Aleš Iglič

Titanium nanostructures for biomedical applications

Titanium and titanium alloys exhibit a unique combination of strength and biocompatibility, which enables their use in medical applications and accounts for their extensive use as implant materials in the last 50 years. Currently, a large amount of research is being carried out in order to determine the optimal surface topography for use in bioapplications, and thus the emphasis is on nanotechnology for biomedical applications. It was recently shown that titanium implants with rough surface topography and free energy increase osteoblast adhesion, maturation and subsequent bone formation. Furthermore, the adhesion of different cell lines to the surface of titanium implants is influenced by the surface characteristics of titanium; namely topography, charge distribution and chemistry. The present review article focuses on the specific nanotopography of titanium, i.e. titanium dioxide (TiO2) nanotubes, using a simple electrochemical anodisation method of the metallic substrate and other processes such as the hydrothermal or sol-gel template. One key advantage of using TiO2 nanotubes in cell interactions is based on the fact that TiO2 nanotube morphology is correlated with cell adhesion, spreading, growth and differentiation of mesenchymal stem cells, which were shown to be maximally induced on smaller diameter nanotubes (15 nm), but hindered on larger diameter (100 nm) tubes, leading to cell death and apoptosis. Research has supported the significance of nanotopography (TiO2 nanotube diameter) in cell adhesion and cell growth, and suggests that the mechanics of focal adhesion formation are similar among different cell types. As such, the present review will focus on perhaps the most spectacular and surprising one-dimensional structures and their unique biomedical applications for increased osseointegration, protein interaction and antibacterial properties.

Thickness of electrical double layer. Effect of ion size

The thickness of a single flat electrical double layer is considered. The electrostatic mean field and the excluded volume effect are taken into account. A simple statistical mechanical approach is used, where the particles in the solution are distributed over a lattice with an adjustable lattice constant. Different sizes of ions are described by different values of the lattice constant. Two measures are introduced that describe an effective thickness of the electrical double layer: a distance where the density of the number of counterions drops to a chosen fraction of its maximal value, and a distance defining a region that contains a chosen fraction of the excess of the counterions. It is shown that the effective thickness of the electrical double layer increases with increasing counterion size and with decreasing bulk concentration of ions, whereas increasing the surface charge may cause either a decrease or an increase of the effective thickness. It is shown that the description of the effective thickness of the electrical double layer by the Debye length differs qualitatively from the description presented for low bulk concentrations of ions.

Mathematical estimation of stress distribution in normal and dysplastic human hips

By using a mathematical model of the adult human hip in the static one‐legged stance position of the body, the forces acting on the hip, peak stress in the hip joint and other relevant radiographic and biomechanical parameters were assessed. The aims were to examine if the peak stress in dysplastic hips is higher than in normal hips and to find out which biomechanical parameters contribute significantly to higher peak stress. The average normalized peak stress in dysplastic hips (7.1 kPa/N) was markedly higher (≈︁100%) than the average normalized peak stress in normal hips (3.5 kPa/N). The characteristic parameters that contributed to higher peak stress in dysplastic hips included the smaller lateral coverage of the femoral head, the larger interhip distance, the wider pelvis, and the medial position of the greater trochanter. These results are consistent with the hypothesis that stress distribution over weight‐bearing surface of the hip joint is the relevant parameter for assessment of the risk for developing coxarthrosis.

Erratum to “Fusion Pore Diameter Regulation by Cations Modulating Local Membrane Anisotropy”.

1 Laboratory of Biophysics, Faculty of Electrical Engineering, University of Ljubljana, 1000 Ljubljana, Slovenia 2 Laboratory of Neuroendocrinology-Molecular Cell Physiology, Faculty of Medicine, University of Ljubljana, 1000 Ljubljana, Slovenia 3 Departamento de Biologia e CESAM, Universidade de Aveiro, 3810-193 Aveiro, Portugal 4 Celica Biomedical Center, Tehnoloski Park 24, 1000 Ljubljana, Slovenia 5 Department of Biology, Biotechnical Faculty, University of Ljubljana, Vecna pot 111, 1000 Ljubljana, Slovenia

The Bernese periacetabular osteotomy: clinical, radiographic and mechanical 7–15-year follow-up of 26 hips

