug resistance. A single dose of the nanowire formulation eradicated OM in a standard chinchilla model in 7 days with no observable tissue toxicity or negative impact on hearing sensitivity.

Design of Polymeric Thin Films to Direct Microbial Biofilm Growth, Virulence, and Metabolism.

Biofilms are ubiquitous in nature, yet strategies to direct biofilm behavior without genetic manipulation are limited. Due to the small selection of materials that have been used to successfully grow biofilms, the availability of functional materials that are able to support growth and program microbial functions remains a critical bottleneck in the design and deployment of functional yet safe microbes. Here, we report the design of insoluble pyridine-rich polymer surfaces synthesized using initiated chemical vapor deposition, which led to modulated biofilm growth and virulence in Pseudomonas aeruginosa (PAO1). A variety of extracellular virulence factors exhibited decreased production in response to the functional polymer, most significantly biomolecules also associated with iron acquisition, validating the material design strategy reported here. This report signifies a rich potential for materials-based strategies to direct the behavior of naturally occurring biofilms, which complement the existing genetic engineering toolkits in advancing microbiology, translational medicine, and biomanufacturing.

Vapor-Deposited Biointerfaces and Bacteria: An Evolving Conversation.

At the biointerface where materials and microorganisms meet, the organic and synthetic worlds merge into a new science that directs the design and safe use of synthetic materials for biological applications. Vapor deposition techniques provide an effective way to control the material properties of these biointerfaces with molecular-level precision that is important for biomaterials to interface with bacteria. In recent years, biointerface research that focuses on bacteria-surface interactions has been primarily driven by the goals of killing bacteria (antimicrobial) and fouling prevention (antifouling). Nevertheless, vapor deposition techniques have the potential to create biointerfaces with features that can manipulate and dictate the behavior of bacteria rather than killing or deterring them. In this review, we focus on recent advances in antimicrobial and antifouling biointerfaces produced through vapor deposition and provide an outlook on opportunities to capitalize on the features of these techniques to find unexplored connections between surface features and microbial behavior.