Silk proteins for biomedical applications: Bioengineering perspectives

Biomaterials of either natural or synthetic origin are used to fabricate implantable devices, as carriers for bioactive molecules or as substrates to facilitate tissue regeneration. For the design of medical devices it is fundamental to use materials characterized by non-immunogenicity, biocompatibility, slow and/or controllable biodegradability, non-toxicity, and structural integrity. The success of biomaterial-derived biodevices tends to be based on the biomimetic architecture of the materials. Recently, proteins from natural precursors that are essentially structural and functional polymers, have gained popularity as biomaterials. The silks produced by silkworms or spiders are of particular interest as versatile protein polymers. These form the basis for diverse biomedical applications that exploit their unique biochemical nature, biocompatibility and high mechanical strength. This review discusses and summarizes the latest advances in the engineering of silk-based biomaterials, focusing specifically on the fabrication of diverse bio-mimetic structures such as films, hydrogels, scaffolds, nanofibers and nanoparticles; their functionalization and potential for biomedical applications.     

Comparative study of mechanical and chemical methods for surface cleaning of a marine shell‐and‐tube heat exchanger

In this article, experimental analysis is done on shell‐and‐tube heat exchanger of a marine vessel for removal of fouling using optimum surface‐cleaning techniques. The main objective is to compare the performance of the heat exchanger before and after maintenance. Two identical deteriorated systems of heat exchangers are taken and real‐time analysis is conducted. The log data are taken before and after undergoing maintenance for the two systems. Two different cleaning techniques are used, namely, chemical cleaning and mechanical cleaning. Detailed calculations are made for the shell‐and‐tube heat exchanger. From the obtained data, comparisons are made for different parameters on the tube side such as friction factor, heat transfer coefficient and pressure drop, as well as total heat transfer rate on the shell side. From the analysis and comparison, it was found that greater heat transfer takes place for the tubes cleaned using the chemical cleaning method than for tubes cleaned by the mechanical cleaning method. Pressure drop is found to be less for chemical cleaning method than mechanical cleaning method. This indicates that the fouling effect is reduced for tubes cleaned by the chemical cleaning method, and furthermore these tubes remain corrosion‐resistant for longer periods of time.     

Fabrication and characterisation of bulk micromachined ZnO energy transducer with interdigitated electrodes

The proposed research work deals with the design, fabrication and characterisation of a ZnO cantilever energy transducer on Si(c) without the use of SOI wafers, thereby, reducing the cost of fabrication. The energy transducer is operated in the longitudinal mode through the interdigitated electrodes. This is for the first time, we have attempted to fabricate a cantilever transducer with interdigitated electrodes on Si(c) in our lab. The design frequency has been chosen in the range of 700–1000 Hz for a typical tire pressure monitoring system application in mind. The experimentally obtained frequency is 876.25 Hz and d₃₃ was calculated as 3.9 pC/N from the measurements. The experimental results are further validated by simulation and the feasibility of its application as energy harvester is demonstrated. The fabrication process is being optimised to fabricate devices with higher piezoelectric coefficients.     

Biosorption of chromium onto Erythrina Variegata Orientalis leaf powder

The biosorption of chromium from an aqueous solution onto Erythrina Variegata Orientalis leaf powder was investigated in batch operations. The equilibrium agitation time was 180 min. The extent of chromium biosorption increased from 74.2% to 86.4% with decrease in biosorbent size from 150 to 45 μm for a dosage of 30 g/L. The biosorption decreased from 99.1 (0.45 mg/g) to 45.5% (1.64 mg/g) with an increase in chromium initial concentration (C _o ) from 22.5 to 180 mg/L. The extent of biosorption was maximum at pH=3. The experimental data were well explained by Langmuir and Redlich-Peterson isotherm models. The biosorption data followed second-order kinetics with a rate constant of 0.078 g/mg-min for 50 g/L of 45 μm size biosorbent. The biosorption was exothermic and feasible. The biosorption was tending towards irreversibility with increasing temperature.     

Serial and parallel Si, Ge, and SiGe direct-write with scanning probes and conducting stamps

Precise materials integration in nanostructures is fundamental for future electronic and photonic devices. We demonstrate Si, Ge, and SiGe nanostructure direct-write with deterministic size, geometry, and placement control. The biased probe of an atomic force microscope (AFM) reacts diphenylsilane or diphenylgermane to direct-write carbon-free Si, Ge, and SiGe nano and heterostructures. Parallel direct-write is available on large areas by substituting the AFM probe with conducting microstructured stamps. This facile strategy can be easily expanded to a broad variety of semiconductor materials through precursor selection.     

POD Evaluation: The Key Performance Indicator for NDE 4.0

The magnified images of thin wires, plastic, steel and lead plates which were obtained using linear microfocus hard bremsstrahlung generated through interaction of an 18 MeV electron beam with a 13 μm thick Ta foil oriented along the internal beam of a B-18 betatron are presented. The images indicate high absorption contrast of the objects due to a small horizontal size of the radiation source the width of which is 115-fold smaller than the diameter of the electron beam. Some results have shown a few peculiarities in the images which were not earlier observed. Several results were compared with the ones obtained earlier using the microfocus bremsstrahlung generated by the 18 MeV electron beam of B-18 in a narrow Si target.

     

Analysis of high contact resistance in silver impregnated graphite (SIG) contacts

Silver impregnated graphite (SIG) contacts are used in high safety applications of railway signaling, traffic signaling, and numerous other applications due to high silver content that eliminates the risk of welding in the presence of graphite. High contact resistance (>200 mΩ) was observed in SIG contacts in a railway signaling operation after a few thousand operations of the relay. The high contact resistance was discovered to be a result of loose dust/foreign particles residing between the two contacts. Silver had been preferentially removed from the contacting surfaces during switching operations by an abrading effect of the dust/foreign particles, leaving only graphite on the contact area. Wear was accentuated by the presence of porosity and low hardness of the contacts, leading to improper interaction between the mating surfaces.     

Wear Performance of Laser Processed Tantalum Coatings

This first generation investigation evaluates the in vitro tribological performance of laser-processed Ta coatings on Ti for load-bearing implant applications. Linear reciprocating wear tests in simulated body fluid showed one order of magnitude less wear rate, of the order of 10(-4)mm(3)(N.m)(-1), for Ta coatings compared to Ti. Our results demonstrate that Ta coatings can potentially minimize the early-stage bone-implant interface micro-motion induced wear debris generation due to their excellent bioactivity comparable to that of hydroxyapatite (HA), high wear resistance and toughness compared to popular HA coatings.     

Functional self-assembled DNA nanostructures for molecular recognition

Nucleic acids present a wonderful toolkit of structural motifs for nanoconstruction. Functional DNA nanostructures can enable protein recognition by the use of aptamers attached to a basic core shape formed by DNA self-assembly. Here, we present a facile, programmable strategy for the assembly of discrete aptamer-tagged DNA shapes and nanostructures that can function for molecular recognition and binding in an aqueous environment. These nanostructures, presented here to bind two different protein targets, are easily synthesized in large numbers, and are portable and stable over long periods of time. This construction modality can facilitate on-demand production of libraries of diverse shapes to recognize and bind proteins or catalyze reactions via functional nucleic acid tags.