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Title Page

Abstract

국문 초록

Contents

List of Abbreviations 21

Chapter 1. Introduction 23

1.1. Overview 24

1.2. Outline of the dissertation 27

Chapter 2. Theoretical Background 28

2.1. Electrospinning: synthesis of PLA fibers and spheres 29

2.2. Hydrothermal method: synthesis of ZnO nanowires 35

2.3. Interfacial assembly of nanoparticles at the interface of the two phases. 40

Chapter 3. Experimental Procedure 48

3.1. Synthesis method of PLA-ZnO heterostructures 49

3.2. Characterization method of PLA-ZnO heterostructures 52

3.3. Antibacterial test of PLA-ZnO heterostructures 53

Chapter 4. Results and discussions 55

4.1. Synthesis of organic-inorganic heterostructures 56

4.2. Interfacial assembly mechanism of nanoparticles 67

4.3. Growth kinetics of nanowires 79

4.4. Topography-Induced surface wettability of PLA-ZnO IOH 85

4.5. Anti-bacterial properties of PLA-ZnO IOH 91

Chapter 5. Conclusion 106

References 108

List of Tables

Table 4.1. Interfacial assembly of ZnO NPs at the chloroform-water interface. 71

Table 4.2. Interfacial assembly of ZnO NPs at the PLA-water interface. 72

List of Figures

Figure 2.1. Schematic illustration of a) horizontal type electrospinning set up and b) the Taylor cone formed at the end of the nozzle tip. 33

Figure 2.2. a. Schematic illustration of electrospinning setup using dual nozzle. b. Example of core-shell structure. TEM image of poly(ethylene oxide) (PEO, shell) and... 34

Figure 2.3. ZnO crystal structures of wurtzite, zinc-blende, and rock salt. 38

Figure 2.4. Schematic illustration of hydrothermal method equipment. 39

Figure 2.5. Schematic illustration of a liquid droplet on a solid surface with interfacial energy and contact angle described by Young's equation. 46

Figure 2.6. Schematic illustration of an interfacially assembled single particle in an oil-water system. Interaction between the interfacial energies of a single particle (left). A description of... 47

Figure 4.1. Bioinspired engineering for micrometer-scale urchin with nanometer-scale spicules. a) Biomineralization process of the sea-urchin spicules. b) The formation process of artificial... 60

Figure 4.2. Schemes for constructing the PLA-ZnO IOH. The mixture of ZnO NPs and PLA was electrosprayed and electrospun into microspheres and microfibers, respectively, with ZnO... 61

Figure 4.3. Characteristics of ZnO NP seeds. a) TEM image and Fast Fourier transform (FFT) pattern of ZnO NPs. b) Diameters and hydrodynamic sizes of ZnO NPs. The hydrodynamic size... 62

Figure 4.4. a,b) SEM images of PLA MS (a) and PLA MF (b) with entrapped ZnO NPs. c,d) SEM images of PLA-ZnO IOHs prepared with PLA MS (c) and PLA MF (d). e,f) Bright-field... 63

Figure 4.5. ZnO NP-embedded PLA MF. a) Bright-field TEM image. b) Dark-field TEM image. c,d) Energy-dispersive X-ray spectroscopy (EDS) analysis for elemental mapping: Zn (red), C (blue). 64

Figure 4.6. a) XRD patterns of ZnO NPs (green) and PLA-ZnO IOH (red). The peaks correspond to the powder diffraction file (PDF no. 36-1451) of the wurtzite ZnO structure. b)... 65

Figure 4.7. Differential scanning calorimetry (DSC) curves of PLA MF (black) and PLA MF-ZnO NP (green). A typical DSC heating thermogram of PLA is represented. Each of the DCS... 66

Figure 4.8. The proposed mechanism for the assembling ZnO NPs at the internal and external PLA-water interfaces. Schematic illustrations for the interface formation and positioning of ZnO... 70

Figure 4.9. Interfacial assembly of ZnO NPs at the PLA-water interfaces. a) Bright-field (left) and dark-field (right) TEM images of PLA MF after incubation in water containing ZnO NPs at... 73

Figure 4.10. Interfacial assembly of ZnO NPs at the chloroform-water interface. a) Schemes for illustrating interfacial assembly. b) Photographs of interfacial assembly of ZnO NP at the water-... 74

Figure 4.11. Interfacial assemblies and migration of pre-entrapped ZnO NPs and growth of ZnO NWs on PLA MF. a) SEM images of growing ZnO NWs. b) Zoomed-in dark-field TEM... 77

Figure 4.12. Formation of bubbles in the ZnO NP-embedded PLA film prepared via spin coating. a,b) Cross-sectional SEM images were taken before (a) and after (b) the PLA film was... 78

Figure 4.13. Temperature-dependent growth kinetics of ZnO NWs on PLA MF. a) SEM images of PLA-ZnO IOH synthesized at different reaction times and temperatures. Scale bar: 2 µm. b)... 82

