Materials Science Forum Vols. 610-613

Abstract: Neovascularization in biomaterials plays a key role in wound healing. In this paper, porous silk fibroin films (PSFFs) whose structure was optimized, as dermis substitutes, were implanted in the back skin of rats for recovery of dermis loss. Results showed that a thin layer of loose connective tissue had formed at the interface between PSFFs and subcutaneous tissues, in which abundant blood vessels could be observed at 24 h after surgery. Whereafter the newly formed connective tissue thickened and the number of microvessels in the tissue increased. Furthermore, a few microvessels could be seen in PSFFs at day 5, most of which were capillaries. By day 10, the density of microvessels in PSFFs increased to a peak while the percentage of capillary decreased. At day 23, both the density of microvessels and the percentage of capillary was almost equal to those of normal tissues. In summary, wound healing with PSFFs as dermis substitutes is the neovascularization process of PSFFs. The process includes three major steps: (1) new formation and growth of loose connective tissue into the pores of PSFFs, (2) proliferation and migration of fibroblasts and endothelial cells, and (3) formation of functional microvessels and their networks.

Abstract: The high-cycle fatigue mechanisms of a NiTi shape memory alloy (SMA) under three different mean strains were investigated. Cold-rolled NiTi SMA specimens were heat treated at 600°C for 30min was selected to perform the fatigue test. Three samples were conducted cyclic deformation up to 2×105 cycles with three mean strains that subjected at full austenite, total stress-induced martensite (SIM) and austenite-martensite coexist status with the same strain amplitude of 0.25%. The cyclic stress-strain (CSS) curves show different cyclic softening and hardening at different mean strains. The S-S curves also reveal that cyclic deformation strain mainly occurred in martensite phase although austenite and martensite (A-M) coexisted. The transmission electron microscopy (TEM) investigation shows that slip dislocations with habit plane and basal plane dislocations were induced during the cycling, and these microstructure evolutions contribute to the cyclic softening and hardening.

Abstract: Ti6Al4V alloy is promising biology material with outstanding properties of low density, high specific strength, and exceptional corrosion resistance. However, one of its disadvantages is the poor tribological property. In this paper Mo-N hard surface modification layers were formed on Ti6Al4V at 900°C substrate temperature by plasma reactive sputtering. The flux ratio N2/Ar is an important parameter and its influence on the composition, structure and hardness of the Mo-N layers is studied. The Mo-N layers are duplex layers, composed of diffusing layer and surface coating. The component of Mo and N elements in the diffusing layer changes gradually which can enhance the load-bearing capacity to the coating and ensure the durability of the coating. With the increase of the flux ratio N2/Ar, the content of N element in the Mo-N layers increases. The Mo-N layers were polycrystalline γ- Mo2N with (200) plane oriented parallel to the substrate surface. The surface hardness of the formed layers is in the range HK1330-1430. The hardness of the Mo-N layers increases with the increase of the flux ratio N2/Ar and the reason is that the content of N element in the Mo-N layers increases.

Abstract: The Nano-HA powder were synthesized by chemical precipitation with Ca(H2PO4)2•H2O and Ca (OH)2 and porous HA was prepared by sintering with magnesium as pore-creator. Nano-HA powder and porous HA were characterized by wide angle X-ray diffraction, transmission electron microscopy(TEM), scanning electron microscopy (SEM), SEM in combination with energy dispersive X-ray spectroscopy (SEM-EDX), X-ray photoelectron spectroscopy. The experimental results show that HA powder synthesized by chemical precipitation is nanometer powder. Magnesium was ideal pore-creator for preparation of porous materials. The grain size of porous HA was sub-micron and MgO which existed in the grain boundary of HA as a second phase particles that played the roles of inhibiting the HA grain growth.

Abstract: Biomineralization on surface-modified poly (ε-caprolactone) (PCL) through an alternate soaking process was investigated. A poly(vinyl alcohol) (PVA)-coating on PCL substrate prepared by repetitive adsorption/ drying in an aqueous PVA solution could accelerate hydroxyapatite (HA) deposition while PVA-PCL soaked in aqueous solutions containing Ca2+ and PO3-4 ions alternately. Fourier transform infrared (FTIR) and X-ray diffraction of the apatite verified the formed hydroxyapatite in these processes exhibited a close resemblance with calcium phosphates (HA, Ca10(PO4)6(OH)2). It was also found that the amount of HA formed increased with both soaking with both soaking cycles and deposition amount of PVA on PCL. This study suggested that simple PVA coating on PCL substrate could serve as a novel way to accelerated HAP formation via alternating soaking.

