Ultrananocrystalline diamond thin films for MEMS and moving mechanical assembly devices

MEMS devices are currently fabricated primarily in silicon because of the available surface machining technology. A major problem with the Si-based MEMS technology is that Si has poor mechanical and tribological properties [J.J. Sniegowski, in: B. Bushan (Ed.), Tribology Issues and Opportunities in MEMS, Kluwer Academic Publisher, The Netherlands, 1998, p. 325; A.P. Lee, A.P. Pisano, M.G. Lim, Mater. Res. Soc. Symp. Proc. 276 (1992) 67.], and practical MEMS devices are currently limited primarily to applications involving only bending and flexural motion, such as cantilever accelerometers and vibration sensors. However, because of the poor flexural strength and fracture toughness of Si, and the tendency of Si to adhere to hydrophilic surfaces, even these simple devices have limited dynamic range. Future MEMS applications that involve significant rolling or sliding contact will require the use of new materials with significantly improved mechanical and tribological properties, and the ability to perform well in harsh environments, Diamond is a superhard material of high mechanical strength, exceptional chemical inertness, and outstanding thermal stability. The brittle fracture strength is 23 times that of Si, and the projected wear life of diamond MEMS moving mechanical assemblies (MEMS MMAs) is 10 000 times greater than that of Si MMAs. However, as the hardest known material, diamond is notoriously difficult to fabricate. Conventional CVD thin film deposition methods offer an approach to the fabrication of ultra-small diamond structures, but the films have large grain size, high internal stress, poor intergranular adhesion, and very rough surfaces, and are consequently ill-suited for MEMS MMA applications. Diamond-like films are also being investigated for application to MEMS devices. However, they involve mainly physical vapor deposition methods that are not suitable for good conformal deposition on high aspect ratio features, and generally they do not exhibit the outstanding mechanical properties of diamond. We demonstrate here the application of a novel microwave plasma technique using a unique C₆₀/Ar or CH₄/Ar chemistry that produces phase-pure ultrananocrystalline diamond (UNCD) coatings with morphological and mechanical properties that are ideally suited for MEMS applications in general, and MMA use in particular. We have developed lithographic techniques for the fabrication of UNCD–MEMS components, including cantilevers and multi-level devices, acting as precursors to microbearings and gears, making UNCD a promising material for the development of high performance MEMS devices.     

Adhesion of Neurons and Glial Cells with Nanocolumnar TiN Films for Brain-Machine Interfaces

Coupling of cells to biomaterials is a prerequisite for most biomedical applications; e.g., neuroelectrodes can only stimulate brain tissue in vivo if the electric signal is transferred to neurons attached to the electrodes’ surface. Besides, cell survival in vitro also depends on the interaction of cells with the underlying substrate materials; in vitro assays such as multielectrode arrays determine cellular behavior by electrical coupling to the adherent cells. In our study, we investigated the interaction of neurons and glial cells with different electrode materials such as TiN and nanocolumnar TiN surfaces in contrast to gold and ITO substrates. Employing single-cell force spectroscopy, we quantified short-term interaction forces between neuron-like cells (SH-SY5Y cells) and glial cells (U-87 MG cells) for the different materials and contact times. Additionally, results were compared to the spreading dynamics of cells for different culture times as a function of the underlying substrate. The adhesion behavior of glial cells was almost independent of the biomaterial and the maximum growth areas were already seen after one day; however, adhesion dynamics of neurons relied on culture material and time. Neurons spread much better on TiN and nanocolumnar TiN and also formed more neurites after three days in culture. Our designed nanocolumnar TiN offers the possibility for building miniaturized microelectrode arrays for impedance spectroscopy without losing detection sensitivity due to a lowered self-impedance of the electrode. Hence, our results show that this biomaterial promotes adhesion and spreading of neurons and glial cells, which are important for many biomedical applications in vitro and in vivo.     

