Rheology of rounded mammalian cells over continuous high-frequencies

Understanding the viscoelastic properties of living cells and their relation to cell state and morphology remains challenging. Low-frequency mechanical perturbations have contributed considerably to the understanding, yet higher frequencies promise to elucidate the link between cellular and molecular properties, such as polymer relaxation and monomer reaction kinetics. Here, we introduce an assay, that uses an actuated microcantilever to confine a single, rounded cell on a second microcantilever, which measures the cell mechanical response across a continuous frequency range ≈ 1–40 kHz. Cell mass measurements and optical microscopy are co-implemented. The fast, high-frequency measurements are applied to rheologically monitor cellular stiffening. We find that the rheology of rounded HeLa cells obeys a cytoskeleton-dependent power-law, similar to spread cells. Cell size and viscoelasticity are uncorrelated, which contrasts an assumption based on the Laplace law. Together with the presented theory of mechanical de-embedding, our assay is generally applicable to other rheological experiments.

Swelling and Drug Release in Polymers through the Theory of Poisson–Kac Stochastic Processes

Experiments on swelling and solute transport in polymeric systems clearly indicate that the classical parabolic models fail to predict typical non-Fickian features of sorption kinetics. The formulation of moving-boundary transport models for solvent penetration and drug release in swelling polymeric systems is addressed hereby employing the theory of Poisson–Kac stochastic processes possessing finite propagation velocity. The hyperbolic continuous equations deriving from Poisson–Kac processes are extended to include the description of the temporal evolution of both the Glass–Gel and the Gel–Solvent interfaces. The influence of polymer relaxation time on sorption curves and drug release kinetics is addressed in detail.

Techniques of Mucilage and Gum Modification and their Effect on Hydrophilicity and Drug Release

Aim: The manuscript aims to describe the techniques of modification of gums and mucilages and their effect on hydrophilicity and drug release. Discussion: The interest is increased in the fields of polymers which is obtained from natural origin and used in the preparation of pharmaceuticals. Mucilage and gum are natural materials, widely used in the preparation of novel dosage form and conventional dosage form. They are used in the pharmaceutical industry for various purposes like suspending, emulsifying, bio-adhesive, binding, matrix-forming, extended release and controlled release agent. Gum and mucilage are biodegradable, less toxic, cheap and easily available. Moreover, mucilage and gum can be changed to acquire tailored materials for the delivery of drugs and allow them to compete with commercially available synthetic products. These polysaccharides have unique swellability in an aqueous medium that can exert a retardant effect on drug release or act as a super disintegrant, depending on the concentration utilized in the preparation. Drug release mechanism from hydrophilic matrices consisting of gums and mucilages is based on solvent penetration-induced polymer relaxation, diffusion of entrapped drug followed by degradation or erosion of the matrix. Conclusion: The present manuscript highlight the advantages, modifications of gum and mucilage, their effects on hydrophilicity and drug release as well as aspects of the natural gums which can be assumed to be bifunctional excipient because of their concentration-dependent effect on drug release and their high degree of swellability.

Postextrusion Heating in Three-Dimensional Printing

Stresses result when polymer feed stock is extruded through the nozzle of a three-dimensional (3D) printer, causing undesirable surface roughness called “sharkskin,” which hinders effective bonding to the substrate. A promising method to remove the sharkskin is to reheat the polymer after extrusion. However, questions remain about the appropriate design parameters to guarantee success. A mathematical model is presented for this system, and both amorphous and crystalline polymers are examined. The former is a heat transfer problem; the latter a Stefan problem. Several effectiveness conditions are considered, including exit temperature and a duration condition related to the polymer relaxation time. Our results provide guidance on designing effective postextrusion heaters.

Analyzing the thermal and hygral behavior of wool and its impact on fabric dimensional stability for wool processing and garment manufacturing

Wool is one of the most moisture sensitive natural fibers. This paper investigated changes of wool fiber diameter, fabric dimensions and fabric dimensional properties, as a function of moisture regain, temperature and pH. Experiments were conducted on fabrics with different weave structures as well as on fabrics with and without a permanent set. Results showed that the fabrics tended to contract when they were subjected to increased temperature at saturated regain. The degree of contraction appeared to depend on the weave structure of the fabrics and permanent setting treatments. Dimensions of the wool fabrics were also found to be dependent on the pH. Greater fabric dimensions were observed at pH 7.2 than at pH 2.1. The contraction effect was almost reversible when unset fabric samples were measured in pH 2.1. The reasons for the changes of dimensional property were analyzed in terms of changes in wool fiber swelling, yarn crimp and polymer relaxation phenomena with changes in regain, temperature and pH. Industrial implications from outcomes of this research to practical wool processing are discussed in the paper.