Krzysztof Zembrzycki

Experimental and numerical evaluation of drug release from nanofiber mats to brain tissue

Drug delivery systems based on nanofibrous mats appear to be a promising healing practice for preventing brain neurodegeneration after surgery. One of the problems encountered during planning and constructing optimal delivery system based on nanofibrous mats is the estimation of parameters crucial for predicting drug release dynamics. This study describes our experimental setup allowing for spatial and temporary evaluation of drug release from nanofibrous polymers to obtain data necessary to validate appropriate numerical models. We applied laser light sheet method to illuminate released fluorescent drug analog and CCD camera for imaging selected cross-section of the investigated volume. Transparent hydrogel was used as a brain tissue phantom. The proposed setup allows for continuous observation of drug analog (fluorescent dye) diffusion for time span of several weeks. Images captured at selected time intervals were processed to determine concentration profiles and drug release kinetics. We used presented method to evaluate drug release from several polymers to validate numerical model used for optimizing nanofiber system for neuroprotective dressing.

Atomic force microscopy combined with optical tweezers (AFM/OT)

The role of mechanical properties is essential to understand molecular, biological materials, and nanostructures dynamics and interaction processes. Atomic force microscopy (AFM) is the most commonly used method of direct force evaluation, but due to its technical limitations this single probe technique is unable to detect forces with femtonewton resolution. In this paper we present the development of a combined atomic force microscopy and optical tweezers (AFM/OT) instrument. The focused laser beam, on which optical tweezers are based, provides us with the ability to manipulate small dielectric objects and to use it as a high spatial and temporal resolution displacement and force sensor in the same AFM scanning zone. We demonstrate the possibility to develop a combined instrument with high potential in nanomechanics, molecules manipulation and biological studies. AFM/OT equipment is described and characterized by studying the ability to trap dielectric objects and quantifying the detectable and applicable forces. Finally, optical tweezers calibration methods and instrument applications are given.

Biocompatibility of electrospun human albumin: a pilot study

Albumin is rarely used for electrospinning because it does not form fibres in its native globular form. This paper presents a novel method for electrospinning human albumin from a solution containing pharmaceutical grade protein and 25% polyethylene oxide (PEO) used as the fibre-forming agent. After spontaneous cross-linking at body temperature, with no further chemicals added, the fibres become insoluble and the excess PEO can be washed out. Albumin deposited along the fibres retains its native characteristics, such as its non-adhesiveness to cells and its susceptibility for degradation by macrophages. To demonstrate this we evaluated the mechanical properties, biocompatibility and biodegradability of this novel product. After subcutaneous implantation in mice, albumin mats were completely resorbable within six days and elicited only a limited local inflammatory response. In vitro, the mats suppressed cell attachment and migration. As this product is inexpensive, produced from human pharmaceutical grade albumin without chemical modifications, retains its native protein properties and fulfils the specific requirements for anti-adhesive dressings, its clinical use can be expedited. We believe that it could specifically be used when treating paediatric patients with epidermolysis bullosa, in whom non-healing wounds occur after minor hand injuries which lead to rapid adhesions and devastating contractures.

Hydrogel Nanofilaments via Core-Shell Electrospinning.

Recent biomedical hydrogels applications require the development of nanostructures with controlled diameter and adjustable mechanical properties. Here we present a technique for the production of flexible nanofilaments to be used as drug carriers or in microfluidics, with deformability and elasticity resembling those of long DNA chains. The fabrication method is based on the core-shell electrospinning technique with core solution polymerisation post electrospinning. Produced from the nanofibers highly deformable hydrogel nanofilaments are characterised by their Brownian motion and bending dynamics. The evaluated mechanical properties are compared with AFM nanoindentation tests.

Lateral migration of electrospun hydrogel nanofilaments in an oscillatory flow

The recent progress in bioengineering has created great interest in the dynamics and manipulation of long, deformable macromolecules interacting with fluid flow. We report experimental data on the cross-flow migration, bending, and buckling of extremely deformable hydrogel nanofilaments conveyed by an oscillatory flow into a microchannel. The changes in migration velocity and filament orientation are related to the flow velocity and the filament’s initial position, deformation, and length. The observed migration dynamics of hydrogel filaments qualitatively confirms the validity of the previously developed worm-like bead-chain hydrodynamic model. The experimental data collected may help to verify the role of hydrodynamic interactions in molecular simulations of long molecular chains dynamics.

Analysis of wall effect on the process of diffusion of nanoparticles in a microchannel

In this preliminary work we introduce a new method for verification of the no-slip boundary condition on the liquid-solid interface, by analyzing variations in Brownian motion coecients of colloidal nanoparticles as a function of distance from the wall. The experimental investigations are performed in a small channel using an epi-fluorescent microscope. For precise measurements close to the wall an evanescent wave illumination is used. The experimental data obtained for 300nm particles gave us evidence of relatively large (0:3m) slip length. The experiments are supplemented by two-dimensional Molecular Dynamics simulations.

Atomic force microscopy combined with optical tweezers (AFM/OT): characterization of micro and nanomaterial interactions

Materials containing suspended micro- or nanomaterials are used extensively in multiple fields of research and industry. In order to understand the behavior of nanomaterials suspended in a liquid, the knowledge of particle stability and mobility is fundamental. For this reason, it is necessary to know the nanoscale solid-solid interaction and the hydrodynamic properties of the particles. In the presented research we used a hybrid Atomic Force Microscope coupled with Optical Tweezers system to measure the femtonewton scale interaction forces acting between single particles and the walls of a microchannel at different separation distances and environmental conditions. We show an important improvement in a typical detection system that increases the signal to noise ratio for more accurate position detection at very low separation distances.

Correction: Hydrogel Nanofilaments via Core-Shell Electrospinning

The images for Figs ​Figs66 and ​and77 are incorrectly switched. The image that appears as Fig 6 should be Fig 7 and the image that appears as Fig 7 should be Fig 6. The figure captions appear in the correct order. Please view the correct figures below. Fig 6 Fluorescence images showing bending dynamics of a nanofilament (Table 1, nanofilament no. 1). Fig 7 a) Plot of the mean square displacement of a filament of contour length 21.5 μm as a function of lag time. The upper two plots are MSDs along the a and b axes in terms of μm2, whereas the bottom one is the angular MSD in terms of mrad ... The fifth sentence in the second paragraph of the Results subsection titled “Mechanical properties of hydrogel nanofilaments” should reference Fig 7b instead of Fig 6b. The tenth sentence in the second paragraph of the Results subsection titled “Mechanical properties of hydrogel nanofilaments” should reference Fig 7c instead of Fig 6c.

Distribution of energy storage rate in area of strain localization during tension of austenitic steel

The present work is devoted to experimental determination of the energy storage rate in the area of strain localization. The experimental procedure involves two complementary techniques: i.e. infrared thermography (IRT) and visible light imaging. The results of experiments have shown that during the evolution of plastic strain localization the energy storage rate in some areas of the deformed specimen drops to zero. To interpret the decrease of the energy storage rate in terms of micro-mechanisms, microstructural observations using electron back scattered diffraction (EBSC) were performed.