Fundamental study of silicate substituted nanostructured calcium phosphates (NanoSiCaPs) and 3-D scaffolds for non-viral gene delivery

Nanostructured calcium phosphate (NanoCaPs) particles are biocompatible and non-toxic bioceramics widely studied owing to their structural and compositional similarity to the mineralized tissue architecture of native bone. They are therefore considered as an ideal choice for gene delivery applications in bone tissue engineering. However, NanoCaPs are typically characterized by variable transfection, short shelf life due to particle aggregation, and difficulties associated with endosomal escape. The objectives of this dissertation were therefore crafted to develop strategies to circumvent, if not eliminate, some of the limitations that have previously stymied the success of NanoCaPs as a non-viral gene delivery vector for bone tissue engineering applications. A modified version of NanoCaPs containing critical concentration of silicate ions substitutions were synthesized, aptly called NanoSiCaPs. Fundamental understanding of the influence of silicate ion substitutions in the NanoCaPs lattice structure was conducted using various materials characterization techniques. In-vitro transfection results indicated, a two-fold increase in transfection levels exhibited by NanoSiCaPs, owing to the enhanced dissolution kinetics and ability to limit particle aggregation. Subsequently, two different strategies were developed to achieve scaffold mediated gene delivery via generation of plasmid DNA bound to NanoSiCaPs (NanoSiCaPs complexes, NC). First, a novel and simple coating methodology was developed using NCs adsorbed on Ti-surfaces coated with polyelectrolyte. Surface characterization results indicated successful generation of the nanoceramic coating on the Ti-surfaces. Additionally, it was demonstrated that the Ti-polyelectrolyte-NC assemblies contribute to surface mediated gene transfection, without eliciting any cytotoxicity. Second, a lyophilization technique was developed that enabled long-term storage of the NCs under ambient conditions, without inducing either a significant change in particle size or loss in gene transfection efficiency. Subsequently, a 3-D gene delivery system comprising fibrin hydrogels and lyophilized NCs was developed. In-vitro transfection results indicated that gene expression mediated via synthesized gels can be meticulously controlled by modulating the amounts of fibrinogen and NCs utilized in the synthesis of the gels. In conclusion, the studies demonstrate creation of next generation NanoCaP vectors, NCs and their implementation in the development of 3-D scaffolds serving as effective gene delivery agents as well as functional scaffolds for bone tissue repair and regeneration

Axial Back Conduction in Cryogenic Fluid Microtube

Cryogenic technology is now a rapidly progressing system which is used in different cooling processes because the behaviour of many physical materials changes beyond our expectations. For example copper behave normally as other materials for electrical conductivity but at the cryogenic temperature it behaves as superconductor. Actually there is no certain temperature from which the cryogenic temperature starts but according to the scientist below -1500C or 123 K cryogenic temperature starts. Also the time is to use products of compactness which is known as miniaturization. In the engineering background there are many researchers who have studied and developed the micro channels as the cooling process is very efficient because the surface area to volume ratio is very less. So it is now a keen interest to use cryogenic temperature in the micro channels. There are different gases present in our atmosphere which are used as cryogenic fluids, example Helium, Nitrogen, Oxygen, etc., as boiling points of these gases are below cryogenic temperature. The boiling point of liquid Nitrogen is 77.2 K and the freezing point is 63 K. In this present work cryogenic gas is intended to flow through a circular micro channel and a two dimensional numerical simulation is carried out for an internal convective laminar flow through the channel, subjected to constant wall heat flux to see the axial back conduction in the solid substrate of the tube which leads to conjugate heat transfer. Nitrogen gas is used as working fluid to flow through the microtube. Thermo-physical properties (e.g. density, viscosity, specific heat and thermal conductivity) of nitrogen gas change appreciably with the temperature, thus thermophysical properties function of temperature are used as UDF as described in numerical simulation chapter. The micro channel of 0.4 mm diameter and 60 mm length are kept constant and δsf (i.e. ratio of wall thickness (δs) to inner radius (δf)) is varied such as 1, 2, 3, 4 & 5 throughout the simulation. Other variable parameters are Reynold’s number varies as 100 & 500 and ksf (i.e. solid conductivity ratio to fluid conductivity ratio) varies from 22.07931 to 45980.71. In this work it is tried to find out most suitable material i.e. ks value as well as suitable wall thickness of the microtube i.e. δs value with the help of change in different parameters. After the completion of the numerical analysis the conclusions found are, (i) wall conductivity ratio and wall thickness ratio play dominant role in the effect of axial back conduction, (ii) there exist an optimum ksf value at which average Nusselt number (Nuavg) is maximum while other parameters are kept constant, (iii) at higher value of δsf, average Nusselt number becomes lower, (iv) Nuavg increases with increase in flow rate i.e. increasing value of Reynolds number

