Literatureo ne lectroless Ni-P deposition, in recent decades, has dwelled primarily on surface engineering and corrosion-resistant applications. By contrast, we havemany researcharticles devoted to the engineering aspects of the electroless Ni-P depositions and their technology. The present article deals with the development of electroless Ni-P bath,a dvantages and mechanisms of deposition, and applications of the Ni-P deposits. We also present acomparison of the properties of electroless Ni-P and Ni-B as well as the recent developments in nickel-phosphorous research. We attempt to review these in ad etailed manner.W ea lso briefly discuss the future developments of electroless Ni-P.

Summary Persistent staphylococcal infections often involve surface-associated communities called biofilms. Staphylococcus aureus biofilm development is mediated by the coordinated production of the biofilm matrix, which can be composed of polysaccharides, extracellular DNA (eDNA), and proteins including amyloid fibers. The nature of the interactions between matrix components, and how these interactions contribute to the formation of matrix, remain unclear. Here we show that the presence of eDNA in S. aureus biofilms promotes the formation of amyloid fibers. Conditions or mutants that do not generate eDNA result in lack of amyloids during biofilm growth despite the amyloidogeneic subunits, phenol soluble modulin peptides, being produced. In vitro studies revealed that the presence of DNA promotes amyloid formation by PSM peptides. Thus this work exposes a previously unacknowledged interaction between biofilm matrix components that furthers our understanding of functional amyloid formation and S. aureus biofilm biology.

We report the application of low-voltage direct current (dc) electric fields to self-assemble close-packed colloidal crystals in nonaqueous solvents from colloidal spheres that vary in size from as large as 1.2 μm to as small as 0.1 μm. The assemblies are created rapidly (∼2 min) from an initially low volume fraction colloidal particle suspension using a simple capacitor-like electric field device that applies a steady dc electric voltage. Confocal microscopy is used to observe the ordering that is produced by the assembly method. This spatial evidence for ordering is consistent with the 6-fold diffraction patterns identified by light scattering. Red, green, and blue structural color is observed for the ordered assemblies of colloids with diameters of 0.50, 0.40, and 0.29 μm, respectively, consistent with spectroscopic measurements of reflectance. The diffraction and spectrophotometry results were found to be consistent with the theoretical Bragg's scattering expected for closed-packed crystals. By switching the dc electric field from on to off, we demonstrate reversibility of the structural color response on times scales ∼60 s. The dc electric field assembly method therefore represents a simple method to produce reversible structural color in colloidal soft matter.

We demonstrate that the microstructural and mechanical properties of bacterial biofilms can be created through colloidal self-assembly of cells and polymers, and thereby link the complex material properties of biofilms to well understood colloidal and polymeric behaviors. This finding is applied to soften and disassemble staphylococcal biofilms through pH changes. Bacterial biofilms are viscoelastic, structured communities of cells encapsulated in an extracellular polymeric substance (EPS) comprised of polysaccharides, proteins, and DNA. Although the identity and abundance of EPS macromolecules are known, how these matrix materials interact with themselves and bacterial cells to generate biofilm morphology and mechanics is not understood. Here, we find that the colloidal self-assembly of Staphylococcus epidermidis RP62A cells and polysaccharides into viscoelastic biofilms is driven by thermodynamic phase instability of EPS. pH conditions that induce phase instability of chitosan produce artificial S. epidermidis biofilms whose mechanics match natural S. epidermidis biofilms. Furthermore, pH-induced solubilization of the matrix triggers disassembly in both artificial and natural S. epidermidis biofilms. This pH-induced disassembly occurs in biofilms formed by five additional staphylococcal strains, including three clinical isolates. Our findings suggest that colloidal self-assembly of cells and matrix polymers produces biofilm viscoelasticity and that biofilm control strategies can exploit this mechanism.

