Aabith, Saja; (2020) High-resolution 3D direct-write prototyping for healthcare applications. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

The healthcare sector has much to benefit from the vast array of novelties erupting from the manufacturing world. 3D printing (additive manufacturing) is amongst the most promising recent inventions with much research concentrated around the various approaches of 3D printing and applying this effectively in the health sector. Amongst these methods, the direct-write assembly approach is a promising candidate for rapid prototyping and manufacturing of miniaturised medical devices/sensors and in particular, miniaturised flexible capacitive pressure sensors. Microstructuring the dielectric medium of capacitive pressure sensors enhances the sensitivity of the capacitive pressure sensor. The structuring has been predominantly achieved with photolithography and similar subtractive approaches. In this project high-resolution 3D direct write printing was used to fabricate structured dielectric mediums for capacitive pressure sensors. This involved the development and rheological characterisation of printability-tuned water soluble polyvinyl pyrrolidone (PVP) based inks (10%-30% polymer content) for stable high-resolution 3D printing. These inks were used to print water soluble micromoulds that were filled and cured with otherwise difficult to structure low G’ materials like PDMS. Our approach essentially decouples ink synthesis from printability at the micrometre scale. The developed micro moulding approach was employed for printing pyramidal micro moulds, that were used as templates for fabricating pyramid structured dielectric mediums for capacitive pressure sensing. The power of the approach was used to alter the microstructures and reap enhanced pressure sensing characteristics for effective miniaturised capacitive pressure sensors. A pressure sensing ring – that could be worn by doctors and surgeons – was prototyped with our approach and employed successfully to monitor in real-time the radial pulse signal of a 29 year old male volunteer. The print resolution of the inks was enhanced by formulating and rheologically characterising a PVP/PVDF polymer blend ink that would wet the printing nozzle less due to the hydrophobicity of the PVDF.

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