Multilayer films of organic compounds on solid surfaces have been studied for more than 60 years because they allow fabrication of multicomposite molecular assemblies of tailored architecture. However, both the Langmuir-Blodgett technique and chemisorption from solution can be used only with certain classes of molecules. An alternative approach—fabrication of multilayers by consecutive adsorption of polyanions and polycations—is far more general and has been extended to other materials such as proteins or colloids. Because polymers are typically flexible molecules, the resulting superlattice architectures are somewhat fuzzy structures, but the absence of crystallinity in these films is expected to be beneficial for many potential applications.

https://science.sciencemag.org/content/sci/277/5330/1232.full.pdf

Fuzzy Nanoassemblies: Toward Layered Polymeric Multicomposites

Microorganisms attach to surfaces and develop biofilms. Biofilm-associated cells can be differentiated from their suspended counterparts by generation of an extracellular polymeric substance (EPS) matrix, reduced growth rates, and the up- and down- regulation of specific genes. Attachment is a complex process regulated by diverse characteristics of the growth medium, substratum, and cell surface. An established biofilm structure comprises microbial cells and EPS, has a defined architecture, and provides an optimal environment for the exchange of genetic material between cells. Cells may also communicate via quorum sensing, which may in turn affect biofilm processes such as detachment. Biofilms have great importance for public health because of their role in certain infectious diseases and importance in a variety of device-related infections. A greater understanding of biofilm processes should lead to novel, effective control strategies for biofilm control and a resulting improvement in patient management.

/pdf/biofilms-microbial-life-on-surfaces-1snm9wt8v9.pdf

Biofilms: microbial life on surfaces.

Microfabricated integrated circuits revolutionized computation by vastly reducing the space, labor, and time required for calculations. Microfluidic systems hold similar promise for the large-scale automation of chemistry and biology, suggesting the possibility of numerous experiments performed rapidly and in parallel, while consuming little reagent. While it is too early to tell whether such a vision will be realized, significant progress has been achieved, and various applications of significant scientific and practical interest have been developed. Here a review of the physics of small volumes (nanoliters) of fluids is presented, as parametrized by a series of dimensionless numbers expressing the relative importance of various physical phenomena. Specifically, this review explores the Reynolds number Re, addressing inertial effects; the Peclet number Pe, which concerns convective and diffusive transport; the capillary number Ca expressing the importance of interfacial tension; the Deborah, Weissenberg, and elasticity numbers De, Wi, and El, describing elastic effects due to deformable microstructural elements like polymers; the Grashof and Rayleigh numbers Gr and Ra, describing density-driven flows; and the Knudsen number, describing the importance of noncontinuum molecular effects. Furthermore, the long-range nature of viscous flows and the small device dimensions inherent in microfluidics mean that the influence of boundaries is typically significant. A variety of strategies have been developed to manipulate fluids by exploiting boundary effects; among these are electrokinetic effects, acoustic streaming, and fluid-structure interactions. The goal is to describe the physics behind the rich variety of fluid phenomena occurring on the nanoliter scale using simple scaling arguments, with the hopes of developing an intuitive sense for this occasionally counterintuitive world.

/pdf/microfluidics-fluid-physics-at-the-nanoliter-scale-4bpahtd8qa.pdf

Microfluidics: Fluid physics at the nanoliter scale

http://experimentationlab.berkeley.edu/sites/default/files/AFMImages/butt_AFM.pdf

Force measurements with the atomic force microscope: Technique, interpretation and applications

The major strategies for designing surfaces that prevent fouling due to proteins, bacteria, and marine organisms are reviewed. Biofouling is of great concern in numerous applications ranging from biosensors to biomedical implants and devices, and from food packaging to industrial and marine equipment. The two major approaches to combat surface fouling are based on either preventing biofoulants from attaching or degrading them. One of the key strategies for imparting adhesion resistance involves the functionalization of surfaces with poly(ethylene glycol) (PEG) or oligo(ethylene glycol). Several alternatives to PEG-based coatings have also been designed over the past decade. While protein-resistant coatings may also resist bacterial attachment and subsequent biofilm formation, in order to overcome the fouling-mediated risk of bacterial infection it is highly desirable to design coatings that are bactericidal. Traditional techniques involve the design of coatings that release biocidal agents, including antibiotics, quaternary ammonium salts (QAS), and silver, into the surrounding aqueous environment. However, the emergence of antibiotic- and silver-resistant pathogenic strains has necessitated the development of alternative strategies. Therefore, other techniques based on the use of polycations, enzymes, nanomaterials, and photoactive agents are being investigated. With regard to marine antifouling coatings, restrictions on the use of biocide-releasing coatings have made the generation of nontoxic antifouling surfaces more important. While considerable progress has been made in the design of antifouling coatings, ongoing research in this area should result in the development of even better antifouling materials in the future.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/adma.201001215

Antifouling coatings: recent developments in the design of surfaces that prevent fouling by proteins, bacteria, and marine organisms.

Novel approach towards versatile and robust nonfouling coatings

In various applications it is desired that biological cells or protein molecules are immobilized at surfaces. Examples are enzymes or cells in bioreactors and biosensors, immuno-proteins in solid-state diagnostics and proteinaceous farmacons in drug delivery systems. In order to retain biological activity, the structural integrity of the immobilized bio-compounds should be preserved. In other cases immobilization of cells and proteins should be avoided. Adsorption of proteins from biofluids is considered to be the first event in the biofouling process. Subsequently, bacterial and/or other biological cells (e.g., blood platelets, erythrocytes) deposit on the adsorbed protein layer and a biofilm is formed. This causes great problems in areas as diverse as biomedicine, food processing and the marine environment. A generic approach to influence the magnitude of the interaction between a particle (e.g., a cell or a globular protein molecule) and a sorbent material is to manipulate both the long- and short-range interaction forces by grafting soluble polymers or oligomers onto the sorbent surface. Application of oligomers of ethylene oxide (EO) prevents the particles from making intimate contact with the surface. Thus, adsorbed enzymes may retain their native structure and, hence, their enzymatic activity. Another interesting example is the steering effect of pre-adsorbed polymers of EO (PEO) on the orientation of subsequently depositing anisotropic particles. For instance, IgG molecules may be forced in the right orientation and conformation in the interstitial spaces between the PEO chains, therewith doubling the specific antigen binding capacity. By far the greatest part of recent research on modifying surfaces by grafting soluble polymers (usually PEO) aims at the prevention of protein adsorption and/or adhesion of biological cells. Suppression of particle deposition depends primarily on two characteristics of the polymer layer: (a) the grafting density, and (b) the extension of the polymer layer into the solution. The efficacy of grafted PEO layers to reduce protein adsorption and microbial adhesion is illustrated for blood plasma proteins, saliva proteins and a number of bacterial and yeast cells.

Willem Norde

Papers

Novel approach towards versatile and robust nonfouling coatings

Surface‐Tethered Polymers to Influence Protein Adsorption and Microbial Adhesion