Browsing by Author "Wei, Li-Ju"

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    Carbon based resistive strain gauge sensor fabricated on titanium using micro-dispensing direct write technology
    (Elsevier, 2016-06-21) Wei, Li-Ju; Oxley, C. H.
    Carbon based resistive strain gauge sensor suitable for medical implant technology has been directly fabricated on a titanium test-plate using Micro-Dispensing Direct Write (MDDW) technology. A 3.5µm biocompatible dielectric layer of parylene C was initially coated on the titanium test-plate. Commercially available screen-print carbon conductive paste was deposited on the parylene C and cured at 80oC for 3 hours; this was to ensure the physical properties and chemical integrity of the parylene C layer was maintained, whilst meeting the electrical conductivity curing requirements for the carbon tracks. The novel integrated strain sensor was experimentally tested and found to have a gauge factor of 10 making it approximately 5 times more sensitive than a commercially available metal foil strain gauge glued to the same titanium plate.
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    The Fabrication of Integrated Strain Sensors for “Smart” Implants using a Direct Write Additive Manufacturing Approach
    (De Montfort University, 2015-05) Wei, Li-Ju
    Over the 1980’s, the introduction of Additive Manufacturing (AM) technologies has provided alternative methods for the fabrication of complex three-dimensional (3D) synthetic bone tissue implant scaffolds. However, implants are still unable to provide post surgery feedback. Implants often loosen due to mismatched mechanical properties of implant material and host bone. The aim of this PhD research is to fabricate an integrated strain gauge that is able to monitor implant strain for diagnosis of the bone healing process. The research work presents a method of fabricating electrical resistance strain gauge sensors using rapid and mask-less process by experimental development (design of experiment) using the nScrypt 3Dn-300 micro dispensing direct write (MDDW) system. Silver and carbon electrical resistance strain gauges were fabricated and characterised. Carbon resistive strain gauges with gauge factor values greater than 16 were measured using a proven cantilever bending arrangement. This represented a seven to eight fold increase in sensitivity over commercial gauges that would be glued to the implant materials. The strain sensor fabrication process was specifically developed for directly fabricating resistive strain sensor structures on synthetic bone implant surface (ceramic and titanium) without the use of glue and to provide feedback for medical diagnosis. The reported novel approach employed a biocompatible parylene C as a dielectric layer between the electric conductive titanium and the strain gauge. Work also showed that parylene C could be used as an encapsulation material over strain gauges fabricated on ceramic without modifying the performance of the strain gauge. It was found that the strain gauges fabricated on titanium had a gauge factor of 10.0±0.7 with a near linear response to a maximum of 200 micro strain applied. In addition, the encapsulated ceramic strain gauge produced a gauge factor of 9.8±0.6. Both reported strain gauges had a much greater sensitivity than that of standard commercially available resistive strain gauges.