Paramecia swimming in viscous flow

Swimming and feeding behaviors of Paramecium multimicronucleatum with fore-aft asymmetric body shapes are studied both experimentally and numerically. Ciliates, like Paramecia, with fore-aft asymmetric shapes preferentially swim along the slender anterior while feeding fluid into the oral groove located at the center of the body. Because both feeding and swimming are governed by fluid flow, it is important to reveal the role of fluid mechanics around a fore-aft asymmetric body. However, to date, Paramecia’s preferred swimming direction has not been investigated in detail and its potential benefits are not understood. In this study, we employ microparticle image velocimetry (µ-PIV) to measure the flow patterns around a swimming Paramecium and we use the boundary element method to investigate the effect of the body shape on the velocity fields, and on the swimming and feeding efficiencies. The simulation and experimental results are in agreement showing that the velocity fields exhibit a fore-aft asymmetry and the magnitude of the velocity decreases as r – 2 from the body surface. These observations are quite different from symmetric flows present in traditional squirmer models where steeper velocity decay (r – 3) is expected. According to our simulation results, this unexpected finding is attributed to the fore-aft body asymmetry. Moreover, the shape asymmetry revealed an optimum combined efficiency of swimming and feeding, which could possibly explain the Paramecium’s preferred swimming direction

Enhancement of solubility of Metaclopramide using solid dispersion technique with different carriers (HPβCD, PVP K-30)

Modern drug discovery has led to the development of drug molecules that exhibit high lipophilicity and poor water solubility, which leads to problematic bioavailability. Approaches have thus been made to enhance dissolution of poorly water soluble drugs through modifications and creation of specific formulations. Metaclopramide is an antiemetic and gastroprokinetic agent, commonly used to treat nausea and vomiting. It is absorbed well after oral administration but a significant first pass effect in some human patients may reduce systemic bioavailability to 30%.The Metaclopramide base is thus modified from Metaclopramide hydrochloride to enhance solubility .This has been achieved by the formulating in solid dispersion since Metaclopramide is poorly water soluble. Though it is absorbed well after oral administration, a significant first pass effect in some patients reduces systemic bioavailability, which can cause adverse side effects. This solid dispersion has then been used through transdermal drug delivery. Enhancement of solubility of poorly water soluble drug by solid dispersion may be attributed to particles modified characters such as particle size reduction, improved wettability, higher porosity, decreased lattice energy, amorphous state. The main objective thus includes modification of drug Metaclopramide  hydrochloride to Metaclopramide base, preparation of solid dispersion of modified Metaclopramide  base drug which has poor water solubility, experimental analysis of Metaclopramide base drug and solid dispersion products with carriers. Keywords: solubility, Metaclopramide, solid dispersion, carriers, HPβCD, PVP K-3

Hierarchical rose-petal surfaces delay the early-stage bacterial biofilm growth

A variety of natural surfaces exhibit antibacterial properties; as a result significant efforts in the past decade have been dedicated towards fabrication of biomimetic surfaces that can help control biofilm growth. Examples of such surfaces include rose petals, which possess hierarchical structures like the micro-papillae measuring tens of microns and nano-folds that range in the size of 700 ±100 nm. We duplicated the natural structures on rose-petal surfaces via a simple UV-curable nanocasting technique, and tested the efficacy of these artificial surfaces in preventing biofilm growth using clinically relevant bacteria strains. The rose-petal structured surfaces exhibited hydrophobicity (contact angle~130.8º ±4.3º) and high contact angle hysteresis (~91.0° ±4.9°). Water droplets on rose-petal replicas evaporated following the constant contact line mode, indicating the likely coexistence of both Cassie and Wenzel states (Cassie-Baxter impregnating wetting state). Fluorescent microscopy and image analysis revealed the significantly lower attachment of Staphylococcus epidermidis (86.1± 6.2% less) and Pseudomonas aeruginosa (85.9 ±3.2% less) on the rose-petal structured surfaces, compared with flat surfaces over a period of 2 hours. Extensive biofilm matrix was observed in biofilms formed by both species on flat surfaces after prolonged growth (several days), but was less apparent on rose-petal biomimetic surfaces. In addition, the biomass of S. epidermidis (63.2 ±9.4% less) and P. aeruginosa (76.0 ±10.0% less) biofilms were significantly reduced on the rose-petal structured surfaces, in comparison to the flat surfaces. By comparing P. aeruginosa growth on representative unitary nano-pillars, we demonstrated that hierarchical structures are more effective in delaying biofilm growth. The mechanisms are two-fold: 1) the nano-folds across the hemispherical micro-papillae restrict initial attachment of bacterial cells and delay the direct contacts of cells via cell alignment, and 2) the hemispherical micro-papillae arrays isolate bacterial clusters and inhibit the formation of a fibrous network. The hierarchical features on rose petal surfaces may be useful for developing strategies to control biofilm formation in medical and industrial contexts

