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

On Comprehension of Genetic Programming Solutions: A Controlled Experiment on Semantic Inference

Applied to the problem of automatic program generation, Genetic Programming often produces code bloat, or unexpected solutions that are, according to common belief, difficult to comprehend. To study the comprehensibility of the code produced by Genetic Programming, attribute grammars obtained by Genetic Programming-based semantic inference were compared to manually written ones. According to the established procedure, the research was carried out as a controlled classroom experiment that involved two groups of students from two universities, and consisted of a background questionnaire, two tests and a feedback questionnaire after each test. The tasks included in the tests required the identification of various properties of attributes and grammars, the identification of the correct attribute grammar from a list of choices, or correcting a semantic rule in an attribute grammar. It was established that solutions automatically generated by Genetic Programming in the field of semantic inference, in this study attribute grammars, are indeed significantly harder to comprehend than manually written ones. This finding holds, regardless of whether comprehension correctness, i.e., how many attribute grammars were correctly comprehended, or comprehension efficiency is considered, i.e., how quickly attribute grammars were correctly comprehended

Sequential finite element model of tissue electropermeabilization

INSPEC Accession Number: 8387301Permeabilization, when observed on a tissue level, is a dynamic process resulting from changes in membrane permeability when exposing biological cells to external electric field (E). In this paper we present a sequential finite element model of E distribution in tissue which considers local changes in tissue conductivity due to permeabilization. These changes affect the pattern of the field distribution during the high voltage pulse application. The presented model consists of a sequence of static models (steps), which describe E distribution at discrete time intervals during tissue permeabilization and in this way present the dynamics of electropermeabilization. The tissue conductivity for each static model in a sequence is determined based on E distribution from the previous step by considering a sigmoid dependency between specific conductivity and E intensity. Such a dependency was determined by parameter estimation on a set of current measurements, obtained by in vivo experiments. Another set of measurements was used for model validation. All experiments were performed on rabbit liver tissue with inserted needle electrodes. Model validation was carried out in four different ways: 1) by comparing reversibly permeabilized tissue computed by the model and the reversibly permeabilized area of tissue as obtained in the experiments; 2) by comparing the area of irreversibly permeabilized tissue computed by the model and the area where tissue necrosis was observed in experiments; 3) through the comparison of total current at the end of pulse and computed current in the last step of sequential electropermeabilization model; 4) by comparing total current during the first pulse and current computed in consecutive steps of a modeling sequence. The presented permeabilization model presents the first approach of describing the course of permeabilization on tissue level.[...]Gamtos mokslų fakultetasVytauto Didžiojo universiteta

Sequential finite element model of tissue electropermeabilization

Sequential model of liver tissue electropermeabilisation around two needle electrodes was designed by computing electric field (E) distribution by means of the finite element (FE) method. Sequential model consists of a sequence of static FE models which represent E distribution during tissue permeabilisation. In the model an S-shaped dependency between specific conductivity and E was assumed. Parameter estimation of S-shaped dependency was performed on a set of current measurements obtained by in vivo experiments. Another set of in vivo measurements was used for model validation. Model validation was carried out in three different ways by comparing experimental measurements and modelled results. The model validation showed good agreement between modelled and measured results. The model also provided means for better understanding processes that occur during permeabilisation. Based on the model, the permeabilised volume of tissue exposed to electrical treatment can be predicted. Therefore, the most important contribution of the model is its potential to be used as a tool for determining the electrode position and pulse amplitude needed for effective tissue permeabilisationVytauto Didžiojo universiteta

Summer Workshop of Applied Mechanics Measurement repeatability of radiographic and biomechanical parameters in anterior-posterior pelvic radiographs

Abstract The measurement of a three-dimensional structure (pelvis) from a two-dimensional source (radiograph) is one of the main limitations of the radiograph analysis. The aim of our paper is to evaluate the measurement repeatability of the same hip in different radiographs. In particular, we are interested in determining the relative influence of the magnification and the specific radiographic parameters on the repeatability of the estimated peak contact hip stress. The study sample consisted of 15 adult patients with hip dysplasia who were operated upon in the years 1987-1994 (osteotomy according to Ganz). The study only included the hips that have NOT undergone any operation. Radiographic and biomechanical parameters of each hip were measured June 2004 Summer Workshop of Applied Mechanics on the preoperative and the postoperative anterior-posterior radiograph. The resultant hip force and the hip stress distribution was computed by using a previously developed analytical three-dimensional biomechanical model. The two consecutive measurements of a given parameter in an individual patient were normalized and the standard deviation of the normalized values was taken as an indicator of the measurement repeatability. It was found that the highest discrepancies between consecutive measurements of the same hip are seen in the vertical coordinate of the trochanteric insertion point and the Wiber centre-edge angle. This phenomenon is reflected in a relatively good repeatability of the resultant hip force and low repeatability of the peak contact hip stress. We conclude that the standardization of the radiographic magnification only solves one part of the repeatability problem. Further improvement in this direction would have to employ methods for more accurate positioning of human pelvis on the radiographic film and possible use of radio-opaque markers