Acknowledgements The author would like to express sincere appreciation for the unconditional and invaluable guidance given by the following people throughout the course of the research project - A/Prof Lim Chwee Teck for his continuous guidance, support and encouragement - A/Prof Sow Chorng Haur for sharing his precious knowledge - Ms Eunice Tan Phay Shing from Nano Biomechanics lab for her mentorship and sharing of invaluable experience on mechanical characterization of nanofibers - Dr Tua Puat Siong from Structural lab for his kind support in fabricating the structural frame needed for the research project - Mr Lim Soon Huat from CICFAR lab for his assistance in operating the environmental scanning electron microscope on in situ observation of nanofiber deformation - Mr Kazutoshi Fujihara, Mr Teo Wee Eong and Mr Ryuji Inai from Nanofiber Processing/ Surface Modification lab for their knowledge on fabrication of nanofibers - Ms Satinderpal Kaur from Physical & Chemical Characterization lab for her assistance for the use of the differential scanning calorimetry i Table of Contents Acknowledgements i Table of Contents ii Summary v List of Tables vii List of Figures viii CHAPTER Introduction 1.1 Background 1.2 Objectives 1.3 Scope 1.3.1 Material and structural characterization 1.3.2 Mechanical characterization CHAPTER Literature Review 2.1 Nanofiber fabrication via electrospinning 2.2 Collection of aligned nanofibers 2.3 Mechanical test of single nanofibers 11 2.4 In situ observation of deformation 15 2.5 Deformation of electrospun nanofibers 17 CHAPTER Fabrication of Nanofibers 19 3.1 Electrospinning 19 3.2 Morphological properties of electrospun non woven mat 20 ii CHAPTER Characterization of Electrospun PCL Nanofibers 22 4.1 Background of PCL 22 4.2 Crystal structure 23 4.3 Thermal properties & crystallinity 24 4.4 Tensile test of single electrospun PCL nanofibers 28 4.4.1 Collection of aligned nanofibers 28 4.4.2 Isolation of single nanofibers 29 4.4.3 Tensile test specimen 30 4.4.4 Results 32 4.5 Discussion 35 4.5.1 Concentration effect 35 4.5.2 Diameter dependency 38 CHAPTER Deformation of Single Electrospun PCL Nanofibers 43 5.1 In situ observation on morphological change 43 5.2 Ex situ observation on morphological change & nanostructural rearrangement45 5.3 Results & discussion 46 5.3.1 Morphological changes 46 5.3.2 Nanostructural rearrangement 50 5.4 Summary 54 CHAPTER Conclusions 58 CHAPTER Recommendations 61 iii References……………………………………………………………………………… 62 Appendix A 71 Appendix B 73 Appendix C 75 Appendix D 78 iv Summary Mechanical characterization of a single electropsun polymeric nanofiber is crucial in order to predict the deformation behavior and failure mechanism of fibrous scaffolds when use in tissue engineering The relationship between nanostructure and mechanical property of single electrospun nanofiber is still unknown although it was reported that crystallinity and molecular orientation determines the strength of a fiber Our objective is to unravel the structure-property relationship of a single electrospun polymeric nanofiber undergoing tensile loading Based on tensile test results, we show that ductility of single electropsun PCL (Polycaprolactone) nanofibers increases with increasing concentration but decreases with increasing crystallinity Furthermore, mechanical properties of a single electrospun PCL nanofiber are dominated by its diameter due to the nanostructure formation during and after electrospinning For crystallization which occurs during