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Doctor of Philosophy(PhD) / Biomedical materials are being extensively researched, and many different types such as metals, metal alloys, and polymers are being used. Currently used biomedical materials are not perfect in terms of corrosion resistance, biocompatibility, and surface properties. It is not easy to fabricate from scratch new materials that can fulfill all requirements and an alternative approach is to modify the surface properties of current materials to cater to the requirements. Plasma immersion ion implantation (PIII) is an effective and economical surface treatment technique and that can be used to enhance the surface properties of biomaterials. The unique advantage of plasma modification is that the surface properties and functionalities can be enhanced selectively while the favorable bulk attributes of the materials such as strength remain unchanged. In addition, the non-line of sight feature of PIII is appropriate for biomedical devices with complex geometries such as orthopedic implants. However, care must be exercised during the plasma treatment because low-temperature treatment is necessary for heat-sensitive materials such as polymers which typically have a low melting point and glass transition temperature. Two kinds of biomedical materials will be discussed in this thesis. One is nickel titanium (NiTi) alloy which is a promising orthopedic implant material due to its unique shape memory and superelastic properties. However, harmful ions may diffuse from the surface causing safety hazards. In this study, we investigate the properties and performance of NiTi after nitrogen and oxygen PIII in terms of the chemical composition, corrosion resistance, and biocompatibility. The XPS results show that barrier layers mainly containing TiN and TiOx are produced after nitrogen and oxygen PIII, respectively. Based on the simulated in vitro and electrochemical corrosion tests, greatly reduced ion leaching and improved corrosion resistance are accomplished by PIII. Porous NiTi is also studied because the porous structure possesses better bone ingrowth capability and compatible elastic modulus with human bones. These advantages promote better recovery in patients. However, higher risks of Ni leaching are expected due to the increased exposed surface area and rougher topography than dense and smooth finished NiTi. We successfully apply PIII to porous NiTi and in vitro tests confirm good cytocompatibility of the materials. The other type of biomedical materials studied here is ultra-high molecular weight polyethylene (UHMWPE) which is a potential material for use in immunoassay plates and biosensors. In these applications, active antibodies or enzymes attached to a surface to detect molecules of interests by means of specific interactions are required. Moreover, the retention of enzyme activity is crucial in these applications. Therefore, the aim of this study is to investigate the use of PIII to prepare UHMWPE surfaces for binding of active proteins in terms of the binding density and ‘shelf life’ of the treated surfaces. Argon and nitrogen PIII treatments are attempted to modify the surface of UHMWPE. Horseradish peroxidase (HRP) is selected to conduct the protein binding test since it is a convenient protein to assay. Experimental results show that both PIII treated surfaces significantly improve the density of active HRP bound to the surface after incubation in buffer containing HRP. Furthermore, the PIII treated surfaces are found to perform better than a commercially available protein binding surface and the shelf life of the PIII treated surfaces under ambient conditions is at least six months. In conclusion, a biocompatible barrier layer on NiTi and a protein binding surface on UHMWPE is synthesized by PIII. The surface properties such as corrosion resistance and functionality on these two different types of substrates are improved by PIII.

Thesis (Ph.D.)--McMaster University (Canada), 1991. / Source: Dissertation Abstracts International, Volume: 53-01, Section: B, page: 0367.

Thesis (Ph. D.)--University of North Texas, Dec., 2007. / Title from title page display. Includes bibliographical references.

Thesis (doctoral)--Technische Universiteit Delft, 2000. / Includes bibliographical references (p. 123-130).

Thesis (doctoral)--Technische Universiteit Delft, 2000. / Includes bibliographical references (p. 123-130).

Thesis (Ph. D.)--University of Texas at Austin, 1999. / Vita. Includes bibliographical references (leaves 153-158). Available also in a digital version from Dissertation Abstracts.