Abstract: Highly-ordered titania nanotube electrodes were fabricated by electrochemical anodization of pure titanium foil in potassium fluoride electrolyte. The nanotube electrodes were then annealed at different temperatures (300°C，500°C and 600°C) in air for 3 hours. The morphology and crystallinity of nanotube arrays were studied by SEM and XRD. The electrochemical properties of titania nanotube electrodes before and after annealed under different temperatures were investigated by means of cyclic voltammetry with 10mM K3[Fe(CN)6] as an electrolyte at a sweep rate of 0.1V/s.A pair of oxidation/reduction peaks was observed during the test. The results show that the higher annealing temperature, the larger oxidation/reduction peak separation. Photocurrent response was also measured in 0.01M Na2SO4 under the UV-Vis illumination.

Abstract: The Mo surface modified layer on Ti6Al4V alloy was obtained by the plasma surface alloying technique. The structure and composition of the Mo modified Ti6Al4V alloy was investigated by X-ray diffraction (XRD) and glow discharge optical emission spectroscopy (GDOES). The Mo modified layer contains Mo coating on subsurface and diffusion layers between the subsurface and substrate. The X- ray diffraction analysis of the Mo modified Ti6Al4V alloy reveals that the outmost surface of the Mo modified Ti6Al4V alloy is composed of pure Mo. The electrochemical corrosion performance of the Mo modified Ti6Al4V alloy in 25°C Hank’s solution was investigated and compared with that of Ti6Al4V alloy. Results indicate that the self-corroding electric potential and the corrosion-rate of the Mo modified Ti6Al4V alloy are higher than that of Ti6Al4V alloy in 25°C Hank’s solution.

Abstract: A novel two-step foaming process has been developed to prepare the porous titanium implant. By using H2O2 and stearic acid as foaming reagent ordinally, a foamed structure with an open, interconnected pore morphology was obtained. The mechanical property was determined by compressive test. In vitro study was conducted to evaluate the ability of the porous titanium to support the growth and differentiation of Human osteosarcoma cell line MG63. The results show that the porous titanium has better interconnection compared to that obtained by traditional slurry foaming and its compressive strength and Young’s modulus were approximate 23.6 MPa and 2.1 GPa, respectively. Cell culture experiment results indicate that the porous titanium has good biocompatibility and acid-alkali treatment facilitates the adherence and proliferation of cells.

Abstract: Magnesium alloys are considered as candidate materials for biodegradable implants. However, the key issue is that they corrode too fast in physiological environment. The aim of this study is to investigate the effect of microstructure and texture of magnesium alloys on their corrosion resistance. Magnesium alloy AZ31 extruded rod, hot rolled sheet and extruded sheet with different initial microstructure and texture were prepared. Then they were immersed in conventional simulated body fluid (SBF) for several days for corrosion evaluation. The corrosion products and precipitates on their surfaces were examined by scanning electron microscopy (SEM). The preliminary results showed that the initial microstructure and texture of AZ31 alloys has considerable effect on the weight loss rate of the alloys, suggesting that it is possible to enhance the corrosion resistance of AZ31 alloys through tailoring the microstructure and texture of the alloys.

Abstract: The aims of this study were to quantify the elements released from a Ni-Cr dental alloy in artificial saliva and saline solution and to test whether immersion time and different immersion media are factors influencing elemental release from a nickel-based dental alloy. Standard sized Ni-Cr alloy castings were put into different immersion media (saline solution or artificial saliva) randomly. Inductively coupled plasma atomic emission spectroscopy (ICP-AES) was used to test the elemental release of the alloy at 1, 3, 7, 30 and 82 days. The surfaces of alloy were observed by scanning electron microscope (SEM). It has been found that except Ni in the artificial saliva, all the other elements remained unchanged statistically in the first week after initial release. The accumulative elemental release showed Cr in both media and Ni in the artificial saliva increased statistically in 30-day period and Ni, Cr, Be, Al, Co increased significantly in 82 days, while Mo in both media and Co in artificial saliva were not yet detected. The total mass of elements released in saline solution was greater than that in artificial saliva. Conclusion: With the immersion time increasing，more kinds of elements were released and more amount of elements released was detected in solutions. The alloy was prone to corrosion in saline solution than in artificial Saliva.