Folk arts-inspired twice-coagulated configuration-editable tough aerogels enabled by transformable gel precursors

Aerogels, as famous lightweight and porous nanomaterials, have attracted considerable attention in various emerging fields in recent decades, however, both low density and weak mechanical performance make their configuration-editing capability challenging. Inspired by folk arts, herein we establish a highly efficient twice-coagulated (TC) strategy to fabricate configuration-editable tough aerogels enabled by transformable gel precursors. As a proof of concept, aramid nanofibers (ANFs) and polyvinyl alcohol (PVA) are selected as the main components of aerogel, among which PVA forms a flexible configuration-editing gel network in the first coagulation process, and ANF forms a configuration-locking gel network in the second coagulation process. TC strategy guarantees the resulting aerogels with both high toughness and feasible configuration editing capability individually or simultaneously. Altogether, the resulting tough aerogels with special configuration through soft to hard modulation provide great opportunities to break through the performance limits of the aerogels and expand application areas of aerogels.

(9) Figure 3g.The hysteresis curve never goes back to zero for higher deformation.In this circumstance, how can the multiple stress-strain curves line up nicely as shown in the figure?The details of the measurement, including the definition of 'zero' for multiple steps, must be described precisely.
(10) In Introduction, "shape memory materials (SMPs)" seems weird as an acronym.The sentence may be revised to make sense.
(11) In introduction, "Biomedical science" does not seem to be a parallel field as other listed fields (i.e., way too broad and non-descriptive).
(12) On page 4, what is meant by "unedited regular aerogel"?Was it created through general polymerization without undergoing the TC strategy?Does it differ in configuration from the coil shape?
(13) In reference to page 6, the author mentions a slight fading of color and a decrease in the UV absorption spectrum in Figure 1c, indicating that ANF did not participate in the formation of the organogel network in the first coagulation step.Can you provide further explanation for readers who may find this part confusing?(14) There seems to be a discrepancy between the "Kevlar fibers" shown in Figure 1b and the protonation of ANF mentioned on page 6. Can you clarify the relationship between the two?Or change the terminology to keep it consistent.
(15) On page 7, the theoretical mass ratio of PVA to ANF was calculated as 5/1 using a weight loss value.While this makes sense, it may be unreasonable if heating above 500 degrees is not taken into account.Could you consider other factors such as the gel formation process or the contribution ratio of each component, such as cross-linking, to determine a more appropriate ratio?Alternatively, could you provide some guidance on how to adjust the ratio based on the intended application of the gel?(16) Building on the point (12), the comparison between the new aerogels and regular aerogels on page 14 and Figure 3h lacks information about the regular aerogels.Could you provide more details on their shape and fabrication method, such as whether they are rectangular or conventionally coiled without TC strategy?(17) There are a few typos in the manuscript, such as "fellow" instead of "follow" on page 16.
Reviewer #2 (Remarks to the Author): In this paper, the authors developed a twice-coagulated (TC) strategy to fabricate the configurationeditable tough aerogels composted of aramid nanofibers (ANFs) and polyvinyl alcohol (PVA).The authors further performed a series of characterization for microstructures and mechanical properties of ANF-PVA (AP) tough aerogels.The results showed that AP aerogels have high both specific modulus and toughness.These excellent mechanical properties of AP aerogels are attributed to the TC processing and the inner cellular 3D networks.The authors also demonstrated some applications of configuration-editable aerogels, such as self-supporting thermal insulation structures, thermal management devices, and shape-memory devices.Overall, the manuscript is well-written and comprehensive.The study results would have significant impact on the design and fabrication of novel aerogels with excellent mechanical properties and remarkable configuration-editable capacity.But the authors have to address the following issues before the currant manuscript can be recommended for publication, 1. Figure 1f shows the SEM image of AP-23 aerogel sample, indicating the cellular structures.The mechanical properties of aerogel samples are determined by such cellar structure.The authors are suggested to add some statements to describe the pore size and associated distributions, and thickness and composition of cell wall.Furthermore, the authors, on page 11, stated the influences of freeze-thaw cycle on the cellular structure to explain the enhancement of mechanical properties.The authors should add more detailed