Controlled self‐assembly of bio‐sourced nanocolloids is of high importance for the development of sustainable and low‐cost functional materials but controlling nanocomposite fabrication with both satisfactory optical properties and composition remains challenging. Silk fibroin (SF) and cellulose nanocrystals (CNCs) have independently demonstrated their ability to produce high‐quality photonic materials, in part due to their low absorbance and their transparency in the visible range. While SF is able to replicate inverse structures by high‐resolution nano‐templating, CNCs can spontaneously assemble into cholesteric liquid crystalline structures that are retained upon solvent evaporation, yielding photonic films. In this work, the conditions of successful co‐assembly of regenerated SF, extracted from silkworm silk, with CNCs extracted from cotton, are investigated. Their co‐assembly is investigated for various relative concentration ratios and pH, combining polarized optical microscopy and spectroscopy, SEM, and other characterization techniques (XRD, ATR‐FTIR, TGA). The appearance of photonic properties is observed when CNC and SF are assembled at pH ≥ 4.15, highlighting the importance of suppressing attractive electrostatic interactions between the two species for an organized structure to emerge. Beyond its fundamental motivations for colloidal co‐assembly with structural proteins, this work is relevant to design sustainable optical materials compatible with food packaging coatings and edible coloring pigments.
This content will become publicly available on June 21, 2024
Considering the design of structures and materials for use as replacements for biological structures, polymer nanocomposites are desirable materials of construction since they have a large design space, allowing property customization. Biobased nanofibers are particularly suited for these applications since they have high specific mechanical properties and cytocompatibility. Motivated by these attributes, this work examines nanocomposite aerogels and an aerogel/hydrogel hybrid structure designed to mimic an intervertebral disc (IVD), with the aerogel and hydrogel serving as analogs for the annulus fibrosus and the nucleus pulposus, respectively. The aerogels and aerogel/hydrogel hybrid structure contain a mixture of biobased nanofibers, cellulose nanocrystals (CNCs) and chitin nanofibers (ChNFs), and a polyvinyl alcohol (PVA) matrix. Characterization of the structure and properties shows that the nanocomposite aerogels containing CNC/ChNF mixtures have larger pores and decreased mechanical properties as compared to aerogels containing only CNCs or only ChNFs. Building on these results, a hybrid comprised of a CNC/PVA aerogel and a CNC/ChNF/PVA hydrogel is constructed with mechanical properties similar to natural IVDs, providing initial validation of the hybrid concept for IVD replacements and pathways to customization through changing material composition in the aerogel and hydrogel and changing the aerogel and hydrogel fractions in the hybrid structure.
more » « less- NSF-PAR ID:
- 10434074
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Journal of Applied Polymer Science
- Volume:
- 140
- Issue:
- 33
- ISSN:
- 0021-8995
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract Aerogels are considered ideal candidates for various applications, because of their low bulk density, highly porous nature, and functional performance. However, the time intensive nature of the complex fabrication process limits their potential application in various fields. Recently, incorporation of a fibrous network has resulted in production of aerogels with improved properties and functionalities. A facile approach is presented to fabricate hybrid sol–gel electrospun silica‐cellulose diacetate (CDA)‐based nanofibers to generate thermally and mechanically stable nanofiber aerogels. Thermal treatment results in gluing the silica‐CDA network strongly together thereby enhancing aerogel mechanical stability and hydrophobicity without compromising their highly porous nature (>98%) and low bulk density (≈10 mg cm−3). X‐ray photoelectron spectroscopy and in situ Fourier‐transform infrared studies demonstrate the development of strong bonds between silica and the CDA network, which result in the fabrication of cross‐linked structure responsible for their mechanical and thermal robustness and enhanced affinity for oils. Superhydrophobic nature and high oleophilicity of the hybrid aerogels enable them to be ideal candidates for oil spill cleaning, while their flame retardancy and low thermal conductivity can be explored in various applications requiring stability at high temperatures.
