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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.

Multi-functional, co-substituted hydroxyapatite thin films (Ag,Si-HA) with a composition of ~ 0.2 wt.% silver (Ag) and ~ 0.7 wt.% silicon (Si), were produced on titanium substrates using the drop-on-demand micro-dispensing (DODMD) process. Scanning electron microscopy images revealed that the coating was made up of rod-like apatite crystals measuring ~ 50 nm in length by ~ 15 nm in width, with no change in the morphology after the deposition process. X-ray diffraction analysis confirmed the presence of single-phase Ag,Si-HA with no other secondary phases such as tricalcium phosphate, tetracalcium phosphate or calcium oxide being detected. A study of the Ag,Si-HA thin film by fourier transform infrared spectroscopy indicated the presence of several phosphate bands in the range of 500–700 and 900–1200 cm− 1, and a hydroxyl band at 3571 cm− 1, which is the characteristic of HA. The surface contact angle measurement for Ag,Si-HA thin film was found to be significantly lower than those of the uncoated substrates, demonstrating the highly hydrophilic nature of these coatings. White light interferometry was used to determine the thickness of the deposited thin film. The thickness was found to be approximately 3.5 μm. A scratch test conducted on the coating revealed an adhesion strength of about 160 mN. Biological results showed that human mesenchymal stem cells grew generally well on Ag,Si-HA thin films and at the same time, a few bacterial colonies were seen attaching on the surface of Ag,Si-HA. All these results demonstrated that multi-functional, single-layered phase-pure Ag,Si-HA thin films could be deposited using the technique of DODMD.

A feedstock consisting of submicron alumina powder and a formulated binder, was developed to fabricate alumina micro-channel part by micro powder injection moulding. During small scale-mixing, the mixing torques of feedstocks with four different powder loadings were used to establish a suitable powder loading. The thermal and rheological properties of the selected feedstock were examined and used to establish conditions for large scale mixing, debinding and injection moulding. The micro-channel parts were pressureless sintered at different temperatures. The results showed that the moulded, debound and sintered micro-channel parts had good shape retention. The dimensions of the micro-channel part changed with the different processing steps. High densification of the micro-channel parts was achieved at sintering temperatures of 1350 °C and above. Above 1350 °C, the grain grew significantly with increasing the sintering temperatures and thus it led to a decrease in the microhardness.

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.

Fabrication of micro components comprising of functional units of different dimensional order, ϕ100 μm, ϕ80 μm and ϕ60 μm, by micro powder injection molding is described in the paper. The microstructure is characterized for various microsize structures and substructures under different sintering conditions. The micro components are successfully molded, debound and sintered based on an in-house feedstock. Although sintered as an integral component, the microsize structure is at final stage sintering whereas the substructure is at intermediate stage sintering within the temperatures studied. The smallest microsize structures, ϕ60 μm, have the highest relative density. Higher surface area/volume ratio of the microsize structures is attributed to the advanced sintering. XPS results show that oxides on the debound micro components and consequent reduction products during hydrogen sintering attribute to the formation and progression of the observed dense layers.

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.

In this paper, 316L stainless steel micro-mixers were fabricated by micro powder injection molding. The tribological behavior of the stainless steel micro-mixer sliding against AISI 52100 steel at low loads was investigated using a ball-on-disk tribometer. The morphologies and compositions of the worn surfaces were analyzed by SEM, Raman and XPS. The results showed that the wear mechanism of stainless steel depended strongly on the microstructure which was influenced by the sintering atmosphere. The friction coefficients and wear rates of the stainless steel sintered in vacuum were lower than that in hydrogen, due to the formation of carbide phase in the former matrix. Tribo-oxidation together with the formation and delamination of tribo-layer were the dominant wear mechanisms for stainless steel sintered in vacuum. The tribo-layer composed of various iron oxides, such as Fe3O4, α-Fe2O3, γ-Fe2O3, and γ-FeOOH, which were favorable and caused mild wear. In the case of the stainless steel sintered in hydrogen, the worn surfaces were very rough with more wear debris entrapped. Adhesive wear was responsible for the material transfer from the stainless steel to the AISI 52100 steel, which led to the transition from mild to severe wear.

