Surface Modification of Additively Manufactured Nitinol by Wet Chemical Etching

Three-dimensional printed nitinol (NiTi) alloys have broad prospects for application in medicine due to their unique mechanical properties (shape memory effect and superplasticity) and the possibilities of additive technologies. However, in addition to mechanical properties, specific physicochemical characteristics of the surface are necessary for successful medical applications. In this work, a comparative study of additively manufactured (AM) NiTi samples etched in H2SO4/H2O2, HCl/H2SO4, and NH4OH/H2O2 mixtures was performed. The morphology, topography, wettability, free surface energy, and chemical composition of the surface were studied in detail. It was found that etching in H2SO4/H2O2 practically does not change the surface morphology, while HCl/H2SO4 treatment leads to the formation of a developed morphology and topography. In addition, exposure of nitinol to H2SO4/H2O2 and HCl/H2SO4 contaminated its surface with sulfur and made the surface wettability unstable in air. Etching in NH4OH/H2O2 results in surface cracking and formation of flat plates (10–20 microns) due to the dissolution of titanium, but clearly increases the hydrophilicity of the surface (values of water contact angles are 32–58°). The etch duration (30 min or 120 min) significantly affects the morphology, topography, wettability and free surface energy for the HCl/H2SO4 and NH4OH/H2O2 etched samples, but has almost no effect on surface composition.

The wettability of electron spun membranes by synovial fluid

Aseptic loosening due to periprosthetic osteolysis has been accepted as one of the leading causes of revision procedures in patients with previous joint arthroplasty. Recently, several strategies for suppression of osteolysis were proposed, mostly based on biological treatment such as mitigation of chronic inflammatory reactions. However, these biological treatments do not stop the debris migration but only reduce the inflammatory reaction. To address this shortcoming, we propose the concept of ultrahigh molecular weighted polyethylene particles filtration storage by electrospun membranes. Firstly, the surface tension of synovial fluid (SF) is obtained by use of a pendant droplet. Secondly, the contact angle of the electrospun membranes wetted by two different liquids is measured to obtain the free surface energy using of the Owens–Wendt model. Additionally, the wettability of electrospun membranes by SF as a function of technology parameters is studied.

Study of the effect of fillers PZT on the structure and physical-mechanical properties of epoxy glue DM-5-65

В работе исследуются структура и физико-механические характеристики наполненного эпоксидного клея ДМ-5-65, применяемого для сборки составных электроакустических преобразователей гидроакустических систем. Особенностью исследования служит использование в качестве дисперсных неорганических наполнителей порошков пьезокерамических материалов системы цирконата-титаната свинца (ЦТС): ЦТСтБС-2 и ЦТБС-3. Приведены результаты морфологического исследования, определены краевой угол смачивания и свободная поверхностная энергия отвержденного клея ДМ-5-65, содержащего указанные наполнители. Определены плотность, деформационно-прочностные и термомеханические свойства отвержденного клея ДМ-5-65. Механическими испытаниями на отрыв установлена прочность соединения эпоксидного клея ДМ-5-65 с металлом. Показано, что химическая природа наполнителей определяет характер их распределения в связующем клея. Установлен преимущественно полярный характер взаимодействий клея ДМ-5-65, содержащего в качестве наполнителя материал ЦТСтБС-2, в отличие от дисперсионной природы взаимодействий клея ДМ-5-65 с наполнителем ЦТБС-3. This paper studies the structure and physical-mechanical properties of filled epoxy glue DM-5-65 used to build a composite electro-acoustic transducers hydroacoustic systems. A special feature of the study is the use of powders of piezoceramic materials of the lead zirconate-titanate (PZT) system as dispersed inorganic fillers: PZTSrB-2 and PZTB-3. The results of morphological research are presented, the wetting angle and free surface energy of the cured DM-5-65 glue containing the specified fillers are determined. The density, strain-strength and thermomechanical properties of the cured DM-5-65 glue were determined. Mechanical separation tests established the strength of the connection of the DM-5-65 epoxy glue with metal. It is shown that the chemical nature of fillers determines the nature of their distribution in the glue binder. The predominantly polar nature of the interactions of DM-5-65 glue containing PZTSrB-2 material as a filler is established, in contrast to the dispersion nature of the interactions of DM-5-65 glue with PZTB-3 filler.

