Thesis (Ph.D.)--University of Nebraska-Lincoln, 2010. / Title from title screen (site viewed July 8, 2010). PDF text: xiv, 323 p. : ill. (some col.) ; 11 Mb. UMI publication number: AAT 3398186. Includes bibliographical references. Also available in microfilm and microfiche formats.

Typically, hermetic feedthroughs for implantable devices, such as pacemakers, use a alumina ceramic insulator brazed to a platinum wire pin. This combination of material has a long history in implantable devices and has been approved by the FDA for implantable hermetic feedthroughs. The growing demand for increased input/output (I/O) hermetic feedthroughs for implantable neural stimulator applications could be addressed by developing a new, cofired platinum/alumina multilayer ceramic technology in a configuration that supports 300 plus I/Os, which is not commercially available. Seven platinum powders with different particle sizes were used to develop different conductive cofire inks to control the densification mismatch between platinum and alumina. Firing profile (ramp rate, burn- out and holding times) and firing atmosphere and concentrations (hydrogen (wet/dry), air, neutral, vacuum) were also optimized. Platinum and alumina exhibit the alloy formation reaction in a reduced atmosphere. Formation of any compound can increase the bonding of the metal/ceramic interface, resulting in enhanced hermeticity. The feedthrough fabricated in a reduced atmosphere demonstrated significantly superior performance than that of other atmospheres. A composite structure of tungsten/platinum ratios graded thru the via structure (pure W, 50/50 W/Pt, 80/20 Pt/W and pure Pt) exhibited the best performance in comparison to the performance of other materials used for ink metallization. Studies on the high temperature reaction of platinum and alumina, previously unreported, showed that, at low temperatures in reduced atmosphere, Pt3Al or Pt8Al21 with a tetragonal structure would be formed. Cubic Pt3Al is formed upon heating the sample to temperatures above 1350 °C. This cubic structure is the equilibrium state of Pt-Al alloy at high temperatures. The alumina dissolves into the platinum ink and is redeposited as a surface coating. This was observed on both cofired samples and pure platinum thin films coated on a 99.6 Wt% alumina and fired at 1550 °C. Different mechanisms are proposed to describe this behavior based on the size of the platinum particle.

Titanium and 316L stainless steel are popular orthopedic implant alloys because of their mechanical properties and corrosion resistance. The central hypotheses of this research were to determine if the adsorption of cells onto implant surfaces would alter their electrochemical corrosion properties and if released metal ions would stimulate macrophages. Analysis of supernatants and electrochemical corrosion tests were conducted on 316L SS and Ti with macrophages attached to evaluate their interactions. Results indicated that cells attached to alloys do alter their corrosion behavior by significantly increasing equilibrium potentials. Cells attached to 316L SS significantly increased charge transfer and the release of Ni, which is known to cause hypersensitivity. A difference in cell stimulation was seen between controls cells on TCP and cells cultured on the alloys. Significant findings of this study include alterations in alloy corrosion behavior and cell stimulation.

No / The prevalence of suboptimal outcome for surgical interventions in the treatment of full-thickness articular cartilage damage suggests that there is scope for a materials-based strategy to deliver a more durable repair. Given that the superficial layer of articular cartilage creates and sustains the tribological function of synovial joints, it is logical that candidate materials should have surface viscoelastic properties that mimic native articular cartilage. The present paper describes force spectroscopy analysis by nano-indentation to measure the elastic modulus of the surface of a novel poly(vinyl alcohol) hydrogel with therapeutic potential as a joint implant. More than 1 order of magnitude decrease in the elastic modulus was detected after adsorption of a hyaluronic acid layer onto the hydrogel, bringing it very close to previously reported values for articular cartilage. Covalent derivatization of the hydrogel surface with fibronectin facilitated the adhesion and growth of cultured rat tibial condyle chondrocytes as evidenced morphologically and by the observance of metachromatic staining with toluidine blue dye. The present results indicate that hydrogel materials with potential therapeutic benefit for injured and diseased joints can be engineered with surfaces with biomechanical properties similar to those of native tissue and are accepted as such by their constituent cell type.

published_or_final_version / abstract / Orthopaedics and Traumatology / Master / Master of Philosophy

Thesis (M.D.S.)--University of Adelaide, 1987. / Typescript. Includes bibliographical references (leaves 131-167).

M. Tech. Metallurgical Engineering / Ti6Al4V alloy is the leading material for hip replacement because of its biocompatibility, elastic modulus and good yield strength, but shows poor corrosion and wear properties in simulated body fluid. Thin coatings were fabricated on Ti6Al4V alloy using Zirconium, Niobium and Titanium reinforcements with the aid of Nd:YAG Rofin Sinar laser system. Niobium reinforcement produced the best coating that displayed the best corrosion resistance and percentage increase in wear resistance in simulated body fluid as compared to the substrate. Therefore, this coating will perform best as orthopaedic implant material.

published_or_final_version / Mechanical Engineering / Doctoral / Doctor of Philosophy

