Supporting Information

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1 Supporting Information Novel Interwoven Polymer Composites via Dual- Electrospinning with Shape Memory/Self-healing Properties Jaimee M. Robertson, Hossein Birjandi Nejad, Patrick T. Mather* Syracuse Biomaterials Institute and Biomedical and Chemical Engineering Department Syracuse University, Syracuse, NY *To which all correspondences should be addressed: Scheme S1. Schematic illustration of the dual-electrospinning setup showing that the two needles are located on opposite sides of the collecting drum. Two separate pumps controlled the flow rates of each solution. The fibers were collected on a rotating drum (diameter of ~5 cm), which rotated at 4 RPM and translated in an oscillatory fashion with a rastering amplitude of ~6 cm. An inherent advantage of this method compared to other methods, such as solvent casting or melt mixing of two immiscible polymers, is that the two different polymeric fibers are uniformly distributed and tightly interwoven with each other throughout the fiber mat. Electrospinning parameters for each polymer solution were set independently: 13. kv applied voltage and 8 cm tip of the needle to collector distance for PVAc and 12. kv applied voltage and 1 cm tip of the needle to collector distance for PCL. 1

2 Figure S1. SEM micrographs of (A) as spun PCL, (B) heated PCL, (C) as spun PVAc and (D) heated PVAc fiber mats. During heating, PVAc polymers chains reconfigure to a relaxed state and the semicrystalline self-healing fibers melt and form a film resulting in significant fiber mat shrinkage. Scale bar represents 5 µm for all SEM micrographs. Figure S2. Scanning electron microscope images of (A) PVAc, (B) PVAc8:CPL2, (C) PVAc6:PCL4 and (D) PCL film cross-sections. Samples were cut with a fresh razor blade and sputter coated for 45 s with gold prior to the experiment. Heating shrinks PVAc fibers and melts the PCL fibers, forming a non-porous composite. Scale bar represents 1 μm for all SEM images. 2

3 Figure S3. (I) Photographs of (A) PVAc6:PCL4, (B) PVAc and (C) PCL fiber mat. Left and right columns represent as spun samples and corresponding heated samples, respectively. During heating, PVAc polymers chains reconfigure to a relaxed state and the semicrystalline self-healing fibers melt and form a film resulting in significant fiber mat shrinkage. (II) Quantitative characterization of fiber mat shrinkage showing average fiber mat sizes and shrinkage percentages for PVAc6:PCL4, PVAc and PCL (n=5). Results showed that the dual-electrospun sample (PVAc6:PCL4) has an intermediate shrinkage % value compared to the two controls (PCL and PVAc fiber mats). All scale bars represent 1 mm. Figure S4. Micrographs of (A) PCL and (B) PVAc fibers. The top and bottom rows represent the bright field and fluorescent micrographs of such fibers, respectively. To take the images, the fibers were electrospun on a thin glass slide for ~1 s. Note that PVAc solution contained ~.5 3

4 wt. % of Rhodamine B. PCL solution however, did not contain any Rhodamine B (fluorescent dye) and did not appear under fluorescent light. Scale bar represents 1 µm for all micrographs. (i) (ii) Heat Flow (W/g) (iii) (iv) (v) Figure S5. DSC thermograms for as-spun (i) PVAc8:PCL2, first heat, (ii) PVAc8:PCL2, second heat, (iii) PVAc6:PCL4, first heat, (iv) PVAc6:PCL4, second heat, and (v) neat PCL film, second heat. The corresponding PCL melting transitions for each are 54.7 (i), 55.1 (ii), 57.6 (iii), 56.2 (iv), and 56.2 C (v). In studying the PCL melting transition, the first and seconding heating cycles for corresponding compositions have some differences, which are postulated to be due to residual stresses in the material. In the first heating cycles, the traces exhibited slight endothermic peaks in the PVAc glass transition. This peak is postulated to be due to the increased chain alignment and packing density resulting from the elongational forces experienced during electrospinning. Further, the first heat of the PVAc8:PCL2 film indicated a higher PCL T m. Again, it is suspected that residual stresses resulting in altered microstructures caused changes in the thermal response. In both cases, after the initial first heat, the transition temperatures returned to the respective transition temperature of the neat component. Namely, the temperatures at the peak of the PCL melting transition in the composites were within 2 C of the T m of the neat PCL film. 4

