Preparation, Surface Properties and Biological Activity of the Composite of Poly (lactide-co-glycolide) and Bioglass Nanoparticles Surface Grafted with Poly(L-lactide)

SiO2-CaO-P2O5 gel bioglass (BG) nanoparticles with the diameter of 40 nm were synthesized by sol-gel approach. The surface of BG nanoparticles was grafted through the ring-open polymerization of the L-lactide to yield poly (L-lactide) (PLLA) grafted gel particle (PLLA-g-BG). The PLLA-g-BG was further blended with poly(lactide-co-glycolide) (PLGA) to prepare the nanocomposites of PLLA-g-BG/PLGA with the various blend ratios of two phases. PLLA-g-BG accounted 10%, 20% and 40% in the composite, respectively. TGA, ESEM and EDX were used to analyze the graft ratio of PLLA-g-BG, the dispersion of nano-particles and the surface elements of the composites respectively. The rabbit osteoblasts were seeded and cultured on the thin films of composites in vitro. The cell adhesion, spreading and growth of osteoblasts were analyzed with FITC staining, NIH Image J software and MTT assay. The change of cell cycle was monitored by flow cytometry (FCM). The results demonstrated that the Surface modification of BG with PLLA could significantly improve the dispersing of the particles in the matrix of PLGA. The nanocomposite with 20% PLLA-g-BG exhibited superior surface properties, including roughness and plenty of silicon, calcium and phosper, to enhance the adhesion, spreading and proliferation of osteoblasts.

Novel coatings for hard tissue implants

A novel deposition process named CoBlastTM, based on grit blasting technology, has been used to deposit hydroxyapatite (HA) onto titanium (Ti) metal using a dopant/abrasive regime. The various powders (HA powder, apatitic abrasives) and the treated substrates were characterised for chemical composition, coating coverage, crystallinity and topography including surface roughness. The surface roughness of the HA surfaces could be altered using apatitic abrasives of different particle sizes. Compared to the standard plasma spraying process, the CoBlast surface produced excellent coating adhesion, lower dissolution, higher levels of mechanical and chemical stability in stimulated body fluid (SBF). Enhanced viability of osteoblastic cells was also observed on the CoBlast HA surfaces compared to the microblast and untreated Ti as well as the plasma HA coating. CoBlast offers an alternative to the traditional methods of coating HA implants with added versatility. Apatites substituted with antimicrobial metals can also be deposited to add functionality to HA coatings without cytotoxicty. The potential use of these coatings as an infection preventing strategy for application on hard tissue implants was assessed in vitro and also in vivo. Surface physicochemical properties and morphology were determined in addition to surface cytocompatibility assessments using a MG-63 osteoblast cell line. The antibacterial potential of the immobilised metal ion on the surface and the eluted ion to a lesser extent, contributed to the anticolonising behaviour of the surfaces against a standard bacteria strain (S. aureus) as well as a number of clinically relevant strains (MRSA, MSSA and S. epidermis). The results revealed that the surfaces coated with silver substituted apatites (AgA) outperformed the other apatites examined (apatites loaded with Zn, Sr and both Ag and Sr ions). Assessment of bacterial adherence on coated K-wires following subcutaneous implantation in a nude mouse infection model (S. aureus) for two days demonstrated that the 12% wt surface outperformed the 5% wt AgA coating. Lower inflammatory responses were activated with the insertion of the Ag loaded K-wires with a localised infection at the implantation site noted over the two day study period. These results indicated that the AgA coating on the surface of orthopaedic implants demonstrate good biocompatibility whilst inhibiting bacterial adhesion and colonising of the implant surface.