descriptions how the freeze-thaw cycle affects the cellular structure, especially the influences of the freeze-thaw cycle on the characteristic size (such as wall thickness and pore size), which is crucial to determine the mechanical properties.2. Figure 2c-d shows the mechanical properties of organogel, hydrogel and aerogel.It is seen in these two figures that both modulus and strength of sample increase significantly with the evolution, but the elongation is reduced.It to some extent implies the conflict between strength and toughness.The authors should mention the reduction in the elongation of materials and further explain the relevant origin of such reduction.3. Figure 2e-f shows the compressive and tensile stress-strain curves of AP aerogels with different densities.It is seen in Fig. 2e-f that the strength of AP aerogel increases with the increasing of density.Can the authors further quantitatively investigate the dependences of compressive and tensile strengths on the density and provide the relevant explanations for such dependence?4. Figure 2a shows the comparison in specific modulus and toughness between AP aerogel and other aerogels.The authors are suggested to further compare the strength between AP aerogel and other aerogels, because the strength is generally a more important mechanical property compared with specific modulus in most practical applications.5. Figure 3g shows the tensile cyclic curves of coil aerogels under different strains.It is seen in Fig. 3g that for the larger applied strains, there exists a hysteresis in the stress-strain curves.The authors should add some statements to discuss such hysteresis.6.The mechanical properties and performances of aerogels are associated with the hybrid networks composed of ANF and PVA.The authors are suggested to add more statements to describe the formation of hybrid networks of ANF and PVA, especially the cross linking among different polymer chains.Recent experimental study (Materials Today, 2023, doi: 10.1016/j.mattod.2023.07.020) showed that after introducing the low content of ANF (about 0.1-0.3wt%), various mechanical properties (including modulus, strength, fracture toughness and fatigue resistance) of 3D printable hydrogel have been improved at least 10 times.In the current study, the content of ANF is up to 2 wt%.The authors are suggested to add some discussions about the mechanical enhancement from ANF with different contents by referring the reference mentioned above.6.In the current manuscript, the authors defined "AP-x" in two different ways.The first one is on page 5, where x means the density; the second one is on page 10, where x means the number of freezethaw cycles.The authors should modify these abbreviation meaning to distinguish them.7. On page 15, the authors mentioned the measurement of tensile modulus of Paraffin@AP.The authors should provide more information (such as sample shape, loading conditions, loading rate) about the tensile tests of Paraffin@AP.
Reviewer #3 (Remarks to the Author): Configuration editing is critical for the practical and flexible application of aerogels.However, this is largely hindered by the high porosity and weak mechanical strength of aerogels.In this study, Li et al. tried to address this challenge by establishing an unique twice coagulation (TC) strategy through the use of transformable gel precursors.This endeavor is conceptually new, which points out a new direction for aerogel fabrication and should greatly advance the controlled fabrication of aerogels with tailored properties/applications.Also, the manuscript is well organized and the conclusion is well supported by the experiments/analysis.After minor revision as shown as follows, I recommend the publication of this paper in Nature Communications.1.The detailed information of TGA and Raman scattering spectra should be provided in Characterization part.2. Schematic diagram was recommended to intuitively represent the difference between cellular network and 3D fiber network.3. It is better to provide evidence to prove the successful fabrication of Paraffin@AP.4. Some format errors should be carefully checked, such as spaces between numbers and units.

Comments:
The manuscript titled "Folk Arts-Inspired, Twice-Coagulated, Configuration-Editable Tough Aerogels Enabled by Transformable Gel Precursors," written by Li and coworkers reports a novel strategy to fabricate aerogels of arbitrary configuration by employing so-called twice-coagulated (TC) strategy.Using aramid nanofibers (ANF) and polyvinyl alcohol (PVA) as main components, an organogel is first formed by freeze-thawing the dimethyl sulfoxide (DMSO) solution (first coagulation), whereas the organogel provides a soft and malleable gel.Origami, weaving, and other fabrication methods were applied in this state.When the shaping is done, the preformed precursor is immersed in dionized water for solvent exchange, resulting in the second coagulation step to fix the morphology.Finally, solvent exchange in ethanol followed by supercricial drying produced aerogels in arbitrary configuration.
