PDMS Microfabrication and Design for Microfluidics and Sustainable Energy Application: Review

The polydimethylsiloxane (PDMS) is popular for wide application in various fields of microfluidics, microneedles, biology, medicine, chemistry, optics, electronics, architecture, and emerging sustainable energy due to the intrinsic non-toxic, transparent, flexible, stretchable, biocompatible, hydrophobic, insulating, and negative triboelectric properties that meet different requirements. For example, the flexibility, biocompatibility, non-toxicity, good stability, and high transparency make PDMS a good candidate for the material selection of microfluidics, microneedles, biomedical, and chemistry microchips as well as for optical examination and wearable electronics. However, the hydrophobic surface and post-surface-treatment hydrophobic recovery impede the development of self-driven capillary microchips. How to develop a long-term hydrophilicity treatment for PDMS is crucial for capillary-driven microfluidics-based application. The dual-tone PDMS-to-PDMS casting for concave-and-convex microstructure without stiction is important for simplifying the process integration. The emerging triboelectric nanogenerator (TENG) uses the transparent flexible PDMS as the high negative triboelectric material to make friction with metals or other positive-triboelectric material for harvesting sustainably mechanical energy. The morphology of PDMS is related to TENG performance. This review will address the above issues in terms of PDMS microfabrication and design for the efficient micromixer, microreactor, capillary pump, microneedles, and TENG for more practical applications in the future.

Configurable 3D Printed Microfluidic Multiport Valves with Axial Compression

In the last decade, the fabrication of microfluidic chips was revolutionized by 3D printing. It is not only used for rapid prototyping of molds, but also for manufacturing of complex chips and even integrated active parts like pumps and valves, which are essential for many microfluidic applications. The manufacturing of multiport injection valves is of special interest for analytical microfluidic systems, as they can reduce the injection to detection dead volume and thus enhance the resolution and decrease the detection limit. Designs reported so far use radial compression of rotor and stator. However, commercially available nonprinted valves usually feature axial compression, as this allows for adjustable compression and the possibility to integrate additional sealing elements. In this paper, we transfer the axial approach to 3D-printed valves and compare two different printing techniques, as well as six different sealing configurations. The tightness of the system is evaluated with optical examination, weighing, and flow measurements. The developed system shows similar performance to commercial or other 3D-printed valves with no measurable leakage for the static case and leakages below 0.5% in the dynamic case, can be turned automatically with a stepper motor, is easy to scale up, and is transferable to other printing methods and materials without design changes.

The Optical Coherence Tomography and Raman Spectroscopy for Sensing of the Bone Demineralization Process

The presented research was intended to seek new optical methods to investigate the demineralization process of bones. Optical examination of the bone condition could facilitate clinical trials and improve the safety of patients. The authors used a set of complementary methods: polarization-sensitive optical coherence tomography (PS-OCT) and Raman spectroscopy. Chicken bone samples were used in this research. To stimulate in laboratory conditions the process of demineralization and gradual removal of the hydroxyapatite, the test samples of bones were placed into 10% acetic acid. Measurements were carried out in two series. The first one took two weeks with data acquired every day. In the second series, the measurements were made during one day at an hourly interval (after 1, 2, 3, 5, 7, 10, and 24 h). The relation between the content of hydroxyapatite and images recorded using OCT was analyzed and discussed. Moreover, the polarization properties of the bones, including retardation angles of the bones, were evaluated. Raman measurement confirmed the disappearance of the hydroxyapatite and the speed of this process. This work presents the results of the preliminary study on the possibility of measuring changes in bone mineralization by means of the proposed methods and confirms their potential for practical use in the future.

The Optical Coherence Tomography and Raman Spectroscopy for Sensing of the Bone Demineralization Process

Aim of the presented research was to develop an optical sensing system to investigate the demineralization process of the bones. Optical measurement techniques are widely used and increasingly adapted in biological and biomedical applications due to their non-destructive nature and safety. Optical examination of the bone condition could facilitate clinical trials and improve the safety of patients. The authors used a set of complementary methods: polarization-sensitive optical coherence tomography (PS-OCT) and Raman spectroscopy. To stimulate the process of demineralization and gradual removal of the hydroxyapatite, the test samples of chicken bones were placed into 10% acetic acid. Measurements were carried out in two series. The first one took two weeks with data acquired every day. In the second series, the measurements were made during one day at an hourly interval (after 1, 2, 3, 5, 7, 10, and 24 hours). Raman spectroscopy was used to evaluate the disappearance of the hydroxyapatite. The relation between the content of hydroxyapatite and images recorded using OCT was analyzed and discussed. Moreover, the polarization properties of the bones have been evaluated. Based on OCT images, the retardation angles of the bones have been calculated. This work presents a preliminary study on the mechanism of bone demineralization and confirms the potential of the applied optical methods.