Determination of the degree of dissociation in an inductively coupled hydrogen plasma using optical emission spectroscopy and laser diagnostics

Gas temperature is of major importance in plasma based surface treatment, since the surface processes are strongly temperature sensitive. The spatial distribution of reactive species responsible for surface modification is also influenced by the gas temperature. Industrial applications of RF plasma reactors require a high degree of homogeneity of the plasma in contact with the substrate. Reliable measurements of spatially resolved gas temperatures are, therefore, of great importance. The gas temperature can be obtained, e.g. by optical emission spectroscopy (OES). Common methods of OES to obtain gas temperatures from analysis of rotational distributions in excited states do not include the population dynamics influenced by cascading processes from higher electronic states. A model was developed to evaluate this effect on the apparent rotational temperature that is observed. Phase resolved OES confirmed the validity of this model. It was found that cascading leads to higher apparent temperatures, but the deviation (~25 K) is relatively small and can be ignored in most cases. This analysis is applied to investigate axially and radially resolved temperature profiles in an inductively coupled hydrogen RF discharge.

Performance and wear of coated carbide drill in machining of carbon fibre reinforced composite/titanium stack

In this research we investigate the performance of drilling process in carbon fibre reinforced composite (CFC) material, titanium alloy and the hybrid stack of these two materials, using coated carbide drill bit. We study the effect of the process parameters such as the feed rate and speed on the induced forces and torques, also on the wear of drill and surface roughness of the holes. In the composite material the percentage of surface damage in both drilling CFC on its own and drilling in stack form is estimated. Also, the effect of worn drill on the surface damage is identified. In the titanium, the burr formation in stack and non-stack form is investigated. The wear of the drill results in increased forces and torques required for drilling. This increases the surface delaminations substantially at the entrance in drilling of CFC. However, the surface roughness of the holes reduces with the wear of the drill in CFC drilling. Also, the surface delamination and surface roughness of the holes in the CFC whilst drilled in hybrid form reduces significantly. This is despite the increase of the forces and torques required in drilling CFC in stack form. Copyright © 2012 Inderscience Enterprises Ltd.

Hole-making Process and Its impacts on the Fatigue Response of Ti -6Al-4V Aircraft Alloy

In this work, the impact of conventional drilling and helical milling processes on the fatigue response Ti-6Al-4V (grade 5 titanium alloy) has been presented. Results show that the work pieces produced by helical milling has a 119% longer fatigue life compared with the drilled pieces under dry machining condition, and a 96% longer fatigue life for helical milled piece under lubricated condition. The use of cutting fluid has led to longer fatigue lives – 15% longer for drilling and 3% longer for helical milling. Other results such as the machined surface roughness, alloy surface and sub-surface microstructures have also been studied in details.

Modifications of Surface Properties of Beta Ti by Laser Surface Treatment

β -type Ti-alloy is a promising biomedical implant material as it has a low Young’s modulus but is also known to have inferior surface hardness. Various surface treatments can be applied to enhance the surface hardness. Physical vapour deposition (PVD) and chemical vapour deposition (CVD) are two examples of this but these techniques have limitations such as poor interfacial adhesion and high distortion. Laser surface treatment is a relatively new surface modification method to enhance the surface hardness but its application is still not accepted by the industry. The major problem of this process involves surface melting which results in higher surface roughness after the laser surface treatment. This paper will report the results achieved by a 100 W CW fiber laser for laser surface treatment without the surface being melted. Laser processing parameters were carefully selected so that the surface could be treated without surface melting and thus the surface finish of the component could be maintained. The surface and microstructural characteristics of the treated samples were examined using X-ray diffractometry (XRD), optical microscopy (OM), 3-D surface profile & contact angle measurements and nano-indentation test.

Effect of the interaction layer on the mechanical properties of Ti–6Al–4V alloy castings

The interaction between the face coat material of a mould and the titanium alloy will cause oxygen penetration during the casting and solidification process, resulting in the formation of an α-case interaction layer at the metal surface that influences the mechanical properties of the cast components. In this study, the influence of α-case thickness and loading positions in a Ti–6Al–4V (Ti64) alloy on metal hardness, impact properties and bending strength was investigated. The results showed that the metal surface α-case consisted of many coarse α laths which has a higher hardness than metal matrix. The mechanical properties of the alloy are influenced by the α-case. The alloy bending strength was observed to have changed linearly with the thickness of sample.

