Effect of pulsed laser process parameters on weld integrity and biocompatibility
by Brendan P. Croom
The effects of pulsed YAG laser welding process parameters on weld integrity and biocompatibility of grade 5 titanium (Ti-6Al-4V) weldments were studied. The laser welds were produced to simulate hermetic seals of titanium packages for biomedical implantable devices. The processing parameters were found to affect to physical characteristics and the fracture strength of the welds. The weld width at half the depth of penetration, and the width of the heat affected zone were dependent on the processing parameters, with the total energy input as the most influential factor. With increasing depth of penetration, the fracture strength of the weldments increased. The weld parameters did not influence the microstructure, crystal structure, or chemical composition of the welds. All welds were found to be biocompatible, as determined by cytotoxicity testing.
Hydrogen plasma surface modification of polytetrafluoroethylene
by Brian K. McCoy
Polytetrafluoroethylene (PTFE) was treated in a glow discharge hydrogen plasma and the subsequent surface modifications were evaluated by contact angle measurement, atomic force microscopy (AFM), and x-ray photoelectron spectroscopy (XPS). The wetting behavior of several test liquids increased with continued exposure to hydrogen plasma. Hydrogen plasma treating the PTFE surface led to an increase in surface tension, as calculated from contact angle data. Surface roughness decreased with increased exposure to the hydrogen plasma. Surface analysis by XPS detected the loss of fluorine and binding of nitrogen, oxygen, and carbon functional groups. Longer plasma treatment times resulted in a greater loss of fluorine and increased functional group binding. Atmospheric exposure post plasma treatment aided in surface sorption of nitrogen and oxygen groups.
Morphological typing of intra arterial embolus using three dimensional computed tomography techniques
by Arundhati Deshpande
Morphological characterization is an attempt made towards assembling functionally related material based on similarity of structure. Such grouping brings about a structural classification to a diverse group of embolic material types. Also, one of the most important reasons for characterizing embolic material is to serve as predictors for treating patients. This research aims at using Three Dimensional Computed Tomography (CT) to determine the constituents of intra arterial emboli.
Three dimensional computer tomography shall be performed on samples of emboli collected within filters to obtain images in the form of slices. These images would then be used to reconstruct and detect the constituents of the emboli. The reflective signatures thus obtained shall be correlated to the results obtained from actual histopathology.
Compression strength in a simulated body condition
by Sindhu Gowri
Name of the company: Skeletal Kinetics, Cupertino, California
In this project, Callos-Inject (calcium phosphate bone cement manufactured by Skeletal Kinetics) intended for spinal applications is tested for compression strength in a simulated body condition. One of its spinal applications called vertebroplasty is discussed. The results obtained from this project are important for the approval of Callos for spinal application by the FDA. In the introduction section, anatomy of spinal cord is explained followed by introduction on vertebroplasty, osteoporosis, market analysis and the role of bone cement in treating osteoporosis.
An introduction to the cement, its chemical and physical properties and the required bone cement volume for vertebroplasty is also given. An overview of the biomechanical behavior of Callos is addressed including the factors which affect its invivo behavior such as mixing methods, environment, etc. In the next section a detailed overview on the method of investigation and experimental procedures practiced is addressed. The software used to run the machine is explained with illustrations. A detailed economic analysis of the project is given which includes income statements, market size and geographic locations of all the competitor companies. The results are tabulated and endurance limit curve is plotted to obtain the final compression strength of the cement. Initial and final elastic moduli values are calculated to understand the brittle nature of the ceramic. Lastly conclusions are given followed by references.
Figure 1. Experimental set up- Instron (servohydraulic) 8872 machine
Figure 2. Creating "blocks" using Wavemaker Editor software
Figure 3. Wavemaker Editor Software showing real time graph
EVALUATING THE EFFECT OF MICROBLASTING ON THE CYTOTOXICITY OF NITI
BY H. Aihara, B. Chun, K. Jaladi, A. M.-C. Kuo
Microblasting, similar to sand blasting, involves the use of high pressure and abrasive powders to remove quantities of surface layers. This research focused on investigating the effect microblasting of NiTi, with Al203 abrasives, would have on its cytocompatibility. The test specimens were weighed before and after microblasting to determine material removal, if any. Surface morphology changes were characterized by Scanning Electron Microscopy (SEM), surface roughness effects were quantified by Atomic Force Microscopy (AFM), and contact angles changes were measured by the sessile drop method. The effect of microblasting on the cytotoxicity of the specimens was determined following the method outlined in ISO 10993-5. The amount of material removed was found to increase with increasing particle size of the abrasive and microblasting pressure. The surface roughness was also found to increase with increasing particle size of the abrasive. However, the contact angle with DI water was found to be not affected by the microblasting parameters. There was no significant change in the cytocompatibility of the specimens, regardless of microblasting conditions. However, the surface was found to contain Al, presumably from the Al203 abrasive used. The detailed chemical nature of this deposit is currently being investigated by X-ray Photoelectron Spectroscopy.
