Design of patient specific implants for amputee prostheses using porous titanium and development of antimicrobial silver coating for implant materials

This thesis presents research for two projects. The first project is based on designing and fabricating porous Ti-based metal implants for amputation prostheses. The implants are patient specific and are based on a computed tomography scan of the patient's bone. The efficient fill and porous structure of the implant has potential to improve load transfer from the prosthesis to the bone, the bone in-growth, and reduce premature loosening, thus decreasing the rehabilitation period for the amputees. Three iterations of this process have been completed. The first design is based on patient bone geometry but uses an elliptical geometric shape as the implant stem. The second design employs a model of the bone cavity as the implant stem, with a sloping area connecting the stem and head. The third design also utilizes the bone cavity as the implant stem, and incorporates a flange where the implant head meets bone. The second design greatly improved on the fit of the implant by using the patient geometry as the implant itself. The third design added further value by increasing the maximum compressive loads the designs could endure. The second project is research into a coating that can be used on implants to reduce the risk of infection. Silver has been utilized for many years as an antimicrobial agent. With an increasing amount of antibiotic-resistant bacteria, silver-coatings and treatments are again being noticed as an effective way to prevent infection. This is especially crucial when surgeries are performed in environments where sanitation is not ensured as well as environments in North American Hospitals. This research presents methods and feasibility of silver coatings on stainless steel (SS) which is a practical material for low cost implants. Parameters have been adjusted in order to optimize the efficacy of the coating. A post deposition heat treat has also been incorporated to increase coating adhesion. The coating has been shown to be safe for use with human cells and to create a 13 fold reduction in bacteria. This coating could also be applied to other implant materials or cases to limit the possibility of infection

Antimicrobial particulate silver coatings on stainless steel implants for fracture management

We have used particulate silver coating on stainless steel to prevent in vivo bacterial infection. Stainless steel is commonly used as an implant material for fracture management. The antimicrobial use of silver has been well documented and studied, therefore the novelty of this research is the use of a particulate coating as well as facing the real world challenges of a fracture repair implant. The variable parameters for applying the coating were time of deposition, silver solution concentration, voltage applied, heat treatment temperature between 400 and 500°C and time. The resultant coating is shown to be non-toxic to human osteoblasts using an MTT assay for proliferation and SEM images for morphology. In vitro silver release studies of various treatments were done using simulated body fluid. The bactericidal effects were tested by challenging the coatings with Pseudomonas aeruginosa in a bioreactor and compared against uncoated stainless steel. A 13-fold reduction in bacteria was observed at 24h and proved to be statistically significant. ► Processing of particulate silver coating that are strongly adherent on SS surface. ► Optimized the amount of silver that is sufficient to reduce bacterial colonization but non-toxic to human bone tissue. ► The adhesion strength of silver was sufficient to survive industrial sterilization steps used for fracture management devices

Patient specific implants for amputation prostheses: Design, manufacture and analysis

Objectives: To design, manufacture and analyze custom implants with functional gradation in macrostructure for attachment of amputation prostheses. Methods: The external shape of the implant was designed by extracting geometrical data of canine cadavers from computed tomography (CT) scans to suit the bone cavity. Three generations of implant designs were developed and were optimized with the help of fit/fill and mechanical performance of implant- cadaver bone assembly using CT analysis and compression testing, respectively. A final optimized, custom Ti6Al4V alloy amputation implant, with approximately 25 porosity in the proximal region and approximaltely zero percent porosity in the distal region, was fabricated using Laser EngineeredNet Shaping (LENS�) - a laser based additive manufacturing technology. Results: The proposed design changes in the second generation designs, in terms of refining thresholds, increased the average fill of the bone cavity from 58 to 83. Addition of a flange between the stem and the head in the second generation designs resulted in more than a seven-fold increase in the compressive load carrying capacity of the assembly. Application of LENS� in the fabrication of present custom fit Ti6Al4V alloy implants enabled incorporation of 20 to 30 porosity in the proximal region and one to two percent residual porosity in the distal portion of the implant. Clinical significance: Patient specific prostheses having direct connection to the skeletal structure can potentially aid in problems related to load transfer and proprioception in amputees. Furthermore, application of LENS� in the fabrication of custom implants can be faster to incorporate site specific porosity and gradients for improving long-term stability. © Schattauer 2012