Made available in DSpace on 2014-06-11T19:32:50Z (GMT). No. of bitstreams: 0 Previous issue date: 2009-11-27Bitstream added on 2014-06-13T20:04:23Z : No. of bitstreams: 1 batocki_rgs_dr_guara.pdf: 753160 bytes, checksum: 45bdf421ee548b969fb254971bfe730c (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Filmes finos polimerizados a plasma apresentam várias aplicações nas indústrias óticas, elétrica, mecânica de alimentos, de biomateriais entre outras, devido suas interessantes propriedades químicas e físicas. No entanto, as aplicações para os filmes finos podem ser limitadas em função de algumas de suas características mecânicas e de superfície. Neste trabalho, filmes finos poliméricos foram depositados por radiofrequência a partir de plasmas de hexametildissilazano mantido a baixa pressão. Posteriormente, foram implantados íons de argônio, hélio e nitrogênio nestes filmes através da implantação iônica por imersão a plasma (IIIP). Após os tratamentos, os filmes finos provenientes da polimerização a plasma do hexametildissilazano apresentaram modificações em suas estruturas moleculares e composição química através das análises infravermelha e XPS. O XPS revelou um aumento nas concentrações de oxigênio e decréscimo de carbono e nitrogênio. Este fato indica aumento no nível e entrelaçamento, ramificação e reticulação das cadeias poliméricas para todos os íons implantados. Verificou-se também que a IIIP promoveu mudanças na molhabilidade com variações nos ângulos de contato de 100° para 10°; alterações nos índices de refração entre 1,65 a 2,10; modificações na dureza e módulo elástico de 0,8 a 3,3 GPa e 6,0 a 52,0 GPa respectivamente, assim como redução na taxa etching de 34,0 para 20,0 Å/min. / Plasma polymerized thin films have many applications in optical, electrical, mechanical, food, biomaterial industries among others, due to their interesting chemical and physical properties. Polymer thin films applications, however, can be limited because of some mechanical and surface characteristics. In this work, thin polymer films were deposited from radiofrequency plasmas of hexamethyldisilazane at low pressure. Then, these films were implanted with argon, helium and nitrogen ion, by plasma immersion ion implantation (PIII). After the treatments, plasma polymerized hexamethyldisilazane thin films presented modifications in their molecular structure and chemical composition by infrared and XPS analysis. XPS revealed an increase in the oxygen, decrease in nitrogen and carbon concentrations. This fact indicates increased crosslinking of the polymeric chains of all implanted ions. It was also verified that a PIII caused modification in wettability, changing the contacts angles from 100° to 10°. Modifications were also observed in the refractive index from 1,65 to 2,10; in hardness and in the elastic modulus from 0,8 a 3,3 GPa and 6,0 to 52,0 GPa respectively. The study showed a decrease in etching rate from 34,0 to 20,0 Å/min.

