Investigation of Impact of Walking Speed on Forces Acting on a Foot-Ground Unit.

Static and dynamic methods can be used to assess the way a foot is loaded. The research question is how the pressure on the feet would vary depending on walking/running speed. This study involved 20 healthy volunteers. Dynamic measurement of foot pressure was performed using the Ortopiezometr at normal, slow, and fast paces of walking. Obtained data underwent analysis in a "Steps" program. Based on the median, the power generated by the sensors during the entire stride period is the highest during a fast walk, whereas based on the average; a walk or slow walk prevails. During a fast walk, the difference between the mean and the median of the stride period is the smallest. Regardless of the pace of gait, the energy released per unit time does not depend on the paces of the volunteers' gaits. Conclusions: Ortopiezometr is a feasible tool for the dynamic measurement of foot pressure. For investigations on walking motions, the plantar pressure analysis system, which uses the power generated on sensors installed in the insoles of shoes, is an alternative to force or energy measurements. Regardless of the pace of the walk, the amounts of pressure applied to the foot during step are similar among healthy volunteers.

Corona Charging of Isotactic-Polypropylene Composites.

A new approach to obtaining piezoelectric polymeric films based on the isotactic-polypropylene (i-PP) using corona discharge with the energy of 45 W·min/m2 was presented. Detailed analyses with Atomic Force Microscopy (AFM) led to the conclusion that the surface quality was the important factor influencing the possibility of charging the i-PP composites, which was necessary to induce the permanent piezoelectric effect. It has been found that the high surface smoothness of the polymer films contributed to improved piezoelectric properties without the need for an additional polymer modification such as orientation, foaming or doping with fillers. The values of the piezoelectric constant, d33, of the studied samples were compared to these values for the analogous systems polarized with a constant electric field of 100 V/µm. The milder conditions of the film polarization during the corona discharge process are sufficient to achieve the electrets in i-PP films. The simple and cheap method proposed can be profitable in obtaining flexible electrets in the form of thin films for the production of personal biomedical sensors.

Cellular Polyolefin Composites as Piezoelectric Materials: Properties and Applications.

Piezoelectric polymers characterized by flexibility are sought for applications in microelectronics, medicine, telecommunications, and everyday devices. The objective of this work was to obtain piezoelectric polymeric composites with a cellular structure and to evaluate their usefulness in practice. Composites based on polyolefins (isotactic-polypropylene and polyethylene) with the addition of aluminosilicate fillers were manufactured by extrusion, and then polarized in a constant electric field at 100 V/µm. The content of mineral fillers up to 10 wt% in the polymer matrix enhances its electric stability and mechanical strength. The value of the piezoelectric coefficient d33 attained ~150 pC/N in the range of lower stresses and ~80 pC/N in the range of higher stresses, i.e., at ~120 kPa. The materials exhibited high durability in time, therefore, they can be used as transducers of mechanical energy of the human motion into electric energy. It was demonstrated that one shoe insert generates an energy of 1.1 mJ after a person walks for 300 s. The miniaturized integrated circuits based on polyolefin composites may be applied for the power supply of portable electronics. Due to their high sensitivity, they can be recommended for measuring the blood pulse.

Piezoelectric Films Based on Polyethylene Modified by Aluminosilicate Filler.

The development, universality and miniaturization of electronic devices leads to the search for new piezoelectric materials, among which recently, polymers play an increasingly important role. In this work, composites based on two types of polyethylene-high density polyethylene (HDPE), and medium density polyethylene (MDPE)-and aluminosilicate fillers were obtained by extrusion process. This method allowed obtaining flexible electrets in the form of a thin film after polarization under a constant electric field of 100 V/µm. The morphology of the composites was characterized by scanning electron microscopy, whereas the crystallinity was determined by X-ray diffraction. The mechanical properties and thermal stability of the composites were examined by means of tensile tests and thermogravimetry, respectively. The piezoelectric characteristics were appointed by measuring the electric charge and the voltage in the polarized samples. Piezoelectric coefficients, and the stability of electrets over time were also determined. Moreover, the effect of film orientation on piezoelectric properties was investigated. Composites with appropriate morphology (i.e., well dispersed filler particles in the polymer matrix and formed holes) were obtained which ensured permanent electrical polarization. It was found that the best piezoelectric, mechanical properties and thermal stability exhibits HDPE composite with 5% of aluminosilicate filler.

Quantitative Analysis of Foot Plantar Pressure During Walking.

BACKGROUND There are many methods of dynamic analysis of foot loading, however, we still need a simple, easily applicable system for foot plantar pressure analysis. In this study we asked the question: "Can a new system for foot evaluation, the ITE System, provide a good quantitative dynamic foot pressure analysis? Can it be used in clinical practice?". MATERIAL AND METHODS Twenty healthy volunteers, 8 females and 12 males, aged 20 to 25 years old took part in this study. Normal static foot loading was tested using a typical pedobarographic platform, followed by a dynamic analysis using the foot-pressure ITE System. A new algorithm for data analysis (from 8 sensors) was proposed. RESULTS The sum of all maximal values from sensors was 11.71 N mean, with relatively low standard deviation (SD) of 1.81. Loading of sensor 1 (heel) was the highest - on average 29.84%. Sensor 2 (medial midfoot) received the lowest loading - normal range for this segment would be 0-4%. The manner of loading heel/toes, dynamics of changes in loading during gait was quite diverse; when analyzing courses of changes on sensors, 4 gait patterns were observed. CONCLUSIONS Use of the ITE System creates a new possibility for dynamic foot evaluation, drawing from pedobarography and methods of gait analysis. The proposed data analysis algorithm is simple and can be applied in all cases. Normally, 30% of the sum of all pressures during stance phase falls on the rearfoot; 39% falls on forefoot.