The strategy is simple, smart, and intuitively well-acceptable.And, to the best of my knowledge, the TC strategy has appreciable novelty.The authors captured the interdisciplinary perspective of the manuscript effectively by (i) comparing different gels at various stages and levels of quality using materials engineering techniques and (ii) showing a wide range of proof-of-concept demonstration of applications.In general, I am supportive of the eventual publication of the manuscript based on the novelty and interdisciplinary application possibility.However, some key details that enables the successful fabrication are either missing or unexplored in the study.Some scientific descriptions in the manuscript are rather obscure or incorrect.These details must be rectified before the manuscript can be considered for publication.

Response:
We appreciate the reviewer's positive evaluation of our manuscript.We thank the reviewer very much for the constructive comments and suggestions to improve our manuscript greatly.We have addressed all the issues in a point-by-point manner and all the changes to the original manuscript are highlighted in blue.
Question 1.The degree of warping, configuration retention, and distortion before/after each coagulation steps must be revealed precisely.It is well known that the configuration fidelity is the challenge in freeze-thawing and solvent exchange processes, and thus the related details must be reported in the publication.
The authors mentioned that cracking may occur when a rectangular aerogel is bent to change its configuration; this statement is insufficient for the readers to pursue reproduction.
Response: Thanks for your this professional constructive advice.Based on this suggestion, AP organogels with different configurations and sizes (e.g., monolith, film, and strip gels) were prepared and the degree of warping, configuration retention, and distortion during each coagulation process steps have been revealed precisely.
More statement about the detail of configuration editing has been provided and a diagram was added to make it easier to understand and reproduce.

Revision: Concise description about configuration fidelity was added in last paragraph of "Mechanical properties of AP organogel, hydrogel and aerogel."
"In addition to configuration editing capabilities, the fidelity of configuration is another crucial parameter for evaluating the feasibility of TC strategy in ensuring consistency between the target and designed configurations.The precise tracking of configuration retention and distortion before/after each coagulation step was conducted.In freezethawing processes, no significant changes in configuration were observed, possibly due to the inhibitory effect of the gel network on continuous growth of DMSO crystals.
During solvent exchange processes in the second coagulation step, a volume shrinkage of approximately 40% occurred (Supplementary Fig. 16) Even so, the overall configuration of the gel remained unchanged.For instance, after secondary coagulation, bending angles such as 90°, 135°, and 180° in a bent rectangular spline remained unaltered (Supplementary Fig. 17).Similarly, samples with twisting and twining editing retained the oringinal configurations after secondary coagulation (Supplementary Fig. 18).Therefore, benefiting from its high fidelity towards maintaining configurations during processing steps, TC strategy enables obtaining aerogels with desired target configurations.(Line23, Page 15) "The cracking would occur if directly editing aerogel such as stretching, compression, bending, and twisting aerogel.For example, in Supplementary Fig. 20, when winding the rectangular spline with 2 mm×2 mm cross section along a cylinder with 8 mm diameter and unwinding outward, the aerogel spline is cracked."Supplementary Fig. 20 Question 2. The TC strategy is smart and interesting, but it necessitates lengthy production steps and configuration fidelity issues during the production.The authors may elaborate the challenges in applying the TC strategy in commercial and engineering applications.
Response: Thank you for your nice suggestion.Indeed, lengthy production steps and configuration fidelity issues should be considered during the production of aerogel.Thus, we have discussed this challenge for future study.
Revision: These challenges have been added to the "Discussion" section.
"In conclusion, we have proposed and established an efficient TC strategy to fabricate configuration-editable tough AP aerogels...Although the TC strategy enable the aerogels with configuration editing capability, when applying it in commercial and engineering applications, there are still some challenges like the energy and time consumption issues in freezing-thawing process, sample volume shrinkage problems during solvent exchange and supercritical drying.We eagerly anticipate further breakthroughs in these areas in the future."(Line 20, Page 23) Question 3. It seems that the authors could achieve some 'sweet-spot' in terms of fabricating malleable organogel after the first coagulation step (freeze-thaw of the DMSO solution).How general is this strategy successful?What happens when ANF-PVA ratio changes and/or when freeze-thaw steps have different thermal history?How long is the organogel malleable yet formative (i.e., the effect of solvent drying in ambient condition)?Any systematic studies in these regards?
Response: Thank you for raising this important point.Actually, ANF-PVA ratio, thermal history, and air humidity will affect the malleability of organogel.We did systematic studies in these regards before, and the related detailed discussion have been added in the revised manuscript.