5 12 1 (i) Weight Remaining (%) (ii) (iii) (iv) Figure S6. High resolution TGA profile of (i) PCL, (ii) PVAc6:PCL4, (iii) PVAc8:PCL2 and (iv) PVAc films. PVAc (ii) showed two decomposition steps onsetting at about 3 and 4 C and PCL (i) showed one step transition onsetting at 35 C. The composites ((ii) and (iii)) showed intermediate decomposition profiles compared to neat PVAc and PCL with three decomposition steps onsetting at 3, 35 and 4 C. For more details, see Figure S7 and Figure S8. 5

6 12 (i) (ii) (iii) Weight Remaining (%) * * * 2 1 dt/dt (C.min -1 ) 2 (iv) Figure S7. High resolution TGA profile (black) and heating rate profile (red) of a PVAc8:PCL2 film. In the high resolution mode, the heating rate was automatically adjusted as a function of weight loss rate as we now explain. In regions that no weight change (i.e. decomposition) is occurring, the heating rate is 2 C. min -1. However, the heating rate is automatically adjusted in response to sample decomposition and the heating decreases as the weight loss rate increases. Such dynamic heating rate provides separation and high resolution in decomposition events. Given that the heating rate slows down only when necessary (at the onset of a decomposition event), high resolution TGA is considered a faster and yet more reliable method to separate weight loss events compared to a static heating rate. Three decomposition steps ((i), (ii) and (iii)) were observed for the PVAc8:PCL2 composite with some residual char at 6 C (iv). Note that the end of each decomposition event was defined as the peak of the heating rate (shown by asterisks), i.e. where the weight loss rate in the decomposition event reaches a minimum value, indicating that the decomposition event concludes. Based on the decomposition profiles of PVAc and PCL, (i) and (iii) correspond to PVAc whereas (ii) 6

7 corresponds to the PCL decomposition event. Given that all of PCL was decomposed in region (ii), the amount of weight loss in region (ii) approximately translates to weight fraction of PCL in the composite. The sum of weight loss in regions (i) and (iii) plus the remaining char mass, (iv), roughly provides the PVAc weight fraction in the composite. For TGA profiles along with analysis of PVAc and PCL weight fraction in the composites, refer to Figure S (A) 12 1 (B) Weight Remaining (%) % Weight Remaining (%) % % % % 12 1 (C) 12 1 (D) Weight Remaining (%) (i) 58.4 % (ii) 2.4 % Weight Remaining (%) (i) 48.6 % (ii) 36.5 % 2 (iii) 17.2 % (iv) 4. % 2 (iii) 1.7 % (iv) 4.2 % Figure S8. High resolution TGA profiles of (A) PVAc, (B) PCL, (C) PVAc8:PCL2 and (D) PVAc6:PCL4 films. (A) PVAc showed two decomposition steps onsetting at about 3 and 4 C where 69.9 and 25.9 % of the sample was decomposed with 4.2 % remaining as the char at 6 C. (B) PCL showed one decomposition step onsetting at about 35 C (in between PVAc s two decomposition events) where 99 % of the sample was decomposed. Note: given that 99 % of PCL weight was lost in the decomposition event, we assumed that the amount of PCL char remaining at 6 C is negligible and any char remaining at 6 C in the composites corresponds to PVAc phase. (C) PVAc8:PCL2 showed three decomposition steps onsetting at 3 (i), 35 (ii) and 4 C (iii). Based on decomposition profiles of PVAc and PCL, (i), (iii) and (iv) correspond to PVAc whereas (ii) corresponds to the PCL decomposition event. Given that all 7

8 of PCL was decomposed in region (ii), the amount of weight loss in this region (2.4 %) approximately translates to weight fraction of PCL in the composite. The sum of (i), (iii) and (iv) gives a weight fraction of 79.6 % for PVAc. (D) PVAc6:PCL4 showed three decomposition events. Again, weight loss in region (ii) (36.5 %) approximately translates to weight fraction of PCL in the composite. The sum of (i), (iii) and (iv) gives a weight fraction of 63.5 % for PVAc. These results are in agreement with DSC results (Refer to Table 1). (i) Heat Flow (W/g) (ii).2 W/g Figure S9. DSC thermograms (2 nd heating cycle) of (i) hydrated PVAc and (ii) hydrated PVAc8:PCL2 composites. Heating rates were 1 C. min -1 and 5 C. min -1 for heating and cooling, respectively. 8