Artificial antibodies for troponin T by its imprinting on the surface of multiwalled carbon nanotubes: Its use as sensory surfaces

A novel artificial antibody for troponin T (TnT) was synthesized by molecular imprint (MI) on the surface of multiwalled carbon nanotubes (MWCNT). This was done by attaching TnT to the MWCNT surface, and filling the vacant spaces by polymerizing under mild conditions acrylamide (monomer) in N,N′-methylenebisacrylamide (cross-linker) and ammonium persulphate (initiator). After removing the template, the obtained biomaterial was able to rebind TnT and discriminate it among other interfering species. Stereochemical recognition of TnT was confirmed by the non-rebinding ability displayed by non-imprinted (NI) materials, obtained by imprinting without a template. SEM and FTIR analysis confirmed the surface modification of the MWCNT. The ability of this biomaterial to rebind TnT was confirmed by including it as electroactive compound in a PVC/plasticizer mixture coating a wire of silver, gold or titanium. Anionic slopes of 50 mV decade−1 were obtained for the gold wire coated with MI-based membranes dipped in HEPES buffer of pH 7. The limit of detection was 0.16 μg mL−1. Neither the NI-MWCNT nor the MWCNT showed the ability to recognize the template. Good selectivity was observed against creatinine, sucrose, fructose, myoglobin, sodium glutamate, thiamine and urea. The sensor was tested successfully on serum samples. It is expected that this work opens new horizons on the design of new artificial antibodies for complex protein structures.

Modification and Analysis of Group-13-Nitride Semiconductor Surfaces: Influence of Adsorbates on Device Characteristics and Processing

Im Rahmen dieser interdisziplinären Doktorarbeit wird eine (Al)GaN Halbleiteroberflächenmodifikation untersucht, mit dem Ziel eine verbesserte Grenzfläche zwischen dem Material und dem Dielektrikum zu erzeugen. Aufgrund von Oberflächenzuständen zeigen GaN basierte HEMT Strukturen üblicherweise große Einsatzspannungsverschiebungen. Bisher wurden zur Grenzflächenmodifikation besonders die Entfernung von Verunreinigungen wie Sauerstoff oder Kohlenstoff analysiert. Die nasschemischen Oberflächenbehandlungen werden vor der Abscheidung des Dielektrikums durchgeführt, wobei die Kontaminationen jedoch nicht vollständig entfernt werden können. In dieser Arbeit werden Modifikationen der Oberfläche in wässrigen Lösungen, in Gasen sowie in Plasma analysiert. Detaillierte Untersuchungen zeigen, dass die inerte (0001) c-Ebene der Oberfläche kaum reagiert, sondern hauptsächlich die weniger polaren r- und m- Ebenen. Dies kann deutlich beim Defektätzen sowie bei der thermischen Oxidation beobachtet werden. Einen weiteren Ansatz zur Oberflächenmodifikation stellen Plasmabehandlungen dar. Hierbei wird die Oberflächenterminierung durch eine nukleophile Substitution mit Lewis Basen, wie Fluorid, Chlorid oder Oxid verändert, wodurch sich die Elektronegativitätsdifferenz zwischen dem Metall und dem Anion im Vergleich zur Metall-Stickstoff Bindung erhöht. Dies führt gleichzeitig zu einer Erhöhung der Potentialdifferenz des Schottky Kontakts. Sauerstoff oder Fluor besitzen die nötige thermische Stabilität um während einer Silicium-nitridabscheidung an der (Al)GaN Oberfläche zu bleiben. Sauerstoffvariationen an der Oberfläche werden in NH3 bei 700°C, welches die nötigen Bedingungen für die Abscheidung darstellen, immer zu etwa 6-8% reduziert – solche Grenzflächen zeigen deswegen auch keine veränderten Ergebnisse in Einsatzspannungsuntersuchungen. Im Gegensatz dazu zeigt die fluorierte Oberfläche ein völlig neues elektrisches Verhalten: ein neuer dominanter Oberflächendonator mit einem schnellen Trapping und Detrapping Verhalten wird gefunden. Das Energieniveau dieses neuen, stabilen Donators liegt um ca. 0,5 eV tiefer in der Bandlücke als die ursprünglichen Energieniveaus der Oberflächenzustände. Physikalisch-chemische Oberflächen- und Grenzflächenuntersuchung mit XPS, AES oder SIMS erlauben keine eindeutige Schlussfolgerung, ob das Fluor nach der Si3N4 Abscheidung tatsächlich noch an der Grenzfläche vorhanden ist, oder einfach eine stabilere Oberflächenrekonstruktion induziert wurde, bei welcher es selbst nicht beteiligt ist. In beiden Fällen ist der neue Donator in einer Konzentration von 4x1013 at/cm-2 vorhanden. Diese Dichte entspricht einer Oberflächenkonzentration von etwa 1%, was genau an der Nachweisgrenze der spektroskopischen Methoden liegt. Jedoch werden die elektrischen Oberflächeneigenschaften durch die Oberflächenmodifikation deutlich verändert und ermöglichen eine potentiell weiter optimierbare Grenzfläche.