Heat Treatment of S.G Cast Iron

S.G Cast iron is defined as a high carbon containing, iron based alloy in which the graphite is present in compact, spherical shapes rather than in the shape of flakes, the latter being typical of gray cast iron . As nodular or spheroidal graphite cast iron, sometimes referred to as ductile iron, constitutes a family of cast irons in which the graphite is present in a nodular or spheroidal form. The graphite nodules are small and constitute only small areas of weakness in a steel-like matrix. Because of this the mechanical properties of ductile irons related directly to the strength and ductility of the matrix present—as is the case of steels. One reason for the phenomenal growth in the use of Ductile Iron castings is the high ratio of performance to cost that they offer the designer and end user. This high value results from many factors, one of which is the control of microstructure and properties that can be achieved in the ascast condition, enabling a high percentage of ferritic and pearlitic structure

Heat treatment of S.G cast iron and its effects

S.G Cast iron is defined as a high carbon containing, iron based alloy in which the graphite is present in compact, spherical shapes rather than in the shape of flakes, the latter being typical of gray cast iron . As nodular or spheroidal graphite cast iron, sometimes referred to as ductile iron,constitutes a family of cast irons in which the graphite is present in a nodular or spheroidal form.The graphite nodules are small and constitute only small areas of weakness in a steel-like matrix. Because of this the mechanical properties of ductile irons related directly to the strength and ductility of the matrix present—as is the case of steels.One reason for the phenomenal growth in the use of Ductile Iron castings is the high ratio of performance to cost that they offer the designer and end user. This high value results from many factors, one of which is the control of microstructure and properties that can be achieved in the ascast condition, enabling a high percentage of ferritic and pearlitic structure.Heat treatment is a valuable and versatile tool for extending both the consistency and range of properties of Ductile Iron castings beyond the limits of those produced in the as-cast condition. Thus, to fully utilize the potential of Ductile Iron castings, the designer should be aware of the wide range of heat treatments available for Ductile Iron, and its response to these heat treatments.The most important heat treatments and their purposes are:Stress relieving - a low-temperature treatment, to reduce or relieve internal stresses remaining after casting Annealing - to improve ductility and toughness, to reduce hardness and to remove carbides Normalizing - to improve strength with some ductility Hardening and tempering - to increase hardness or to give improved strength and higher proof stress ratio Austempering - to yield bainitic structures of high strength, with significant ductility and good wear resistance Surface hardening - by induction, flame,or laser to produce a local wearresistant hard surface1 Although Ductile Iron and steel are superficially similar metallurgically, the high carbon and silicon levels in Ductile Iron result in important differences in their response to heat treatment. The higher carbon levels in Ductile Iron increase hardenability, permitting heavier sections to be heat treated with lower requirements for expensive alloying or severe quenching media.These higher carbon levels can also cause quench cracking due to the formation of higher carbon martensite,and/or the retention of metastable austenite. These undesirable phenomena make the control of composition, austenitizing temperature and quenching conditions more critical in Ductile Iron. Silicon also exerts a strong influence on the response of Ductile Iron to heat treatment. The higher the silicon content, the lower the solubility of carbon in austenite and the more readily carbon is precipitated as graphite during slow cooling to produce a ferritic matrix. Although remaining unchanged in shape, the graphite spheroids in Ductile Iron play a critical role in heat treatment, acting as both a source and sink for carbon. When heated into the austenite temperature range, carbon readily diffuses from the spheroids to saturate the austenite matrix.On slow cooling the carbon returns to the graphite "sinks",reducing the carbon content of the austenite. This availability of excess carbon and the ability to transfer it between the matrix and the nodules makes Ductile Iron easier to heat treat and increases the range of properties that can be obtained by heat treatment.Austempered Ductile Irons (ADI) are the most recently developed materials of the DI family. By adapting the austempering treatment initially introduced for steels to DI, it has been shown that the resulting metallurgical structures provide properties that favorably compare to those of steel while taking advantage of a near-net-shape manufacturing process