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No description available.

Regarding the higher demand of the total joint replacement (TJR) and revision surgeries in recent years, an implant material should provide much longer lifetime without failure. Nickel titanium (NiTi) is the most popular shape memory alloy in the industry, especially in medical devices due to its unique mechanical properties such as pseudo-elasticity, damping capacity, shape memory and good biocompatibility. However, concerns of nickel ion release of this alloy still exist if it is implanted for a prolonged period of time. Nickel is well known for the possibility of causing allergic response and degeneration of muscle tissue as well as being carcinogenic for the human body beyond a certain threshold. Therefore, drastically improving the surface properties (e.g. wear resistance) of NiTi is a vital step for its adoption as orthopaedic implants. To overcome the above-mentioned risks, different surface treatment techniques have been proposed and investigated, such as Physical Vapour Deposition (PVD), Chemical Vapour Deposition (CVD), ion implantation, plasma spraying, etc. Yet all of these techniques have similar limitations such as high treatment temperature, poor metallurgical bonding between coated film and substrate, and lower flexibility and efficiency. As a result, laser gas nitriding would be an ideal treatment method as it could overcome these drawbacks. Moreover, the shape memory effect and pseudo-elasticity of NiTi from a reversible phase transformation between the martensitic phase and the austenitic phase are very sensitive to heat. Hence, NiTi implant is subjected to the following provisions of the thermo-mechanical treatment process, and this implant provides desired characteristics. It is important to suggest a surface treatment, which would not disturb the original build-in properties. As a result, the low-temperature methods for substrate have to be employed on the surface of NiTi. This present study aims to investigate the feasibility of applying diffusion laser gas nitriding technique to improve the wettability and wear resistance of NiTi as well as establish the optimization technique. The current report summaries the result of laser nitrided NiTi by continuous-wave (CW) fibre laser in nitrogen environment. The microstructure, surface morphology, wettability, wear resistance of the coating layer has been analysed using scanning electron microscopy (SEM), X-ray diffractometry (XRD), sessile drop technique, 3-D profile measurement and reciprocating wear test. The resulting surface layer is free of cracks, and the wetting behaviour is better than the bare NiTi. The wear resistance of the optimised nitride sample with different hatch patterns is also evaluated using reciprocating wear testing against ultra-high-molecular-weight polyethylene (UHMWPE) in Hanks’ solution. The results indicate that the wear rates of the nitride samples and the UHMWPE counter-part were both significantly reduced. It is concluded that the diffusion laser gas nitriding is a potential low-temperature treatment technique to improve the surface properties of NiTi. This technique can be applied to a femoral head or a bone fixation plates with relatively large surface area and movable components.

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The unlubricated sliding wear behaviour of gas nitrided, plasma nitrided, and ferritic nitrocarburized BS970,905M39 (EN41B) steels was investigated systematically from an engineering point of view. Commercial nitriding processes were employed, and the wear studies were carried out using a pin-on-disc machine over a wide range of sliding speeds and applied loads. The worn specimens and wear debris were examined by several techniques; including optical and electron microscopy and X-ray analysis. A sharp wear rate transition between mild and severe regimes was identified by varying the load for both untreated and gas nitrided steels. The wear rate was reduced by gas nitriding by up to two orders of magnitude, depending on the sliding condition. Moreover, gas nitriding expanded the mild wear region toward higher loads and sliding speeds. In the mild regime an oxidative wear mechanism operated, contrasting with the metallic wear in the severe regime. Wear maps for untreated and gas nitrided steels have been constructed, which show the dominant regimes of the wear mechanisms. A "wear-face-limited" gas nitrided pin test showed that the benefit of the treatment was lost once the effective surface layer was completely worn away. It is suggested that hardness has a crucial role in determining the wear rate through nitrided diffusion layers. A thick and porous compound layer produced by gas nitriding showed a poor wear behaviour owing to its brittleness, while a thin nitrocarburized E-Fe3N compound layer exhibited a low wear rate. There was no significant difference between the nitride steels in terms of transition load and wear rate. However, the wear lives of the nitrided layers were dependent on their case depth. Severe wear should be avoided in engineering component design, and operating conditions should ensure that only mild wear occurs. Both the hardness profiles and the cost performance of nitriding processes should be considered in the selection of nitriding treatments.