Biofilms are microbial communities that are characterized by the presence of a viscoelastic extracellular polymeric substance (EPS). Studies have shown that polysaccharides, along with proteins and DNA, are a major constituent of the EPS, and play a dominant role in mediating its microstructure and rheological properties. Here, we investigate the possibility of entanglements and associative complexes in solutions of extracellular polysaccharide intercellular adhesin (PIA) extracted from Staphylococcus epidermidis biofilms. We report that the weight average molar mass and radius of gyration of PIA isolates are 2.01 × 105 ± 1200 g/mol and 29.2 ± 1.2 nm respectively. The coil overlap concentration, c*, was thus determined to be (32 ± 4) × 10−4 g/mL. Measurements of the in situ concentration of PIA (cPIA,Biofilm) was found to be (10 ± 2) × 10−4 g/mL. Thus, cPIA,Biofilm < c* and the amount of PIA in the biofilm is too low to cause polymer chain entanglements. In the pH range 3.0 to 5.5, PIA was found to both self-associate and to form complexes with bovine serum albumin (BSA). By static light scattering, both self-association and complex formation with 0.5 %(w/v) BSA were found to occur at PIA concentrations of 0.30 × 10−4 g/mL and greater, which is about 30 times lower than the measured cPIA,Biofilm. These results suggest that the microscopic origin of EPS viscoelasticity is unlikely to be due to polysaccharide entanglements. Furthermore, the onset of self-association and protein complexation of PIA occurs at concentrations far lower than the native PIA concentration in biofilms. This finding therefore suggests a critical role for those two association mechanisms in mediating biofilm viscoelasticity.

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We report the viscosity of semidilute solutions of a bacterially synthesized polysaccharidea partially deacetylated poly-N-acetylglucosamineas measured by microrheology. This polymer, commonly called polysaccharide intercellular adhesin (PIA), is synthesized by Staphylococcal strains; it is a principal component of the biofilms of these bacteria. We show that the concentration-dependent viscosity of PIA at a pH in which it is associated can be predicted using the Heo–Larson equation for entangled polymers [J. Rheol.20054911171128], if the molecular parameters of the equation are measured in its associated state. This agreement is consistent with PIA adopting a concentration-dependent scaling of the viscosity that is dominated by entanglements and intermolecular associations, as described in the theory of Rubinstein and Semenov [Macromolecules20013410581068]. The zero-shear specific viscosity, ηsp, measured in the concentration range, c PIA = 0.1–13 wt %, scales as ηsp ∼ c PIA 1.27±0.15 up to an entanglement concentration, c e = 3.2 wt %, after which ηsp ∼ c PIA 4.25±0.30. In the presence of urea, a known disruptor of associations, these scaling shifts to ηsp ∼ c PIA 1.02±0.2 and ηsp ∼ c PIA 2.57±0.6, respectively; no shift in c e is observed. The urea effect is consistent with an associative contribution to viscosity in the aqueous solution case. The invariance of c e suggests that the rheology of this polymer–solvent system also includes an entanglement contribution. With independent estimates of the PIA weight-average molar mass, M w, entanglement molecular weight, M e, hydrodynamic radius, R H, and excluded volume, ν, we use the Heo–Larson equation to predict ηsp as a function of c PIA. With the use of parameters from the associated stateparticularly the hydrodynamic radiuswe find good agreement between the model and data for aqueous PIA solutions. This study offers a means to predict the rheology of associating polysaccharides using correlations for nonassociating polymers adjusted with minimal a priori data from their associated state.

Results of permeation experiments involving finite dose diffusion c :Ils with hairless mouse skin as the membrane indicate that neither intact liposome; nor the phospholipid of which they are comprised diffuses across the skin. Lipoph lit drugs like progesterone and hydrocortisone, which are intercalated within th: bilayer structure of the phospholipid in miltilamellar liposomes. seem to pass thr Dugh the skin with comparable facility to free drug (comparable mass transfer toe Ticients). On the other hand, highly polar glucose entrapped in the aqueous compar: ments of the liposome is poorly available for transport. The results of in vitro release rate studies and theoretical calculations indicate that the very slight flux of lif osomally incorporated glucose seen experimentally is attributable to a slow release rate of glucose out of the liposome followed by relatively rapid skin permeation o!f the free solute. On the other hand, for hydrophobic progesterone and hydrocort isone the experimental results and supportive theoretical analysis suggest direct tr.ansfer of drug from liposome to the skin. Considering this mechanism and owing to increased soluble payloads of lipophilic drugs through liposomal incorporation, n ore total drug may be delivered through skin via liposomes relative to simple aqueous solutions.