Effectiveness Evaluation Criteria of Using Fine Powders of Secondary Concrete as a Component of Composite Binder

The paper considers the possibility of using energy criteria (surface activity, free surface energy) to quantify the efficiency of a highly dispersed system consisting of fine particles of secondary concrete as a component of composite binder of the hydration type of hardening. Using the G.A. Zisman method, the value of the critical surface tension was determined for secondary concrete fractions with different degrees of dispersion, which gives an idea of the free surface energy of a surface area unit. Based on the experimental data for determining the specific surface area and critical surface tension, the free surface energy and surface activity of the studied concrete powder were calculated, which can serve as criteria for quantitative energy characteristics of raw materials for the production of composite binders. Calorimetric studies related to measurements of the thermal effects of the hydration reaction of highly dispersed samples of secondary concrete have shown that this process is exothermic, the enthalpy of hydration of which is comparable to a similar parameter for cement. It was experimentally shown that fine powders of secondary concrete are effective as components of a composite binder, but they need to be pre-activated to optimal parameters, one of which is surface activity. In addition, the symbasis of changes in surface activity, the specific heat of the hydration reaction of highly dispersed concrete fractions and the compressive strength of fine-grained concrete samples made by using a composite binder containing a highly dispersed fraction of secondary concrete was established.

Aspects of determining the surface activity of dispersed systems based on mineral powders

Samples of mechanically activated quartz sand powder were obtained by grinding on a planetary ball mill to different specific surface values (1200-3000 m2/kg). For these dispersed systems, the surface activity criterion (kS) was calculated as a value equal to the ratio of the free surface energy of the system to its total potential value (specific mass energy of atomization). It is established that the value of this criterion does not depend linearly on the time parameters of mechanical dispersion of the initial samples. The kS parameter is recommended for evaluating the effectiveness of the process of mechanical activation of rocks.

Composite materials based on polyacrylamide and gelatin reinforced with polypropylene microfiber

The conditions for preparation of a composite hydrogel based on polyacrylamide and gelatin, which is reinforced with polypropylene microfiber, were determined to increase its strength. The conditions of modification of polypropylene microfiber were established under which its surface is hydrophilized, which was confirmed by a significant increase in the water retention of microfiber by 11.0–15.2 times. Under the same conditions, an increase in the values of the hydrogen component of free surface energy on planar samples of polypropylene was observed (from 2.81.0 mN m–1 to 29.81.0 mN m–1). Optimal conditions (minimum limits of component concentrations, temperature range, and pH of a medium) were determined, under which a hydrogel based on polyacrylamide and gelatin with satisfactory physicochemical and mechanical properties can be formed. A composite hydrogel, based on polyacrylamide and gelatin reinforced with modified polypropylene microfiber, was prepared. It was found that the introduction of modified microfiber increases the limits of the beginning of destruction from 20–30 to 130 kPa. The results of the investigation of the drug release from the hydrogel indicated that the obtained composites can be used as matrices to create a hydrogel therapeutic bandages with the function of prolonged drug delivery.