A novel porous Ti–6Al–4V with an open cell structure was fabricated by powder metallurgy process with the addition of TiH 2 as the pore forming and active agent. Control of porosity of porous Ti alloy made it possible to obtain the porous Ti with the Young's modulus value of 5.8–9.5 GPa, which was similar to that of human cancellous bone. This kind of porous Ti alloy with good biomechanical properties is potential to alleviate the problem of mechanical mismatch between the bone and the Ti implant. The porous Ti alloy prepared by the addition of TiH 2 as foaming agent had a uniform distribution of pores with pore size of 90–190 μm and porosity of 43–59%. In order to improve the biological properties, the duplex titania/apatite coatings were applied onto the surface of porous Ti alloy. The titania coating was deposited by chemical treatment and the apatite coating was subsequently applied by immersing the samples in a simulated body fluid. Results showed that a homogeneous nanocrystallite titania coating with a thickness of 0.8 μm was formed on the surface of the Ti alloy after chemical treatment. The carbonate-containing apatite coating with a thickness of 1 μm was deposited on the surface of titania coating after immersion in simulated body fluid for 7 days. The nucleation of the carbonate-containing apatite can be induced from the electrostatic interaction between the OH-containing groups on the surface of titania coating and the calcium and phosphate ions in the metastable simulated body fluid on those specific superficial sites. The growth kinetics of the coatings was also discussed. Cell culture test showed the well stretched and proliferated cells on the surface of the sample, indicating the good biocompatibility of porous Ti alloy.

The paper describes the fabrication of micro gears of diameter and height 1 mm by micro powder injection moulding. 316L stainless steel powder of 2.4 µm ( d 50 ) is mixed with a multi-component wax-based binder system. The feedstock is then injection-moulded into micro gears followed by debinding and sintering. The microstructure of the micro gear at its tooth and hub is studied by electron backscattered diffraction. The average grain size at the hub is ~ 5 µm. However, a high content of annealing twin and a significant grain growth is found at the tooth.

A constitutive model based on Besson and Abouaf’s constitutive equation was established to simulate densification of 316L stainless steel microstructured components fabricated by micro powder injection molding. A new sintering stress expression for final stage sintering was established by including the variation in grain number during grain growth. Different diffusional creep, sintering stress and internal gas pressure were assumed for the substructure, in the millimeter regime, and the microsize structures, respectively. The predictive capability of the model was verified by comparing the theoretical calculations with the experimental results. The calculations agreed reasonably well with the experimental results. Neglecting the variation in grain number in the sintering stress was found to yield lower predicted densities of the microsize structures.

Porous NiTi shape memory alloy has been an active area of research for medical application due to their similar microstructure to human bone. In this study, porous product was obtained by self-propagating high-temperature synthesis (SHS) of compacts prepared from elemental nickel and titanium powders and the effects of the green porosity and preheating temperature were examined. The porosity in the synthesised products was in the range of 45–59 vol.%, with the green porosity being the primary source of final porosity. NiTi was present as the dominant phase in the porous product with other secondary intermetallic compounds and element powders. The effect of green porosity and preheating temperature was found to have an effect on the pore morphology and microstructure.

Mesoporous SnO 2 /SnO 2 –SiO 2 with disordered pores and high thermal stability up to 600 °C were fabricated using hydrothermal treatment with/without impurity oxide (SiO 2 ) doping. Neutral surfactant (tetradecylamine, TDA) was selected as the structure directing agent based on a sol–gel-derived process. The results showed that with careful control of the synthesis condition, mesoporous SnO 2 –SiO 2 with small SnO 2 nanocrystallites (∼25 A), large specific surface area (211–340 m 2 /g), and pore volume (0.23–0.3 cm 3 /g) could be obtained after the removal of template at temperatures of 400–600 °C. The effects of synthesis parameters such as aging time, hydrothermal treatment, Si/Sn molar ratio and calcination temperature were characterized by thermogravimetric analysis, wide/small-angle X-ray scattering (SAXS), HRTEM, and BET gas (N 2 ) adsorption/desorption measurements.