electrospinning, there will be formation of fibrillar structures which results in higher crystallinity due to the higher degree of molecular orientation; however for crystallization which occurs after the electrospinning jet reaches the collector, fibers will have the form of lamellar structures In-situ observation on deformation of single electrosun PCL nanofiber undergoing tensile loading was achieved by using field emission scanning electron microscope (FESEM) It was observed that nanofibers failed by multiple necking phenomenon This study also provides direct visualization of nanostructural rearrangement of nanofiber by using atomic force microscopy (AFM) AFM phase image shows that the deformation v behavior of single nanofibers can be elucidated by a series of nanostructural rearrangements during critical stages of tensile loading, namely linear elastic deformation, yielding, plateau and strain hardening In conclusion, nanofibers with fibrillar structures exhibited brittle behavior as they not experience plateau in view of the fact that fibrils have already been established In contrast, nanofibers with lamellar structures exhibited ductile behavior as strain are required to transform lamellar structures into fibrillar structures and that explains the existence of the plateau vi List of Tables Table 2.1 Summary of the effects of electrospinning parameters Table 2.2 Schematics of different configurations for the collection of aligned nanofibers 10 Table 2.3 Overview of mechanical tests for mechanical properties measurement of nanoscale materials 13 Table 2.4 Summary of the use of various microscopes and the coupled mechanical test device for in situ observation of deformation 16 Table 3.1 Electrospinning parameters used for fabrication of nanofibers 20 Table 4.1 Thermal properties of electrospun PCL at various concentrations 25 vii List of Figures Figure 2.1 Schematic diagram of eletrospinning set up Figure 2.2 Fiber deposition mechanism for a frame collector with two parallel strips [13] Reprinted from Biomaterials, 26, Tan, E P S., Ng, S Y Lim, C T., Tensile testing of a single ultrafine polymeric fiber, 1453-1456, Copyright (2005), with permission from Elsevier 10 Figure 2.3 Nanofibers suspended over etched grooves of silicon wafer: (a) Electron micrograph of PLLA nanofibers deposited onto the silicon wafer (b) AFM contact mode image of a single nanofiber (300 nm diameter) suspended over an etched groove (c) schematic diagram of a nanofiber with mid-span deflected by an AFM tip [6] Reused with permission from E P S Tan, Applied Physics Letters, 84, 1603 (2004) Copyright 2004, American Institute of Physics 14 Figure 2.4 (a) AFM phase image of a PLLA nanofiber revealing the fibrillar structure (b) a closeup view of the surface of the nanofiber showing the shish-kebab morphology [6] Reused with permission from E P S Tan, Applied Physics Letters, 84, 1603 (2004) Copyright 2004, American Institute of Physics 16 Figure 2.5 Electron micrographs of multiple neck formation in electrospun nanofibers (a) and (b) wt% PEO electrospun nanofibers (c) and (d) wt% PEO electrospun nanofibers [56] Reused with permission from E Zussman, Applied Physics Letters, 82, 3958 (2003) Copyright 2003, American Institute of Physics 18 Figure 3.1 SEM images of PCL non woven mats at various concentrations (a) wt% PCL (b) 10 wt% PCL (c) 12 wt% PCL (d) 14 wt% PCL Scale bars represent 50 μm 21 Figure 4.1 Chemical structure of PCL 22 Figure 4.2 XRD profile of electrospun PCL scaffolds at various