Mechanical degradation of TiO2 nanotubes with and without nanoparticulate silver coating

The primary objective of this research was to evaluate the extent of mechanical degradation on TiO(2) nanotubes on Ti with and without nano-particulate silver coating using two different lengths of TiO(2) nanotubes- 300nm and ~ 1µm, which were fabricated on commercially pure Titanium (cp-Ti) rods using anodization method using two different electrolytic mediums - (1) deionized (DI) water with 1% HF, and (2) ethylene glycol with 1% HF, 0.5 wt%. NH(4)F and 10% DI water. Nanotubes fabricated rods were implanted into equine cadaver bone to evaluate mechanical damage at the surface. Silver was electrochemically deposited on these nanotubes and using a release study, silver ion concentrations were measured before and after implantation, followed by surface characterization using a Field Emission Scanning Electron Microscope (FESEM). In vitro cell-material interaction study was performed using human fetal osteoblast cells (hFOB) to understand the effect of silver coating using an MTT assay for proliferation and to determine any cytotoxic effect on the cells and to study its biocompatibility. No significant damage due to implantation was observed for nanotubes up to ~1 µm length under current experimental conditions. Cell-materials interaction showed no cytotoxic effects on the cells due to silver coating and anodization of samples

Antimicrobial particulate silver coatings on stainless steel implants for fracture management

We have used particulate silver coating on stainless steel to prevent in vivo bacterial infection. Stainless steel is commonly used as an implant material for fracture management. The antimicrobial use of silver has been well documented and studied, therefore the novelty of this research is the use of a particulate coating as well as facing the real world challenges of a fracture repair implant. The variable parameters for applying the coating were time of deposition, silver solution concentration, voltage applied, heat treatment temperature between 400 to 500 °C and time. The resultant coating is shown to be non-toxic to human osteoblasts using an MTT assay for proliferation and SEM images for morphology. In vitro silver release studies of various treatments were done using simulated body fluid. The bactericidal effects were tested by challenging the coatings with P. aeruginosa in a bioreactor and compared against uncoated stainless steel. A 13-fold reduction in bacteria was observed at 24 hours and proved to be statistically significant

Antibacterial and biological characteristics of silver containing and strontium doped plasma sprayed hydroxyapatite coatings

Infection in primary total joint prostheses is estimated to occur in up to 3% of all surgeries. As a measure to improve the antimicrobial properties of implant materials, silver (Ag) was incorporated into plasma sprayed hydroxyapatite (HA) coatings. To offset potential cytotoxic effects of Ag in the coatings, strontium (Sr) was also added as a binary dopant. HA powder were doped with 2.0 wt% Ag(2)O, 1.0 wt% SrO and the powder was then heat treated at 800° C. Titanium substrates were coated using a 30 kW plasma spray system equipped with a supersonic nozzle. X-ray diffraction (XRD) confirmed the phase purity and high crystallinity of the coatings. Samples were evaluated for mechanical stability by adhesive bond strength testing. Results show that the addition of dopants did not affect the overall bond strength of the coatings. The antibacterial efficacies of the coatings were tested against Pseudomonas aeruginosa. Samples that contained the Ag(2)O dopant were found to be highly effective against the bacterial colonization. In vitro cell-material interactions using human fetal osteoblast (hFOB) cells were characterized by 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay for cell viability, field emission scanning electron microscopy (FESEM) for cell morphology and confocal imaging for the important differentiation marker alkaline phosphatase (ALP). Our results showed evidence of cytotoxic effects in the Ag-HA coatings, characterized by poor cellular morphology and cell death and nearly complete impediment of functional ALP activity. The addition of SrO to Ag-HA coatings was able to effectively offset these negative effects and improve the performance when compared to pure HA coated samples

Fluorescent labelling of proteins

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