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Abstract Polyvinyl alcohol (PVA) is a water-soluble synthetic polymer that can be used to make hydrogels for biomedical applications as well as biodegradable bags and films; however, compared to other plastics currently used for containers, it lacks mechanical strength, thermal stability, and can easily absorb water from humid environments. Although mechanical improvement has been observed by blending PVA with collagen in a hybrid hydrogel, there is a lack of fundamental understanding of the molecular mechanism, and it is not clear whether the improvement is limited to a hydrated state. Here, using classical molecular dynamics simulations based on fully atomistic models, we develop the equilibrated molecular structure of PVA with collagen and characterize its mechanics. We show that by interacting with a collagen molecule, PVA is equilibrated to a more ordered structure with each residue interacting with the near neighbors by forming more hydrogen bonds locally, making the structure stiffer than pure PVA. The structure shows higher thermal stability before melting, as well as higher rigidity in water. Our results provide the mechanism of the mechanical advantages of hybrid PVA-collagen polymer. The study demonstrates that the structure and mechanics of a synthetic polymer can be tuned by a tiny amount of a natural polymer at the molecular interface. Moreover, it may shed light on identifying a way to improve the mechanics of biodegradable polymer materials without adding much cost, which is crucial for environmental safety.
Impact statement Blending natural and synthetic polymers (e.g., polyvinyl alcohol [PVA] and collagen in a hybrid hydrogel) has shown advantages in polymer mechanics, but there is a lack of fundamental understanding. Using molecular dynamics (MD) simulations based on fully atomistic models, we develop the equilibrated structure of the PVA with collagen and characterize its mechanics. We show that by interacting with a collagen molecule, PVA is equilibrated to a more ordered structure with each residue interacting with the near neighbors by forming more H-bonds locally and the structure is stiffer than pure PVA. Moreover, the structure shows a higher thermal stability before the melting point of PVA, as well as higher rigidity in water. Our results demonstrate that the structure and mechanics of a synthetic polymer can be tuned by a tiny amount of a natural polymer at the molecular interface. It provides the mechanism of the mechanical advantages as experimentally observed. This study paves the way for the multiscale modeling and mechanical design of the hybrid polymer material. It sheds light on identifying a way to improve the mechanics of biodegradable materials without adding much cost for both material functionality and environmental safety.
Graphical abstract -
Inspired by spider silk's hierarchical diversity, we leveraged peptide motifs with the capability to tune structural arrangement for controlling the mechanical properties of a conventional polymer framework. The addition of nanofiller with hydrogen bonding sites was used as another pathway towards hierarchical tuning via matrix–filler interactions. Specifically, peptide–polyurea hybrids (PPUs) were combined with cellulose nanocrystals (CNCs) to develop mechanically-tunable nanocomposites via tailored matrix–filler interactions (or peptide–cellulose interactions). In this material platform, we explored the effect of these matrix–filler interactions on the secondary structure, hierarchical ordering, and mechanical properties of the peptide hybrid nanocomposites. Interactions between the peptide matrix and CNCs occur in all of the PPU/CNC nanocomposites, preventing α-helical ordering, but promoting inter-molecular hydrogen bonded β-sheet formation. Depending on peptide and CNC content, the Young's modulus varies from 10 to 150 MPa. Unlike conventional cellulose-reinforced polymer nanocomposites, the mechanical properties of these composite materials are dictated by a balance of CNC reinforcement, peptidic ordering, and microphase-separated morphology. This research highlights that leveraging peptide–cellulose interactions is a strategy to create materials with targeted mechanical properties for a specific application using a limited selection of building blocks.more » « less
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Abstract Stretchable conductive hydrogels with simultaneous high mechanical strength/modulus, and ultrahigh, stable electrical conductivity are ideal for applications in soft robots, artificial skin, and bioelectronics, but to date, they are still very challenging to fabricate. Herein, sandwich‐structured hybrid hydrogels based on layers of aramid nanofibers (ANFs) reinforced polyvinyl alcohol (PVA) hydrogels and a layer of silver nanowires (AgNWs)/PVA are fabricated by electrospinning combined with vacuum‐assisted filtration. The hybrid ANF‐PVA hydrogels exhibit excellent mechanical properties with the tensile modulus of 10.7–15.4 MPa, tensile strength of 3.3–5.5 MPa, and fracture energy up to 5.7 kJ m−2, primarily attributed to the strong hydrogen bonding interactions between PVA and ANFs and in‐plane alignment of the fibrous structure. Rational design of heterogeneous structure endows the hydrogels with ultrahigh apparent electrical conductivity of 1.66 × 104S m−1, among the highest electrical conductivities ever reported so far for conductive hydrogels. More importantly, this ultrahigh conductivity remains constant upon a broad range of applied strains from 0–90% and over 500 stretching cycles. Furthermore, the hydrogels exhibit excellent Joule heating and electromagnetic interference shielding performances due to the ultrahigh electrical conductivity. These mechanically strong, hybrid hydrogels with ultrahigh and strain‐invariant electrical conductivity represent great promises for many important applications such as flexible electronics.