polymer concentrations 23 Figure 4.3 DSC thermograms for raw PCL 26 Figure 4.4 DSC thermograms for wt% PCL 26 Figure 4.5 DSC thermograms for 10 wt% PCL 27 Figure 4.6 DSC thermograms for 12 wt% PCL 27 Figure 4.7 DSC thermograms for 14 wt% PCL 28 viii Figure 4.8 (a) Primary collector with parallel strips (b) Side view of primary collector 29 Figure 4.9 Secondary collector which consists of upper and lower frame 30 Figure 4.10 Nanofiber span across the perforated lower frame was shown at (a) lower and (b) higher magnification 31 Figure 4.11 Upper frame mounted on a nano tensile tester (Nano Bionix System, MTS, 31 TN, USA) Figure 4.12 Fiber diameter distribution for 10 wt% PCL nanofibers 33 Figure 4.13 Fiber diameter distribution for 12 wt% PCL nanofibers 34 Figure 4.14 Fiber diameter distribution for 14 wt% PCL nanofibers 34 Figure 4.15 Plot of stress-strain curves for different concentrations at nanofiber diameter of 350 nm 37 Figure 4.16 Concentration effect on Young’s modulus (E), Yield stress (σy), Ultimate tensile stress (σu), and Ultimate strain (εu) 37 Figure 4.17 Diameter dependency of Young’s modulus (E) for different concentrations 40 Figure 4.18 Diameter dependency of Yield stress (σy) for different concentrations 40 Figure 4.19 Diameter dependency of Ultimate tensile stress (σu) for different concentrations 41 Figure 4.20 Diameter dependency of Ultimate strain (εu) for different concentrations 41 Figure 4.21 AFM phase image showing the surface morphology of (a) 150 nm (scan size = 600 nm) (b) 450 nm (scan size = μm) nanofibers fabricated from 10 wt% 42 PCL Scale bars represent 250 nm Figure 5.1 Slideable collector was used for observation on nanofibers deformation 44 Figure 5.2 Experimental setup for in situ observation on morphological change: Top layer of slideable collector was mounted where bottom layer was glued on stage 45 Figure 5.3 Schematic of mica substrate for AFM imaging 46 Figure 5.4 Sequential deformation behavior of nanofibers undergoing tensile loading 49 ix Figure 5.5 Nanostructures of nanofibers revealed by AFM phase imaging (a) Neck region showing aligned and misaligned lamellae as well as surface depressions (b) Interlamellar fragmentation (scan size = μm) (c) Crystallites connecting two fibrils at high strain levels (scan size = μm) (d) Developed and developing fibrils at high strain levels (scan size = μm) (e) Fibrillar structures of a nearfailure fiber (scan size = μm) Scale bars represent 250 nm 56 Figure 5.6 Schematics of nanostructural rearrangement of nanofiber undergoing tensile 57 loading x Table D.21 Individual values of E, σy, σu, and εu for 12 wt% PCL nanofibers with diameter ranging from 1100 to 1199 nm (average diameter was round up to the nearest 5) Diameter(nm) (S63) 1155 (S64) 1170 1165 E (MPa) 97.9 110.2 104.1 ± 8.7 σy (MPa) 5.8 8.0 6.9 ± 1.5 σu (MPa) 37.6 16.0 26.8 ± 15.3 εu (mm/mm) 2.90 2.64 2.77 ± 0.18 Engineering Stress (MPa) 50 40 30 20 10 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 Engineering Strain (mm/mm) S63_1155 nm S64_1170 nm Figure D.21 Plot of stress-strain curves for 12 wt% PCL nanofibers with diameter ranging from 1100 to 1199 nm 98 Table D.22 Individual values of E, σy, σu, and εu for 12 wt% PCL nanofibers with diameter ranging from 1200 to 1300 nm (average diameter was round up to the nearest 5) Diameter(nm) (S65) 1225 (S66) 1240 1235 E (MPa) 62.8 67.2 65.0 ± 3.1 σy (MPa) 4.8 4.4 4.6 ± 0.3 σu (MPa) 24.5 28.4 26.5 ± 2.7 εu (mm/mm) 3.08 2.91 3.00 ± 0.12 Engineering Stress (MPa) 30 20 10 