OBJECTIVES: The aim of this in-vitro study is to evaluate the effect of different zirconia surface pretreatments, different cement types and the effect of accelerated aging on the adherence of bonding cements to zirconia. MATERIALS AND METHODS: 64 zirconia 3Y-TZP tapered rings were pressed from TZ-3YSB-E zirconia powder, pre-treated with different surface treatments, then cemented to titanium abutment pins using 8 different cements: Maxcem Elite chroma (Kerr), TheraCem (Bisco), RelyX Unicem2 (3M ESPE), Multilink Automix (Ivoclar Vivadent), Panavia SA Cement Plus (Kuraray), Ceramir C&B (Doxa), CemEZ Universal (Zest Dental), and Bifix SE (VOCO). The partitally sintered zirconia specimens were divided according to design of experment (DOE). Zirconia surface treatments: 1) control group with no surface treatment, 2) airborne particle abrasion of fully sintered zirconia ring (FS-APA50), 3) airborne particle abrasion of partially sintered zirconia (PS-APA50), 4) tribochemical silica coating of fully sintered zirconia (FS-CoJet30), 5) tribochemical silica coating of partial sintered zirconia (PS-CoJet30), and 6) nano-structured alumina coating of fully sintered zirconia (NanoAl). Zirconia rings were subjected to post-treatment:1) control 24h incubation after cementing proceedure, and 2) accelerated aging . The pull-out axial tensile retention load was tested using an Instron Model 5566A. Multi factorial linear regression model (JMP Pro 15) was used for data analysis (α=0.05). RESULTS: The retention force (N) of zirconia rings to titanium abutment pins was evaluated using a pull-out test. Four key factors were investigated in this study: zirconia surface pre-treatment, cement type, post-treatment and firing effect. There was a significant effect of zirconia surface pre-treatment on retention force (nano-structured alumina coating ≥ tribochemical abrasion = airborne-particle abrasion ≥ control). There was a significant effect of cement type on retention force [Multilink AM ≥ (Cem EZ = TheraCem = Panivia SA = RelyX Unicem2 = BiFix) ≥ Ceramir CB = Maxcem Elite]. There is a significant difference in retention strength to zirconia among post-treatment effect, with accelerated aging groups achieving slightly higher bond strength than 24h water storage groups. CONCLUSIONS: Significant different retention loads were found among tested groups. Nano-structured alumina coating surface pre-treatment has significantly higher bond strength than other treatments. Some cement systems with functional monomer had significant higher bond strengths.