Synthetic Hydrogels as Substrata for Cell Adhesion Studies

Synthetic polymer hydrogels have many proven and potential biomedical applications as wound coverings, drug delivery systems, surgical prostheses, contact lenses and in extracorporeal circuitry. Their success in long-term contact with biological fluids and cellular tissue depends upon their interfacial properties in such environments, and in turn, upon their physical and chemical nature. One approach to defining requirements for interfacial events at polymer surfaces in vivo is to investigate cell adhesion behaviour on these materials in culture, and to correlate this behaviour with polymer structure and theories of in vivo biocompatibility. At the same time, polymer hydrogels provide the opportunity to extend existing cell culture systems for the study of environmental cues for cell behaviour under normal and pathological circumstances.     

Synthesis of polymer materials for use as cell culture substrates

Up to today, several techniques have been used to maintain cells in culture for studying many aspects of cell biology and physiology. More often, cell culture is dependent on proper anchorage of cells to the growth surface. Thus, poly-l-lysine, fibronectin or laminin are the most commonly used substrates. In this study, electrosynthesized biocompatible polymer films are proposed as an alternative to these standard substrates. The electrosynthesized polymers tested were polyethylenimine, polypropylenimine and polypyrrole. Then, the adhesion, proliferation and morphology of rat neuronal cell lines were investigated on these polymer substrates in an attempt to develop new and efficient polymer materials for cell culture. During their growth on the polymers, the evolution of the cell morphology was monitored using both confocal microscopy and immunohistochemistry, leading to the conclusion of a normal development. An estimation of the adhesion and proliferation rates of rat neuronal cell cultures indicated that polyethylenimine and polypropylenimine were the best substrates for culturing olfactory neuronal cells. A method to favour the differentiation of the neuronal cells was also developed since the final aim of this work is to develop a biosensor for odour detection using differentiated neuronal cells as transducers. Consequently, a biosensor was microfabricated using silicon technology. This microsystem allowed us to culture the cells on a silicon wafer and to position the cells on certain parts of the silicon wafer.     

Surface Modification of Polydimethylsiloxane via Combined Aminolysis and Alcoholysis Generating Cell Adhesive and Antifouling Properties

Polydimethylsiloxane (PDMS) is an elastomeric polymer frequently used as implant material, for flexible tubing and in microfluidic devices. The pronounced hydrophobic surface of this unique material impedes many applications where a good wetting behavior is required. Consequentially, various ways of surface modifications have been used to introduce new properties. Plasma treatment is the most popular technique in this respect, but is not generally applicable, especially if hardly accessible surfaces are to be modified. A novel wet-chemistry-based modification scheme yielding an amino-functionalized PDMS surface using a combined alcoholysis/aminolysis reaction is presented. Biological applications are exemplified by the conjugation of the RGD peptide, or polyethylene glycol (PEG) and heparin, yielding surfaces with cell-adhesive or nonthrombogenic properties, respectively. The effect of subsequent conjugation with an adhesive peptide is tested in cell culture. Additionally, two antifouling surfaces generated by coupling heparin and polyethylene glycol respectively are shown to improve the materials resistance to platelet adhesion drastically while simultaneously preventing hydrophobic recovery of the PDMS surface. The findings provide a versatile means of surface functionalization of PDMS substrates and is suitable for many biomedical applications.     

Biocompatibility and antibacterial performance of titanium by surface treatment

Titanium (Ti) and its alloys are used extensively in implants due to their excellent biocompatibility and mechanical properties. However, Ti-based implant materials have specific complications associated with their applications, such as the loosening of implanted host interface owing to unsatisfactory cell adhesion and the susceptibility of the implants to bacterial infections. Hence, a surface that displays selective biointeractivity, i.e., enhancing beneficial host cell responses but inhibiting pathogenic microbial adhesion, would be highly desirable. This study aims to confer long-lasting antibacterial properties and good biocompatibility on Ti via the microarc oxidation technique. The biocompatibility of the Ti surface was evaluated by cytotoxicity test, and the bacteriostasis rate was evaluated by antibacterial efficacy. The results showed that the implant surface might be nontoxic to cell and its long-lasting antibacterial properties could be significantly improved. These results indicate that such microarc oxidation coatings are expected to have good potential in transcutaneous implant applications.     