Light optical and Ultrastructural Characteristics of the Maral Liver with Chronic Dicrocoeliasis

BACKGROUND: Dicrocoeliasis is caused by trematode Dicrocoelium lanceatum from the family Dicrocoeliidae, a parasite in the bile ducts of the liver of domestic and wild animals. Dicrocoeliasis mainly affects sheep, cattle, camels, zebu, deer, fallow deer, argali, less often – horses, donkeys, dogs, rabbits, hares and bears, as well as humans. Dicrocoeliasis of ruminants is widespread across the whole Kazakhstan. Invasive diseases represent a significant obstacle in the development of domestic maral breeding, among which trematodoses, and particularly dicrocoeliasis of maral play a major role. AIM: The aim of the research was to study the influence of dicrocoelia on the ultrastructural organization of the liver of maral. MATERIALS AND METHODS: For examination under electron microscope, biopsy pieces of liver tissue of maral were fixed in 2.5% solution of glutaraldehyde with post-fixation in 1% solution of osmium tetroxide, conducted according to a conventional method, and enclosed in epon. Semi-thin and ultra-thin sections were prepared on the ultra-microtome Leica. Semi-thin sections were stained with methylene blue, azure 2, and studied at a high-resolution light optical level. The ultra-thin sections were contrasted with uranyl acetate and lead citrate according Reynolds method and examined under electron microscope Libra 120 (C. Zeiss). RESULTS: The light optical examination of half-thin sections revealed that the morphological pattern of pathological changes in liver tissue was polymorphic, even within a single hepatic lobe. CONCLUSIONS: In the liver of maral infected with chronic dicrocoeliasis, dystrophic and destructive pathological changes developed in all the cellular structures of the hepatic lobules: In the form of plethora and vast enlargement of sinusoids, vacuolar and lipodegeneration of hepatocytes, destruction of the hepatic tissue with edema, hemorrhages, in the appearance of cells associated with inflammation, and the deposition of hematin crystals.

Дослідження ефективності електрохімічного полірування зразків змінного перерізу з різною шорсткістю зі сталі AISI 316L, виготовлених за технологією SLM

Additive manufacturing technology, also known as 3D printing, has become an increasing amount of popular lately, and the number of materials and methods that can be used is expanding. As manufacturing processes continue to improve and evolve, the demand for faster, less expensive manufacturing processes has enabled a range of Rapid Prototyping (RP) processes to be developed. Since production processes continue to evolve and grow, the demand for faster and less expensive production processes has allowed the development of a series of processes of rapid prototyping (RP). With additive manufacturing, virtually any geometry with variations in size and complexity can be produced with a high degree of accuracy. The typical microstructure of the metal after the completion of the construction process is the dispersed dendritic and cellular structures of the γ-phase within the melt baths of single tracks, because of the overlap of which a part is created layer by layer. The main problems of ensuring high-quality products using SLM technology are porosity, hot cracking, anisotropy, surface roughness, and ensuring the necessary microstructure of the synthesized material. Improvement of surface roughness, the brilliance of stainless steel surface elements after electrochemical polishing (EP) is one of the most important characteristics of the process. Samples were made using the SLM technology from austenitic steel powder AISI 316L with a controlled defect in the form of local overheating, because of which an orange variability is formed, which is formed during 3-D printing. The samples are inversely symmetrical, have an equilateral trapezoid shape with bases of 20 and 5 mm, a height of 10 mm, and a thickness of 5 mm. The main body of both samples was printed in the same modes at a power of 220 W, a speed of 1000 mm / s, and a track spacing of 0,14 mm. To form a controlled defect when printing the boundaries of the samples, the following modes were used: power 120 W, speed 1050 mm / s, and distance between tracks 0,02 mm. The samples were printed in an Alfa-280 3D printer manufactured by ALT Ukraine. Etching to reveal the microstructure of the samples was conducted using an HCl + HNO3 solution. Electropolishing was conducted in a solution of orthophosphoric acid (H3PO4) with glycerol (C3H8O3) at a current density of 3 A / cm2. Metallographic studies have shown that the configuration of the tracks in the area of increasing the cross-section of the samples is more uniform. Based on this study, schemes for distributing zones with varying degrees of track equiaxiality and structure uniformity were constructed. A more intense interaction of the reagent with the microstructure near the surface with greater roughness was found. The electropolishing of isosceles trapezoids occurred in three stages: 1) visual - optical examination with fixation, control of roughness, weight, and geometry before starting the process; 2) control of roughness and geometry after 3 min. process; 3) visual - optical examination with fixation, control of roughness, weight, and geometry after 6 min electropolishing. From the analysis of the obtained roughness data and the real volt-ampere curve, it was found that zone 2 with the largest area had an insignificant change in roughness, zone 1 and zone 3 with a decrease in the area had a more significant loss on average by 33%. Controlling the weight before and after the test showed that the samples lost approximately the same weight of about 1,5%. Based on the ratio of the results obtained, it was found that when a fixed current strength and constant power are applied, electropolishing is not effective for active uniform anodization of the surface of a simple figure with a change in the area in the section. It was found that electropolishing most intensively occurs in an area with a smaller cross-sectional area.

