Phase transformation behaviour of porous NiTi alloys fabricated by capsule-free hot isostatic pressing

Differential scanning calorimetry (DSC) was used to characterize the phase transformation behaviour of porous Ni50Ti50 alloys fabricated by capsule-free hot isostatic pressing (CF-HIP) with different cold compaction pressures. Experimental results reveal that a multi-stage martensitic transformation (MST) exists in the sintered porous NiTi alloys on cooling while the reverse transformation upon heating is either a single or two-stage phase transformation. The DSC thermal analysis indicates that the cold compaction pressure has great effect on the subsequent transformation temperatures. Generally, the phase transformation temperatures of porous NiTi alloys with lower cold compaction pressure are higher than those compacted with higher pressure. With increase in the annealing time, the transformation temperatures increase quickly when the cold compaction pressure was 150MPa. On the other hand, the transformation temperatures change only slightly when the cold compaction pressure was varied from 300MPa to 400MPa. These phenomena can be attributed to the combined effect of larger plastic deformation with higher dislocations density produced by cold compaction and the precipitation of the second phase in the porous NiTi alloys.published_or_final_versio

Corrosion products and mechanism on NiTi shape memory alloy in physiological environment

Despite many investigations on the corrosion behavior of NiTi shape memory alloys (SMAs) in various simulated physiological solutions by electrochemical measurements, few have reported detailed information on the corrosion products. In the present study, the structure and composition of the corrosion products on NiTi SMAs immersed in a 0.9% NaCl physiological solution are systematically investigated by scanning electron microscopy (SEM), x-ray energy dispersion spectroscopy (EDS), and x-ray photoelectron spectroscopy (XPS). It is found that attack by Cl - results in nickel being released into the solution and decrease in the local nickel concentration at the pitting sites. The remaining Ti reacts with dissolved oxygen from the solution to form titanium oxides. After longterm immersion, the corrosion product layer expands over the entire surface and XPS reveals that the layer is composed of TiO 2, Ti 2O3, and TiO with relatively depleted Ni. The growth rate of the corrosion product layer decreases with immersion time, and the corrosion product layer is believed to impede further corrosion and improve the biocompatibility of NiTi alloy in a physiological environment. It is found that the release rate of nickel is related to the surface structure of the corrosion product layer and immersion time. A corrosion mechanism is proposed to explain the observed results. © 2010 Materials Research Society.published_or_final_versio

Biomimetic deposition of apatite on surface chemically modified porous NiTi shapememory alloy

Porous NiTi shape memory alloy (SMA) with 48% porosity and an average pore size of 50800 μm was synthesized by capsule-free hot isostatic pressing (CF-HIP). To enhance the surface bioactivity, the porous NiTi SMA was subjected to H"2O"2 and subsequent NaOH treatment. Scanning electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy analyses revealed that a porous sodium titanate (Na"2TiO"3) film had formed on the surface of the porous NiTi SMA. An apatite layer was deposited on this film after immersion in simulated body fluid at 37°C, while no apatite could be found on the surface of the untreated porous NiTi SMA. The formation of the apatite layer infers that the bioactivity of the porous NiTi SMA may be enhanced by surface chemical treatment, which is favorable for its application as bone implants. © 2008 World Scientific Publishing Company.postprin

The mechanical and biological properties of a novel biodegradable polycaprolactone-magnesium porous scaffold for bone tissue engineering

Session: Biomaterial-based Tissue Regeneration: abstract no. 150INTRODUCTION: Bone tissue engineering offers an alternative solution to the traditional methods of bone replacement including allografts and autografts. Tissue grafting has been used since 1660s1. However, there are concerns of tissue shortage and transmission of disease. Therefore, the use of scaffold is the most common technique and good approach to regenerate diseased or damaged bone tissue. Polycaprolactone (PCL) is one of the suitable candidates to be used as the scaffold material since it has a low degradation rate when compared with other polymers. However, the low mechanical strength and intrinsic …postprintThe 2010 North America Conference of the Tissue Engineering and Regenerative Medicine International Society (TERMIS-NA 2010), Orlando, FL., 5-8 December 2010