Optimization of Cell Adhesion on Mg Based Implant Materials by Pre-Incubation under Cell Culture Conditions

Magnesium based implants could revolutionize applications where orthopedic implants such as nails, screws or bone plates are used because they are load bearing and degrade over time. This prevents a second surgery to remove conventional implants. To improve the biocompatibility we studied here if and for how long a pre-incubation of the material under cell culture conditions is favorable for cell attachment and proliferation. For two materials, Mg and Mg10Gd1Nd, we could show that 6 h pre-incubation are already enough to form a natural protective layer suitable for cell culture.     

Fabrication and Applications of Microfluidic Devices: A Review

Microfluidics is a relatively newly emerged field based on the combined principles of physics, chemistry, biology, fluid dynamics, microelectronics, and material science. Various materials can be processed into miniaturized chips containing channels and chambers in the microscale range. A diverse repertoire of methods can be chosen to manufacture such platforms of desired size, shape, and geometry. Whether they are used alone or in combination with other devices, microfluidic chips can be employed in nanoparticle preparation, drug encapsulation, delivery, and targeting, cell analysis, diagnosis, and cell culture. This paper presents microfluidic technology in terms of the available platform materials and fabrication techniques, also focusing on the biomedical applications of these remarkable devices.     

Nanostructured porous silicon micropatterns as a tool for substrate-conditioned cell research

ABSTRACT: The localized irradiation of Si allows a precise patterning at the microscale of nanostructured materials such as porous silicon (PS). PS patterns with precisely defined geometries can be fabricated by using ion stopping masks. The nanoscale textured micro patterns were used to explore their influence as microenviroments for human mesenchymal stem cells (hMSCs). In fact, the change of photoluminescence emission from PS upon aging in physiological solution suggests the intense formation of silanol surface groups, which may play a relevant role in ulterior cell adhesion. The experimental results show that hMSCs are sensitive to the surface micropatterns. In this regard, preliminary -catenin labeling studies reveal the formation of cell-cell interaction structures, while microtubule orientation is strongly influenced by the selective adhesion conditions. Relevantly, Ki67 assays support a proliferative state of hMSCs on such nanostructured micropatterns comparable to that of standard cell culture platforms, which reinforces the candidature of porous silicon micropatterns to become a conditioning structure for in-vitro culture of hMSCs.     

Morphological Factors Involved in Adhesion of Acid-Cleaned Diatom Silica

Purpose

Diatoms, unicellular microalgae with silica cell walls, have strong adhesive properties, which are dominated by chemical interactions between secreted organic material and the substrate. Possible technological applications of diatoms are likely to involve the adhesion of silica particles, or derivatives, which have been cleaned of organic material. Because the morphologies of diatom cell walls are far more complex than defined model structures, the relationship between morphology and adhesion for such materials is unknown.

Methods

In this paper we develop a new approach to monitor the adhesion of acid-cleaned diatom silica using parallel-plate flow chambers. We have evaluated factors such as settling time, extent of dryness, and substrate properties, and compared diatom species with silica features differing in size, shape, and percentage of surface contact area.

Results

Results indicated better adhesion of particles with higher surface contact area below a threshold of overall size, and a contribution by the number of possible contact surfaces to initial adhesion. We identified two stages in adhesion response to increasing shear stress. In the first stage, at low shear stress, species-dependent morphology played a major role in determining the strength of adhesion. After loosely adhered particles were removed at low shear, a second stage of persistent adhesion emerged at higher shear stresses. In the second stage, variations in morphology had a much smaller effect on adhesion.