Microstructural and Rheological Transitions in Bacterial Biofilms

Abstract Biofilms are aggregated bacterial communities structured within an extracellular matrix (ECM). ECM controls biofilm architecture and confers mechanical resistance against shear forces. From a physical perspective, biofilms can be described as colloidal gels, where bacterial cells are analogous to colloidal particles distributed in the polymeric ECM. However, the influence of the ECM in altering the cellular packing fraction (ϕ) and the resulting viscoelastic behavior of biofilm remains unexplored. Using biofilms of Pantoea sp. (WT) and its mutant (ΔUDP), the correlation between biofilm structure and its viscoelastic response is investigated. Experiments show that the reduction of exopolysaccharide production in ΔUDP biofilms corresponds with a seven‐fold increase in ϕ, resulting in a colloidal glass‐like structure. Consequently, the rheological signatures become altered, with the WT behaving like a weak gel, whilst the ΔUDP displayed a glass‐like rheological signature. By co‐culturing the two strains, biofilm ϕ is modulated which allows us to explore the structural changes and capture a change in viscoelastic response from a weak to a strong gel, and to a colloidal glass‐like state. The results reveal the role of exopolysaccharide in mediating a structural transition in biofilms and demonstrate a correlation between biofilm structure and viscoelastic response

Antiwetting and Antifouling Performances of Different Lubricant-Infused Slippery Surfaces

The concept of slippery lubricant-infused surfaces has shown promising potential in antifouling for controlling detrimental biofilm growth. In this study, nontoxic silicone oil was either impregnated into porous surface nanostructures, referred to as liquid-infused surfaces (LIS), or diffused into a polydimethylsiloxane (PDMS) matrix, referred to as a swollen PDMS (S-PDMS), making two kinds of slippery surfaces. The slippery lubricant layers have extremely low contact angle hysteresis, and both slippery surfaces showed superior antiwetting performances with droplets bouncing off or rolling transiently after impacting the surfaces. We further demonstrated that water droplets can remove dust from the slippery surfaces, thus showing a “cleaning effect”. Moreover, “coffee-ring” effects were inhibited on these slippery surfaces after droplet evaporation, and deposits could be easily removed. The clinically biofilm-forming species P. aeruginosa (as a model system) was used to further evaluate the antifouling potential of the slippery surfaces. The dried biofilm stains could still be easily removed from the slippery surfaces. Additionally, both slippery surfaces prevented around 90% of bacterial biofilm growth after 6 days compared to the unmodified control PDMS surfaces. This investigation also extended across another clinical pathogen, S. epidermidis, and showed similar results. The antiwetting and antifouling analysis in this study will facilitate the development of more efficient slippery platforms for controlling biofouling

When the path is never shortest: a reality check on shortest path biocomputation

Shortest path problems are a touchstone for evaluating the computing performance and functional range of novel computing substrates. Much has been published in recent years regarding the use of biocomputers to solve minimal path problems such as route optimisation and labyrinth navigation, but their outputs are typically difficult to reproduce and somewhat abstract in nature, suggesting that both experimental design and analysis in the field require standardising. This chapter details laboratory experimental data which probe the path finding process in two single-celled protistic model organisms, Physarum polycephalum and Paramecium caudatum, comprising a shortest path problem and labyrinth navigation, respectively. The results presented illustrate several of the key difficulties that are encountered in categorising biological behaviours in the language of computing, including biological variability, non-halting operations and adverse reactions to experimental stimuli. It is concluded that neither organism examined are able to efficiently or reproducibly solve shortest path problems in the specific experimental conditions that were tested. Data presented are contextualised with biological theory and design principles for maximising the usefulness of experimental biocomputer prototypes.Comment: To appear in: Adamatzky, A (Ed.) Shortest path solvers. From software to wetware. Springer, 201