Effect of mechanical coating with Ni and Ni-5% Al on the structure and electrochemical properties of the Mg-50% Ni alloy

The Mg-Ni metastable alloys (with amorphous or nanocrystalline structures) are promising candidates for anode application in nickel-metal hydride rechargeable batteries due to its large hydrogen absorbing capacity, low weight, availability, and relative low price. In spite of these interesting features, improvement on the cycle life performance must be achieved to allow its application in commercial products. In the present paper, the effect of mechanical coating of a Mg-50 at.% Ni alloy with Ni and Ni-5 at.% Al on the structure, powder morphology, and electrochemical properties is investigated. The coating additives, Mg-Ni alloy and resulting nanocomposites (i.e., Mg-Ni alloy + additive) were investigated by means of X-ray diffraction and scanning electron microscopy. The Mg-Ni alloy and nanocomposites were submitted to galvanostatic cycles of charge and discharge to evaluate their electrode performances. The mechanical coating with Ni and Ni-5% Al increased the maximum discharge capacity of the Mg-Ni alloy from of 221 to 257 and 273 mA h g(-1), respectively. Improvement on the cycle life performance was also achieved by mechanical coating.

Porous TiNbZr alloy scaffolds for biomedical applications

In the present study, porous Ti–10Nb–10Zr alloy scaffolds with different porosities were successfully fabricated by a ‘‘space-holder” sintering method. By the addition of biocompatible alloying elements the porous TiNbZr scaffolds achieved significantly higher strength than unalloyed Ti scaffolds of the same porosity. In particular, the porous TiNbZr alloy with 59% porosity exhibited an elastic modulus and plateau stress of 5.6 GPa and 137 MPa, respectively. The porous alloys exhibited excellent ductility during compression tests and the deformation mechanism is mainly governed by bending and buckling of the struts. Cell cultures revealed that SaOS2 osteoblast-like cells grew on the surface and inside the pores and showed good spreading. Cell viability for the porous scaffold was three times higher than the solid counterpart. The present study has demonstrated that the porous TiNbZr alloy scaffolds are promising scaffold biomaterials for
bone tissue engineering by virtue of their appropriate mechanical properties, highly porous structure and excellent biocompatibility.

Study on the role of stearic acid and ethylene-bis-stearamide on the mechanical alloying of a biomedical titanium based alloy

The present study examines the influence of different contents and types of process control agent (PCA), i.e., stearic acid (SA) and ethylene-bis-stearamide (EBS), on the microstructural evolution and characteristics of Ti-16Sn-4Nb (wt pct) alloy powders and bulk samples. The characterization of the powders and bulk samples was carried out by using chemical analysis, optical microscopy, scanning electron microscopy (SEM) combined with energy-dispersive spectrometry (EDS), and X-ray diffractometry. Results indicated that the powder recovered from the ball milling containers increased with increasing amounts of SA and EBS. Furthermore, adding more SA or EBS to the powder mixture resulted in a considerably smaller particle size, with a flaky-shaped morphology for the given ball milling time. Also, a slightly higher effectiveness was found for EBS when compared to SA. Meanwhile, the addition of both SA and EBS led to a delay in the alloy formation during mechanical alloying (MA) and caused contamination of the material with mainly carbon (C) and oxygen (O). An optimum amount of 1 wt pct PCA led to a good balance between cold welding and fracturing, and thus favored the formation of the titanium alloy. The microstructural observation of the bulk alloy showed a homogeneous distribution of fine Nb-rich ß-phase colonies within the α-Ti matrix with the addition of PCA less than 1 wt pct.

