Yazar "Cho, Yonghyun" seçeneğine göre listele

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    Design and fabrication of auxetic PCL nanofiber membranes for biomedical applications
    (Elsevier, 2017) Bhullar, Sukhwinder Kaur; Rana, Deepti; Lekesiz, Hüseyin; Bedeloğlu, Ayşe; Ko, Junghyuk; Cho, Yonghyun
    The main objective of this study was to fabricate poly (e-caprolactone) (PCL)-based auxetic nanofiber membranes and characterize them for their mechanical and physicochemical properties. As a first step, the PCL nanofibers were fabricated by electrospinning with two different thicknesses of 40 pm (called PCL thin membrane) and 180 pm (called PCL thick membrane). In the second step, they were tailored into auxetic patterns using femtosecond laser cut technique. The physicochemical and mechanical properties of the auxetic nanofiber membranes were studied and compared with the conventional electrospun PCL nanofibers (non-auxetic nano fiber membranes) as a control. The results showed that there were no significant changes observed among them in terms of their chemical functionality and thermal property. However, there was a notable difference observed in the mechanical properties. For instance, the thin auxetic nanofiber membrane showed the magnitude of elongation almost ten times higher than the control, which clearly demonstrates the high flexibility of auxetic nanofiber membranes. This is because that the auxetic nanofiber membranes have lesser rigidity than the control nanofibers under the same load which could be due to the rotational motion of the auxetic structures. The major finding of this study is that the auxetic PCL nanofiber membranes are highly flexible (10-fold higher elongation capacity than the conventional PCL nanofibers) and have tunable mechanical properties. Therefore, the auxetic PCL nanofiber membranes may serve as a potent material in various biomedical applications, in particular, tissue engineering where scaffolds with mechanical cues play a major role.
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    Design and fabrication of auxetic stretchable force sensor for hand rehabilitation
    (Iop Publishing Ltd, 2015) Ko, Junghyuk; Bhullar, Sukhwinder Kaur; Cho, Yonghyun; Lee, Patrick C.; Jun, Martin Byung-Guk
    Using a melt electrospinning technique, stretchable force sensors were designed for use in an application of hand rehabilitation. The main purpose of this study was to verify that the use of auxetic sensors improved hand rehabilitation practices when compared to their absence. For this study, novel stretchable poly (epsilon-caprolactone) (PCL) force sensors were fabricated into the following formations: auxetic microfiber sheets (AMSs), auxetic solid sheets (ASSs), microfiber sheets (MSs), and solid sheets (SSs). A femtosecond laser device was used to make an auxetic structure in the MSs and SSs. Subsequently, these sensors were coated with gold particles to make them conductive for the electrical current resistance assays. Through the cycles of applied stress and strain, auxetic structures were able to retain their original shape once these forces have been dissipated. This stretchable sensor could potentially measure applied external loads, resistance, and strain and could also be attachable to a desired substrate. In order to verify the workability and practicality of our designed sensors, we have attempted to use the sensors on a human hand. The AMS sensor had the highest sensitivity on measuring force and resistance among the four types of sensors. To our knowledge, this is the first study to form a stretchable force sensor using a melt electrospinning technique.
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    Fabrication and Characterization of Nonwoven Auxetic Polymer Stent
    (Taylor & Francis Inc, 2015) Bhullar, Sukhwinder Kaur; Ko, Junghyuk; Cho, Yonghyun; Jun, Martin B. G.
    Synthetic biomaterials have better controlled physical and mechanical properties and can be used to tailor both soft and hard tissues. A tiny, expandable mesh tubes called stents keep blood vessels open and allow blood flow and treat blockage to improve quality of patient's life. The main focus of this work is to (i) fabricate a polymeric sheet of melt electrospun polycaprolactone microfibers; (ii) tailor auxetic geometry by micromachining on polycaprolactone microfiber and polycaprolactone sheet; (iii) fabricate a cylindrical tube to make auxetic stents. Final results for mechanical characterization and performance analysis of auxetic polymer stents are discussed.