Malignant bone tumours often require a patient to make the choice between limb salvage surgery and complete amputation. The Ti-6Al-4V alloy is the material of choice for implantable orthopaedic devices as it provides a favourable combination of biocompatibility, corrosion resistance and mechanical properties. The only drawback of titanium is that, owing to its bio-inertness, living tissue struggles to attach, creating an opportunity for bacterial adhesion. The “race for the surface” is the term given for the competition between living tissue and bacteria to colonise the implant surface. If bacterial adhesion occurs at a higher rate than tissue adhesion, the chance of infection rises significantly. It has been shown that there is an opportunity to give tissue adhesion the edge by slowing down the initial colonisation of the implant surface by free-swimming bacteria. Silver has a relatively low toxicity level of 28 mg/kg in the body. Current research has focussed mainly on reducing bio-inertness and improving the antimicrobial properties of titanium via the incorporation of silver. In general, the studies conducted on antibacterial surfaces are limited to testing the final sample directly in contact with bacteria, with no attempt to measure silver release rate profiles. The research in this dissertation aimed to investigate methodologies for the incorporation of silver into a modified surface of Ti-6Al-4V in order to facilitate an antimicrobial effect for use in orthopaedic implants. The methodologies investigated were: anodic oxidation of Ti-6Al-4V, followed by silver ion exchange; Ag-doped TiO2 fused to the surface of Ti-6Al-4V via anodic oxidation; and Ag ion implantation into anodically oxidised and polished Ti-6Al-4V. The generated surfaces and sub-surfaces were characterised microstructurally via SEM, FIB, TEM and AFM and chemically by RBS, XRD, AAS and EDS. Ag+ release rate investigations were conducted with the use of ICP-MS. This study was limited to the use of two anodising electrolytes (i.e. 0.5M H2SO4 and 2.1M H3PO4) and altering the AgNO3 concentration (0.05 - 5.0M) and Ag implantation dosage (0.4 - 1.2x1017 ions/cm2 ), where applicable to the method. Results from the Ag ion exchanged samples showed that, microstructurally, the surface produced via anodising in 0.5M H2SO4 and 2.1M H3PO4 were different in terms of pore morphology, Ra, pore homogeneity across the surface and crystal structure. Sub-surface analysis via FIB/TEM found that the ca. 200nm thick TiO2 samples all contained silver nanoparticles (AgNPs). Samples anodised in 0.5M H2SO4 produced an anatase crystal structure, whilst those anodised in 2.1M H3PO4 produced rutile crystal structures. Silver uptake by samples anodised in 0.5M H2SO4 showed decreases in Ag absorption at high (5.0M) AgNO3 ion exchange concentrations, relative to low (0.05M) concentrations. The opposite effect was observed for samples anodised in 2.1M H3PO4. Ag+ release curves corroborated the absorption data by displaying the same trends in terms of Ag+ release post ion exchange. It was concluded that it was a combination of diffusion bottlenecking and higher reactivity of the anatase phase formed during anodising in 0.5M H2SO4 with Ag+ versus the rutile phase that led to these trends. Synthesis of TiO2 powders showed that increasing the AgNO3 concentration (0.05-5M) resulted in AgTiO2 powders with increasing Ag content. Ag-TiO2 powder was successfully fused to the surfaces via anodic oxidation in 0.5M H2SO4 and 2.1M H3PO4 at 100V. Ag-TiO2 powder fused preferentially in areas where downward pressure was present. Microstructurally, the sub-surfaces produced an anodic oxide approximately 200nm thick, to which a significantly thicker, AgNP-containing, TiO2 was attached. XRD data indicated additional Brookite (020) peaks, owing to the presence of the attached Ag-TiO2 powder on the surfaces. Ag-TiO2 powders attached via 0.5M H2SO4 showed a higher overall Ag+ release at all investigated powder concentrations (0.48 - 76.93 wt% Ag) versus those attached via 2.1M H3PO4. This was concluded to be due to the anatase phase produced by 0.5M H2SO4 having greater oxidative power, thus accelerating oxidative dissolution of the AgNPs. RBS data corroborated these trends. Relative to their Ag ion exchange counterparts, the Ag-TiO2 samples had a lower Ag+ release at 0.05M and 0.5M AgNO3 concentrations. However, at 5.0M AgNO3 the Ag-TiO2 samples had a higher Ag+ release. This was the trend irrespective of the anodising electrolyte. Both the anatase and rutile TiO2s showed a reduction in Ra post Ag ion implantation and the polished Ti6Al4V samples showed an increase in Ra. This was due to preferential erosion of areas with high free surface energy. In the case of both TiO2s these were “high points” in the oxide and for polished Ti6Al4V these were the grain boundaries. Both TiO2s were amorphised during ion implantation. All ion implanted TiO2 showed the presence of AgNPs within the first 50nm of the surface. These AgNPs increased in size as the implantation dosage was increased. Polished Ti6Al4V showed no AgNP formation but EDS mapping confirmed that the silver was also located 50nm within the surface. TiO2 Ag+ release was similar for both implantation dosages because the surfaces had been supersaturated at the low dose, thus an increase in implantation dose had no significant effect on further silver uptake. The release rates were also similar between the oxides because of amorphisation. Polished Ti6Al4V showed an increase in Ag uptake and Ag+ release when the implantation dose was increased. RBS results corroborated the observed Ag+ release results. In comparison, both the ion exchanged samples and the Ag-TiO2 fused samples showed performances in similar ranges of Ag+ release. The Ag-TiO2 samples showed a greater degree of tailorability of the Ag+ release, whereas the ion exchanged samples showed a lesser sensitivity to an increase in AgNO3 concentration. Ag ion implanted samples showed an order of magnitude lower Ag+ release relative to the other studied methods. In comparison to literature, all ion exchanged and Ag-TiO2 samples had the potential to have a 100% antimicrobial effect (AE). Ion implanted oxides had a 55-100% potential, while the polished Ti6Al4V had a 55% AE at low dose and a 100% AE at high dose. In order to achieve maximum silver ion release and the associated antimicrobial effect, the technique of Ag-TiO2 fused to the surface using the 2.1M H3PO4 and 0.5M H2SO4 electrolytes yielded the best results, with a silver ion release of 550 and 600 ppb respectively over two weeks. This technique also satisfied the research aim, in that the methodology offered a combination of tailorability of silver release and commercial scalability.

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