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 Engineering Strain (mm/mm) S65_1225 nm S66_1245 nm Figure D.22 Plot of stress-strain curves for 12 wt% PCL nanofibers with diameter ranging from 1200 to 1300 nm 99 Table D.23 Individual values of E, σy, σu, and εu for 14 wt% PCL nanofibers with diameter ranging from 200 to 299 nm (average diameter was round up to the nearest 5) Diameter(nm) (S67) 255 E (MPa) 1040.4 ± 0.0 σy (MPa) 66.0 ± 0.0 σu (MPa) 388.6 ± 0.0 εu (mm/mm) 3.28 ± 0.00 Engineering Stress (MPa) 400 300 200 100 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 Engineering Strain (mm/mm) C_255 Figure D.23 Plot of stress-strain curves for 14 wt% PCL nanofibers with diameter ranging from 200 to 299 nm 100 Table D.24 Individual values of E, σy, σu, and εu for 14 wt% PCL nanofibers with diameter ranging from 300 to 399 nm (average diameter was round up to the nearest 5) Diameter(nm) (S68) 340 (S69) 345 (S70) 395 360 E (MPa) 673.2 810.3 461.7 648.4 ± 175.6 σy (MPa) 46.1 68.4 39.7 51.4 ± 15.1 σu (MPa) 265.9 306.3 283.0 285.1 ± 20.3 εu (mm/mm) 3.31 0.66 2.02 2.00 ± 1.33 Engineering Stress (MPa) 400 300 200 100 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 Engineering Strain (mm/mm) S68_340 nm S69_345 nm S70_395 nm Figure D.24 Plot of stress-strain curves for 14 wt% PCL nanofibers with diameter ranging from 300 to 399 nm 101 Table D.25 Individual values of E, σy, σu, and εu for 14 wt% PCL nanofibers with diameter ranging from 400 to 499 nm (average diameter was round up to the nearest 5) Diameter(nm) (S71) 455 (S72) 495 475 E (MPa) 399.0 380.83 389.9 ± 12.8 σy (MPa) 32.8 25.2 29.0 ± 5.3 σu (MPa) 153.6 201.6 177.6 ± 34.0 εu (mm/mm) 2.15 2.04 2.10 ± 0.08 Engineering Stress (MPa) 250 200 150 100 50 0.0 0.5 1.0 1.5 2.0 2.5 Engineering Strain (mm/mm) S71_455 nm S72_495 nm Figure D.25 Plot of stress-strain curves for 14 wt% PCL nanofibers with diameter ranging from 400 to 499 nm 102 Table D.26 Individual values of E, σy, σu, and εu for 14 wt% PCL nanofibers with diameter ranging from 500 to 599 nm (average diameter was round up to the nearest 5) Diameter(nm) (S73) 535 (S74) 550 545 E (MPa) 380.6 305.2 342.9 ± 53.3 σy (MPa) 24.5 16.7 20.6 ± 5.5 σu (MPa) 150.3 164.5 157.4 ± 10.0 εu (mm/mm) 2.01 1.86 1.95 ± 0.13 Engineering Stress (MPa) 200 150 100 50 0.0 0.5 1.0 1.5 2.0 2.5 Engineering Strain (mm/mm) S73_535 nm S74_550 nm Figure D.26 Plot of stress-strain curves for 14 wt% PCL nanofibers with diameter ranging from 500 to 599 nm 103 Table D.27 Individual values of E, σy, σu, and εu for 14 wt% PCL nanofibers with diameter ranging from 600 to 699 nm (average diameter was round up to the nearest 5) Diameter(nm) (S75) 600 (S76) 605 (S77) 685 630 E (MPa) 284.2 265.0 249.6 266.3 ± 17.3 σy (MPa) 16.8 26.3 18.0 20.3 ± 5.1 σu (MPa) 109.8 120.4 131.4 120.6 ± 10.8 εu (mm/mm) 2.87 1.35 2.42 2.21 ± 0.78 Engineering Stress (MPa) 150 100 50 0.0 0.5 1.0 1.5 2.0 2.5 3.0 Engineering Strain (mmn/mm) S75_600 nm S76_605 nm S77_685 nm Figure D.27 Plot of stress-strain curves for 14 wt% PCL nanofibers with diameter ranging from 600 to 699 nm 104 Table D.28 Individual values of E, σy, σu, and εu for 14 wt% PCL nanofibers with diameter ranging from 700 to 799 nm (average diameter was round up to the nearest 5) Diameter(nm) (S78) 700 (S79) 720 (S80) 750 (S81) 785 740 E (MPa) 240.0 223.1 274.7 269.6 251.9 ± 24.5 σy (MPa) 12.5 15.1 14.7 19.0 15.3 ± 2.7 σu (MPa) 127.8 118.4 79.1 120.4 111.4 ± 21.9 εu (mm/mm) 2.93 2.81 2.86 3.04 2.91 ± 0.10 Engineering Stress (MPa) 150 100 50 