Hydroxyapatite (HA) is a biologically active ceramic used in surgery to replace bone. While HA promotes bone growth, it suffers from weak mechanical properties and does not possess any antibacterial property. Multi walled carbon nanotubes (MWCNTs), as one of the strongest and stiffest materials, have the potential to strengthen and toughen HA, thus expanding the range of clinical uses for the material. Furthermore, Silver nanoparticles (Ag NPs) can be decorated to sidewalls of the MWCNTs which could be released over a period of time to prevent infection following surgery. This work sought to develop and characterise Ag NPs- MWCNTs – HA composites in four main areas: 1) production and characterisation of the composite, 2) evaluation of mechanical properties, 3) investigation of antimicrobial property and 4) assessment of biological response to in vitro cell culture. Pristine (p-MWCNTs) and acid treated MWCNTs (f-MWCNTs) were decorated with Ag NPs. In the presence of 0.5 wt % Ag NPs-MWCNTs, HA was precipitated by the wet precipitation method in the presence of either poly vinyl alcohol (PVA) or Hexadecyl trimethyl ammonium bromide (HTAB) as the surfactant. Composites were characterised using various techniques and the diameteral tensile strength and compressive strength of the composites were measured. The antibacterial effect of these composites was investigated against clinically relevant microbe, Staphylococcus aureus. To determine the ability of the HOB cells to differentiate and mineralize in the presence of the composite, HOB cells were cultured on the composites for 21 days. Gene expression studies was performed along with the biochemical assays and scanning electron microscopy was used for qualitative analysis. Pure HA was used as control in all the studies. The study revealed that both the MWCNTs and surfactants play a crucial role in the nucleation and growth of the HA. XRD and FTIR characterisation revealed that HA was the primary phase in all the synthesised powders. Composites made with f-MWCNTs were found to have better dispersion and better interaction with the HA compared to composites with p-MWCNTs. Although mechanical strength was improved in all the composites, p-MWCNTs composites exhibiting maximum strength. Antibacterial studies showed 80% bacterial reduction in the treatment composites compared to pure HA. The biocompatibility study showed reduced activity of the HOB cells, however, no significant difference was observed between the control and the treatments. This systematic study of the synthesis and properties of the Ag NPs- MWCNTs-HA composites has resulted in improved understanding of the production and processing of these materials and the effect of MWCNTs and silver nanoparticles on primary human osteoblast cells. Additionally, it has yielded interesting biocompatibility result favouring the use of MWCNTs in the development of implants. There is potential to translate Ag NPs-MWCNTs-HA composites into clinically approved product.

The adaptation of standard integrated circuit (IC) technology for biosensors in drug discovery pharmacology, neural interface systems, environmental sensors and electrophysiology requires electrodes to be electrochemically stable, biocompatible and affordable. Unfortunately, the ubiquitous IC technology, complementary metal oxide semiconductor (CMOS), does not meet the first of these requirements. For devices intended only for research, modification of CMOS by post-processing using cleanroom facilities has been achieved by others. However, to enable adoption of CMOS as a basis for commercial biosensors, the economies of scale of CMOS fabrication must be maintained by using only low-cost post-processing techniques. The scope of this work was to develop post-processing methods that meet the electrochemical and biocompatibility requirements but within the low-cost constraint. Several approaches were appraised with the two most promising designs taken forward for further investigation. Firstly, a process was developed whereby the corrodible aluminium is anodised to form nanoporous alumina and further processed to optimise its impedance. A second design included a noble metal in the alumina pores to enhance further the electrical characteristics of the electrode. Experiments demonstrated for the first time the ability to anodise CMOS metallisation to form the desired electrodes. Tests showed the electrode addressed the problems of corrosion and presented a surface that was biocompatible with the NG108-15 neuronal cell line. Difficulties in assessing the influence of alumina porosity led to the development of a novel cell adhesion assay that showed for the first time neuronal cells adhere preferentially to large pores rather than small pores or planar aluminium. It was also demonstrated that porosity can be manipulated at room temperature by modifying the anodising electrolyte with polyethylene glycol. CMOS ICs were designed as multiple electrode arrays and optimised for neuronal recordings. This utilised the design incorporating a noble metal deposited into the porous alumina. Deposition of platinum was only partially successful, with better results using gold. This provided an electrode surface suitable for electric cell-substrate impedance sensors (ECIS) and many other sensor applications. Further processing deposited platinum black to improve signal-to-noise ratio for neuronal recordings. The developed processes require no specialised semiconductor fabrication equipment and can process CMOS ICs on laboratory or factory bench tops in less than one hour. During the course of electrode development, new methods for biosensor packaging were assessed: firstly, a biocompatible polyethylene glycol mould process was developed for improved prototype assembly. Secondly, a commercial ‘partial encapsulation’ process (Quik-Pak, U.S.) was assessed for biocompatibility. Cell vitality tests showed both methods were biocompatible and therefore suitable for use in cell-based biosensors. The post-processed CMOS electrode arrays were demonstrated by successfully recording neuronal cell electrical activity (action potentials) and by ECIS with a human epithelial cell line (Caco2). It is evident that these developments may provide a missing link that can enable commercialisation of CMOS biosensors. Further work is being planned to demonstrate the technology in context for specific markets.