Study of Biofilm Growth on Slippery Liquid-Infused Porous Surfaces Made from Fluoropor

<p>Avoiding undesired growth of biofilm is a fundamental challenge for all surfaces in long-term contact with aqueous media. Slippery liquid infused porous substrates (SLIPS) are a promising type of surface for preventing biofilm attachment. The effectiveness of SLIPS is based on the liquid/liquid interface between the medium and the surface, which prevents biofilm attachment. However, the long-term stability of these surfaces is problematic: under shear force, the oil layer is removed and the repellent effect is lost. Here, we study correlations between the porosity of the infused substrate and the ability to uphold the SLIPS oil-film under low shear and high shear force conditions. For this purpose, we manufacture substrates with different porosity and surface roughness in porous fluorinated polymer “Fluoropor”, which we have recently introduced. The porous layers were infused with fluorinated oil and their roughness was studied by white light interferometry. We find that SLIPS samples with smaller pores more effectively reduce Pseudomonas aeruginosa biofilm growth in a seven-day microfluidic flow cell experiment. With its easy production, simple adjustment of porosity and the possibility to attach the polymer to various technical substrates during polymerization, Fluoropor is a very promising material for producing stable SLIPS. When produced with small pores, Fluoropor is also transparent and enables the real-time observation of biofilm growth by optical examination. Thus, Fluoropor SLIPS provides an easy approach to reduce bacteria adhesion and bio fouling in many technical applications.</p>

Corrosion of titanium implants and connected prosthetic alloys using lactic acid immersion test

Background/purpose: Combination of dental titanium implants with other prosthetic metallic components may lead to metal ion release that increases the risk of adverse reactions in patients. The present study therefore aimed to determine in vitro metal ion dissolution from different alloy combinations. Materials and methods: Dental alloys were subjected to a lactic acid immersion test together with titanium implants and matched with controls. Between day 1 and 38, open direct current potentials (DCP) between the samples and the electrolyte were recorded and metal dissociation inside the electrolyte was assessed using ICP-MS. Results: Absolute DCPs of the different alloys increased significantly (p<0.001) from 100-150mV to 490-580 mV within the first two weeks of immersion, dropping to about 450mV later on largely independent of the material. Titanium showed highest dissociation rates (2.00-12.06µg/cm2 per day; p=0.0002); all other components demonstrated poor corrosive dissolution (<0.6µg/cm2 per day). After immersion of 38 days, titanium still yielded high dissociation (0.64-1.38µg/cm2 per day) for all test groups. Presence of fine gold inside the electrolyte significantly increased dissociation of titanium (p=0.027). Dissociation of iron indicated contamination from tool components used for implant production. Optical examination of non-precious metal surfaces showed no corrosive discoloration after 5 or 26 weeks of lactic acid immersion. Conclusion: Within the limitations of this study, there is no objection against the use of non-precious alloys for the fabrication of components and prostheses supported on titanium implants if gold is not present inside the same electrolyte.

Physico-Chemical and Optical Examination of Water Stored in Copper Vessels

Storage of water in copper vessels is traditionally followed in past and many reports have been published about the antibacterial growth in copper vessel. It is essential to determine the water purity for drinking purposes in daily life through low cost approach. In the present work an attempt has been made to investigate the effect of storage of different drinking water in copper vessel for two week. The corresponding values of pH and TDS meter for different waters were recorded and analyzed. The optical properties such as UV-Vis and Raman studies along with physio-chemical parameters like pH and TDS were analyzed for 3weeks against different water sources kept in copper vessel. The Raman spectra provide information for different water sources. Similarly the UV-Vis spectroscopy provide the peak variation for different waters, however the effect of days and copper concentration analysis are in investigation. The Results obtained in this study reveals that water stored in copper vessel reduces the TDS level of bore water Tirunelveli and maintains its pH at 8.0 after 2 weeks. The bore water in Krishnan kovil (virudhunagar district) shows no variation in TDS after 1 week, but in 2nd week there is sudden decrease in TDS from 1050 to 944ppm and pH level decreases to 8.3 showing alkaline nature. Throughout the experiment we have noticed that the colour of copper vessel changes in case of bore water. For variation in studies we have also studied the pH and TDS of Drinking water at Kalasalingam Academy of Research and Education. There is no change in colour of copper vessel and TDS and pH remains same up to one week, but in second week TDS increases to 100ppm while the pH remain constant at 7.4. These studies will help future researcher for designing of copper vessels and will help them to analyze the Physio-chemical studies of water. Moreover the chemical mechanism and reaction between copper vessel and leaching out of copper into water data base will be generated in future based on UV and Raman studies.