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 Engineering Strain (mm/mm) S78_700 nm S79_720 nm S80_750 nm S81_785 nm Figure D.28 Plot of stress-strain curves for 14 wt% PCL nanofibers with diameter ranging from 700 to 799 nm 105 Table D.29 Individual values of E, σy, σu, and εu for 14 wt% PCL nanofibers with diameter ranging from 800 to 899 nm (average diameter was round up to the nearest 5) Diameter(nm) (S82) 800 (S83) 800 (S84) 820 (S85) 835 (S86) 850 (S87) 860 830 E (MPa) 166.2 144.6 165.6 158.2 190.2 163.2 164.7 ± 14.8 σy (MPa) 10.7 8.7 9.9 8.6 11.3 8.7 9.6 ± 1.2 σu (MPa) 108.4 94.2 100.0 92.6 92.6 80.8 94.8 ± 9.1 εu (mm/mm) 2.63 2.52 1.97 2.34 2.58 2.84 2.48 ± 0.30 Engineering Stress( MPa) 120 90 60 30 0 0.5 1.5 2.5 3.5 Engineering Strain (mm/mm) S82_800 nm S86_850 nm S83_800 nm S87_860 nm S84_820 nm S85_835 nm Figure D.29 Plot of stress-strain curves for 14 wt% PCL nanofibers with diameter ranging from 800 to 899 nm 106 Table D.30 Individual values of E, σy, σu, and εu for 14 wt% PCL nanofibers with diameter ranging from 900 to 999 nm (average diameter was round up to the nearest 5) Diameter(nm) (S88) 910 (S89) 910 (S90) 910 (S91) 930 (S92) 940 (S93) 950 (S94) 950 930 E (MPa) 159.0 122.5 174.0 171.3 184.8 115.7 138.5 152.2 ± 26.9 σy (MPa) 9.2 8.0 8.2 9.8 9.7 7.0 7.5 8.5 ± 1.1 σu (MPa) 69.8 71.2 65.6 49.5 66.2 77.1 63.7 66.1 ± 8.6 εu (mm/mm) 2.90 1.99 3.24 3.36 3.67 2.82 3.26 3.03 ± 0.54 Engineering Stress (MPa) 100 80 60 40 20 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 Engineering Strain (mm/mm) S88_910 nm S92_940 nm S89_910 nm S93_950nm S90_910 nm S94_950 nm S91_930 nm Figure D.30 Plot of stress-strain curves for 14 wt% PCL nanofibers with diameter ranging from 900 to 999 nm 107 Table D.31 Individual values of E, σy, σu, and εu for 14 wt% PCL nanofibers with diameter ranging from 1000 to 1099 nm (average diameter was round up to the nearest 5) Diameter(nm) (S95) 1010 (S96) 1040 (S97) 1055 1035 E (MPa) 138.3 131.9 141.8 137.3 ± 5.0 σy (MPa) 9.6 6.7 9.0 8.4 ± 1.5 σu (MPa) 47.2 65.4 67.4 60.0 ± 11.1 εu (mm/mm) 3.03 3.30 3.21 3.18 ± 0.14 Engineering Stress (MPa) 80 60 40 20 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 Engineering Strain (mm/mm) S95_1010 nm S96_1040 nm S97_1055 nm Figure D.31 Plot of stress-strain curves for 14 wt% PCL nanofibers with diameter ranging from 1000 to 1099 nm 108 Table D.32 Individual values of E, σy, σu, and εu for 14 wt% PCL nanofibers with diameter ranging from 1100 to 1199 nm (average diameter was round up to the nearest 5) Diameter(nm) (S98) 1110 E (MPa) 130.0 ± 0.0 σy (MPa) 7.0 ± 0.0 σu (MPa) 62.9 ± 0.0 εu (mm/mm) 4.05 ± 0.00 Engineering Stress (MPa) 80 60 40 20 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 Engineering Strain (mm/mm) S98_1110 nm Figure D.32 Plot of stress-strain curves for 14 wt% PCL nanofibers with diameter ranging from 1100 to 1199 nm 109 Table D.33 Individual values of E, σy, σu, and εu for 14 wt% PCL nanofibers with diameter ranging from 1200 to 1300 nm (average diameter was round up to the nearest 5) Diameter(nm) (S99) 1300 E (MPa) 111.7 ± 0.0 σy (MPa) 6.2 ± 0.0 σu (MPa) 46.6 ± 0.0 εu (mm/mm) 4.86 ± 0.00 Engineering Stress (MPa) 50 40 30 20 10 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 Engineering Strain (mm/mm) S99_1300 nm Figure D.33 Plot of stress-strain curves for 14 wt% PCL nanofibers with diameter ranging from 1200 to 1300 nm 110 The average values of E, σy, σu, and εu for nanofibers fabricated from different concentrations Table C.34 Young’s modulus (E, MPa) for different