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Chitosan-based composite films with different amounts of grapefruit seed extract (GFSE) (0.5, 1.0 and 1.5% v/v) were fabricated via solution casting technique. Experimental results showed that GFSE was uniformly dispersed within all chitosan film matrices. The presence of GFSE made the films more amorphous and tensile strength decreased, while elongation at break values increased as GFSE content increased. Results from the measurement of light transmission revealed that increasing amounts of GFSE (from 0.5 to 1.5% v/v) did not affect transparency of the films. Furthermore, packaging of bread samples with chitosan-based GFSE composite films inhibited the proliferation of fungal growth as compared to control samples. Hence, chitosan-based GFSE composite films have the potential to be a useful material in the area of food technology.

Given the dimension of the micro component to be replicated, it is crucial to study sintering for dimensional and property control in micro powder injection molding. In the paper, 316 L stainless steel micro components with two different microsize structure dimensions, ϕ100 μm × height 200 μm and ϕ60 μm × height 191 μm, are fabricated from in-house feedstock. Shrinkage, microstructure, microindentation hardness and sintering trajectory are investigated for the micro components. The linear shrinkage rate of the micro component reaches the maximum at 1180 °C, after which it begins to decline. Porosity (volume fraction of pores) decrease, pore migration and breakaway, grain growth and the formation of a dense layer are observed for the microsize structures. The microindentation hardness of the dense layer in the rim of the microsize structures is lower than the microindentation hardness of the substructure. It is found that if the relative density is below 0.98, densification is promoted when the structure size reduces from the substructure in the millimeter regime to the microsize structures of ϕ60 μm. This is attributed to the oxides on the debound micro components and internal gas pressure produced by hydrogen sintering.

Alumina micro-channel parts were produced by micro powder injection molding. The debound part was rapidly densified by pressuresless spark plasma sintering. Rapid densification of the micro-channel part proved to be feasible. Good shape retention and high densification were achieved for the final micro-channel part. The microstructural analysis revealed that fine-grained microstructures were obtained at the sintering temperatures of 1250–1300 °C. The nanoindentation tests showed that the nanohardness and Young’s modulus were dependent on the porosity and grain size.

A 316L stainless steel feedstock suitable for micro powder injection molding was discussed. The homogeneity, thermal and rheological properties of the 316L stainless steel feedstock were characterized by means of SEM, TGA, DSC and capillary rheometer. The 316L stainless steel powder was uniformly distributed within the binder. The 316L stainless steel micro-mixer was well replicated by micro powder injection molding. The molded, debound and sintered micro-mixers had good shape retention, without visible defects, such as warpage, incomplete filling, crack, etc. The dimensional change and surface roughness of the micro-mixer were investigated. The dimensional shrinkage of the micro-mixer took place mainly in the sintering step, whilst the dimensional change was not noticeable in the debinding step. The surface topography of the silicon mold insert was well replicated in the stainless steel micro-mixer. The surface roughness of molded, debound and sintered micro-mixer increased with consecutive processing steps. After sintering, the relative density of the micro-sized structure was 96.56% and there was excessive grain growth.

We demonstrate the aqueous self-assembly of ligand-assisted SnO2 sol precursors onto preformed poly-l-lysine templates through interfacial electrostatic forces (COO−/NH3+). On the removal of organics, two unique coral-like and sea worm-like textures consisting of hierarchical pores (macropores and mesopores) and nanocrystalline SnO2 frameworks are synthesized, mainly depending on the chelator/Sn molar ratio. Structural formation is discussed based on acid-base interaction and interfacial charge density matching. For the first time, metal oxide structures mediated by polypeptides are reported. More importantly, the method described here might open a generally attractive route for synthesizing complex nanostructures of other oxides (e.g., ZnO, TiO2, and ZrO2).