Biomimetic porous titanium scaffolds for orthopaedic and dental applications

The development of artificial organs and implants for replacement of injured and diseased hard tissues such as bones, teeth and joints is highly desired in orthopedic surgery. Orthopedic prostheses have shown an enormous success in restoring the function and offering high quality of life to millions of individuals each year. Therefore, it is pertinent for an engineer to set out new approaches to restore the normal function of impaired hard tissues.

Over the last few decades, a large number of metals and applied materials have been developed with significant improvement in various properties in a wide range of medical applications. However, the traditional metallic bone implants are dense and often suffer from the problems of adverse reaction, biomechanical mismatch and lack of adequate space for new bone tissue to grow into the implant. Scientific advancements have been made to fabricate porous scaffolds that mimic the architecture and mechanical properties of natural bone. The porous structure provides necessary framework for the bone cells to grow into the pores and integrate with host tissue, known as osteointegration. The appropriate mechanical properties, in particular, the low elastic modulus mimicking that of bone may minimize or eliminate the stress-shielding problem. Another important approach is to develop biocompatible and corrosion resistant metallic materials to diminish or avoid adverse body reaction. Although numerous types of materials can be involved in this fast developing field, some of them are more widely used in medical applications. Amongst them, titanium and some of its alloys provide many advantages such as excellent biocompatibility, high strength-to-weight ratio, lower elastic modulus, and superior corrosion resistance, required for dental and orthopedic implants. Alloying elements, i.e. Zr, Nb, Ta, Sn, Mo and Si, would lead to superior improvement in properties of titanium for biomedical applications.

New processes have recently been developed to synthesize biomimetic porous titanium scaffolds for bone replacement through powder metallurgy. In particular, the space holder sintering method is capable of adjusting the pore shape, the porosity, and the pore size distribution, notably within the range of 200 to 500 m as required for osteoconductive applications. The present chapter provides a review on the characteristics of porous metal scaffolds used as bone replacement as well as fabrication processes of porous titanium (Ti) scaffolds through a space holder sintering method. Finally, surface modification of the resultant porous Ti scaffolds through a biomimetic chemical technique is reviewed, in order to ensure that the surfaces of the scaffolds fulfill the requirements for biomedical applications.

Use of low-level plasma for enhancing the shrink resistance of wool fabric treated with a silicone polymer

This study examines the effects of an atmospheric pressure plasma (APP) pre-treatment on the shrink resistance of wool fabric treated subsequently, by the pad/dry method, with an aqueous emulsion of the amino-functional polydimethylsiloxane, SM 8709. Optimal shrink resistance (with no impairment of fabric handle) was obtained after a low-level plasma treatment (1-3 s exposure time), using 5% of the polymer emulsion. Higher levels of silicone polymer could be used to achieve shrink resistance in the absence of a plasma pre-treatment, but the fabric handle would be adversely affected. X-ray photoelectron spectroscopy (XPS) studies showed that the bulk of the covalently bound surface lipid layer was removed after a plasma exposure time of 30 s. For treatment times of 3 s or less, however, the removal was incomplete, suggesting that optimum shrink resistance (after treatment with the silicone polymer) was associated with the modification of the surface layer rather than its complete destruction. Scanning electron micrographs (SEMs) revealed that the plasma pre-treatment did not lead to any physical modifications (such as smoothening of the scale edges), even for long exposure times, and had no significant impact on the extent or nature of the inter-fibre bonding of the polymer. Confocal microscopy showed uniform spread of polymer on single fibres. It is concluded that the main impact of the plasma pre-treatment was to enhance the distribution of polymer both on and between fibres and to improve adhesion of polymer to the fibre.