concentrations Diameter range 200-299 300-399 400-499 500-599 600-699 700-799 800-899 900-999 1000-1099 1100-1199 1200-1300 10 wt% PCL 1689.5 ± 701.8 882.5 ± 310.3 634.6 ± 240.6 303.0 ± 25.3 270.4 ± 21.0 201.6 ± 25.0 145.0 ± 22.8 136.1 ± 11.8 108.3 ± 17.7 114.4 ± 0.0 95.9 ± 0.0 12 wt% PCL 1431.8 ± 112.6 810.9 ± 367.2 531.1 ± 66.0 346.8 ± 28.3 320.8 ± 14.8 254.9 ± 28.6 169.7 ± 14.4 109.4 ± 10.9 131.0 ± 0.0 104.1 ± 8.7 65.0 ± 3.1 14 wt% PCL 1040.4 ± 0.0 648.4 ± 175.6 389.9 ± 12.8 342.9 ± 53.3 266.3 ± 17.3 251.9 ± 24.5 164.7 ± 14.8 152.2 ± 26.9 137.3 ± 5.0 130.0 ± 0.0 111.7 ± 0.0 Table C.35 Yield stress (σy, MPa) for different concentrations Diameter range 200-299 300-399 400-499 500-599 600-699 700-799 800-899 900-999 1000-1099 1100-1199 1200-1300 10 wt% PCL 107.5 ± 14.4 63.5 ± 16.3 38.2 ± 13.9 21.0 ± 1.0 18.9 ± 6.4 12.4 ± 1.6 9.9 ± 2.6 9.7 ± 1.3 6.4 ± 2.6 6.0 ± 0.0 6.7 ± 0.0 12 wt% PCL 95.6 ± 5.3 58.2 ± 15.4 33.3 ± 5.3 22.2 ± 2.0 21.1 ± 4.9 16.1 ± 2.2 13.2 ± 3.0 6.1 ± 1.2 7.3 ± 0.0 6.9 ± 1.5 4.6 ± 0.3 14 wt% PCL 66.0 ± 0.0 51.4 ± 15.1 29.0 ± 5.3 20.6 ± 5.5 20.3 ± 5.1 15.3 ± 2.7 9.6 ± 1.2 8.5 ± 1.1 8.4 ± 1.5 7.0 ± 0.0 6.2 ± 0.0 111 Table C.36 Ultimate tensile stress (σu, MPa) for different concentrations Diameter range 200-299 300-399 400-499 500-599 600-699 700-799 800-899 900-999 1000-1099 1100-1199 1200-1300 10 wt% PCL 589.4 ± 80.3 325.7 ± 76.7 180.7 ± 16.8 119.2 ± 30.4 101.8 ± 26.4 80.5 ± 16.9 52.4 ± 5.2 51.6 ± 5.5 36.8 ± 12.5 23.3 ± 0.0 24.5 ± 0.0 12 wt% PCL 546.8 ± 39.8 285.2 ± 53.2 172.8 ± 48.6 130.6 ± 25.0 129.7 ± 41.8 87.0 ± 17.6 55.3 ± 20.1 40.5 ± 5.8 38.8 ± 0.0 26.8 ± 15.3 26.5 ± 2.7 14 wt% PCL 388.6 ± 0.0 285.1 ± 20.3 177.6 ± 34.0 157.4 ± 10.0 120.6 ± 10.8 111.4 ± 21.9 94.8 ± 9.1 66.1 ± 8.6 60.0 ± 11.1 62.9 ± 0.0 46.6 ± 0.0 Table C.37 Ultimate strain (εu, mm/mm) for different concentrations Diameter 200-299 300-399 400-499 500-599 600-699 700-799 800-899 900-999 1000-1099 1100-1199 1200-1300 10 wt% PCL 1.83 ± 0.73 1.85 ± 0.89 1.37 ± 0.86 1.82 ± 0.50 2.40 ± 0.31 3.05 ± 0.43 2.44 ± 0.54 2.76 ± 0.08 3.16 ± 0.88 3.16 ± 0.0 3.49 ± 0.0 12 wt% PCL 1.90 ± 0.36 1.54 ± 1.40 1.71 ± 0.49 1.71 ± 0.28 2.20 ± 0.50 1.93 ± 0.65 2.65 ± 0.15 2.59 ± 0.23 3.47 ± 0.00 2.77 ± 0.18 3.00 ± 0.12 14 wt% PCL 3.28 ± 0.00 2.00 ± 1.33 2.10 ± 0.08 1.95 ± 0.13 2.21 ± 0.78 2.91 ± 0.10 2.48 ± 0.30 3.03 ± 0.54 3.18 ± 0.14 4.05 ± 0.00 4.86 ± 0.00 112 [...]...CHAPTER 1 Introduction 1.1 Background The increasing demand of biodegradable polymeric scaffolds that is analogous to nature’s extracellular matrix generates interest for the mechanical characterization of single nanofibers in order to ensure the mechanical compatibility of scaffolds An understanding of the structural and nano mechanical properties of individual nanofibers is crucial in order... materials’ such as carbon and quartz is relatively easier compare to soft materials like polymers as manipulation of soft materials might alter its mechanical properties significantly since thermal history influences greatly the mechanical properties of polymers AFM based resonance test has been used for characterizing nanorods/nanowires made of hard materials such as quartz (silicon dioxide) and carbon... PCL nanofibers Table 2.3 gives an overview of all the above mentioned mechanical tests and their respective characterized materials 12 Table 2.3 Overview of mechanical tests for mechanical properties measurement of nanoscale materials Materials Fabrication Measured [Reference] methods properties PAN1 nanofibers Electrospinning bend test [12] PAN-derived