Figure 4.14. a) Growth diagram showing the length of the ZnO NPs as a function of reaction time and temperature. The length of the ZnO NWs was measured using SEM images in Figure... 83

Figure 4.15. The structural stability of PLA-ZnO IOH. a) SEM images of PLA-ZnO IOH before and after being incubated in an aqueous solution and left under atmospheric conditions. b)... 84

Figure 4.16. Wettability analysis of PLA MF, PLA MF-ZnO NP, and PLA-ZnO IOH. a) Schematic illustration of topography-induced super-hydrophilicity. b) Wettability of PLA-ZnO... 87

Figure 4.17. The contact angle of hexane on PLA MF, PLA MF-ZnO NP, and PLA-ZnO IOH. From left to right: hexane droplet dispensed from the needle. The sample on the stage was... 88

Figure 4.18. The contact angle of water for all growth and surface growth of PLA-ZnO IOH. In the case of all growth, ZnO NWs grew between PLA matrices, but in surface growth, ZnO NWs... 89

Figure 4.19. Effect of the surface coverage of ZnO NWs on water wettability on PLA-ZnO IOHs. a-c) SEM images and contact angle measurement of PLA-ZnO IOH with different... 90

Figure 4.20. The schematic illustration of bactericidal properties of PLA-ZnO IOH. Both ROS generation (material property) and physical interaction (structural property) are applied to bacteria. 97

Figure 4.21. Metabolic activity of S. aureus and E. coli after incubation on PLA MF, PLA MF-ZnO NP, and PLA-ZnO IOH. The error bars represent the standard deviations of triplet measurements. 98

Figure 4.22. Metabolic activity of S.aureus (a) and E. coli (b) after incubation on PLA MF, PLA MF-ZnO NP, and PLA-ZnO IOH. Before this, each samples were treated in the Luria-... 99

Figure 4.23. Analysis of the contribution of ROS in the bactericidal effect. a) The chemical mechanism of measuring the amount of ROS (represented by hydrogen peroxide here) b,c) ROS... 100

Figure 4.24. SEM images S.aureus and E.coli after incubation on PLA MF, PLA MF-ZnO NP, and PLA-ZnO IOH, respectively. Each scale bar is 1 μm. 101

Figure 4.25. Fluorescence microscopy images of S. aureus and E. coli on PLA MF, PLA MF-ZnO NP, and PLA-ZnO IOH. In all cells, live and dead cells were stained with SYTO 9 (green... 102

Figure 4.26. The concentration of nucleic acids released from S. aureus and E. coli incubated on PLA MF, PLA MF-ZnO NP, and PLA-ZnO IOH. The error bars represent the standard... 103

Figure 4.27. Photographs of S.aureus and E. coli bacterial colonies formed on LB after incubation with PLA MS-Fe₃O₄ NP-ZnO NW and PLA MS-Fe₃O₄ NP 104

Figure 4.28. The SEM images of MCF10A cells after incubation on PLA-ZnO IOH. MCF10A cells were anchored on the ZnO NWs; Low-magnification (a) and high-magnification (b). 105

초록보기

자연을 모사하여 인공적으로 구현한 무기-유기 헤테로 구조체(IOH)는 무기물과 유기물 각각의 특성이 결합되어 시너지 효과를 보여주기 때문에 다양한 응용 분야에서 떠오르는 기술입니다. 특히, 높은 생체적합성을 갖는 유기물을 사용하는 IOH 구조체는 바이오 분야에서 많은 주목을 받고 있습니다. 하지만 여전히 복잡한 자연의 IOH를 모사하는 합성 기술과 그에 따른 구조적 기능을 보여주는 데에는 어려움이 있습니다. 이 논문에서는 성게 가시의 뾰족한 구조와 그에 따른 보호기능을 모방한 마이크로 미터규모의 폴리젖산(PLA) 입자 및 섬유에서 성장한 나노미터 규모의 산화아연(ZnO) 가시 합성법 및 살균 특성에 대해 소개합니다. 유리 전이 온도보다 높은 조건에서 PLA 템플릿 내부에 미리 탑재된 ZnO 나노입자가 유동성을 갖게 되어 PLA-물 계면으로 이동하는 열역학적 메커니즘을 밝혀냈습니다. 이 나노입자는 ZnO 나노선으로 성장하게 된다. 성게와 같은 ZnO 나노선으로 형성된 지형은 물이 완전하게 스며드는 초친수성을 유도하여 활성 산소의 생성과 박테리아 접촉(찌르는 효과)이 가능하도록 합니다. 이러한 특성들은 그람양성균과 그람음성균 모두에 대하여 유례없이 효과적인 방식으로 살균 효과를 높이는데 도움이 됩니다. 이 연구 결과는 폴리머-액체 계면에서 나노입자를 자발적으로 배열하는 새로운 전략을 개념화하여 지형적 특성을 갖는 다양한 헤테로 구조체를 구현할 수 있게 합니다.

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