Conclusions

These results identify conditions and fundamental morphological features for adhesion that can be utilized in future technological applications of silica particles with complex shapes.     

The adhesive properties of chlorinated ultra-high molecular weight polyethylene

Ultra-high molecular weight polyethylene (UHMW-PE) is well known for its abrasion and chemical resistance. Recently we developed a new application for UHMW-PE as a liner in elastomeric hoses. It was found that the adhesion between UHMW-PE and elastomers such as ethylene-propylene-diene monomer (EPDM) and styrene-butadiene rubber (SBR) is sufficient for practical applications, but the adhesion to nitrile rubber (NBR) is poor. In order to improve the adhesion between NBR and the UHMW-PE liner, (nascent) powder chlorinated polyethylenes were used as interlayers between UHMW-PE and NBR. These powder chlorinated polyethylenes are polymers with a dual nature and are composed of highly chlorinated polyethylene segments compatible with NBR and polyethylene segments compatible with UHMW-PE. In order to achieve sufficient adhesion, the chlorine content of the chlorinated blocks should be at least 15 wt%. If these powder chlorinated UHMW-PEs have a chlorine content of 15 wt% in the chlorinated blocks, dilution with polyethylene hardly affects the adhesive properties, which is an advantage in the practical use of these materials as interlayers.     

Residual stress and adhesion experiment on the capacitive MEMS power sensor based on GaAs MMIC process

This article investigates the failure due to collapse of the MEMS beams in capacitive MEMS power sensor based on GaAs MMIC process. Generally, the residual stress and adhesion are the main causes of the collapse of the MEMS beams. So, this article investigates the residual stress of the MEMS beams with an improved rotating technique. In addition, a resonant method has been used to investigate the adhesion of the MEMS beams. The measurement result shows that the buckling due to the residual stress is very small. Also, the finite analysis results show the rotating angle θ should be less than 0.12°. Thus, the collapse of the MEMS beams is mainly caused by adhesion.     

Chemico-physical characterization of hybrid composites based on hydroxyethyl methacrylate and nanosilica

Novel hydrogels are often designed to mimic the transport and mechanical properties of natural soft tissue such as ligaments, tendons, intervertebral discs, or to be exploited as scaffold for tissue engineering. Recently, novel hydrogels based on 2-hydroxylethyl methacrylate and fumed silica nanoparticles (5–25% w/w) were synthesized by our group and demonstrated to improve cell adhesion and proliferation. The chemico-physical properties and mechanical behaviour of these new polymers have been studied and are presented in this article. The swelling equilibria in water and water solutions were evaluated in relation to ionic strength and pH. The sorption kinetic estimated through gravimetric analysis showed a diffusive transport behaviour of the hybrid composite materials as of early stages of the process. The elastic modulus was evaluated by Dynamic-Mechanical Analyses and proved to increase with the filler content reaching values compatible with the mechanical characteristics of natural material. This result supports the possibility of future applications of the novel hybrid composite in several fields, in dentistry as dental filling or in systems for the controlled released of drugs.     

An Assessment of Bulk Metallic Glasses for Microelectromechanical System Devices

Metallic glasses were born purely of academic interest and earlier commercial attempts were limited due to the low thickness of the samples. However, with the successful fabrication of bigger samples using multicomponent system, there has been renewed interest in the commercial applicability of bulk metallic glasses (BMGs) as they offer promising mechanical, tribological and other properties which make the commercialization aspect lucrative. Through this study, an attempt has been made to assess the applicability of bulk metallic glasses as a material for Microelectromechanical System (MEMS) applications. Ranking and comparison, with the current MEMS material set, has been made using multiple criteria decision making (MCDM) approach. Performance index (PIs) was calculated using Ashby approach and Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) was used to rank the materials on a collective basis. Additional features have been investigated to assess their suitability as a MEMS material. It was observed that BMGs offer promising prospects as a suitable MEMS material based on their overall performance when compared to the current material set being used for MEMS applications.     