carbon nanofibers Electrospinning [11] resonance... [41-43] Measurement of Young’s modulus on electrospun polymeric nanofibers was also carried out in which the nanofibers were reinforced by carbon [11] There was also AFM based bend test [12] reported for mechanical characterization of single electrospun polymeric nanofibers All these methods are capable of determining the Young’s modulus (E) of the tested materials Nonetheless, as the length of nanofibers... test Silicon dioxide (SiO2) and carbon Vapor-liquidnanorods/nanowires solid technique [41-43] PEO2 and glass Young’s nanofibers Electrospinning AFM based modulus [4] Titanium dioxide three-point (TiO2) nanofibers Electrospinning bend test [5] PLLA3 nanofibers Phase separation [6] Gold nanowires Electrodeposition [44] nanoPLLA nanofibers Phase separation indentation [7] PCL4 nanofibers Young’s Electrospinning... on the mechanical properties of nanofibers obtained from the tensile test of single electrospun polymeric nanofibers Polycaprolactone (PCL) nanofibers are chosen due to its extensive applications in areas of tissue engineering [20-22] Under physiological conditions, PCL is degraded by the hydrolysis of its ester linkages and thus, makes it a suitable candidate for use as an implantable biomaterial In... tension Mechanical characterization will involve three main components: specimen preparation, force application and measurement, and displacement or strain measurement Due to the difficulty in measuring the small load required to deform a single nanofiber, different innovative and sophisticated systems had been developed to determine the mechanical properties of single nanofibers Characterization of hard... behavior of single nanofibers will be obtained and this will be used to correlate the deformation behavior and failure mode of nanofibers 5 CHAPTER 2 Literature Review 2.1 Nanofiber fabrication via electrospinning Electrospinning fabricates superfine fibers with diameter ranging from 10 μm down to 10 nm [16] via the application of electric field that is capable of drawing polymer solution through a. .. beam bending theory [6] Similarly, these tests are able to determine the Young’s modulus of nanofibers The fact that AFM was used in conjunction with all these tests is because of the capability of AFM to attach a single rod/wire/fiber, impose small loads, and measure small displacements Apart from the above mentioned tests, tensile test of single polymeric nanofibers was also reported [13, 40] Comparatively,... (the ratio of the cross-sectional area of the undrawn material to that of the drawn material) will result in more oriented polymer chains being formed in the nanofibers, and this leads to higher strength nanofibers However, there is no direct evidence in literature to support this unique characteristic of electrospun nanofibers The 2 purpose of this study is to provide quantitative and qualitative analysis ... the mechanical properties of single nanofibers Characterization of hard materials’ such as carbon and quartz is relatively easier compare to soft materials like polymers as manipulation of soft... quantitative and qualitative analysis on the mechanical properties of nanofibers obtained from the tensile test of single electrospun polymeric nanofibers Polycaprolactone (PCL) nanofibers are... visualization of nanostructural rearrangement of nanofiber by using atomic force microscopy (AFM) AFM phase image shows that the deformation v behavior of single nanofibers can be elucidated by a series of