Revision: At the beginning of "Twice-coagulated (TC) strategy" part in the main text, these influencing factors are summarized.
"Twice-coagulated (TC) strategy.The specific twice-coagulated process and the network transition mechanism were primarily investigated.First of all, to determine the optimal experimental conditions, a comprehensive investigation and detailed discussion on the influence of ANF-PVA ratio, freezing to thawing cycles, and ambient conditions on the TC process were conducted and presented in the Supplementary Information (Supplementary Fig. 1-5).The optimal organogel-hydrogel-aerogel transition was performed as follows: firstly, 4.0 wt%, 4.5 wt%, 5.0 wt%, 5.5 wt%, 6.0 wt% ANF-PVA mixed solutions in alkali (KOH or t-BuOK) DMSO with 5:1 mass ratio of PVA to ANF were prepared.In the first coagulation setp, the mixed solutions were coagulated into red ANF-PVA composite organogels (AP organogels) after three freeze-thawing cycles, which need to be sealed to avoid humidity absorption from ambience."(Line 6, Page 5) We then discussed in detail the influence of different factors on the gel malleability, including 1) the ratio of ANF to PVA, 2) thermal history, and 3) ambient condition in in revised Supplementary Note 1.
1) The ratio of ANF to PVA.To investigate the impact of the ANF to PVA ratio on the malleability of organogels, we examined the mechanical strength of AP organogels at various ANF/PVA ratios.The experimental design was: initially, different ratios of ANF and PVA (ANF/PVA=1/80, 1/40, 1/20, 1/10, 1/5, 1/2.5, and 1/1.25) were mixed.Supplementary Fig. 1 shows that gel formation occurred immediately after mixing when the ANF/PVA ratio was below 1/20 or above 1/1.25.At a ratio of 1/2.5, heterogeneous solutions with noticeable small gel particles were observed.The presence of gel monoliths and small gel particles indicated inadequate mixing between and PVA and ANF at these ratios, which were not suitable for TC strategy.After conducting more detailed experiments, we finally confirmed that elastic organogels could be formed within the range of ANF to PVA ratios from 1/15 to 5/1.When the ANF to PVA ratio exceeded 1:5 or fell below 1:15, insufficient mixing or excessive gelling occurred and the resulted organgels are too weak to be edited after freeze-thaw treatment (Supplementary Fig. 2).The possible reason is that excessive PVA content leads to protonation of ANF by hydrogen on the PVA, thereby promoting the formation of ANF gels.Conversely, an excessive amount of ANF induces gelation of PVA at room temperature due to the presence of excess alkali in ANF.Moreover, excessive ANF affects the crosslinking of PVA gels by wrapping or obstructing PVA molecular chains, consequently reducing the strength of organogels.Subsequently, we conducted further investigations on the mechanical strength of organogels and hydrogels with an ANF/PVA ratio ranging from 1/15 to 1/5 (Supplementary Fig. 3).The strength of organogels increases gradually with the increase of ANF content.When the ANF/PVA ratio increases from 1/15, 1/10 to 1/5, the compression modulus increases from 5 kPa, 9 kPa to 14 kPa.The tensile elongation at break was significantly enhanced from 45% and 73% to 110%.This improvement can be attributed to the proportional increase in the number of cross-linking points of PVA induced by the ANF.Similarly, the strength of hydrogels exhibited a positive correlation with ANF content, owing to the formation of a highly cross-linked hybrid network between ANF and PVA that effectively transfers applied stress within the hydrogel.The higher the content of ANF, the higher the crosslinking density and mechanical strength.Different from organic gels, the elongation at break of hydrogel decreases with the increase of ANF content.This is because in organogels with low crosslinking densities, the increasing crosslinking density can better resist stress and reduce the risk of fracture.While in hydrogel with high crosslinking densities, as the crosslink density increased, the elastic PVA molecular chain length between crosslinkers decreased.According to rubber-like elasticity theory, the extensibility of elastomers is generally proportional to the number of monomer units between crosslinkers (Matter 2022, 5, 237-252;Chem. Rev. 2021, 121, 4309).Therefore, the elongation at break of the AP hydrogel was reduced with the ANF content increase.(Mater. Today 2023, 68, 84-95)