Lubricant-infused surfaces (LIS) are created by modifying chemical and physical properties of surfaces with aim of lowering surfaces energy where designed surface will possess liquid-repelling behaviors under low tilting angles. LIS has great potential to be applied on implantable devices due to it is stable anti-biofouling properties under fluidic environment. However, a few studies have reported that the existing research on implant surface uses complicated methods and high cost fabrication to create LIS on titanium implants. Furthermore, current limitation of LIS coatings for titanium implants lies in the lack of tissue integration and cell interaction. As a result, LIS prevents both bacteria and bone cells from adhering to the interface between implant and natural bone. This unselective blocking is problematic for titanium implants used in orthopaedic surgery when devices are required to possess tissue integration properties to facilitate long term fixation in the human body. The overall objective of this thesis is to apply LIS on titanium surfaces via a chemical modification technique and simultaneously integrate bio-functional features onto LIS to promote osteoblasts adhesion. In this project, chitosan and collagen were used to facilitate cell adhesion. To start with, three methods were used to immobilize chitosan on titanium to obtain the desired bio-functional LIS coatings: (1) LIS on top of (3-Glycidyloxypropyl)trimethoxysilane (GPTMS) crosslinked chitosan; (2) LIS on dip-coated chitosan; (3) LIS generated from GPTMS and Trichloro(1H,1H,2H,2H-perfluorooctyl) silane (TPFS) mixed silanes modified titanium surface followed by chitosan functionalization. Among these modification techniques, method (3) showed optimal anti-biofouling and osseointegration properties. Since collagen is well known for increase of cell interactions, it was used via mixed silanes functionalization method. Finally, the properties were compared with chitosan coated surfaces. During tests, surface wettability was measured, anti-biofouling properties and osseointegration was examined with staphylococcus aureus and SAOS-2 cells, respectively. We found that chitosan modified surfaces using method (3) not only significantly increased cell adhesion in comparison with the other two modification methods, but also dramatically decreased bacterial adhesion compared to collagen coated LIS on titanium. Although collagen has better cell adhesion properties than chitosan, collagen coated surface significantly decreased antibiofouling properties. In conclusion, bio-functional lubricant-infused titanium surfaces created by chemical vapor deposition (CVD) method with mixed silanes is a feasible and straightforward method to immobilize biomaterials and stabilize the lubricant layer on titanium substrates. Chitosan coated LIS on titanium prevents bacterial adhesion and simultaneously promotes targeted cell binding. / Thesis / Master of Applied Science (MASc) / Biofouling is a major issue in implantable titanium devices such as coronary stents, plates and nails, and formation of biofilm on implants can lead to infection and failure of the device. Biofilms formed by bacterial adhesion could be resistant to antibiotics and can provoke a series of inflammatory response. Recent advances in anti-biofouling surface treatment has resulted in designing supper slippery lubricant-infused omniphobic surfaces which are inspired from the Nepenthes pitcher plant. Liquid which is tethered on the surface offers a stable liquid interface, repelling both aqueous and organic liquids meanwhile showing excellent bacteria repellency. Lubricant-infused surfaces (LIS) are resistant towards biofilm formation and produce a stable surface that prevent non-specific adhesion. As a result of this repellent properties, LIS also repels the adhesion of desired biomolecules and cells such as osteoblasts, bone cells and growth factors which are essential factors for bone recovery at the implant-bone interface. Our motivation in this thesis is to create a lubricant-infused coating on titanium surfaces that possesses both bio-functional and blocking features. We designed surfaces that decrease implant infection caused by non-specific adhesion and simultaneously promote targeted binding of biomolecules and cells that will increase osseointegration of the implant to enable long-term fixation.