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.

The study investigated the processing of biodegradable porous scaffold of polycaprolactone (PCL). Commercially available PCL powder was blended with poly(vinyl alcohol) powder at various compositions to fabricate pre-scaffolds using the three-dimensional printing (3DP) technique followed by particulate-leaching. Structures at different porosity (50–70%) were processed and their properties were characterised using differential scanning calorimetry, dynamic mechanical analyser, scanning electronic micrography and gel-permeable chromotography. The scaffolds produced in this route displayed open cellular structures with macropores with pores sizes ranging between 100 and 500 μm. No significant degradation of PCL was detected. The storage modulus of the scaffold ranged 0.03–0.19 MPa.

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.

Mesoporous SnO2/SiO2 composite particles (Si/Sn < or = 0.25) sustainable to calcination up to 600 degrees C have been fabricated using a stepwise sol-gel technique on nonionic surfactant template (tetradecylamine, TDA). The newly designed preparation method involved the pre-formation of SnO2 sol solution from SnCl4. Subsequently, SnO2 nanocrystals were covered by the silicate species (from the hydrolysis of tetraethylorthosilicate, TEOS) in a pH controlled colloidal solution. Upon mixing with the surfactant solution, mesophase composite was obtained. After the removal of templates at various temperatures (400 to 600 degrees C), worm-like mesoporous SnO2/SiO2 with large specific surface area and pore volume as high as 362 m2/g and 0.33 cc/g were obtained, respectively. High thermal stability is mainly due to the effective inhibition of SnO2 crystal growth (mean crystallite size

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.

To enhance the bioactivity of NiTi alloy, the surface oxidation layers were synthesized by heat treatment in air in the temperature range of 300–800 °C. The surface oxidation layer on NiTi alloy was characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. The heat treated sample was soaked in simulated body fluid (SBF) to study the bioactivity of the thermally grown oxide layer. Results showed that a protective layer of TiO 2 was formed on the surface of NiTi alloy at heat treatment temperatures of 600 °C or higher with varying degree of anatase and rutile. Small amount of nickel oxide was found on the surface of 300 and 400 °C treated samples by X-ray photoelectron spectroscopy. With further increase in the heat treatment temperature, the nickel concentration on the surface decreased and there was almost no nickel species on the surface after heat treatment at 600 °C or 800 °C. Depth profiling revealed that the amount of TiO 2 (Ti 4+ ) decreased with depth with a concomitant increase of metallic Ti. In addition, both TiO (Ti 2+ ) and Ti 2 O 3 (Ti 3+ ) increased initially and then decreased gradually with depth. Ni existed mainly in the oxidized state on the surface of heat treated samples and it changed to metallic state with increasing depth. In vitro test revealed that the titanium oxide layer formed on the 600 and 800 °C heat treated samples was bioactive, and a layer of apatite was formed on the surface of the titanium oxide layer after soaking in simulated body fluid.

The micro powder injection molding (μPIM) process was used to fabricate metallic microstructures in this paper. The production of 316L stainless steel microstructures arrays with the dimensions of ∅ 100 μm×height200 μmand∅ 60 μm × height 191 μm is presented. Injection molding was conducted on a conventional injection molding machine and silicon mold inserts with vertical sidewall made by deep reactive ion etching (DRIE) were used. Molded parts with microstructures were well obtained after selecting suitable processing parameters based on the feedstock characteristics. Then the molded parts were debound catalytically and sintered. Sintering at different temperature was conducted under vacuum. The effects of sintering temperatures were evaluated based on the polished and etched micrographs of the sintered microstructures. Finally Young’s Modulus of sintered microstructure was evaluated using nano-indenter.

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 ...

Micro powder injection molding (μPIM) is a potential manufacturing process for microstructured components used in Microsystems Technology (MST). In this paper, the replication of 316L stainless steel microstructure by μPIM was studied. The feedstock comprised of 316L stainless steel and a wax-based binder enhanced with low-density polyethylene to improve green strength for demolding. The feedstock was characterized to enable the selection of suitable processing parameters. The effects of melt temperature, mold temperature and packing pressure on the filling, microstructure replication and demolding were discussed. The results show that 316L stainless steel microstructures could be successfully replicated through the μPIM route.