Photochemical surface modification of polymers for improved adhesion

A method using photoactivatable reagents is described to modify organic polymer surfaces without changing the bulk properties of the material. The reagents contain a benzophenone or other photoactivatable group which, when exposed to light of appropriate wavelength, generates highly reactive intermediates that covalently bond with nearly any organic material. Some general surface characteristics that can be achieved by this approach, on a wide range of materials, are good wettability, good lubricity, passivation, and priming for either adhesion or immobilization of other molecules. This technology provides tremendous flexibility for tailoring surface characteristics for a broad range of applications. Some materials that have desirable bulk properties for specific applications, however, have surface characteristics that make bonding them to other materials difficult. By photocoupling water-soluble polymers onto the surfaces of such materials, the surface properties can be modified to achieve greatly increased bond strengths with conventional adhesives. For example, using such techniques, the strength of bonding two pieces of high-density polyethylene to each other using a cyanoacrylate adhesive was increased by about 17-fold. Similarly, in preliminary experiments, the bond strengths of silicone rubber to polyvinyl chloride, using cyanoacrylate adhesive, were increased by more than 18-fold. This technology offers great potential for surface modification for improved adhesion.     

Ionomer‐based polyurethanes: a comparative study of properties and applications

Polyurethanes cover a large range of materials exhibiting various physical and mechanical properties making them useful in different applications such as elastomers or biomaterials, for instance. The introduction of ionic groups in the polyurethane backbone opens the way to new applications where the ionic groups can act as physical crosslinkers that greatly modify the final mechanical and thermal properties of the materials. Furthermore, the hydrophilicity of the chains can be enhanced by the presence of the ionic species, and so the materials can be processed as conventional dispersions even in a polar solvent such as water. As a consequence the applications are numerous; the main commercial outlets are focused on coatings and textiles industries where they can be used as waterproof coatings or substitutes for leather. But these materials can also be used in high‐tech industries for shape memory materials, biomedical devices and biocompatible materials. This review summarizes the latest developments of this class of promising materials and provides the reader with the potentialities of these polymers in various areas.     

Biological and mechanical enhancement of zirconium dioxide for medical applications

Extensive research in global biomedical industry has been driven rapidly due to problems faced in bone implants such as loosening of implants in knee and hip prosthesis as well as short service life of orthopaedic implants. Advances in biomedical engineering have resulted in formation of various materials utilized for orthopaedic transplants and artificial implants. Among the various available materials zirconium dioxide is observed as potential material for biomedical application due to its superior biocompatibility, good compression resistance (2000 MPa), good viability of cell culture, good opacity, and radiopacifying capacity showcasing it's diverse applications in bone and tissue regeneration, orthopaedic implants as well as bone resorption. Bone tissue regenerative modifications is accompanied with coating of zirconium dioxide on metal alloys or 316 L SS substrate, composite formation with silica carbide or organic acids (usnic acid), surface propargylation achieved using chemical treatment of propargyl bromide, electrochemical treatment of zirconium dioxide to evaluate corrosion resistance, etc. Zirconium dioxide is also recorded for exhibiting enhanced mechanical properties as well as biocompatibility in hip arthroplasty as well as bone implants; it also serves application in bone cement to provide adhesion between the biomedical implants. The review paper majorly focuses on effective utilization of zirconium dioxide with various additive materials and functionalization techniques used for enhancement of properties, enabling the application of material in orthopaedic implants as well as bone tissue applications. The mechanical and biological performance analysis of various orthopaedic implants containing zirconium dioxide has been elaborately discussed along with possible measures implemented to enlarge the life of biomedical implant.     