Nanocrystalline Ni–Ti was used in self-propagating high-temperature synthesis (SHS) to fabricate porous NiTi. The SHS of porous NiTi using elemental powders was also prepared for comparison. Results showed that the main phase was NiTi with unreacted Ni when using elemental powders, which is detrimental to medical use. A large amount of Ti2Ni secondary phase was also detected. By employing mechanically alloyed nanocrystalline Ni–Ti as a reaction agent, the secondary intermetallic phase (i.e. Ti2Ni) was significantly reduced and the unreacted Ni was eliminated. The addition of 25 wt% nanocrystalline Ni–Ti reaction agent produced porous NiTi with an average porosity of 52–55 vol% and a general pore size of 100–600 μm under preheating temperatures of 200 and 300 °C. This general pore size in the range of 100–600 μm is beneficial to biomedical application for osseointegration. By further increase of the reaction agent to 50 wt% in the reactant, a porous NiTi part was produced at ambient temperature (i.e. no preheating was necessary) and a dense part was formed at preheated temperature of 200 °C due to the large amount of energies in the nanocrystalline reaction agent. This revealed that the use of nanocrystalline reaction agent effectively lowered the activation barriers for combustion synthesis reaction.

Micro metal injection molding (μMIM) is a promising process for the replication of metallic microstructures. In the micrometer regime, surface roughness is important in view of the dimensional tolerance and the applications of microstructured parts. In this paper, the effects of debinding on the surface roughness of 316 L stainless steel microstructured parts were investigated. Experimental results showed that using higher heating rates during debinding increased the weight loss of debound parts. The debound parts of higher weight loss gave better surface finish after sintering. Comparing the increase of sintering time and temperature, the surface finish improvement was more significant for increasing temperature.

The sintering kinetics of microsize structures (diameter 80 μm) and substructure (in the millimeter range) fabricated by micro powder injection molding were studied. The microsize structures had lower porosity than the substructure, indicating that size reduction increases densification. The densification mechanism varies with size, lattice diffusion (for the microsize structures) and boundary diffusion (for the substructure). The activation energies for the control mechanism during grain growth and densification are reported.

Successful synthesis of silica shells templated by polypeptide spheres stabilized by citric acid inspired us to explore the possibility of realizing aqueous self-assembly of metal oxides using the same template. As a specific case in the present study, we have begun with tin (IV) oxide. Initially, we failed to control the assembly process due to strong hydrolysis of Sn4+ ions and agglomeration of tin hydrates. After modification by a proper amount of citric acid which was trapped onto the surface of the tin hydrates through the chelating bond between RCOO− groups and Sn4+ ions, finely dispersed and stabilized tin oxide precursors have been obtained through electrostatic repulsion or/and steric hindrance. As a result, aqueous self-assembly of surface functional SnO2 building blocks mediated by the pre-formed polypeptide templates has been successfully achieved through interfacial columbic forces (COO−/NH3+). Samples fabricated from systematic processing control were characterized by thermogravimetric (TG) analysis, field-emission scanning electron microscopy (SEM), x-ray powder diffraction, high-resolution transmission electron microscopy (HRTEM), infrared (IR) absorption and N2 gas sorption experiments. Unique coral- and sea worm-like multilevel porous/hollow frameworks consisting of SnO2 nanocrystallites (4–5 nm) were synthesized. The samples also demonstrated improved H2 gas sensing property due to the large specific surface area (180–210 m2 g−1) as well as easy gas diffusion.

In this paper, two sets of arrays of 24 × 24 316L stainless steel micro rods of ϕ 100 and ϕ 80 μm are replicated on ϕ 15 mm substructures by injection molding, debinding and sintering through micro metal injection molding. The microstructure, shrinkage, porosity and Vickers microhardness of the micro rod and the substructure of the as-sintered micro-component are characterized. Shrinkage in the micro rod is near isotropic but is higher than the substructure on which micro rods are located. Lower porosity is also observed concomitantly on the micro rod. Similar microhardness values are measured on the polished cross-sections of the substructures on which the ϕ 100 and ϕ 80 μm micro rod arrays are located but differing values are measured on the cross-sections of the two micro rods.