Powder-bed 3D printing (3DP) is a versatile additive manufacturing technique that uses ink binder deposition to bind loose powder particles together. This paper evaluates the work using powder-bed 3DP technology as a low-cost manufacturing system to print non-proprietary materials for biomedical scaffold and implant applications. The work presents development of suitable binder-powder feedstock coupled with the suitable printing and post-processing methodologies for respective biomaterial. Published version

Constitutive model is useful to predict the final shape of sintered microsize structures. In this paper, the contribution of lattice diffusion (Nabarro-Herring creep) is considered and a constitutive model is established to simulate densification of 316L stainless steel microsize structures fabricated by micro metal injection molding. The predictive capability of the model is verified by comparing the theoretical calculations with the experimental results. The influences of boundary energy on modeling results are discussed. It is found that the modeling results agree reasonably well with the experimental results.

Porous NiTi with an average porosity of 55 vol % and a general pore size of 100–600 μm was synthesized by self-propagating high temperature synthesis (SHS) with the addition of mechanically alloyed nanocrystalline Ni-Ti as the reaction agent. The SHS of porous NiTi using elemental powders was also performed for comparison. To enhance the bioactivity of the metal surface, porous NiTi synthesized by nanocrystalline Ni-Ti was subjected to chemical treatment to form a layer of TiO2 coating. The porous NiTi with TiO2 coating was subsequently immersed in a simulated body fluid (SBF) to investigate its apatite forming ability. The effects of the addition of nanocrystalline Ni-Ti as reaction agent and the application of apatite coating on osteoblastic behavior were studied in primary cultures of human osteoblast cells. Results showed that the main phases in porous NiTi synthesized by elemental powders were NiTi, Ti2Ni, and unreacted free Ni. By using nanocrystalline Ni-Ti as reaction agent, the secondary intermetallic phase of Ti2Ni was significantly reduced and the free Ni was eliminated. TiO2 coating with anatase phase was formed on the surface of porous NiTi after the chemical treatment. A layer consisting of nanocrystalline carbonate-containing apatite was formed on the surface of TiO2 coating after soaking in SBF. The preliminary cell culture studies showed that the porous NiTi synthesized with the addition of nanocrystalline Ni-Ti attracted marked attachment and proliferation of the osteoblast cells. This gives the evidence of the potential biomedical applications of the porous NiTi. © 2006 Wiley Periodicals, Inc. J Biomed Mater Res, 2006

TiO(2) coatings were prepared on NiTi alloy by heat treatment in air at 300, 400, 600 and 800 degrees C. The heat-treated NiTi alloy was subsequently immersed in a simulated body fluid for the biomimetic deposition of the apatite layer onto the surface of TiO(2) coating. The apatite coatings as well as the surface oxide layer on NiTi alloy were characterized using scanning electron microscopy equipped with energy dispersive spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy and Raman spectroscopy. Results showed the samples heat-treated at 600 degrees C produced a layer of anatase and rutile TiO(2) on the surface of NiTi. No TiO(2) was detected on the surface of NiTi after heat treatment at 300 and 400 degrees C by X-ray diffraction, while rutile was formed on the surface of the 800 degrees C heat-treated sample. It was found that the 600 degrees C heat-treated NiTi induced a layer consisted of microcrystalline carbonate containing hydroxyapatite on its surface most effectively, while 300 and 400 degrees C heat-treated NiTi did not form apatite. This was due to the presence of anatase and/or rutile in the 600 and 800 degrees C heat-treated NiTi which could provide atomic arrangements in their crystal structures suitable for the epitaxy of apatite crystals, and anatase had better apatite-forming ability than rutile. XPS and Raman results revealed that this apatite layer was a carbonated and non-stoichiometric apatite with Ca/P ratio of 1.53, which was similar to the human bone. The formation of apatite on 600 degrees C heat-treated NiTi following immersion in SBF for 3 days indicated that the surface modified NiTi possessed excellent bioactivity.

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.