Influence of the β− Radiation/Cold Atmospheric-Pressure Plasma Surface Modification on the Adhesive Bonding of Polyolefins

The goal of this research was to examine the effect of two surface modification methods, i.e., radiation cross-linking and plasma treatment, on the adhesive properties and the final quality of adhesive bonds of polypropylene (PP), which was chosen as the representative of the polyolefin group. Polymer cross-linking was induced by beta (accelerated electrons—β−) radiation in the following dosages: 33, 66, and 99 kGy. In order to determine the usability of β− radiation for these applications (improving the adhesive properties and adhesiveness of surface layers), the obtained results were compared with values measured on surfaces treated by cold atmospheric-pressure plasma with outputs 2.4, 4, and 8 W. The effects of both methods were compared by several parameters, namely wetting contact angles, free surface energy, and overall strength of adhesive bonds. Furthermore, Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM) were conducted. According to our findings the following conclusion was reached; both tested surface modification methods significantly altered the properties of the specimen’s surface layer, which led to improved wetting, free surface energy, and bond adhesion. Following the β− radiation, the free surface energy of PP rose by 80%, while the strength of the bond grew in some cases by 290% in comparison with the non-treated surface. These results show that when compared with cold plasma treatment the beta radiation appears to be an effective tool capable of improving the adhesive properties and adhesiveness of PP surface layers.

Influence of curing technology on morphology and physical characteristics of epoxy glue DM-5-65

Проведено комплексное исследование воздействия энергетических полей различной физической природы – электротермического (ЭТ), ультразвукового (УЗ), сверхвысокочастотного (СВЧ) и комбинации этих полей на морфологию, удельную плотность и свободную поверхностную энергию промышленного эпоксидного клея ДМ-5-65, содержащего в качестве одного из неорганических наполнителей титанат бария (BaTiO3). В соответствии с технологией изготовления составных электроакустических преобразователей гидроакустических систем клей наносился на поверхность пьезокерамики, металлизированную серебром высокотемпературным методом «вжигания». Экспериментально установлено существенное варьирование характера расположения наполнителя BaTiO3 в матрице связующего, плотности химических связей и адгезии образующегося соединения клей – металл при изменении технологии отверждения клея. Анализ полученных результатов свидетельствует о возможности регулирования в широких пределах плотности и однородности клея, а также смачиваемости клеем поверхности твердого тела. A comprehensive study of the effect of energy fields of various physical nature – electrothermal (ET), ultrasonic (US), microwave and a combination of these fields on the morphology, specific density and free surface energy of industrial epoxy glue DM-5-65, containing barium titanate (BaTiO3) as one of the non-organic fillers. In accordance with the technology of manufacturing composite electroacoustic transducers of hydroacoustic systems, glue was applied to the surface of piezoceramics, metallized with silver by the high-temperature "burning" method. Experimentally, a significant variation in the nature of the location of the BaTiO3 filler in the binder matrix, the density of chemical bonds, and the adhesion of the resulting glue-metal compound when the glue curing technology changes. The analysis of the obtained results shows that it is possible to control the density and uniformity of the glue, as well as the wettability of the solid surface by the glue, within a wide range.

A study on the bacterial adhesion of Streptococcus mutans in various dental ceramics: In vitro study

Streptococcus mutans (S. mutans) has been identified as a major etiologic agent of human dental caries and forms a significant proportion of oral streptococci in carious lesions. This study investigates the correlation of surface properties (effect of contact angle [CA] and free surface energy) on three restorative materials (zirconia, nickel–chromium–molybdenum alloy and composites) used in dental prosthetics with bacterial adhesion to S. mutans. Ten samples of each material (zirconia, nickel–chromium–molybdenum alloy and composites) of 8 mm diameter and 2.5 mm thickness were used. Aqueous CA measurements, free surface energy and bacterial adhesion to the sample surfaces were performed. Bacterial adhesion is determined by planting samples in the blood agar cultures and using an electron microscope (scanning electron microscopy [SEM]). The highest values of bacterial adhesion are found in composites, followed by the metal alloy, while the lowest values are observed in zirconia. Measurements show that zirconia has 17 bacteria; Ni–Cr–Mo alloy has 65, while the composite has 80 bacteria. The composites showed the highest degree of bacterial adhesion, compared to the other investigated materials, which correlates with the free surface energy of the samples (24.31 mJ/m2 for zirconia, 31.78 mJ/m2 for Ni–Cr–Mo alloy and 48.82 mJ/m2 for the composite).