Recent Advances in Metal-Based Magnetic Composites as High-Efficiency Candidates for Ultrasound-Assisted Effects in Cancer Therapy

Metal-based magnetic materials have been used in different fields due to their particular physical or chemical properties. The original magnetic properties can be influenced by the composition of constituent metals. As utilized in different application fields, such as imaging monitoring, thermal treatment, and combined integration in cancer therapies, fabricated metal-based magnetic materials can be doped with target metal elements in research. Furthermore, there is one possible new trend in human activities and basic cancer treatment. As has appeared in characterizations such as magnetic resonance, catalytic performance, thermal efficiency, etc., structural information about the real morphology, size distribution, and composition play important roles in its further applications. In cancer studies, metal-based magnetic materials are considered one appropriate material because of their ability to penetrate biological tissues, interact with cellular components, and induce noxious effects. The disruptions of cytoskeletons, membranes, and the generation of reactive oxygen species (ROS) further influence the efficiency of metal-based magnetic materials in related applications. While combining with cancer cells, these magnetic materials are not only applied in imaging monitoring focus areas but also could give the exact area information in the cure process while integrating ultrasound treatment. Here, we provide an overview of metal-based magnetic materials of various types and then their real applications in the magnetic resonance imaging (MRI) field and cancer cell treatments. We will demonstrate advancements in using ultrasound fields co-worked with MRI or ROS approaches. Besides iron oxides, there is a super-family of heterogeneous magnetic materials used as magnetic agents, imaging materials, catalytic candidates in cell signaling and tissue imaging, and the expression of cancer cells and their high sensitivity to chemical, thermal, and mechanical stimuli. On the other hand, the interactions between magnetic candidates and cancer tissues may be used in drug delivery systems. The materials’ surface structure characteristics are introduced as drug loading substrates as much as possible. We emphasize that further research is required to fully characterize the mechanisms of underlying ultrasounds induced together, and their appropriate relevance for materials toxicology and biomedical applications.     

Preparation of Single,Heteromorphic Microspheres,and Their Progress for Medical Applications

Microspheres applied in medical applications experience explosive development in recent years, such as drug release, cell culture, and bone tissue engineering, etc. However, there are still some bottlenecks both in economy and technology lay that cannot be ignored. For instance, microsphere technology has not been used in cell culture widely because of its uneconomical cost; as the core of drug-loaded microsphere, targeted microsphere technology is still not mature enough. Besides, the common microsphere fabrication methods: microfluidic or emulsion technology is difficult to guarantee high biocompatibility of microsphere due to utilization of photoinitiator, crosslinking agent, surfactant, and other substances. Therefore, gas-shearing technology has been proposed to solve these above shortcomings successfully. This paper focuses more on heteromorphic microspheres rather than on single microspheres which begins with a minute introduction of microsphere preparation methods: microfluidic, coaxial electrospray, emulsion, and gas-shearing technology. Then its medical applications: drug release, cell culture, bone tissue engineering, and hemostasis are discussed in detail. The disadvantages of fabrication methods and bottlenecks for medical applications at present are also stated. At the end, perspectives of microsphere development are put forward.     

Fabrication of crescent-shaped ceramic microparticles based on single emulsion microfluidics

Ceramic microparticles have great potentials in various fields such as materials engineering, biotechnology, microelectromechanical systems, etc. Morphology of the microparticle performs an important role on their application. To date, it remains difficult to find an effective and controllable way for fabricating nonspherical ceramic microparticles with 3D features. This work demonstrates a method that combines UV light lithography and single emulsion opaque-droplet-templated microfluidic molding to prepare the crescent-shaped ceramic microparticles. By tailoring the intensity of UV light and flow rate of fluid, the shapes of microparticles are accordingly tuned. Therefore, varieties of crescent-shaped microparticles and their variations have been fabricated. After sintering, the crescent-shaped alumina ceramic microparticles were obtained. Benefitting from the light absorption and scattering behavior of most ceramic nanoparticles, this system can serve as a general platform to produce crescent-shaped microparticles made from different materials, and hold great potentials for applications in microrobotics, structural materials in MEMS, and biotechnology.