TiO2/apatite coating on metal implants is an effective method to enhance the biological properties of the metal surface. In this study, porous NiTi with a banded structure of channels and an average porosity of 45?vol% was prepared by self-propagating high-temperature synthesis. Samples were subjected to chemical treatment in H2O2/HCl to form a layer of nanocrystallite TiO2 coating. A biomimetic process of soaking the samples in a simulated body fluid (SBF) was subsequently employed to deposit a nanocrystallite apatite coating on the surface of the TiO2 coating. Analysis of the coatings showed that a nanocrystallite TiO2 coating with anatase phase was formed on the surface of porous NiTi. A carbonated and non-stoichiometric nanocrystallite apatite coating with Ca/P ratio of 1.49 was biomimetically deposited on the surface of TiO2, which has similar mineral composition to that of natural bone. The thickness of the TiO2 and apatite coatings increased with increasing chemical treatment time and the immersion period in SBF, respectively. The growth kinetics and mechanism are also discussed. Results suggested that the TiO2/apatite nanocomposite coatings can be deposited on porous NiTi by chemical treatment and a subsequent biomimetic process.

Micro metal injection moulding (μMIM) is being developed for possible mass production of metallic microstructured components. In the micrometer regime, consideration of surface roughness becomes more important as dimensional tolerance is towards the range of surface roughness and surface force becomes dominant at the surface-to-volume ratio encountered. In this paper, the effects of sintering temperature and time on surface roughness ( R a ) and surface grain size ( G ) of 316L stainless steel microstructured components fabricated by μMIM were investigated. In particular, the top surface of the microstructure and the substructure area, on which the microstructures were positioned, were characterised. After sintering, R a values at these areas were similar even though disparate magnitudes were measured in the mould insert and the moulded microstructured component. R a and G were found to increase with sintering temperature for the top surface of the microstructure. A smaller G tended to yield lower R a and the substructure had smaller grain size and lower R a value than the comparatively free-standing microstructures.

In recent years, micro powder injection molding (μPIM) is being explored as an economical fabrication method for microcomponents. μPIM, adapted from powder injection molding (PIM), has the same four main processing steps as PIM: mixing of powder and binder system to form the feedstock, injection molding, debinding and sintering. Unlike PIM, the feedstock for μPIM requires more stringent characteristics. Thus, commercial feedstock may not be suitable especially for microstructures with high aspect ratio. In this paper, the mixing, characterisation and feasibility of an in-house feedstock for the injection molding of microstructures, each of ϕ100 μm×height 200 μm, is reported. The feedstock comprises 316L stainless steel and a multi-component binder system. The effects of powder loading and extrusion on mixing and feedstock homogeneity were investigated. The rheological and thermal characteristics of the feedstock were determined and used in subsequent processing steps. The results show that the feedstock can be used for the fabrication of the microstructures with good shape retention.

A nanocrystalline/amorphous 50Ni-50Ti alloy was produced by solid state synthesis via mechanical alloying from elemental Ti and Ni powders. Using X-ray diffraction analysis and transmission electro ...

Given the small dimensions to be replicated for micro components, knowledge into their microstructure evolution is crucial for dimensional and property control. Constitutive model is useful to predict the final shape of the sintered micro components. In this paper, the microstructure evolution of 316L stainless steel microsize structures of Φ60 µm that was fabricated by micro metal injection moulding was examined via SEM and XRD. A constitutive model is established to simulate densification of the microsize structures and the contribution of lattice diffusion (Nabarro-Herring creep) is considered. The predictive capability of the model is verified by comparing the theoretical calculations with the experimental results. The influences of boundary energy on modelling results are discussed. It is found that the modelling results agree reasonably well with the experimental results.

This paper studies the demolding of an array of powder injection molded micro-structures based on a variotherm mold. The demolding of the micro-structures array was analyzed both theoretically and experimentally. Finite element method (FEM) software ABAQUS was used to analyze and simulate the demolding of an array of 24 × 24 (total of 576) micro-structures. It was found that there exists a 'critical temperature' at which the demolding force for the micro-structures array is a minimum. The stress distribution of the micro-structures and demolding force for the micro-structures during the course of demolding were analyzed for both demolding temperatures higher and lower than the critical temperature. Packing pressure and demolding temperature have an apparent impact on the demolding force. A series of demolding force measuring experiments at different packing pressures and demolding temperatures were conducted to verify the theoretical results.