Environmental response as determined by the cell-polymer interaction stands as the greatest restriction to the implementation of new polymeric materials. Cell-polymer interactions are most influenced by substrate surface free energy, surface chemistry, topography, and rigidity[1]. Alteration of these properties through surface treatment has become a common approach to attain the desired cellular interaction. This study investigates Kr-F excimer laser(248 nm) surface modification of poly(methyl methacrylate), glycol-modified poly(ethylene terephthalate), and polytetrafluoroethylene and its effect on the adhesion of Escherichia Coli K-12 bacteria. These three polymers were chosen for their very different mechanisms of ablation as well as their range of surface free energies and bacterial responses[2-4]. Polymers were ablated using a pulsed Kr-F excimer laser with a dose of 3.3x 10-9 W/cm2 per pulse. This high level of UV radiation was sufficient to cause significant surface damage on both PMMA and PTFE. PETG showed some signs of wavering in the surface and material removal was confirmed through optical microscopy. Due to the extensive damage associated with ablation, a much lower-powered, continuous beam Kr-F laser was used for contact angle samples. It delivered a dose of 1.27 W/cm2. Contact angle measurements were then taken which showed dose-dependent surface free energy in all three polymers. Following ablation, bacterial adhesion to PETG was improved two-fold, while it decreased in both PTFE and PMMA. Surface chemistry analysis supported the idea that the ablation occurred through chain scission, since there were no new surface groups created. There were significan texture modifications observed in PTFE and PMMA whicle PETG demonstrated the rolling structure characteristic of polyesters following laser ablation described in Wefers et al [4] and Hopp et al [5]. Contact angle measurements showed a correlation between radiation dose and surface free energy of all three polymers. / Master of Science

O objetivo deste estudo foi avaliar o efeito do tratamento ultrassônico como tratamento de superfície da zircônia tetragonal policristalina estabilizada por ítria (YTZP) e depois da sinterização final, por meio de mensuração da rugosidade superficial e teste de resistência adesiva por microsisalhamento. Para tanto, discos de Y-TZP foram confeccionados e distribuídos em 4 grupos (n=7), conforme o tratamento de superfície: 1-PRE: sonicação pré-sinterização; 2-POS: sonicação póssinterização; 3-JAT: jateamento com partículas óxido de alumínio 50μm; 4-CON: sem tratamento. Os espécimes foram polidos e padronizados e posteriormente submetidos aos tratamentos de acordo com cada grupo. Os grupos POS, JAT e COM foram sinterizados previamente ao tratamento e o grupo PRE após a sonicação. Os grupos PRE e POS foram submetidos a tratamento em processador ultrassonico (Sonics VCX-750) em potência nominal de 30% durante 15 minutos. O grupo JAT foi jateado com partículas de alumínio 50μm a uma distância de 15 cm, enquanto o grupo CON não recebeu nenhum tratamento. A mensuração de rugosidade superficial média (Ra) foi feita em Microscópio Confocal (MC), em seguida cilindros de cimento resinoso foram preparados e fotoativados na superfície do Y-TZP para serem submetidos ao ensaio mecânico de microcisalhamento realizado em máquina de ensaios universal (INSTRON). Os valores de rugosidade superficial e resistência de união obtidos foram submetidos a ANOVA a um critério e teste de Tukey. Quanto aos valores de rugosidade superficial, o grupo PRE (299,91 Mpa) e POS (291,23 Mpa) não apresentaram diferença estatística significante e o grupo JAT (925,21 Mpa) mostrou maiores valores de rugosidade superficial quando comparado ao PRE e POS. Para o teste de microcisalhamento não foram observadas diferenças estatisticamente significantes entre os grupos. Por meio dos resultados obtidos foi possível observar que o tratamento ultrassonico é capaz de alterar a superfície da Y-TZP e influenciar na resistência adesiva ao cimento resinoso. / The objective of this study was to evaluate the effect of ultrasonic treatment as surface treatment of Y-TZP before and after the final sintering, through measurement of surface roughness and bond strength by microshear test. Therefore, Y-TZP discs were made and distributed in 4 groups (n = 7), as surface treatment: 1-PRE: Presintering sonication; 2-POS: Post-sintering sonication; 3-JAT: air abrasion with aluminum oxide particles 50μm; 4-CON: no treatment. The specimens were polished and standardized and subsequently submitted to the treatments according to each group. The POS, JAT and CON groups been previously sintered to treatment and the PRE group after sonication. The PRE and POS groups were submitted to Ultrasonic Processor treatment (Sonics VCX-750) at 30% power for 15 minutes. The JAT group received air abrasion with aluminum particles 50μm at distance of 15 cm, while group received no treatment. The measurement of surface roughness was made in Confocal Microscope (MC), then resin cement cylinders were prepared and polymerized in Y-TZP surface to be subjected to mechanical testing microshear performed on universal testing machine (INSTRON). The values of surface roughness and bond strength were subjected to ANOVA and Tukey testAbout the values of surface roughness, the PRE group (299.91 MPa) and POS (291.23 MPa) showed no statistically significant difference and the JAT group (925.21 MPa) showed higher surface roughness values when compared to PRE and POS. For icroshear test statistically significant differences were observed between the groups. Through the results it was observed that the ultrasonic treatment is able to change the surface of the Y-TZP and influence the bond strength to resin cement.