Enhanced cell adhesion and proliferation on dual plasma modified titanium surfaces

Session: Biomaterials Fabrication and Synthesis: abstract no. 47INTRODUCTION: Ti-6Al-4V is widely used in present orthopedic applications, owing to a combination of good mechanical properties and excellent corrosion resistance. However, long-term success of Ti-6Al-4V implants and the completeness of their osteointegration still need to be addressed [1]. Since the biofunctionality of the implant is strongly affected by its surface characteristics, to promote osteointegration, considerable efforts have focused on modifying the surface of the implants. Alternatively, surface modification using plasma immersion ion implantation (PIII) has been developed in order to incorporate new biofunctional groups onto titanium alloy surfaces [2]. The present study aims at investigating the impact of carbon-nitrogen (Car-Nit) dual plasma surface treatment on …postprintThe 2010 North America Conference of the Tissue Engineering and Regenerative Medicine International Society (TERMIS-NA 2010), Orlando, FL., 5-8 December 2010

Effects of long pulse width and high pulsing frequency on surface superhydrophobicity of polytetrafluoroethylene in quasi-direct-current plasma immersion ion implantation

Long pulse, high frequency quasi-direct-current (dc) oxygen plasma immersion ion implantation (PIII) is utilized to create a superhydrophobic polytetrafluoroethylene (PTFE) surface with a water contact angle of over 150°. This technique allows the use of a high duty cycle without deleterious effects such as extensive sample heating encountered in conventional PIII. Scanning electron microscopy images review submicrometer-nanometer structures on the PTFE surface after long pulse, high frequency PIII indicative of ion implantation. On the other hand, plasma modification is the dominant effect in short pulse, low frequency PIII. Quasi-dc PIII is demonstrated to offer adjustable synergistic plasma and ion beam effects. © 2009 American Institute of Physics.published_or_final_versio

An economical fabrication technique for SIMOX using plasma immersion ion implantation

Buried oxide layers in Si were fabricated using non-mass analyzed plasma immersion ion implantation (PIII). The implantation was carried out by applying a large negative bias to a Si wafer immersed in an oxygen plasma and a dose of 3×1017 cm-2 of oxygen was implanted in about three minutes. Cross section transmission electron microscopy (XTEM) and Rutherford backscattering spectrometry (RES) were used to characterize the wafers. Our results indicate that a continuous buried oxide layer with a single crystal silicon overlayer was synthesizedpublished_or_final_versio

Engineered magnesium-based resorbable porous scaffold for bone tissue engineering

INTRODUCTION: Bone tissue engineering offers an alternative solution to the traditional methods of bone replacement including allografts and autografts [1]. Although these biological materials possess good osteoinductive and osteoconductive properties, both of them have limitations in terms of the availability, donor site morbidity and the risk of disease transmission with the use of allografts [2]. Therefore, the use of synthetic scaffold is the most common technique and good approach to regenerate diseased or damaged bone tissue. An ideal bone substitute should possess certain properties including ...postprin

Low modulus novel bone substitutes for osteoporotic vertebral fracture management

Oral presentationpublished_or_final_versioneCM XIII - Bone Fixation, Repair & Regeneration, Davos Platz, Switzerland, 24-26 June 2012. In European Cells & Materials, 2012, v. 24 n. Suppl. 1, p. 1

Magnesium plasma modified bone allograft for Large Bone Defect Treatment

Invited TalkBone allograft is the most widely accepted approach in treating patients suffering from large segmental bone defect regardless of the advancement of synthetic bone substitutes[ I, 2]. However, the long-term complications of allograft application in term of delayed union or even nonunion were reported due to the stringent sterilization process prior to clinical implantation[3, 4]. Our previous studies demonstrated that the incorporation of magnesium ions (Mg2+) into biomaterials could …postprin