9 Table S1. Summary of thermomechanical properties of current SMASH composites (Dual electrospun PVAc:PCL interwoven composites) compared to the first SMASH system reported by our group 9 (crosslinked PCL (n-pcl):linear (l-pcl) interpenetrating network). Note that for any given weight fraction of self-healing agent, the storage modulus of the former is about 5 times higher than the latter at 25 C. Dual Electrospun PVAc:PCL Interwoven Composite Self-Healing Agent wt. % E (25 C, MPa) E (6 C, MPa) Crosslinked PCL (n-pcl)/linear (l-pcl) Interpenetrating Network Self-Healing Agent wt. % E (25 C, MPa) E (6 C, MPa) (.9 at 65 C) a a : At 6 C, the sample has not gone through the PCL melting transition. At 65 C, the composite has reached a rubbery plateau above PCL s T m. For more details about the thermal behavior of the composite system, refer to our previous publication. 9 9

10 4 3 Tan ( Figure S1. Tan (δ) traces of (-) PVAc6:PCL4 film, (-) PVAc8:PCL2 film and (-) PVAc films. The loss tangent (tan(δ)) profiles for PVAc6:PCL4 and PVAc8:PCL2 shows double peaks, indicative of both PVAc T g and PCL T m and which was in agreement with DSC results. Therefore, we anticipated that a simple heating step above both transitions (i.e. 75 C) would simultaneously trigger both the SM response of the PVAc phase and melting of the PCL phase, yielding the two step SMASH mechanism. 1

11 Figure S11. Photographs of a PCL film (A) before and (B) after heating at 75 C for 2 min. All scale bars represent 1 cm. The film was freely hung from a binder clip in the isothermal oven with no external stress applied. Above melting temperature, PCL becomes a viscous liquid that flows yielding alteration in sample geometry. The storage modulus (E ) trace of PCL as a function of temperature (C) shows a sharp drop in storage modulus as PCL goes through its melting transition and transforms from a solid to a liquid. These results indicate that PCL by itself cannot hold any applied stress and requires a second phase (PVAc in our case) for mechanical support to keep the integrity of the composite when heated above the PCL melting transition. Note that with the presence of PVAc, PVAc8:PCL2 and PVAc6:PCL4 showed soft rubber characteristics and had storage modulus values of.6 and.3 MPa, respectively at 65 C. For a summary of the mechanical properties of composites at 25 and 65 C, refer to Table S1. 11

12 d-spacing (Å) (i) (ii) Intensity (a.u.) (iii) (iv) (v) (vi) (Degree) Figure S12. Intensity vs. 2θ profiles of (i) PVAc6:PCL4 film, (ii) PVAc6:PCL4 fibers, (iii) PVAc film, (iv) PVAc fibers, (v) PCL film and (vi) PCL fibers. The X-ray wavelength (λ) is Å. 12

13 Figure S13. Photographs of PVAc6:PCL4 composite showing (A) scratched and (B) thermally mended (75 C for 1 min) samples. Scale bars denote 1 mm Virgin Notched Notched and Stretched Healed 25 Force (N) Displacement (mm) Figure S14. Force vs displacement curves for the virgin, damaged and healed state of a PVAc film. In the absence of PCL (self-healing agent), the damaged PVAc film did not recover its original properties after heating. The PVAc films had a relatively lower self-healing efficiency (89 %) and failed at significantly lower displacement compared to virgin PVAc. We attribute this observation to the fact that even though the cracks were closed after heating the PVAc film, the crack surfaces were not rebonded and were not able to withstand the same stress as the virgin sample. 13

14 Figure S15. (A) Stress vs. strain profiles for PVAc and PVAc8:PCL2 films in both the dry and hydrated state. Samples were stretched at 5 μm. s -1 at RT. In the dry state, both composites showed stiff characteristics with low strain to failure and high modulus at RT. Upon hydration, they became elastomeric with low modulus and high strain to failure. (B) Photograph of a hydrated PVAc8:PCL2 dogbone sample pre and post stretching on the Linkam. Hydrated samples were immersed in water for at least 24 prior to the experiment. Sample was kept hydrated during the experiment by constantly pipetting water onto it. Figure S16. Dual shape memory demonstration of PVAc8:PCL2 composite showing (A) permanent shape at RT, (B) a temporary spiral shape, which was deformed at 8 C and fixed by quenching at -17 C (temporary shape) and (D) the recovered shape. Scale bar represents 1 cm. 14