Background The Bernese periacetabular osteotomy is used in dysplastic hips to increase the load-bearing area of the hip and to prevent osteoarthritis.The aim of our work was to determine the contact hip stress before and after the osteotomy and to compare the relief of stress with the long-term radiographic and clinical outcome. Patients and methods We followed 26 dysplastic hips (26 patients) for 7–15 years after the index operation. Clinical evaluation was based on the WOMAC score, osteoarthrosis was evaluated with the Tönnis classification, the angles of lateral (CE) and anterior (VCA) femoral coverage were measured, and biomechanical parameters were studied. Results Periacetabular osteotomy increased the mean CE from 15° to 37°, and the mean VCA from 22° to 38°. The mean normalized peak contact stress was reduced from 5.2 to 3.0 kPa/N. Four hips required total hip arthroplasty after an average of 4.5 years, 8 hips showed considerable arthrosis progression, and 14 hips had no or mild arthrosis at follow-up. Preoperative WOMAC score, preoperative Tönnis grade and postoperative normalized peak contact stress were the most important predictors of outcome. Interpretation The Bernese periacetabular osteotomy improves the mechanical status of the hip. Long-term success depends on the grade of arthrosis preoperatively and on the magnitude of operative correction of the contact hip stress.   ▪

Mathematical modelling of stress in the hip during gait

A mathematical model is developed for calculating the contact stress distribution in the hip for a known resultant hip force and characteristic geometrical parameters. Using a relatively simple single nonlinear algebraic equation, the model can be readily applied in clinical practice to estimate the stress distribution in the most frequent body positions of everyday activities. This is demonstrated by analyzing the data on the resultant hip force obtained from laboratory observations where a stance period of gait is considered.

Adhesion of osteoblasts to a nanorough titanium implant surface

This work considers the adhesion of cells to a nanorough titanium implant surface with sharp edges. The basic assumption was that the attraction between the negatively charged titanium surface and a negatively charged osteoblast is mediated by charged proteins with a distinctive quadrupolar internal charge distribution. Similarly, cation-mediated attraction between fibronectin molecules and the titanium surface is expected to be more efficient for a high surface charge density, resulting in facilitated integrin mediated osteoblast adhesion. We suggest that osteoblasts are most strongly bound along the sharp convex edges or spikes of nanorough titanium surfaces where the magnitude of the negative surface charge density is the highest. It is therefore plausible that nanorough regions of titanium surfaces with sharp edges and spikes promote the adhesion of osteoblasts.

Effect of surfactant polyoxyethylene glycol (C12E8) on electroporation of cell line DC3F

Abstract Surfactant polyoxyethylene glycol (C12E8) decreases the voltage required for irreversible electroporation in planar lipid bilayers. In our study the effect of non-cytotoxic concentration of C12E8 on cell membrane reversible and irreversible electroporation voltage was investigated in DC3F cell line. Cell suspension was exposed to a train of 8 electric pulses of 100 μs duration, repetition frequency 1 Hz and amplitudes from 0 to 400 V at electrode distance 2 mm. The effect of C12E8 on the reversible and irreversible electroporation was investigated. We found that C12E8 decreases the voltage necessary for irreversible electroporation but has no effect on reversible electropermeabilization. Cell membrane fluidity measured by electron paramagnetic resonance spectrometry, using the spin probe methylester of 5-doxyl palmitate was not significantly changed due to the addition of C12E8. Based on this we conclude that the main reason for the observed effect were not the changes in the membrane fluidity. As an alternative explanation we suggest that C12E8 induced anisotropic membrane inclusions may stabilize the hydrophilic pore, by accumulating on a toroidally shaped edge of the pore and attaining favorable orientation.

Curvature-dependent lateral distribution of raft markers in the human erythrocyte membrane.

The distribution of raft markers in curved membrane exvaginations and invaginations, induced in human erythrocytes by amphiphile-treatment or increased cytosolic calcium level, was studied by fluorescence microscopy. Cholera toxin subunit B and antibodies were used to detect raft components. Ganglioside GM1 was enriched in membrane exvaginations (spiculae) induced by cytosolic calcium and amphiphiles. Stomatin and the cytosolic proteins synexin and sorcin were enriched in spiculae when induced by cytosolic calcium, but not in spiculae induced by amphiphiles. No enrichment of flotillin-1 was detected in spiculae. Analyses of the relative protein content of released exovesicles were in line with the microscopic observations. In invaginations induced by amphiphiles, the enrichment of ganglioside GM1, but not of the integral membrane proteins flotillin-1 and stomatin, was observed. Based on the experimental results and theoretical considerations we suggest that membrane skeleton-detached, laterally mobile rafts may sort into curved or flat membrane regions dependent on their intrinsic molecular shape and/or direct interactions between the raft elements.

A possible mechanism determining the stability of spiculated red blood cells

In this work the stability of spiculated red blood cells, called echinocytes, is studied. It is assumed that the stable echinocyte shape corresponds to the minimum of its membrane elastic energy. It is shown that if the membrane skeleton shear elasticity is not taken into account the calculated stable echinocyte shapes always have only one spicule. However, by considering the skeleton shear elastic energy also, the calculated stable echinocyte shapes have many spicula in agreement with experimental observations.